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Although a resonant antenna has a purely resistive feed-point impedance at a particular frequency, many (if not most) applications require using an antenna over a range of frequencies. An antenna's bandwidth specifies the range of frequencies over which its performance does not suffer due to a poor impedance match. Also in the case of a Yagi-Uda array, the use of the antenna very far away from its design frequency reduces the antenna's directivity, thus reducing the usable bandwidth regardless of impedance matching.
Instead, it is often desired to have an antenna whose impedance does not vary so greatly over a certain bandwidth. It turns out that the amount of reactance seen at the terminals of a resonant antenna when the frequency is shifted, say, by 5%, depends very much on the diameter of the conductor used. A long thin wire used as a half-wave dipole (or quarter wave monopole) will have a reactance significantly greater than the resistive impedance it has at resonance, leading to a poor match and generally unacceptable performance. Making the element using a tube of a diameter perhaps 1/50 of its length, however, results in a reactance at this altered frequency which is not so great, and a much less serious mismatch which will only modestly damage the antenna's net performance. Thus rather thick tubes are typically used for the solid elements of such antennas, including Yagi-Uda arrays.
Rather than just using a thick tube, there are similar techniques used to the same effect such as replacing thin wire elements with cages to simulate a thicker element. This widens the bandwidth of the resonance. On the other hand, amateur radio antennas need to operate over several bands which are widely separated from each other. This can often be accomplished simply by connecting resonant elements for the different bands in parallel. Most of the transmitter's power will flow into the resonant element while the others present a high (reactive) impedance and draw little current from the same voltage. A popular solution uses so-called traps consisting of parallel resonant circuits which are strategically placed in breaks along each antenna element. When used at one particular frequency band the trap presents a very high impedance (parallel resonance) effectively truncating the element at that length, making it a proper resonant antenna. At a lower frequency the trap allows the full length of the element to be employed, albeit with a shifted resonant frequency due to the inclusion of the trap's net reactance at that lower frequency.
Gain is a parameter which measures the degree of directivity of the antenna's radiation pattern. A high-gain antenna will radiate most of its power in a particular direction, while a low-gain antenna will radiate over a wider angle. The antenna gain, or power gain of an antenna is defined as the ratio of the intensity (power per unit surface area) radiated by the antenna in the direction of its maximum output, at an arbitrary distance, divided by the intensity radiated at the same distance by a hypothetical isotropic antenna which radiates equal power in all directions. This dimensionless ratio is usually expressed logarithmically in decibels, these units are called "decibels-isotropic" (dBi)
High-gain antennas have the advantage of longer range and better signal quality, but must be aimed carefully at the other antenna. An example of a high-gain antenna is a parabolic dish such as a satellite television antenna. Low-gain antennas have shorter range, but the orientation of the antenna is relatively unimportant. An example of a low-gain antenna is the whip antenna found on portable radios and cordless phones. Antenna gain should not be confused with amplifier gain, a separate parameter measuring the increase in signal power due to an amplifying device.
Due to reciprocity (discussed above) the gain of an antenna used for transmitting must be proportional to its effective area when used for receiving. Consider an antenna with no loss, that is, one whose electrical efficiency is 100%. It can be shown that its effective area averaged over all directions must be equal to λ2/4π, the wavelength squared divided by 4π. Gain is defined such that the average gain over all directions for an antenna with 100% electrical efficiency is equal to 1. Therefore, the effective area Aeff in terms of the gain G in a given direction is given by:
The radiation pattern of an antenna is a plot of the relative field strength of the radio waves emitted by the antenna at different angles. It is typically represented by a three-dimensional graph, or polar plots of the horizontal and vertical cross sections. The pattern of an ideal isotropic antenna, which radiates equally in all directions, would look like a sphere. Many nondirectional antennas, such as monopoles and dipoles, emit equal power in all horizontal directions, with the power dropping off at higher and lower angles; this is called an omnidirectional pattern and when plotted looks like a torus or donut.
The radiation of many antennas shows a pattern of maxima or "lobes" at various angles, separated by "nulls", angles where the radiation falls to zero. This is because the radio waves emitted by different parts of the antenna typically interfere, causing maxima at angles where the radio waves arrive at distant points in phase, and zero radiation at other angles where the radio waves arrive out of phase. In a directional antenna designed to project radio waves in a particular direction, the lobe in that direction is designed larger than the others and is called the "main lobe". The other lobes usually represent unwanted radiation and are called "sidelobes". The axis through the main lobe is called the "principal axis" or "boresight axis".
As an electro-magnetic wave travels through the different parts of the antenna system (radio, feed line, antenna, free space) it may encounter differences in impedance (E/H, V/I, etc.). At each interface, depending on the impedance match, some fraction of the wave's energy will reflect back to the source, forming a standing wave in the feed line. The ratio of maximum power to minimum power in the wave can be measured and is called the standing wave ratio (SWR). A SWR of 1:1 is ideal. A SWR of 1.5:1 is considered to be marginally acceptable in low power applications where power loss is more critical, although an SWR as high as 6:1 may still be usable with the right equipment. Minimizing impedance differences at each interface (impedance matching) will reduce SWR and maximize power transfer through each part of the antenna system.
Efficiency of a transmitting antenna is the ratio of power actually radiated (in all directions) to the power absorbed by the antenna terminals. The power supplied to the antenna terminals which is not radiated is converted into heat. This is usually through loss resistance in the antenna's conductors, but can also be due to dielectric or magnetic core losses in antennas (or antenna systems) using such components. Such loss effectively robs power from the transmitter, requiring a stronger transmitter in order to transmit a signal of a given strength.
For instance, if a transmitter delivers 100 W into an antenna having an efficiency of 80%, then the antenna will radiate 80 W as radio waves and produce 20 W of heat. In order to radiate 100 W of power, one would need to use a transmitter capable of supplying 125 W to the antenna. Note that antenna efficiency is a separate issue from impedance matching, which may also reduce the amount of power radiated using a given transmitter. If an SWR meter reads 150 W of incident power and 50 W of reflected power, that means that 100 W have actually been absorbed by the antenna (ignoring transmission line losses). How much of that power has actually been radiated cannot be directly determined through electrical measurements at (or before) the antenna terminals, but would require (for instance) careful measurement of field strength. Fortunately the loss resistance of antenna conductors such as aluminum rods can be calculated and the efficiency of an antenna using such materials predicted.
However loss resistance will generally affect the feedpoint impedance, adding to its resistive (real) component. That resistance will consist of the sum of the radiation resistance Rr and the loss resistance Rloss. If an rms current I is delivered to the terminals of an antenna, then a power of I2Rr will be radiated and a power of I2Rloss will be lost as heat. Therefore, the efficiency of an antenna is equal to Rr / (Rr + Rloss). Of course only the total resistance Rr + Rloss can be directly measured.
According to reciprocity, the efficiency of an antenna used as a receiving antenna is identical to the efficiency as defined above. The power that an antenna will deliver to a receiver (with a proper impedance match) is reduced by the same amount. In some receiving applications, the very inefficient antennas may have little impact on performance. At low frequencies, for example, atmospheric or man-made noise can mask antenna inefficiency. For example, CCIR Rep. 258-3 indicates man-made noise in a residential setting at 40 MHz is about 28 dB above the thermal noise floor. Consequently, an antenna with a 20 dB loss (due to inefficiency) would have little impact on system noise performance. The loss within the antenna will affect the intended signal and the noise/interference identically, leading to no reduction in signal to noise ratio (SNR).
The definition of antenna gain or power gain already includes the effect of the antenna's efficiency. Therefore, if one is trying to radiate a signal toward a receiver using a transmitter of a given power, one need only compare the gain of various antennas rather than considering the efficiency as well. This is likewise true for a receiving antenna at very high (especially microwave) frequencies, where the point is to receive a signal which is strong compared to the receiver's noise temperature. However, in the case of a directional antenna used for receiving signals with the intention of rejecting interference from different directions, one is no longer concerned with the antenna efficiency, as discussed above. In this case, rather than quoting the antenna gain, one would be more concerned with the directive gain which does not include the effect of antenna (in)efficiency. The directive gain of an antenna can be computed from the published gain divided by the antenna's efficiency.
This is fortunate, since antennas at lower frequencies which are not rather large (a good fraction of a wavelength in size) are inevitably inefficient (due to the small radiation resistance Rr of small antennas). Most AM broadcast radios (except for car radios) take advantage of this principle by including a small loop antenna for reception which has an extremely poor efficiency. Using such an inefficient antenna at this low frequency (530–1650 kHz) thus has little effect on the receiver's net performance, but simply requires greater amplification by the receiver's electronics. Contrast this tiny component to the massive and very tall towers used at AM broadcast stations for transmitting at the very same frequency, where every percentage point of reduced antenna efficiency entails a substantial cost.
The polarization of an antenna refers to the orientation of the electric field (E-plane) of the radio wave with respect to the Earth's surface and is determined by the physical structure of the antenna and by its orientation; note that this designation is totally distinct from the antenna's directionality. Thus, a simple straight wire antenna will have one polarization when mounted vertically, and a different polarization when mounted horizontally. As a transverse wave, the magnetic field of a radio wave is at right angles to that of the electric field, but by convention, talk of an antenna's "polarization" is understood to refer to the direction of the electric field.
Reflections generally affect polarization. For radio waves, one important reflector is the ionosphere which can change the wave's polarization. Thus for signals received following reflection by the ionosphere (a skywave), a consistent polarization cannot be expected. For line-of-sight communications or ground wave propagation, horizontally or vertically polarized transmissions generally remain in about the same polarization state at the receiving location. Matching the receiving antenna's polarization to that of the transmitter can make a very substantial difference in received signal strength.
Polarization is predictable from an antenna's geometry, although in some cases it is not at all obvious (such as for the quad antenna). An antenna's linear polarization is generally along the direction (as viewed from the receiving location) of the antenna's currents when such a direction can be defined. For instance, a vertical whip antenna or Wi-Fi antenna vertically oriented will transmit and receive in the vertical polarization. Antennas with horizontal elements, such as most rooftop TV antennas in the United States, are horizontally polarized (broadcast TV in the U.S. usually uses horizontal polarization). Even when the antenna system has a vertical orientation, such as an array of horizontal dipole antennas, the polarization is in the horizontal direction corresponding to the current flow. The polarization of a commercial antenna is an essential specification.
Polarization is the sum of the E-plane orientations over time projected onto an imaginary plane perpendicular to the direction of motion of the radio wave. In the most general case, polarization is elliptical, meaning that the polarization of the radio waves varies over time. Two special cases are linear polarization (the ellipse collapses into a line) as we have discussed above, and circular polarization (in which the two axes of the ellipse are equal). In linear polarization the electric field of the radio wave oscillates back and forth along one direction; this can be affected by the mounting of the antenna but usually the desired direction is either horizontal or vertical polarization. In circular polarization, the electric field (and magnetic field) of the radio wave rotates at the radio frequency circularly around the axis of propagation. Circular or elliptically polarized radio waves are designated as right-handed or left-handed using the "thumb in the direction of the propagation" rule. Note that for circular polarization, optical researchers use the opposite right hand rule from the one used by radio engineers.
It is best for the receiving antenna to match the polarization of the transmitted wave for optimum reception. Intermediate matchings will lose some signal strength, but not as much as a complete mismatch. A circularly polarized antenna can be used to equally well match vertical or horizontal linear polarizations. Transmission from a circularly polarized antenna received by a linearly polarized antenna (or vice versa) entails a 3 dB reduction in signal-to-noise ratio as the received power has thereby been cut in half.
Maximum power transfer requires matching the impedance of an antenna system (as seen looking into the transmission line) to the complex conjugate of the impedance of the receiver or transmitter. In the case of a transmitter, however, the desired matching impedance might not correspond to the dynamic output impedance of the transmitter as analyzed as a source impedance but rather the design value (typically 50 ohms) required for efficient and safe operation of the transmitting circuitry. The intended impedance is normally resistive but a transmitter (and some receivers) may have additional adjustments to cancel a certain amount of reactance in order to "tweak" the match. When a transmission line is used in between the antenna and the transmitter (or receiver) one generally would like an antenna system whose impedance is resistive and near the characteristic impedance of that transmission line in order to minimize the standing wave ratio (SWR) and the increase in transmission line losses it entails, in addition to supplying a good match at the transmitter or receiver itself.
In some cases this is done in a more extreme manner, not simply to cancel a small amount of residual reactance, but to resonate an antenna whose resonance frequency is quite different from the intended frequency of operation. For instance, a "whip antenna" can be made significantly shorter than 1/4 wavelength long, for practical reasons, and then resonated using a so-called loading coil. This physically large inductor at the base of the antenna has an inductive reactance which is the opposite of the capacitative reactance that such a vertical antenna has at the desired operating frequency. The result is a pure resistance seen at feedpoint of the loading coil; unfortunately that resistance is somewhat lower than would be desired to match commercial coax.[citation needed]
So an additional problem beyond canceling the unwanted reactance is of matching the remaining resistive impedance to the characteristic impedance of the transmission line. In principle this can always be done with a transformer, however the turns ratio of a transformer is not adjustable. A general matching network with at least two adjustments can be made to correct both components of impedance. Matching networks using discrete inductors and capacitors will have losses associated with those components, and will have power restrictions when used for transmitting. Avoiding these difficulties, commercial antennas are generally designed with fixed matching elements or feeding strategies to get an approximate match to standard coax, such as 50 or 75 Ohms. Antennas based on the dipole (rather than vertical antennas) should include a balun in between the transmission line and antenna element, which may be integrated into any such matching network.
Unlike the above antennas, traveling wave antennas are nonresonant so they have inherently broad bandwidth. They are typically wire antennas multiple wavelengths long, through which the voltage and current waves travel in one direction, instead of bouncing back and forth to form standing waves as in resonant antennas. They have linear polarization (except for the helical antenna). Unidirectional traveling wave antennas are terminated by a resistor at one end equal to the antenna's characteristic resistance, to absorb the waves from one direction. This makes them inefficient as transmitting antennas.
The radiation pattern and even the driving point impedance of an antenna can be influenced by the dielectric constant and especially conductivity of nearby objects. For a terrestrial antenna, the ground is usually one such object of importance. The antenna's height above the ground, as well as the electrical properties (permittivity and conductivity) of the ground, can then be important. Also, in the particular case of a monopole antenna, the ground (or an artificial ground plane) serves as the return connection for the antenna current thus having an additional effect, particularly on the impedance seen by the feed line.
The net quality of a ground reflection depends on the topography of the surface. When the irregularities of the surface are much smaller than the wavelength, we are in the regime of specular reflection, and the receiver sees both the real antenna and an image of the antenna under the ground due to reflection. But if the ground has irregularities not small compared to the wavelength, reflections will not be coherent but shifted by random phases. With shorter wavelengths (higher frequencies), this is generally the case.
The phase of reflection of electromagnetic waves depends on the polarization of the incident wave. Given the larger refractive index of the ground (typically n=2) compared to air (n=1), the phase of horizontally polarized radiation is reversed upon reflection (a phase shift of radians or 180°). On the other hand, the vertical component of the wave's electric field is reflected at grazing angles of incidence approximately in phase. These phase shifts apply as well to a ground modelled as a good electrical conductor.
When an electromagnetic wave strikes a plane surface such as the ground, part of the wave is transmitted into the ground and part of it is reflected, according to the Fresnel coefficients. If the ground is a very good conductor then almost all of the wave is reflected (180° out of phase), whereas a ground modeled as a (lossy) dielectric can absorb a large amount of the wave's power. The power remaining in the reflected wave, and the phase shift upon reflection, strongly depend on the wave's angle of incidence and polarization. The dielectric constant and conductivity (or simply the complex dielectric constant) is dependent on the soil type and is a function of frequency.
The effective area or effective aperture of a receiving antenna expresses the portion of the power of a passing electromagnetic wave which it delivers to its terminals, expressed in terms of an equivalent area. For instance, if a radio wave passing a given location has a flux of 1 pW / m2 (10−12 watts per square meter) and an antenna has an effective area of 12 m2, then the antenna would deliver 12 pW of RF power to the receiver (30 microvolts rms at 75 ohms). Since the receiving antenna is not equally sensitive to signals received from all directions, the effective area is a function of the direction to the source.
The bandwidth characteristics of a resonant antenna element can be characterized according to its Q, just as one uses to characterize the sharpness of an L-C resonant circuit. However it is often assumed that there is an advantage in an antenna having a high Q. After all, Q is short for "quality factor" and a low Q typically signifies excessive loss (due to unwanted resistance) in a resonant L-C circuit. However this understanding does not apply to resonant antennas where the resistance involved is the radiation resistance, a desired quantity which removes energy from the resonant element in order to radiate it (the purpose of an antenna, after all!). The Q is a measure of the ratio of reactance to resistance, so with a fixed radiation resistance (an element's radiation resistance is almost independent of its diameter) a greater reactance off-resonance corresponds to the poorer bandwidth of a very thin conductor. The Q of such a narrowband antenna can be as high as 15. On the other hand, a thick element presents less reactance at an off-resonant frequency, and consequently a Q as low as 5. These two antennas will perform equivalently at the resonant frequency, but the second antenna will perform over a bandwidth 3 times as wide as the "hi-Q" antenna consisting of a thin conductor.
For example, at 30 MHz (10 m wavelength) a true resonant 1⁄4-wavelength monopole would be almost 2.5 meters long, and using an antenna only 1.5 meters tall would require the addition of a loading coil. Then it may be said that the coil has lengthened the antenna to achieve an electrical length of 2.5 meters. However, the resulting resistive impedance achieved will be quite a bit lower than the impedance of a resonant monopole, likely requiring further impedance matching. In addition to a lower radiation resistance, the reactance becomes higher as the antenna size is reduced, and the resonant circuit formed by the antenna and the tuning coil has a Q factor that rises and eventually causes the bandwidth of the antenna to be inadequate for the signal being transmitted. This is the major factor that sets the size of antennas at 1 MHz and lower frequencies.
Consider a half-wave dipole designed to work with signals 1 m wavelength, meaning the antenna would be approximately 50 cm across. If the element has a length-to-diameter ratio of 1000, it will have an inherent resistance of about 63 ohms. Using the appropriate transmission wire or balun, we match that resistance to ensure minimum signal loss. Feeding that antenna with a current of 1 ampere will require 63 volts of RF, and the antenna will radiate 63 watts (ignoring losses) of radio frequency power. Now consider the case when the antenna is fed a signal with a wavelength of 1.25 m; in this case the reflected current would arrive at the feed out-of-phase with the signal, causing the net current to drop while the voltage remains the same. Electrically this appears to be a very high impedance. The antenna and transmission line no longer have the same impedance, and the signal will be reflected back into the antenna, reducing output. This could be addressed by changing the matching system between the antenna and transmission line, but that solution only works well at the new design frequency.
Recall that a current will reflect when there are changes in the electrical properties of the material. In order to efficiently send the signal into the transmission line, it is important that the transmission line has the same impedance as the elements, otherwise some of the signal will be reflected back into the antenna. This leads to the concept of impedance matching, the design of the overall system of antenna and transmission line so the impedance is as close as possible, thereby reducing these losses. Impedance matching between antennas and transmission lines is commonly handled through the use of a balun, although other solutions are also used in certain roles. An important measure of this basic concept is the standing wave ratio, which measures the magnitude of the reflected signal.
An electromagnetic wave refractor in some aperture antennas is a component which due to its shape and position functions to selectively delay or advance portions of the electromagnetic wavefront passing through it. The refractor alters the spatial characteristics of the wave on one side relative to the other side. It can, for instance, bring the wave to a focus or alter the wave front in other ways, generally in order to maximize the directivity of the antenna system. This is the radio equivalent of an optical lens.
The actual antenna which is transmitting the original wave then also may receive a strong signal from its own image from the ground. This will induce an additional current in the antenna element, changing the current at the feedpoint for a given feedpoint voltage. Thus the antenna's impedance, given by the ratio of feedpoint voltage to current, is altered due to the antenna's proximity to the ground. This can be quite a significant effect when the antenna is within a wavelength or two of the ground. But as the antenna height is increased, the reduced power of the reflected wave (due to the inverse square law) allows the antenna to approach its asymptotic feedpoint impedance given by theory. At lower heights, the effect on the antenna's impedance is very sensitive to the exact distance from the ground, as this affects the phase of the reflected wave relative to the currents in the antenna. Changing the antenna's height by a quarter wavelength, then changes the phase of the reflection by 180°, with a completely different effect on the antenna's impedance.
For horizontal propagation between transmitting and receiving antennas situated near the ground reasonably far from each other, the distances traveled by tne direct and reflected rays are nearly the same. There is almost no relative phase shift. If the emission is polarized vertically, the two fields (direct and reflected) add and there is maximum of received signal. If the signal is polarized horizontally, the two signals subtract and the received signal is largely cancelled. The vertical plane radiation patterns are shown in the image at right. With vertical polarization there is always a maximum for θ=0, horizontal propagation (left pattern). For horizontal polarization, there is cancellation at that angle. Note that the above formulae and these plots assume the ground as a perfect conductor. These plots of the radiation pattern correspond to a distance between the antenna and its image of 2.5λ. As the antenna height is increased, the number of lobes increases as well.
On the other hand, classical (analog) television transmissions are usually horizontally polarized, because in urban areas buildings can reflect the electromagnetic waves and create ghost images due to multipath propagation. Using horizontal polarization, ghosting is reduced because the amount of reflection of electromagnetic waves in the p polarization (horizontal polarization off the side of a building) is generally less than s (vertical, in this case) polarization. Vertically polarized analog television has nevertheless been used in some rural areas. In digital terrestrial television such reflections are less problematic, due to robustness of binary transmissions and error correction.
Current circulating in one antenna generally induces a voltage across the feedpoint of nearby antennas or antenna elements. The mathematics presented below are useful in analyzing the electrical behaviour of antenna arrays, where the properties of the individual array elements (such as half wave dipoles) are already known. If those elements were widely separated and driven in a certain amplitude and phase, then each would act independently as that element is known to. However, because of the mutual interaction between their electric and magnetic fields due to proximity, the currents in each element are not simply a function of the applied voltage (according to its driving point impedance), but depend on the currents in the other nearby elements. Note that this now is a near field phenomenon which could not be properly accounted for using the Friis transmission equation for instance.
This is a consequence of Lorentz reciprocity. For an antenna element not connected to anything (open circuited) one can write . But for an element which is short circuited, a current is generated across that short but no voltage is allowed, so the corresponding . This is the case, for instance, with the so-called parasitic elements of a Yagi-Uda antenna where the solid rod can be viewed as a dipole antenna shorted across its feedpoint. Parasitic elements are unpowered elements that absorb and reradiate RF energy according to the induced current calculated using such a system of equations.
The difference in the above factors for the case of θ=0 is the reason that most broadcasting (transmissions intended for the public) uses vertical polarization. For receivers near the ground, horizontally polarized transmissions suffer cancellation. For best reception the receiving antennas for these signals are likewise vertically polarized. In some applications where the receiving antenna must work in any position, as in mobile phones, the base station antennas use mixed polarization, such as linear polarization at an angle (with both vertical and horizontal components) or circular polarization.
Loop antennas consist of a loop or coil of wire. Loops with circumference of a wavelength or larger act similarly to dipole antennas. However loops small in comparison to a wavelength act differently. They interact with the magnetic field of the radio wave instead of the electric field as other antennas do, and so are relatively insensitive to nearby electrical noise. However they have low radiation resistance, and so are inefficient for transmitting. They are used as receiving antennas at low frequencies, and also as direction finding antennas.
It is a fundamental property of antennas that the electrical characteristics of an antenna described in the next section, such as gain, radiation pattern, impedance, bandwidth, resonant frequency and polarization, are the same whether the antenna is transmitting or receiving. For example, the "receiving pattern" (sensitivity as a function of direction) of an antenna when used for reception is identical to the radiation pattern of the antenna when it is driven and functions as a radiator. This is a consequence of the reciprocity theorem of electromagnetics. Therefore, in discussions of antenna properties no distinction is usually made between receiving and transmitting terminology, and the antenna can be viewed as either transmitting or receiving, whichever is more convenient.
The flowering plants (angiosperms), also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants, with about 350,000 species. Like gymnosperms, angiosperms are seed-producing plants; they are distinguished from gymnosperms by characteristics including flowers, endosperm within the seeds, and the production of fruits that contain the seeds. Etymologically, angiosperm means a plant that produces seeds within an enclosure, in other words, a fruiting plant. The term "angiosperm" comes from the Greek composite word (angeion-, "case" or "casing", and sperma, "seed") meaning "enclosed seeds", after the enclosed condition of the seeds.
Fossilized spores suggest that higher plants (embryophytes) have lived on land for at least 475 million years. Early land plants reproduced sexually with flagellated, swimming sperm, like the green algae from which they evolved. An adaptation to terrestrialization was the development of upright meiosporangia for dispersal by spores to new habitats. This feature is lacking in the descendants of their nearest algal relatives, the Charophycean green algae. A later terrestrial adaptation took place with retention of the delicate, avascular sexual stage, the gametophyte, within the tissues of the vascular sporophyte. This occurred by spore germination within sporangia rather than spore release, as in non-seed plants. A current example of how this might have happened can be seen in the precocious spore germination in Selaginella, the spike-moss. The result for the ancestors of angiosperms was enclosing them in a case, the seed. The first seed bearing plants, like the ginkgo, and conifers (such as pines and firs), did not produce flowers. The pollen grains (males) of Ginkgo and cycads produce a pair of flagellated, mobile sperm cells that "swim" down the developing pollen tube to the female and her eggs.
The apparently sudden appearance of nearly modern flowers in the fossil record initially posed such a problem for the theory of evolution that it was called an "abominable mystery" by Charles Darwin. However, the fossil record has considerably grown since the time of Darwin, and recently discovered angiosperm fossils such as Archaefructus, along with further discoveries of fossil gymnosperms, suggest how angiosperm characteristics may have been acquired in a series of steps. Several groups of extinct gymnosperms, in particular seed ferns, have been proposed as the ancestors of flowering plants, but there is no continuous fossil evidence showing exactly how flowers evolved. Some older fossils, such as the upper Triassic Sanmiguelia, have been suggested. Based on current evidence, some propose that the ancestors of the angiosperms diverged from an unknown group of gymnosperms in the Triassic period (245–202 million years ago). Fossil angiosperm-like pollen from the Middle Triassic (247.2–242.0 Ma) suggests an older date for their origin. A close relationship between angiosperms and gnetophytes, proposed on the basis of morphological evidence, has more recently been disputed on the basis of molecular evidence that suggest gnetophytes are instead more closely related to other gymnosperms.[citation needed]
The evolution of seed plants and later angiosperms appears to be the result of two distinct rounds of whole genome duplication events. These occurred at 319 million years ago and 192 million years ago. Another possible whole genome duplication event at 160 million years ago perhaps created the ancestral line that led to all modern flowering plants. That event was studied by sequencing the genome of an ancient flowering plant, Amborella trichopoda, and directly addresses Darwin's "abominable mystery."
The earliest known macrofossil confidently identified as an angiosperm, Archaefructus liaoningensis, is dated to about 125 million years BP (the Cretaceous period), whereas pollen considered to be of angiosperm origin takes the fossil record back to about 130 million years BP. However, one study has suggested that the early-middle Jurassic plant Schmeissneria, traditionally considered a type of ginkgo, may be the earliest known angiosperm, or at least a close relative. In addition, circumstantial chemical evidence has been found for the existence of angiosperms as early as 250 million years ago. Oleanane, a secondary metabolite produced by many flowering plants, has been found in Permian deposits of that age together with fossils of gigantopterids. Gigantopterids are a group of extinct seed plants that share many morphological traits with flowering plants, although they are not known to have been flowering plants themselves.
The great angiosperm radiation, when a great diversity of angiosperms appears in the fossil record, occurred in the mid-Cretaceous (approximately 100 million years ago). However, a study in 2007 estimated that the division of the five most recent (the genus Ceratophyllum, the family Chloranthaceae, the eudicots, the magnoliids, and the monocots) of the eight main groups occurred around 140 million years ago. By the late Cretaceous, angiosperms appear to have dominated environments formerly occupied by ferns and cycadophytes, but large canopy-forming trees replaced conifers as the dominant trees only close to the end of the Cretaceous 66 million years ago or even later, at the beginning of the Tertiary. The radiation of herbaceous angiosperms occurred much later. Yet, many fossil plants recognizable as belonging to modern families (including beech, oak, maple, and magnolia) had already appeared by the late Cretaceous.
Island genetics provides one proposed explanation for the sudden, fully developed appearance of flowering plants. Island genetics is believed to be a common source of speciation in general, especially when it comes to radical adaptations that seem to have required inferior transitional forms. Flowering plants may have evolved in an isolated setting like an island or island chain, where the plants bearing them were able to develop a highly specialized relationship with some specific animal (a wasp, for example). Such a relationship, with a hypothetical wasp carrying pollen from one plant to another much the way fig wasps do today, could result in the development of a high degree of specialization in both the plant(s) and their partners. Note that the wasp example is not incidental; bees, which, it is postulated, evolved specifically due to mutualistic plant relationships, are descended from wasps.
Animals are also involved in the distribution of seeds. Fruit, which is formed by the enlargement of flower parts, is frequently a seed-dispersal tool that attracts animals to eat or otherwise disturb it, incidentally scattering the seeds it contains (see frugivory). Although many such mutualistic relationships remain too fragile to survive competition and to spread widely, flowering proved to be an unusually effective means of reproduction, spreading (whatever its origin) to become the dominant form of land plant life.
Flower ontogeny uses a combination of genes normally responsible for forming new shoots. The most primitive flowers probably had a variable number of flower parts, often separate from (but in contact with) each other. The flowers tended to grow in a spiral pattern, to be bisexual (in plants, this means both male and female parts on the same flower), and to be dominated by the ovary (female part). As flowers evolved, some variations developed parts fused together, with a much more specific number and design, and with either specific sexes per flower or plant or at least "ovary-inferior".
Flower evolution continues to the present day; modern flowers have been so profoundly influenced by humans that some of them cannot be pollinated in nature. Many modern domesticated flower species were formerly simple weeds, which sprouted only when the ground was disturbed. Some of them tended to grow with human crops, perhaps already having symbiotic companion plant relationships with them, and the prettiest did not get plucked because of their beauty, developing a dependence upon and special adaptation to human affection.
The exact relationship between these eight groups is not yet clear, although there is agreement that the first three groups to diverge from the ancestral angiosperm were Amborellales, Nymphaeales, and Austrobaileyales. The term basal angiosperms refers to these three groups. Among the rest, the relationship between the three broadest of these groups (magnoliids, monocots, and eudicots) remains unclear. Some analyses make the magnoliids the first to diverge, others the monocots. Ceratophyllum seems to group with the eudicots rather than with the monocots.
The botanical term "Angiosperm", from the Ancient Greek αγγείον, angeíon (bottle, vessel) and σπέρμα, (seed), was coined in the form Angiospermae by Paul Hermann in 1690, as the name of one of his primary divisions of the plant kingdom. This included flowering plants possessing seeds enclosed in capsules, distinguished from his Gymnospermae, or flowering plants with achenial or schizo-carpic fruits, the whole fruit or each of its pieces being here regarded as a seed and naked. The term and its antonym were maintained by Carl Linnaeus with the same sense, but with restricted application, in the names of the orders of his class Didynamia. Its use with any approach to its modern scope became possible only after 1827, when Robert Brown established the existence of truly naked ovules in the Cycadeae and Coniferae, and applied to them the name Gymnosperms.[citation needed] From that time onward, as long as these Gymnosperms were, as was usual, reckoned as dicotyledonous flowering plants, the term Angiosperm was used antithetically by botanical writers, with varying scope, as a group-name for other dicotyledonous plants.
In most taxonomies, the flowering plants are treated as a coherent group. The most popular descriptive name has been Angiospermae (Angiosperms), with Anthophyta ("flowering plants") a second choice. These names are not linked to any rank. The Wettstein system and the Engler system use the name Angiospermae, at the assigned rank of subdivision. The Reveal system treated flowering plants as subdivision Magnoliophytina (Frohne & U. Jensen ex Reveal, Phytologia 79: 70 1996), but later split it to Magnoliopsida, Liliopsida, and Rosopsida. The Takhtajan system and Cronquist system treat this group at the rank of division, leading to the name Magnoliophyta (from the family name Magnoliaceae). The Dahlgren system and Thorne system (1992) treat this group at the rank of class, leading to the name Magnoliopsida. The APG system of 1998, and the later 2003 and 2009 revisions, treat the flowering plants as a clade called angiosperms without a formal botanical name. However, a formal classification was published alongside the 2009 revision in which the flowering plants form the Subclass Magnoliidae.
The internal classification of this group has undergone considerable revision. The Cronquist system, proposed by Arthur Cronquist in 1968 and published in its full form in 1981, is still widely used but is no longer believed to accurately reflect phylogeny. A consensus about how the flowering plants should be arranged has recently begun to emerge through the work of the Angiosperm Phylogeny Group (APG), which published an influential reclassification of the angiosperms in 1998. Updates incorporating more recent research were published as APG II in 2003 and as APG III in 2009.
Recent studies, as by the APG, show that the monocots form a monophyletic group (clade) but that the dicots do not (they are paraphyletic). Nevertheless, the majority of dicot species do form a monophyletic group, called the eudicots or tricolpates. Of the remaining dicot species, most belong to a third major clade known as the magnoliids, containing about 9,000 species. The rest include a paraphyletic grouping of primitive species known collectively as the basal angiosperms, plus the families Ceratophyllaceae and Chloranthaceae.
The number of species of flowering plants is estimated to be in the range of 250,000 to 400,000. This compares to around 12,000 species of moss or 11,000 species of pteridophytes, showing that the flowering plants are much more diverse. The number of families in APG (1998) was 462. In APG II (2003) it is not settled; at maximum it is 457, but within this number there are 55 optional segregates, so that the minimum number of families in this system is 402. In APG III (2009) there are 415 families.
In the dicotyledons, the bundles in the very young stem are arranged in an open ring, separating a central pith from an outer cortex. In each bundle, separating the xylem and phloem, is a layer of meristem or active formative tissue known as cambium. By the formation of a layer of cambium between the bundles (interfascicular cambium), a complete ring is formed, and a regular periodical increase in thickness results from the development of xylem on the inside and phloem on the outside. The soft phloem becomes crushed, but the hard wood persists and forms the bulk of the stem and branches of the woody perennial. Owing to differences in the character of the elements produced at the beginning and end of the season, the wood is marked out in transverse section into concentric rings, one for each season of growth, called annual rings.
The characteristic feature of angiosperms is the flower. Flowers show remarkable variation in form and elaboration, and provide the most trustworthy external characteristics for establishing relationships among angiosperm species. The function of the flower is to ensure fertilization of the ovule and development of fruit containing seeds. The floral apparatus may arise terminally on a shoot or from the axil of a leaf (where the petiole attaches to the stem). Occasionally, as in violets, a flower arises singly in the axil of an ordinary foliage-leaf. More typically, the flower-bearing portion of the plant is sharply distinguished from the foliage-bearing or vegetative portion, and forms a more or less elaborate branch-system called an inflorescence.
The flower may consist only of these parts, as in willow, where each flower comprises only a few stamens or two carpels. Usually, other structures are present and serve to protect the sporophylls and to form an envelope attractive to pollinators. The individual members of these surrounding structures are known as sepals and petals (or tepals in flowers such as Magnolia where sepals and petals are not distinguishable from each other). The outer series (calyx of sepals) is usually green and leaf-like, and functions to protect the rest of the flower, especially the bud. The inner series (corolla of petals) is, in general, white or brightly colored, and is more delicate in structure. It functions to attract insect or bird pollinators. Attraction is effected by color, scent, and nectar, which may be secreted in some part of the flower. The characteristics that attract pollinators account for the popularity of flowers and flowering plants among humans.
While the majority of flowers are perfect or hermaphrodite (having both pollen and ovule producing parts in the same flower structure), flowering plants have developed numerous morphological and physiological mechanisms to reduce or prevent self-fertilization. Heteromorphic flowers have short carpels and long stamens, or vice versa, so animal pollinators cannot easily transfer pollen to the pistil (receptive part of the carpel). Homomorphic flowers may employ a biochemical (physiological) mechanism called self-incompatibility to discriminate between self and non-self pollen grains. In other species, the male and female parts are morphologically separated, developing on different flowers.
Double fertilization refers to a process in which two sperm cells fertilize cells in the ovary. This process begins when a pollen grain adheres to the stigma of the pistil (female reproductive structure), germinates, and grows a long pollen tube. While this pollen tube is growing, a haploid generative cell travels down the tube behind the tube nucleus. The generative cell divides by mitosis to produce two haploid (n) sperm cells. As the pollen tube grows, it makes its way from the stigma, down the style and into the ovary. Here the pollen tube reaches the micropyle of the ovule and digests its way into one of the synergids, releasing its contents (which include the sperm cells). The synergid that the cells were released into degenerates and one sperm makes its way to fertilize the egg cell, producing a diploid (2n) zygote. The second sperm cell fuses with both central cell nuclei, producing a triploid (3n) cell. As the zygote develops into an embryo, the triploid cell develops into the endosperm, which serves as the embryo's food supply. The ovary now will develop into fruit and the ovule will develop into seed.
The character of the seed coat bears a definite relation to that of the fruit. They protect the embryo and aid in dissemination; they may also directly promote germination. Among plants with indehiscent fruits, in general, the fruit provides protection for the embryo and secures dissemination. In this case, the seed coat is only slightly developed. If the fruit is dehiscent and the seed is exposed, in general, the seed-coat is well developed, and must discharge the functions otherwise executed by the fruit.
Agriculture is almost entirely dependent on angiosperms, which provide virtually all plant-based food, and also provide a significant amount of livestock feed. Of all the families of plants, the Poaceae, or grass family (grains), is by far the most important, providing the bulk of all feedstocks (rice, corn — maize, wheat, barley, rye, oats, pearl millet, sugar cane, sorghum). The Fabaceae, or legume family, comes in second place. Also of high importance are the Solanaceae, or nightshade family (potatoes, tomatoes, and peppers, among others), the Cucurbitaceae, or gourd family (also including pumpkins and melons), the Brassicaceae, or mustard plant family (including rapeseed and the innumerable varieties of the cabbage species Brassica oleracea), and the Apiaceae, or parsley family. Many of our fruits come from the Rutaceae, or rue family (including oranges, lemons, grapefruits, etc.), and the Rosaceae, or rose family (including apples, pears, cherries, apricots, plums, etc.).
Traditionally, the flowering plants are divided into two groups, which in the Cronquist system are called Magnoliopsida (at the rank of class, formed from the family name Magnoliaceae) and Liliopsida (at the rank of class, formed from the family name Liliaceae). Other descriptive names allowed by Article 16 of the ICBN include Dicotyledones or Dicotyledoneae, and Monocotyledones or Monocotyledoneae, which have a long history of use. In English a member of either group may be called a dicotyledon (plural dicotyledons) and monocotyledon (plural monocotyledons), or abbreviated, as dicot (plural dicots) and monocot (plural monocots). These names derive from the observation that the dicots most often have two cotyledons, or embryonic leaves, within each seed. The monocots usually have only one, but the rule is not absolute either way. From a diagnostic point of view, the number of cotyledons is neither a particularly handy nor a reliable character.
Hyderabad (i/ˈhaɪdərəˌbæd/ HY-dər-ə-bad; often /ˈhaɪdrəˌbæd/) is the capital of the southern Indian state of Telangana and de jure capital of Andhra Pradesh.[A] Occupying 650 square kilometres (250 sq mi) along the banks of the Musi River, it has a population of about 6.7 million and a metropolitan population of about 7.75 million, making it the fourth most populous city and sixth most populous urban agglomeration in India. At an average altitude of 542 metres (1,778 ft), much of Hyderabad is situated on hilly terrain around artificial lakes, including Hussain Sagar—predating the city's founding—north of the city centre.
Established in 1591 by Muhammad Quli Qutb Shah, Hyderabad remained under the rule of the Qutb Shahi dynasty for nearly a century before the Mughals captured the region. In 1724, Mughal viceroy Asif Jah I declared his sovereignty and created his own dynasty, known as the Nizams of Hyderabad. The Nizam's dominions became a princely state during the British Raj, and remained so for 150 years, with the city serving as its capital. The Nizami influence can still be seen in the culture of the Hyderabadi Muslims. The city continued as the capital of Hyderabad State after it was brought into the Indian Union in 1948, and became the capital of Andhra Pradesh after the States Reorganisation Act, 1956. Since 1956, Rashtrapati Nilayam in the city has been the winter office of the President of India. In 2014, the newly formed state of Telangana split from Andhra Pradesh and the city became joint capital of the two states, a transitional arrangement scheduled to end by 2025.
Relics of Qutb Shahi and Nizam rule remain visible today, with the Charminar—commissioned by Muhammad Quli Qutb Shah—coming to symbolise Hyderabad. Golconda fort is another major landmark. The influence of Mughlai culture is also evident in the city's distinctive cuisine, which includes Hyderabadi biryani and Hyderabadi haleem. The Qutb Shahis and Nizams established Hyderabad as a cultural hub, attracting men of letters from different parts of the world. Hyderabad emerged as the foremost centre of culture in India with the decline of the Mughal Empire in the mid-19th century, with artists migrating to the city from the rest of the Indian subcontinent. While Hyderabad is losing its cultural pre-eminence, it is today, due to the Telugu film industry, the country's second-largest producer of motion pictures.
Hyderabad was historically known as a pearl and diamond trading centre, and it continues to be known as the City of Pearls. Many of the city's traditional bazaars, including Laad Bazaar, Begum Bazaar and Sultan Bazaar, have remained open for centuries. However, industrialisation throughout the 20th century attracted major Indian manufacturing, research and financial institutions, including Bharat Heavy Electricals Limited, the National Geophysical Research Institute and the Centre for Cellular and Molecular Biology. Special economic zones dedicated to information technology have encouraged companies from across India and around the world to set up operations and the emergence of pharmaceutical and biotechnology industries in the 1990s led to the area's naming as India's "Genome Valley". With an output of US$74 billion, Hyderabad is the fifth-largest contributor to India's overall gross domestic product.
According to John Everett-Heath, the author of Oxford Concise Dictionary of World Place Names, Hyderabad means "Haydar's city" or "lion city", from haydar (lion) and ābād (city). It was named to honour the Caliph Ali Ibn Abi Talib, who was also known as Haydar because of his lion-like valour in battles. Andrew Petersen, a scholar of Islamic architecture, says the city was originally called Baghnagar (city of gardens). One popular theory suggests that Muhammad Quli Qutb Shah, the founder of the city, named it "Bhagyanagar" or "Bhāgnagar" after Bhagmati, a local nautch (dancing) girl with whom he had fallen in love. She converted to Islam and adopted the title Hyder Mahal. The city was renamed Hyderabad in her honour. According to another source, the city was named after Haidar, the son of Quli Qutb Shah.
Archaeologists excavating near the city have unearthed Iron Age sites that may date from 500 BCE. The region comprising modern Hyderabad and its surroundings was known as Golkonda (Golla Konda-"shepherd's hill"), and was ruled by the Chalukya dynasty from 624 CE to 1075 CE. Following the dissolution of the Chalukya empire into four parts in the 11th century, Golkonda came under the control of the Kakatiya dynasty from 1158, whose seat of power was at Warangal, 148 km (92 mi) northeast of modern Hyderabad.
The Kakatiya dynasty was reduced to a vassal of the Khilji dynasty in 1310 after its defeat by Sultan Alauddin Khilji of the Delhi Sultanate. This lasted until 1321, when the Kakatiya dynasty was annexed by Malik Kafur, Allaudin Khilji's general. During this period, Alauddin Khilji took the Koh-i-Noor diamond, which is said to have been mined from the Kollur Mines of Golkonda, to Delhi. Muhammad bin Tughluq succeeded to the Delhi sultanate in 1325, bringing Warangal under the rule of the Tughlaq dynasty until 1347 when Ala-ud-Din Bahman Shah, a governor under bin Tughluq, rebelled against Delhi and established the Bahmani Sultanate in the Deccan Plateau, with Gulbarga, 200 km (124 mi) west of Hyderabad, as its capital. The Bahmani kings ruled the region until 1518 and were the first independent Muslim rulers of the Deccan.
Sultan Quli, a governor of Golkonda, revolted against the Bahmani Sultanate and established the Qutb Shahi dynasty in 1518; he rebuilt the mud-fort of Golconda and named the city "Muhammad nagar". The fifth sultan, Muhammad Quli Qutb Shah, established Hyderabad on the banks of the Musi River in 1591, to avoid the water shortages experienced at Golkonda. During his rule, he had the Charminar and Mecca Masjid built in the city. On 21 September 1687, the Golkonda Sultanate came under the rule of the Mughal emperor Aurangzeb after a year-long siege of the Golkonda fort. The annexed area was renamed Deccan Suba (Deccan province) and the capital was moved from Golkonda to Aurangabad, about 550 km (342 mi) northwest of Hyderabad.
In 1713 Farrukhsiyar, the Mughal emperor, appointed Asif Jah I to be Viceroy of the Deccan, with the title Nizam-ul-Mulk (Administrator of the Realm). In 1724, Asif Jah I defeated Mubariz Khan to establish autonomy over the Deccan Suba, named the region Hyderabad Deccan, and started what came to be known as the Asif Jahi dynasty. Subsequent rulers retained the title Nizam ul-Mulk and were referred to as Asif Jahi Nizams, or Nizams of Hyderabad. The death of Asif Jah I in 1748 resulted in a period of political unrest as his sons, backed by opportunistic neighbouring states and colonial foreign forces, contended for the throne. The accession of Asif Jah II, who reigned from 1762 to 1803, ended the instability. In 1768 he signed the treaty of Masulipatnam, surrendering the coastal region to the East India Company in return for a fixed annual rent.
In 1769 Hyderabad city became the formal capital of the Nizams. In response to regular threats from Hyder Ali (Dalwai of Mysore), Baji Rao I (Peshwa of the Maratha Empire), and Basalath Jung (Asif Jah II's elder brother, who was supported by the Marquis de Bussy-Castelnau), the Nizam signed a subsidiary alliance with the East India Company in 1798, allowing the British Indian Army to occupy Bolarum (modern Secunderabad) to protect the state's borders, for which the Nizams paid an annual maintenance to the British.
After India gained independence, the Nizam declared his intention to remain independent rather than become part of the Indian Union. The Hyderabad State Congress, with the support of the Indian National Congress and the Communist Party of India, began agitating against Nizam VII in 1948. On 17 September that year, the Indian Army took control of Hyderabad State after an invasion codenamed Operation Polo. With the defeat of his forces, Nizam VII capitulated to the Indian Union by signing an Instrument of Accession, which made him the Rajpramukh (Princely Governor) of the state until 31 October 1956. Between 1946 and 1951, the Communist Party of India fomented the Telangana uprising against the feudal lords of the Telangana region. The Constitution of India, which became effective on 26 January 1950, made Hyderabad State one of the part B states of India, with Hyderabad city continuing to be the capital. In his 1955 report Thoughts on Linguistic States, B. R. Ambedkar, then chairman of the Drafting Committee of the Indian Constitution, proposed designating the city of Hyderabad as the second capital of India because of its amenities and strategic central location. Since 1956, the Rashtrapati Nilayam in Hyderabad has been the second official residence and business office of the President of India; the President stays once a year in winter and conducts official business particularly relating to Southern India.
On 1 November 1956 the states of India were reorganised by language. Hyderabad state was split into three parts, which were merged with neighbouring states to form the modern states of Maharashtra, Karnataka and Andhra Pradesh. The nine Telugu- and Urdu-speaking districts of Hyderabad State in the Telangana region were merged with the Telugu-speaking Andhra State to create Andhra Pradesh, with Hyderabad as its capital. Several protests, known collectively as the Telangana movement, attempted to invalidate the merger and demanded the creation of a new Telangana state. Major actions took place in 1969 and 1972, and a third began in 2010. The city suffered several explosions: one at Dilsukhnagar in 2002 claimed two lives; terrorist bombs in May and August 2007 caused communal tension and riots; and two bombs exploded in February 2013. On 30 July 2013 the government of India declared that part of Andhra Pradesh would be split off to form a new Telangana state, and that Hyderabad city would be the capital city and part of Telangana, while the city would also remain the capital of Andhra Pradesh for no more than ten years. On 3 October 2013 the Union Cabinet approved the proposal, and in February 2014 both houses of Parliament passed the Telangana Bill. With the final assent of the President of India in June 2014, Telangana state was formed.
Situated in the southern part of Telangana in southeastern India, Hyderabad is 1,566 kilometres (973 mi) south of Delhi, 699 kilometres (434 mi) southeast of Mumbai, and 570 kilometres (350 mi) north of Bangalore by road. It lies on the banks of the Musi River, in the northern part of the Deccan Plateau. Greater Hyderabad covers 650 km2 (250 sq mi), making it one of the largest metropolitan areas in India. With an average altitude of 542 metres (1,778 ft), Hyderabad lies on predominantly sloping terrain of grey and pink granite, dotted with small hills, the highest being Banjara Hills at 672 metres (2,205 ft). The city has numerous lakes referred to as sagar, meaning "sea". Examples include artificial lakes created by dams on the Musi, such as Hussain Sagar (built in 1562 near the city centre), Osman Sagar and Himayat Sagar. As of 1996, the city had 140 lakes and 834 water tanks (ponds).
Hyderabad has a tropical wet and dry climate (Köppen Aw) bordering on a hot semi-arid climate (Köppen BSh). The annual mean temperature is 26.6 °C (79.9 °F); monthly mean temperatures are 21–33 °C (70–91 °F). Summers (March–June) are hot and humid, with average highs in the mid-to-high 30s Celsius; maximum temperatures often exceed 40 °C (104 °F) between April and June. The coolest temperatures occur in December and January, when the lowest temperature occasionally dips to 10 °C (50 °F). May is the hottest month, when daily temperatures range from 26 to 39 °C (79–102 °F); December, the coldest, has temperatures varying from 14.5 to 28 °C (57–82 °F).
Hyderabad's lakes and the sloping terrain of its low-lying hills provide habitat for an assortment of flora and fauna. The forest region in and around the city encompasses areas of ecological and biological importance, which are preserved in the form of national parks, zoos, mini-zoos and a wildlife sanctuary. Nehru Zoological Park, the city's one large zoo, is the first in India to have a lion and tiger safari park. Hyderabad has three national parks (Mrugavani National Park, Mahavir Harina Vanasthali National Park and Kasu Brahmananda Reddy National Park), and the Manjira Wildlife Sanctuary is about 50 km (31 mi) from the city. Hyderabad's other environmental reserves are: Kotla Vijayabhaskara Reddy Botanical Gardens, Shamirpet Lake, Hussain Sagar, Fox Sagar Lake, Mir Alam Tank and Patancheru Lake, which is home to regional birds and attracts seasonal migratory birds from different parts of the world. Organisations engaged in environmental and wildlife preservation include the Telangana Forest Department, Indian Council of Forestry Research and Education, the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), the Animal Welfare Board of India, the Blue Cross of Hyderabad and the University of Hyderabad.
The Greater Hyderabad Municipal Corporation (GHMC) oversees the civic infrastructure of the city's 18 "circles", which together encompass 150 municipal wards. Each ward is represented by a corporator, elected by popular vote. The corporators elect the Mayor, who is the titular head of GHMC; executive powers rest with the Municipal Commissioner, appointed by the state government. The GHMC carries out the city's infrastructural work such as building and maintenance of roads and drains, town planning including construction regulation, maintenance of municipal markets and parks, solid waste management, the issuing of birth and death certificates, the issuing of trade licences, collection of property tax, and community welfare services such as mother and child healthcare, and pre-school and non-formal education. The GHMC was formed in April 2007 by merging the Municipal Corporation of Hyderabad (MCH) with 12 municipalities of the Hyderabad, Ranga Reddy and Medak districts covering a total area of 650 km2 (250 sq mi).:3 In the 2016 municipal election, the Telangana Rashtra Samithi formed the majority and the present Mayor is Bonthu Ram Mohan. The Secunderabad Cantonment Board is a civic administration agency overseeing an area of 40.1 km2 (15.5 sq mi),:93 where there are several military camps.:2 The Osmania University campus is administered independently by the university authority.:93
The jurisdictions of the city's administrative agencies are, in ascending order of size: the Hyderabad Police area, Hyderabad district, the GHMC area ("Hyderabad city") and the area under the Hyderabad Metropolitan Development Authority (HMDA). The HMDA is an apolitical urban planning agency that covers the GHMC and its suburbs, extending to 54 mandals in five districts encircling the city. It coordinates the development activities of GHMC and suburban municipalities and manages the administration of bodies such as the Hyderabad Metropolitan Water Supply and Sewerage Board (HMWSSB).
The HMWSSB regulates rainwater harvesting, sewerage services and water supply, which is sourced from several dams located in the suburbs. In 2005, the HMWSSB started operating a 116-kilometre-long (72 mi) water supply pipeline from Nagarjuna Sagar Dam to meet increasing demand. The Telangana Southern Power Distribution Company Limited manages electricity supply. As of October 2014, there were 15 fire stations in the city, operated by the Telangana State Disaster and Fire Response Department. The government-owned India Post has five head post offices and many sub-post offices in Hyderabad, which are complemented by private courier services.
Hyderabad produces around 4,500 tonnes of solid waste daily, which is transported from collection units in Imlibun, Yousufguda and Lower Tank Bund to the dumpsite in Jawaharnagar. Disposal is managed by the Integrated Solid Waste Management project which was started by the GHMC in 2010. Rapid urbanisation and increased economic activity has also led to increased industrial waste, air, noise and water pollution, which is regulated by the Telangana Pollution Control Board (TPCB). The contribution of different sources to air pollution in 2006 was: 20–50% from vehicles, 40–70% from a combination of vehicle discharge and road dust, 10–30% from industrial discharges and 3–10% from the burning of household rubbish. Deaths resulting from atmospheric particulate matter are estimated at 1,700–3,000 each year. Ground water around Hyderabad, which has a hardness of up to 1000 ppm, around three times higher than is desirable, is the main source of drinking water but the increasing population and consequent increase in demand has led to a decline in not only ground water but also river and lake levels. This shortage is further exacerbated by inadequately treated effluent discharged from industrial treatment plants polluting the water sources of the city.
The Commissionerate of Health and Family Welfare is responsible for planning, implementation and monitoring of all facilities related to health and preventive services. As of 2010[update]–11, the city had 50 government hospitals, 300 private and charity hospitals and 194 nursing homes providing around 12,000 hospital beds, fewer than half the required 25,000. For every 10,000 people in the city, there are 17.6 hospital beds, 9 specialist doctors, 14 nurses and 6 physicians. The city also has about 4,000 individual clinics and 500 medical diagnostic centres. Private clinics are preferred by many residents because of the distance to, poor quality of care at and long waiting times in government facilities,:60–61 despite the high proportion of the city's residents being covered by government health insurance: 24% according to a National Family Health Survey in 2005.:41 As of 2012[update], many new private hospitals of various sizes were opened or being built. Hyderabad also has outpatient and inpatient facilities that use Unani, homeopathic and Ayurvedic treatments.
In the 2005 National Family Health Survey, it was reported that the city's total fertility rate is 1.8,:47 which is below the replacement rate. Only 61% of children had been provided with all basic vaccines (BCG, measles and full courses of polio and DPT), fewer than in all other surveyed cities except Meerut.:98 The infant mortality rate was 35 per 1,000 live births, and the mortality rate for children under five was 41 per 1,000 live births.:97 The survey also reported that a third of women and a quarter of men are overweight or obese, 49% of children below 5 years are anaemic, and up to 20% of children are underweight,:44, 55–56 while more than 2% of women and 3% of men suffer from diabetes.:57
When the GHMC was created in 2007, the area occupied by the municipality increased from 175 km2 (68 sq mi) to 650 km2 (250 sq mi). Consequently, the population increased by 87%, from 3,637,483 in the 2001 census to 6,809,970 in the 2011 census, 24% of which are migrants from elsewhere in India,:2 making Hyderabad the nation's fourth most populous city. As of 2011[update], the population density is 18,480/km2 (47,900/sq mi). At the same 2011 census, the Hyderabad Urban Agglomeration had a population of 7,749,334, making it the sixth most populous urban agglomeration in the country. The population of the Hyderabad urban agglomeration has since been estimated by electoral officials to be 9.1 million as of early 2013 but is expected to exceed 10 million by the end of the year. There are 3,500,802 male and 3,309,168 female citizens—a sex ratio of 945 females per 1000 males, higher than the national average of 926 per 1000. Among children aged 0–6 years, 373,794 are boys and 352,022 are girls—a ratio of 942 per 1000. Literacy stands at 82.96% (male 85.96%; female 79.79%), higher than the national average of 74.04%. The socio-economic strata consist of 20% upper class, 50% middle class and 30% working class.
Referred to as "Hyderabadi", the residents of Hyderabad are predominantly Telugu and Urdu speaking people, with minority Bengali, Gujarati (including Memon), Kannada (including Nawayathi), Malayalam, Marathi, Marwari, Odia, Punjabi, Tamil and Uttar Pradeshi communities. Hyderabad is home to a unique dialect of Urdu called Hyderabadi Urdu, which is a type of Dakhini, and is the mother tongue of most Hyderabadi Muslims, a unique community who owe much of their history, language, cuisine, and culture to Hyderabad, and the various dynasties who previously ruled. Hadhrami Arabs, African Arabs, Armenians, Abyssinians, Iranians, Pathans and Turkish people are also present; these communities, of which the Hadhrami are the largest, declined after Hyderabad State became part of the Indian Union, as they lost the patronage of the Nizams.
In the greater metropolitan area, 13% of the population live below the poverty line. According to a 2012 report submitted by GHMC to the World Bank, Hyderabad has 1,476 slums with a total population of 1.7 million, of whom 66% live in 985 slums in the "core" of the city (the part that formed Hyderabad before the April 2007 expansion) and the remaining 34% live in 491 suburban tenements. About 22% of the slum-dwelling households had migrated from different parts of India in the last decade of the 20th century, and 63% claimed to have lived in the slums for more than 10 years.:55 Overall literacy in the slums is 60–80% and female literacy is 52–73%. A third of the slums have basic service connections, and the remainder depend on general public services provided by the government. There are 405 government schools, 267 government aided schools, 175 private schools and 528 community halls in the slum areas.:70 According to a 2008 survey by the Centre for Good Governance, 87.6% of the slum-dwelling households are nuclear families, 18% are very poor, with an income up to ₹20000 (US$300) per annum, 73% live below the poverty line (a standard poverty line recognised by the Andhra Pradesh Government is ₹24000 (US$360) per annum), 27% of the chief wage earners (CWE) are casual labour and 38% of the CWE are illiterate. About 3.72% of the slum children aged 5–14 do not go to school and 3.17% work as child labour, of whom 64% are boys and 36% are girls. The largest employers of child labour are street shops and construction sites. Among the working children, 35% are engaged in hazardous jobs.:59
Many historic and tourist sites lie in south central Hyderabad, such as the Charminar, the Mecca Masjid, the Salar Jung Museum, the Nizam's Museum, the Falaknuma Palace, and the traditional retail corridor comprising the Pearl Market, Laad Bazaar and Madina Circle. North of the river are hospitals, colleges, major railway stations and business areas such as Begum Bazaar, Koti, Abids, Sultan Bazaar and Moazzam Jahi Market, along with administrative and recreational establishments such as the Reserve Bank of India, the Telangana Secretariat, the Hyderabad Mint, the Telangana Legislature, the Public Gardens, the Nizam Club, the Ravindra Bharathi, the State Museum, the Birla Temple and the Birla Planetarium.
North of central Hyderabad lie Hussain Sagar, Tank Bund Road, Rani Gunj and the Secunderabad Railway Station. Most of the city's parks and recreational centres, such as Sanjeevaiah Park, Indira Park, Lumbini Park, NTR Gardens, the Buddha statue and Tankbund Park are located here. In the northwest part of the city there are upscale residential and commercial areas such as Banjara Hills, Jubilee Hills, Begumpet, Khairatabad and Miyapur. The northern end contains industrial areas such as Sanathnagar, Moosapet, Balanagar, Patancheru and Chanda Nagar. The northeast end is dotted with residential areas. In the eastern part of the city lie many defence research centres and Ramoji Film City. The "Cyberabad" area in the southwest and west of the city has grown rapidly since the 1990s. It is home to information technology and bio-pharmaceutical companies and to landmarks such as Hyderabad Airport, Osman Sagar, Himayath Sagar and Kasu Brahmananda Reddy National Park.
Heritage buildings constructed during the Qutb Shahi and Nizam eras showcase Indo-Islamic architecture influenced by Medieval, Mughal and European styles. After the 1908 flooding of the Musi River, the city was expanded and civic monuments constructed, particularly during the rule of Mir Osman Ali Khan (the VIIth Nizam), whose patronage of architecture led to him being referred to as the maker of modern Hyderabad. In 2012, the government of India declared Hyderabad the first "Best heritage city of India".
Qutb Shahi architecture of the 16th and early 17th centuries followed classical Persian architecture featuring domes and colossal arches. The oldest surviving Qutb Shahi structure in Hyderabad is the ruins of Golconda fort built in the 16th century. The Charminar, Mecca Masjid, Charkaman and Qutb Shahi tombs are other existing structures of this period. Among these the Charminar has become an icon of the city; located in the centre of old Hyderabad, it is a square structure with sides 20 m (66 ft) long and four grand arches each facing a road. At each corner stands a 56 m (184 ft)-high minaret. Most of the historical bazaars that still exist were constructed on the street north of Charminar towards Golconda fort. The Charminar, Qutb Shahi tombs and Golconda fort are considered to be monuments of national importance in India; in 2010 the Indian government proposed that the sites be listed for UNESCO World Heritage status.:11–18
Among the oldest surviving examples of Nizam architecture in Hyderabad is the Chowmahalla Palace, which was the seat of royal power. It showcases a diverse array of architectural styles, from the Baroque Harem to its Neoclassical royal court. The other palaces include Falaknuma Palace (inspired by the style of Andrea Palladio), Purani Haveli, King Kothi and Bella Vista Palace all of which were built at the peak of Nizam rule in the 19th century. During Mir Osman Ali Khan's rule, European styles, along with Indo-Islamic, became prominent. These styles are reflected in the Falaknuma Palace and many civic monuments such as the Hyderabad High Court, Osmania Hospital, Osmania University, the State Central Library, City College, the Telangana Legislature, the State Archaeology Museum, Jubilee Hall, and Hyderabad and Kachiguda railway stations. Other landmarks of note are Paigah Palace, Asman Garh Palace, Basheer Bagh Palace, Errum Manzil and the Spanish Mosque, all constructed by the Paigah family.:16–17
Hyderabad is the largest contributor to the gross domestic product (GDP), tax and other revenues, of Telangana, and the sixth largest deposit centre and fourth largest credit centre nationwide, as ranked by the Reserve Bank of India (RBI) in June 2012. Its US$74 billion GDP made it the fifth-largest contributor city to India's overall GDP in 2011–12. Its per capita annual income in 2011 was ₹44300 (US$660). As of 2006[update], the largest employers in the city were the governments of Andhra Pradesh (113,098 employees) and India (85,155). According to a 2005 survey, 77% of males and 19% of females in the city were employed. The service industry remains dominant in the city, and 90% of the employed workforce is engaged in this sector.
Hyderabad's role in the pearl trade has given it the name "City of Pearls" and up until the 18th century, the city was also the only global trading centre for large diamonds. Industrialisation began under the Nizams in the late 19th century, helped by railway expansion that connected the city with major ports. From the 1950s to the 1970s, Indian enterprises, such as Bharat Heavy Electricals Limited (BHEL), Nuclear Fuel Complex (NFC), National Mineral Development Corporation (NMDC), Bharat Electronics (BEL), Electronics Corporation of India Limited (ECIL), Defence Research and Development Organisation (DRDO), Hindustan Aeronautics Limited (HAL), Centre for Cellular and Molecular Biology (CCMB), Centre for DNA Fingerprinting and Diagnostics (CDFD), State Bank of Hyderabad (SBH) and Andhra Bank (AB) were established in the city. The city is home to Hyderabad Securities formerly known as Hyderabad Stock Exchange (HSE), and houses the regional office of the Securities and Exchange Board of India (SEBI). In 2013, the Bombay Stock Exchange (BSE) facility in Hyderabad was forecast to provide operations and transactions services to BSE-Mumbai by the end of 2014. The growth of the financial services sector has helped Hyderabad evolve from a traditional manufacturing city to a cosmopolitan industrial service centre. Since the 1990s, the growth of information technology (IT), IT-enabled services (ITES), insurance and financial institutions has expanded the service sector, and these primary economic activities have boosted the ancillary sectors of trade and commerce, transport, storage, communication, real estate and retail.
The establishment of Indian Drugs and Pharmaceuticals Limited (IDPL), a public sector undertaking, in 1961 was followed over the decades by many national and global companies opening manufacturing and research facilities in the city. As of 2010[update], the city manufactured one third of India's bulk drugs and 16% of biotechnology products, contributing to its reputation as "India's pharmaceutical capital" and the "Genome Valley of India". Hyderabad is a global centre of information technology, for which it is known as Cyberabad (Cyber City). As of 2013[update], it contributed 15% of India's and 98% of Andhra Pradesh's exports in IT and ITES sectors and 22% of NASSCOM's total membership is from the city. The development of HITEC City, a township with extensive technological infrastructure, prompted multinational companies to establish facilities in Hyderabad. The city is home to more than 1300 IT and ITES firms, including global conglomerates such as Microsoft (operating its largest R&D campus outside the US), Google, IBM, Yahoo!, Dell, Facebook,:3 and major Indian firms including Tech Mahindra, Infosys, Tata Consultancy Services (TCS), Polaris and Wipro.:3 In 2009 the World Bank Group ranked the city as the second best Indian city for doing business. The city and its suburbs contain the highest number of special economic zones of any Indian city.
Like the rest of India, Hyderabad has a large informal economy that employs 30% of the labour force.:71 According to a survey published in 2007, it had 40–50,000 street vendors, and their numbers were increasing.:9 Among the street vendors, 84% are male and 16% female,:12 and four fifths are "stationary vendors" operating from a fixed pitch, often with their own stall.:15–16 Most are financed through personal savings; only 8% borrow from moneylenders.:19 Vendor earnings vary from ₹50 (74¢ US) to ₹800 (US$12) per day.:25 Other unorganised economic sectors include dairy, poultry farming, brick manufacturing, casual labour and domestic help. Those involved in the informal economy constitute a major portion of urban poor.:71
Hyderabad emerged as the foremost centre of culture in India with the decline of the Mughal Empire. After the fall of Delhi in 1857, the migration of performing artists to the city particularly from the north and west of the Indian sub continent, under the patronage of the Nizam, enriched the cultural milieu. This migration resulted in a mingling of North and South Indian languages, cultures and religions, which has since led to a co-existence of Hindu and Muslim traditions, for which the city has become noted.:viii A further consequence of this north–south mix is that both Telugu and Urdu are official languages of Telangana. The mixing of religions has also resulted in many festivals being celebrated in Hyderabad such as Ganesh Chaturthi, Diwali and Bonalu of Hindu tradition and Eid ul-Fitr and Eid al-Adha by Muslims.

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