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7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.6.4.2 Coherent data communications (direct modulation) | The BER as a function of SNRb, the signal to noise ratio per bit for coherent binary systems is: BER (SNRb) = 0,5 × erfc (√SNRb) (6.12) where erfc (x) is defined as: dt e erfc(x) -t x 2 2 ∫ ∞ = π (6.13) It is not possible to calculate the integral part of formula (6.11) analytically, but the BER as a function of the si... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.6.4.3 Coherent data communications (subcarrier modulation) | If a subcarrier frequency modulation is used in the data communication the functions related to direct coherent data communication apply, but in this case they give the relationship between BER and the signal to noise of the subcarrier. To be able to transform BER uncertainty to RF input level uncertainty the relations... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.6.4.4 Non coherent data communication | Non coherent modulation techniques disregard absolute phase information. Communications based on non coherent modulation tend to be more sensitive to noise, and the techniques used may be much simpler. A typical non coherent demodulation technique is used with FSK, where only the information of the frequency of the sig... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.6.4.5 Non coherent data communications (direct modulation) | The BER as a function of the SNRb in this case is: ( ) 2 2 1 b SNR b e SNR BER − = (6.17) provided that the cross correlation coefficient ccross between the two frequencies defining the zeros and the ones is 0. The cross correlation coefficient ccross of two FSK signals with frequency separation fδ and the bit time T i... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.6.4.6 Non coherent data communications (subcarrier modulation) | If a subcarrier modulation is used in the data communication the functions related to direct non coherent data communications apply, but in this case they give the relation between BER and signal to noise ratio of the subcarrier. To be able to transform BER uncertainty to RF input level uncertainty the relationship bet... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.6.5 Effect of BER on the RF level uncertainty | The SNRb to BER function is used to transform BER uncertainty to RF input level uncertainty. In the measurements on PMR equipment the RF input level is adjusted to obtain a specified BER. A sufficiently large number of bits are examined to measure the BER, but still there is a (small) measurement uncertainty contributi... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.6.5.1 BER at a specified RF level | If the purpose is to measure the BER at a specific input level, the transformation is more of a problem. The BER function is so non-linear that the approximation where (dBER)/(dSNRB) is used as the dependency function is no longer sufficient. One approach is to calculate the uncertainty limits of the RF input level at ... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.6.6 Limitations in the applicability of BER uncertainty calculations | As mentioned earlier the above figures and formulas are not applicable to all BER measurements; the conditions for applicability are: - the noise is white Gaussian noise; - the signal-to-noise ratio is constant; - each bit error is statistically independent; - the transmission channel delay is constant. These 4 conditi... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.7 Uncertainty in measuring messages | |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.7.1 General | If the EUT is equipped with message facilities the characteristic used to assess the performance of the equipment is the message acceptance ratio. The message acceptance ratio is the ratio of the number of messages accepted to the total number of message sent. Normally it is required to assess the receiver performance ... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.7.2 Statistics involved in the measurement | When considering messages, parameters such as message length (in bits), type of modulation (direct or sub-carrier, coherent or non-coherent), affect the statistics that describe the behaviour of the receiver system. Performance of the receiver is assessed against a message acceptance ratio set by the appropriate standa... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.7.4 Detailed example of uncertainty in measuring messages | For this example a theoretical system with 50 bit message length and 1 bit error correction will be considered, although the principles can be applied to all practicable message and correction lengths. a) Calculate the message acceptance ratio (formula (6.22)) for the given message length and given number of bit error ... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.8 Uncertainty of fully automated test systems | So far the uncertainty calculations for manual measurements have been examined. But in many radio technologies testing is performed using fully automated test systems. In technologies such as GSM, DECT and Bluetooth, certification and type approval is based on measurements using such test systems. This gives an improve... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.8.1 Test system properties | A fully automated test system normally consists of a set of test instruments (usually exactly the same as the ones used in the manual measurements), but in addition it contains a switch unit. The purpose of the switch unit is to create the correct set-ups using attenuators, power combiners, filters, amplifiers, and cab... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.8.2 General aspects of the measurement uncertainty | As indicated previously, the main difference between manual testing and a fully automated test system is how the correction factors are generated. From a measurement uncertainty point of view this is very important because this is X one of the major contributions to the overall RF level uncertainty of the actual measur... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.8.3 The "simple" test system | The test system is shown in figure 21: Signal analyser Generator 1 Generator 2 Generator 3 Power combiner Filters and attenuators Switch 2 Switch 1 Sig. gen. out EUT EUT conn. Figure 21: The "simple" test system |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.8.3.1 Transmitter measurement | For the "simple" test system the path compensation procedures and the actual measurement for transmitter measurements using the correction factors, are as follows: The path compensation is performed as follows: Switch 1 is set so the generators are connected to the Sig. gen. out connector. Switch 2 is set so the signal... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.8.3.1.1 Error analysis | The combined path compensation procedure and the actual test consist of 3 individual measurements as shown in figure 22: two measurements in the path compensation part and one in the actual measurement. In each of the 3 measurements a signal source is connected to a measuring instrument through a network consisting of ... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.8.3.1.2 Mismatch uncertainty | For each measurement there is a mismatch uncertainty which is the combination of all the mismatch uncertainties between all of the parts in the path between the signal source and the measuring instrument. Fortunately many of the mismatch uncertainties are cancelled due to the total procedure. Firstly the two measuremen... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.8.3.2 Receiver measurements | For the "simple" test system the path compensation procedures for receiver measurements and the actual measurement using the correction factors, are as follows: The path compensation (measurement 1) is done as follows: Switch 1 and switch 2 is set so the generators are connected to the EUT connector. Then the power met... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.8.3.2.2 Mismatch uncertainty | Signal analyser Generator Attenuators, cables, and filters Combiner and cables Switch unit Switch 2 Switch 1 Sig. gen. out EUT conn. Path compensation: power meter reading Power meter Signal analyser Generator Attenuators, cables, and filters Combiner and cables Switch unit Switch 2 Switch 1 Sig. gen. out EUT conn. The... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.8.4 The "complex" test system | As the "simple" test system, the "complex" system consists of a set of measuring instruments and a switch unit. And as with the "simple" test system the RF level traceability is provided by very accurate power meters rather than the other RF instruments. The main difference between the "simple" and the "complex" test s... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.8.4.1 Receiver measurements | For the purpose of analysing receiver measurements the "complex" test system can be simplified as shown in figure 25: EUT Sub network A Sub network B Generator Power meter A EUT conn S4 Sub network C Switch unit Figure 25: Model for analysis of receiver measurements In figure 25: Sub network A consists of everything be... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.8.4.1.1 Error analysis | The combined path compensation procedure and the actual test consists of 4 individual measurements as shown in figure 26 to figure 28: two measurements in the external the path compensation part, one in the internal path compensation and one in the actual measurement. In each of the 4 measurements a signal source is co... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.8.4.1.2 Mismatch uncertainties | For the analysis of the overall mismatch uncertainty, firstly the external path compensation is analysed. The settings are shown on figure 26. (The reason for introducing sub network D is that it is not necessarily the same sub network used in the actual measurement): Power meter B Sub network D Sub network B Generator... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.8.4.2 Transmitter measurements | For the purpose of analysing receiver measurements the test system can be simplified as showed in figure 29: Signal analyser Sub network A Power meter A Sub network B Sub network F Sub network D Sub network E Generator EUT conn. Sig. Gen. out S9 S5 S8 EUT Switch unit Sub network C Figure 29: Model for analysis of trans... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.8.4.2.1 Error analysis | The combined path compensation procedure and the actual test described consist of 5 individual measurements as shown in figure 30 to figure 32: two measurements in external the path compensation part, two in the internal path compensation and one in the actual measurement. In each of the 5 measurements a signal source ... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.8.4.2.2 Mismatch uncertainties | For the analysis of the mismatch uncertainty, firstly the external path compensation is analysed. It consists of two measurements, and the settings are shown in figure 30: Signal analyser Sub network A Sub network B Sub network F Sub network D Sub network E Generator EUT conn. Sig. Gen. out S9 S5 S8 Power meter B Switc... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.8.5 Summary | As mentioned earlier the individual components can be calculated when their individual losses and reflection coefficients are known. The main problem is that some of the components are internal, so the relevant parameters cannot be measured directly without taking the switch unit apart. The appropriate reflection coeff... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 6.8.5.1 Typical mismatch example | This example shows the calculation of the mismatch uncertainty between sub network C and sub network E through sub network G (from measurement 2, figure 30) in the external path compensation procedure related to a transmitter measurement. Some details for the calculations must be assumed: Generator 2 is the generator, ... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7 Theory of test sites | |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.1 Introduction | The aim of this clause is to derive, starting from a basic theory of propagation, a theoretical model of an "ideal" test site i.e. a site completely devoid of all error sources. The model is then extended to different types of test site (e.g. Anechoic Chamber, Open Area Test Site, etc.) giving a theoretical baseline ag... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.1.1 Basic concepts | In an alternating current circuit, the term impedance is used for the complex resistive and reactive attributes of a component. In the context of electromagnetic radiation, where energy is transferred in the form of a wave through a homogeneous medium, an equivalent term - intrinsic impedance - is used for that medium.... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.2 Radiated fields | This clause essentially deals with the fields radiated by an isotropic radiator in free Space. After some discussion, directivity is then given to this radiating source and the implications discussed. Finally the Friis transmission formula is derived. |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.2.1 Fields radiated by an isotropic radiator | The starting point for the model of the ideal test site is to consider the nature of the amplitude and phase of the electromagnetic field generated by an isotropic radiator in free Space. As stated in clause 7.1.1, the key characteristic of the isotropic radiator is that it radiates with equal intensity in all directio... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.2.2 Directivity implications on the ideal radiator | Directivity is a parameter which quantifies how directional the radiated fields from a source are. In the spherical co-ordinates system (r,θ,φ), the source directivity can be represented by: D(θ,φ) in which case the power density equation now becomes: ( ) 2 4 r , D tP o W π φ θ = W/m2 Consequently, the introduction of ... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.2.3 The nature of the fields around a source of finite size | All electromagnetic waves consist of two essential components: a magnetic field and an electric field. For transverse electromagnetic waves these two fields have only one component each. These are perpendicular to each other, and the direction of propagation is at right angles to the plane containing these two componen... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.2.5 Choice of physical antenna for the "ideal" model | Before developing the model further, consideration is first given to other radiating sources. |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.3 Ideal radiating sources | There are several ideal radiating sources which, despite their idealistic nature have important roles to play in electromagnetic theory. For example the usage of the ideal isotropic radiator as a basis for the definition of antenna gain is one such role. As well as the isotropic radiator there are two other ideal sourc... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.3.1 Electric current element | The electric current element is a fundamental theoretical concept, the analysis of which is applied to wire type antennas in general to calculate radiation patterns, radiation resistance, etc. The electromagnetic fields and other theoretical data are presented next. ETSI ETSI TR 102 273-1-1 V1.2.1 (2001-12) 116 Conside... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.3.2 Magnetic current element | The magnetic current element occurs in the analysis of the loop antenna whose main usage, as far as testing is concerned, is in the frequency band of a few Hz to 30 MHz. They do find a use as the radiating element within body-worn devices such as pagers at frequencies up to 1 GHz but since they do not feature as antenn... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.4 Theoretical analysis of the dipole | Having given the ideal source some directivity (see clause 7.2.2) the next stage is to select a real physical antenna for inclusion into the "ideal" model. Amongst the various antennas used commonly on test sites (dipoles, bicones, log-periodic dipole arrays, waveguide horns, etc.) by far the most practical, most commo... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.5 Model of the ideal test site | This clause collates all the theory and concepts of the preceding clauses of clause 7 with the aim of defining the model of the "ideal" test site. A formula for the site attenuation (i.e. the magnitude of the loss of power between the terminals of the two dipoles) of that test site will then be determined. Components t... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.6 Ideal practical test sites | In this clause, ideal practical sites are examined. All types of practical test site (i.e. Anechoic Chamber, Anechoic Chamber with a Ground Plane, Open Area Test Site and stripline) are considered and an ideal, lossless formula for the site attenuation is given for each case. Additionally, Test Fixtures and salty man/s... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.6.1 Anechoic Chamber | An Anechoic Chamber is an enclosure, usually shielded, whose internal surfaces are covered with radio absorbing material. It is intended to simulate a free Space environment by absorption of all the RF energy incident on the absorbing panels. The truly ideal Anechoic Chamber should behave as an infinite empty space i.e... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.6.2 Anechoic Chamber with a Ground Plane | A variation on the design of the Anechoic Chamber (see clause 7.6.1) is the inclusion of a ground plane, in an attempt to emulate the Open Area Test Site (historically, the reference site upon which the majority of the specification limits have been set). The ideal Anechoic Chamber with a Ground Plane is, conceptually,... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.6.3 Open Area Test Site | An Open Area Test Site is usually constructed in an outdoors, unprotected environment. An ideal Open Area Test Site should be situated in an area that is completely devoid of buildings, electric lines, fences, trees etc., is perfectly level and does not suffer from ambient transmissions. The reflecting ground plane sho... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.6.4 striplines | A stripline is essentially a transmission line (i.e. similar to coaxial cable, waveguide, etc.) in which RF energy is assumed to propagate with the properties of a Transverse ElectroMagnetic (TEM) wave i.e. the wave is assumed to comprise single electric and magnetic components only and, further, that these components ... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.7 Verification | |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.7.1 Introduction | The verification procedure is a process carried out on all Open Area Test Sites, anechoic facilities (both with and without a ground plane) and striplines to prove their suitability as free field test sites. A verification procedure is also applied to Test Fixtures and the saltwater column/salty man. In these cases, ho... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.7.1.1 Anechoic Chamber | In an ideal Anechoic Chamber where there are: - no unwanted reflections (ground reflected or others); - no interaction between transmit and receive dipoles; - no coupling of the dipoles to the absorbing material; - and where perfectly aligned, loss-less, matched tuned dipoles are used. the coupling between the dipoles ... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.7.1.2 Anechoic Chamber with a Ground Plane and Open Area Test Site | The formula for ED(H or V) in the site attenuation equation for the fully Anechoic Chamber, given above, is only applicable if no reflections (ground or otherwise) are present. In the case of an Anechoic Chamber with a Ground Plane or the Open Area Test Site, where a ground reflection is present, the formula is modifie... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.7.1.3 Improvements to the formulas for EDHmax and EDVmax | In the verification procedures for Anechoic Chambers with Ground Planes and Open Area Test Sites (see clauses 7.7.3 and 7.7.4 respectively), the performance of a facility is measured for a number of transmitting dipole positions within a specified volume. This results in several positions for which off-boresight angles... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.7.1.4 Mutual coupling | For both types of anechoic facilities (i.e. with and without a ground plane) as well for Open Area Test Sites there may be mutual coupling (see clause 7.2.3) between the antennas (see figure 52). This will serve to modify the results since mutual coupling changes both antenna input impedance/voltage standing wave ratio... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.8 The nature of the testing field on free field test sites | |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.8.1 Fields in an Anechoic Chamber | Since the far-field formula (2(d1+d2)2/λ) contains a wavelength term, the frequency has a major impact on the available volume in which testing can be carried out. For a fixed separation (range length), assuming a point source for the transmitter, the length of the side of an approximate cube within which 22,5° maximum... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.8.1.1 Practical uniform field testing | The practical situation however is illustrated in figure 57 where the volume of the cube is fixed i.e. there are specific dimensions associated with the EUT and source antenna. In some cases it is not possible to have a separation distance ≥ 2(d1+d2)2/λ and as a result more than 22,5° phase variation exists over the me... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.8.1.2 Sensitivity considerations | As discussed in clause 10.6.3, the sensitivity of the measuring receiver becomes a significant limiting factor in a measurement at high frequencies. For a given size of EUT, as the frequency increases, so does the far-field distance. Consequently the path loss will also increase. To make accurate measurements on, say, ... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.8.1.3 Appreciable size source | This situation is more complicated, since the source is almost certainly of appreciable size. In this case the phase variation, as seen across the receiving aperture, is larger since longer path lengths are involved (see clause 7.2). To maintain a maximum phase variation of 22,5 ° across the receive aperture, the far-f... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.8.1.4 Minimum separation distance | Measurements at reduced separations from the EUT will result in larger uncertainties in the measurement until, at very close distances, the mutual interaction between source and receive apertures mean the measurement no longer has any validity. The separation at which the measurement becomes meaningless occurs when the... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.8.1.5 Summary | Many test engineers think of far-field problems as low frequency concerns only. Provision of the far-field distance is often overlooked therefore, at the top end of the frequency band. This problem is not limited to "in situ" or "on site" testing that may be carried out at remote premises, it also applies to test sites... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 7.8.2 Fields over a ground plane | In clause 7.8.1 we considered a spherically spreading wavefront. The wavefront is spherical in the x and y directions travelling along the z direction as illustrated in figure 59. Z Y X Figure 59: Spherically spreading wavefront This model enables us to determine the appropriate value for a given phase error across the... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8 Practical test sites | |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.1 Introduction | Practical test sites are often far from the ideal sites described in clause 7. The deviations from the ideal are due to many factors such as test site construction, materials used, test methodology employed, operation quality procedures, etc. To quantify the amount of deviation from the ideal site, verification is carr... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.1.1 Test types | Normally, two types of radiated tests are carried out. Transmitter tests (maximum carrier power, spurious emissions, cabinet radiation, etc.) and receiver tests (average or maximum usable sensitivity, spurious emissions, cabinet radiation, spurious response immunity, etc.). These tests are carried out with the EUT in o... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.2 Test sites | The very brief overview of the type of tests to be carried out using the various test sites (given in clause 8.1) is intended as a reminder of the practical testing problems. The following clauses give an overview of practical test sites and the variations caused by their individual characteristics compared to the othe... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.2.1 Description of an Anechoic Chamber | As stated in clause 7.6.1 an Anechoic Chamber is an enclosure, usually shielded, whose internal walls, floor and ceiling are covered with radio absorbing material, normally of the pyramidal urethane foam type. The chamber usually contains an antenna support at one end and a turntable at the other. A typical Anechoic Ch... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.2.2 Description of an Anechoic Chamber with a Ground Plane | As stated in clause 7.6.2 an Anechoic Chamber with a Ground Plane is an enclosure, usually shielded, whose internal walls and ceiling are covered with radio absorbing material, normally of the pyramidal urethane foam type. The floor, which is metallic, is not covered and forms the ground plane. The chamber usually cont... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.2.3 Description of an Open Area Test Site | An Open Area Test Site comprises a turntable at one end and an antenna mast of variable height at the other set above a ground plane which, in the ideal case, is perfectly conducting and of infinite extent. In practice, whilst good conductivity can be achieved, the ground plane size has to be limited. A typical Open Ar... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.2.4 Description of striplines | As stated in clause 7.6.4 a stripline is essentially a transmission line in the same sense as a coaxial cable (see clause 10.2). It sets up an electromagnetic field between the plates in a similar way that a coaxial cable sets up fields between inner and outer conductors. In both cases, the basic mode of propagation is... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3 Facility components and their effects | For the facilities outlined in clause 8.2 the following comprise the major components: - a metallic shield lined with radio absorbing material for the Anechoic Chamber; - a metallic shield, radio absorbing material and a highly reflective ground plane for the Anechoic Chamber with a Ground Plane; - a highly reflective ... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.1 Effects of the metal shielding | The benefits of shielding a testing area can be seen by considering the situation on a typical Open Area Test Site where ambient RF interference can add considerable uncertainty to measurements. Such RF ambient signals can be continuous sources e.g. commercial radio and television, link services, navigation etc. or int... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.1.1 Resonances | Any metal shield will act as a reflecting surface and grouping six of them together to form a metal box makes it possible for the chamber to act like a resonant waveguide cavity, if excited. Whilst these resonance effects tend to be narrowband, their peak magnitudes can be high resulting in a significant disruption of ... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.1.2 Imaging of antennas (or an EUT) | The shield can have a significant impact on the overall performance of the chamber if the absorbing material has inadequate absorption characteristics. In the limiting case of 0 dB return loss (i.e. zero absorption/perfect reflection) an antenna or EUT will "see" an image of itself in the end wall close behind, the two... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.2 Effects of the radio absorbing materials | |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.2.1 Introduction | Absorption is the irreversible conversion of the energy of an electromagnetic wave into another form of energy as a result of wave interaction with matter "The new IEEE standard dictionary of electrical and electronic terms" [16] (i.e. it gets hot!). The efficiency with which the material absorbs energy is determined b... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.2.2 Pyramidal absorbers | This type of absorber is manufactured from polyurethane foam impregnated with carbon, and moulded into a pyramidal shape, see figure 70. This shape has inherently wide bandwidth, small polarization dependence and gives reasonably wide angular coverage. Pyramidal absorbers behave as lossy, tapered transitions, ranging f... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.2.3 Wedge absorbers | Wedge absorbers (see figure 70), are a variation of the polyurethane pyramidal foam type, which tend to overcome the degradation of reflectivity with increasing angle of incidence suffered by pyramidal cones, but at some performance cost. This improvement is only for cases where the incident wave direction is parallel ... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.2.4 Ferrite tiles | Ferrite is a ferromagnetic ceramic material. Its susceptibility and permeability are dependant on the field strength and magnetization curves (which have hysterisis). Its magnetic characteristics can be affected by pressure, temperature, field strength, frequency and time. Its mechanical and electromagnetic characteris... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.2.5 Ferrite grids | Ferrite grids are typically 10 cm by 10 cm by 2,5 cm thick. They provide absorption from 30 MHz to 1 000 MHz. The grid structure provides better power handling characteristics and avoids the installation problems associated with plain tiles. Their absorption characteristics are basically the same as for ferrite tiles (... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.2.6 Urethane/ferrite hybrids | Urethane/ferrite hybrid absorbers (as introduced in clause 8.3.2.4) consist of pyramidal foam absorber bonded to a ferrite tile backing. They are designed in such a way that the ferrite tiles are active at the low frequencies, where the pyramidal foam absorbers are not very efficient, whilst the pyramidal absorbers tak... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.2.7 Floor absorbers | Anechoic materials (except ferrite tiles and grids) cannot, in general, support loads. Normally, therefore, a false floor of RF transparent material is built above the anechoic materials, to enable access to the test antenna and turntable. It is, however, very difficult to obtain a floor that is truly RF transparent an... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.2.8 Performance comparison | Table 4 and table 5 detail numerous relative parameters for the different absorber types discussed above. Table 4 gives the physical parameters relating to an Anechoic Chamber of internal testing dimensions of 8 m by 3 m by 3 m. Table 5 details the return loss (at 0° angle of incidence) for the various absorber types c... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.2.9 Reflection in an Anechoic Chamber | As has been stated, the absorbing materials used and their layout play a critical role in the chamber's performance. A plan view of an Anechoic Chamber with its end and side walls covered in pyramidal foam absorbers is shown in figure 75. Mounted in the chamber are two dipoles (shown for illustration purposes only, alt... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.2.10 Reflections in an Anechoic Chamber with a Ground Plane | The discussion given in clause 8.3.2.9 for the fully Anechoic Chamber is fully applicable to the case of an Anechoic Chamber with a Ground Plane with the exception that the floor reflection becomes a wanted signal and is of higher magnitude. |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.2.11 Mutual coupling due to imaging in the absorbing material | Mutual coupling is the mechanism which produces changes in the electrical behaviour of an EUT or antenna when placed close to a conducting surface, another antenna, etc. The changes can include, amongst others, de-tuning, gain variation and changes to the radiation pattern. Whilst the absorbing materials help to reduce... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.2.12 Extraneous reflections | Within the chamber, reflecting objects such as internal lighting, cameras and safety circuits (which are normally used in chambers where high power fields are generated) should be avoided (or their effects minimized) as they will have a direct effect on the quality of the measurement at that site. Similarly, the materi... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.3 Effects of the ground plane | A conducting ground plane should be made from metals preferably of a non ferrous nature such as copper or aluminium. It does not have to be constructed of solid sheet but can be perforated metal, welded mesh, metal gratings, etc. Wherever a gap or a void occurs within the screen, it should not measure more than λ/10 at... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.3.1 Coatings | Where thick dielectric coatings have been applied to a metal ground plane e.g. asphalt, gravel, concrete, etc., or where a layer of snow has fallen, the nature of the reflection can be significantly changed, particularly for vertical polarization. This effect is illustrated in figure 77 where the patterns above ground ... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.3.2 Reflections from the ground plane | Far from a perfectly conducting ground plane, at a distance sufficient to make the difference between the direct and reflected path lengths negligible and the direct and reflected waves appear parallel to each other, the amplitude of the reflected wave is equal to the amplitude of the direct wave. When these two waves ... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.3.3 Mutual coupling to the ground plane | Mutual coupling, as stated in clause 8.3.2.11, is the mechanism which produces changes in the electrical behaviour of an EUT (or antenna) when placed close to a conducting surface, another antenna, etc. The changes can include detuning, gain variation and distortion of the radiation pattern. To illustrate the effects o... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.4 Other effects | |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.4.1 Range length and measurement distance | Range length is defined as the horizontal distance between the phase centres (or volume centres) of the EUT and test antenna or between antennas. Measurement distance, on the other hand, is defined as the actual distance between the phase centres (or volume centres) of the EUT and test antenna. The distinction between ... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.4.2 Minimum far-field distance | The recommended minimum conditions for a plane wave to exist, for testing purposes, is when the separation is equal to or greater than 2(d1+d2)2/λ. Generally this gives less than 0,06 dB of amplitude loss in either received or transmitted signal level for the apertures involved. |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.4.2.1 Measurement distances | Clause 3.3.1.1 of the original edition of TR 100 027 [10] stated: "Measuring distances of 3 m, 5 m, 10 m, and 30 m are in common use. The EUT size (excluding the antenna) shall be less than 20 % of the measuring distance". This allowed EUT sizes of up to 0,6 m maximum dimension on a 3 m site, 1 m on a 5 m site, 2 m on ... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.4.3 Antenna mast, turntable and mounting fixtures | As the turntable and mounting fixtures are in close proximity to the EUT/antenna they can significantly change its performance. The antenna mast likewise for the test antenna. The antenna mast, turntable and mounting fixtures should, therefore, be constructed from non conducting, low relative dielectric constant plasti... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.4.4 Test antenna height limitations | All tests on ground reflection sites are carried out so that the peak signal level is detected by varying the height of the antenna on the mast. For an EUT with an omni-directional pattern in the vertical plane above a perfectly conducting ground, theoretically, this peak for vertical polarization occurs on the surface... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.4.5 Test antenna cabling | There are radiating mechanisms by which RF cables can introduce uncertainties into radiated measurements: - leakage; - acting as a parasitic element to the test antenna; - introducing common mode current to the balun of the test antenna. Leakage allows electromagnetic coupling into the cables. Because the electromagnet... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.4.6 EUT supply and control cabling | EUT cable layout can contribute significantly to the uncertainty of the measurement. Large variations can occur when measuring spurious emissions for example, as a result of the positions of the supply and control cables. These cables can act as parasitic elements and can receive radiated fields. The effects vary with ... |
7806589cb221af5f58e72478b546c108 | 102 273-1-1 | 8.3.4.7 Positioning of the EUT and antennas | The phase centre of an EUT or an antenna is the point within the EUT or antenna from which it radiates. If the EUT or antenna was rotated about this point, the phase of the received/transmitted signal would not change. For some test procedures, especially those which require an accurate knowledge of the measurement dis... |
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