1、 Report ITU-R M.2141(06/2009)Study of the isolation between VHF land mobile radio antennasin close proximityM SeriesMobile, radiodetermination, amateurand related satellite servicesRep. ITU-R M.2141 ii Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient
2、 and economical use of the radio-frequency spectrum by all radiocommunication services, including satellite services, and carry out studies without limit of frequency range on the basis of which Recommendations are adopted. The regulatory and policy functions of the Radiocommunication Sector are per
3、formed by World and Regional Radiocommunication Conferences and Radiocommunication Assemblies supported by Study Groups. Policy on Intellectual Property Right (IPR) ITU-R policy on IPR is described in the Common Patent Policy for ITU-T/ITU-R/ISO/IEC referenced in Annex 1 of Resolution ITU-R 1. Forms
4、 to be used for the submission of patent statements and licensing declarations by patent holders are available from http:/www.itu.int/ITU-R/go/patents/en where the Guidelines for Implementation of the Common Patent Policy for ITU-T/ITU-R/ISO/IEC and the ITU-R patent information database can also be
5、found. Series of ITU-R Reports (Also available online at http:/www.itu.int/publ/R-REP/en) Series Title BO Satellite delivery BR Recording for production, archival and play-out; film for television BS Broadcasting service (sound) BT Broadcasting service (television) F Fixed service M Mobile, radiodet
6、ermination, amateur and related satellite services P Radiowave propagation RA Radio astronomy RS Remote sensing systems SA Space applications and meteorology SF Frequency sharing and coordination between fixed-satellite and fixed service systems SM Spectrum management Note: This ITU-R Report was app
7、roved in English by the Study Group under the procedure detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2009 ITU 2009 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without written permission of ITU. Rep. ITU-R M.2141 1 REPORT ITU-R M.2141
8、*Study of the isolation between VHF land mobile radio antennas in close proximity (Question ITU-R 7/5) (2009) 1 Introduction This Report provides information on calculation and measurement techniques for isolation of VHF land mobile antennas located in close proximity. A major challenge is the manag
9、ement of co-site interference between various radio systems operating in close proximity. In this Report the isolation between antennas are investigated and quantified. The antenna isolation is theoretically analysed, numerically simulated and experimentally verified for the case of separation in th
10、e order of 1 to 7.6 m. 2 Scope This Report provides information on the determination of isolation for mobile radio antennas separated horizontally less than a few wavelengths in the 30 to 108 MHz bands. The study presents analytical and experimental isolation results for two antennas. The impact of
11、isolation to the operation of radio systems and effect of the physical characteristics of the antenna platform are not studied. 3 Related ITU-R Recommendations Recommendation ITU-R SM.337 Frequency and distance separations. 4 Abbreviations NEC Numerical electromagnetics code EZNEC The electromagneti
12、cs simulation program based on NEC USUL Unmatched source-unmatched load model MSUL Matched source-unmatched load model AWG American wire gauge VSWR Voltage standing wave ratio. 5 Approach used to compute antenna coupling This study is specifically aimed at investigating the horizontal isolation betw
13、een a two-vertical-antenna configuration. Of particular interest here is the canonical problem of two antennas separated by a specified distance and how the coupling between the two antennas varies with carrier frequency. *This Report should be brought to the attention of Radiocommunication Study Gr
14、oup 1. 2 Rep. ITU-R M.2141 Mutual impedance between antennas was evaluated on the basis of theoretical techniques used in electromagnetics and applied to the two antenna configuration. Coupled power was computed using standard circuit theory governing voltage, current and power. The theoretical pred
15、ictions were validated against accepted theoretical results in the literature. Following this first order confirmation, independent calculations using an electromagnetic simulation package based on the numerical electromagnetics code (NEC) was employed to further confirm the validity of the theoreti
16、cal results. The benefit of using the theoretical techniques over the NEC package is that: the expressions are in closed form; and relationships between electrical and physical parameters to impedance are seen clearly in the expressions. Based on the theoretical and simulation results, experiments w
17、ere then devised to investigate predictions of coupled power levels. 6 Determination of self and mutual impedance The problem under consideration is that of evaluating the power coupled between two antennas separated by a distance d, as illustrated in Fig. 1. Fortunately, this problem is addressed i
18、n books dealing with electromagnetics and antenna systems Jordan and Balmain, 1968. Closed form expressions and simulation of self mutual impedance between antennas are presented in this section. FIGURE 1 Geometry for fields near the antennas Report 2141-01dAnt 1No. Ant 2No. H2zdHorizontal isolation
19、Antenna 1No. Antenna No. 2H2H1H1r1r0r26.1 Theoretical expressions for mutual impedance In Fig. 2, with the terminals at antenna 2 open circuit, the impedance seen looking into the terminals at antenna 1 is simply the self-impedance of antenna 1 in isolation, Z11. Similarly, the impedance seen lookin
20、g into the terminals of antenna 2 with the terminals of antenna 1 open circuit, the impedance seen is simply the self-impedance of antenna 2 in isolation, Z22. By inspection: Rep. ITU-R M.2141 3 FIGURE 2 Definitions of quantities used for derivation of self and mutual impedance Report 2141-02+-+-Z1Z
21、2I2V2V1I1ZZ ZZZ Z1 11 2 22 =MMZMThe mutual impedance of the pair 2112ZZZM= is computed by solving: )()(,1211,12ininZZZZZZZM+=iteratively for ZM. Here Z1,inis the Norton equivalent impedance at the terminal of antenna 1 when antenna 2 is short circuited: MMMinZZZZZZZZZ+=22121,1and is a non-linear fun
22、ction of ZM. Finally, the notation used for resistance and reactance is: MMMjXRZ += Once these impedances are known, the quantities of interest such as the input impedance, VSWR, and isolation can be computed. What remains for analytical purposes is to determine Z1, Z2and ZMfor a 2-element monopole
23、antenna using the problem geometry in Fig. 1, which shows two element monopoles, with each element of height H1= H2= H. The general mutual impedance expressions for the two monopole antennas on a perfect reflecting plane and separated by distance d are taken from Jordan and Balmain, 1968. Mutual res
24、istance is: +=)()(2)()()()(2)(2)(222cos)(2)(2)()(cossin30101221011122vCiuCiuCivCiuCivCiuCiuCiHuSivSivSiuSiHHRMand mutual reactance is: +=)()(2)()()()(2)(2)(22cos)()2()(2)(2cossin3010122101211vSiuSiuSivSiuSivSiuSiuSiHuCivCiuCivCiHHXM4 Rep. ITU-R M.2141 where: d: distance between antennas H: height of
25、 each antenna element, and half of the total antenna height : carrier wavelength =2: wave number (or propagation constant). Currents and voltages used in XMare: du =0+= HHdu221+= HHdu 2)2(222+= HHdv221+= HHdv 2)2(222Ci(x) is commonly defined as cosine integral of x, and has the property: )(ln)(1xSCx
26、xCi += where: vvvxSxdcos1)(01= and C = 0.5772157 is Eulers Constant. The companion integral Si (x) is ,dsin)(0vvvxSix= and is known as sine integral of x. The cosine integral of x and sine integral of x are evaluated from 0 to H. The self-impedance of a single antenna can be calculated using the for
27、mulas used for calculating ZM, byevaluating the near-field on the surface of a single antenna and setting d equal to antenna radius to obtain Z11 and Z22. 6.2 Mutual impedance through calculation The results in Table 1 through Table 3 contain a comparison of mutual impedances for numerical calculati
28、ons based on the expressions presented in 6.1, as well as those obtained from Balmain and Jordans 1968 (Mutual impedance between monopole antennas of equal height from page 541 Fig. 14-3). Rep. ITU-R M.2141 5 TABLE 1 Antenna heights H1= H2= /4 d/ ZM (Jordan and Balmain) ZM (Numerical) 1/8 33.3334 +
29、j 0.0000 32.0911 j 0.0364 1/4 21.0533 j 14.9710 20.3929 j 14.1745 3/8 3.79590 j 19.6436 5.8804 j 18.8891 1/2 6.3781 j 15.3981 6.2660 j 14.9643 5/8 13.1658 j 5.2304 12.2781 j 5.9581 3/4 12.1648 + j 5.4586 11.2484 + j 3.3161 TABLE 2 Antenna heights H1= H2= /2 d/ ZM (Jordan and Balmain) ZM (Numerical)
30、1/8 86.6668 + j 0.0000 86.1492 j 0.4936 1/4 53.6517 j 38.1517 51.4186 j 40.8743 3/8 10.0241 j 52.3829 9.2218 j 52.1955 1/2 17.5396 j 42.3447 24.4226 j 37.7734 5/8 37.1739 j 14.7682 38.3842 j 9.4549 3/4 33.4533 + j 15.0111 30.9104 + j 17.4653 TABLE 3 Antenna heights H1= H2= 5/8 d/ ZM (Jordan and Balm
31、ain) ZM (Numerical) 1/8 41.5393 j 19.3701 46.0515 j 19.3203 1/4 25.2835 j 24.2036 27.4183 j 28.9481 3/8 3.1925 j 27.3143 5.0070 j 30.4951 1/2 12.9055 j 18.4310 12.4704 j 20.7838 5/8 19.7446 j 3.1861 19.1637 j 5.0009 3/4 15.0940 + j 10.4062 14.5008 + j 9.0260 6.3 Self and mutual impedance through sim
32、ulation The electromagnetics simulation program EZNEC is based on the numerical electromagnetics code (NEC), and is used in addition to the theoretical results to assess the overall behaviour of the system of coupled antennas. Two different models were studied: the unmatched source-unmatched load mo
33、del (USUL) and the matched source-unmatched load model (MSUL). 7 Calculation of power coupling between antennas 7.1 Unmatched source-unmatched load model (USUL) 7.1.1 Analytical expressions With this model, no attempt has been made to match the impedance of the source or load to the antenna systems
34、to which they are connected. Of importance here is to determine the power delivered to the load, ZL, by the source. This ratio will be referred to here as the isolation, and is derived from the Thevenin equivalent circuit depicted in Fig. 3. 6 Rep. ITU-R M.2141 FIGURE 3 Thevenin equivalent circuit f
35、or unmatched source and unmatched load model Report 2141-03+-ZLSource Antennas LoadZMZ2Z1ZSVSZ1, Z2and ZMwere defined in 6.1. The source and the load impedances are Zsand ZL. Define: Vs: source voltage that produces the source power when terminated with 50 matched load Zin: the impedance seen lookin
36、g into the antenna terminals with the load impedance terminating the second antenna Zeq: the Thevenin equivalent impedance seen looking into the antenna terminals with the source connected Vin: voltage across the input terminals to the network Voc: the Thevenin equivalent source voltage (including a
37、ntenna impedance) VL: voltage across the load. These quantities are used to calculate the power coupled to the antenna via the near field interactions using: LMLMMLMinZZZZZZZZZZZZZZ+=221211SMMMSMSegZZZZZZZZZZZZZZ+=122112MSSMOCZZZVZV+=1LegLOCLZZZVV+= inSinSinZZZVV+= Rep. ITU-R M.2141 7 and power expr
38、essions: dBlog10Isolation*Re21*Re2110=inlPPZinVinVinPinZlVlVlPlwhere PLis the average power delivered to ZLand Pinis the average power delivered to the input of the network. Isolation is a measure of the proportion of power transferred from the co-site antenna into the receiver. 7.1.2 Simulation res
39、ults (USUL) Calculations were performed using theoretical values for the USUL model impedances and simulated values with EZNEC, and through direct calculation through EZNEC power measurements. The antenna parameters for the simulations are: for antenna spacing 1 m and length 3.5 m, wire diameter 2 m
40、m (AWG No. 12) with 40 segments/wire simulating the system in Fig. 1. The load and source impedances are ZL = Zs = 50 and the source power is Ps = 50 W. Figure 4 shows the isolation plots calculated and simulated for two 3.5 m antennas separated by 1 m. The peaks in the isolation curves give the max
41、imum power transferred to the receiver from the co-site antenna. It was hypothesized that the peaks in the isolation curves could be related to the antenna length. Simple calculations show that the dipoles under consideration are approximately /2 in length at a frequency of 42.85 MHz. Then m5.32=giv
42、ing = 7.0 m. The corresponding resonance frequency is: MHz85.420.710998.28=CF The corresponding nulls in Fig. 4 appear to be at twice the resonance frequency according to the theoretical isolation calculations. In Fig. 4 there is a discrepancy between the theoretical results, and those obtained nume
43、rically using EZNEC. The EZNEC results demonstrated a resonance at the same frequency as the theoretical results, however the null appears most vividly only in the theoretical results. The EZNEC results were obtained using 40 segments per wire, while the theoretical results treated the antennas as t
44、wo wires each. It is hypothesized that the simplicity of the theoretical model failed to model the null correctly. 8 Rep. ITU-R M.2141 FIGURE 4 3.5 m dipole antenna 1.0 m separation Unmatched source unmatched load (USUL) model Report 2141-04EZNEC (USUL)Theoretical (USUL)EZNEC (direct calculation)Iso
45、lation (dB)Frequency (MHz)051015202530354030 40 50 60 70 80 90 100 1107.2 Matched source-unmatched load model (MSUL) Calculations were performed using theoretical values for the MSUL Fig. 5 model impedances and simulated with EZNEC, and for a direct calculation of EZNEC power measurements. Results o
46、btained using MSUL model are essentially the same as those obtained on the USUL case in Fig. 4. FIGURE 5 Equivalent circuit for matched source and unmatched load model (MSUL) Report 2141-05Matching network1:aZs-ZmaZ1Z1VsZ3ZL+Rep. ITU-R M.2141 9 and therefore will not be included. Matching parameters
47、 for the MSUL technique were varied at each frequency so that the transformation ratio and matching reactance provide a match for a single antenna, i.e. for matching to Z11at each frequency. 8 Experimental evaluation of antenna coupling To verify the theoretical and simulation results for antenna co
48、upling, two 3.5 m VHF (30-108 MHz) vertically polarized centre-fed whip (dipole) antennas were placed at separation distances of 1 to 7.6 m. Two experimental set-ups have been used. The first method used direct power measurements and the second method used a network analyser for the isolation measur
49、ements. 8.1 Direct power measurement of antenna coupling The power delivered to the transmitter antenna was measured with a directional power meter and the received power was recorded with a spectrum analyser, see Fig. 6. The cable losses and transmitter power delivered to the Tx antenna were accounted i
