1、SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirelyvoluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefro
2、m, is the sole responsibility of the user.”SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions.Copyright 2003 SAE InternationalAll rights reserved. No part of this publication may be
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4、-776-0790Email: custsvcsae.orgSAE WEB ADDRESS: http:/www.sae.orgAEROSPACE RECOMMENDED PRACTICEARP958REV.DIssued 1968-03Revised 1999-03Reaffirmed 2003-02Superseding ARP958CElectromagnetic Interference Measurement Antennas;Standard Calibration MethodTABLE OF CONTENTS1. SCOPE . 31.1 Purpose 31.2 Applic
5、able Antennas 31.3 General Background and Limitations. 42. REFERENCES . 43. RATIONALE FOR APPROACH 53.1 Antenna Factor 53.2 General Antenna Gain . 63.3 Using Two Identical Antennas 63.4 Gain and 1 m Gain. 73.4.1 Need for Gain and 1 m Gain 73.4.2 Distance for Gain Measurements. 73.4.3 Distance for 1
6、m Gain Measurements 73.4.4 Necessary Number of Measurements 73.5 Determining Antenna Factors 83.5.1 Antenna Factor For Gain (AF1) 83.5.2 Antenna Factor for 1 m Gain (AF2) 83.5.3 Calculation . 83.6 Use of Antenna Factor . 93.6.1 Correction of Signal Levels 93.6.2 Polarization Considerations . 9SAE AR
7、P958 Revision D- 2 -TABLE OF CONTENTS (Continued)4. PROCEDURE FOR TWO IDENTICAL ANTENNA 1 m GAIN MEASUREMENTS. 94.1 Apparatus. 94.2 Setup 94.3 Measurement . 105. THE ROD ANTENNA115.1 Rod Antenna Theory115.2 Rod Antenna Calibration126. LOOP ANTENNAS .126.1 Operating Theory .126.1.1 Calculation for RE
8、01/RE101 Loop .126.1.2 Calculation for 4 cm Calibration Loop 136.1.3 Loading Effect on the Loops 136.2 Calibration156.2.1 Test Equipment Specification.156.2.2 RS101 (4 cm) Calibration Loop166.2.3 Procedure 167. LOOP ANTENNAS AT 1 m SEPARATION .177.1 Theory177.2 Test Method .177.3 Sample Calculations
9、 198. NOTES20APPENDIX A ANTENNA FACTOR DERIVATION .29APPENDIX B CIRCULAR/LINEAR POLARIZATION.31APPENDIX C THREE ANTENNA DETERMINATION .32APPENDIX D EXPECTED RESULTS33SAE ARP958 Revision D- 3 -1. SCOPE:1.1 Purpose:This SAE Aerospace Recommended Practice (ARP) outlines a standard method for the checko
10、ut and calibration of electromagnetic interference measurement antennas. Its primary application is for use when measuring a source 1 m from the antenna in a shield room versus a source at a greater distance (far field). This is the typical distance used in performing military EMC testing. Thus, thi
11、s is a method of calibration. Shield room characteristics are not considered. It does not address an unknown distributed source. Yet it is close to reality since it is based on another antenna that represents a distributed source. This document presents a technique to determine antenna factors for a
12、ntennas used primarily in performing measurements in accordance with 2.1 and 2.2. The purpose of Revision B is to include the calibration of other antennas, such as small loop antennas that are also specified for use in these same references. Revision D includes a specific procedure for loop antenna
13、s that are separated by 1 m from the device under test.1.2 Applicable Antennas:The intent of Revisions A and B is to make this document applicable to passive and active antennas that may be used to measure signals from a source 1 m distant. Typical antennas being considered are the following:a. Bico
14、nicalb. Resonant dipolec. Log periodic dipoled. Log spiral (200 MHz to 1 GHz)e. Log spiral (1 GHz to 10 GHz)f. Double ridged horng. Log periodich. Standard gain hornsi. Loop antennasj. Vertical monopoleMost present day “104 cm“ (41 in) rod antennas are of the active type and not calibratable per the
15、 previous issue of ARP958. The theoretical behavior of rod antennas is well understood. Therefore, the calibration really involves verifying the gain of the electronics in the antenna base. These antennas are calibrated by the use of a signal substitution source as defined in Revision B.A separate s
16、ection is included to cover the “RE01/RE101” loop and “RS01/RS101” loop even though they are used much closer than 1 m from the equipment under test.SAE ARP958 Revision D- 4 -1.3 General Background and Limitations:This document originally was limited to determining antenna factors for conical logari
17、thmic spiral antennas. It has been expanded to cover other antennas as indicated in 1.2. Antenna factors can be determined and calculated for the far field condition independent of ground refections. The method, described in this document, of moving from the far field to a 1 m distance results in ch
18、anges in antenna factors of a few decibels. The primary conditions which influence the antenna factors are the antenna separation, the height of the antenna above the ground plane, the orientation of the antenna relative to the ground plane, and the conductivity of the ground plane.2. REFERENCES:2.1
19、 MIL-STD-461 Requirements for The Control of Electromagnetic Interference Emissions And Susceptibility2.2 MIL-STD-462 Measurement Of Electromagnetic Interference Characteristics2.3 Microwave Antenna Theory and Design by Silver, Vol. 12, Radiation Laboratory Series, McGraw - Hill, 1949, pp. 582-5852.
20、4 Antennas by Kraus, McGraw - Hill, 1950, pp. 455-4572.5 Standard Site Method For Determining Antenna Factors, IEEE EMC Transactions, Vol. EMC-24, No. 3, August 1982, pp 316-3222.6 ANSI C63.5 American National Standard for Electromagnetic Compatibility - Radiated Emission Measurements in Electromagn
21、etic Interference (EMI) Control - Calibration of Antennas2.7 IEEE Std 291 Standard Methods For Measuring Electromagnetic Field Strength of Sinusoidal Continuous Waves, 30 Hz to 30 GHz2.8 IEEE Std 149 IEEE Standard Test Procedures For Antennas2.9 SAE J551/5 Performance Levels and Methods of Measureme
22、nt of Magnetic and Electric Field Strength from Electric Vehicles, Broadband, 9 kHz to 30 Mhz2.10 NBS Circular 517, Calibration of Commercial Radio Field-Strength MetersSAE ARP958 Revision D- 5 -3. RATIONALE FOR APPROACH:3.1 Antenna Factor:For an antenna to be useful in measuring EMI, an antenna fac
23、tor (AF) must be specified which permits converting voltage at the input of a receiver (V) to field strength (E) in volts per meter (V/m) or into units suitable for comparison with radiated emission limits (dBV/m) of reference 2.1. Thus,(Eq. 1)where:E = V/mV = voltswhere:AF is the antenna factor bas
24、ed upon power gain of the antenna (it is derived from the square root of the power density (W/m2). Converting to dB:(Eq. 2)where:E = dBV/mV = VAF is the antenna factor based upon an antenna calibration similar to gain, henceforth referred to as 1 m gain, but performed under conditions characteristic
25、 of the actual use (1 m from the source) of the antenna for component-level EMC specification compliance testing. Numeric antenna gain (G) and wavelength () (in meters) in a 50 system express the antenna factor (see Appendix A) as follows:(Eq. 3)Antenna gain is the ratio of the radiated power densit
26、y in a certain direction to the average radiated power density.The average radiated power density is the isotropic radiation intercepted by a surface area of a sphere of unit radius (see 2.3 and 2.4).E = AF x VE = 20 log10(AF x V)AF9.73-1G-9.73 G-=SAE ARP958 Revision D- 6 -3.2 General Antenna Gain:A
27、ntenna gain may be obtained by antenna pattern measurements which satisfy the following expression of antenna gain in integral form:(Eq. 4)where:, = spherical coordinates in radians = power radiated per unit solid angle in a given direction3.3 Using Two Identical Antennas:The term “1 m gain“ has bee
28、n selected in lieu of “apparent gain,“ since “1 m“ defines the conditions under which “apparent“ applies. The 1 m gain determination can be calculated by the antenna gain equation. This method uses two identical (see Appendix C when there are significant differences) antennas aligned on axis with po
29、larization matched. The relationship for power received is:(Eq. 5)where:GTand GR= numeric power gain of the transmitting and receiving antennas respectivelyPR= power received in wattsPT= power transmitted in wattsr = distance between antennas in meters = wavelength in meters(Eq. 6)G,()14- ,() d sin
30、d020-=PRPTGT4r2-24- GR=If GTGR, then G2= 4r- 2PRPT-=SAE ARP958 Revision D- 7 -3.3 (Continued):If both receiving and transmitting systems are matched (50 ), voltage measurements may be made in lieu of power measurements so that:(Eq. 7)where:VR= voltage across the receive antenna terminalsVT= voltage
31、across the transmit antenna terminals(It should be noted that G is the numeric power gain even though it is determined by two voltage measurements since these are used to form a ratio which is dimensionless.)3.4 Gain and 1 m Gain:3.4.1 Need for Gain and 1 m Gain: Because the antenna may be used to m
32、ake field strength measurements and specification compliance measurements, the gain, as well as the 1 m gain, is often needed. Accordingly, gain measurements are discussed in this document and a recommended measurement method is presented as an appendix to this document. However, the procedure speci
33、fied in the document is only for determining the 1 m gain.3.4.2 Distance for Gain Measurements: The gain is measured using the three identical antenna technique (see Appendix C). The distance between the antennas is 3 m. (See Figure 2 of this document.)3.4.3 Distance for 1 m Gain Measurements: Measu
34、re the 1 m gain using the two identical antenna technique at a 1 m distance between the antennas. This is equal to that required between the antenna and the test sample for EMC specification compliance testing of components and subsystems. Some antennas have an “electrical“ center that is used as th
35、e antenna position for theoretical calculations and measurements. Antennas, such as the log spiral, where the electrical center is not defined or is a function of frequency use the “nearest“ point approach. (See Figure 2 of this document.)3.4.4 Necessary Number of Measurements: Measurements should b
36、e made at a sufficient number of frequencies to describe their 1 m gain within the specified operating bandwidth of the antenna. A 1 m gain should be measured at frequencies as specified in 4.3(g). Such additional measurement frequencies should be chosen to precisely identify and define any anomalie
37、s in the 1 m gain characteristics.G4r-VRVT-=SAE ARP958 Revision D- 8 -3.5 Determining Antenna Factors:3.5.1 Antenna Factor for Gain (AF1): The AF for gain in the far field (referred to as gain and defined as AF1) is calculated from Equation 3 where G was determined per 3.4.2.3.5.2 Antenna Factor for
38、 1 m Gain (AF2): The antenna factor for 1 m measurements (defined as AF2) is calculated from Equation 3 where G was determined per 3.4.3.3.5.3 Calculation: The antenna factors AF1and AF2are calculated by the same method and by Equation 3 by using either the value G1or G2in the equation. To simplify
39、the calculation it may be performed in logarithmic form. For this reason, Figure 1 was plotted which is a plot of 20 log109.73/ as a function of frequency.When the 1 m gain, G2, is a numeric, AF2in decibels may be found by the following expression:(Eq. 8)where: = metersWhen the 1 m gain, G2, is in d
40、ecibels, AF2may be found by:For example, at 200 MHz the 1 m gain was 10 dB. What is the antenna factor AF2?From Figure 1, 20 log (9.73/) = 16Therefore, AF2= 16 - 10 = 6 dB.AF (db) 20 log109.73- 10 log10G=AF (db) 20 log109.73- - G=SAE ARP958 Revision D- 9 -3.6 Use of Antenna Factor:3.6.1 Correction o
41、f Signal Levels: The appropriate antenna factor is added to the voltage at the receiver input which is indicated in decibels above 1 V, along with cable-loss factors to obtain field intensity in decibels above 1 V/m.(Eq. 9)3.6.2 Polarization Considerations: Section 4 outlines the procedure for obtai
42、ning gain of the antenna utilizing the two identical antenna technique. If the conical logarithmic spiral antenna is used, the gain so determined is that for a circularly polarized wave (see 3.3). When making field intensity measurements with linearly polarized received waves, the gain used to calcu
43、late the antenna correction factor, AF1, must be decreased by 3 dB (which means the antenna factor goes up by 3 dB. See Appendix B). The 1 m antenna factor, AF2, should also be based on the gain for linearly polarized signals.4. PROCEDURE FOR TWO IDENTICAL ANTENNA 1 m GAIN MEASUREMENTS:4.1 Apparatus
44、:a. Signal generators with 50 output impedance capable of generating test levels over the frequency range specified for the antenna typeb. Two 6 dB, 50 attenuatorsc. Calibrated receiver (or spectrum analyzer) tuning over the frequency range specified for the antenna type. The receiver input impedanc
45、e should be 50 and a VSWR 1.25. An isolating attenuator can be used at the receiver input to achieve 1.25 VSWR.d. Coaxial cables of 50 characteristic impedance and appropriate connectors for mating with antennas, 6 dB attenuator, signal generators, and receiverse. Adapter for connecting two coaxial
46、cables4.2 Setup:The basic setup is shown in Figure 3. The area in which the setup is situated should be clear of obstructions to achieve a free-space environment. A chamber permitting the 1 m spacing between antennas is acceptable if the chamber is anechoic, except for the floor, at all measurement
47、frequencies. It also needs to maintain a ground plane to simulate open field sites. The antenna height above the ground influences the results and should be standard. A 3 m height for the center of the antenna is defined.E (dBV/m) = V (dBV) + AF (dB) + Cable Loss (dB)SAE ARP958 Revision D- 10 -4.3 M
48、easurement:At each measurement frequency using the receiver as a transfer device the following operations shall be performed.a. Adjust signal generator output to obtain a receiver indication. Be sure the receiver is tuned for maximum response to the signal.b. Make fine adjustment of the alignment of
49、 the antennas for maximum indication and record the signal generator setting. (VT)c. Disconnect the receiver and signal generator cables from their respective antennas and connect the signal generator and the receiver to each other using the same cables with the addition of a 50 , calibrated coupling adapter.d. Reduce the s
