MIL-STD-469B APPENDIX A
where Dl and D2 are the maximum aperture dimensions for the radar and test antennas respectively, and all parameters are in the same dimensional units. The test antenna height should coincide with a horizontal plane through the radar antenna. Both the test antenna site and the path to the radar antenna should be free from obstructions and objects which could cause reflections. Elevate the test antenna for the maximum received signal level.
50.2.3.5 For those systems where the test antenna cannot be located in the radar main beam maximum, this measurement should be performed using near-field measurement techniques. If near- field techniques are employed, the equivalent far-field patterns should be determined using appropriate techniques before comparing the results to the requirements (see 5.4).
50.2.3.6 The antenna pattern recording system (test receiver plus recorder) should have a dynamic range of at least (G + 20)dB where G is the gain, in dB, of the radar antenna main beam, with a minimum of 40 dB for the system. The dynamic range can be expanded by removing attenuation at the test receiver input, then obtaining a second antenna pattern recording. With this procedure, the second recording should show the higher pattern levels off-scale but the lower levels should be reproduced. The calibration procedure should be as described for the initial antenna pattern recording which shows the main lobe on-scale.
50.2.3.7 Statistical measurements of the transmitted beam should be taken with the main beam scanning the solid sector in the normal scanning mode. Time should be allowed at each test position and frequency for at least l0 complete scan cycles of the solid scan sector to be made by the main beam. Where possible, the
scanning measurements should be synchronized in time so that the outputs of each complete scan cycle should be correlated with the other scan cycles. The output data should be used to determine the statistical mean and the deviation from the mean of the power density for the fundamental frequency at each test point. For frequency-scanning or frequency-agile radars, either a receiver bandwidth wide enough to encompass the
radar scanning bandwidth or a number of receivers, each tuned to a separate frequency employed in the agile mode, should be used. As an alternate, for frequency agile radars with a limited number of discrete frequencies, one receiver should be used. The receiver can be tuned successively to each frequency and statistics collected.
50.2.3.8 The procedures for measuring the receiver antenna patterns should be similar to those specified for the transmit pattern, except that the test signal is radiated from each test site location to the array antenna.
50.2.4 Procedure. The block diagram for the antenna pattern test should be as shown on figure 23. This test should be performed at the mid-band test frequency, or at the horizon frequency for
frequency-to-elevation scanning radars.
50.2.4.1 The output of the test antenna should be connected to the input of the test receiver via a length of transmission line with attenuators as required to prevent overloading. The test receiver should be adjusted as described for measuring the peak level of the radar signal (see 40.2).
50.2.4.2 With the radar and test antennas aligned for maximum power transfer, the test receiver should be tuned for maximum response at the radar fundamental frequency (F o). For frequency-to- elevation scanning radars, the test receiver should be tuned to the horizon beam frequency. The recorder should connect to the
test receiver. The recorder gain controls should be adjusted for nearly full scale deflection of the recorder pen. The level and frequency of the radar F o should be measured using the procedure given for measuring peak power output (see 40.2). In this test the signal sample should be provided by the test antennas rather than from a signal sampler. Calculate the radar power density using the following equation:
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