MIL-STD-469B APPENDIX A
50. RADAR ANTENNA MEASUREMENTS
50.1 Requirements summary. The radar antenna measurements and procedures described in this section should provide data to be compared to the radar antenna characteristics, requirements, and limits specified in 5.4.
50.2 Antenna characteristics.
50.2.1 Objective. For antennas operated by their rotation through 360 degrees of the horizontal plane, the objective should be to determine the median gain of the antenna, in the principal horizontal plane, by measurement of the antenna pattern. Median gain should be defined as that level over an angular region at which the probability is 50 percent that the observed or measured gain at any position of the antenna will be less than or equal to that level. For other antennas, the objective should be to determine the antenna pattern, including the sidelobe levels, relative to the main lobe.
50.2.2 Requirements. The radar antenna should provide sidelobe characteristics within the limits (see
5.4) for the appropriate radar category.
50.2.3 Application notes. For radar systems other than the types described, appropriate test procedures should be determined and described in a test plan developed for the cognizant activity directing the test. Upon approval of the test plan and subsequent execution of the tests, any departure from the test plan should
require approval. Guidance in planning antenna pattern and median gain tests on these types of systems should be provided as specified in MIL-STD-449.
50.2.3.1 The spatial distribution of power radiated into space, if site effects are minimized, should describe the amount of relative antenna gain existing in directions removed from the main beams of an antenna. The recorded information, commonly referred to as antenna patterns, presents a graphical representation of the energy distribution about the system antenna.
50.2.3.2 The primary procedure uses the radar transmitter, operating in its normal mode with the rated power output, as the transmit signal source. A secondary procedure, which replaces the radar transmitter with a substitute signal source such as a high level CW signal generator is acceptable. With either transmit signal source, the power level delivered to the radar antenna terminals should be measured and the results noted in the test data.
50.2.3.3 Mechanically rotatable antennas should be tested (see 50.2.4 through 50.2.4.5). Systems with electronic beam-scanning and limited or no mechanical rotational ability, yet with antennas small and light enough for mounting on a mechanically-rotatable platform, should use the procedure (see 50.2.4 through
50.2.4.5). Electronic beam-scanning antennas which cannot be mechanically rotated should use the procedures listed (see 50.2.4.6 and 50.2.4.7).
50.2.3.4 The receiving test antenna should be positioned at a location which is separated from the radar antenna by a distance (R) determined from the following equation.
R > (DI
2 + D 2)/wavelength of test frequency
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