MIL-STD-469B APPENDIX A
40.3.5.2 Sample data forms for pulse width, risetime, and PRF measurements are shown on figures 6 through 8.
40.4 Emission bandwidth.
40.4.1 Objective. The objective of this test is to determine the radar emission characteristics for comparison to the emission limits specified in 5.3.1.
40.4.2 Requirements. The radar emission bandwidth at the B
40dB points and over the rolloff region
extending beyond each B
40dB point should not exceed the values as specified in table IV and the emission
limits as specified in table V for the applicable radar category.
40.4.3 Application notes. The pulse width and rise time should be measured for each transmitter modulation mode and tuned frequency used in the radar emission bandwidth test. For phased array systems with less than fifteen transmitters or tubes, the power output of each transmitter or tube should be measured. For phased-array systems with fifteen or more transmitters or tubes, the power should be either measured in the far-field or statistically determined by measuring the power outputs (corrected for any antenna weighing) of a selected number of transmitters or tubes. The transmitters or tubes to be tested should be determined using a table of random numbers for selection. Initially, fifteen of the transmitters or tubes should be selected for measurement purposes. The standard deviation of measured data should be calculated. If the standard deviation is greater than 2.0 dB, additional transmitters or tubes should be measured. The number of transmitters or tubes to be measured can be determined using the student-t distribution. The mean of the measured data should be calculated giving the power output per transmitter or tube. The total power output is then the mean power output in watts, corrected for any antenna weighing, times the total number of transmitters or tubes. A power meter with a recorder output is desirable to permit recording a sample level of
the transmitter power output providing a permanent record of any power fluctuation occurring during this test.
40.4.3.1 For certain radars such as frequency hopping or pulse compression radars, it may be necessary to
supplement the data which shows the B
40dB points on a single photograph with additional analyzer
presentations in which the frequency sweep width is narrowed to show greater rolloff detail. The
additional data is needed to show the relationship between the 40 dB emission bandwidth frequencies and the lowest and highest transmit frequencies (frequency hopping radars) or the end points of the frequency deviation (pulse compression radars).
40.4.3.2 To obtain the power spectral level at the signal sampler (or antenna) output of a pulse type radar, it is essential to know the IF bandwidth of the spectrum analyzer. With all analyzer controls unchanged, connect the signal generator to the analyzer and tune it for a centered frequency display. With a CW output,
determine the signal generator output level required for a mid-scale vertical display. Record this value as P 1.
Repeat this procedure except with the signal generator output pulse-modulated with a 2.0 microseconds width
at the radar PRF (pulse repetition frequency). Record this value as P 2. Calculate the alpha factor from the relationship, alpha factor (dB) = P 1(dBm) P2(dBm). Using the alpha factor, the bandwidth-pulsewidth (Bxt)
product is determined (see figure 9). The (Bxt) product divided by 2 x 10
6 yields the analyzer IF bandwidth
(B). The IF bandwidth of the spectrum analyzer must be detemined for each frequency used in the radar emission bandwidth test.
40.4.3.3 In the data reduction, the signal sampler coupler factor is required for converting the power spectral levels of the sampled signal into the equivalent levels at the radar antenna input. If the signal sampler is not located at the antenna input, the attenuation of the transmission line components between the sampler and the antenna should be determined for use in the data reduction. When emission spectrum data are
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