error which would otherwise exist. No such phase trimming would be required in a practical ARA consisting of many identical PCC’s. This ARA uses the two pilot tone system described in Figure 8b. The two pilot tones, f^ and f?, are the upper and lower sidebands respectively produced by modulating a carrier at 9675.0 MHz with a phase stable signal at frequency []. The two-tone receivers recover the []=49.612005 MHz IF signal uncorrupted by the phase noise of the pilot carrier or the receiver LO. The conjugated signal at 2f is multiplied up to X-band by a phase-locked X85 multi- plier whose [] MHz output is fed to the horn via the X-band diplexer. The antenna range set-up is shown in Figure 13. The ARA is mounted on the antenna positioner at right which rotates only in azimuth. The two ARA elements are identical rectangular horns mounted at the same 2.4m height with E planes vertical. The horns look through apertures cut in the large absorber panel fastened in front of the ARA. The horn separation is [], where [] [] cm is the transmitted wavelength. The E and H plane 3 dB beamwidths of the horns are both about 30 degrees. The rack at left is the pilot source. A test receiver diplexed to the pilot horn provides the signal for the pattern recorder. The distance between the ARA and the pilot source is about 10m. A considerable amount of absorbing material is required to minimize reflections in this very compact range. The ARA pattern is shown as the dashed curve in Figure 14; i.e. this curve is the output of the test receiver diplexed to the pilot horn as a function of ARA rotation in azimuth. An interferometer pattern (solid curve), produced by driving both elements from the same source at [] = 8434.04 MHz, is superimposed on the ARA pattern by way of comparison. The actual ARA "pattern," as the term
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