INFLIGHT VERTICAL ANTENNA PATTERNS FOR SIR-C FROM AMAZON RAIN-FOREST OBSERVATIONS

The full pattern for a large antenna is usually not wen known because of the difficulty in measuring it on a range. For spaceborne synthetic aperture radar (SAR), the antenna may also be subjected to different gravitational stresses and temperature gradients that might deform ifs structure, so it is very likely that its pattern will be different fr om that on the ground. Moreover loss of elements on a distributed arra y can distort its pattern. In these cases, one can extract the relativ e vertical antenna pattern from the SAR images of target areas that ar e uniform, on average. In this report, images taken from the Amazon ra in-forest region are analyzed to yield an estimate of the inflight rel ative-gain vertical antenna pattern for the SIR-C. The method is the s ame as that used with SIR-B (Moore and Hemmat, 1988), with X-SAR (Fang and Moore, 1995), and for scatterometer antennas on Seasat. Here we g ive the SIR-C vertical (elevation) antenna patterns for different inci dent angles and beam spoiling modes over a range of 6 dB for SIR-C. Be cause only a few of the antenna modes were used over the Amazon, these patterns are only representative. (C)Elsevier Science Inc., 1997.