INFLIGHT VERTICAL ANTENNA PATTERNS FOR X-SAR FROM AMAZON RAIN-FOREST OBSERVATIONS

The full pattern for a large antenna is usually not well known because of the difficulty in measuring it on a range. For a spaceborne SAR, t he antenna may also experience different gravitational stresses and te mperature gradients that might deform its structure, so it is very lik ely that its pattern will be different from that on the ground, In the se cases, one can extract the relative vertical antenna pattern from t he SAR images of target areas that are uniform on average. In this not e, images taken from Amazon rain forest region are analyzed to yield a n estimate of the in-flight relative-gain vertical antenna pattern for the X-SAR, The method is the same as that Moore and Hemmat used with SIR-B and used for scatterometer antennas on Seasat. Here we give the vertical antenna pattern over an angular range of 8 degrees for X-SAR. The two-way 6-dB elevation beamwidth of the X-SAR antenna is found to be 5.9 degrees, which is fairly close to the 5.46 degrees preflight b eamwidth given by DLR, Deutsche Forsehungsanstalt fur Luft-und Raumfah rt, but somewhat larger.