411 
In Fig. 10 to 12 an example is shown for HH, VV and HV polarization. In reality, the power 
is not adjusted to the various levels shown, but rather, varies due to pulse length, pulse repetition 
rate (PRF) and output power of each T/R module (ca. 4.5 W) in the order of 400 W. Therefore, 
the S/N of the system exceeds 10 dB quite noticeably. 
It should be noted, that for transmitting, the amplitude distribution across the antenna is 
constant. In the receiving case, controllable attenuators connected to the outputs of the LNAs 
allow the necessary sidelobe suppression for range ambiguity reductions. The phase control of each 
individual slotted waveguide radiator serves two purposes; on the one hand, it steers the antenna 
beam in the wanted direction, on the other hand it is used for beam broadening (and therefore gain 
reduction). 
6 - CONCLUSION 
Application of active phased array technology for spacebome SAR is a very promising con 
cept, if GaAs MMIC’s are used for T/R modules. Low loss antenna designs are advisable in order 
to keep the power demand of SAR in reasonable limits. This paper showed that even in X-Band 
polarimetric operation is feasable. Such concepts allow in addition internal calibration, but of 
course external calibration [?] is needed in regular intervalls. Electronic beam steering and beam 
broadening increase the data take opportunities considerable and are the basis for a multitude of 
operational modes. 
References 
[1] Skolnik, M. I., “Radar Handbook,” McGraw-Hill, 1970. 
[2] F. T. Ulaby and M. C. Dobson, “Handbook of Radar Scattering Statistics for Terrain,” Artech 
House, 1989. 
[3] Zink M., F. Heel and H. Kietzmann, 1991. The Oberpfaffenhofen SAR Calibration Experiment 
of 1989. Journal of Electromagnetic Waves and Applications, Vol. 5, No. 9, pp. 935-951.