Development of a 20 GHz modulator for the payload of a satellite for propagation and transmission experiments, including the required converters of the test equipment

Design and performance of a 20 GHz QPSK modulator for a 20/30 GHz satellite system and the related test equipment for bit error rate measurements are described. The modulator is of the serial type realized in waveguide techniques (evanescent mode with PIN diodes and circulators). With a bandwidth of 800 MHz and a temperature range from 10 to 40 C, the mean phase deviation is 3 deg with a maximum amplitude deviation of 0.3 dB. The modulator switching times are 1nsec, allowing transmission rates of 200 Mbit/sec. Measurements carried out with the test equipment prove that in the AM operating range the degradation increases by maximum 0.3 dB.