A 14 GHz DCPSK direct demodulator for satellite applications

A direct 14 GHz DCPSK demodulator for regenerative satellites is described. The circuit makes extensive use of microstrip quadrature hybrids implemented as Lange-type couplers. The delay element is composed of three five-pole 0.1 dB ripple Chebishev filters in cascade. The amplitude and group delay response of the delayed path is shown. Phase detectors are designed as singly balanced mixers and employ beam-lead low-barrier Schottky diodes. The circuit allows some degree of experimental adjustment. Output peak and offset voltages are shown for different operating temperatures. Results of BER measurements are exhibited, including DCPSK repeater BER versus C/N ratio for an RF input power level of approximately 6 dBm, and system performance degradation vs the RF input power level for a BER of 0.0001. The use of the low-loss delay element allows a reduction of the minimum input power necessary to achieve a correct demodulation.