An X-band even harmonic type direct converter for CDMA satellite communications

This paper describes an X-band even harmonic type direct converter(EH-DC) used in earth stations for CDMA satellite communications. Technical features of this EH-DC are as follows: (a) Carrier leakage of a modulator is extremely low by employing an even harmonic mixer(EH-MIX). (b) High accuracy of a demodulator(low amplitude error and phase error) is achieved by employing an even harmonic quadrature mixer(EH-QMIX). (c) Automatic frequency control(AFC) function is realized by employing a PLL frequency synthesizer driven by a direct digital synthesizer(DDS) with Hz-order tuning. Experimental results in X-band indicate that the proposed EH-DC has no degradation of BER characteristics compared with a heterodyne type transceiver.