Distortion characteristics of an even harmonic type direct conversion receiver for CDMA satellite communications

This paper describes the distortion characteristics of an even harmonic typ e direct converter (EH-DC) used in earth stations for CDMA satellite commun ications. Direct conversion technique is known as a method to simplify circ uit topologies of microwave transceivers. In satellite communications, mult i carriers which have high and nearly equal level are provided to a quadrat ure mixer of the EH-DC. Hence, the third-order inter modulation degrades re ceiving characteristics. In this paper, we show the relationship between th e distortion characteristics and noise figure of the EH-DC for CDMA satelli te communication systems. Furthermore, we show NPR of even harmonic quadrat ure mixers caused by the third-order intermodulation. Experimental results in X-band indicate that the proposed EH-DC has almost the same BER characte ristics compared with a heterodyne type transceiver.