A DRAIN MIXER WITH LOW SPURIOUSNESS FOR SATELLITE TRANSPONDERS

In satellite installed transponder mixers based on direct frequency co nversion, the local oscillator signal has a lower frequency than the i nput and output signals. In this situation, harmonics and higher-order modulated signals produce spurious components near the output frequen cy that are difficult to suppress by using the filter. This paper show s that a drain mixer is useful in suppressing such spurious components . Initially we consider excitation caused by a local oscillator signal . The SBD mixer current, the drain mixer current, and the conductance are examined using a Fourier analysis for the harmonics. Based on the static characteristics, we find that the level of spuriousness of the drain mixer rapidly decreases as the order is increased. We then show by experiment and simulation that the same tendency exists, not only i n fundamental operation following the static characteristics, but also in the Ka band. A balanced drain mixer for satellite use in the Ka ba nd is developed. A performance with a conversion loss of 9 dB, and lev el of spuriousness -67 dBc, are attained. (C) 1998 Scripta Technica.