TABLE OF CONTENTS A vast amount of theoretical and practical work has been published in the field of mixer design using diodes, FETs and other more complex structures. In recent years, much of the experience gained, together with new ideas, has been applied to realising the circuits in monolithic form. Although many of the active forms using FETs look promising and show good small signal-performance, it should be noted that the noise performance and dynamic range are often rather poor. If a publication does not give the noise figure, then it is probably bad! The best mixer conversion performances and noise figures appear to be obtained when switching devices are used together with distributed (sometimes folded to reduce the size) or lumped-element coupling structures. In this type of circuit, one must then consider carefully whether it would be more cost effective to put the coupling structure on a separate MIC substrate, rather than use costly GaAs real estate for a purely passive circuit. This is especially true if multilayer multi-chip module technology is used for the complete transceiver module.
The key parameters of the most notable diode, active and resistive FET mixers are summarised in Tables 7.2, 7.3 and 7.4, respectively. Note that the figures in square brackets are not given in the references, and are based on the assumption that the single-sideband noise figure is equal to the conversion loss, and that the single-sideband noise figure is 3 dB higher than the double-sideband noise figure. They...
