Equal-gain loci and stability of a microwave GaAs MESFET gate mixer

The performance of a microwave GaAs MESFET gate mixer is theoretically investigated to clarify the existence of a conditionally stable RF frequency range as well as an unconditionally stable frequency range in which maximum available conversion gain (MACG) can be defined. For the unconditionally stable range, the MACG and load and source impedances are calculated as functions of RF frequency. For the conditionally stable range, the stability circle and equal gain loci are shown for source RF and load IF impedances. The conditionally stable region of the GaAs MESFET mixer appears around F/sub T/ of the MESFET. Higher conversion gain is easily obtained by choosing a MESFET for which the F/sub T/ is close to the RF frequency. >