Noise - Figure Reduction in MESFET Mixers by IF Feedback

The effect of the RF feedback on noise-figure and conversion-loss of the gate pumped MESFET mixers are investigated. The optimum values of the reactive feedback elements for various pump levels and bias conditions which provide the minimum noise -figure conditions are calculated from the noise equivalent circuit of MESFET. It has been shown that the noise - figure inprovement of around 3.5 and 2 dB can be obtained when the input impedance is tuned for maximum gain and minimum noise-figure, respectively. The theoretical outcomes are subtantiated by a microwave mixer in microstrip form operating at 10 GHz with 70 MHz IF.