A 14 GHz-Low Noise-Down-Converter with Sum and Image Rejection

The design and the experimental performance of a single-ended waveguide-mixer operating at a signal frequency of 14 GHz - 14.5 GHz and an IF of 3.7 GHz to 4.2 GHz is reported. The conversion loss over the IF bandwidth of 500 MHz was < 3.5 dB. The optimum load impedance for the mixer diode at the sum frequency is provided by a bandstop-filter, whereas at the image-frequency band the cut-off property of the waveguide is used. Also the theory of the mixing process of a Z and Y mixer is given. A computer analysis of the influence of the diode series resistance and junction capacitance on the conversion loss is presented.