Design of millimetre-wave monolithic balanced diode mixer

The authors describe the process used to design a 28 GHz single-balanced mixer. The procedure consists of two steps, diode modelling, and analysis. The design of diode mixers for minimum conversion loss and noise figure requires knowledge of the diode impedance when pumped by a local oscillator (LO), so that the optimum matching circuit can be designed. This impedance is difficult to measure, particularly at millimetre-wave frequencies, and so the alternative is to simulate the diode operation in the time domain, using a nonlinear equivalent circuit model for the diode. The impedances at the various mixing frequencies are then obtained by analysing the voltage and current waveforms in the circuit predicted by a nonlinear analysis program. The harmonic balance method is preferred and analysis software adopting this approach is discussed