18–40 GHz low conversion loss double-balanced star mixer using bilateral finline and antipodal finline

Abstract

A unique broadband millimetre-wave low conversion loss double-balanced mixer based on a star configuration has been designed and demonstrated. The ridged waveguide to bilateral finline transition and the ridged waveguide to antipodal finline transition are used as the local oscillator (LO) and radio frequency (RF) port of the mixer, respectively. The intermediate frequency (IF) signal is orthogonally extracted from the common star-configuration point. The height of the ridge of the double-ridged waveguide is reduced gradually to improve the impedance match and ensure enough space to mount the diodes. The leakage RF signal launched by the antipodal finline is terminated by six plated-through holes through the slot line conductors. A short-circuit formed by the bifurcation of the balanced microstrip line is used to terminate the leakage LO signal launched by the bilateral finline. The measured results show the mixer has low conversion loss (from 3.8 to 7.0 dB), high isolation between all ports (>26 dB), as well as low return loss of the RF port over the frequency range of 18 to 40 GHz. Compared with previously published mixers, this work demonstrates the best performances of the most important parameters of 18–40 GHz mixers.