A wideband subharmonic passive image rejection mixer

This article presents a circuit topology for a wideband subharmonic image rejection mixer. The mixer circuit is realized by employing two identical subharmonic mixers based on Schottky antiparallel diode pair, a wideband 90° differential phase shifter and a band pass filter without involving bonding wires, high impedance or tightly coupled arms. To demonstrate the topology, a mixer with 1 GHz as the fixed intermediate frequency is fabricated for 6 to 10 GHz of RF frequency. The lower side band is considered as the undesired band. Measurement results exhibit a minimum conversion loss of 7.87 dB and a maximum image rejection ratio of 41 dB at a local oscillator drive level of 9 dBm. Measured 1 dB compression point is 3 dBm. There is no requirement of DC bias.