W‐band inductor compensated doubly balanced I/Q mixer

The development of a W‐band inductor compensated doubly balanced I/Q mixer in 0.1 μm GaAs pHEMT technology is presented. The I/Q mixer consists of two ring‐diode mixer cells, Marchand balun and Lange coupler for quadrature LO input signal. An inductance is utilised to resonate with the parasitic capacitance of the mixer core. The relationship between the compensating inductance and the diode model parameter is theoretically analysed and derived for the first time. With the compensating inductance, the return loss of the LO port is greatly improved, and thus no need for the matching network of LO port. Measured results show good performance: the typical conversion gain is −10 dB for RF from 75 to 96 GHz, and intermediate frequency of DC to 12 GHz, with the LO power level of +14 dBm. Image rejection is above 21 dB. Due to the doubly balanced topology, high LO‐RF isolation is observed with a minimum value of 43 dB across the whole operation frequency band.