Low Conversion Loss Ka-Band GaAs Monolithic Diode Mixers

The design and test of two 35GHz low-loss GaAs monolithic balanced diode mixers are reported. A proprietary harmonic balance simulator was used to design the mixers which were fabricated at the Alpha Industries foundry. A first-pass design success was achieved. Measurements of the mixers performance on-wafer at 35GHz indicate wide-band operation with a best conversion loss of 4.6dB for an IF of 100MHz. Measured performance was shown to be within 0.8dB of the harmonic balance analysis for local oscillator drive levels between 9dBm and 15dBm and helped to confirm the accuracy of the harmonic balance method for millimetre wave large-signal circuit designs. We believe these results to be some of the lowest reported to date for a monolithic design at 35GHz. In designing these mixers, particular attention was paid to the design of embedding networks at the pump harmonic and mixed product frequencies in order to minimise conversion loss and LO power.