Monolithic Ka band VCO using quarter micron GaAs MESFETs and integrated high-Q varactors

High-Q GaAs abrupt varactor diodes and 0.25- mu m GaAs MESFETs have been combined on a semi-insulating GaAs substrate for millimeter-wave MMIC (monolithic microwave integrated circuit) applications. Based on the measured series resistance and capacitance, the diodes have a calculated Q at -4 V, 50 MHz of approximately 19000. The MESFETs have a measured gain of >6 dB at 35 GHz with extrapolated values for f/sub t/ and f/sub max/ of 32 GHz and 78 GHz, respectively. A monolithic Ka-band VCO using these devices has been built and tested. Output powers of 60 mW with 70 MHz of tuning bandwidth and 40 mW with 120 MHz of tuning bandwidth have been measured at 32 GHz.<
>