A High-Bit Rate Ka-Band Direct Conversion $QPSK$ Demodulator

This letter presents a $Ka$ -band high bit rate direct conversion $QPSK$ demodulator. The demodulator was monolithically implemented using GaInP-GaAs HBT process. Measured results of the packaged demodulator show a conversion gain of 8 dB, LO and RF port match better than 10 dB, input 1-dB gain compression point occurring at 3 dBm, and I/Q phase and amplitude mismatch within $\pm {\hbox{3}}^{\circ}$ and $\pm$0.5 dB, respectively. The detection performance of the developed demodulator has been examined with bit rates up to 1 Gb/s and excellent performance has been obtained.