A rapid carrier recovery loop for direct conversion receivers

Direct conversion receiver (DCR) is an alternative wireless architecture to the well established super-heterodyne, particularly for low-power and low-cost terminals [A. A. Abidi, December 1995]. A new Ka-band high-speed direct conversion wideband six-port receiver was designed for wireless communications. This QPSK six-port receiver operates using analog signal processing (ASP). The QPSK DCR consists of a receiver front-end, a QPSK demodulator and a carrier recovery module. A reverse modulation loop (RML) was used to provide a rapid carrier recovery. The maximum bit rate, around 120 MB/s, is limited by the speed of the base-band circuits. The new hardware receiver is proposed for use in wide Ka-band wireless mass-market QPSK communications such as LMDS services. Bit error rate (BER) results versus the noise and reference signal phase shift are presented.