A QPSK direct-conversion receiver for wireless communications

The design and development of a compact receiver front-end comprised of two even-harmonic direct-conversion mixers, a quadrature hybrid coupler, two bandpass filters, two lowpass filters and a Wilkinson power divider are presented. The subharmonic mixer utilizes a well-matched antiparallel diode (APD) pair. The design helps improve the 2(nd)-order intermodulation performance (IM2) due to the suppression of the even-order mixing products and LO noises. The receiver front-end is able to generate in-phase I and quadrature-phase Q baseband outputs at 35 MHz. The detailed design of radio frequency (RF) components at the C-band and a quadrature intermediate frequency (IF) carrier signal in the I and Q waveforms are demonstrated successfully with a 9-dB effective IF conversion loss at 10-dBm LO power at the C-band. (C) 2004 Wiley Periodicals, Inc.