10-Gbit/s QPSK modulator and demodulator for a 120-GHz-band wireless link

This paper describes a 120-GHz-band quadrature phase shift keying (QPSK) modulator and demodulator fabricated on microwave monolithic integrated circuits (MMICs) for a 10-Gbit/s wireless link. The MMICs were fabricated using 0.1-μm-gate InP HEMTs and coplanar waveguides. The direct-conversion modulator consists of hybrid couplers, gain-control amplifiers, and combiners. The delay demodulator has a 200-ps delay line, distribution amplifiers, a voltage-controlled phase shifter, and detectors. The modulator and demodulator MMICs were mounted in WR-8 waveguide modules to evaluate the characteristics of 10-Gbit/s transmission. The bit error rate (BER) for 10-Gbit/s pseudorandom binary sequence (PRBS) 2⁷-1 data was smaller than 10^-10.