Direct carrier quadrature modulator and Demodulator MMICs for 60 GHz gigabit wireless communications

A 60 GHz direct carrier quadrature modulator is designed and fabricated in 0.15 μm mHEMT technology. The design is based on passive mixers and therefore reciprocal which makes it possible to be used both as modulator and demodulator. The modulator has an input bandwidth of 0-5 GHz on each of the I and Q ports and an RF bandwidth of 53-68 GHz. Carrier leakage to the output port is eliminated by addition of an inductive path from the LO port to the RF port. The modulator requires 5 dBm LO power and can output up to -6 dBm RF power in linear region and up to -4 dBm when driven into saturation. When operated as an SSB mixer, the conversion loss is measured to be 11 dB and image and LO signals are suppressed by as much as 30 dB compared to the desired signal. For demonstration, a pair of the presented modulator/demodulator is used to transmit 7Gbps BPSK signal over 1m and 10Gbps QPSK signal over 0.5m wireless link.