High-Speed Millimeter-Wave Modulator/Demodulator

We report on the performance of a 38 GHz Quaternary phase shift keyed (QPSK) modulator/demodulator at information rates up to 8 Gbit/s. The circuit was originally designed and characterized at a carrier frequency of 13 GHz and subsequently scaled to 38 GHz. The hybrid structure was pumped at half the carrier frequency. The demodulator output data streams showed clean eye diagrams with corresponding bit error rates of less than 10 sup (-11) up to the highest rate measured (8 Gbit/s total information rate).