High-speed QPSK modulator and demodulator with subharmonic pumping

A high-speed quadrature-phase-shift-keying (QPSK) modulator-demodulator is described. Both units are pumped with a common 6.5-GHz local oscillator giving a modulated carrier at 13 GHz. The performance of each unit was evaluated and adjusted to give satisfactory performance with a single tuning element in the local oscillator circuits. Bit error rates were measured for transmission of pseudorandom data streams through the modulator-demodulator pair. Typical operating conditions and bit error rates for the combination are summarized. Data can be transmitted and recovered at speeds up to a total information rate of 3.6 Gb/s with an error rate less than 10/sup -11/. >