Design and Specification of a Broadband R.F. QPSK Modulator for an 11 GHz 140 Mbit/s Digital Radio System using MIC Techniques

The design of a broadband QPSK R.F. phase modulator for use in an 11 GHz 140 Mbit/s digital radio system is described, in which attention was given to achieving as large an instantaneous bandwidth as possible. A new switching accuracy specification for such modulators is outlined which is directly related to system requirements. The modulator described employs PIN diode switches serially connected on a single MIC. Cross-talk degradations inherent in this approach are negligible due to the very short transition times achieved. The unit operates without adjustment over a minimum of half the 10.7-11.7 GHz band, and maintains this performance over a temperature range of 10°-60°C. Good system performance has been demonstrated.