Monolithic amplitude and phase control circuits for 17/18 GHz indoor radio applications

Analogue MMIC amplitude and phase control circuits have been designed, fabricated and tested. These reflection-type analogue control devices are intended for direct carrier modulation in 17/18 GHz indoor radio LAN applications. The circuits were fabricated on the GMMT F20 standard foundry. The phase shifter uses varactor diodes and four 90° phase shifter sections were cascaded to achieve 360° for direct QPSK modulation. The attenuator uses cold-FETs as variable resistance elements. At 18 GHz the parasitic reactance is found to lead to very high phase variations. To combat this a simple symmetrical control method is presented for a two-stage attenuator