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The design and performance of microwave and mmwave baluns using multilayer GaAs MMIC technology is presented. For mm-wave designs a compact overlaid coupler is employed. For lower frequencies it is shown that novel spiral couplers can be used. Results for baluns operating at 30-40 GHz and 5-I5 GHz are presented.

This paper describes the design and performance of millimeter-wave balanced vector modulators employing the Marconi HBT MMIC technology. Two versions have been fabricated for operation at 38 GHz; the first employs normal Lange couplers whilst the second employs miniaturised microstrip couplem, which reduce the MMIC chip area by more than 40%. With a simple bias Calibration technique the circuits achieve near-perfect constellations w&h negligible amplitude and phase errors Over a wide bandwidth INTRODUCTIONIn recent years there has been a considerable interest in the use of direct carrier modulation in order to reduce the complexity and cost of microwave circuits [l-71. High performance direct vector modulators are required in modem microwave systems like phasedarrays, VSATs, LOS communications and radar applications, with the I-Q vector modulator being widely employed for quadrature modulation schemes [3-51. It consists of a phase splitting power divider that creates two orthogonal channels. Each channel consists of a bi-phase amplitude modulator, which is individually modulated and then combined at the output of the vector modulator. A common technique for realising the single stage bi-phase amplitude modulators in each channel is to a employ reflection topology using a Lange coupler with either coldFETs or cold-HBTs acting as switches on the direct and coupled ports [3-71. The cold-transistors can be controlled with an analogue bias signal to give a continuous range of resistance. Ideally, when the switches are ON the resistance would be zero (thus r=l), whilst when the switches are OFF the

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