An efficient technique for designing balanced vector modulators with low insertion loss

This paper describes and analyses an improved technique for the realization of balanced vector modulators. The analysis focuses on the effect of the Lange coupler characteristic impedance on the modulator minimum insertion loss. A method of adjusting the impedance to a calculated optimum value is used to reduce the loss and achieve a more symmetrical constellation. Based on this technique, a balanced vector modulator MMIC for millimeter-wave communication applications is fabricated on a 100μm thick GaAs substrate with 0.15μm pHEMT devices. This circuit is operating at 40GHz and has a chip size of 1.9×1.5mm². The static constellation has been obtained with swept bias voltage control, and shows good agreement with the analysis.