A Novel Microwave Modulator Based on Complex Impedance Loads

A compact circuit architecture for a direct-carrier modulator is proposed. It consists of a quadrature hybrid coupler connected to two variable loads capable of producing a wide range of complex reflection coefficients. The loads are controlled by two baseband signals for generating different modulation schemes, including M-ary quadrature amplitude modulation (M-QAM). A theoretical model of the proposed modulator is derived. To validate the proposed architecture, a prototype that operates at a center frequency of 2.4 GHz is designed and implemented. Measurements carried out verify the theory and show that our approach achieves good performance for various modulations.