Design and Performance Evaluation of Broadband Quadrature Modulator Using 90° Coupler

This paper presents a wide-band quadrature modulator's design, simulation, and performance evaluation using a 90°-hybrid coupler. Three different center frequencies of 3.0 GHz, 3.5 GHz, and 4.0 GHz were studied. The hybrid couplers are used in communication devices such as power combiners, amplifiers, mixers, dividers, and modulators. The four-port component splits the output signal with a resulting 90° phase shift while maintaining excellent output port isolation. The coupler was first designed and synthesized using ADS design tools, and the branch lengths (L) and widths (W) of the sections were then optimized in the schematic structure to get the ideal needed values. Then, excitation and simulation were performed using the Keysight ADS Momentum tool at the 2.5D EM simulator. The performance of the device at three different center frequencies was evaluated in terms of bandwidth, insertion loss, and phased difference, and found that the device operating at 3.5GHz center frequency was the best and in good correlation with the ideal quadrature modulator available in the literature.