Compact Filtering Branch-Line Coupler With Source-Load Coupling

Abstract

Source-load coupling is inserted to a compact filtering branch-line coupler for generating transmission zeros. Quarter-wavelength stepped-impedance resonators are employed as the resonating elements for circuit miniaturization. All inter-resonator couplings are of inductive type, and the source-load coupling between adjacent feeds is of capacitive type. Proper source-load coupling is extracted for control of attenuation level in stopband. The realized circuit area is only 31.4% of that of a conventional branch-line coupler. Measurement results have good agreement with the simulation data.