A novel compact filtering hybrid coupler with arbitrary coupling levels and phase differences

Abstract

In this paper, a novel compact hybrid coupler was proposed, for the first time, with filtering integration, arbitrary coupling levels and arbitrary phase differences. Based on an improved branch-line coupler, a kind of coupling structure is designed to replace the transmission lines of the branch-line coupler for the narrow-band filtering function. The equivalence process of the replacement is derived using the transmission-line theory. A design flow of the presented filtering coupler is given and all of the parameters are analytical. With the design equations, the coupling levels and the phase differences between two output ports can be set flexibly in terms of the practical application requirements. Moreover, DC block between input and output ports is achieved by the coupling structure. A prototype of the filtering coupler with the coupling level of −4.77 dB and the phase difference of 60 degrees is fabricated and measured for verification. The experimental data are well identical with the simulation ones.