Broadband compact rat-race hybrid and its application to mixers

A broadband rat-race hybrid with compact size using multilayer technology is presented. The bandwidth is 90% for amplitude balance <±0.5 dB, phase balance <±5°, isolation <−20 dB and return loss <−10 dB, while it is only 16% for a conventional microstrip rat-race hybrid. Meanwhile, this rat-race hybrid occupies only about 33% area of the conventional one. The theory of the proposed rat-race and the factors affecting the performance of the rat-race are studied. Furthermore, by properly integrating the double-sided parallel-strip line with microstrip line, this rat-race can facilitate circuit implementation. A single balanced mixer is designed and fabricated based on the new rate-race hybrid. It has several desirable features such as compactness, wide bandwidth, good interport isolations, and there is no need of wire jumper for intermediate frequency combining.