Table of Contents
International Journal of Microwave Science and Technology
Volume 2013, Article ID 567342, 10 pages
Research Article

Compact and Wideband Parallel-Strip 180° Hybrid Coupler with Arbitrary Power Division Ratios

Department of Electronic Engineering, City University of Hong Kong, Hong Kong

Received 13 September 2013; Revised 15 November 2013; Accepted 2 December 2013

Academic Editor: Paolo Colantonio

Copyright © 2013 Leung Chiu and Quan Xue. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


This paper presents a class of wideband 180° hybrid (rat race) couplers implemented by parallel-strip line. By replacing the 270° arm of a conventional 180° hybrid coupler by a 90° arm with phase inverter, the bandwidth of the coupler is greatly enhanced and the total circuit size is reduced by almost half. Simple design formulas relating the characteristic impedance of the arms and power division ration are derived. To demonstrate the concept, four couplers with different power division ratios of 1, 2, 4, and 8 were designed, fabricated, and tested. -parameters of the coupler are simulated and measured with good agreement. All working prototypes operate more than 112% impedance bandwidth with more than 25 dB port-to-port isolation and less than 5° absolute phase imbalance. The proposed 180° hybrid couplers can be employed as a wideband in-phase/differential power divider/combiner, which are essential for many RF and microwave subsystem designs.