A double-side-swap phase inverter is proposed in the rat-race hybrid. This phase inverter with a 90° line replaces the conventional 270° line in the hybrid, which results in a size reduction and widening of the bandwidth. In microwave components, a large ground plane has the advantages of acting as an effective reflector in antenna systems and providing excellent heat sinking in high power applications. Experiment shows that this proposed hybrid has good performance from 1.2 to 2.8 GHz (fo = 2 GHz). The bandwidth is increased from 10 to 80 %, respectively, and a 43 % size reduction is obtained compared with the conventional rat-race hybrid. Copyright © 2013 The Institution of Engineering and Technology.