Design of a compact wideband planar 180° Hybrid ring using the composite right/left-handed transmission line

In this paper, a compact wideband planar 180° hybrid ring is presented. The proposed 180° hybrid ring is composed of a wideband branch-line coupler and a wideband 90° phase shifter. On the basis of the composite right/left-handed transmission line theory, one wideband 90° phase shifter can be realized by adopting lumped capacitors and inductances. In order to achieve size reduction, the branch-line coupler consists of meandering line style. The simulated results have demonstrated that the proposed 180° hybrid ring has a fractional bandwidth (FBW) of 43%, and the amplitude and phase imbalances are less than 0.7dB and 2.8° during the operated frequency band, respectively. The proposed 180° hybrid ring can find wide application in the planar monopulse antenna systems.