Novel microstrip branch-line coupler with low phase shift for WLANs

Abstract

In this work, a novel branch-line coupler is presented using a new type of microstrip cells. The proposed structure is consisting of high and low impedance sections and a main small square closed loops. It operates at 2.4 GHz for WLAN applications. Using the introduced structure, a good passband performance is achieved. An excellent phase balance closed to ideal is obtained with a phase difference of 270 ± 0.037° between output ports. Furthermore, there are low return loss and high isolation better than − 29 and − 30 dB respectively. Meanwhile, the designed coupler has a good insertion loss and coupling factor. Despite of having a high performance, this coupler is relatively compact with an overall size of 0.037 λg2. The designing method is based on proposing an LC model of a basic microstrip cell and finding the effective parameters to obtain a high performance. In order to validate the designing method and simulation results, the presented coupler is fabricated and measured. There is a good agreement between the simulated and measured results.