Design and analysis of a stub-less capacitive loaded branch line coupler with improved bandwidth performance

Abstract

In this paper, a novel branch line coupler with improved bandwidth and reduced size is presented. The size reduction is achieved by means of capacitive loading. The capacitive loaded transmission line implemented in the proposed design eliminates the need of open stubs. The mechanism of size reduction and bandwidth enhancement of the coupler is discussed analytically with the help of its equivalent circuit. A prototype is fabricated and tested to validate the concept. The measured fractional bandwidth is 40%, ranging from 2.8 GHz to 4.2 GHz which is suitable for 5G systems. Moreover, the obtained phase imbalance between the output ports is less than ±5◦ for the entire operating range.