Realization of a compact branch line coupler using semi-lumped element

Abstract

A single band branch line coupler for butler matrix with semi-lumped element has been proposed in this paper. The coupler is designed to operate properly at 5.8 GHz operating frequency. The capacitors with the value of 33 pF and 4.7 pF are realized as suitable values for lumped element components. It is found that the lumped element implementation is capable to greatly influence the size compactness of the coupler. The equivalent circuit is designed and simulated by using Agilent Advance Design System (ADS) software. As a result, the length of the fabricated proposed coupler is reduced by approximately 50% compared to the conventional coupler when the capacitors are embedded together with the transmission line. Moreover, the design which is etched on 1.6 mm thickness of FR4 substrate leads to the cost effectiveness. Prototypes of the proposed coupler have been constructed and successfully tested. The simulated and measurement results show the potential of the proposed coupler in the applications of butler matrix such as multi-port power amplifier, wireless local loop and transmit combining network in cellular Digital Cellular System (DCS) 1800 base station.