Compact planar microstrip branch‐line coupler using equal difference structure

ABSTRACT A compact planar microstrip branch‐line coupler using equal difference structures was implemented and measured. Using the equal difference structure effectively reduced the quarter‐wavelength microstrip line and minimized the branch‐line coupler dimension as a result of a novel triangular profile of the structure streamlining the circuit area. Compared with that of conventional planar microstrip branch‐line couplers, the optimized area of the proposed coupler was reduced by 84.2% at a 900 MHz operating frequency. The measured insertion loss, isolation, and return loss performances achieved superior results than 3.9, 23, and 16 dB, respectively, and the measured phase difference between the two output ports was 90° ± 0.1°. Notably, a coupler using equal difference structures can be implemented in standard printed circuit board processes without any lumped elements, bonding wires, or via‐holes, easing integration with wireless communication systems. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:664–668, 2017