Miniaturization of three-section branch-line coupler using diamond-series stubs microstrip line

Abstract

A three-section branch-line coupler is miniaturized using diamond-series stubs microstrip lines. The modified coupler is capable of operating from 1.6GHz to 3GHz with a return loss of less than −20 dB, phase imbalance of less than 2.5°, insertion loss and coupling of −4.5±1.5 dB and −2.5±0.5 dB, respectively over the operating range. The bandwidth of the coupler has been extended up to 1.4GHz. In addition, it achieves up to 83.3% size reduction as compared to the conventional three-section coupler. Furthermore, its performance and circuit size are compared with another modified coupler with normal open-stubs microstrip lines. Significantly, this study focuses on analyzing and discussing the effects of diamond structure and number of stubs. Furthermore, the achieved results are superior to the previous studies.