Miniaturized and harmonics‐rejected slow‐wave branch‐line coupler based on microstrip electromagnetic bandgap element

Abstract

AbstractThis article presents a planar branch‐line hybrid coupler with an effective technique for harmonic suppression and size reduction. The proposed technique served by a microstrip electromagnetic bandgap element entitled MEBE (compact microstrip resonant cell) is used to suppress the harmonics and reduce the length of a quarter wavelength line when compared with the conventional branch‐line coupler. The planar structure enables an easy circuit implementation in printed circuit boards without any additional process and lumped elements. From the measured results, better than 30 dB suppression for the second harmonic and 18 dB suppression for the third harmonic are obtained while maintaining the characteristics of conventional branch‐line hybrid coupler. It is able to achieve two insertion losses of less than 3.5 dB, the return loss of 18 dB, and isolation of 19 dB at operating frequency. With our improved beeline compact microstrip resonant cell, compact branch‐line coupler occupying areas of 35.86% relative to conventional designs has been realized. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1080–1084, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24241