Design of a compact rat-race coupler employing electromagnetic bandgap (EBG)-loaded and composite right/left-handed (CRLH) half-mode substrate integrated waveguides (HMSIWs).

A new type of rat-race coupler, based on electromagnetic bandgap (EBG)-loaded half-mode substrate integrated waveguide (HMSIW) and composite right/left-handed (CRLH) HMSIW, has been proposed and investigated comprehensively. It consists of three sections of EBG-loaded HMSIWs with 90° phase delay and one section of CRLH HMSIW with −90° phase advance. Due to the evanescent-mode of EBG-loaded HMSIW and the backward behavior of the CRLH HMSIW in the left-handed region, the size of such a miniaturized rat-race coupler is reduced about 65.7% in comparison with its conventional counterpart. The rat-race coupler with the central frequency of 5.5 GHz has been designed and fabricated so as to validate our method, and its good performance is demonstrated by both simulated and measured results. [ABSTRACT FROM AUTHOR]