Application of composite right/left-handed half-mode substrate integrated waveguide to the design of a dual-band rat-race coupler

"Summary form only given, as follows." Based on the composite right/left-handed (CRLH) half-mode substrate integrated waveguide (HMSIW) transmission line (TL), a dual-band rat-race coupler is implemented and presented in this paper. The CRLH behavior of the HMSIW TL is obtained by etching interdigital slot on the waveguide surface. It supports the propagation of the backward-wave below the characteristic waveguide cutoff frequency in the left-handed (LH) region and the forward-wave in the right-handed (RH) region. This attribute (phase advance and phase delay at different frequencies) is applied to the design of a dual-band rat-race coupler. Equivalent circuit and dispersion diagram are discussed. Theory and synthesis procedures are provided. Couplers based on the conventional HMSIW and CRLH HMSIW are designed, fabricated and compared. Their 180°-out-of-phase and in-phase operations are verified. Good agreement between the simulation and measurement is observed.