Compact wideband rat-race hybrid utilizing composite right/left-handed transmission lines

This paper presents a compact wideband rat-race hybrid composed of composite right/left-handed transmission lines (CRLH-TLs). Using CRLH-TLs with phase delays of -90 degrees and a right-handed transmission line (RH-TL) with 90 degrees at a design frequency, a relative bandwidth of about 36% can be obtained at the design frequency of 4 GHz. Furthermore, size reduction of about 60% can be simultaneously achieved compared with a conventional rat-race hybrid utilizing only RH-TLs based on a distributed circuit theory. The validity of this design procedure has been demonstrated by em-simulations and experiments. Moreover, a trial rat-race hybrid can maintain wideband characteristics and no variation of insertion losses up to 20 dBm input power.