A circuit construction of parallel ring-line rat-race circuit with very loose coupling utilizing CRLH-TLs

This paper treats parallel ring-line rat-race circuits with very loose coupling utilizing composite right-/left-handed transmission lines (CRLH-TLs). We have already reported the parallel ring-line rat-race circuits composed of four CRLH-TLs and two right-handed transmission lines (RH-TLs), and successfully designed −20dB rat-race circuits with broadband characteristics. In this paper, to reduce the number of CRLH-TLs we propose the parallel ring-line rat-race circuit composed of two CRLH-TLs with electrical length of −90 degrees and four RH-TLs with 90 degrees. As a result of designing the circuit at 4GHz, a relative bandwidth of about 27% can be obtained for the -20dB rat-race circuit. Furthermore, high power durability for the trial −20dB circuit has been also demonstrated.