Abstract
In this paper, we consider a parallel ring-line rat-race circuit realized by replacing some parts of the ring-lines with composite right-/left-handed transmission lines (CRLH-TLs). For a conventional rat-race circuit, the minimum coupling factor is limited by the highest impedance of the ring-lines that can be manufactured by general printed circuit board (PCB) technologies. However, the coupling factor of the parallel ring-line type rat-race circuit proposed in this paper is determined by the difference between the admittances of the parallel ring-lines. As a result of designing parallel ring-line rat-race circuits having coupling factors of -20 and -30 dB for an operation frequency of 4 GHz, the proposed rat-race circuit realizes broadband characteristics of about 35.5% according to the numerical results for the -20 dB circuit. Furthermore, broadband characteristics including reflection, isolation, and couplings can be maintained for the fabricated -20 dB rat-race circuit up to an input power of 40 dBm.
