A Miniaturized 3-dB Microstrip Rat-Race Coupler Using Shorted Trans-Directional Coupled Lines

摘要

A miniaturized 3-dB microstrip rat-race coupler is proposed by using shorted trans-directional (TRD) coupled lines to replace the 3λ/4 microstrip line. The TRD coupled lines having tight coupling characteristics are realized with capacitor-loaded weakly coupled microstrip lines. The coupler has 38.6% physical size of a conventional one. The measured results show that the fractional bandwidth for return loss of more than 10 dB is 43.9% and that for isolation of better than 15 dB is 31.2% with a maximum isolation of 44.9 dB.