A novel compact dual-band branch-line coupler

A novel compact dual-band branch-line coupler is proposed, which consists of four E-shaped dual-band transmission lines. The even-odd mode method is adopted to obtain the input admittance of the E-shaped transmission line. Letting the admittance matrix of the E-shaped transmission line and the conventional quarter-wavelength transmission line be identical in two frequencies, then the dual-band coupler is obtained. For verification, a 3-dB microstrip coupler operating at 900 and 2000 MHz is fabricated and measured. Simulated and measured results are in good agreement.