Compact Design of Filtering Branch Line Coupler for GSM Frequencies Using Coupled TL

This paper presents the design of compact filtering branch line coupler (BLC) with coupled transmission line (TL) for the Global System of Mobile Communications application. The presented BLC provides equal power split among output ports ± 1.0 dB imbalance of amplitude and phase variation from $145^{0}$ to $-125^{0}$ at an operating frequency of 0.83 GHz. It occupies $0.07 \lambda_{0} \times 0.06 \lambda_{0}(26.0 \mathrm{~mm} \times 22.5 \mathrm{~mm})$ at 0.83 GHz, provides 92 % compactness over the conventional design of branch line coupler at the identical operating frequency. It gives 10 dB fractional bandwidth of 38.5 %(0.67-0.99 GHz) with reflection coefficient 37.5 dB and isolation of 43.0 dB at operating frequency.