Design of Compact Hybrid Branch Line Coupler (BLC) for GSM Application

Abstract

This paper presents a compact design of a hybrid branch line coupler (BLC) operating at 1.8 GHz frequency for the global system for mobile communication (GSM) applications. The miniaturization is achieved by using two short circuited stubs and one series transmission line (TL) instead of series quarter wavelength line of conventional BLC. The characteristic impedance of the shunt quarter wavelength section is optimized to improve the overall performances. Therefore, the proposed technique is 59% compact in size is compared to conventional BLC. The outputs at two ports (|S21| = |S31|) are 3.5 ± 0.3 dB with return loss (|S11|) and isolation (|S41|) is better than 20 dB. The prototype coupler is simulated using ANSYS HFSS EM simulator and fabricated on a substrate of dielectric constant (er) = 2.2, thickness (h) = 0.787 mm and loss tangent of 0.0009 and tested. The measured result is completely compiled with the simulated one.