A compact microstrip coupler using T-shape and open stubs for fifth generation applications

Abstract

The paper presents a new design of a compact branch-line coupler (BLC) operating at 3.5 GHz, that is suitable for 5G applications. In order to miniaturize the proposed coupler, two miniaturization methods are combined where a T-shaped structure is used instead of quarter wavelengths parallels, as well as open stubs are introduced into the series lines resulting in a size reduction of 52.56% with 25.05% fractional bandwidth (FBW). The frequency responses indicate that the presented coupler is able to operate at 3.04 GHz to 3.91 GHz with a low return loss and high isolation that is improved to -28.9 and -31.1 dB in 3.5 GHz, insertion loss and coupling of -3.6 dB and -3.5 dB, respectively, and a phase difference of about 90°±1°. The strong agreement of measurement and simulation results indicated the suitability of this proposed design for 5G microwave integrated circuits (ICs) that require a small size.