A Compact Planar 90° Branch Line Coupler Using S-Shaped Structure Loading for Wideband Application

Abstract

This paper presents the design of a wideband microstrip branched branch line coupler (BLC). The wideband performance of the BLC means that it possesses equal coupling and difference of phases throughout the operating frequency band, from 4 GHz to 6 GHz (based on a 10 dB, i.e., VSWR ? 2). The compactness of the proposed design is depending on the replacement of the branched transmission lines (TL) instead of the ordinary TLs. Small and easy to fabricate microstrip layout topology for the BLC has been designed and constructed relying on a low cost dielectric material, the well-known FR4. In addition, the proposed coupler can be easily fabricated on the printed circuit board without any lumped element. The proposed BLC exhibits couplings and phase errors within ?3.75 ± 1 dB and 4° over a 60 % bandwidth (BW) with a center frequency of 5 GHz (based on 15 dB).