Broadband Directional Coupler with High Isolation

Abstract

A novel wideband microstrip directional coupler operating at 1 to 5 GHz with high isolation is presented in this paper. Parallel coupling lines replace the traditional coupling transmission lines, providing broadband characteristics. The rectangular defected ground structure (DGS) on the RF ground on the back increases the isolation. The coupler was designed using 3D electromagnetic simulations. FR4-type dielectric substrate has been used due to its low cost. Simulation results prove that the proposed directional coupler provides an isolation of at least 20 dB on the full frequency band from 1 to 5 GHz, and reaches 66 dB at 2.89 GHz. The coupling degree is about 12 dB. Moreover, the proposed design can also achieve wide operating bandwidth (approximately 139% fractional bandwidth).