Design of Wideband 3dB Quadrature Coupler Based on Offset-Coupled Striplines

In this paper, a 3dB quadrature coupler based on multisection coupler and offset-coupled striplines is presented. Wide bandwidth with better amplitude balance is obtained by connecting two 8.34dB multisection uniform coupled-line coupler in series with compensated matching stubs. The proposed coupler consists of a three-layer printed circuit board. The proposed design has the bandwidth larger than 125% from 2GHz to 12GHz. Measurements show that the given design can achieve coupling coefficient of 3.7±0.8dB and phase difference between the two output ports of 86°±4° in the whole operation band.