Design of a 3-dB Directional Coupler in S-Band Using Symmetric Coupled-Lines

In this paper, analysis and design of a 3-dB 90° directional coupler operating in S-band is proposed. The coupler employs symmetrical multi-section coupled lines designed in a strip line technique. The theory of symmetrical directional coupler synthesis method was employed to achieve results for the ideal conditions. Subsequently, through a tuning process, the objective was to adjust these results using full-wave EM simulation to obtain a balanced coupler design concerning amplitude and phase response. The simulation results show that the coupler maintains magnitude consistency within ± 0.3 dB, isolation and return loss parameters are better than 16 dB and phase difference between two output ports is 88° ± 0.6° in 1.7 - 4.35 GHz frequency range. This simulation results indicate an improvement which is achieved in fractional bandwidth (FBW) performance around the center frequency (fo = 3 GHz).