A Novel Broadband 3 dB Branch Waveguide Directional Coupler With Ultra-Low Amplitude Imbalance

A novel broadband 3dB branch waveguide directional coupler with ultra-low amplitude imbalance is proposed in this paper. By introducing 10 circular cutouts inside the main waveguide, the amplitude imbalance in operating band is greatly improved. The results show that the proposed coupler has a working frequency band of 133.2 GHz to 163.3 GHz, a fractional bandwidth of 20.3%, the amplitude imbalance is less than 0.4dB, while the amplitude imbalance is less than 0.13dB in the center frequency, and the phase imbalance is better than ±0.94°. The amplitude imbalance in the center of the operating band is improved by about 70% compared to the traditional 5-branch waveguide coupler.