A method of designing an E-plane power combiner composed of two quarter-arc bent rectangular waveguides is proposed for sub-THz and THz waves.The quarter-arc bent-waveguide power combiner has a simple geometry which is easy to design and fabricate.By HFSS codes,the physical mechanism and performance of the power combiner are analyzed,and the relationship between the output characteristics and the structure/operating parameters is given.Simulation results show that our power combiner is suitable for the combining of two equalpower and reversed-phase signals,the bandwidth of the combiner is wide and can be adjusted by the radius of the quarter-arc,and the isolation performance of the combiner can be improved by adding thin film resistive septa at the junction of two quarter-arc bent waveguides.Meanwhile,an approximate method based on the analytic geometrical analysis is given to design this power combiner for different frequency bands.