A Compact Wideband Branch Line Coupler for Lower 5G Applications

- This paper presents a new design approach of a compact wideband branch line coupler based on waveguide technique at 3.5 GHz. At the lower band of 5G technology, microwave devices such as hybrid couplers tend to be narrower in bandwidth and big in size, in addition to the phase difference error produced by using common planar technology. Therefore, waveguide technology aims to solve those challenges. This work aims to design a compact wideband coupler by implementing a direct coupling aperture between two waveguides with a cutting in the narrow wall of the structure. This technique helps in obtaining a wide bandwidth and reduces the size of the whole structure. The coupler is simulated using computer software technology and fabricated using CNC machining. The measured S-parameters of the coupler are observed to have low loss properties with return loss and isolation less than - 10 dB. The coupling factor at the outputs are - 3.21 dB with low loss of - 0.2 dB. The measured phase error is about 2 degrees at 3.5 GHz. A size reduction of 70% is observed compared to conventional waveguides and planar couplers. Overall, this coupler shows great performance that could be used for 5G beamforming applications.