Miniaturized Quadrature Hybrid Couplers based on Novel U-shaped Transmission Lines

In this paper, a miniaturized microstrip quadrature hybrid coupler (QHC) using U-shaped transmission lines (USTLs) is presented. The proposed approach replaces all arms of the conventional QHC with its equivalent USTL to achieve compactness. The proposed coupler structure is designed to operate in the 1.5 GHz (1427-1518 [MHz]) band which is one of the 5G bands of interest. At such low RF/microwave bands below 3-4 GHz, the size of the conventional coupler is considerably very large which raises a concern for the next generation networks. The pro- posed coupler is designed, simulated and fabricated using Rogers 5880 with thickness of 0.79 mm, dielectric con- stant (er) of 2.2 and loss tangent of 0.0021. The proposed QHC size is 70% smaller in circuit area (30% relative area) than the conventional equivalent. Simulation and mea- sured results are presented and good matching between the results is observed, confirming the outstanding coupler performance properties. The proposed miniaturized QHC structure will play a vital role for next generation 4G and 5G wireless communication systems operating below 6 GHz.