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 proposed coupler is designed, simulated and fabricated using Rogers 5880 with thickness of 0.79 mm, dielectric constant (εr) 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 measured 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.

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This article presents a highly linear balanced power amplifier with miniaturized quadrature hybrid coupler for carrier aggregation (CA). The miniaturized quadrature coupler is designed using a novel U‐shaped transmission line (USTL) concept to achieve good size reduction. The novel branch‐line coupler is used to design a wideband balanced PA. The performance of the balanced PA is compared to a single PA solution. The balanced PA shows better performance with improved matching properties and better electrical stability. There was an increase in saturated maximum output power (Pout) from 8 dBm for the individual PA to 13.41 dBm for the balanced with a power‐aided efficiency (PAE) of 43.92%. The highly linear balanced PA achieves a 14 dB ACPR reduction and also improves ACPR by 12 dB for noncontiguous and 9 dB for contiguous carrier aggregation.

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