A Novel Miniaturized X‐band Coplanar Waveguide Branch‐line Coupler Using T‐ and 𝜋‐type Equivalent Transmission Lines

This article reports a novel compact branch‐line coupler (BLC) in coplanar waveguide technology for X‐band monolithic microwave integrated circuit (MMIC) applications. This article consists of theoretical basis, design, and measurement results of the developed miniaturized BLC. In this study, the theoretical basis of the miniaturized BLCs were analyzed and the T‐ and π‐type equivalent transmission line approaches and meandering technique were utilized to significantly miniaturize the conventional BLC. The proposed BLC was manufactured with gallium nitride MMIC technology. The manufactured BLC has a return loss of better than −12 dB over 8.5–11.1 GHz which yields a 26.8% bandwidth. In addition, the insertion losses |S21| and |S31| were measured as −3.5 dB and −3.6 dB at 9.6 GHz. Moreover, the phase difference between the output ports were 90° ± 5° over the frequency bandwidth of 9.2–11.6 GHz. Furthermore, the proposed BLC has a size of 3.9 mm2 (0.152λ × 0.156λ) and this achieves 62% size reduction with respect to the conventional BLC design. The developed novel miniaturized BLC can be utilized in the X‐band applications.