In this study, a novel ka‐band compact‐size branch‐line coupler was proposed. The coupler was designed and fabricated with WIN Semiconductors 0.15‐μm pseudomorphic high electron‐mobility transistor process. The design method, simulation data, and measurement results of the proposed coupler were also discussed. The coupler occupied less than 45% of the circuit area compared with conventional design at 30 GHz, and did not implement any lumped elements via‐hole grounding, and bonds wire, making it simpler to design, easier to fabricate, and lower cost. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2950–2953, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22941

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In this article, an extremely compact dual‐band branch‐line coupler is presented. The miniaturized design saved 74% circuit dimension comparing to the original dual‐band branch‐line coupler. Several design methods and miniaturization techniques were involved in this study to achieve the criteria, including stepped‐impedance resonators (SIR) structure, symmetrical T‐shape structure, bended and folded of transmission lines, and the coupling effect of microstrip‐lines. Good agreements between the simulated and measured results were also observed. Furthermore, no lumped elements, via‐holes, and bonding wires are necessary for this miniaturized coupler, making it very useful for the modern wireless communication systems. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 3011–3014, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22895

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