In this letter, a compact branch-line coupler using a new type of uniplanar composite right/left-handed transmission line (CRLH-TL) is proposed. The transmission line is obtained by etching spiral structure and series meandered capacitive gaps at both ends on the host line. With the aid of lumped element equivalent circuit model and dispersion relations, the CRLH property of the line is studied. By using the proposed structures, the 90-degree phase shift 35.35 ohm and 50 ohm transmission lines are designed for a compact branch-line coupler operating at 1 GHz. It's occupied size is only 32.5% of that of the conventional one. Its uniplanar prototype makes it very useful for wireless communication systems requiring high encapsulation quality.
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