This paper presents design and application of a varactor loaded tunable coupled line for a polarization agile antenna. Based on the investigations, a method is proposed to reduce the required varactor tunability. Later on, the results are verified by prototyping an antenna, which consists of a liquid crystal based tunable coupled line. The antenna operates at 13.75 GHz with a return loss of better than 10 dB. The measurement results confirm that the polarization state of the antenna can be changed continuously between linear and circular polarizations by applying a DC bias voltage to the varactors.
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