A novel method of exciting a circularly polarised (CP) loop antenna is proposed using the moment method. A horizontal square loop above the ground plane has two corners connected to a vertical, branched feedline with one source. First, the authors show the radiation characteristics of a reference antenna whose corners are excited with two sources having the same amplitudes and a phase difference of 90°. Next, we excite the loop corners with one source using the branched feedline. It is found that when the branch location along the feedline is selected, the antenna radiates a CP wave. The frequency responses of the antenna show that the 3 dB axial-ratio bandwidth is 12%, where the gain is more than 7.3 dBi. The simulated results are verified with experimental ones.
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