Using the moment method, we analyze a loop antenna with a perturbation segment in the presence of a ground plane. First, the radiation characteristics versus loop height above the ground plane are investigated. It is found that as the loop height increases to more than 0.2 wavelengths a novel antenna other than a conventional one can exist, showing an enlarged bandwidth of 9% for a 3 dB axial-ratio criterion. Next, the radiation mechanism of the novel antenna is compared with that of the conventional one. Last, the novel loop is used in a comb-line antenna as a radiation element. It is found that the CP wave bandwidth is five times as wide as that of a conventional comb-line antenna. The analysis results are verified by experimental work.
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