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The axial‐mode helical antennas with finitely large reflectors radiate sharp, circularly polarized beams along the antenna axis when the circumference of the helix is about one wavelength long and the pitch angle is 12° ∼ 14°. Although experimental results and approximate theories have been reported, no detailed theory has ever appeared. This paper discusses the radiation characteristics of the axial‐mode helical antenna with the reflector both theoretically and experimentally. First, assuming the reflector is infinite in size, we solve an integral equation satisfying the boundary conditions and obtain the current distributions on the antenna. Characteristics have been studied even for the case with a large number of turns. Next, using the current distribution thus obtained, we find the current distributions on the reflector. By means of the induced emf method, we analyze the radiation characteristics (directivity, power gain and axial ratio) of the axial‐mode helical antenna. Further, we confirmed the analysis experimentally.
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Shiokawa et al. (1980) studied this question.
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