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The frequency characteristics of a modified backfire bifilar helical antenna are numerically and experimentally investigated and those of a conventional bifilar and conical bifilar helical are also shown for comparison. The radiation characteristics are evaluated from the current distribution determined by an integral equation. It is found that tapering only the feed end greatly contributes to the improvement of front to back ratio over a wide band frequency range.
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Nakano et al. (1983) studied this question.
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