In practical applications, the low-profile spiral antennas suffer from the lack of proper planar feeding ways. The vertical balun always has a significantly long length, inconsistent with the requirements of the low profile spiral antenna geometry. A spiral antenna with integrated parallel-plane feeding structure is proposed in this paper. The antenna used has obviously improved axial ratio compared to the equiangular spiral antenna at low frequencies. And the traditional balun in the third dimension is moved to the planar plane. The antenna and Dyson-style balun have been integrated into a multi-layer structure. The resulting structure maintains the typical radiation behavior and broadband operation of spiral antennas, but the vertical balun is integrated at the same plane with the antenna. The overall size of the spiral antenna is largely reduced.
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