A Coaxial Feeder with Two Pairs of Parasitic Pins for Realizing Rotationally Symmetric Aperture Illumination in Spiral Array Radial Line Slot Antennas

Hideki UEDA  Jiro HIROKAWA  Makoto ANDO  Matteo ALBANI  

IEICE TRANSACTIONS on Communications   Vol.E93-B   No.10   pp.2554-2561
Publication Date: 2010/10/01
Online ISSN: 1745-1345
DOI: 10.1587/transcom.E93.B.2554
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Advanced Technologies in Antennas and Propagation in Conjunction with Main Topics of ISAP2009)
Category: Antennas
spiral array radial line slot antenna,  sidelobe,  aperture efficiency,  feeding structure,  

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A spiral array radial line slot antenna (SA-RLSA) is designed in 22 GHz band. A SA-RLSA excited with a coaxial feeder suffers from aperture illumination fluctuation in amplitude and phase in the circumferential (φ-) direction while in the radial direction, reasonably uniform distribution is observed. Rotational symmetry of radiation patterns is degraded and especially the sidelobe levels are unbalanced. This fluctuation is associated with the generation of the higher order modes in the φ-direction and is the unique defect of SA-RLSA which uses oversized waveguide. In this paper, a novel feeding structure with two pairs of parasitic pins around a coaxial feeder is proposed and designed so as to compensate the rotational asymmetry of aperture illumination. A measurement using the model antenna designed in 22 GHz band demonstrates the enhancement of the rotational symmetry; the circumferential fluctuation is reduced from 5.1 dB and 33 degrees to 1.8 dB and 12 degrees, while the fluctuation in the first sidelobe level suppressed from 10.7 dB to 1.2 dB.