Abstract
The paper presents a circularly polarized radial line slot array (CP RLSA) antenna with a nearly optimal monotonic variation of slot length with radius, in order to simultaneously reduce antenna side-lobe levels and to make the aperture phase distribution nearly uniform. It has additional advantages of excellent radiation efficiency, high gain and good overall bandwidth. The antenna comprises a single-layer radial transverse electromagnetic quasi-TEM waveguide with radiating slots on the aperture. The amplitude tapering is implemented by gradually varying slot lengths on the antenna aperture as a function of radial distance, utilizing a slot coupling analysis. Several antenna designs were investigated, each having a physical diameter of 345 mm ( $23\lambda _{0}$ ) and a thickness of 4.6 mm ( $0.3\lambda _{0}$ ), where $\lambda _{0}$ is the free-space wavelength at the operating frequency of 20 GHz. A prototype was fabricated and measured, showing a good agreement between the predicted and measured results. The sidelobe levels at the operating frequency are less than −20 dB due to tapering in the near-field amplitude distribution. The measured magnitude of the input reflection coefficient ( $S_{11}$ ) of the antenna is below −10 dB within the frequency range of 19 GHz to 21 GHz. The antenna has a measured peak directivity and a peak gain of 34.3 dBic and 33.8 dBic, respectively. Both the measured 3dB directivity bandwidth and 3dB gain bandwidth are 5.4%. Aperture efficiency is 48% and radiation efficiency is 94.2% at the operating frequency. The fabricated antenna also successfully fulfilled the condition of circular polarization with an axial ratio bandwidth exceeding 5%.
Highlights
A n unprecedented growth and dependency on wireless devices and components have steered a global effort to provide on-the-move connectivity to onboard mobile platforms using satellites and other high-altitude platforms
This paper presents an extremely highgain radial-line slot array (RLSA) antenna that is useful as the base antenna in such systems
A thorough investigation on RLSA side-lobe reduction methods is yet to be conducted [10], [36]–[44]. This paper addresses this need by developing a method that substantially reduces CP-RLSA side-lobe levels and at the same time enhances phase coherence across the aperture
Summary
A n unprecedented growth and dependency on wireless devices and components have steered a global effort to provide on-the-move connectivity to onboard mobile platforms using satellites and other high-altitude platforms. Y. Koli et al.: RLSA Antenna With Low Side Lobes and a Uniform-Phase, Tapered-Amplitude Aperture Field Distribution on-the-move connectivity applications and low-cost reflector dishes are often used for stationary platforms. The RLSA antennas are parallel plate waveguide antennas with a radiating slot pattern on the top plate and have been investigated in the past as an alternative to parabolic dishes [1], [2], [8], [20]–[26] It is because of their extremely low height, they can conveniently be installed or even concealed on moving platforms. The aim of this paper is to develop a highly directive CP RLSA antenna that has extremely low sidelobes with excellent pattern quality and has near-field radiation characteristics needed for beam steering applications.
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