Title: Considerations on Relatively Stable Characteristics of Omnidirectional Circularly Polarized Antennas for Less Effect of Ground Plane Size
Takeshi Fukusako
Dept of Computer Science and Electrical Engineering
Kumamoto University
Abstract—This paper deals with the way of thinking to obtain stable characteristics of omnidirectional circularly polarized monopole antennas (OCPA) using, for example, single-annular (SA-AMC) and dual-annular artificial magnetic conductor (DA-AMC) ground planes. Circularly polarized (CP) antennas are still important for many applications. Especially, CP antennas that radiates circular polarization with sufficiently low axial ratio (AR), typically AR < 3dB. Omni-directional CP antennas (OCPAs) [1]-[3] are one of those that generates CP wave covering horizontal plane.
The main target of the discussed antenna is to reduce the design rigidity of conventional OCPA whose inherent shortcoming is fixed bottom ground plane size. From this viewpoint, this talk focuses on the design of ground planes for omnidirectional circularly polarized antennas, and provides an opportunity to discuss the proposed design and the method of generating the horizontal component. In this talk, the speaker’s group would propose using a circular l ground structure (AMC) instead of using the conventional ground plane. Here, the element to generate CP wave on the AMC consists of a monopole and parasitic elements to convert liner polarization (LP) to CP wave. The concrete structures will be presented and discussed.
When the AMC is used, the ability to have a horizontal component of the electric field near ground is an advantage in dealing with circularly polarized waves. As a result, the integration of the AMC structure with OCPA circumvents the design rigidity as the bottom ground plane radius, underneath the AMC structure, can be varied between 18.4 – 188.4 mms without significantly affecting the omnidirectionality and the impedance and AR bandwidths at 6 GHz. As discussed here, the horizontal component can exist on around ground plane. Next, we would discuss this relative stability using the AMCs on the characteristics with respect to ground radius. According to the simulation, the current on the AMC is roughly concentrated on the AMC structure around the vicinity of the monopole element. Therefore, no or very weak current exist on the edge of the ground plane resulting in stable characteristics, such as S11 and AR. I hope the above discussion will be a good reference for future circularly polarized antenna design.
Keywords— Circular polarization, Omnidirectional radiation pattern, Artificial ground plane, Axial ratio
References
- W. W. Li and K. W. Leung, “Omnidirectional Circularly Polarized Dielectric Resonator Antenna With Top-Loaded Alford Loop for Pattern Diversity Design,” in IEEE Transactions on Antennas and Propagation, vol. 61, no. 8, pp. 4246-4256, Aug. 2013.
- K. Lertsakwimarn, C. Phongcharoenpanich and T. Fukusako, “Design of Circularly Polarized and Electrically Small Antenna with Omnidirectional Radiation Pattern,” IEICE Trans. Commun., vol. E97-B, 12, pp. 2739-2746, Dec. 2014.
- S. Karki, M. Sabbadini, K. Alkhalifeh and C. Craeye, “Metallic Monopole Parasitic Antenna With Circularly Polarized Conical Patterns,” in IEEE Transactions on Antennas and Propagation, vol. 67, no. 8, pp. 5243-5252, Aug. 2019.
- P. Janpangngern, R. Kuse, C. Phong charoenphanich, and T. Fukusako, “Omnidirectional Circularly Polarized Monopole Antennas on Artificial Magnetic Conductor”, IEEE Access, to be appered.
