Analysis of Slot Coupling in a Corrugated Radial Waveguide

A radial line slot antenna (RLSA) in Fig.1 is a high-gain, high-efficiency and low-cost planer antenna, which was originally proposed for satellite TV reception at 12GHz band [1]. Recently this antenna has been designed for a space solar power system (SSPS) [2],[3]. Figure 2 shows the relationship between the slow-wave factor and the aperture efficiency. The slow-wave factor ξ is defined as ξ=λg/λ0 where λg is the guided wavelength and λ0 is the free space wavelength. The slow-wave factor ξ affects aperture efficiency of RLSAs. A dielectric material is generally filled in a radial waveguide to create a slow wave structure. The efficiency is degraded because of the grating lobes for too small dielectric constant while it is narrow banded because of the long line effect of a series fed array for too large constant [4]. The proper slow-wave factor is 0.8 to 0.9 in terms of the efficiency and the bandwidth [5]. Since antennas for SSPS are excited with high power energy and used in space, a hollow structure without a dielectric is desired. A corrugation structure was proposed as a slow-wave structure for a radial waveguide of RLSAs as shown in Fig.1 [6]. The slow-wave factor depends on the parameters of the corrugation height, corrugation space, corrugation width and waveguide height. In this paper, the