Experimental Investigations of Planar Dielectric Disk Antennae

Abstract

The results of experimental investigations of planar dielectric disk antennae with different dielectric substrates and radiating elements are represented. Geometric and electric parameters of antenna prototypes have been chosen in accordance with the theoretical calculations [1] to provide the conditions of the ТМ01 mode excitation in the electromagnetic structure under study. It has been determined that the use of substrates with different values of the permittivity gives rise to the change in the antenna patterns and the field intensity in their lobes. Moreover, the use of dielectric disks with high permittivity (ed =90) provides an increase in the power radiated into the free space as well as a frequency band enhancement. Recently dielectric disk antennae have been used in increasing frequency as an alternative analogue of well-known planar disk metallic antennae. In accordance with the theoretical prerequisites [1] the use of a dielectric radiating element instead of metallic one must lead to an increase in the level of the power radiated into the free space as well as a frequency band enhancement of the antennae of this type. In this case, the using of disks and substrates, as elements of the antenna, with different values of the dielectric permittivity can have an influence on radiation characteristics of this type antennae. The purpose of this paper is the investigation of planar dielectric antennae and the determination of influence of permittivities of substrates and radiating elements on their characteristics. EXPERIMENT The results of experimental investigations of planar disk antennae are represented in the paper (Fig. 1). They consist of a dielectric substrate with the radius rs and a * Originally published in Radiophysics and Electronics, Vol. 10, No 1, 2005, pp. 98–101. ISSN 0040-2508 © 2005 Begell House, Inc. 727 A.S. ANDRENKO, I. V. IVANCHENKO, N. A. POPENKO, AND M. M. KHRUSLOV dielectric disk with the radius rd placed on a metal shield. To minimize the influence of the edge effects on the antenna pattern, we have taken the diameter of the substrate which is 3.5 times larger then the diameter of the disk. In the operating frequency band 8-10 GHz, the ratio of the dielectric permittivities ed and es of the disk and the substrate correspondingly as well as the diameter of the disk and the thickness hs of the substrate have been determined from the conditions of the ТМ01 resonant mode excitation in the structure [1]. As an antenna exciter we have used a vertical electric dipole in the form of a piece of the coaxial cable central core. The length of this piece is determined by the thickness of the substrate (Fig. 1). FIGURE 1. The configuration of the structure under the study: 1 is a dielectric disk; 2 is a dielectric substrate; 3 is a perfectly conducting shield; 4 is a coaxial cable We have measured the standing wave ratio, the near field distribution, and the antenna pattern with the following configuration (Table 1). Table 1 No Dielectric disks Substrates 1 rd = 22 mm, hd = 0.25 mm, ed = 7 rs = 220 mm, hs = 4 mm, es = 2.5 2 rd = 22 mm, hd = 0.25 mm, ed = 7 rs = 80 mm, hs = 4 mm, es = 2.05 3 rd = 25 mm, hd = 0.5 mm, ed = 90 rs = 220 mm, hs = 4 mm, es = 2.5 4 rd = 25 mm, hd = 0.5 mm, ed = 90 rs = 80 mm, hs = 4 mm, es = 2.05 1