PROPAGATION AND RADIATION CHARACTERISTICS OF DIELECTRICLOADED AXIAL-MODE HELICAL ANTENNA

摘要

This article presents theoretical and/or experimental study of the propagation and radiation characteristics of dielectric-loaded axial-mode helical antenna at 8.985 and 10.0 GHz. Characteristic equations for the sheath helix model are derived for three different dielectric loadings viz. loading with two coaxial dielectric layers, single dielectric layer, and air. These equations are solved for the propagation constant and hence the phase velocity for n=1 higher order spatial harmonic mode. The variation in phase velocity with wavelength normalized helix circumference is studied for different ratio of outer to inner helix radii, ratio of outer to inner radii of the dielectric tube containing a solid dielectric cylinder inside the helix, and the dielectric constant of the dielectrics used. The results for variation in phase velocity of the wave for n=1 mode propagating in sheath helix with wavelength normalized helix circumference for pitch angle of 7° are compared with the available theoretical data. The theoretical expression for the radiation field of the helical antenna is obtained through the application of magnetic vector potential for n=1 mode. The theoretical E{sub}θ and E{sub}φ patterns of the helical antenna with three different dielectric loadings are compared among themselves and also with respective experimental results at 8.985 and 10.0 GHz in X-band. The gain, input VSWR, and axial ratio of antenna with three different dielectric loadings are also measured at 8.985 and 10.0 GHz. The work presented here can provide useful design guidelines for development of optimum dielectric-loaded helical antenna, which may find potential application in satellite communication.