Antenna with an anisotropic sheath inside a parallel-plate waveguide - Theoretical and experimental studies

Closed-form expressions for the current distribution and impedance of an antenna with a magnetised ferrite sheath inside a parallel-plate waveguide have been obtained by a modal-expansion technique. Numerical results have been obtained with a model 7090 computer, for applied direct magnetic fields below resonance. Particular emphasis has been paid to studying the following aspects of the problem: (a) the effect of the birefringent properties of the magnetised-ferrite sheath on the current and charge distribution of the antenna (b) the behaviour of the antenna at waveguide-mode cutoff frequency, and at ferromagnetic resonance (c) the effect of the feed-point singularity on antenna characteristics. In order to verify some of the theoretical predictions, experiments have been made at 1 Gc/s using a Mg-Mn-Al ferrite sample. The experimental results agree qualitatively with theory. A description of the apparatus is included in the paper. Utilising the duality between ferrites and plasmas, the properties of the magnetoplasma-coated antenna at the Pythagoras and plasma-resonance frequencies are also discussed briefly.