Substrate size selection of microstrip-fed cylindrical dielectric resonator antennas for lowering the cross-polarisation

Abstract

A cylindrical dielectric resonator antenna (DRA) has been excited with a microstrip line in the HEM11δ mode. It is demonstrated that at the operating frequency, minimum cross-polarisation occurs when the lateral dimension of the substrate is slightly higher than half a free-space wavelength (λ0). This occurs when direct waves from the DRA interfere appropriately with the waves that are diffracted from the substrate edges. For a 50 Ω microstrip-fed cylindrical DRA, numerical prediction suggests a substrate of lateral dimension 0.58λ0 for the lowest possible cross-polarisation. In addition, the above optimum substrate size is constant irrespective of the substrate shape (square or circle) or dielectric resonator (DR) properties (permittivity and aspect ratio) for a given substrate permittivity. Numerical results are experimentally verified for a DRA with permittivity 24 and aspect ratio 1.33, for both square and circular substrates at the respective operating frequencies.