A wide-band, circularly polarized, magnetodielectric resonator antenna

Previously insurmountable challenges posed by stringent requirements of simultaneous compact size, high bandwidth, high to moderate efficiency, and circular polarization operation at UHF have been surpassed by a unique design employing layered magnetodielectric materials. To achieve percentage bandwidth values in excess of 50% for an antenna with a maximum dimension of 0.15/spl lambda/ three approaches for bandwidth enhancement are combined in a proper fashion. A volumetric source, as opposed to printed planar or wire sources, inherently provides higher bandwidth and is used as the fundamental radiating element of the antenna. The radiating structure is made up of layered magnetodielectric material with proper design of permittivity and permeability values forming a magnetodielectric resonator antenna (MDRA). Noting that miniaturization and wave impedance in the MDRA are, respectively, proportional to the square-root of the product and ratio of the permeability and permittivity, moderate values of permittivity and permeability are used to enhance the bandwidth while achieving considerable miniaturization. The third method for bandwidth enhancement is based on the integration of a resonant feed and many parasitic elements into the MDRA structure. Square symmetry of the MDRA is used to obtain circular polarization operation. A prototype small UHF antenna operating over 240-420 MHz with a linear dimension smaller than 0.15/spl lambda/ at the lowest frequency is fabricated and tested; the results are summarized in this paper.