Tunable miniaturized patch antennas with self-biased multilayer magnetic films

Magneto-dielectric substrates with thin magnetic films show great potential in realizing electrically small tunable antennas with enhanced bandwidth, improved directivity, and high efficiency. This communication introduces self-biased NiCo-ferrite magnetic films as a practical mean to tune a patch antenna by loading single layer and multilayer self-biased ferrite films. The central resonant frequency of the unloaded patch antenna is measured at 2.1 GHz with a bandwidth of 18 MHz. However, with ferrite loading of the alumina substrate, this frequency is shown to be tunable within a range of 12 MHz-40 MHz, and the antenna efficiency is increased from 41% of the non-magnetic antenna to 56%, 65%, and 74% for the three magnetic antennas. The omnidirectional radiation pattern is significantly enhanced with the -5 dBic gain beamwidth increased from 140° to 155°, 156° and 160°, respectively for the three ferrite loaded antennas. In addition, the gains of the three magnetic antennas are enhanced by 0.32, 0.77, and 1.1 dB, respectively, over the unloaded antenna.