Tunable Miniaturized Patch Antennas With Self-Biased Multilayer Magnetic Films

Abstract

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> 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 <formula formulatype="inline"> <tex Notation="TeX">${-}5$</tex></formula> dBic gain beamwidth increased from 140<formula formulatype="inline"><tex Notation="TeX">$^{\circ}$</tex></formula> to 155<formula formulatype="inline"><tex Notation="TeX">$^{\circ}$</tex></formula>, 156<formula formulatype="inline"><tex Notation="TeX">$^{\circ}$</tex></formula> and 160<formula formulatype="inline"><tex Notation="TeX">$^{\circ}$</tex></formula>, 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. </para>