Low Profile Miniaturized Planar Antenna With Omnidirectional Vertically Polarized Radiation

Abstract

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A novel miniaturized cavity-backed composite slot loop antenna (CBCSLA) with low profile and omnidirectional radiation similar to a short dipole is presented. The antenna displays vertical polarization while having less than <formula formulatype="inline"><tex>$\lambda/100$</tex></formula> dimension in height. The geometry of the antenna is inspired from a small magnetic loop which is realized using a slot configuration on metallic ground. Since a small slot loop antenna cannot be impedance matched, a composite geometry is devised that acts like as a small slot loop and can easily be impedance matched using this configuration. The diameter of the CBCSLA can be made as small as <formula formulatype="inline"><tex>$\lambda/10$</tex></formula> or smaller. The feeding mechanism is designed in a manner to create a circumferentially-constant current distribution around the composite loop while effectively matching to a 50 <formula formulatype="inline"><tex>$\Omega$</tex></formula> coaxial feed from the antenna center. Additional methods are discussed to further enhance the bandwidth and achieve a dual-band response. The antennas are designed, fabricated, and measured. It is shown that despite their small lateral dimension and extremely small height, the miniaturized cavity-backed slot loop features extremely well input impedance match, uniform radiation pattern, low cross-polarization levels and expected gain. </para>