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Description
The goal of this research was to create wideband (100% impedance bandwidth) beam scanning array elements with improved radiation performance (invariant patterns with no multi-lobe problem and low cross-polarization) and a frequency reconfigurable option. A novel planar monopole antenna configuration, the spirograph planar monopole antenna (SPMA) is presented. The omnidirectional SPMA is used to design the following antennas: a 1x4 bi-directional SPMA array, a frequency reconfigurable SPMA (omnidirectional), a uni-directional SPMA, and a uni-directional 1x4 SPMA array. In all cases the cross-polarization is relatively low. Originally designed to cover C- and X-band (4-12 GHz), the SPMA element is compact (< _/2 at the highest frequency of operation), and has an invariant omnidirectional radiation pattern (with 2-4.1 dBi gain) across the frequency band with no multi-lobe effect. A 5-pointed SPMA was fabricated and measured for impedance and radiation performance. The radiation patterns are invariant over 4.4-12.56 GHz (96%) with S__ ≤ -10 dB impedance matching. The 1x4 bi-directional array covering 3.85-12.64 GHz (107%) is created using 16-pointed SPMA elements. The interelement spacing is 0.7_ at 12 GHz, and the beam scan range is _ = ±90° at 4 GHz to _ = ±40° at 12 GHz. The broadside realized gain varies from 4.38 to 9.64 dBi over 4-12 GHz. The SPMA is scaled to operate in the 1-3 GHz range to create the frequency reconfigurable SPMA, which was experimentally verified. It has 3 configurations: case 1, 2.17-3.36 GHz (43.0%); case 2, 1.21-2.50 GHz (69.5%); and case 3, 1.07-2.92 GHz (92.7%). This antenna provides continuous coverage for 1.07-3.36 GHz (103%). Acceptable measured omnidirectional patterns are achieved for all cases. A broadband ground plane was designed and combined with a 5-pointed SPMA to create a uni-directional SPMA covering 1.14-2.90 GHz (87.1%), which was also experimentally verified. The antenna has a directional pattern with a single main lobe, which is mostly invariant over the entire frequency range, and relatively low cross-polarization. Finally a 15-pointed SPMA was used as the radiating element to form a 1x4 uni-directional array (using the broadband ground plane) covering 1.1-3.25 GHz (99%). The interelement spacing is 0.8__ at 3.2 GHz, the beam scanning range is _ = ±50° at 1.1 GHz to _ = ±30° at 3.1 GHz, and the broadside realized gain for all cases ranges from 7.84 to 11.46 dBi.
