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Improving The Performance Of Spiral Antennas By Using Passive Scatterers.
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH
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The purpose of this study was to explore the viability of improving the performance of cavity-backed antennas. Traditionally antenna cavities are filled with electromagnetic absorber to mitigate interference effects that would otherwise cause the antenna radiation pattern to vary widely at different frequencies. The approach used in this research was to replace the absorber with dielectric slabs, some of which contained arrays of dipoles. These dipole arrays were modeled as frequency selective surfaces using two periodic moment method based - computer programs and one transmission line program. A systematic study was performed that identified the effect of changing the dipole array parameters on prospective cavity designs. Seven different cavity configurations were tested using a log periodic trapezoid wire antenna system designed to support 2.3 - 12.4 0Hz. Cavity configurations using one, two, and three layers of dipole arrays were tested and compared to both absorber-filled and dielectric-filled cavity configurations. The results were inconclusive because even though some two layer designs and one three layer design had better gain almost entirely throughout the 2- 12 GHz region, the gain of the baseline absorber-filled and dielectric-filled cavities varied widely over this bandwidth. No cavity condition provided an extended 3 dB bandwidth. Additional research is recommended.
APPROVED FOR PUBLIC RELEASE