DESIGN OF A RING-SLOT ANTENNA LOADED BY A PARASITIC PATCH FOR WIDE BAND CIRCULAR POLARIZATION

Abstract

In this dissertation, a slot ring antenna loaded by a parasitic patch is designed and optimized for wide band circular polarization performance. A slot ring antenna provides both higher bandwidth and compactness which are the two important constraints • for wireless application. The design and optimization is first done for a simple square slot ring and the optimized antenna provided a simulated axial-ratio bandwidth of 3% and VSWR bandwidth of 6% at a center frequency of 2.4GHz. Then this square slot was loaded by a patch with proper air gap and based on the parametric study conducted, the antenna structure was optimized for wide axial-ratio bandwidth. A modified slot ring was proposed and designed in the stacked configuration. This modified structure provided better impedance match compared to the square slot for same axial-ratio performance. The dependence of the structure on the size of the ground plane required retuning the entire structure on a finite ground plane. The measured- 3 dB axial-ratio and VSWR bandwidth of the final optimized structure were 17.8% and 33.6% respectively at a center frequency of 2.4GHz. The stacked configuration also provided better gain performance compared to simple slot ring. The simulated and measured peak gain of the antenna was at 7.6dB and 6.98 dB, respectively. Using this optimized structure, a sequentially rotated 2x2 array was designed and tested for performance. The measured 3dB axial-ratio bandwidth covered a 2.06-2.77GHz frequency range with 29.58% bandwidth at center frequency of 2.4GHz while VSWR bandwidth spanned more than I GHz providing 53% bandwidth at the center frequency of 2.4GHz. A comparison of simulated and experimental results is also presented. iii