Improving the radiation characteristics of shorted annular ring antennas through symmetric aperture-coupled feeding

In this paper, a novel feeding method for shorted annular ring (SAR) antennas is presented. SAR antennas can be designed to not excite surface waves and hence have desirable properties for many applications. The traditional method of feeding a SAR is through a single probe. Using two probes i.e. a differential feeding method, the current distribution and hence the pattern become more symmetric. However, steep current gradients on the patch make it difficult to obtain a robust design against manufacturing tolerances. A novel feeding method based on a dual aperture coupling approach is proposed to overcome the limitations of a dual-probe feeding approach while still maintaining the reduced surface wave characteristics. Additionally, this feeding method is shown to provide an increase in broadside gain of almost 3dB through eliminating disturbances in the current density on the SAR.