Resonant frequencies of a circularly polarized nearly Circular Annular Ring Microstrip Antenna with superstrate loading and airgaps

This paper presents an analysis for the resonant frequencies and its various harmonics of a nearly Circular Annular Ring Microstrip Antenna (ARMSA) with and without air gaps and superstrate loadings. This ARMSA is studied for various radii of the inner and outer radiating circular edges of disc. Three such nearly circular ARMSA are analyzed with an Aspect Ratio of 0.98. By diagonal feeding at the center of ARMSA, circular polarizations are observed with generation of fundamental resonant frequency and higher order modes. Multilayer dielectric ARMSA with and without air gaps are analyzed using effective quasi-static capacitance approach and compared with experimental results using Vector Network Analyzer to provide less than 1% deviation in the resonant frequency. Also the full wave simulated and experimental readings go in good agreement for all the three nearly circular ARMSA for with and without air gaps along with superstrate loadings of various height and dielectric constant material as cover. This closed form model of nearly circular ARMSA is suitable for covered antenna devices CAD and is directly applicable for integration of microstrip antennas beneath protective dielectric superstrates in portable wireless equipments.