Effect of superstrates on the resonant frequency of a circularly polarized nearly circular annular ring patch

This paper presents the effect on resonant frequency of multilayer circular annular ring microstrip antenna. Three nearly circular annular ring microstrip antennas (ARMSA) have been fabricated on FR4 substrate of dielectric constant 4.3 and thickness 1.53mm of various dimensions. Experimental resonant frequency of simple circular ARMSA, covered circular ARMSA, spaced dielectric circular ARMSA and circular ARMSA with two superstrates have been measured and compared with the calculated resonant frequency from full wave analysis. The average % deviation of all these ARMSA are respectively found as -0.278%, 1.03%, -0.535% and 0.5%. The measured and calculated resonant frequencies are in good agreement. The Simple nearly circular ARMSA, fed diagonally at the center of the radiating patch is studied for circular polarization (CP) with 3dB Axial Ratio bandwidth. The three types of ARMSA has been designed and fabricated and found to have a CP-3 dB axial ratio bandwidth of 5.2%, 4.16% and 2.06% at their center fundamental resonant frequency. This type of study is useful for wideband, high gain antenna and to calculate the radome and environmental effect on resonant frequency.