Semi-Analytical Design Approach to Quasi-Electrically Small Microstrip Annular Sector Patch Antennas

Semi-analytical design approach to circularly polarized (CP) tilted-beam microstrip antenna with quasi-electrically small annular sector patch is presented. At first, the relationship between normalized outer radius $\bar b$, central angle α and outer/inner radii ratio γ=b/a, is studied basing on the eigenfunction family of the asymmetric annular sector patch. In this way, microstrip annular sector patch antenna (MASPA) under dual-mode resonance with quasi-electrically small radius and tilted circularly polarized beam characteristic can be attained. For validations, MASPA with central angle of 355° on air substrate (with a profile less than 0.05-wavelength) is investigated. As is revealed, the antenna can exhibit maximum radius of 0.185-wavelength (quasi-electrically small), tilted CP 3 dB axial ratio (AR) bandwidth of 15.2%, and tilted CP angle ranging from 0° to 20° in the elevation plane.