Theoretical and experimental investigation of the elliptical annular ring antenna

Analysis of a confocal elliptical annular ring microstrip antenna is carried out using the generalized transmission line model. It is found that a circularly polarized wave can be obtained over a wider frequency range than for conventional structures. It is also found that unlike the elliptical patch the resonant frequency for the odd mode is lower than that of the even mode. Therefore, for a left-handed circularly polarized wave, the feed is to be placed at an angle of -45° with the major axes of the ellipses instead of +45° as in the elliptical patch. An elliptical ring is fabricated, and its input impedance and the radiation patterns are tested. Very good agreement between the theory and the experiment is obtained. Experimental radiation patterns show an excellent circularly polarized wave with an axial ratio less than 1 dB in the broadside direction