AN ANALYSIS OF SINGLE-FEED CIRCULARLY-POLARIZED MICROSTRIP ANTENNA USING BOUNDARY-ELEMENT METHOD

This paper presents an analysis method of a single-feed circularly pol arized microstrip antenna (MSA) by means of the boundary element metho d. When the boundary element method is applied to such open planar cir cuits as the microstrip antenna, the loss due to radiation must be tak en into consideration. As the radiation loss, it is proposed that the radiation admittance obtained from the radiated field from a microstri p antenna with a basic shape be used as the load. This radiation admit tance can be derived easily without any complicated calculations. As e xamples of the application of this analysis method, the computed value s of the input impedance and the axial ratio are compared for the circ ular and rectangular MSAs with small sectors to remove the degeneracy and for the circular MSA with a shorting pin inside so that the effect iveness of the method is demonstrated. Also, an impedance matching met hod is proposed at the frequency for the minimum axial ratio by cancel ling the inductance of the feed pin by means of the change of the posi tional relationship of the feed point and the small sectors.