Abstract
The directivity of the circular polarized antenna composed of an unbalanced fed ultra low profile inverted L antenna and L shaped slot on the square conducting plane is improved by adding the square reflector located back of the conducting plane for the application of 900 MHz band RFID reader antenna. The size pf conducting plane is 135.6 mm by 135.6 mm and that of the reflector is 133 mm by 133 mm. In the numerical analysis, the electromagnetic simulator "WIPL-D" based on the Method of Moments is used.