Suppressing undesired modes in a higher-order mode microstrip ring patch antenna

The authors propose the principles for a higher-order mode ring patch antenna with a conical pattern with good symmetry for suppressing undesired modes and a simple configuration for creating such an antenna. In addition, the authors propose loading a degenerate separation element as a means to implement circular polarization in a higher-order mode ring patch antenna of this configuration and then confirm the circular polarization through experiments. The antenna has a simple configuration in which a microstrip line is positioned inside the ring and power is fed from the rear at the central point. The antenna offers the following advantages: line length to the edge of the power supply point and the ring patch that is roughly lambda /4; and impedance at the power supply point that can be readily matched. Moreover, because the power supply point is at the central point of the ring patch antenna, this configuration is also beneficial in that it can be easily used for an array antenna by using it as an element of an array antenna that needs to be rotated and positioned, such as a sequential array antenna or a radial array antenna. (C) 2001 Scripta Technica.