INTRODUCTION It is commonly known that circularly polarized (CP) compact printed antennas are required in satellite communications [1], GPS, etc. Many designs of single feed circularly polarized compact microstrip antennas have been reported so far [2][3]. Compact single feed CP patch antennas can be obtained by using high permittivity substrate or slit loaded patch. However, in case of using high permittivity substrate, not only the resonant frequency but also the gain and band width performances are decreased. On the other hand, although slit loaded patch antennas can achieve a 36 % reduction in size, unequal slot length [2] or both slit and perturbation segments have to be optimized to obtain a CP radiation [3]. In this paper, a miniaturized circularly polarized patch antenna is presented. This patch antenna consists of a circular sector element with square notches. Normal circular sector patch antenna generates two different resonant modes. Theoretically, one mode induces a polarization that is perpendicular to the polarization of the second mode. In this study, the resonant frequency and relative phase of these two modes are controlled by varying only the size of the square notches allowing the generation of a CP. This time, the basic design and performances of such a circular sector patch antenna are numerically and experimentally discussed. It should be noted that the size of the proposed antenna is half the one of usual corner-truncated square patch antennas, hence enabling the composition of a compact circularly polarized patch array antenna.
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