Slanted strip pair circularly polarized microstrip antennas

Currently, narrow bandwidth wireless card systems have spread widely in Japan. In these systems, the bandwidth can be nearly one percent and high gain circularly polarized base station antennas are required. Typical examples are the 2.4 GHz band wireless card system and ETC (Electronic Toll Collection) system. Widely used antennas for these systems are circularly polarized microstrip array antennas. In this paper, we present, for use in these systems, a slanted strip pair (SSP) circularly polarized microstrip antenna (CPMA), which is one of the herringbone array antennas. In Ito et al. (1978), the change of field strength due the change of gap between the feed line and strip element, was discussed. However, there are no data to design practical CPMAs. This paper first investigates the coupling characteristics between the feed line and one slanted strip, and next investigates in detail antenna characteristics of the CPMA element consisting of a pair of slanted strips, that is, S-parameters, gain, axial ratio, and radiation pattern. Then, we show the characteristics of a four element array. These data seem to be useful to design the CPMA.