A New Design of Circular Polarized Planar Antennae

Newly designed planar antennae which radiate circularly polarized waves at the UHF band are presented in this paper. The antennae presented have the following attractive features : They are (a) single layered perfectly planar antennae, (b) antennae that radiate circularly polarized waves by balanced feeding to one port without any phase shifters, (c) antennae whose half-power beam width is very wide, and (d) useful when in use at the UHF band. The antennae have been named “Cross Spiral Antennae,” abbreviated hereafter as CSAs, for they are spiral antennae wound in the form of a cross. CSAs are expected to be used as UHF band RFID antennas due to their single layered structure which can be made easily by means of printing techniques, etc. and to their ability to radiate circularly polarized waves by mounting on each of them an IC chip that has been used conventionally with linearly polarized antennae for RFID tags.