Circularly polarized double- and plate-loop antennas with a single feed

Three types of square loop antennas with the same side length L and spacing S have been analyzed. The analysis of a discrete DL antenna reveals that one of the loops radiates a CP wave when its circumference is approximately one wavelength. It follows that the antenna has two minima in the frequency response of the axial ratio. In contrast to the discrete DL antenna, a modified DL antenna has an axial ratio with a wide-band frequency response, which is more than 1.5 times as wide as that of the reference (single loop) antenna. Further analysis demonstrates that a plate-loop antenna has an axial-ratio bandwidth similar to that of the modified DL antenna.