Dual-band circularly polarised microstrip antennas with a single feed

The authors present a novel technique for obtaining circularly polarised (CP) dual frequency operation by using two spur-link band-stop filters within the perimeter of a microstrip patch antenna with optimum feed point location and aspect ratio. This circularly polarised dual frequency operation can be obtained without increasing either the size or the thickness of the patch. Furthermore, through several experiments the authors also demonstrate that the location of the feed point establishes and controls a trade-off between axial ratio and impedance bandwidth