Ultrawideband Circularly Polarized Antenna With Shared Semicircular Patches

A low-profile ultrawideband antenna of circular polarization (CP) is proposed in this communication. This antenna consists of two layers of Rogers RT/Duroid 5880 PCB board of 0.79 mm thickness. The size of the top PCB is 54.6 mm ×54.6 mm, and four pairs of semicircular patches are printed on both its top and bottom sides. This top PCB is placed 10.5 mm above the bottom PCB, which is 95 mm ×95 mm in size. On the top side of the bottom PCB is a 1-to-4 microstrip feeding network with 90° phase difference between the adjacent ports, while the ground plane is on its bottom side. The top PCB is supported by four small trapezoid-shaped PCB boards at the center of its four edges, respectively. A slot line is printed on each trapezoidal PCB to feed the patches. Both the simulation and measurement results show that this low-profile antenna has a very wide 10 dB return loss bandwidth from 2.9 to 9 GHz. Meanwhile, lower than 3 dB axial ratio can be achieved from 3 to 7.8 GHz and its right-hand circular polarized (RHCP) gain is higher than 8 dBic. The good performance of this antenna can justify that it is a promising candidate for indoor positioning applications that require CP.