Design of a Linearly Dual-Polarized Dual-Band and Wideband Multi-Ring Microstrip Antenna with a Via Fed by Two L-Probes

Wideband and multi-band antennas are strongly attracted for various wireless applications recently. Microstrip antennas (MSAs) are widely used for such as mobile communication, broadcasting, and radar applications because of small size, low profile, light weight, and low fabrication cost. The authors have developed multi-ring microstrip antennas (MR-MSAs) as a multiband planar antenna [1] . The MR-MSA consists of multiple ring patches arranged concentrically on the upper layer and an L-shaped feeding probe (L-probe) on the lower layer of a thin double-layered dielectric substrate. The MR-MSA exhibits excellent multiband performance because operating frequencies of the MR-MSA can be designed flexibly with stable radiation patterns. Another feature of the MR- MSA is that linear or circular polarization of each operating frequency can be designed individually. Only disadvantage of the MR-MSA is that the bandwidth of each operating frequency is narrow. On the other hand, the MR-MSA fed by an L-probe with a thick dielectric substrate for dual-band and wideband operation has been developed where a triple-layered thick dielectric substrate with a thickness of approximately 0.11 wavelengths at the center frequency of the lower band and with a relative dielectric constant of 2.6 is used [2] . Approximately 20% and 15% fractional bandwidths of less than -10 dB reflection are obtained for the lower and upper bands, respectively. Furthermore, a linearly dual-polarized MR-MSA for dual-band and wideband operation has been proposed by placing two L-probes at the orthogonal positions of the ring patches [3] . The port-to-port isolation for the dual-polarizations is more than 13 dB over the lower and upper bands where the fractional bandwidths of less than -10 dB reflection are 21.7% and 10.6%, respectively.