Design of a Wideband Ring Microstrip Antenna Fed by an L-probe with a Single-Layered Dielectric Substrate

Recently, wideband and multi-band microstrip antennas are demanded for broadband wireless communication systems. Microstrip antennas (MSAs) are commonly used for various applications such as mobile communication, broadcasting, and radars because MSAs have advantages of small size, low profile, light weight, and low manufacturing cost. Multi -ring microstrip antennas (MR -MSAs) have been proposed by the authors as a multiband planar antenna [1] . The MR-MSA is composed of a double-layered dielectric substrate; multiple ring patches are concentrically arranged on the top substrate and an L-shaped feeding probe (L-probe) [2] , [3] to excite the ring patches is situated on the bottom substrate. The MR-MSA provides excellent multiband performance because the resonant frequencies are flexibly designed with stable unidirectional radiation patterns. Linear or circular polarization of each resonant frequency can be also designed individually. Only disadvantage is narrow bandwidth characteristic when a thin dielectric substrate is used for the MR-MSA. On the other hand, the MR-MSA fed by an L-probe with a thick dielectric substrate for single- and dual-band operations has been presented [4] . The wideband MR-MSA for a single-band operation which consists of one ring patch and an L-probe exhibits approximately 45% fractional reflection bandwidth of less than –10 dB reflection, where a thick double-layered substrate with a thickness of approximately 0.15 wavelengths at the center frequency and with a relative dielectric constant of 2.6 is used. One of the wideband MR-MSA fed by an L-probe is to use the double-layered dielectric substrate.