Dual-Band and Wideband Design of a Single-Layer Multi-Ring Microstrip Antenna Fed by an L-Probe

Multi-band and wideband planar antennas are strongly desired for recent wireless applications. Microstrip antennas (MSAs) are attracted by various wireless applications due to the practical advantages of small size, low profile, light weight, and low-cost manufacturing. The authors have developed multi-ring microstrip antennas (MR-MSAs) as multiband planar antennas [1]. The MR-MSA consists of multiple ring patches arranged concentrically and an L-shaped feeding probe (L-probe) with a double-layered dielectric substrate. The MR-MSA exhibits flexible multiband design capability because the resonant frequencies can be tuned flexibly and because stable unidirectional radiation patterns are obtained. Furthermore, linear and circular polarizations can be also designed individually at the resonant frequencies. However, bandwidths of the MR-MSA become narrow when a thin dielectric substrate is used. In order to solve this problem, the authors have presented single- and dual-band MR-MSAs fed by an L-probe with a thick dielectric substrate for wideband operation [2]. The single-band and wideband ring MSA provides approximately 45% fractional reflection bandwidth of below −10 dB reflection, where a thick double-layered dielectric substrate with a thickness of approximately 0.15 wavelengths at the center frequency is used. On the other hand, a single-layer wideband ring MSA fed by an L-probe have been proposed [3]. A split ring patch and an L-probe are arranged in the same layer of a thick substrate with a thickness of approximately 0.12 wavelengths at the center frequency and approximately 30% fractional reflection bandwidth is obtained.