Single-layer multiband ring microstrip antennas fed by a co-planar waveguide

This paper presents single-layer multiband microstrip antennas (MSAs) fed by a co-planar waveguide (CPW) for linear and circular polarizations (LP and CP). Multiple square ring MSAs with concentric arrangement are placed on the top surface of a dielectric substrate and are fed by a CPW formed on the back surface of the substrate. The ring MSAs can radiate LP at the respective resonant frequencies. In order to realize good impedance matching to the ring MSAs, tuning stubs are connected to the CPW under the ring MSAs, respectively. Therefore, this antenna serves as a LP multiband planar antenna. Furthermore, a CP multiband ring MSA is designed. In order to obtain good axial ratio characteristics, lateral and longitudinal widths of the ring MSAs with truncated corners are varied. In this paper, multiband performances with good radiation patterns as well as low cross polarization of the proposed antennas for LP and CP are demonstrated.