Novel dual-band antenna with simultaneous linear and circular polarizations

A multi-function microstrip antenna for simultaneous operation at two different frequency bands (centered at 1.575 GHz and 2.4 GHz) is presented. In contrast to the traditional dual-band antennas, the presented antenna design is unique as it can achieve two different polarizations simultaneously. Such a configuration makes the proposed antenna suitable for receiving signals from entirely different systems using a single antenna. In order to achieve the dual-band operation, a stacked configuration of microstrip antennas has been used where the top patch is designed to operate at 2.4 GHz with linear (vertical) polarization while the bottom patch is designed to operate at 1.575 GHz with right hand circular polarization. Although the proposed antenna is a typical dual-band stacked configuration, it is the antenna feed that makes it a novel design. The antenna feed consists of a broadband branch-line coupler but its connection to the antenna is non-symmetric thereby forcing the two different patches to produce different polarizations. Antenna simulation results show that the dual-band antenna achieves greater than 5 dBi gain at both frequency bands whereas the axial ratio remains less than 3 dB at the GNSS band (1.575 GHz). The axial ratio at the ISM band (2.4 GHz) is shown to be greater than 35 dB demonstrating a linearly polarized operation. The antenna has a compact size and low cost, suitable for portable terminal antennas receiving signals at both GNSS and ISM frequency bands.