As is known in the art, in array antennas, performance is often limited by the size and bandwidth limitations of the antenna elements which make up the array. Improving the bandwidth while maintaining a low profile enables array system performance to meet bandwidth and scan requirements of next generation of communication applications, such as software defined or cognitive radio. These applications also frequently require antenna elements that can support either dual linear or circular polarizations.
As is also known, attempts have been made to fabricate low profile antenna elements and array antennas. Such array antennas include an array of tightly coupled dipole elements which approximates the performance of an ideal current sheet, as well as so-called “bunny ear” antennas, and tightly coupled patch arrays. While these antenna element designs are all low profile, they either fail to operate over a desired bandwidth or present significantly increased complexities to provide feed structures necessary to support either dual linear or circular polarizations (e.g. requiring external components difficult to fit within the unit cell of an array antenna). Other antenna elements, such as Vivaldi notch antenna elements, can provide a relatively wide bandwidth, but are not low profile.
It would, therefore, be desirable to provide an antenna element and an array antenna having a relatively low profile and which is responsive to either dual linear or circular polarization over a wide frequency bandwidth and scan volume.