Frequency bandwidth adjustment of dual-polarized four-arm Archimedean spiral antennas

In center-fed four-arm Archimedean spiral antennas, broadside radiation patterns with dual-polarized operations in both senses of circular polarization can be realized by confining the spiral circumference to less than three wavelengths. Such antennas with orthogonal circularly polarized waves are excellent candidates for frequency reuse applications, such as multimode Global Positioning Systems (GPS), modern satellite navigation, and radar systems. These dual-polarized antennas improve the wireless channel capacities with higher bit-rate capabilities. A compact, unidirectional, and air-filled structure of the four-arm Archimedean spiral antenna has been proposed by the authors in [1], where both right- and left-handed circularly polarized waves are produced over a respectable frequency band. As it is known, inserting dielectric materials into an antenna structure is widely used to miniaturize the antenna structure, as it leads to an increased electrical path length [2]. Generally, high-contrast substrates are needed in order for a significant reduction in the antenna size. However, the associated dielectric loss becomes particularly troublesome, which deteriorates the antenna efficiency performance. Low contrast dielectric materials, on the other hand, become quite beneficial for frequency tuning of already compact antenna structures, without a significant degradation in antenna performance.