An Ultrawideband Interwoven Spiral Array with Improved Polarization Characteristics

A compact ultrawideband (UWB) tightly coupled array unit cell with improved circular polarization (CP) is proposed. Previous studies have obtained impedance bandwidth of 10:1 on a ground plane by increasing mutual coupling between array elements by using self-complementary square spiral elements having interweaved arms. However, the axial ratio (AR) of these structures is more than 3-dB in the entire frequency band, thus their use in applications requiring CP is limited. In this study, the interweaved arms of the modified periodic unit cell were resistively loaded. Hence, while achieving both size reduction and improved CP performance, antenna gain is maintained. Simulated AR is less than 3-dB over almost the entire 0.38 - 1.18 GHz frequency band. Simulated voltage standing wave ratio (VSWR) remains below 2.2 in the 0.1 - 1.25 GHz frequency range.