Four-Arm Spiral Antenna Fed by Tapered Transmission Line

This letter presents a four-arm Archimedean spiral antenna with a novel integrated tapered transmission line feed structure. The center-fed spiral antenna consists of a radiation region with an Archimedean spiral configuration and a transmission region that comprises four spiral-shaped transmission lines with exponentially decreasing widths. The tapered transmission line, acting as an impedance transformer, provides a broadband matching network between the 50-Ω input impedance and the higher impedance of the radiation region. Using this design, a mode-1 spiral antenna attains a return loss of greater than 15 dB and a 3-dB broadside axial ratio throughout the 0.8-3-GHz band. The fabricated antenna demonstrates good agreement between the simulated and measured results.