A Miniaturized Ultra-Wideband Spiral Antenna Loaded with Absorber

An ultra-wideband planar spiral antenna operating from 0.6 to 18 GHz is proposed in this paper. The proposed antenna employs a two-arm planar Archimedean spiral structure as the radiating element. To achieve enhanced low-frequency performance down to 0.6 GHz while simultaneously improving the axial ratio characteristics, an absorber is strategically integrated on the antenna's rear surface. Furthermore, terminal resistors are incorporated at the spiral ends to effectively suppress terminal effects, thereby realizing significant antenna miniaturization. The proposed antenna exhibits a compact diameter of 101 mm, achieving a remarkable 58 % reduction in aperture size compared to conventional Archimedean spiral antenna configurations. Numerical simulation results indicate that the proposed antenna exhibits outstanding performance across the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.6-18 \text{GHz}$</tex> frequency range, achieving a 187 % fractional bandwidth with return loss below −10 dB, VSWR less than <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2: 1$</tex>, axial ratio under 3 dB, and a maximum gain of 4.27 dB in the main radiation direction. The radiation patterns demonstrate excellent characteristics, suggesting promising applications in ultra-wideband communication systems.