Low-Profile Ultrawideband Double-Side Postwall Spiral Antenna Using Resistive Split-Ring Resonator Array

A low-profile ultrawideband double-side postwall spiral antenna is proposed. The whole antenna consists of a low-impedance spiral element, a resistive split-ring resonator (SRR) array, a metallic-backed cavity, and a feeding balun serving as an impedance transformer. The proposed spiral element is composed of two double-side parallel spiral arms connected by the postwall, leading to low impedance and reduced balun profile. In addition, a hybrid absorbing technique, including a resistive SRR array and dual resistor loading technology, is proposed to improve the low-frequency performances deteriorated by the backed cavity. As a verification, a prototype is fabricated and measured. The physical dimensions of the whole antenna are $68\times 68\times 5.5$ mm. The measurements demonstrate that the proposed spiral antenna can operate across 2–18 GHz with S $_{11} \lt -10$ dB and axial ratio < 3 dB, which shows promising applications for spectrum sensing applications in wireless communications.