Design, characterization, and optimization of ultrawideband cavity-backed spiral antennas at microwave frequencies

In this paper, we have presented a methodology for the design and optimization of UWB, absorptive cavity-backed spiral antennas from a microwave material measurement standpoint. We have used a precision transmission-reflection (T/R) based waveguide measurement technique to determine the complex permittivity and permeability of linear dielectric and magnetic materials from 2-40 GHz. From the measured data, we have designed a multi-layer absorbing structure that offers minimum reflection and maximum absorption from 2-18 GHz. We inserted the composite material in the lossy cavity of a 2-arm Archimedean spiral antenna and simulated its radiation patterns. We optimized the thicknesses of each absorbing layer and the air gap in the antenna model such that a lightweight, shallow cavity can be obtained that retains maximum radiation performance. Our methodology can be extended to the accurate and efficient development of any UWB communication system or sub-system in general.