Polarization- and Incident-Angle Independent Wideband Microwave Absorber Using Ruthenium Oxide on a Single-Layer LTCC Substrate

This article presents an ultrathin single-layer broadband microwave absorber operating at the frequency band of 22.6–33 GHz with a fractional bandwidth of 37.4%. The absorber is designed on a low-temperature co-fired ceramic substrate using ruthenium oxide (RuO ₂ ) at the top and silver at the bottom of the substrate. The overall thickness of the absorber is 1.02 mm, i.e., 0.076 λ _L , where λ _L is the free space wavelength at the frequency of 22.6 GHz. The absorber is polarization-insensitive to the incident EM wave due to its fourfold symmetrical structure, and it absorbs more than 90% of the incident EM wave for oblique incidence up to ± 40°. In comparison to a same-sized metal sheet, the radar cross-section reduction obtained by the proposed absorber is more than 10 dB throughout the entire operating frequency band and the reduction reaches 32 dB at the frequency of 29 GHz. The absorber shows good absorption stability with the variation of ambient temperature and humidity. This absorber can be instrumental for electromagnetic interference shielding and stealth technology.