Design of Broadband Circuit Analog Absorber With Optimal Thickness for Stable Angular Response in C, X, Ku, and K Bands

In this letter, a 2-layer thin wideband circuit analog absorber based on the concept of multiple resonances is realized with a thickness close to Rozanov's theoretical thickness. The absorber consists of circular loop arrays loaded with lumped resistors on FR4 substrate, backed by a metal plane, with a thickness of 0.40 λ
_center
(wavelength at the center frequency). The absorber offers 149% fractional bandwidth under normal incidence with a 10-dB reflectivity reduction in the frequency band of 3.6–24.6 GHz (C, X, Ku, and K bands). The structure is angularly stable for incidence angles up to 50° and 40° for TE and TM polarization, respectively. To analyze the resonances of the absorber, an equivalent circuit model is developed, and the results agree with the full-wave simulation. The designed absorber is validated with the measurements.