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

xIn 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 ametal plane, with a thickness of 0.40 lambda(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 degrees and 40 degrees 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.