Efficient synthesis of low-profile angularly-stable and polarization-independent frequency-selective absorbers with a reflection band

A fast and efficient synthesis procedure for a new class of low-profile frequency selective electromagnetic absorbers with well-defined absorption and reflection bands as well as steep selectivity between the two is proposed. One contribution of this work lies with the combined use of nonresonant subwavelength capacitive and inductive arrays, which leads to low-profile polarization-insensitive and angularly stable designs. Another novelty stems from the use of rigorous synthesis techniques that enable efficiently selecting the cutoff frequencies, reflectivity level, and skirt selectivity for an arbitrary order of the absorption response. Significantly, here we investigate for the first time the out-of-band characteristics of flat absorbers and demonstrate designs which, at frequencies lower than the absorption band, present high reflectivity with a flat reflection phase. Beyond traditional applications, such as stealth, the combination of a well-defined absorption band with such out-of-band reflection properties makes the proposed frequency-selective absorbers pertinent for dual-band satellite-communication antenna reflectors with congruent beams in transmit and receive bands, where the ratio of 1:1.5 between the two bands is normally required.