Dual-Polarized Three-Dimensional Ultrawideband Microwave Absorbers under Extremely Oblique Incidence

This paper proposes a dual-polarized threedimensional (3D) ultrawideband microwave absorber based on a polarization separation design method under extremely oblique incidence, which can achieve desired second-order absorption responses independently. Each microwave absorber element is composed of two slotline resonators and thin-film resistors on orthogonally inserted printed circuit boards (PCBs). The proposal is able to achieve arbitrary in-band return loss (RL) level and flexible fractional bandwidth (FBW) under various oblique incidence angles by resorting to the synthesis method. The more generalized prototype with different design specifications for$\boldsymbol{y}$and$x$-polarization is designed, fabricated, and measured for validation. The measured results demonstrate accuracy and efficiency in designing dual-polarized 3D microwave absorbers under extremely oblique incidence.