Three-Dimensional Rotation of FSS Unit Cell in Broadband Microwave Absorber for Large Oblique Incidence Response

In this article, the performance of polarization-insensitive absorbers is improved under the oblique incidence over wide-angle and wideband by rotating the frequency selective surface (FSS) unit cell in 3-D planes through various rotation schemes. The proposed schemes are realized using 3-D printing technology. A stereolithography-based 3-D printer is used to print a precise substrate that provided a well-suited frame for mounting oriented unit cells. The resistive ink is used to print unit cell patterns on the top of the polyethylene terephthalate (PET) sheet using screen printing technology. The patterns are then cut and mounted on top of a 3-D-printed honeycomb substrate. The proposed absorber consists of a periodic array of oriented unit cells. This exercise of 3-D rotation leads to better stability of the absorption profile in terms of angle of incidence. Above 90% absorption is achieved for
$\theta _{i} = \text{60}^\circ$
and above 70% absorption is achieved even for
$\theta _{i} = \text{75}^\circ$
in
X-
and
Ku
-band. The novelty of the proposed design lies in introducing and studying rotation as a degree of freedom to tune an FSS-based absorber for a suitable absorption signature. To verify the simulation response, a prototype has been fabricated, tested, and validated.