Fabrication and characterization of multiband polarization independent 3-d-printed frequency selective structures with ultrawide fields of view

Recently, a robust and versatile multiobjective lazy ant colony optimization technique was introduced for inverse design of 3-D frequency selective structures (FSSs) with remarkable polarization independent filtering performance for incidence angles up to 80°. However, fabricating and characterizing these elements present many challenges that have yet to be addressed. For example, conventional free-space measurement techniques require intractably large arrays to uniformly illuminate the sample and mitigate edge diffraction at extreme incidence angles. To mitigate these effects, a broadband focused beam measurement technique is proposed to characterize a finite 24 × 48 element 3-D FSS array optimized for C-band operation. Elements are fabricated using PolyJet 3-D printing, metallized, and encapsulated in a Sylgard-527 substrate over a polymethylmethacrylate lattice resulting in a low-loss, low-cost, low-profile, and lightweight array that is suitable for conformal surfaces and can be easily repaired. A comparison of simulated and measured results is presented, and a discussion of the implications of the array and measurement system is offered. The fully fabricated 3-D FSS array achieves a 6.25%-10 dB rejection band and 8.26% 3 dB passband at 5.6 and 7.75 GHz, respectively, for both TE and TM polarizations and incidence angles up to 72°.