Electromagnetic Functional Surfaces Related to Frequency Response Control Using Back-Loaded Radio Frequency Circuits

A novel scheme for designing electromagnetic functional surfaces (EMFSs) is proposed in this article. Different from traditional frequency selective surface (FSS), this scheme uses the antenna array and the back-loaded radio frequency circuit (BLRFC) to control the frequency response of EMFSs. The antenna array and the BLRFC can be designed independently resulting in great design flexibility and functional diversity. The sharp skirt out-of-band suppression and tunable frequency response can be achieved by using this scheme. Three design levels (element level, subarray level, and array level) are introduced to illustrate the design philosophy. Several EMFSs are designed, and one of them has been fabricated and measured. Actually, the prototype is a dual-polarized absorptive frequency selective reflector (AFSR). For both TE and TM polarizations with normal incidence, the AFSR exhibits one reflection band with 3 dB bandwidth from 10.6 to 16.3 GHz, two absorption bands with the absorptivity greater than 90% from 6 to 10 GHz, and from 16.8 to 19 GHz. The AFSR has a stable angular performance up to 50°. All the design examples and fabricated prototype verify the flexibility and the superiority of the novel scheme, and a multiplicity of EMFSs can be realized by using the BLRFC technique.