The use of cutting carbon fiber fabric/epoxy composites as band-pass frequency selective surfaces

Sandwich structures with frequency selective surfaces have been widely used to fabricate low-observable radomes. Traditional frequency selective surfaces were made of metals, such as copper and aluminum. There were problems when used the frequency selective surfaces with the sandwich structures, such as a bonding layer and thermal mismatch. Because of the thermal mismatch between the sandwich structures and the metals, mechanical properties of the sandwich structures usually decreased. To avoid these disadvantages, a new type of composite frequency selective surface was put forward in this study. A four-legged slot-array frequency selective surface and a square-aperture array frequency selective surface were fabricated by cutting carbon fiber/epoxy composites. Free-space method and finite-element method were carried out to evaluate the electromagnetic transmission characteristics of the frequency selective surface specimens, respectively. Results show that the composite frequency selective surface with four-legged slot array can realize the function of frequency selection, and its minimum transmission loss can be decreased by increasing the electrical conductivities of the composite material, adjusting the thickness, and increasing the aperture-to-cell ratio of it. For the composite frequency selective surface with square-aperture array, grating lobes come closely after its resonant frequency, although its minimum transmission loss is very close to zero.