I. Introduction
Microwave absorber structures are designed and shaped to attenuate the incident electromagnetic (EM) radiation and often useful in radar cross section reduction applications. Earlier absorbers were designed from single- or multi-layer topologies, but at the expense of having large thicknesses [1]. With the advent of metamaterial absorbers, near-unity absorption can be realized from ultra-thin geometries [2]. Since then, a wide variety of microwave absorbers have been developed on metamaterial concept, exhibiting various characteristics. However, most of these designs are manufactured using conventional printed circuit board (PCB) technique, where metallic patterns are etched on dielectric substrates. This puts a restriction in the use of dielectric textures due to its unavailability of selective etching in PCB technique. Three dimensional (3-D) printing technique, in contrast, can not only fabricate dielectric patterns, but the architecture can also be designed in different ways based on the requirement [3]. Further, manufacturing time, fabrication cost, etc. can significantly be improved by using 3-D printing. Recently, a few 3-D printed metamaterial absorbers are reported [4],[5], but the use of perforation in narrow-band absorber structures is yet to be investigated.