Three-dimensional microwave broadband metamaterial absorber with broad transmission window based on the coupled symmetric split ring resonators

A novel three-dimensional (3-D) microwave metamaterial absorber (MA) is presented, which exhibits the characteristics of broadband absorption with broad low insertion-loss transmission window. The proposed absorber is constructed by fabricating a 3-D backplane-less periodic interlocking lattice array consisting of resistors-loading symmetrical split ring resonators. By optimizing the geometry parameters and the resistance values, a broad absorption band with the relative bandwidth of 40.8% is achieved at lower frequencies, together with a low insertion-loss (<1 dB) transmission window with a relative bandwidth of 60% at upper frequencies. The design is polarization insensitive and the absorption peaks remain high level with large angles of oblique incidence for both transverse electric (TE) and transverse magnetic (TM) polarizations. The effective constitutive parameters are derived and the physical mechanisms are also investigated. The measurements on the metamaterial absorber (MA) prototype show good agreement with the simulated results, which further prove the validity of the design. It is expected that the proposed MA may improve the flexibilities for the designs of MA with transmission window and be favorable for some potential applications such as electromagnetic interference and stealth radome technologies.