Polarization-Insensitive Single-/Dual-Band Tunable Absorber With Independent Tuning in Wide Frequency Range

In this communication, polarization-insensitive tunable absorbers are presented for single-and dual-band applications with wide tuning range. The proposed designs consist of periodic patterns of split square loops connected with cross-dipoles through varactor diodes which exhibit tunable performances. Due to four-fold symmetry, the structures have the novel characteristic of polarization insensitivity unlike the earlier reported tunable absorbers. Moreover, the designs are comprised of vias to provide required biasing to the diodes, which also result wide frequency tuning. Two single-band tunable absorbers are initially designed, which are combined to exhibit a dual-band tunable absorber with independent tuning of absorption frequencies. A novel biasing methodology has been developed to provide bias voltages to the semiconductor diodes without disturbing the original frequency response. The fabricated sample, while measured, shows good agreement with the simulated responses under normal incidence.