A tightly-coupled planar absorber with broadband and wide-angle

Most planar absorbers are designed under normal incidence, leading to a sharp decline in absorber performance under oblique incidence, especially when the incidence angle exceeds 30 degrees. Three-dimensional structured absorbers ensure the performance of the absorber under oblique incidence, but they lack practicality due to their complex processing and assembly. In this letter, a tightly-coupled planar absorber (TCPA) is proposed. Its design method combines the reciprocity principle and tightly-coupled structure, incorporating a wide-angle matching layer and interdigitated structures to improve planar absorber's performance under oblique incidence. A sample is fabricated and measured for verification. The measurement results show that the absorber has a fractional bandwidth of 102.0% with an absorption rate of at least 90% under normal incidence. When the incident angle reaches 50 degrees, the absorber maintains good performance under both transverse electric and transverse magnetic polarization.