A dual-transmission-bands rasorber with improved absorption and oblique incidence performance

In this paper, a high-absorption and dual-transmission-bands rasorber (HADTR) was proposed. Different from the reported designs, a foam layer and a FR4 layer are added as top layers in HADTR to improve its absorption and oblique incidence performance. The unit cell of resistive layer is concentric metallic rings loaded with chip resistors based on absorption enforced design to ensure its dual-transmission-bands at the same time. The unit cell of band-stop frequency selective surface (BS-FSS) is double metallic square loops loaded with chip inductors on both sides of FR4 substrate, which expands its reflection band (|S₁₁|≥ - 1.0 dB) without destroying its dual-transmission-bands effectively. At normal incidence, for TE and TM polarization, the HADTR has a low-frequency passband up to 1.34 GHz (|S₂₁|≥ - 1.5 dB), a high-frequency passband from 16.04 to 18.00 GHz (|S₂₁|≥ - 1.5 dB) and a wide 90% absorption band from 5.01 to 10.56 GHz; and the reflection coefficient below - 10 dB and - 20 dB is in the range of 4.48-11.70 GHz and 5.48-9.96 GHz, respectively. For TE/TM polarization, the 90% absorption of oblique incidence stability is 40° and 30° respectively. Strong association between measurement and simulation results validates the design method and the HADTR.