Ultrawideband Rasorber With Quasi-Square Frequency Response Based on Dispersion Engineering

A smart stealth radome should absorb incident electromagnetic (EM) waves across an ultra-wide frequency band while maintaining transparency in specific windows for radar and communications signals. This can be achieved using absorption-transmission-absorption (ATA) frequency selective rasorbers (FSRs), though realizing ATA FSRs with both broad bandwidths and sharp transitions remains challenging. Here, we combine multiple dispersion anomalies to construct an ATA FSR with nearly square window-like spectral response. The proposed structure adopts a cascaded configuration comprising two lossy layers and a bandpass frequency selective surface (FSS). Through collaborative dispersion engineering and equivalent circuit model, theoretical guidance is provided for the design and optimization of the spectral response. Simulated results show that the FSR achieves a wide −1 dB transmission band from 7.9 to 12.1 GHz (42%), along with two absorption bands exceeding 90% in 1.81~6.7 GHz (115%) and 13~18.55 GHz (35%). The average roll-off rate of transmission (−20 to −1 dB) reaches about 19.2 dB/GHz, while that of absorption (20% to 80%) is approximately 280%/GHz, outperforming previously reported designs. The measured results of the fabricated samples are generally consistent with the simulated ones. Our design holds significant potential for various radomes, which are quite effective in facilitating high performance EM compatibility and stealth.