A graphene-based controllable broadband terahertz metamaterial absorber with transmission band is presented in this paper. It consists of a graphene-SiO₂-frequency selective surface (FSS) sandwich structure. The sinusoidal graphene layer supports continuous plasmonic resonances, forming a broad electric-tuning absorbing band. Bandpass FSS constructs a transmission window outside the absorbing band. The simulation results indicate that the absorption from 0.5 THz to 1 THz can be tuned continuously from 0.4 to 0.9 with angle and polarization independence. A transparent window peaking at 1.65 THz maintains high transmittance over 0.7. The metamaterial absorber has potential applications for detection, stealth, filtering, and electromagnetic compatibility.

A frequency selective rasorber (FSR) with three transmission bands and three absorption bands is proposed in this paper. The FSR is constructed via cascading a lossy resistive surface and a multiple bandstop frequency selective surface (FSS) separated by air spacer. The transmission characteristics are obtained by the impedance poles of the interdigital capacitor-meander inductor resonators in the resistive surface and also the rectangular loop resonators in the FSS. The absorption bands are achieved using the ohmic loss of the resistors in the resistive surface along with the reflections of the FSS. The physical principle of operation of the multiband FSR is explained based on an equivalent circuit model. A prototype is fabricated and measured. The experimental results exhibit three transmission bands at 6.1 GHz, 8 GHz and 10 GHz with insertion loss below 0.9 dB, 0.8 dB and 0.8 dB, respectively. The effective absorption bands are in range of 7.05 GHz - 7.55 GHz, 8.87 - 9.35 GHz and 12.59 GHz - 14.22 GHz, respectively. The simulation results show the angular stability of the FSR response. In addition, the effect of FSR dimensions on the transmission/absorption bands is studied.

A dual-frequency broadband terahertz metamaterial absorber, composed of a periodically ellipse-shaped graphene array placed over a thin SiO₂ layer and a lossy polyimide layer backed with a gold ground, is proposed in this article. The numerical simulation results reveal that the effective absorption band (absorption > 0.9) ranges from 0.3 THz to 0.75 THz and 1.57 THz to 1.87 THz, with a favorable independence of incident angle. Furthermore, replacing the gold ground with a frequency selective surface inserted with graphene, another absorbing peak appears between two broad absorbing bands and can be continuously tuned from 1 THz to 1.3 THz by controlling the chemical potential of graphene from 0 eV to 0.5 eV in the FSS. To improve the absorbance of the tunable absorbing peak, a backed cavity is added to the structure, which promotes the absorbance from 0.6 to more than 0.9 with unaffected tunability. These designs overcome limitations of traditional absorbers and have promising applications for filtering, detecting, and sensing.

This paper presents an ultra-wideband antipodal Vivaldi antenna from 1-40 GHz for photonic-assisted reconnaissance. The antenna's performance is enhanced through a systematic optimization progress. By embedding a director into the tapered slot, the gain and the directivity at the high frequency are significantly improved without increasing the size. By emploing periodic slots and double split ring resonators around the radiators, the impedance bandwidth is effectively extended at low frequency. The optimized antenna demonstrates excellent impedance matching across L to Ka band with a gain ranging from 4-17 dBi. The measured results of the fabricated prototype align well with the simulated results. Furthermore, a pair of proposed antennas are implemented in a photonic-assisted system to validate the transceiving performance.

This letter proposes a frequency selective rasorber (FSR), whose transmission and absorption bands can be controlled independently by the Schottky barrier diode (SBD) and stepper motor, respectively. The FSR is composed of a resistive sheet, a switchable bandpass frequency selective surface (FSS), and four stepper motors. The transmission band can be switched to the stopband with the SBD turned on. And the location of absorption bands can be adjusted by the stepper motors. Both the simulated and measured results show that the transmission band and the absorption band can be independently controlled and do not affect each other.