Sub-terahertz Frequency Range Research Articles

Design and Simulation of High-Power Planar Čerenkov Oscillators with Two-Dimensional Distributed Feedback in the Subterahertz Frequency Range

Design and Simulation of High-Power Planar Čerenkov Oscillators with Two-Dimensional Distributed Feedback in the Subterahertz Frequency Range

The wireless communications systems in subterahertz frequency range

Background. The subterahertz and terahertz frequency ranges are very promising for development of high speed wireless communications systems because of possibility to get the bandwidth about some tens of GHz, which provides the high channel capacity. However fast signal attenuation at its propagation in atmosphere complicate the operation of communications systems in these ranges.
 Aim. Use of fixed narrow-beam antennas with high antenna power gain allows to provide the direct surface communications distance to some kilometers. The communications distance limitation can be partially removed decreasing the frequency down to 200 GHz and narrowing the channel bandwidth down to some GHz.
 Methods.The model of transmitter-receiver system (200-220 GHz) based of modern semiconductor devices is described in the manuscript. Results. The possibility of digital signals transmission with speed up to 1 Gbit/s at the distance of 1 km is experimentally shown.
 Conclusion. According to calculations the output power of transmitter about some hundreds mW is enough for data transmission at the distance up to 1.5 km with antenna power gain of no less than 50 dB.

Investigation of Small Scatterers by the Resonator Method in the Subterahertz Frequency Range

Investigation of Small Scatterers by the Resonator Method in the Subterahertz Frequency Range

Low-Cost and Low-Profile Sub-Terahertz Luneburg Lens Beamformer on Polymer

A Luneburg lens is used to excite a leaky-wave antenna (array of slots) in the sub-terahertz (sub-THz) frequency range. The antenna is built on a 140-μm thick Cyclic Olefin Copolymer (COC) substrate. The radiating slots (58×24 slots) are etched on the polymer by a photolithographic process, for which the gold (Au) layers are first deposited by evaporation on the COC and, then, patterned by chemical etching. No metalized vias or drilling are applied to the substrate. The full system is fed by a standard WR03 waveguide, and it has been fabricated and tested. Experimental results show an input reflection coefficient better than −7 dB over a 25% fractional bandwidth, spanning from 220 GHz to 290 GHz. The radiated beam can be steered in elevation from −80° to −20° over the same band. The antenna efficiency is estimated to be 20% at the center frequency (260 GHz). This solution provides a simple alternative for low-cost and low-profile beam scanning antennas in the sub-THz range.

SIGNAL PROCESSING IN A ROBOTIC VEHICLE OBSTACLE WARNING RADIO SYSTEM IN THE SUBTERAHERTZ FREQUENCY RANGE

The article describes the features of the implementation of radars with the synthesis of the anterolateral viewing aperture in the subterahertz frequency range, designed to implement an obstacle warning system for a robotic vehicle. It is shown that vibrations with standard deviation systems of about 1 mm representa significant problem for the implementation of SAR modes in the W range. In order to overcome this problem, it is proposed to use Bayesian algorithms for the formation of radar images in conditions of a priori uncertainty.

Ferrimagnet based spin Hall detector of subterahertz frequency signals

A concept of a subterahertz (sub-THz) frequency range signals detector based on a ferrimagnet/normal metal (FiM/NM) heterostructure is proposed. An external linearly polarized electromagnetic (EM) wave excites precession in the FiM and spin pumping at the FiM/NM interface. The excited spin current in the NM converts into a direct current via the inverse spin Hall effect. We show that non-zero uncompensation between magnetic spins in FiM gives a non-zero output rectified voltage for both “easy axis” and “easy plane” uniaxial anisotropies. The increase in the uncompensation parameter removes degeneracy from two normal resonance modes and changes the sensitivity to the EM wave. Namely, the sensitivity of the higher mode increases, and the lower mode decreases with increasing the uncompensation parameter. We believe that our results can be helpful for the practical development of sub-THz frequency tunable resonance detector based on the FiM.

Superconducting Sub-Terahertz Oscillator with Continuous Frequency Tuning

The development and approbation of a superconducting local oscillator based on a long Josephson junction made it possible to create a fully superconducting integrated receiver in sub-terahertz frequency range, which was successfully tested both on board a high-altitude balloon and in the laboratory. In order to expand the frequency range of a superconducting integrated local oscillator, it is necessary to ensure the continuous tuning of its frequency at an arbitrary bias current, including a so-called resonant mode regime. The resonant mode regime takes place for high-quality tunnel junctions with low leakage; in this regime, stable generation is possible only at Fiske steps, the distance in frequency between which is tens of GHz. A method for suppressing resonances has been proposed and implemented; this method is based on the introduction of normal metal layers into the region near the long Josephson junction. Modeling of the propagation of electromagnetic waves in the proposed integrated structure was carried out; experimental samples were fabricated, and their comprehensive study was performed. The complete suppression of resonances and the possibility of the continuous tuning of the frequency of a superconducting local oscillator in the range of 200–700 GHz have been demonstrated. The linewidth of the FFO radiation does not exceed 15 MHz over the entire frequency range, which makes it possible to implement the phase locked loop mode in an integrated receiver intended for spectral studies.

Atmospheric Propagation Studies and Development of New Instrumentation for Astronomy, Radar, and Telecommunication Applications in the Subterahertz Frequency Range

Current progress in the development of new subterahertz instruments discussed in this paper, including antennas, high-power gyrotrons, and low-noise receivers, provides a wide range of possible applications. Atmospheric absorption has now become a major limitation in the application of such high-performance subTHz systems, and the choice of the optimal location of antennas for astronomical, radar, and communication systems is important. The latest results of studying the microwave astroclimate in northern Eurasia are presented. Based on these studies, new perspectives and corrected plans for installing new antennas at the Suffa Plateau and in the Caucasus are formulated, and possible applications of new instruments such as radars for locating space debris and communication hubs for deep space communications, which are based on extremely-high-power gyrotrons and low-noise superconducting receivers, are discussed.

Influence of transmission line parameters on the degree of matching of the generator with the SIS-mixer in the frequency range 200-700 GHz

This work is aimed at the development, research and optimization of superconducting integrated circuits designed to match the impedances of a long Josephson junction generator, the so-called flux generator (FFO) and a superconductor--insulator--superconductor (SIS) detector in the sub-terahertz frequency range. Numerical calculations of integrated circuits designed to optimize the parameters of transmission lines are presented. The main parameters of the lines and their influence on signal propagation are determined. The results of optimization of integrated matching circuits in the range of 450-700 GHz are demonstrated. Keywords: integrated matching circuits, Josephson junctions, sub-terahertz generator.

Atmospheric Propagation Of SubTHz Waves And Space, 6G & 7G Communications

The work is devoted to the actual problem of data rate of wireless telecommunication channels. Presented analysis of the telecommunication channel subterahertz (subTHz) frequency range - as the most promising band for the implementation of wireless telecommunications for space links and terrestrial cellular communications of high capacity. A channel considered as a combination of high effective transponder / transmitter duplex together with an open high dissipative atmospheric line. The means to achieve a high signal / noise ratio is usage of low-noise cryogenic receivers. The theoretical analysis of data rates for various atmospheric conditions and technical implementations of communication channels demonstrated reasonable limits of cooling of receivers, providing a weighty increase channel capacity, while deeper cooling is impractical due to weather restrictions in certain ranges and conditions of signal propagation, including altitude and seasonal features.

A Study of Terahertz-Wave Cylindrical Super-Oscillatory Lens for Industrial Applications.

This paper describes the design and development of a cylindrical super-oscillatory lens (CSOL) for applications in the sub-terahertz frequency range, which are especially ideal for industrial inspection of films using terahertz (THz) and millimeter waves. Product inspections require high resolution (same as inspection with visible light), long working distance, and long depth of focus (DOF). However, these are difficult to achieve using conventional THz components due to diffraction limits. Here, we present a numerical approach in designing a 100 mm × 100 mm CSOL with optimum properties and performance for 0.1 THz (wavelength λ = 3 mm). Simulations show that, at a focal length of 70 mm (23.3λ), the focused beam by the optimized CSOL is a thin line with a width of 2.5 mm (0.84λ), which is 0.79 times the diffraction limit. The DOF of 10 mm (3.3λ) is longer than that of conventional lenses. The results also indicate that the generation of thin line-shaped focal beam is dominantly influenced by the outer part of the lens.

A Wide-Angle Scanning Sub-Terahertz Leaky-Wave Antenna Based on a Multilayer Dielectric Image Waveguide

This paper presents a new layered dielectric leaky-wave antenna (LWA) for the sub-terahertz (THz) frequency range capable of efficient operation at the broadside with a wide beam scanning angle and stable gain. It consists of a conductor-backed alumina dielectric image line (DIL) with two different dielectric layers mounted on top of each other for performance improvement. The upper layer is a high permittivity RO6010 substrate to enhance the directivity as a superstrate and the lower layer is a low-permittivity RT/duroid 5880 substrate stacked on the alumina DIL to prevent the probable excitation of higher-order modes in the DIL channel. A 15-element linear array of radiating overlapped discs is used to mitigate the open stop-band (OSB) problem, fed by the mentioned waveguide, was designed and simulated at frequencies around 170 GHz. The dominant mode of the layered dielectric waveguide is perturbed by the infinite space harmonics generated by two sets of overlapped discs periodically sandwiched between the layers. It exhibited a relatively wide impedance bandwidth of 28.19% (157.5–206 GHz). Its radiation mechanism has been widely studied through simulations. The results revealed that the antenna provides a wide scanning capability through the broadside from −23° to 38°, covering the frequency range between 157.5 GHz and 201.5 GHz. For an array with 15 radiating elements, the simulated peak gain in the band is 15 dBi and the broadside gain is 13.6 dBi at 172 GHz.

Micromachined Subterahertz Waveguide-Integrated Phase Shifter Utilizing Supermode Propagation

In this work, we propose a new concept of phase shifting by tuning the coupling distance between two parallel silicon slabs that support the propagation of an in-phase supermode. A prototype device was implemented in the 220-330-GHz band by integrating the micro-electro-mechanical system (MEMS)-actuated phase-shifting mechanism, based on two moveable parallel-coupled high-resistivity silicon slabs, inside a metallized hollow rectangular waveguide in silicon-on-insulator (SOI) micromachining technology. The prototype device has been characterized to a maximum continuous phase tunability of 550° with a maximum insertion loss of 1.87 dB achieved at 330 GHz. A maximum figure-of-merit (FOM) of 375°/dB is achieved at around 320 GHz, which presently is the highest FOM value reported for any phase shifter in the subterahertz (sub-THz) frequency range. The bandwidth covers the whole waveguide band with an average and worst case insertion loss of 1.94 and 2.5 dB, respectively, a worst case insertion-loss variation of 0.7 dB and a phase error better than 4° for all phase states. A large displacement of MEMS electrostatic comb-drive actuators that are co-fabricated in the micromachined waveguide platform is achieved by a driving voltage of 50 V. The prototype footprint is 7.3 ×5.3 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Nonthermal excitation effects mediated by sub-terahertz radiation on hydrogen exchange in ubiquitin

Water dynamics in the hydration layers of biomolecules play crucial roles in a wide range of biological functions. A hydrated protein contains multiple components of diffusional and vibrational dynamics of water and protein, which may be coupled at ∼0.1-THz frequency (10-ps timescale) at room temperature. However, the microscopic description of biomolecular functions based on various modes of protein-water-coupled motions remains elusive. A novel approach for perturbing the hydration dynamics in the subterahertz frequency range and probing them at the atomic level is therefore warranted. In this study, we investigated the effect of klystron-based, intense 0.1-THz excitation on the slow dynamics of ubiquitin using NMR-based measurements of hydrogen-deuterium exchange. We demonstrated that the subterahertz irradiation accelerated the hydrogen-deuterium exchange of the amides located in the interior of the protein and hydrophobic surfaces while decelerating this exchange in the amides located in the surface loop and short 310 helix regions. This subterahertz-radiation-induced effect was qualitatively contradictory to the increased-temperature-induced effect. Our results suggest that the heterogeneous water dynamics occurring at the protein-water interface include components that are nonthermally excited by the subterahertz radiation. Such subterahertz-excited components may be linked to the slow function-related dynamics of the protein.

Application of terahertz (sub-terahertz) inspection systems in the integrated security systems

The subject of this research is methods of application of terahertz (sub-terahertz) inspection systems for detecting concealed carry weapon, makeshift explosive devices made of nonstandard materials and other prohibited substances. The object of this research is the detection of concealed carry weapon, makeshift explosive devices made of nonstandard materials and other prohibited substances. The authors examine the application of terahertz (sub-terahertz) inspection systems of compact and portal (stationary) types in the integrated security systems. Special attention is given to the options of using these complexes for expanding the capabilities of the subsystems of video monitoring and detection of sabotage and terrorist means. The conclusion is made on the need to develop the tactics for application of the existing systems of personal security screening, the operation of which is based on radio camera imaging in terahertz (sub-terahertz) frequency range. The authors&amp;rsquo; special contribution lies in formulation of recommendations that contain the options of using terahertz (sub-terahertz) inspection systems of various types for detecting concealed carry weapon, makeshift explosive devices made of nonstandard materials and other prohibited substances. The acquire results would help to improve the efficiency of organizing the onsite pass control. The scientific novelty consists in fact that the authors are first within the framework of development of the tactic of using terahertz (sub-terahertz) inspection system to develop proposals of implementation of such means as part of the integrated security systems for detecting concealed carry weapon, makeshift explosive devise made of nonstandard materials and other prohibited substances that differ in carrying out the inspection procedures.

A Highly Linear Dual-Stage Amplifier With Beyond 1.75-THz Gain–Bandwidth Product

This work reports a multipurpose highly linear ultrawideband amplifier with a gain-bandwidth product (GBP) of 1.75 THz, the highest reported in any monolithic microwave integrated circuit (MMIC) process. A transimpedance amplifier is cascaded with a distributed amplifier, emulating a receiver subsystem. Using a diamond heat spreader, to dissipate heat from transistors, the cascaded amplification subsystem can achieve very high output third-order-intercept point (OIP3) from 20 to 24 dBm when measured between 5 and 65 GHz. A small-signal average gain of 24 dB is observed over a frequency range exceeding the maximum measurable bandwidth from dc to 110 GHz. Compared with other ultrawideband MMIC amplifiers beyond 110-GHz bandwidth, the circuit offers a unique combination of high linearity (OIP3) and high gain. As a result, the cascaded amplifier is suitable for applications in optical-electrical converters, spectroscopy, and ultrawideband measurement systems in the subterahertz frequency range.

Dual-mode terahertz extended interaction oscillator driven by a pseudospark-sourced sheet electron beam

A terahertz dual-mode extended interaction oscillator (EIO) driven by a pseudospark-sourced sheet electron beam (SEB) was presented. The major advantages of the newly developed circuit include 1) high-density SEB interacting with the TM11 and TM31 modes, respectively, and 2) high output power of over 1 ​kW ​at the sub-terahertz frequency range. Two different types of 2π modes and their output characteristics were studied, and the circuit was optimized to ensure efficient outputs of two standing-wave modes. The three-dimensional (3D) particle-in-cell (PIC) simulation predicts the maximum output power of 1.3 ​kW with a 3-dB bandwidth of ~0.5 ​GHz ​at 303 ​GHz when operating at the TM11 mode, and 3.18 ​kW, 3-dB bandwidth of ~0.85 ​GHz ​at 364 ​GHz when operating at the TM31 mode.

Faraday Rotation Due to Quantum Anomalous Hall Effect in Cr-Doped (Bi,Sb)2Te3

Quantum anomalous Hall effect (QAHE) represents a quantized version of the classical anomalous Hall effect. In the latter case the magnetization takes over the role of magnetic field and induces nonzero off-diagonal elements in the conductivity matrix. In magnetic topological insulators with the band inversion the QAHE can be reached due to quantized conduction channel at the sample edge if the Fermi energy is tuned into the surface magnetic gap. In the static regime the QAHE is seen as a zero-field step in the Hall resistivity. At optical frequencies this step is transformed into a quantized value of the polarization rotation approaching the fine structure constant α=e2/2ε0hc≈1/137. However, due to material issues the steps reach the predicted values at millikelvin temperatures only. In this work we investigate the Faraday polarization rotation in thin films of Cr-doped topological insulator and in the sub-terahertz frequency range. Well defined polarization rotation steps can be observed in transmittance in Faraday geometry. At temperatures down to T=1.85 K the value of the rotation reached about 20% of the fine structure constant and disappeared completely for T&gt;20 K.

A new approach to the development of perspective compact frequency multipliers of the subterahertz and terahertz bands for on-board electronic equipment

Currently, the increasing interest of researchers is attracted by the theoretical and practical problems of mastering the sub-terahertz and terahertz frequency range. Electronic devices operating in these ranges find effective applications in various fields of science and technology: aerospace equipment, security systems, spectroscopy, medicine, biology and many others. The purpose of this work is to focus on a frequency multiplication device that allows using basic sources of relatively low frequency generation to enter the terahertz frequency range. The results of recent years obtained both on the basis of solid-state effects and with the help of vacuum electronics, in particular, magnetron-type devices, which are characterized by compactness, high resistance to radiation loads, mechanical influences, which is important for on-board equipment, are considered. It is known that at high frequencies, vacuum devices require super-precision manufacturing of decelerating systems. This is essentially the main difficulty. The article proposes a new approach based on the hypothesis of P.L. Kapitsa, which allows to significantly simplify the anode structure of a magnetron multiplier with an acceptable level of output parameters. The achievements of recent years in the field of creating sub-terahertz and terahertz frequency multipliers, mainly for on-board equipment of mobile platforms, taking into account the requirements of aerospace systems, first of all, are noted.

МЕТОД ВИЗНАЧЕННЯ ДІЕЛЕКТРИЧНОЇ ПРОНИКНОСТІ ДІЕЛЕКТРИКІВ У ММ ТА СУБММ ДІАПАЗОНАХ ДОВЖИН ХВИЛЬ НА ПІДСТАВІ ВИМІРЮВАННЯ ПАРАМЕТРІВ ПЛАЗМОН-ПОЛЯРИТОННОГО РЕЗОНАНСУ

МЕТОД ВИЗНАЧЕННЯ ДІЕЛЕКТРИЧНОЇ ПРОНИКНОСТІ ДІЕЛЕКТРИКІВ У ММ ТА СУБММ ДІАПАЗОНАХ ДОВЖИН ХВИЛЬ НА ПІДСТАВІ ВИМІРЮВАННЯ ПАРАМЕТРІВ ПЛАЗМОН-ПОЛЯРИТОННОГО РЕЗОНАНСУ