Journal of Infrared, Millimeter, and Terahertz Waves最新文献

In this article, the designing and analysis of a compact novel dual-port multiple-input multiple-output (MIMO) printed antenna are investigated for 30 GHz mm-wave applications. The single antenna unit is having modified C-shaped radiator and an attached rectangular stub with an overall dimension of 10 × 7 × 0.8 mm³. The dual-element MIMO antenna is achieved by creating a back mirror of the single antenna element around the x-axis. This back mirror composition of the MIMO antenna elements is introducing the high level of inter-element isolation (> 20 dB). The proposed antenna prototype is built on a Roger RT/duriod substrate with a loss tangent (tanδ) of 0.0009 and a relative constant (ε_rsub) of 2.2. As a way to determine the capabilities of the proposed MIMO antenna, many diversity parameters are computed, including the envelope correlation coefficient (ECC < 0.05), diversity gain (DG > 9.99 dB), channel capacity loss (CCL < 0.2 bits/s/Hz), mean effective gain (MEG < − 3 dB), and total active reflection coefficient (TARC). The suggested MIMO antenna is appropriate for 5G new radio frequency bands under mm-wave communication as it has 8.36% impedance bandwidth across the frequency range of simulated (29.04–31.57 GHz)/measured (28.82–31.30 GHz). The antenna under consideration is constructed, and the simulated outcomes are verified by the measurement results.

Terahertz (THz) backward wave oscillators (BWOs) hold immense potential for a broad range of industrial and military applications. This study presents a comparative analysis of 0.34 THz sheet beam (SB) and circular beam (CB) folded waveguide (FWG) BWOs. We examined the design, simulation (CST MWS and PS, HFSS), and performance, revealing that sheet beam BWO outperforms circular beam BWO in terms of interaction impedance, power, efficiency, and bandwidth. Under 20 kV beam voltage and 10 mA beam current conditions, sheet beam BWO achieves 0.47 (Omega ) (0.34 THz) interaction impedance, 0.65 W output power, and a bandwidth of approximately 12 GHz, surpassing the 0.18 (Omega ), 0.23 W, and 8.5 GHz values of circular beam BWO, respectively. Furthermore, this study encompasses the fabrication and thorough characterization of the sheet beam BWO’s slow-wave structure. Experimental validation confirms its effectiveness, with measured (S_{11}) demonstrating reflection below (-)10 dB and (S_{21}) exhibiting transmission above (-)2 dB.

Abstract

The present work proposes three MIMO antennas with different configurations for the future applications of wireless communications in the Q-band of the frequency to realize both spatial and polarization diversities. A circularly polarized (CP) printed antenna operating over two frequency bands at 37.8 and 50 GHz is utilized as a single element to construct the proposed MIMO antennas. Two-element MIMO antenna systems arranged in two configurations, side-by-side and face-to-face, are proposed to achieve spatial diversity. Also, a four-element MIMO antenna system is designed to achieve polarization diversity in addition to spatial diversity. The proposed MIMO antenna systems are designed with the aid of the CST simulator. The three MIMO antennas are fabricated and their performance is experimentally evaluated regarding the circular polarization, impedance matching, antenna gain, envelope correlation coefficient (ECC), and diversity gain (DG). The experimental results for the single-element as well as the MIMO antennas come in good agreement with simulation results showing high performance. Both the numerical and experimental investigations reveal that the mutual coupling between any two ports of the proposed MIMO antennas is below (-25 {text{dB}}) . Also, for any two ports it is shown that the ECC is below (1times {10}^{-7}) and the diversity gain is higher than (9.99) . The impedance matching bandwidths (for (left|{S}_{11}right|<-10 {text{dB}}) ) are shown to be (1.53) and (1.88) GHz at (37.8) and (50mathrm{ GHz}) , respectively, and the corresponding 3-dB axial ratio bandwidths are (700) and (130mathrm{ MHz}) , respectively.

This paper presents a full-wave method, based on the method of moments (MoM), to calculate the (bar{varvec{S}}) matrix from a two-dimensional complex sample in millimeter and submillimeter W and J bands. From the surface currents obtained by inverting the impedance matrix and from the Huygens principle, the reflection and transmission coefficients are computed. This allows us to obtain the four elements of the (bar{varvec{S}}) matrix. Firstly, the method is validated from canonical samples (a dielectric slab and a stack of two dielectric slabs) by applying the well-known Fresnel coefficients. Secondly, for the W (75 to 110 GHz) and J (220 to 330 GHz) bands, a PVC slab covered by water drops is considered, for which the (bar{varvec{S}}) matrix is compared with measurements made in quasi-optical free space. A satisfactory agreement is obtained between the measurements and the model.

In this paper, we present a terahertz transmission frequency-selective quasi surface (FSQS) that exhibits strong absorption lines and a periodic band-pass characteristic. The FSQS structure is created by laterally combining Fabry-Pérot resonators with different thicknesses. The transfer function of the FSQS can serve as a broadband reference for testing the signal integrity of the transmission path for broadband terahertz systems. The transfer function achieves a combination of band-pass characteristics and sharp resonances with a theoretical attenuation of over 80 dB and with quality factors of more than 40,000 for a combination of 36 resonators. A single FSQS made up of four resonators is 3D printed by fused deposition modeling using a low-loss cyclic olefin copolymer (COC) filament. Finally, the 3D-printed FSQS is characterized using both frequency-domain and time-domain terahertz spectroscopy. The results show an attenuation of over 42 dB and a quality factor above 100.

THz technology has the potential to revolutionize various fields, including high-speed wireless communication, medical imaging, and spectroscopy. One challenge facing THz technology, however, is the limited output power (on the order of microwatts) of photonic THz sources (e.g., uni-traveling-carrier photodiode). Researchers are therefore exploring THz beam steering techniques to maximize their power effectiveness. To this end, we propose a photonic THz beam steering method that utilizes fiber chromatic dispersion, eliminating the need for energy-consuming active electronics. This paper explains its basic operating principle, fabrication and performance analysis of the associated THz array antenna, and demonstrates the feasibility of achieving a 300 GHz beam steering within 10(^circ ) by means of dispersion-varied polarization-maintaining fibers. In conclusion, the present scheme can greatly enhance the power efficiency of photonic THz sources, and enable the potential advantages of seamless integration with fiber-optic networks, including reduced complexity, simplified operation, low power consumption, and cost-effectiveness.

Abstract

The ionization of a silicon surface layer induced by an electric field with a strength of up to 17 MV/cm and a rise time of (approx ) 245 fs has been studied for the first time. The generation rate of free carriers induced by electric field has been experimentally determined. It has been shown that the average concentration of electrons in the conduction band in surface layer reaches (sim 3times 10^{19})  cm (^{-3}) , which corresponds to the ionization rate of (1.4times 10^{14})  s (^{-1}) . A new method is proposed for synchronizing the THz pulse temporal profile measured by electro-optical sampling with the results of pump-probe measurements based on second harmonic generation.

This paper presents a high gain diagonally-probe-fed multi-layered dielectric resonator antenna (DPF-ML-DRA) designed for 77 GHz automotive radar applications. A comparison with the conventional probe-fed ML-DRA demonstrates that the proposed DPF-ML-DRA achieves higher antenna gain by 1 dB. The sub-array utilizing the proposed DPF-ML-DRA is tailored to meet specific radar system requirements, including a broad impedance bandwidth (> 5 GHz), high antenna gain (> 12 dBi), and wide half-power beamwidth (> ± 60°). Simulated results validate that the sub-array performance meets the aforementioned antenna requirements. To attain high azimuthal and elevational angular detecting resolution, 3 sub-arrays with 12 DF-ML-DRA for the Tx channel and 4 sub-arrays with 10 DF-ML-DRA for the Rx channel were designed and simulated. The fabricated radar system underwent field testing, demonstrating a maximum range of up to 160 m and a field of view of 120° for 100 m. Remarkably, the proposed DPF-ML-DRA exhibits equivalent radar performance while featuring a smaller form-factor compared to commercially available state-of-the-art automotive radar systems. Consequently, the proposed DPF-ML-DRA proves to be well-suited for 77 GHz automotive radar applications.

Terahertz backward wave oscillators based on double corrugated waveguides are enabling devices for modern satellite communication systems. This research focuses on the design of a 0.34 THz double corrugated waveguide-based interaction structure using a sheet beam. This choice allows the use of shorter pillars along with a narrow gap between pillar rows. Shorter pillars are easier to manufacture and a narrow gap is required for better interaction impedance. Circular beams restrict the use of larger pillars and narrow gap between pillars. The performance of this interaction structure is compared with a folded waveguide. Under the same operating conditions involving a 20 kV beam voltage and a 30 mA beam current, the double corrugated waveguide interaction structure exhibits impressive performance in simulations, featuring an interaction impedance of 0.52 ({varOmega }) at 0.34 THz, an output power of 3.2 W, and a bandwidth extending to approximately 20 GHz. In contrast, the folded waveguide, as per simulation results, registers values of 0.43 ({varOmega }), 2.6 W, and a 12 GHz bandwidth, respectively. The proposed double corrugated waveguide-based interaction structure is fabricated using modern CNC machining. Experimental validation reinforces the effectiveness of this design, with measurements indicating reflection below −20 dB and transmission exceeding −2 dB.

In this paper we present a comprehensive overview of the theoretical and experimental studies on gyrotrons operating at harmonics of the electron cyclotron frequency. Besides the conventional (small-orbit) gyrotrons, three other types of such devices are considered, namely large-orbit gyrotrons (LOG), double-beam gyrotrons, and gyro-devices with a frequency multiplication. Based on a comparison between them and the devices that work on the fundamental resonances, both the advantages and disadvantages of the harmonic gyrotrons are critically examined. Such an analysis is helpful for choosing between different alternative concepts in the design process of appropriate radiation sources for various applications.