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Abstract: Abstract This paper presents a dual-band 28/38 GHz two elements multiple-input multiple-output (MIMO) antenna with high isolation for 5G applications. The suggested antenna is a monopole with rectangular and triangle stubs added to the patch and a partial ground plane to achieve the dual band’s behavior. Two elements of the suggested antenna are combined and placed orthogonally to achieve the high isolation features of the MIMO configuration at 28/38 GHz. The MIMO configuration has a size of 27.65 \(\times\) 12 \(\times\) 0.273 mm3. The suggested MIMO prototype is fabricated and tested. The tested results achieved dual frequency bands with S11 lower than − 10 dB within two frequency bands (26–30 GHz and 36–41.5 GHz) and S21 lower than − 20 dB through the two operated bands. The suggested antenna has semi-omnidirectional radiation patterns in both planes. As well, its measured peak gain is 5.2 dBi and 5.3 dBi at the two operated frequency bands, respectively. Also, the MIMO parameters are extracted to validate the simulated results. The simulated and tested results have a good matching within the two operating bands which suggests the proposed structure be utilized in 5G communications. PubDate: 2022-05-19
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Abstract: Abstract This work proposes a high-linearity down-conversion mixer with a modified transconductance stage of Gilbert cell at about 120 GHz in a 55-nm CMOS process. The mixer attains at least 2 dBm input-referred 1 dB compression point (IP1dB) by adopting Gilbert cell with multiple gate transistors (MGTR) technology, source degeneration technology, and drain-gate parallel inductors. The improvement of traditional MGTR technology enables it to be applied in a sub-terahertz band and still has a certain effect on linearity improvement. Compared with other MGTR manufacturing, the improvement of linearity is no longer sensitive to bias voltage, which is helpful for practical applications. The measurement results show that the proposed mixer exhibits good linearity performance in a sub-terahertz band, and the frequency conversion loss is within an acceptable range. The RF, LO, and IF ports are measured to match 90–123 GHz,50–67 GHz, and 52–67 GHz, respectively. Under the consideration of a low-cost design, the DC power consumption of the proposed mixer is only 8.2 mW. The core chip occupies only 0.28 × 0.28 mm. This is the first application of MGTR mixers in a sub-terahertz band. PubDate: 2022-05-12
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Abstract: Abstract The 45-GHz quasi-optical transmission line including three quasi-optical mirrors for melting rock as an advanced drilling technology has been designed, machined, and experimentally tested in this paper. Based on the Stratton–Chu formula and the mirror optimization program, the surface structure of the three quasi-optical mirrors which transmit the Gaussian wave beam from the 45-GHz gyrotron to the sample rock surface has been obtained. The gyrotron output power is adjustable from 0 to 20 kW. The experiment results show that when the output power of the gyrotron was 5 kW in a continuous wave (CW) regime (30 s), the maximum power density reached is 552 W/cm2 and the maximum temperature of the sample stone reached is 968.9 °C. When the output power of the gyrotron was 15 kW in a CW regime (60 s), the maximum power density reached is 1650 W/cm2 and the maximum temperature of the sample stone reached is 2032.6 °C. Meanwhile, it is important to process the high-density plasma produced by the vaporized rock in time. PubDate: 2022-05-07
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Abstract: Abstract This paper presents a novel W-band AiP array based on the wafer-level packaging technology with through silicon via (TSV). The proposed antenna array is composed of 2 × 4 radiation elements, a grounded coplanar waveguide (GCPW) to strip line (SL) vertical transition, and a GCPW power divider network. The substrate of the radiation element is quartz, which is welded to the silicon by ball grid array (BGA). The GCPW-to-SL vertical transition based on TSV and ball bumping realizes low-loss interconnection between different silicon layers. The GCPW power divider network feeds the 2 × 4 radiation elements with equal amplitudes and equal phases. The measured results show that the insertion loss of the GCPW-to-SL vertical transition is less than 2 dB in the working frequency range of 90–96 GHz and the gain of the proposed AiP array is about 9.5 dBi at 93 GHz, which verify the feasibility of the AiP solution at W-band. PubDate: 2022-04-30
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Abstract: Abstract A Ka-band wide-isolation-bandwidth waveguide power divider using a microstrip-probe isolation circuit is proposed in this paper. A novel microstrip-probe isolation circuit is presented and applied to the waveguide Gysel power divider to improve the output isolation. At the same time, the proposed microstrip-probe isolation network has a wider bandwidth compared with the conventional isolation network. The proposed wideband waveguide Gysel power divider is designed, fabricated, and measured. Good agreement between simulated and measured results is found for the proposed power divider. The measured results show that the average insertion loss is about 0.45 ± 0.25 dB within the frequency range from 26.5 to 35.7 GHz. The measured output return loss is greater than 20 dB within the frequency range of 26.5 to 35.5 GHz (28.6% fractional bandwidth), and its phase imbalance between the two output ports is ± 1° in the frequency range of 27.5 to 36.5 GHz. Moreover, the measured output isolation is greater than 14 dB from 26.5z to 36.3 GHz (31.1% fractional bandwidth ). PubDate: 2022-04-21
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Abstract: Abstract In this letter, an E-plane substrate is inserted into the W-band standard waveguide to construct a bandpass filter (BPF) with high selectivity. This E-plane waveguide BPF with three transmission zeroes (TZs) is developed by using a novel compact beeline resonant cell (CBRC) and uniform-impedance resonant cells (UIRCs). It is shown that the locations of the TZs can be designed. Three TZs, with two located in the upper stopband, and the other one located in the lower stopband, are produced by a novel CBRC and two UIRCs, respectively. For verification, the BPF prototype is designed, fabricated and measured, whose total length is just 3.21 mm, namely, less than 0.83 λg (λg is the waveguide wavelength at the center frequency). Moreover, the minimum insertion loss (IL) is only 1.02 dB, and the measured return loss (RL) of the proposed BPF is greater than 14 dB at the frequency range of 94 to 99.3 GHz. The 3-dB fractional bandwidth (FBW) is 6.5%, which is from 93.6 to 99.9 GHz. Good agreement between the simulations and measurements validates the design method. The proposed W-band E-plane waveguide BPF and the efficient design method used in their design are believed to be of importance for future filter device applications in millimeter wave systems. PubDate: 2022-04-18
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Abstract: Abstract In this paper, a new terahertz solid-state frequency doubler design method named function-based harmonic impedance optimization method (FHIOM) is reported to improve the simulation iteration speed and accuracy of terahertz solid-state circuit design. Obtaining the matching impedance of the diode part in the optimal operating condition and realizing this impedance through the input-output matching structure are the two main steps in the design of the terahertz doubler. In this design method, harmonic impedance optimization and function-based impedance optimization are applied to quickly obtain the best input and output embedded impedance of the broadband frequency doubler device, which reduces the blindness of tentative optimization. This method innovatively estimates the impedance of the matching structure through the formula, which strengthens the connection between impedance optimization and matching structure realization. Based on the function-based harmonic impedance optimization method, a 220 GHz doubler is designed, processed, and measured. Measured results show that the doubler exhibits a bandwidth from 212 GHz to 230 GHz, with a conversion efficiency of above 15.0% a mean output power of 9.12 mW when supplied with up to 32 mW of input power. A 16 mW peak output power with a 16.4% efficiency was measured at 228 GHz when the input power was 97.55 mW. The frequency doubler design method presented in this work has the advantages of high efficiency and accuracy, which makes it very attractive for practical broadband terahertz applications. PubDate: 2022-04-18
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Abstract: Abstract Millimeter waves (MMW) absorbed by skin or cornea may induce damage by heat. We have developed a 60 GHz MMW exposure-induced eye injury model that reproducibly presents the extent of such ocular injury, including its clinical process and healing process. Findings by the model suggested an ocular damage threshold for an exposure dose of about 60 GHz 200–300 mW/cm2 for 6 min. Using the probit model, DD50, defined as the dose to cause ocular damage with 50% probability, was estimated to be 233 mW/cm2. A novel finding was that exposure of 60 GHz 400 mW/cm2 to a closed eyelid for 6 min not only damaged the eyelid (including the palpebral conjunctiva), but the eyeball surface beneath (the bulbar conjunctiva and cornea) it. PubDate: 2022-04-13
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Abstract: Abstract This paper considers an industrial machine, where wireless sensor nodes (denoted as tags or nodes) support control applications. This scenario poses very challenging communication requirements: hundreds of tags per cubic meter can provide an overall offered throughput of tens of Gbit/s; at the same time, control applications require a latency of less than 0.1 ms. To fulfill them, this work proposes an Orthogonal Chirp Division Multiple Access (OCDMA) scheme to be used in the TeraHertz (THz) frequency band. With THz communications, even at short distances, propagation delays can be of the same order of magnitude as the packet transmission time. This requires proper consideration of such delays in the protocol design and performance evaluation. This paper mathematically derives network throughput and latency of the proposed protocol, comparing it to benchmarks; two scenarios are considered, where tags are in fixed positions or move. Results show that OCDMA outperforms the two benchmark protocols, Aloha and Polling, for static and crowded networks, and the performance is compatible with the communication requirements of industrial control applications. PubDate: 2022-04-02
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Abstract: Abstract For terahertz spectroscopy on single crystals, the wavelength \(\lambda\) often is comparable to the size of the studied samples, emphasizing diffraction effects. Using a continuous-wave terahertz spectrometer in transmission geometry, we address the effect of the sample size on the achievable accuracy of the optical properties, focusing in particular on the phase data. We employ \(\alpha\) -lactose monohydrate as a paradigmatic example and compare data that were measured using apertures with diameters D in the range from 10 to 0.2 mm. For small D, strong diffraction typically invalidates a quantitative analysis of the transmitted amplitude at low frequencies. The phase data, however, can be evaluated to lower frequency and show a more systematic dependence on D. For a quantitative analysis, we employ a waveguide picture for the description of small apertures with a cylindrical bore. For D as small as 0.2 mm, corresponding to 1/D = 50 cm \(^{-1}\) , a circular waveguide does not support propagating waves below its cut-off frequency \(1/\lambda _c\) = \(\omega _c/2\pi c \approx 29\) cm \(^{-1}\) . Experimentally, we confirm this cut-off for cylindrical apertures with a thickness \(d_{\text {ap}}\) = 1 mm. Close to \(\omega _c\) , the measured phase velocity is an order of magnitude larger than c, the speed of light in vacuum. The cut-off is washed out if a sample is mounted on a thin aperture with a conical bore. In this case, the phase data of \(\alpha\) -lactose monohydrate for D = 0.2 mm can quantitatively be described down to about 10 cm \(^{-1}\) if the waveguide-like properties of the aperture are taken into account in the analysis. PubDate: 2022-03-25
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Abstract: Abstract This paper presents measurements using a dual-polarised radiometer operating at 93 GHz to detect ice or water on asphalt in laboratory conditions. The brightness temperatures of both H and V polarizations were measured for a dry surface, liquid water, and ice on asphalt at observation angles of 50° and 56°. The results presented in this paper demonstrate that the studied road conditions can be identified by the radiometer. The measurements are compared with a model and surface parameters, such as dielectric constant and roughness are fitted and compared to reference values. The experiments and results, described in this article, are the first steps towards the future installation of a polarimetric sensor on a moving vehicle for traffic safety. PubDate: 2022-03-21
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Abstract: Abstract The studies on mode interaction in gyrotrons had always been an active field of research due to their theoretical and practical importance for better understanding of the underlying physical principles and the development and optimization of various gyro-devices. However, lately, the problems that stem from the mode interaction have become more pronounced and severe due to the recently demonstrated advancement of gyrotrons towards higher (terahertz) frequencies at which, for keeping the same power level, the gyrotrons should operate in higher order modes. So the mode spectrum of the gyrotron cavity is significantly denser, and, hence, the mode competition is inevitable. In this overview, we present both the evolution and the progress of these investigations that assist the further development of high-performance sub-THz and THz gyrotrons for numerous novel and emerging applications in the broad fields of science and technologies. The targeted readership of this paper includes not only the experts in gyrotron development but rather a wider community of specialists working on other vacuum microwave devices seeking a synergy between different research fields. PubDate: 2022-03-19
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Abstract: Abstract Terahertz imaging and spectroscopy is an exciting technology that has the potential to provide insights in medical imaging. Prior research has leveraged statistical inference to classify tissue regions from terahertz images. To date, these approaches have shown that the segmentation problem is challenging for images of fresh tissue and for tumors that have invaded muscular regions. Artificial intelligence, particularly machine learning and deep learning, has been shown to improve performance in some medical imaging challenges. This paper builds on that literature by modifying a set of deep learning approaches to the challenge of classifying tissue regions of images captured by terahertz imaging and spectroscopy of freshly excised murine xenograft tissue. Our approach is to preprocess the images through a wavelet synchronous-squeezed transformation (WSST) to convert time-sequential terahertz data of each THz pixel to a spectrogram. Spectrograms are used as input tensors to a deep convolution neural network for pixel-wise classification. Based on the classification result of each pixel, a cancer tissue segmentation map is achieved. In experimentation, we adopt leave-one-sample-out cross-validation strategy, and evaluate our chosen networks and results using multiple metrics such as accuracy, precision, intersection, and size. The results from this experimentation demonstrate improvement in classification accuracy compared to statistical methods, an improvement to segmentation between muscle and cancerous regions in xenograft tumors, and identify areas to improve the imaging and classification methodology. PubDate: 2022-02-10 DOI: 10.1007/s10762-021-00839-x
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Abstract: Abstract This article presents a new method to achieve a well-matched and balanced impedance matching using a magnetic-electric coupled (MEC) transformer model. Both the MEC transformer model and its matching method are analyzed comprehensively. The MEC model takes the common-mode effects into consideration and improves accuracy FoM value (AFV) in the 1 \(\sim\) 100 GHz frequency band compared to the magnetically coupled transformer model in a 1:2 transformer example, which can provide higher accuracy for designing a better transformer. The proposed matching approach in this article can determine a well-matched and balanced MEC transformer matching network according to the target impedance. Mapping relationships between the parameters of the MEC transformer model and the geometric parameters of the transformer are further discussed to achieve a practical and optimal transformer simulation prototype. The methods to control the common-mode effects of the transformer are discussed both at the physical and circuit levels. The full-scalable parameters extraction methodology is verified over broadband by full-wave electromagnetic (EM) simulations and measurements. The proposed well-matched and balanced impedance matching approach is proven by the HFSS (3D High Frequency Simulation Software) simulation and structure measurements. PubDate: 2022-01-30 DOI: 10.1007/s10762-021-00836-0
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Abstract: Abstract Synchrotron-based terahertz and far-infrared spectra of aerographite and single-walled carbon nanotube aerogel were acquired using the terahertz/far-infrared beamline at the Australian Synchrotron in the frequency range of 7–1000 cm−1 and temperature range of 6–300 K. We observe infrared absorption features at ~ 35, ~ 79, and ~ 889 cm−1 for aerographite and ~ 35, ~ 79, ~ 685, ~ 923, and ~ 950 cm−1 for single-walled carbon nanotube aerogel. Temperature dependences of the terahertz and far-infrared spectra reveal frequency shifts of the infrared absorption peaks with temperature. The “red-shift” behavior of peak positions (~ 35 and ~ 79 cm−1) can be attributed to the anharmonicity of vibrational potentials. The ~ 35 cm−1 mode is expected to be only Raman active. Its appearance in our infrared spectra suggests that structural disorder in our samples relaxed this selection rule. PubDate: 2022-01-29 DOI: 10.1007/s10762-022-00841-x
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Abstract: Abstract This paper presents a circularly polarized (CP) slot antenna array using substrate integrated waveguide (SIW)–feeding network at Q-band. To achieve CP radiation and high-gain performance simultaneously, a metallic radiating slanted cross slot is stacked atop an SIW coupling slot in the CP antenna element design. The fabricated CP antenna element features 14.6% (42.6–49.3 GHz) measured impedance bandwidth for S11 ≤ −10 dB, 9.1% (42–46 GHz) measured 3-dB axial ratio (AR) bandwidth for AR ≤ 3, and 8.3 dBic measured peak gain, respectively. Then, a 1 × 8 antenna array is designed, fabricated, and measured. The measured results demonstrated that the impedance bandwidth and 3-dB AR bandwidth of the proposed 1 × 8 array are 14.8% (41.9–48.6 GHz) and 11% (43–48 GHz), respectively. The measured peak gain of the 1 × 8 array is 14.7 dBic at 44 GHz. PubDate: 2022-01-24 DOI: 10.1007/s10762-021-00837-z
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Abstract: Abstract For duplex using the antenna in a wireless transceiver, a transmit/receive (Tx/Rx) switch is usually adopted for selecting transmitter or the receiver chain. This paper proposes a single-pole double-throw (SPDT) Tx/Rx switch which was implemented by using Taiwan Semiconductor Manufacturing Company Limited (TSMC) 90-nm complementary metal–oxide–semiconductor (CMOS) process technologies for 60-GHz application purpose. The proposed SPDT Tx/Rx switch adopted the leakage cancellation method and the body bias technique to improve its performance. Transistors in parallel layout strategy were employed to reduce the on-state resistance, and the off-state parasitic capacitance was eliminated by using a parallel inductor for resonance. To achieve the required leakage cancellation, two lumped π-shape 90° phase shifters were inserted in an auxiliary path. In the 57 to 64 GHz frequency range, the measured results under Tx mode show an insertion loss less than 3.2 dB between antenna (Ant) and Tx ports, an isolation larger than 21.3 dB between Tx and Rx ports, and an isolation larger than 19.1 dB between Ant and Rx ports, respectively. The measured input return losses are 11.5–13.7 dB for the Ant port and 12.2–13 dB for the Rx or Tx ports, respectively. The simulated input 1-dB compression point (P1 dB) is 15.4 dBm. PubDate: 2022-01-24 DOI: 10.1007/s10762-021-00835-1
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Abstract: Abstract In our 0.22 THz gyrotron system, the overmoded conversion sequence is the critical component to convert the TE03 output mode of the gyrotron oscillator to the TE10 input mode of the gyrotron traveling wave amplifier (gyro-TWA). However, with the increase of the gyrotron’s operating frequency and output power, the output waveguide generally adopts highly overmoded structures, increasing the longitudinal size and narrowing the bandwidth of the traditional mode converter with uniform period and radial perturbation. Due to a much more significant coupling strength factor, a faster power increment in target modes TE02 and TE01 causes the axial length to decrease significantly in the proposed converters with nonuniform double perturbations. In our numerical and simulation results, compared to the traditional uniform-ripple-wall converters, the proposed nonuniform circular TE03-TE02-TE01 converter shortens 44.18% of the total length and increases the bandwidth over 95% conversion efficiency by 150%. Meanwhile, we employed a sidewall converter other than the inline converter to complete the CWG TE01-RWG TE10 conversion for its high efficiency and compactness. Based on the operation principle of the monostatic radar imaging system, the mode pattern measurement corroborates the desired electric field distributions near the waveguide port. The experimental results indicate the proposed mode conversion sequence has advantages of high conversion efficiency over 80%, low loss, and compact structure. PubDate: 2022-01-20 DOI: 10.1007/s10762-022-00840-y
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Abstract: Abstract We demonstrate the design and analysis of Ka-band miniature four-way Wilkinson power dividers (with CRC or RC isolation network) and variable-gain low-noise amplifier (VGLNA) for 5G systems. The four-way Wilkinson power divider with CRC (or RC) isolation network constitutes three two-way Wilkinson power dividers with CRC (or RC) isolation network. For the two-way power divider, a parallel capacitor is included at the input to compensate the imaginary part of the input admittance for input matching. Dual spiral structure with transmission line length of about λ/14 and symmetrical layout is adopted to achieve miniature chip area and small amplitude imbalance (AI) and phase difference (PD). Remarkable results are achieved. For instance, at 28 GHz, the two-way power divider (with CRC isolation network) achieves prominent S11 of − 12.1 dB, S22 and S33 of − 27 dB, S32 of − 17.4 dB, S21 of − 3.989 dB, S31 of − 3.964 dB, AI of − 0.025 dB, and PD of 0.171°. The normalized chip area is 9.8×10−5λ02. This is one of the smallest normalized chip areas ever reported for millimeter-wave power dividers. Moreover, the VGLNA constitutes a cascode input stage followed by a cascode output stage. To tune the power gain of the VGLNA, a current-steering transistor switch in parallel with the input transistor of the cascode output stage is adopted. A large gain tuning range of 14.9 dB is achieved. PubDate: 2022-01-19 DOI: 10.1007/s10762-021-00829-z
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Abstract: Abstract Periodically modulated laser pulses have been widely used in electron accelerators to generate coherent terahertz (THz) radiation. Researches show that frequency-chirped microbunching in an electron beam can be achieved by interacting with intensity modulated laser pulses of chirped frequency. Such microbunched electron beam can be utilized for the chirp control and ultra-short pulse emission of THz radiation sources. In this paper, we experimentally demonstrate a method to generate such a frequency-chirped intensity modulation in the laser pulse. The central modulation frequency and chirp rate can be easily adjusted in a wide range. By using the obtained laser pulse as interaction seed source, the generation of desired electron beams is discussed briefly. The usage of such density modulated electron beam for ultra-short THz generation is also simulated numerically. PubDate: 2022-01-17 DOI: 10.1007/s10762-021-00838-y
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