- 标题
- 摘要
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- 实验方案
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Simulation and comparative analysis of the DC characteristics of submicron GaN HEMTs for use in CAD software
摘要： Bearing in mind the requirements of design engineers, a nonlinear model is developed to simulate the temperature-dependent I–V characteristics of submicron high-electron-mobility transistors (HEMTs). Self- and ambient heating effects are incorporated into the model expression to cater for both the negative and positive conductance of the device, after the onset of the saturation current. It is shown that the accuracy of numerical models previously developed for metal–semiconductor field-effect transistors (MESFETs) deteriorates when simulating the I–V characteristics of gallium nitride (GaN) HEMTs, primarily due to the self-heating effects. The validity of the proposed model is checked for GaN HEMTs with gate length ( Lg ) ranging from 0.12 to 0.7 μm in the temperature range of T = 298 to T = 773 K. It is demonstrated that the proposed model simulates, with a good degree of accuracy, the output characteristics of such devices exhibiting negative conductance in the saturation region of operation. It is observed that, for devices exhibiting negative conductance in the saturation region, the peak transconductance ( gm ) occurs at a relatively higher negative gate bias while the peak value reduces with increasing ambient temperature. The root-mean-square errors reveal that the proposed model is better than other similar models reported in the literature, with an improvement varying from 17 to 50 % depending on the device characteristics.
关键词： Nonlinear model,Submicron HEMTs,Optimization,DC characteristics
更新于2025-09-04 15:30:14
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Robust fusion algorithm based on RBF neural network with TS fuzzy model and its application to infrared flame detection problem
摘要： A robust fusion algorithm based on Radial Basis Function (RBF) neural network with Takagi-Sugeno (TS) fuzzy model is proposed in view of the data loss, data distortion or signal saturation which is usually occurred in the process of infrared flame detecting with multiple sensors. To initialize the model, the traditional K-means clustering algorithm is used to obtain the number of the fuzzy rules and the center of the membership function. Compared with the traditional RBF neural network with TS fuzzy model, the output of the node in the proposed model is constructed taking into account the membership degree of the feature components in each item of the output polynomial of the hidden layer nodes in consequent fuzzy network. A new weighted activation degree (WAD) is defined to calculate the firing strength (i.e., fuzzy rule applicability) of the fuzzy node instead of the commonly used Mahalanobis distance. The feature representation coefficients used in the above WAD fully consider the variant representation degree of different features in different fuzzy clusters, thus the developed method can deal with the abnormal outputs of the fuzzy rules caused by the variation of the feature components of the raw data obtained from the complex industrial environments. The robustness of the proposed approach is validated with experimental data obtained from a developed triple-channel infrared flame detector and the experiment results show that the convergence rate, accuracy and generalization ability of the proposed method are improved compared with the traditional RBF neural network with TS fuzzy model in [1] and the GA-BP (Genetic Algorithm-Back Propagation) model in [2]. In particular, the required number of the hidden layer nodes in the proposed approach is the least among the aforementioned methods.
关键词： robustness,feature representation coefficient,Infrared flame detector,TS fuzzy model,RBF neural network
更新于2025-09-04 15:30:14
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Near-Infrared (NIR) Spectrometry as a Fast and Reliable Tool for Fat and Moisture Analyses in Olives
摘要： The evaluation of fat and moisture contents for olive fruits is crucial for both olive growers and olive oil processors. Reference methods, such as Soxhlet extraction, used for fat content determination in olive fruits are time- and solvent- consuming and labor intensive. Near-infrared (NIR) spectroscopy is proposed as a solution toward rapid and nondestructive analyses of olive fruit fat and moisture contents. In the present work, comparative studies of the fat and moisture quantification methods were performed on four cultivars (Arbosana, Arbequina, Chiquitita, and Koroneiki) during six different harvesting time points to determine the potential of NIR as an alternative methodology. The impact of olive paste crushing degree on NIR performance was also investigated using three different grid sizes (4, 6, and 8 mm) on a hammer mill, in addition to a blade crusher. Results indicate a satisfactory correlation between the reference Soxhlet and NIR methods with R2 = 0.995. A comparison study of moisture content was also done on NIR and the use of conventional oven with the R2 value of 0.995. The crushing blade produced higher values in both moisture and fat contents in comparison to the hammer mill. The evaluation indicates that when building a chemometric model, all crush sizes and blade sizes should be represented in the model for highest accuracy.
关键词： Soxhlet extraction,Near-infrared (NIR) spectroscopy,moisture content,olive fruit,fat content,chemometric model
更新于2025-09-04 15:30:14
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[Institution of Engineering and Technology 12th European Conference on Antennas and Propagation (EuCAP 2018) - London, UK (9-13 April 2018)] 12th European Conference on Antennas and Propagation (EuCAP 2018) - Equivalent circuit model for cross-shaped frequency selective surface absorbing material
摘要： The equivalent circuit model is used to analyze the actual structure of the multilayer frequency selective surface absorbing. The transmission line model and equivalent impedance are provided for the transmissivity of electro- magnetic waves. The results are validated by comparison with the Ansoft HFSS. In addition, the in?uences of different parameters are discussed. It is found that such a multilayer absorbing material has a good tenability and independence for the absorption frequency.This can be used to design absorbing material for different requirements.
关键词： HFSS,circuit model,frequency selective surface
更新于2025-09-04 15:30:14
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[Institution of Engineering and Technology 12th European Conference on Antennas and Propagation (EuCAP 2018) - London, UK (9-13 April 2018)] 12th European Conference on Antennas and Propagation (EuCAP 2018) - An Absorptive Frequency-selective Reflector Based on Miniaturized Square-loop Resonator
摘要： A new method for the design of an absorptive frequency selective reflector (AFSR) with a sharp roll-off reflection band is presented. The proposed AFSR is based on a miniaturized square-loop resonator to produce two resonances within the absorption band. The shunt resonance of top loops is utilized to bypass the lossy path. The series resonance of bottom loops is generated to improve the reflection band. selectivity and bandwidth of Furthermore, the principles of operation are explained with the aid of an equivalent circuit model. A prototype of AFSR is simulated, fabricated and measured to verify this design concept. It is demonstrated with experiment that the AFSR exhibits a flat reflection band with a 8.45% bandwidth and two wide absorption bands with fractional bandwidths of 47.4% and 31.4%, respectively.
关键词： equivalent circuit model,absorptive frequency selective reflector,square-loop resonator
更新于2025-09-04 15:30:14
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[Institution of Engineering and Technology 12th European Conference on Antennas and Propagation (EuCAP 2018) - London, UK (9-13 April 2018)] 12th European Conference on Antennas and Propagation (EuCAP 2018) - An Ultra-thin Triple-band Metamaterial Absorber with Equivalent Circuit Analysis
摘要： A compact ultra-thin triple-band metamaterial absorber with polarization insensitiveness and wide-angle stability is presented in this paper. The unit cell of the absorber consists of a Jerusalem cross and a concentric circular ring imprinted on a dielectric substrate backed with a metal ground plane. Simulated results exhibit that the proposed absorber has three discrete absorption peaks at 4.4, 6.05, and 13.9 GHz with excellent absorption rates over 0.95. The current distribution and equivalent circuit analysis are investigated to analyze the near-unity absorption mechanism. The structure is then fabricated and experimentally characterized. The measured absorption response shows a good agreement with the simulated and calculated results.
关键词： metamaterial absorber,triple-band,equivalent circuit model
更新于2025-09-04 15:30:14
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A Non-Stationary 3-D Wideband GBSM for HAP-MIMO Communication Systems
摘要： The measurement results in land mobile satellite (LMS) communication scenario have shown that the propagation characteristic of LMS channel is a non-stationary process. In this paper, a non-stationary three-dimensional (3-D) wideband geometry-based stochastic model (GBSM) and the corresponding simulation model are proposed for high altitude platform (HAP) multiple-input multiple-output (MIMO) communication system. The proposed GBSM uses two-dimensional (2-D) one-ring and 3-D multi-cylinders to model moving scatterers and near and far stationary scatterers, respectively. In the proposed GBSM, we assume that the multipath components (MPCs) scattering from the far stationary scatterers could appear again after their disappearance, and a two-state continuous-time Markov process is used to model the dynamic properties of MPCs such as MPCs appearance and disappearance, and the closed-form expressions of the survival probabilities of MPCs are derived. In the proposed GBSM, the long distance and small-scale time-variant parameters are also used to investigate the non-stationarities of HAP-MIMO channel. Using the survival probabilities of MPCs, the statistical properties of the proposed 3-D GBSM are derived. The numerical the proposed 3-D GBSM is more results demonstrate that practical to characterize the HAP-MIMO channel.
关键词： High Altitude Platform (HAP),wideband channel,two-state continuous-time Markov process,geometry-based stochastic model (GBSM),non-stationarities
更新于2025-09-04 15:30:14
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[Institution of Engineering and Technology 12th European Conference on Antennas and Propagation (EuCAP 2018) - London, UK (9-13 April 2018)] 12th European Conference on Antennas and Propagation (EuCAP 2018) - Behavioural Modelling for Adaptive Array Systems Incorporating High-Power Amplifier Nonlinearities
摘要： We develop a novel method for the behavioural modelling of adaptive array systems (AASs) incorporating high-power ampli?er (HPA) nonlinearities. The model is motivated by the need to better de?ne the spatial and spectral interference pro?le of AASs. We provide a simulated proof of concept as a precursor to experimental validation. In our demonstration, the model is identi?ed using simulated near-?eld measurements made while the antenna’s input channels are undergoing a representative excitation. These measurements are used to identify a large number of memory polynomials (MPs) which characterise the transfer function from the antenna inputs to the near-?eld. We then use the array of MPs and a near-?eld to far-?eld transformation to obtain the far-?eld pattern of the antenna for arbitrary input. We show the impact of antenna element HPA nonlinearities on the far-?eld pattern, and our ability to predict them via the developed model.
关键词： smart antenna,adaptive antenna,behavioural model
更新于2025-09-04 15:30:14
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[Institution of Engineering and Technology 12th European Conference on Antennas and Propagation (EuCAP 2018) - London, UK (9-13 April 2018)] 12th European Conference on Antennas and Propagation (EuCAP 2018) - Circuit-model approach for polarizing surfaces based on stacked meander-line gratings
摘要： This manuscript reports the design of polarizers consisting of stacks of several meander-line gratings for axial-ratio enhancement. Analysis and design are carried out with analytical equivalent circuits that fully characterize periodic meander-line architectures. The advantage of using the analytical equivalent-circuit approach lies on its accuracy as well as in the better physical insight of the structure’s behavior provided by this approach. Extension to the case of oblique incidence is also carried out. Comparisons between results obtained by a commercial software and by the circuit model will evidence the good accuracy of the proposed approach.
关键词： meander-line gratings,Circuit model,periodic surfaces,polarizers
更新于2025-09-04 15:30:14
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[Institution of Engineering and Technology 12th European Conference on Antennas and Propagation (EuCAP 2018) - London, UK (9-13 April 2018)] 12th European Conference on Antennas and Propagation (EuCAP 2018) - Numerical Weather Prediction Models for the Estimate of Clear-Sky Attenuation Level in Alphasat Beacon Measurement
摘要： With the move of satellite systems towards Ka and QIV bands, the Alphasat TDPS Aldo Paraboni scientific experiment aims to characterize atmospheric attenuation in those bands. However, during the retrieval of the attenuation from the measured beacon signal, the clear-sky contribution to attenuation is lost. Microwave radiometers give the clear sky absolute reference level, but these are costly and not always available. This paper proposes Numerical Weather Prediction models as an alternative source of clear-sky attenuation. Three months of beacon and radiometric data from Spino d' Adda the Alphasat receiving station are used as benchmark for validation of the method. A preliminary conclusion is that gaseous attenuation is well predicted, but cloud attenuation is underestimated.
关键词： microwave radiometer,Numerical Weather Prediction model,radiowave propagation,clear-sky attenuation,Alphasat
更新于2025-09-04 15:30:14