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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) - Reliability of Disdrometer-derived W-Band Attenuation Predictions
摘要： applications W-band frequencies are used for radar observations of clouds. In a undergo underneath potential significant attenuation. Also in satellite telecommunications the use of W-band frequencies is planned, to transfer the ever increasing amount of data. Rain attenuation is one of the most significant atmospheric effects influencing propagation, and precise knowledge is important for system design. signals the Often the specific rain attenuation is given as a function of rain rate, but at higher frequencies, such as W-band, the sensitivity to the shape of the drop size distribution (DSD) increases. Incorporating DSD measurements in the prediction process is recommended. In this study the reliability of the on DSD attenuation measurements is confirmed through comparison with radiometric attenuation data, acquired from an Atmospheric Propagation and Profiling System (ATPROP). 90 GHz, 2D-Video-Disdrometer predictions (2DVD), based of at a
关键词： W-band frequencies,electromagentic wave propagation,specific rain attenuation
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) - Antenna and Propagation Aspects of a Future GNSS-Reflectometry Mission
摘要： Global System Reflectometry (GNSS-R) is a passive sensing method to measure properties of the Earth’s surface, of oceans, or of the atmosphere by analyzing reflected navigation signals from GNSS satellites such as GPS (Global Positioning System). The reflected signals can be measured with ground based, air borne, or space based sensors, and the applications reach from altimetry, ocean wind retrieval, soil moisture to vegetation growth analysis. The principle of GNSS-R was presented a few decades ago. Meanwhile, GNSS-R is already used in ground based GNSS sites, performance analyses/demonstrations for in-orbit measurements are carried out, and orbit missions are ongoing. The present study introduces the concept and some of its variations. It describes initial and ongoing research, and it presents propagation aspects of a future CubeSat mission to measure the height of oceans and ice areas and study the sea ice extend. Finally, the design of a L-band patch antenna array is presented that will be used to detect both the direct and the reflected GNSS signals.
关键词： L-band patch antenna array,GNSS-reflectometry,altimetry,PRETTY mission,propagation,low earth orbit,remote sensing
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) - Cloud Attenuation Prediction Statistics for GEO and NGSO Satellite Communication Systems Operating at Q/V Band and Above
摘要： The employment of extremely high frequency bands (like Q/V and W bands) in the next generation satellite communication system has been proposed for feeder links operation in order to satisfy the ever growing satellite users’ demands. For the feeder links’ reliable performance analysis, the total atmospheric attenuation has to be taken into account. In this paper, a methodology for the estimation of cloud attenuation induced on a satellite slant path, through time series generation of Integrated Liquid Water Content (ILWC), for GEO satellites is presented and modified to consider joint attenuation statistics of cloud attenuation for multiple slant paths and also for the cloud attenuation prediction for NGSO links (MEO and LEO cases). The models are derived from cloud attenuation time series synthesizers, based on stochastic differential equations (SDEs), that incorporate properly the spatial and temporal behavior of ILWC and the time dependence of the elevation angle for NGSO links. Numerical results for GEO, MEO and LEO satellite systems operating at Q and W band are reported. The single link cases are tested with the ITU-R. P. 840-6 model. Interesting conclusions are drawn.
关键词： Cloud attenuation,Feeder Links,diversity gain,NGSO systems,Q and W band,joint cloud attenuation statistics
更新于2025-09-04 15:30:14
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Lasing in optimized two-dimensional iron-nail-shaped rod photonic crystals
摘要： We demonstrated lasing at the Γ-point band-edge (BE) modes in optimized two-dimensional iron-nail-shaped rod photonic crystals by optical pulse pumping at room temperature. As the radius of the rod increased quadratically toward the edge of the pattern, the quality factor of the Γ-point BE mode increased up to three times, and the modal volume decreased to 56% compared with the values of the original Γ-point BE mode because of the reduction of the optical loss in the horizontal direction. Single-mode lasing from an optimized iron-nail-shaped rod array with an InGaAsP multiple quantum well embedded in the nail heads was observed at a low threshold pump power of 160 μW. Real-image-based numerical simulations showed that the lasing actions originated from the optimized Γ-point BE mode and agreed well with the measurement results, including the lasing polarization, wavelength, and near-field image.
关键词： optical pulse pumping,photonic crystals,iron-nail-shaped rod,lasing,band-edge modes
更新于2025-09-04 15:30:14
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Band-fluctuations model for the fundamental absorption of crystalline and amorphous semiconductors: a dimensionless joint density of states analysis
摘要： We develop a band-fluctuations model which describes the absorption coefficient in the fundamental absorption region for direct and indirect electronic transitions in disordered semiconductor materials. The model accurately describes both the Urbach tail and absorption edge regions observed in such materials near the mobility edge in a single equation with only three fitting parameters. An asymptotic analysis leads to the universally observed exponential tail below the bandgap energy and to the absorption edge model at zero Kelvin above it, for either direct or indirect electronic transitions. The latter feature allows the discrimination between the absorption edge and absorption tails, thus yielding more accurate bandgap values when fitting optical absorption data. We examine the general character of the model using a dimensionless Joint Density of States formalism with a quantitative analysis of a large amount of optical absorption data. Both heavily doped p-type GaAs and nano-crystalline Ga1?xMnxN, as examples for direct bandgap materials, as well as amorphous Si:Hx, SiC:Hx and SiNx, are modeled successfully with this approach. We contrast our model with previously reported empirical models, showing in our case a suitable absorption coefficient shape capable of describing various distinct materials while also maintaining the universality of the exponential absorption tail and absorption edge.
关键词： band-fluctuations model,fundamental absorption,disordered semiconductor materials,absorption edge,Joint Density of States,Urbach tail
更新于2025-09-04 15:30:14
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Influence of Post-deposition Heat Treatments on the Optical Properties of Chemically Deposited Nanocrystalline TiO2 Thin Films
摘要： The aim of this study is to investigate the potentials of TiO2 thin films for device applications. Nanocrystalline single phase of rutile TiO2 thin films have been prepared by Chemical Bath Deposition (CBD) technique at bath temperature range from 75-80°C, keeping other deposition variables constant. The films were then subjected to post-deposition heat treatments with annealing temperatures in the range 373 to 673 K. The optical characterisation was done using the Elmer Lambda-2 spectrometer to investigate the transmittance and absorbance versus wavelength measurements. The data obtained from the transmittance and absorbance measurements were used to deduce the important optical constants. The results show that the energy bandgap was direct, with values in the range ≤1.8 eV for the as-deposited layers and ≥2.2 eV for the annealed layers. At lower temperatures, the band gaps of the annealed samples did not differ significantly from the energy gap (1.8 eV) of the as-deposited film. At higher thermal treatment, the energy gaps increased with the increase in annealing temperatures and a maximum of 2.2 eV for the energy gap was determined for TiO2 film annealed at 673 K. The values of the energy bandgap obtained in study, are within the range suitable for application in photovoltaic solar cell devices and in related photonic applications.
关键词： thermal annealing,Energy band gap,solar cells,TiO2
更新于2025-09-04 15:30:14
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Carbon-Related Defects as a Source for the Enhancement of Yellow Luminescence of Unintentionally Doped GaN
摘要： Yellow luminescence (YL) of unintentionally doped GaN (u-GaN) peaking at about 2.2 eV has been investigated for decades, but its origin still remains controversial. In this study, ten u-GaN samples grown via metalorganic chemical vapor deposition (MOCVD) are investigated. It is observed from the room temperature (RT) photoluminescence (PL) measurements that the YL band is enhanced in the PL spectra of those samples if their MOCVD growth is carried out with a decrease of pressure, temperature, or flow rate of NH3. Furthermore, a strong dependence of YL band intensity on the carbon concentration is found by secondary ion mass spectroscopy (SIMS) measurements, demonstrating that the increased carbon-related defects in these samples are responsible for the enhancement of the YL band.
关键词： yellow luminescence band,carbon impurity,unintentionally doped GaN
更新于2025-09-04 15:30:14
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High-Gain Fabry-Perot Antennas with Wideband Low Monostatic RCS Using Phase Gradient Metasurface
摘要： The design of two high-gain Fabry-Perot (F-P) antennas with wideband low monostatic radar cross section (RCS) is presented in this paper. Firstly, a phase gradient metasurface (PGM) without lossy layer is used to realize in-band RCS reduction and high aperture efficiency simultaneously. The simulated results show that its peak gain is 19.2 dBi and a high aperture efficiency of 58.6% is achieved. By utilizing the PGM structure, the monostatic RCS is reduced from 7GHz to 11GHz and the in-band co-polarization RCS is reduced by 13.1 dB. After that, a PGM with metamaterial absorber (MA) is designed to broaden the bandwidth of RCS reduction. A prototype antenna is fabricated and measured. The peak gain of 17.9 dBi is obtained and the monostatic RCS is reduced in a wider frequency band of 7GHz to 15GHz.
关键词： radar cross section reduction (RCSR),Fabry-Perot antenna,phase gradient metasurface (PGM),high gain,in-band RCSR
更新于2025-09-04 15:30:14
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[IEEE 2018 IEEE 7th Global Conference on Consumer Electronics (GCCE) - Nara, Japan (2018.10.9-2018.10.12)] 2018 IEEE 7th Global Conference on Consumer Electronics (GCCE) - Spiral Planar Antenna for MIMO
摘要： A high gain spiral planar antenna for the multiple-input and multiple-output (MIMO) is proposed and fabricated in the frequency band of 2.4GHz. Its maximum and average gains are higher than those of the commercialized antenna. Two fabricated antennas are put adjacent to the same and reverse direction, and MIMO antennas are composed. The return losses in two MIMO antennas are about the same as those in the single antenna. Also, the isolation losses in two MIMO antennas are less than -10dB in 2.4GHz band even if the distance between two antennas is 0mm. The average gains of two MIMO antennas are less than those of the single antenna, but high enough to be practical.
关键词： 2.4GHz band,high gain,spiral planar antenna,MIMO
更新于2025-09-04 15:30:14
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[Lecture Notes in Electrical Engineering] Recent Trends in Communication, Computing, and Electronics Volume 524 (Select Proceedings of IC3E 2018) || Magnetic Field Sensitivity in Depressed Collector for a Millimeter-Wave Gyrotron
摘要： The electron beam trajectories were simulated in a single-stage depressed collector for a millimeter-wave gyrotron. This collector was designed to handle the spent beam obtained after beam-wave interaction in the 100 kW gyrotron (accelerating voltage 55 kV and beam current 5 A). Similar to other high-power gyrotrons, this collector has larger volume considered at ground potential. The cathode and the beam-wave interaction cavity were considered at ?40 kV and +15 kV, respectively. The collector sees the depression of 15 kV. The geometry of the collector is considered as three sections: (i) the open entrance conical section, (ii) the smooth cylindrical section, and (iii) the closed conical section. In order to simulate the beam trajectory from nonlinear taper to collector, the electron trajectories and spent beam power distribution data obtained from large-signal analysis have been fed at the entrance of mode converter of the gyrotron with required potentials applied. The collector geometry and the magnetic ?eld are pro?led to ensure the landing of the gyrating electrons to the wider smooth cylindrical section for better thermal management. The sensitivity of the magnetic ?eld pro?le is studied and observed that for ±5% variation in the magnetic ?eld pro?le would not shift the electron beam landing to conical sections, and the spent electron beam has no interception. The power dissipation on the collector is found to be 80.55 kW. The collector ef?ciency is calculated as ~48% for 120 kW RF output. The maximum thermal loading on collector inner surface is estimated as 0.38 kW/cm2.
关键词： Millimeter-wave gyrotron,Electron trajectory simulation,W-band gyrotron,Depressed collector
更新于2025-09-04 15:30:14