| 391. |
- Vosoogh, Abbas, 1984, et al.
(författare)
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Simple and Broadband Transition Between Rectangular Waveguide and Groove Gap Waveguide for mm-Wave Applications
- 2018
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Ingår i: IEEE Antennas and Propagation Society International Symposium. - 1522-3965. - 9781538671023 ; , s. 1101-1102
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Konferensbidrag (refereegranskat)abstract
- A vertical wideband transition between a standard WR-15 rectangular waveguide (RW) and groove gap waveguide (GGW) in the V-band is presented. A simple step is applied to achieve a good impedance matching in transition between the RW and the GGW. A back-to-back transition is designed and fabricated to verify the simulation results. The measured results of the fabricated prototype show the insertion loss of less than 0.2 dB and the input reflection coefficient better than -16 dB over almost the whole V-band (50-75 GHz).
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| 392. |
- Vosoogh, Abbas, 1984, et al.
(författare)
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W-Band Low-Profile Monopulse Slot Array Antenna Based on Gap Waveguide Corporate-Feed Network
- 2018
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 66:12, s. 6997-7009
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a gap waveguide-based compact monopulse array antenna, which is formed with four unconnected layers, for millimeter-wave tracking applications at W-band (85–105 GHz). Recently developed gap waveguide technology removes the need for galvanic contact among metallic layers of waveguide structures, and thereby, makes the proposed antenna suitable for easy and low-cost manufacturing. In this context, a low-loss planar Magic-Tee is designed to be used in a monopulse comparator network consisting of two vertically stacked layers. The gap waveguide planar monopulse comparator network is integrated with a high-efficiency 16x16 corporate-fed slot array antenna. The measured results of the comparator network show the amplitude and phase imbalance values to be less than 0.5 dB and 2°, respectively, over the frequency band of interest. The fabricated monopulse array antenna shows relative impedance bandwidths of 21% with input reflection coefficients better than −10 dB for the sum and difference ports. The null in the difference radiation pattern is measured to be 38 dB below the peak of the sum radiation pattern at 94 GHz. The measured gain is about 30 dBi for the same frequency. The low-loss performance of the comparator network and the feed network of the proposed array, together with the simple and easy manufacturing and mechanical assembly, makes it an excellent candidate for W -band compact direction-finding systems.
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| 393. |
- Vosoogh, Abbas, 1984, et al.
(författare)
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Zero-Gap Waveguide: A Parallel Plate Waveguide With Flexible Mechanical Assembly for mm-Wave Antenna Applications
- 2018
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Ingår i: IEEE Transactions on Components, Packaging and Manufacturing Technology. - 2156-3985 .- 2156-3950. ; 8:12, s. 2052-2059
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Tidskriftsartikel (refereegranskat)abstract
- A new gap waveguide concept is presented, where the air gap between the perfect electric conductor and artificial magnetic conductor (AMC) parallel plates of a conventional gap waveguide structure has been reduced to almost zero. When the air gap is reduced, the periodic metal pin layer (which emulates the AMC characteristics) may come in contact with the top metal layer. A statistical analysis of a random contact of the pin texture and the top metal plate in this new type of gap technology guiding structure, so-called zero-gap, is elaborated in this paper. The periodic pin texture creates a stopband for parallel plate modes, and it is also used as a mechanical support while assembling the waveguide structure. This presents a significant manufacturing advantage, especially for corporate feed-network of array antennas at millimeter-wave frequencies. A V -band 8×8 slot array fed with this new waveguide is also designed and manufactured to show the potential of this newly proposed zero-gap waveguide structure. The measured results show 20% of relative impedance bandwidth ( |S11|<−10 dB) and an overall antenna efficiency larger than 60% over the 56.5–69-GHz frequency band.
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| 394. |
- Wan, Cheng-Liang, et al.
(författare)
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Dynamics of slow electrons transmitting through straight glass capillary and tapered glass capillary
- 2016
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Ingår i: Wuli xuebao. - : Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences. - 1000-3290. ; 65:20
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Tidskriftsartikel (refereegranskat)abstract
- It has been found that the transmission rate of the electrons through insulating capillaries as a function of time/incident charge is not the same as that of the ions. The question arises that by using the electrons, if the negative charge patches can be formed to facilitate the transmission of the following electrons, thereby substantiating that the so-called guiding effect works also for electrons. This study aims to observe the time evolutions of the transmission of electrons through a straight glass tube and a tapered glass capillary. This will reveal the details of how and (or) if the negative charge patches can be formed when the electrons transport through them. In this work, a set of MCP/phosphor two-dimensional detection system based on Labview platform is developed to obtain the time evolution of the angular distribution of the transmitted electrons. The pulsed electron beams are obtained to test our detection system. The time evolution of the angular profile of 1.5 keV electrons transmitting through the glass tube/capillary is observed. The transmitted electrons are observed on the detector for a very short time and disappear for a time and then appear again for both the glass tube and tapered glass capillary, leading to an oscillation. The positive charge patches are formed in the insulating glass tube and tapered glass capillary since the secondary electron emission coefficient for the incident energy is larger than 1. It is due to the fact that fast discharge of the deposited charge leads to the increase of the transmission rate, while the fast blocking of the incident electrons due to the deposited positive charge leads to the decrease of the transmission rate. The geometrical configuration of the taper glass capillary tends to make the secondary electrons deposited at the exit part to form the negative patches that facilitate the transmission of electrons. This suggests that if the stable transmission needs to be reached for producing the electron micro-beam by using tapered glass capillaries, the steps must be taken to have the proper grounding and shielding of the glass capillaries and tubes. Our results show a difference in transmission through the insulating capillary between electrons and highly charged ions.
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| 395. |
- Wan, Kang, et al.
(författare)
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A Multilayer-Stacked UWB Yagi Antenna
- 2017
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Ingår i: 2017 International Symposium on Antennas and Propagation, ISAP 2017. - 9781538604656 ; Volume 2017-January, s. 1-2
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Konferensbidrag (refereegranskat)abstract
- By taking advantage of a wideband bow-tie antenna in the Yagi configuration, a novel multilayer-stacked ultra-wideband (UWB) Yagi antenna is proposed. First, the fundamental 3-layered UWB Yagi model is studied with respect to a few critical dimensions. Then, several directors are added to form a multilayer-stacked Yagi antenna, where the width of the directors is optimized in a monotonic decreasing manner. A sixlayered UWB Yagi antenna is studied by simulations. It covers 3.4-10.6 GHz with its return loss better than 10 dB, and it achieves a high directivity up to 13 dBi and a relative cross-polar level better than -10 dB in the whole band.
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| 396. |
- Wang, Bo, et al.
(författare)
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Unprecedented differences in the diamond nucleation density between carbon- and silicon-faces of 4H-silicon carbides
- 2020
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Ingår i: Chinese Chemical Letters. - : ELSEVIER SCIENCE INC. - 1001-8417 .- 1878-5964. ; 31:7, s. 2013-2018
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Tidskriftsartikel (refereegranskat)abstract
- 4H-silicon carbides deposited by diamond films have wide applications in many fields such as semiconductor heterojunction, heat sink and mechanical sealing. Nucleation plays a critical role in the deposition of the diamond film on 4H-silicon carbides. Nevertheless, as a typical polar material, the fundamental mechanism of diamond nucleation on different faces of 4H-silicon carbides has not been fully understood yet. In this contribution, nucleation of diamond was performed on the carbon- and silicon-faces of 4H-silicon carbides in a direct current chemical vapor deposition device. The nucleation density on the carbon-face is higher by 2-3 orders of magnitude compared to the silicon-face. Transmission electron microscopy verifies that there are high density diamond nuclei on the interface between the carbon-face and the diamond film, which is different from columnar diamond growth structure on the silicon-face. Transition state theory calculation reveals that the unprecedented distinction of the nucleation density between the carbon-face and the silicon-face is attributed to different desorption rates of the absorbed hydrocarbon radicals. In addition, kinetic model simulations demonstrate that it is more difficult to form CH2(s)-CH2(s) dimers on silicon-faces than carbon-faces, resulting in much lower nucleation densities on silicon-faces. (C) 2019 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.
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| 397. |
- Wang, Chunlin, et al.
(författare)
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High throughput sequencing reveals a complex pattern of dynamic interrelationships among human T cell subsets
- 2010
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 107:4, s. 1518-1523
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Tidskriftsartikel (refereegranskat)abstract
- Developing T cells face a series of cell fate choices in the thymus and in the periphery. The role of the individual T cell receptor (TCR) in determining decisions of cell fate remains unresolved. The stochastic/selection model postulates that the initial fate of the cell is independent of TCR specificity, with survival dependent on additional TCR/coreceptor "rescue" signals. The "instructive" model holds that cell fate is initiated by the interaction of the TCR with a cognate peptide-MHC complex. T cells are then segregated on the basis of TCR specificity with the aid of critical coreceptors and signal modulators [Chan S, Correia-Neves M, Benoist C, Mathis (1998) Immunol Rev 165: 195-207]. The former would predict a random representation of individual TCR across divergent T cell lineages whereas the latter would predict minimal overlap between divergent T cell subsets. To address this issue, we have used high-throughput sequencing to evaluate the TCR distribution among key T cell developmental and effector subsets from a single donor. We found numerous examples of individual subsets sharing identical TCR sequence, supporting a model of a stochastic process of cell fate determination coupled with dynamic patterns of clonal expansion of T cells bearing the same TCR sequence among both CD4(+) and CD8+ populations.
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| 398. |
- Wang, Enlin, 1998, et al.
(författare)
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A 50 dBi E-Band Dual-reflector Antenna for 5G Backhauling with Auto-beam-tracking Function
- 2024
-
Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 72:6, s. 4874-4887
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Tidskriftsartikel (refereegranskat)abstract
- An ultra-high-gain E-band dual-reflector antenna for 5G backhaul with beam tracking function is proposed in this paper. Beam tracking is achieved by defocussing the feed away from the focus point of the sub-reflector, while keeping the interface with the transmit-receive unit stationary by applying a movable gap-waveguide configuration. The antenna has been prototyped and measured. The measured reflection coefficients remain below –10 dB for both horizontal and vertical polarizations over 71 – 86 GHz, almost independent from the offset positions of the feed. The measured radiation patterns agree well with the simulated ones, with a peak gain of about 50 dBi in the band and less than 1 dB gain drop for beam steering within ±2°. Finally, a low-cost and environmentally friendly mechanical tracking system is proposed, prototyped, and tested. Measurements have verified that the tracking system functions well for slow sways.
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| 399. |
- Wang, Enlin, et al.
(författare)
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A Compact Double-Layer Groove Gap Waveguide Power Divider with High Isolation
- 2020
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Ingår i: 14th European Conference on Antennas and Propagation, EuCAP 2020.
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Konferensbidrag (refereegranskat)abstract
- A compact double-layer power divider with high isolation between output ports based on the groove gap waveguide (GGW) is presented in this paper. A five-port 1-to-2 power divider is designed base on the gap waveguide technology. Then a 1-to-8 power divider is built up by connecting seven 1-to-2 five-port power dividers. To achieve a compact size, the 1-to-8 power divider adopts a double-layer structure. The top layer is the feeding structure of the power divider, and the bottom layer contains the loads. The simulated results show that the proposed power divider exhibits the impedance matching bandwidth for the reflection coefficient below -15 dB is from 23.7 GHz to 30.3 GHz, and isolations between the output ports is more than 18 dB.
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| 400. |
- Wang, Enlin, 1998, et al.
(författare)
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A Compact Gap-Waveguide Dual-Polarized Ka-Band Feed for 50dBi Reflector Antennas With Tracking Function
- 2022
-
Ingår i: IEEE Access. - 2169-3536 .- 2169-3536. ; 10, s. 91622-91630
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Tidskriftsartikel (refereegranskat)abstract
- A dual-polarized Ka-band feed based on gap waveguide (GW) technology for an ultra-high-gain reflector antenna is presented. The feed provides SUM-beams for data transfer and DIFF-beams for tracking. The whole reflector antenna is composed of the feed and a dual-reflector Cassegraine antenna. The feed has been prototyped, and the measured reflection coefficients for the horizontally and the vertically polarized SUM-beam ports are below -10 dB and -8 dB over 30.8-38 GHz, respectively. The measured feed radiation patterns agree well with the simulated ones. The dual-reflector Cassegraine antenna has been designed and simulated by using GRASP with the simulated far-field function of the proposed feed, showing that the reflector antenna achieves SUM-beam gains above 50 dBi and the null depth of the DIFF-beams are more than 30 dB below the maximum of SUM-beams.
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