1,721,385 research outputs found
A Smart Cable System Offering Selective and Distributed Antenna Radiation using RF Switches and Non-Conventional Hybrid Couplers
No full textA smart cable system and its elements for selective communications and sensor-based data collection within corridors, subways, and tunnels is proposed with applications to the aeronautical, transportation, and space sectors. The main hardware components of the cable system are defined by active and programmable RF switches which can enable controlled radiation at specific nodes or hotspots. More importantly, our proposed cable concept provides an evolution from the conventional coaxial cable with distributed antennas, as well as the classic leaky feeder cable, which is typically employed for communications within corridors and mines. Moreover, the proposed smart cable moves towards a hybrid wireless node and programmable system for selective coverage. Planar circuits and low-profile RF electronic components are employed for lowcost implementation. In this work, our focus is on the assessment of the proposed smart cable system, its radiating nodes (RNs), as well as the estimation of the system performance based on the measurements of the RN prototypes.Wireless networks, RFID sensors, and power transmission systems can be additional applications for the proposed smart cable. System performance estimations for a real corridor satisfy typical RFID sensitivity requirements with received power levels between -39 dBm and -46 dBm in the worst case
Compact Leaky SIW Feeder Offering TEM Parallel Plate Waveguide Launching
Full text linkA planar and low-cost parallel-plate waveguide (PPW) launcher based on substrate integrated waveguide (SIW) technology is proposed. It can launch the fundamental TEM mode with a collimated wave front into a PPW structure while also being low profile and easy to fabricate. The launcher is implemented using a network of SIW transmission lines and its design is based on the leaky-wave (LW) theory. In our proposed structure, a selection of the SIW lines is made to leak power into the desired PPW region by means of a partially reflective surface, enabling planar wave front propagation of the TEM mode where efficiency values of over 90% are achieved. Measurements of a fabricated prototype are also reported at 15 GHz to demonstrate the design procedure and validate structure operation. When compared with similar co-axial and metallic waveguide launchers, our proposed SIW structure represents a compact, integrated, and unique design solution which may be useful to feed planar parallel-plate slot arrays and end-fire antennas. In addition, our novel and simple approach for PPW excitation can also be applied to other parallel-plate-based guides, low-cost transitions, and compact dividing/combining circuits for a new antenna and non-radiating LW feed systems at microwave and millimeter-wave frequencies
Design considerations for frequency scanning transmit antennas in wireless power transmission applications
No full textScanning transmit antennas can be used in wireless power transmission systems in order to optimize the power budget and energy consumption in the far-field. Here we present a concept for beam scanning that minimizes the need for reconfigurable RF components, such as diodes or varactors, and therefore reduces cost and power handling considerations. Instead the beam steering relies on a frequency scanning principle. In this paper we present the basic theory for designing such a frequency scanning antenna and by means of an example, that conforms with 2.45 GHz ISM band requirements, we evaluate its performance. Analytical and numerical simulations are presented
Smart cable for Radio Frequency Identification in aeronautical applications
No full textA smart cable for Radio Frequency Identification (RFID) aeronautical and transportation applications is proposed. The cable is designed to provide RFID connectivity at 2.45 GHz inside airplanes, subways, tunnels, etc. and can be made of five hotspot periodically separated by a distance of 3.2 m. Each hotspot consists of one switch, one patch antenna and one Wilkinson power combiner, except the last hotspot which consists of one switch, one inset feed patch antenna and one load. The system ensures a coverage area of 16 m length by 2.5 m height with at least a power level of -39 dBm to be received at the tag assuming an input power of 30 dBm
New achievements and configurations of helical resonator filters for space applications - theory and design
Full text linkThe satellite for communication uses frequencies from UHF band (300MHz to 3 GHz) up to Ka band (40GHz). The dimensions of the components in the satellite transponder, usually decrease with the frequency increment. For the Ka band typical dimensions of the microwave components are in the order of 10mm while for lower frequencies such as UHF band, the dimensions are in the order of 100mm. For this last case, there is the necessity of the reduction of the size of the component to save mass and minimize the footprint in the satellite transponders.
This work focuses on the filters that compose the input and output multiplexer (IMUX and OMUX) for the UHF band applications. In particular, the OMUX manage several hundred of watts of RF power, so, in this case, the filters has to be designed for high power, maintaining the small dimensions and low mass. In the thesis, prototypes waveguide filters loaded by single helical resonator were designed and manufactured. The prototypes were tested for high power in ESA-VSC High Power RF Laboratory in Valencia to verify their power handling characteristics.
For the IMUX, the thesis concentrates on the mass and dimensions saving due to the fact that, for UHF band, typical size of waveguide filters is higher than 100mm. the proposed solution is to use a dual mode concentric helices filters. The novelty of this kind of solution required the development of the mathematical background for the first dimensioning and analysis of filter characteristics. All the theory developed is reported in this work. The output of this procedure is the design and simulation of a very compact dual mode concentric helices filter (28.08mmx28.08mmx10.36mm). A prototype is produced using 3D additive manufacturing technique and the test campaign is in progress.
In conclusion, for the helical resonator filter in OMUX, the high power test confirms that this technology is promising for power handling purposes and gives some suggestions for future development such as changing the helix geometry and loading the helices with dielectrics. For the dual mode concentric helices filter, the hope is that the test campaign will confirm the designed results and after, the possible next step is to improve the design for high power applications
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Antenna technology for satellite communication
Full text linkSatellite-based systems have become indispensable for modern life, serving as platforms
for global communication, navigation, and Earth monitoring. Antennas play a central role
in ensuring the efficient functioning of these systems, both in the space and ground
segments.
In this thesis, technology advancements on the ground segments are achieved with the
design of two different unit cells, suitable for phased array applications. Such antennas
are fully compatible with a Printed Circuit Board (PCB) process, without the need of
further assembly. Specifications such as dual circular polarization, steering capabilities
up to ±40° and the frequency range from 17.7 to 20.2 GHz, make them an ideal candidate
for Satellite Communication On the Move (SOTM) Receivers (RX) terminals. 2x2 Arrays
have been prototyped and tested.
Two antennas have been presented in relation to the Space segment. An end-fire antenna
operating at S-band has been integrated within the solar module of a CubeSat by the use
of miniaturization techniques. Characterizations of Photovoltaic (PV) cells and space
qualified materials have been included in the same framework. The measurements of the
antenna on the chassis show good agreement with simulated results. Simulated results of
a second antenna operating at S- / X- band, exhibiting circular polarization over a wide
bandwidth, is secondly presented. The antenna is based on a multilayer PCB, where the
two different frequency bands are enabled by two separate radiating elements sharing the
same aperture.
A Near Field measurement system for phased arrays has also been developed within the
scope of the thesis, allowing a quick characterization of antennas, being able to extract
information such as radiation pattern, along with the amplitude and phase at each sampled
point of the scanned area
Theoretical and experimental satellite channel characterisation
Full text linkThe proliferation of very high throughput satellite systems offering Terabit/s of system
capacities, puts a large strain on the gateway feeder link requirements. This is leading to the
exploitation and use of communication link systems using higher frequencies for data
transmission, as it offers a larger bandwidth than the traditional Ka-band channels. Even with
the exploitation of the Q/V-band (40/50 GHz), the number of required gateways may be such
that the cost of the ground segment exceeds the cost of the satellite. The use of W-band (70/80
GHz) as an additional feeder link frequency band in future very high throughput satellite
systems could significantly reduce the cost of the ground segment. This would also offer an
opportunity for the user links to migrate to higher frequencies, improving their capacity and
helping into decongesting the current occupied channels. Atmospheric impairments, including
sky noise, play a major role towards the design of future satellite systems and their mitigation
techniques as higher bands magnify these impairments.
Within this thesis, an overview of the current communication satellite systems, propagation
campaign heritage and current atmospheric impairment models is shown. Furthermore, the
design and development of a geostationary beacon payload for propagation measurements
premiering W-band is shown. Ground receivers are also significant towards the collection of
propagation measurements. The design, development and implementation of such a receiver at
Ka-band is shown. Moreover, beacon measurements at Ka- and Q-band using the Aldo
Paraboni payload are processed to reflect excess and total atmospheric fading respectively.
Concurrent recordings of the sky noise enable radiometric measurements from the
implemented receiver terminals, which can enable sky monitoring. Calibration of the noise
channel at Q-band and validation of the fading with that from a beacon power measurement is
also shown.Heriot-Watt University DTP scholarship funded by the Engineering and Physical Sciences Research Council (EPSRC)
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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