1,721,258 research outputs found
Parametric Design of Parabolic Reflector Antenna with Switchable Cosecant-Squared Pattern
No full textThis paper deals with the parametric analysis of multi-beam parabolic reflector antennas employed for air and coastal surveillance radars. Novel designs are introduced to obtain electronically switchable cosecant-squared and pencil beam radiation patterns, without making any changes on the reflector geometry. The analytical regularization method (ARM) is used as a fast and accurate way to solve the problem of E-polarized wave diffraction by parabolic shaped perfectly electrical conductive (PEC) cylindrical reflector with finite thickness. The numerical procedure is initially verified by the analytical and numerical methods, and the calculated radiation characteristics are presented for the proposed antenna configurations
Indirect microwave holographic imaging of concealed ordnance for airport security imaging systems
Full text linkIn this paper, indirect microwave holographic imaging of concealed ordnance is demonstrated. The proposed imaging technique differs from conventional microwave imaging methods in that it does not require the direct measurement of the complex field scattered from the imaged object but mathematically recovers it from intensity-only scalar microwave measurements. This brings the advantages of simplifying the hardware implementation and significantly reducing the cost of the imaging system. In order to demonstrate the ability of the proposed technique to reconstruct good quality images of concealed ordnance, indirect microwave holographic imaging of a metallic gun concealed in a pouch is carried out for airport security imaging applications. It is demonstrated that good resolution amplitude and phase images of concealed objects can be recovered when back-propagation is applied
Direct-fed reduced size patch antenna using array of cSRR in the ground plane
No full textIn this article, a novel design for a reduced size microstrip patch antenna is presented and discussed. It is demonstrated that by embedding an array of complimentary split ring resonators in the ground plane, size reduction of 11.2%, together with an increased bandwidth of 202.6% can be achieved
Indirect Microwave Holography and Through Wall Imaging
Full text linkIn this paper, a review of indirect microwave holography for through-wall imaging is presented. Indirect microwave holography is an imaging technique, enabling the complex object scattered fields (amplitude and phase) to be mathematically recovered from intensity-only, scalar microwave measurements. By removing the requirement to use vector measurement equipment to directly measure the complex fields, indirect microwave holography significantly reduces the cost of the imaging system and simplifies the hardware implementation. The application of a back-propagation algorithm enables the reconstructed amplitude and phase images to be obtained at the plane of the concealed object. In order to demonstrate the validity of the reviewed approach, experimental work is carried out on a metallic gun concealed under a 5 cm thick plywood wall and it is demonstrated that the indirect microwave holographic through wall imaging can produce good resolution amplitude and phase images when back-propagation is applied. Through wall imaging of a concealed dielectric box representing non-metallic ordnance is also performed to demonstrate the ability of the technique to reconstruct through-wall images of concealed dielectric objects. An investigation of the resolution characteristics of the system suggests diffraction limited resolution can be achieved
Integration of Microwave Antennas with Solar PV for Multiband and Wideband Mobile, WLAN and WiMAX Applications
No full textThe primary goal of this research is to investigate the existing photovoltaic antenna integration techniques and develop a new solar antenna integration topology in order to address the drawbacks of these techniques.
With the increasing demands for low-profile antennas and a growing move towards the microgeneration of electricity, primarily by photovoltaics, photovoltaic antennas are of
increasing importance with a growing amount of research in this area being developed. At present there are a number of designs for photovoltaic antennas which could be divided
into two distinct categories. The first type is the use of solar cells as an RF ground plane, whilst the second type involves the use of solar cells as an RF radiating element. Both techniques bring significant challenges if they are to be widely adopted. Considering the first technique, using a solar cell as an RF ground plane introduces an optical shading problem, which significantly reduces the solar efficiency of the solar antennas using this integration topology. To this end, meshing the RF radiating element is investigated in this thesis to achieve optical transparency at the expense of increasing the cost and complexity
of the fabrication process of photovoltaic antennas. Conversely, using a solar cell as an RF radiating element limits the ability to modify the resonance response using traditional RF bandwidth enhancement techniques due to the fact that solar cells need to have a homogeneous structure to achieve optimum solar performance.
In order to address these challenges, a third solar antenna integration topology is proposed in this thesis. This method is based upon the use of solar cells as an RF stacked parasitic patch element suspended above the conventional RF radiating element of the integrated antennas. This integration topology enables the integrated solar cells to achieve an optimum solar efficiency due to their suspended position eliminating the shading problem. It also enables the RF radiating element to be modified to excite multiple TMmn propagation modes to achieve enhanced resonance response for multiband and wideband applications. This new topology has been further developed and applied to design a dual-polarised photovoltaic antenna for polarisation diverse communication systems, which has been extended to produce a photovoltaic array antenna for beam steering applications.
This thesis addresses a major knowledge gap in the field of photovoltaic antennas. As a result of this, greater understanding of the design procedures of photovoltaic antennas and associated trade-offs from such designs is developed. Using this knowledge, novel designs that overcome the associated problems of current photovoltaic antennas are presented
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
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Solar cell stacked dual-polarised patch antenna for 5.8 GHz band WiMAX network
No full textA novel combination of a two-port slant +/- 45 degrees dual-polarised microstrip patch antenna with a polycrystalline silicon (poly-Si) solar cell operating as an RF stacked parasitic patch element is presented and discussed for 5.8 GHz band polarisation diverse multifunctional WiMAX systems. To minimise the effect of the solar operation on the RF antenna performance, an effective DC/RF isolation circuit consisting of quarter-wavelength microstrip transmission lines is demonstrated. The proposed solar patch provides identical E-plane and H-plane far-field radiation patterns for +45 degrees and -45 degrees polarisations with a gain of 7.8 dBi and operates at the frequency band of 5.66-5.91 GHz
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