1,721,066 research outputs found
Study on isolation and radiation behaviours of a 34×34 array-antennas based on SIW and metasurface properties for applications in terahertz band over 125–300 GHz
No full textThis paper describes the feasibility of conceptual design of a 34 x 34 array antenna for operation at Terahertz over a frequency range of 125-300 GHz for S-11 <= -10dB, which corresponds a fractional bandwidth of 82.35%. Each radiation element constituting the array consists of a square patch of dimensions of 2 x 2 mm(2) that are excited by a matched microstrip line. Each patch is isolated from each other with metallic via-holes, which are implemented based on the substrate integrated waveguide (SIW) technique. This technique is shown to effectively reduce mutual coupling between adjacent radiation elements that can otherwise undermine the arrays radiation gain and pattern. Periphery of each patch is embedded with circular dielectric slots, which are created based on the metasurface concept to enhance the radiation gain and efficiency performances. With the proposed approaches (1) the mutual coupling is suppressed on average by 25dB over its operating frequency range, and (2) the effective aperture area of the array antenna is extended without increase in the array's physical dimensions. Radiation gain and efficiency of the proposed array antenna over its operating range vary from 7.51 dBi to 40.08 dBi, and from 70.51% to 90.11%, respectively. Improvement in gain and efficiency of approximately 60% and 30%, respectively, is achieved with the inclusion of the metasurafce slots. The proposed 34 x 34 array antenna is proper candidate for applications in Terahertz wireless communication systems
Miniaturised planar-patch antenna based on metamaterial L-shaped unit-cells for broadband portable microwave devices and multiband wireless communication systems
No full textThis study describes the design of a metamaterial planar antenna for multi-octave band operation. The metamaterial unit-cell comprises L-shaped slit which is etched inside a rectangular patch with a grounded inductive spiral. The slit essentially behaves as a series left-handed capacitance and the spiral as a shunt left-handed inductance. The antenna was modelled and optimised for impedance bandwidth, gain and efficiency performance using commercial three-dimensional full-wave electromagnetic simulation tools. The antenna has a measured impedance bandwidth of 6.02GHz for S-11<-10dB. This corresponds to a fractional bandwidth of 172.49%, which is higher than multiband planar antennas reported to date. The antenna has a maximum gain and efficiency performance of 3.7dBi and 73%, respectively, at 3.25GHz. The physical footprint of the antenna is comparable to other wideband planar antennas reported to date. The overall size of the antenna is 0.037(0)x0.027(0)x0.002(0) and 0.25(0)x0.18(0)x0.017(0), where (0) is free-space wavelength at 0.48 and 3.25GHz, respectively
Compact Single-Layer Traveling-Wave Antenna DesignUsing Metamaterial Transmission Lines
No full textThis paper presents a single-layer traveling-wave antenna (TWA) that is based on composite right/left-handed (CRLH)-metamaterial (MTM) transmission line (TL) structure, which is implemented by using a combination of interdigital capacitors and dual-spiral inductive slots. By embedding dual-spiral inductive slots inside the CRLH MTM-TL results in a compact TWA. Dimensions of the proposed CRLH MTM-TL TWA is 21.5 x 30.0 mm(2) or 0.372 lambda(0) x 0.520 lambda(0) at 5.2 GHz (center frequency). The fabricated TWA operates over 1.8-8.6 GHz with a fractional bandwidth greater than 120%, and it exhibits a peak gain and radiation efficiency of 4.2 dBi and 81%, respectively, at 5 GHz. By avoiding the use of lumped components, via-holes or defected ground structures, the proposed TWA design is economic for mass production as well as easy to integrate with wireless communication systems
A Technique to Suppress Mutual Coupling in Densely Packed Antenna Arrays Using Metamaterial Supersubstrate
No full textA simple and practical technique for reducing the mutual coupling between neighbouring antennas is presented for application in densely packed antenna arrays. This is achieved by locating between the radiation elements a smaller patch with metamaterial decoupling structure (MTM-DS). In this case the radiating elements are circular patches and the MTM-DS is constructed from a hexagonal slit resonator. The consequence of implementing the MTM-DS patch is significant reduction in mutual coupling between adjacent radiating patches by 60%, improvement in impedance match by 200% and substantial increase in the antenna's fractional bandwidth by 369%. Since the ground plane is unaltered the front-to-back ratio is unaffected too. The proposed technique is easily realizable and can be used effectively in beam scanning applications
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
An innovative and simple impedance matching network using stacks of metasurface sheets to suppress the mismatch between antennas and RF front-end transceivers circuits
No full textCompact and low-profile on-chip antenna using underside electromagnetic coupling mechanism for terahertz front-end transceivers
Get PDFThe results presented in this paper show that by employing a combination of metasurface and substrate integrated waveguide (SIW) technologies, we can realize a compact and low-profile antenna that overcomes the drawbacks of narrow-bandwidth and low-radiation properties encountered by terahertz antennas on-chip (AoC). In addition, an effective RF cross-shaped feed structure is used to excite the antenna from its underside by coupling, electromagnetically, RF energy through the multi-layered antenna structure. The feed mechanism facilitates integration with the integrated circuits. The proposed antenna is constructed from five stacked layers, comprising metal-silicon-metal-silicon-metal. The dimensions of the AoC are 1 x 1 x 0.265 mm(3). The AoC is shown to have an impedance match, radiation gain and efficiency of <= -15 dB, 8.5 dBi and 67.5%, respectively, over a frequency range of 0.20-0.22 THz. The results show that the proposed AoC design is viable for terahertz front-end applications
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
- …
