Nowadays synthetic aperture radar (SAR) and multiple-input-multiple-output (MIMO) antenna systems with the capability to radiate waves in more than one pattern and polarization are playing a key role ...in modern telecommunication and radar systems. This is possible with the use of antenna arrays as they offer advantages of high gain and beamforming capability, which can be utilized for controlling radiation pattern for electromagnetic (EM) interference immunity in wireless systems. However, with the growing demand for compact array antennas, the physical footprint of the arrays needs to be smaller and the consequent of this is severe degradation in the performance of the array resulting from strong mutual-coupling and crosstalk effects between adjacent radiating elements. This review presents a detailed systematic and theoretical study of various mutual-coupling suppression (decoupling) techniques with a strong focus on metamaterial (MTM) and metasurface (MTS) approaches. While the performance of systems employing antenna arrays can be enhanced by calibrating out the interferences digitally, however it is more efficient to apply decoupling techniques at the antenna itself. Previously various simple and cost-effective approaches have been demonstrated to effectively suppress unwanted mutual-coupling in arrays. Such techniques include the use of defected ground structure (DGS), parasitic or slot element, dielectric resonator antenna (DRA), complementary split-ring resonators (CSRR), decoupling networks, P.I.N or varactor diodes, electromagnetic bandgap (EBG) structures, etc. In this review, it is shown that the mutual-coupling reduction methods inspired By MTM and MTS concepts can provide a higher level of isolation between neighbouring radiating elements using easily realizable and cost-effective decoupling configurations that have negligible consequence on the array's characteristics such as bandwidth, gain and radiation efficiency, and physical footprint.
Multibeam by Metasurface Antennas Gonzalez-Ovejero, David; Minatti, Gabriele; Chattopadhyay, Goutam ...
IEEE transactions on antennas and propagation,
06/2017, Letnik:
65, Številka:
6
Journal Article
Recenzirano
We explore various possibilities for designing multibeam antennas using a single metasurface (MTS) aperture. Both single-source and multisource feeding schemes are considered. For the single-source ...case, two approaches are investigated. In the first one, the MTS aperture is divided into several angular sectors, each one devoted to the formation of a beam in a given direction. In the second approach, the whole aperture is shared by a superposition of individual modulations, which correspond to those required to obtain beams in the desired set of directions. It is shown that the latter solution provides beams with a higher gain. The configuration based on a multisource feeding scheme is also tailored by a superposition of modulation patterns. The main advantage of the latter approach is the possibility of having one independent beam at a time when each of the sources are active, as opposed to the single-source case where all the beams coexist at the same time. Closed-form expressions are provided for the MTS surface impedance in each of the proposed solutions. The design equations include appropriate amplitude tapering to improve the beam efficiency. Numerical results based on the method of moments are presented for validation.
This paper examines Badenian (middle Miocene) macroinvertebrates – corals and molluscs – from the Pécs-Danitzpuszta sand pit (Mecsek Mts, SW Hungary) in order to extend our knowledge on Miocene ...normal marine deposits of the Mecsek region. Corals occur reworked in the upper Miocene sand that was deposited in the brackish Lake Pannon, and presumably originate either from the middle Badenian Pécsszabolcs or the upper Badenian Rákos Member of the Lajta Formation. A total of seven taxa were identified. These taxa suggest subtropical conditions and a lack of coral reefs in the Badenian. Molluscs were found in situ in the upper Badenian Szilágy Clay Marl Member of the Baden Formation and the Rákos Member of the Lajta Formation. They dominantly consist of bivalves and represent benthic assemblages typical of the middle Miocene Central Paratethys.
Continuous urbanization, development of the economy, and the unrestrained exploitation and use of natural resources, the earth's ecosystems have been severely damaged by various types of frequently ...occurring natural and man-made disasters. Agricultural water and soil resources as a basic national strategic resources, a conflict is increasingly prominent between the available supply of and the increasing demand for these resources. Under such circumstances, the need for a quantitative diagnosis of the resilience of these types of has drawn increasing attention in China and abroad. A Technique for the Order of Preference by Similarity to an Ideal Solution (TOPSIS) evaluation model based on weighted Mahalanobis distance and gray relational analysis (MTS-GRA-TOPSIS) was proposed to evaluate the resilience of a combined regional agricultural water and soil resource (CRAWSR) system. For this purpose, a case study of the Jiansanjiang Administration of Agricultural Reclamation in Heilongjiang Province, China, was conducted. A total of 15 farms under its administration were used as evaluation objects, using information substitutability to screen out 12 indicators used to evaluate resilience. A MTS-GRA-TOPSIS model was used to evaluate the resilience rating of a CRAWSR system for 15 farms. The results show that the current resilience level of Jiansanjiang was rather low and that it should be improved. Specific countermeasures and suggestions were proposed, including increasing the utilization ratio of water and soil resources, returning farmland to forests, reducing groundwater use for agricultural irrigation, balancing the development of various industries, and improving the level of agricultural water conservation and mechanization. Verification of the rationality and reliability of the evaluation results obtained by the MTS-GRA-TOPSIS model was conducted which may be valuable for the formulation of related resource development strategies.
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•Fifteen farms in Jiansanjiang, Heilongjiang Province, China, were chosen to produce model resilience matrices•Weighted Mahalanobis distance and gray correlation analysis were used to improve the traditional TOPSIS evaluation model•The information alternative method screened out 12 indicators for resilience evaluation•Resilience of farms was rated at I, II, and III based on distribution and causes of resilience•Degree of discrimination theory was used to analyze the reliability of model results
A metasurface (MTS) lens array (MLA) fed by a phased array with less phase shifters (PSs) is proposed for compact low-cost beamsteering applications. By dividing a single-large-aperture lens into ...<inline-formula> <tex-math notation="LaTeX">N </tex-math></inline-formula> small-aperture lens elements with the focus-to-diameter ratio of a lens antenna unchanged, the overall thickness of the proposed antenna is reduced by <inline-formula> <tex-math notation="LaTeX">N </tex-math></inline-formula> times. The beamsteering is achieved in two steps. First, the main beam direction of MLA antenna is switched over a large angular step by shifting the feeding antennas beneath each lens element. Then, the switched beams are fine steered by a low-cost <inline-formula> <tex-math notation="LaTeX">N </tex-math></inline-formula>-element phased array. Theoretical analysis using array theory is performed to work out a general design method with discussion on the taper and spillover effect of feed-power pattern on the lens array. Based on the proposed method, a three-lens linear MLA fed by a phased array is designed to operate at 10 GHz. The proposed antenna achieves a 3 dB beamwidth coverage range of ±30° with a beam crossing level higher than −3 dB and a gain tolerance of 1.6 dB with a maximum gain of 19.1 dBi. The presented antenna can be used to achieve volumetric beamsteering performance directly. The proposed design features the merits of higher gain, lower cost, simpler feeding network, less PSs, and lower profile compared with conventional full phased arrays and single-aperture lens antennas.
The aim of this study is to know the influence of Two Stay-Two Stray (TSTS) technique on students’ reading comprehension. Reading is one of essential ways in building students’ knowledge. The ...researcher uses experimental research which uses two groups, those are experimental group and control group that consist of 46 students. The researcher elaborated the topics that were suitable for narrative text. Finding shows that the students who are taught by using conventional method, it can be proved from the average of speaking achievement. The students who are taught by using two-stay two-stray (76,43) have higher score than those taught by using direct method (68,21). Furthermore, based on the result of T-test, it is shown that sig.(0,002)<0,05. It means that the study indicated Two-stay Two-stray method is effective.
Blockchain can help edge IoT-enabled Maritime Transportation Systems (MTS) in solving its privacy and security problems. In this paper, a lightweight blockchain called LBlockchainE is designed for ...edge IoT-enabled MTS to guarantee the security of sensor data stored in an edge computing environment. To save the resources of edge servers on ship, a data placement strategy is proposed. To encourage edge servers to positively contribute to storing data generated by sensor devices, storage resource consumption is employed as an influencing parameter, and servers with abundant resources are selected for priority storage. The data placement strategy also takes care of the access delay between servers and selects the nodes with the least access and storage costs as the priority storage choice. LBlockchainE applies the low-energy-consumption characteristics of Proof of Stake to determine the ownership of bookkeeping rights through a small number of competitive calculations and the resources of the node. Experimental results indicate that compared with Ethereum, the consensus mechanism of LBlockchainE consumes less energy and occupies less storage space. On average, the new system uses 1.6% less time and consumes 78% less battery power compared with traditional blockchain systems. In comparison to the random storage, the best storage, and the optimal data storage strategies, the proposed strategy maintains the same message costs.
This article details the analysed results of the recent study on heleomyzid flies (Diptera: Heleomyzidae) that occurred in the caves of Kraków-Częstochowa Upland. Additionally, all accessible ...information about those flies from the Polish caves has been compiled. In effect, 23 species from seven genera were identified. Among these determined species, one was considered as troglobiont, eleven as eutroglophiles, nine as subtroglophiles, and two as trogloxenes. Dominant species were Scoliocentra brachypterna, Heleomyza captiosa and Eccoptomera pallescens. The highest number of species has currently been found in the Kraków-Częstochowa Upland.
Efficiency of Metasurface Antennas Minatti, Gabriele; Martini, Enrica; Maci, Stefano
IEEE transactions on antennas and propagation,
2017-April, 2017-4-00, Letnik:
65, Številka:
4
Journal Article
Recenzirano
Different types of efficiencies are introduced for metasurface (MTS) antennas based on single point-source excitation: 1) the feed efficiency ε feed is the power delivered by the feed to surface wave ...(SW) over the input power; 2) the tapering efficiency ε tap quantifies the deviation with respect to a uniform illumination; 3) the conversion efficiency ε conv defines the capability of the MTS to transform the SW power into leaky-wave power; and 4) the ohmic efficiency ε Ω accounts for the antenna losses. The product of all of these factors provides the overall efficiency of the antenna. New, quite general analytical formulas are suggested to estimate any individual efficiency. In particular, it is seen that ε feed can reach also 90% by using planar or quasiplanar circularly symmetric sources. It is also proven that the product ε conv ε tap cannot be larger than 58% for a uniform modulation; however, by using a nonuniform modulation, it can be increased to reach ε conv ε tap ≈ a/λ/(a/λ + 2), where a/λ is the antenna radius in free-space wavelengths. A new closedform formula for estimating the losses is given. In accordance with the prescription given here, one can reach 75% of global efficiency, including losses, until a radius of 20 wavelengths with commercially available substrates.
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