Broadband Radar Cross-Section Reduction Using AMC Technology Iriarte Galarregui, Juan Carlos; Tellechea Pereda, Amagoia; Martinez de Falcon, Jose Luis ...
IEEE transactions on antennas and propagation,
12/2013, Letnik:
61, Številka:
12
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This paper presents the design, fabrication, and characterization of a planar broadband chessboard structure to reduce the radar cross-section (RCS) of an object. The chessboard -like configuration ...is formed by combining two artificial magnetic conductor (AMC) cells. The bandwidth limitations intrinsic to AMC structures are overcome in this work by properly selecting the phase slope versus frequency of both AMC structures. A 180 ° phase difference has been obtained over more than 40% frequency bandwidth with a RCS reduction larger than 10 dB. The influence of the incidence angle in the working bandwidth has been performed. A good agreement between simulations and measurements is achieved.
A thin artificial magnetic conductor (AMC) structure is designed and breadboarded for radar cross-section (RCS) Reduction applications. The design presented in this paper shows the advantage of ...geometrical simplicity while simultaneously reducing the overall thickness (for the current design ). The design is very pragmatic and is based on a combination of AMC and perfect electric conductor (PEC) cells in a chessboard like configuration. An array of Sievenpiper's mushrooms constitutes the AMC part, while the PEC part is formed by full metallic patches. Around the operational frequency of the AMC-elements, the reflection of the AMC and PEC have opposite phase, so for any normal incident plane wave the reflections cancel out, thus reducing the RCS. The same applies to specular reflections for off-normal incidence angles. A simple basic model has been implemented in order to verify the behavior of this structure, while Ansoft-HFSS software has been used to provide a more thorough analysis. Both bistatic and monostatic measurements have been performed to validate the approach.
This paper reviews the different remote sensing techniques found in the literature to monitor plant water status, allowing farmers to control the irrigation management and to avoid unnecessary ...periods of water shortage and a needless waste of valuable water. The scope of this paper covers a broad range of 77 references published between the years 1981 and 2021 and collected from different search web sites, especially Scopus. Among them, 74 references are research papers and the remaining three are review papers. The different collected approaches have been categorized according to the part of the plant subjected to measurement, that is, soil (12.2%), canopy (33.8%), leaves (35.1%) or trunk (18.9%). In addition to a brief summary of each study, the main monitoring technologies have been analyzed in this review. Concerning the presentation of the data, different results have been obtained. According to the year of publication, the number of published papers has increased exponentially over time, mainly due to the technological development over the last decades. The most common sensor is the radiometer, which is employed in 15 papers (20.3%), followed by continuous-wave (CW) spectroscopy (12.2%), camera (10.8%) and THz time-domain spectroscopy (TDS) (10.8%). Excluding two studies, the minimum coefficient of determination (R2) obtained in the references of this review is 0.64. This indicates the high degree of correlation between the estimated and measured data for the different technologies and monitoring methods. The five most frequent water indicators of this study are: normalized difference vegetation index (NDVI) (12.2%), backscattering coefficients (10.8%), spectral reflectance (8.1%), reflection coefficient (8.1%) and dielectric constant (8.1%).
This paper presents the design of a modulated metasurface (MTS) antenna capable to provide both right-hand (RH) and left-hand (LH) circularly polarized (CP) boresight radiation at Ku-band (13.5 GHz). ...This antenna is based on the interaction of two cylindrical-wavefront surface wave (SW) modes of transverse electric (TE) and transverse magnetic (TM) types with a rotationally symmetric, anisotropic-modulated MTS placed on top of a grounded slab. A properly designed centered circular waveguide feed excites the two orthogonal (decoupled) SW modes and guarantees the balance of the power associated with each of them. By a proper selection of the anisotropy and modulation of the MTS pattern, the phase velocities of the two modes are synchronized, and leakage is generated in broadside direction with two orthogonal linear polarizations. When the circular waveguide is excited with two mutually orthogonal TE11 modes in phase-quadrature, an LHCP or RHCP antenna is obtained. This paper explains the feeding system and the MTS requirements that guarantee the balanced conditions of the TM/TE SWs and consequent generation of dual CP boresight radiation.
Today, telecommunication satellite horn antennas are required to be wideband mainly because of the additional bandwidth necessary to accommodate more transponders to increase the capacity of the new ...satellite services. In this aspect, horn antennas play a key role in the development of wider bandwidth services on board satellites because now-a-days, with recent advances in orthomode junctions and transducers, they are usually the bandwidth limiting component of a satellite antenna as often low crosspolar level is the toughest specification parameter. In this paper, the design guidelines for horn antennas that combine horizontal and vertical corrugations are explained, the method to prepare a preliminary profile for optimization is shown, and an example of a satellite feedhorn with severe requirements is presented.
This work addresses the lack of moisture content estimation models for food products in the millimeter-wave frequency range and showcases the potential of this range for designing compact, ...cost-effective, and in-line food moisture sensors. The moisture content estimation models developed in this study are intended for flour-based mixtures in the 67-110 GHz frequency range and are derived by means of a nondestructive and contactless monitoring system. To this aim, data obtained by continuous-wave (CW) vector network analyzer (VNA) spectroscopy is used to create two different models, both with a coefficient of determination (<inline-formula> <tex-math notation="LaTeX">R^{2} </tex-math></inline-formula>) of 0.97. One model is based on the theoretical response obtained by means of the Looyenga effective medium theory (EMT) model, while the other is based on measured data. Both models have been experimentally validated with root mean square error (RMSE) values of 0.4% and 0.35%, respectively. These small estimation errors show the potential of this frequency range to design compact, cost-effective, and in-line food moisture sensors. This research contributes to improving quality control and monitoring of moisture levels in flour-based mixtures.
The physical limitations on time-harmonic scattering processes are investigated on the basis of the optical theorem. Previously derived least upper bounds on the total scattering and absorption cross ...sections are obtained from it in a straightforward manner. In addition, it reveals a practical upper bound for the bistatic cross-section when evaluated in any direction. It is proved further that the maximum upper bound of the bistatic cross section occurs in the forward-scattering direction and that the corresponding upper bound for the backscattering direction is four times smaller than this maximum value. Metamaterial-inspired electrically small antennas and scattering particles that approach these upper bounds are demonstrated. These examples numerically validate the derived upper bounds, as well as illustrate the important physical principles underlying them.
The physiological and metabolic mechanisms behind the humic acid-mediated plant growth enhancement are discussed in detail. Experiments using cucumber (Cucumis sativus) plants show that the shoot ...growth enhancement caused by a structurally well-characterized humic acid with sedimentary origin is functionally associated with significant increases in abscisic acid (ABA) root concentration and root hydraulic conductivity. Complementary experiments involving a blocking agent of cell wall pores and water root transport (polyethylenglycol) show that increases in root hydraulic conductivity are essential in the shoot growth-promoting action of the model humic acid. Further experiments involving an inhibitor of ABA biosynthesis in root and shoot (fluridone) show that the humic acid-mediated enhancement of both root hydraulic conductivity and shoot growth depended on ABA signaling pathways. These experiments also show that a significant increase in the gene expression of the main root plasma membrane aquaporins is associated with the increase of root hydraulic conductivity caused by the model humic acid. Finally, experimental data suggest that all of these actions of model humic acid on root functionality, which are linked to its beneficial action on plant shoot growth, are likely related to the conformational structure of humic acid in solution and its interaction with the cell wall at the root surface.
The experimental validation of a Ku-band dual-circularly polarized (CP) broadside-beam metasurface (MTS) antenna is presented. A radially modulated anisotropic single-layer MTS has been synthesised ...employing subwavelength elliptical slotted metallic patches printed on top of a thin Arlon grounded substrate. In the structure, two decoupled phase-matched transverse magnetic and transverse electric surface waves (SWs) are excited, which interact with the modulated surface leading to a CP broadside radiation. Two different orthomode transducers have been designed to excite the SWs with orthogonal polarization and equal amplitude. The first feeding system is composed of a metallic stepped septum inside an air-filled square waveguide. A conical section is included to match the output port of the square waveguide with the terminal, dielectric filled circular waveguide. The second feed is much more compact and efficient, and it is composed of a circular waveguide completely filled by a dielectric. Depending on the input port excited on the feeds, two TE 11 modes are excited with ±90° phase shift, which determine the right-hand or left-hand sense of the broadside beam generated by the MTS. Manufacturing details of the MTS and excitations are given, and the measurements are compared with the simulation results. Finally, conclusions are drawn.
Superbackscattering Antenna Arrays Liberal, Inigo; Ederra, Inigo; Gonzalo, Ramon ...
IEEE transactions on antennas and propagation
63, Številka:
5
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This paper discusses the theory, design, and practical implementation of superbackscattering antenna arrays. In analogy with Uzkov's maximal directivity theorem, it is demonstrated that the maximal ...backscattering cross-section, normalized to the wavelength squared, of a linear array of N isotropic scatterers whose separation tends to zero is N 2 (N+1) 2 /(4π). This analytical result is validated via numerical optimization of the excitation coefficients, and the same procedure is utilized to assess the maximal backscattering of arrays of electric Hertzian dipoles (EHDs). It is found that electrically small arrays of two and three EHDs can enhance the backscattering by factors of 6.22 and 22.01, respectively, with respect to the maximum value generated by a single element. In addition, physical realizations of arrays featuring comparable enhancement factors can be straightforwardly designed by using a simple procedure inspired by Yagi-Uda antenna concepts. The practical implementations of such arrays based on copper wires and printed circuit technologies is also addressed.
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