Divitha Seetharamdoo

Phase-compensated metasurface for a conformal microwave antenna

The in-phase radiation from a conformal metamaterial surface is numerically and experimentally reported. The LC-resonant metasurface is composed of a simultaneously capacitive and an inductive grid constituted by copper strips printed on both sides of a dielectric board. The metasurface is designed to fit a curved surface by modifying its local phase. The latter phase-compensated metasurface is used as a reflector in a conformal Fabry-Perot resonant cavity designed to operate at microwave frequencies. Far-field measurements performed on a fabricated prototype allow showing the good performances of such a phase-compensated metasurface in restoring in-phase emissions from the conformal surface and producing a directive emission in the desired direction.

Novel electromagnetic field measuring instrument with real-time visualization

Nowadays, a wide variety of terminals are proposed to nomadic users. Generally, these terminals provide wireless communication operating at frequencies between one and a few GHz. For technical reasons, including multiple access to the communication channel and battery autonomy, these terminals transmit only during very short periods i.e. transmission bursts. For a direct observation of certain characteristics of the transmitted signals radiated by such terminals, only a few measurement setups exist. This paper proposes such a novel real-time 3D electromagnetic field measurement instrument with direct visualization. The prototype used for validation is based on an array of probes regularly attached on a non conductive rigid loop which is put into fast rotation around the terminal under test.

Thin Conformal Directive Fabry–Pérot Cavity Antenna

A compensated-phase partially reflective surface (PRS) is proposed in this letter. It is used together with a metallic ground plane to form a low-profile Fabry-Pérot (FP) cavity antenna conformed on a cylindrical surface. A microstrip patch antenna is embedded inside the cavity to act as the primary feed. To validate the proposed PRS, an antenna is designed to operate at the 5.7-GHz Wi-Fi frequency. The subwavelength FP cavity with a fixed overall thickness of λ0/10 (where λ0 is the free-space operating wavelength) is fabricated and measured. The impact of compensating the PRS phase is analyzed.

Evaluating the potential shielding properties of periodic metamaterial slabs

Metamaterials can prove to be good candidates for shields in EMC applications where weight reduction is a challenge. Indeed metamaterial slabs can provide the same reflective properties as conventional metallic screens but with a lower density and reduced weight. Another advantage is that they can be tailored to exhibit required frequency-selective properties. However, their performance in terms of shielding performance has yet to be evaluated. In this paper, a method to evaluate the shielding performance of a metamaterial slab consisting of arbitrary-shaped metallic inclusions in a dielectric host is proposed. The specific case of periodic metamaterials will be considered for both resonant and non-resonant inclusions in the effective-homogeneity limit.

Novel Miniature Extremely-Wide-Band Antenna With Stable Radiation Pattern for Spectrum Sensing Applications

A planar extremely-wide-band antenna is designed and simulated. Measurements are presented. The proposed antenna is a printed elliptical slotted monopole with a triangular ground plane, fed by a semi-ring trident arm followed by a tapered CPW line. The frequencies covered for a VSWR ≤ 2 extend from 0.67 GHz to 12 GHz with stable radiation patterns to ensure minimal pulse distortion. This is guaranteed by multimodal analysis of the radiating current on the radiator using the theory of characteristic modes. Numerical and experimental results are in good agreement. This novel miniaturized antenna ( 0.15 ×0.07λl, where λl corresponds to the wavelength of the lowest matched frequency) is a good candidate for wide-band spectrum sensing in the TV white space band in the context of cognitive radio applications.

Electromagnetic modeling and definition of antenna specifications and positions for radio system deployment in confined environments

In this paper, the definition of antenna specifications for radio system deployment as well as a methodology to integrate them in confined environments is presented. Modal-based analysis and optimization techniques for mode-weight adjustments are used to determine correct co-excitation of the propagating modes and fulfill the desired specifications.

Analysis of Miniature Metamaterial and Magnetodielectric Arbitrary-Shaped Patch Antennas Using Characteristic Modes: Evaluation of the

Evaluating the Q factor of antennas using metamaterial substrates is a challenge and requires new analysis techniques. This challenge is even more important for arbitrary-shaped antennas. In this paper, we address the problem of analysis and evaluation of metamaterial-based antennas through the use of characteristic modes. We propose a new expression for the total Q factor, which is independent of the excitation and based on the eigenvalues of the structure. The proposed expression is used to compute the Q factor of an arbitrary-shaped resonant antenna and shows excellent agreement with other expressions in the literature such as the ones proposed by Yaghjian, Best, and Gustafsson. The approach is then used to analyze small patch antennas over metamaterial and magnetodielectric substrates. It is shown using the defined Q factor expression that a magnetic substrate offers a significant bandwidth enlargement for the first active modes, and a dielectric substrate presents the opposite effect. This agrees with other works based on analytical approaches. Furthermore, we demonstrate that a reactive impedance metamaterial substrate presents identical modal significances that are identical to a conventional magnetodielectric substrate when associated with a patch antenna. This analysis is suitable for structures presenting noncanonical geometries and arbitrary shapes such as metamaterial inclusions.

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In this letter, new metrics are proposed to provide physical insight into the behavior of metamaterial-based structures by means of the theory of characteristic modes. A relationship between the first eigenmode and an expression of the polarizability is proposed for a split-ring resonator. It thus allows us to describe a link between the artificial magnetic response of a split-ring resonator and modal characteristics. Using the new metrics proposed, a reactive impedance substrate based on metal-dielectric metamaterial excited by a parallel magnetic field is shown to exhibit artificial magnetism. These metrics are shown to propose good agreement with other analytical and numerical methods. This analysis should be useful when such metal-dielectric metamaterial structures are associated to radiating elements like antennas since it could be performed in the near-field region, unlike common approaches based on plane wave and far-field assumptions.

Factor

This paper presents a procedure to implement the concept of surface impedance boundary condition (SIBC) for lossy dielectrics in time domain. The SIBC formulation, validation, and results are obtained with a time domain numerical method, namely the transmission-line matrix (TLM). The formulation of surface impedance in frequency domain is converted to the time domain using a rational approximation followed by a bilinear transform with a canonical representation in the state-space. This surface impedance formulation has been implemented in TLM. Simulations show that the proposed model is valid for interfaces between air and a lossy dielectric, and arbitrary conductivity

New Metrics for Artificial Magnetism From Metal-Dielectric Metamaterial Based on the Theory of Characteristic Modes

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