Modelling cascaded cylindrical metasurfaces using sheet impedances and a transmission matrix formulation

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163795/1/mia2bf00746.pd

Construction of Green's functions of parallel plates with periodic texture with application to gap waveguides - A plane wave spectral domain approach

This study presents Green's functions of parallel-plate structures, where one plate has a smooth conducting surface and the other an artificial surface realised by a one-dimensional or two-dimensional periodic metamaterial-type texture. The purpose of the periodic texture is to provide cut-off of the lowest order parallel-plate modes, thereby forcing electromagnetic energy to follow conducting ridges or strips, that is, to form a gap waveguide as recently introduced. The Green's functions are constructed by using the appropriate homogenised ideal or asymptotic boundary conditions in the plane-wave spectral domain, thereby avoiding the complexity of the Floquet-mode expansions. In the special case of a single ridge or strip, an additional numerical search for propagation constants is needed and performed in order to satisfy the boundary condition on the considered ridge or strip in the spatial domain. The results reveal the dispersion characteristics of the quasi-transverse electromagnetic modes that propagate along the ridges or strips, including their lower and upper cut-off frequencies, as well as the theoretical decay of the modal field in the transverse cut-off direction. This lateral decay shows values of 50-100 dB per wavelength for realisable geometries, indicating that the gap waveguide modes are extremely confined. The analytical formulas for the location of the stopband of the lowest order parallel-plate modes obtained by small-argument approximation of the dispersion equation are also shown. To verify the proposed analysis approach, the results are compared with the results obtained with a general electromagnetic solver showing very good agreement

Analytical modeling and experimental verification of coupling between transmission lines in gap-waveguides

Modeling of gap-waveguide structures with single and multiple transmission lines is performed using spectral domain Green's functions approach. The approach is extended using even/odd mode analysis in order to also estimate the crosstalk levels between neighboring transmission lines. The results of this analysis are compared with the results of a commercial electromagnetic solver and with the measured results

Caracterización de la impedancia de superficie para el cálculo del acoplo mutuo en un cilindro circular conductor cubierto por una dieléctrico multicapa

A novel formulation for the surface impedance characterization is introduced for the canonical problem of surface fields on a perfect electric conductor (PEC) circular cylinder with a dielectric coating due to a electric current source using the Uniform Theory of Diffraction (UTD) with an Impedance Boundary Condition (IBC). The approach is based on a TE/TM assumption of the surface fields from the original problem. Where this surface impedance fails, an optimization is performed to minimize the error in the SD Green's function between the original problem and the equivalent one with the IBC. This new approach requires small changes in the available UTD based solution with IBC to include the geodesic ray angle and length dependence in the surface impedance formulas. This asymptotic method, accurate for large separations between source and observer points, in combination with spectral domain (SD) Green's functions for multidielectric coatings leads to a new hybrid SD-UTD with IBC to calculate mutual coupling among microstrip patches on a multilayer dielectric-coated PEC circular cylinder. Results are compared with the eigenfunction solution in SD, where a very good agreement is met

Surface impedance for electromagnetic fields over a dielectric-coated circular cylinder

For small or medium size conformal array antennas in terms of the wave length, modal solutions in spectral domain for mutual coupling analysis are convenient for canonical shapes such as circular cylinder [1] or sphere [2], but as the antenna dimensions increase a large number of terms are necessary. For large structures the uniform theory of diffraction (UTD) is commonly used to solve this problem for canonical and arbitrarily convex shaped perfect electric conductor (PEC) surfaces [3]. A UTD solution for mutual coupling on an impedance cylinder has been introduced in [4], [5] but using a constant surface impedance

An Asymptotic Solution for Surface Fields on a Dielectric-Coated Circular Cylinder with an Effective Impedance Boundary Condition.

Reverberation chambers are well known for providing a random-like electric field distribution. Detection of directivity or gain thereof requires an adequate procedure and smart post-processing. In this paper, a new method is proposed for estimating the directivity of radiating devices in a reverberation chamber (RC). The method is based on the Rician K-factor whose estimation in an RC benefits from recent improvements. Directivity estimation relies on the accurate determination of the K-factor with respect to a reference antenna. Good agreement is reported with measurements carried out in near-field anechoic chamber (AC) and using a near-field to far-field transformation

Surface Impedance Characterization for Mutual Coupling Calculation of Patches on a Dielectric-Coated PEC Circular Cylinder

A novel formulation for the surface impedance characterization is introduced for the canonical problem of surface fields on a perfect electric conductor (PEC) circular cylinder with a dielectric coating due to a electric current source using the Uniform Theory of Diffraction (UTD) with an Impedance Boundary Condition (IBC). The approach is based on a TE/TM assumption of the surface fields from the original problem. Where this surface impedance fails, an optimization is performed to minimize the error in the SD Green?s function between the original problem and the equivalent one with the IBC. This asymptotic method, accurate for large separations between source and observer points, in combination with spectral domain (SD) Green?s functions for multidielectric coatings leads to a new hybrid SD-UTD with IBC to calculate mutual coupling among microstrip patches on a multilayer dielectric-coated PEC circular cylinder. Results are compared with the eigenfunction solution in SD, where a very good agreement is met

Glide-symmetric holey structures applied to waveguide technology: Design considerations

This article belongs to the Special Issue Antennas and PropagationRecently, there has been an increased interest in exploring periodic structures with higher symmetry due to various possibilities of utilizing them in novel electromagnetic applications. The aim of this paper is to discuss design issues related to the implementation of holey glide-symmetric periodic structures in waveguide-based components. In particular, one can implement periodic structures with glide symmetry in one or two directions, which we differentiate as 1D and 2D glide symmetry, respectively. The key differences in the dispersion and bandgap properties of these two realizations are presented and design guidelines are indicated, with special care devoted to practical issues. Focusing on the design of gap waveguide-based components, we demonstrate using simulated and measured results that in practice it is often sufficient to use 1D glide symmetry, which is also simpler to mechanically realize, and if larger attenuation of lateral waves is needed, a diagonally directed 2D glide symmetric structure should be implemented. Finally, an analysis of realistic holes with conical endings is performed using a developed effective hole depth method, which combined with the presented analysis and results can serve as a valuable tool in the process of designing novel electrically-large waveguide-based components.This work was supported by the Croatian Science Foundation (HRZZ) under the projects IP-2018-01-9753 and IP-2019-04-1064, by the Spanish Government under the projects PID2019-107688RB-C21 and TEC2016-79700-C2-R, and by the European COST Action CA18223-SYMAT

Periodic Structures With Higher Symmetries: Their Applications in Electromagnetic Devices

Higher symmetries frequently amaze human beings because of the illusions and incredible landscapes such symmetries can produce. For example, imagine the unearthly pictures of the Dutch graphic artist M.C. Escher. He made use of glide symmetry and reflection to produce unbelievable transitions and transformations of objects and beings, as illustrated in Figure 1(a). However, the history of higher symmetries started much earlier. Escher was partially inspired by the Moorish tessellations in the Alhambra in Granada, Spain, such as the ones pictured in Figure 1(b).The authors would like to thank Oskar Zetterström for providing the photo in Figure 5(a). This work was partly funded by the Spanish Government, under grant TEC2016-79700-C2-2-R; the French Government, under National Research Agency (ANR) Modeling and De - sign of Holey Metasurfaces project grant ANR JCJC 2016, ANR-16-CE24-0030; the Vinnova project High-5 (grant 2018-01522), under the Strategic Program on Smart Electronic Systems; the Stiftelsen Åforsk project Higher-Symmetric Materials for 5G Communications (grant 18-302); and COST Action SyMat CA18223, supported by COST (European Cooperation in Science and Technology), www.cost.eu

Cost-Effective Gap Waveguide Technology Based on Glide-Symmetric Holey EBG Structures

We present a novel electromagnetic bandgap (EBG) structure, which can be used to manufacture low-cost waveguiding structures at high frequencies. The unit cell of the proposed EBG consists of glide-symmetric holes in parallel plate waveguide. Using this unit cell in groove gap waveguide technology has a number of advantages over pin-type EBG at high frequencies, such as acquiring higher accuracy because of larger periodicity as well as an easier and cheaper manufacturing process. The performance of the proposed waveguiding structure is demonstrated using both a straight and a double 90 degrees bent lines through simulation and measurement.This work was supported in part by the Swedish STINT Postdoctoral Transition Grants Programme under Grant PT2014-5813, in part by the Spanish Government under Project TEC2013-44019-R and Project TEC2016-79700-C2-2-R, and in part by the Madrid Regional Government under Project S2013/ICE-3000