| 11. |
- Larsson, Christer, et al.
(författare)
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Waveguide measurements of the permittivity and permeability at temperatures up to 1000 C
- 2010
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This paper describes a method to measure the permittivity and the permeability at temperatures from room temperature up to 1000 C using a single rectangular waveguide. The hardware design of the setup that can handle these temperatures and the procedure that is required to correct for the thermal expansion is developed. This includes the sample displacement, the displacement of the calibration reference planes, the thermal expansion of the waveguide and the gap between the sample and the waveguide wall. Measurements on Macor\textregistered and NiZn Ferrite samples are performed in order to evaluate the performance of the setup and the procedure that is used to determine the permittivity and permeability from the measured S-parameters.
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| 12. |
- Ludvig-Osipov, Andrei, et al.
(författare)
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Fundamental bounds on extraordinary transmission with experimental validation
- 2018
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents a study of extraordinary transmission (EoT) through arrays of sub-wavelength apertures. Fundamental limitations for this phenomenon are formulated as a sum rule, relating the transmission coefficient over a bandwidth to the static polarizability. The sum rule is rigorously derived for arbitrary periodic apertures in thin screens. By this sum rule we establish a physical bound on the bandwidth of EoT which is verified numerically for a number of aperture array designs. We utilize the sum rule to design and optimize sub-wavelength frequency selective surfaces with a bandwidth close to the physically attainable. Finally, we verify the sum rule and simulations by measurements of an array of horseshoe-shaped slots milled in aluminum foil.
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| 13. |
- Lundgren, Johan, et al.
(författare)
-
Design and Optimization of Dual Band Circular Polarization Selective Structures
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We present a non-resonant, dual band circular polarization selective structure (CPSS) for satellite communication applications in the K- and Ka-band. The structure consists of multiple layers of cascaded anisotropic sheets, with printed meander lines, separated by low permittivity spacers. It reflects right hand circular polarization and transmits left hand circular polarization in the lower frequency band. In the upper frequency band the opposite polarization selectivity is achieved. The theory of dual band circular polarization selectivity from cascaded anisotropic sheets is presented, and it is concluded that the separation between the frequency bands of operation is governed by the relative rotation between subsequent layers. An optimization routine for synthesizing dual band CPSSs from predefined design requirements is introduced, where a number of different optimization algorithms are utilized. A simulated design is presented which fulfills the strict design requirements of insertion loss and return loss less than 0.5dB, and axial ratio less than 0.78dB, in the frequency bands 17.7–20.2GHz and 27.5–30.0GHz. A prototype of the optimized design has been fabricated and characterized experimentally, both in transmissionandreflection,andgoodagreementisobservedbetweensimulated and experimental results. This type of structure is a potential candidate for implementation in dual band multiple spot beam systems utilizing frequency and polarization reuse schemes.
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| 14. |
- Lundgren, Johan, et al.
(författare)
-
Near-Field Measurement and Calibration Technique for RF EMF Exposure Assessment of mm-wave 5G Devices
- 2019
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Accurate and efficient measurement techniques are needed for exposure assessment of 5G portable devices---which are expected to utilize frequencies beyond 6 GHz---with respect to the radio frequency electromagnetic field exposure limits. Above 6 GHz, these limits are expressed in terms of the incident power density, thus requiring that the electromagnetic fields need to be evaluated with high precision in close vicinity to the device under test (DUT), i.e., in the near-field region of the radiating antenna. This work presents a cutting-edge near-field measurement technique suited for these needs. The technique---based on source reconstruction on a predefined surface representing the radiating aperture of the antenna---requires two sets of measurements; one of the DUT, and one of a small aperture. This second measurement functions as a calibration of both the measurement probe impact on the received signal, and the experimental setup in terms of the relative distance between the probe and the DUT. Results are presented for a 28 GHz and a 60 GHz antenna array; both developed for 5G applications. The computed power density agrees well with simulations at evaluation planes residing as close as one fifth of a wavelength away from the DUT.
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| 15. |
- Sjöberg, Daniel, et al.
(författare)
-
A Floquet-Bloch decomposition of Maxwell's equations, applied to homogenization
- 2003
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Using Bloch waves to represent the full solution of Maxwell’s equations in periodic media, we study the limit where the material’s period becomes much smaller than the wavelength. It is seen that for steady-state fields, only a few of the Bloch waves contribute to the full solution. Effective material parameters can be explicitly represented in terms of dyadic products of the mean values of the non-vanishing Bloch waves, providing a new means of homogenization. The representation is valid for an arbitrary wave vector in the first Brillouin zone.
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| 16. |
- Sjöberg, Daniel
(författare)
-
An inverse scattering problem in metallic waveguides filled with bianisotropic material
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents an analysis with the aim of characterizing an arbitrary linear, bianisotropic material inside a metallic waveguide. The result is that if the number of propagating modes are the same inside and outside the material under test, it is possible to determine the propagation constants of the modes inside the material by using scattering data from two samples with different lengths. Some information can also be obtained on the cross-sectional shape of the modes, but it remains an open question if this information can be used to characterize the material. The method is illustrated by numerical examples, determining the complex permittivity for lossy isotropic and anisotropic materials.
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| 17. |
- Sjöberg, Daniel
(författare)
-
Analysis of large finite periodic structures using infinite periodicity methods
- 2006
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We present a method for studying large finite periodic structures using soft- ware developed for infinite periodic structures. The method is based on the Floquet-Bloch transformation, which splits the spatial description into one microscopic spatial variable inside the unit cell, and one macroscopic wave vector describing the variations on a scale encompassing many unit cells. The resulting algorithm is iterative, and solves an infinite periodic problem in each step, where the sources have been filtered through a windowing function. The computational cost for the iterations is negligible compared to computing the impedance matrices for the infinite periodic problems, and it is shown that the algorithm converges if the periodic structure is large enough.
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| 18. |
- Sjöberg, Daniel
(författare)
-
Circuit analogs for stratified structures
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We present an overview of how circuit models can be used for wave propaga- tion in stratified structures. Homogeneous slabs are modeled as transmission lines, and thin sheets between the slabs are modeled as lumped elements. It is seen that electric material properties contribute as shunt elements, and mag- netic material properties contribute as series elements. When the sheets have periodic patterns, they can be represented with resonant circuits. The circuit models should be used as a starting point, to derive a basic, stable design, which can later be optimized using full wave simulations if necessary.
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| 19. |
- Sjöberg, Daniel
(författare)
-
Coherent effects in single scattering and random errors in antenna technology
- 2002
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Lack of knowledge prevents us from exactly calculating the behavior of electromagnetic fields. We study two extremes in this respect: scattering against randomly distributed particles (no idea of the position or orientation of the scatterers), and random errors in antenna technology (small deviations from what we think are the proper parameters). Random variables are used to model our lack of knowledge, and far field expressions are studied. Using the concept of characteristic functions from probability theory, results for arbitrary probability distributions are obtained. We explain an anomaly in the forward scattering direction in single scattering theory, present simple formulas for the directivity, side lobe level, and beam efficiency for a general array antenna with random errors, and a simple formula for the scattering coefficient from a general frequency selective structure with random errors.
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| 20. |
- Sjöberg, Daniel
(författare)
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Computation of radome reference cases using a rotationally symmetric full wave solver
- 2022
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We demonstrate how to compute radome reference cases for benchmarkingradome codes. Radomes are electrically large structures, and to facilitate thecomputations a rotationally symmetric structure is assumed. We show howto implement this in the commercial software Comsol Multiphysics, and howto extract the relevant data for comparison. Two example geometries areanalyzed: a spherical shell radome, and an ogive shaped radome. In eachcase, the radome is in the order of ten wavelengths, but it is still possible tosimulate on a regular laptop platform in about a minute. Using a platform withmore memory and spending more time to simulate more modes and synthesizethe results, reference cases for even larger radomes with realistic feeds can besimulated, which is suggested as a topic for future studies. Results for anogive shaped radome with a diameter of 30 and 50 wavelengths using a highlysymmetrical antenna are provided.
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