Showing papers by "Zvonimir Sipus published in 2005"

Waveguide miniaturization using uniaxial negative permeability metamaterial

Abstract: A rectangular waveguide filled with anisotropic uniaxial metamaterial with transversal negative effective permeability is investigated both theoretically and experimentally. It is shown that such a waveguide supports propagation of the backward wave below the cutoff frequency, thus, it can be considered as a dual of the ordinary waveguide. The transversal dimension of this waveguide can be arbitrarily smaller than half of a wavelength in the filling material, provided that the transversal permeability is negative. This peculiar behavior may be used for fabrication of miniaturized rectangular waveguides. Several experimental miniaturized waveguides loaded with double ring resonators in 7 GHz frequency band have been designed, fabricated and tested. The measured results revealed backward-wave passband located below the cutoff frequency. Furthermore, it was experimentally shown that the increase of the physical length of the waveguide caused the decrease of the electrical length. This is a direct proof of the backward-wave propagation since the phase of the backward wave increases along the waveguide.

Analysis and measurements of conformal patch array antennas on multilayer circular cylinder

Abstract: In this paper, we present a method of moments (MoM) program to analyze different configurations of arrays of cylindrical-rectangular patches. The patches can be located inside or on the surface of a multilayer circular-cylindrical structure and can be arbitrarily rotated. The antenna structure is rigorously taken into account by using proper Green's functions, and the array is analyzed by using an element-by-element approach. The elements of the MoM matrix are calculated in the spectral domain, and special attention is given to their numerical treatment when analyzing cylindrical antennas with large radii. A laboratory model is built to test different configurations of patches and to validate calculated results. The agreement between measurements and calculations is very good.

Numerical and Experimental Investigation of Field Distribution in Waveguide Filled with Anisotropic Single Negative Metamaterial

Abstract: A field distribution in a rectangular waveguide filled with anisotropic single-negative (SNG) metamaterial is analyzed theoretically, numerically and experimentally. A highly simplified scenario with ideal lossless, continuous (either mu-negative (MNG) or epsilon-negative (ENG)) filling material is used in theoretical analysis. The results show that distributions of magnitudes of E and H fields are similar to the associated distributions in ordinary waveguide (filled with double-positive (DPS) material) that operates above cut-off frequency. However, the crucial difference, responsible for recently demonstrated peculiar phenomenon of backward wave propagation below cut-off is a pattern of field lines of either H field (a case with MNG filling) or E field (a case with ENG filling). Numerical approach that dealt with realistic structures (double-ring-resonator-based MNG metamaterial and thin-wire-based ENG metamaterial) confirmed existence of backward-wave propagation. Two experimental waveguides filled with double-ring resonators (an MNG filling) and thin wires (an ENG filling) were successfully designed, manufactured and tested in 8 GHz band. The backward-wave propagation was verified by measurement of a phase distribution along a waveguide with the help of a small E field probe

Waveguide Miniaturization Using Uniaxial Negative

Abstract: A rectangular waveguide filled with anisotropic uni- axial metamaterial with transversal negative effective permeability is investigated both theoretically and experimentally. It is shown that such a waveguide supports propagation of the backward wave below the cutoff frequency, thus, it can be considered as a dual of the ordinary waveguide. The transversal dimension of this waveguide can be arbitrarily smaller than half of a wavelength in the filling material, provided that the transversal permeability is negative. This peculiar behavior may be used for fabrication of miniaturized rectangular waveguides. Several experimental miniaturized waveguides loaded with double ring resonators in 7 GHz frequency band have been designed, fabricated and tested. The measured results revealed backward-wave passband located below the cutoff frequency. Furthermore, it was experimentally shown that the increase of the physical length of the waveguide caused the decrease of the electrical length. This is a direct proof of the backward-wave propagation since the phase of the backward wave increases along the waveguide.

Moment method analysis of rectangular microstrip antennas on spherical structures

Abstract: The interest for spherical arrays is based on their possibility to direct single or multiple beams through a complete hemisphere. Arrays of rectangular microstrip patches embedded in a multilayer spherical structure are analyzed using the spectral-domain approach and the moment method. In order to avoid numerical problems a modified vector-Legendre transformation and normalized Legendre polynomials are defined and applied to the solution procedure. The influence of structure radius on the input impedance and the resonant frequency of the spherical rectangular microstrip patch antenna are studied. A laboratory model is built to test different configurations of patches and to validate the calculated results.

Moment Method Analysis of a Spherical FSS in Free Space

Abstract: A program for analysing spherical patch antennas by means of the moment method in spectral domain is adapted to the analysis of frequency-selective surfaces (FSS). In the new model, a plane wave is impinging on a dipole array lying in free space. The plane wave is expanded into a series of spherical harmonics while the Green's functions of the spherical structure are found with the aid of the GIDMULT algorithm. The developed code is verified against a commercial MoM simulator (FEKOtrade). Frequency selective behaviour of one dipole array is investigated in terms of varying radius of curvature and array size and compared to the results of a planar FSS built with the elements of the same dimensions. Results for the monostatic and bistatic radar cross section (RCS) of the array are presented

Performance Analysis of Spherical Stacked-Patch Antennas

Abstract: The interest for spherical arrays is based on their possibility to direct single or multiple beams through complete hemisphere. In this article, circular stacked-patch antennas embedded in a multilayer spherical structure are analyzed using the spectral-domain approach and the moment method. The influence of structure radius on input impedance, mutual coupling and radiation pattern is investigated. It is shown that the properties the most affected by the variation of structure radius are the resonant frequency and the mutual coupling level. The results confirm the importance of rigorous analysis of curved patch antennas. Furthermore, a laboratory model is built to validate the developed program. The agreement between measured and calculated results is good

Study of High-Efficiency Corrugated Hard-Horn Antennas Using Classical Approaches: Hard Circular Waveguide Mode, Phase Factor, and Aperture Integration

Abstract: In this paper, a classical-type approach is used to analyze the hard horn antenna. The quasi-TEM mode in the longitudinally corrugated cylindrical waveguide is found by using the homogenized asymptotic boundary conditions. The finite horn length is accounted for by including a phase factor in the waveguide-aperture fields, and the radiation patterns are finally obtained by aperture integration. The bandwidth is found to be much wider than previously anticipated with respect to low cross-polarization. Also, an advanced mode-matching code has been used for verification of the aperture field and the radiation patterns obtained with the much faster classical model.

Spectral domain analysis of dipole coupling over different electromagnetic band gap structures

Abstract: The paper aims to determine the Green's functions for different realizations of electromagnetic band-gap (EBG) structures and to calculate the coupling between two dipoles placed above these EBG structures. The applied method avoids the complexity of the Floquet mode approach and the limitations of the surface wave approach. For each considered structure, some sort of asymptotic boundary conditions are derived in which the periodicity of the structure is assumed to be negligible compared to the wavelength. The goal (and the test) of the applied method is to determine properties of each considered EBG structure. Therefore, all important physical phenomena should be taken into account. In order to be able to analyze multilayer structures, the analysis model has been implemented in the G1DMULT algorithm that calculates the spectral domain Green's functions of planar, circular-cylindrical and spherical multilayer structures (Sipus, Z. et al., App. Computational Electromagnetics Soc. J., vol.13, p.243-54, 1998).

Radiation Pattern of Arrays Mounted on Conical Structures

Abstract: The paper discusses the method for determining radiation pattern of an array mounted on a conical structure. Two types of antenna elements are considered: waveguide openings and microstrip patch antennas. The analysis method is based on the modal representation of the EM field, i.e. the solution procedure takes advantage of representing the fields as a sum of spherical harmonics with unknown amplitudes. By introducing normalized associate Legendre functions, together with pre-calculation of terms that depend only on conical geometry, an accurate and efficient program has been developed. A comparison was made between the calculated radiation pattern and the measurements of different waveguide and patch array configurations. All the considered results showed high accuracy of the developed method

Mutual coupling analysis of cylindrical waveguide arrays using hybrid SD-UTD method

Abstract: The shape of a conformal antenna is mainly determined by radiation and scanning requirements, or by considerations, other than electromagnetic, such as aerodynamic/hydrodynamic shape demands. One way of analyzing conformal arrays is to use the separation of variables. This method can be generalized to include an arbitrary number of dielectric layers. The structures under consideration have one property in common: they are homogeneous in two dimensions and vary in the third. For each spectral component of the source, the excited electromagnetic field in the two directions for which the structure is homogeneous has the same harmonic variation as the source. Therefore, the original three-dimensional problem is transformed into a spectrum of simpler one-dimensional problems. Since each one-dimensional problem is solved in the spectral domain, this approach is called the spectral domain (SD) method. If the structure to be analyzed has a general, non-canonical shape (i.e. the structure is neither circular-cylindrical nor spherical), one can approximate the structure shape locally as cylindrical or spherical, or one can use some approximate method like the uniform theory of diffraction (UTD) (Pathak, P.H. et al., 1981). Although there are benefits in applying UTD, it is an approximate method and requires extra precautions before applying it. For example, it is very hard to analyze structures covered with a dielectric, especially if the dielectric is multilayered (Persson, P. and Rojas, R.G., 2003). The paper examines a hybrid SD-UTD analysis method.

Accuracy of Hybrid Spectral Domain-UTD Method

Abstract: The analysis of an array of waveguide openings placed at a conformal ground plane and covered with a multilayer radome is approached using the moment method in spectral domain. The main disadvantage of the spectral domain method lies in numerical problems appearing when the structures with large radii are analyzed. We have developed a hybrid spectral domain-UTD method in order to overcome these difficulties and to obtain a fast and accurate analysis method that keeps all advantages of the spectral domain technique. The accuracy of the proposed hybrid method is discussed in the paper. It is shown that the method is not sensitive to the thickness and permittivity of the dielectric layer nearby to the source, which is used in the UTD asymptotic solution

Analysis of Conformal Stacked-Patch Arrays

Abstract: : 1) Formulation of the problem. 2) Modeling single circular stacked-patch antenna on spherical structures. 3) Modeling patch arrays on spherical structures. 4) Development of experimental model.