Pavel Hamouz

Bio: Pavel Hamouz is an academic researcher from Czech Technical University in Prague. The author has contributed to research in topics: Antenna (radio) & Fractal antenna. The author has an hindex of 6, co-authored 18 publications receiving 150 citations.

A Method for Tracking Characteristic Numbers and Vectors

Abstract: A new method for tracking characteristic numbers and vectors appearing in the Characteristic Mode Theory is presented in this paper. The challenge here is that the spectral decomposition of the moment impedance-matrix doesn't always produce well ordered eigenmodes. This issue is addressed particularly to flnite numerical accuracy and slight nonsymmetry of the frequency- dependent matrix. At speciflc frequencies, the decomposition problem might be ill-posed and non-uniquely deflned as well. Hence an advanced tracking procedure has been developed to deal with noisy modes, non-continuous behavior of eigenvalues, mode swapping etc. Proposed method has been successfully implemented into our in-house Characteristic Mode software tool for the design of microstrip patch antennas and tested for some interesting examples.

Implementation of the Theory of Characteristic Modes in MATLAB

Abstract: This paper describes the implementation of a complex MATLAB tool to calculate the characteristic modes and associated antenna parameters. The first code, written in FORTRAN, was presented in the early seventieths by Harrington and Mautz. Here, we utilize MATLAB, which is widely known and used in the antenna community these days. Because eigen-decomposition is time consuming, parallel and distributed computing is used. Thanks to the hundreds of built-in functions in MATLAB, computation of the surface currents from the eigenvectors obtained, as well as other important characteristics, are very easy and effective. The practical features are discussed with two examples.

Design of a Dual-Band Orthogonally Polarized L-Probe-Fed Fractal Patch Antenna Using Modal Methods

Abstract: Modal methods are used to effectively design a dual-band orthogonally polarized fractal patch antenna. This letter summarizes the workflow from generating a fractal motif through modal analysis to feeding design and full-wave analysis. As the antenna's feeding and matching structure, a dual L-probe was proposed to widen its bandwidth. The full-wave simulation is in very good agreement with the measurement. The motif size is 50 t 50 mm2, and the antenna operates at 1.25 and 2.1 GHz. The relative bandwidths are 4.18% and 11.4%, respectively.

Software tools for efficient generation, modelling and optimisation of fractal radiating structures

Abstract: This study describes in-house developed software tools for designing micro-strip patch fractal antennas. As the fractal geometry is quite complex, IFSMaker application was developed purposely for an easy definition and maintaining of planar fractal structures. In the next step, the authors use the cavity model technique for modal analysis of internal fields of the patch. This simplified model is reasonably fast, so that the optimisation loop may be employed in order to reduce the fundamental mode resonant frequency. This is accomplished with the EvalInFEM, PSOoptimizer and IFSLimiter applications. The theory of characteristic modes is then used to refine the results and finally the antenna is simulated with a full-wave CST simulator, built and measured.

Radiation efficiency and Q factor study of franklin antenna using the Theory of Characteristic Modes

Abstract: This paper presents the analysis of Franklin antenna by the Theory of Characteristic Modes. Modal radiation efficiencies are calculated and used to obtain the overall radiation efficiency. For each mode also the Q factor is calculated. On these results the influence of distance between arms of the folded part of antenna is demonstrated.

Design of Bandwidth-Enhanced and Multiband MIMO Antennas Using Characteristic Modes

Abstract: Recent work has shown that, with the help of the Theory of Characteristic Modes (TCM), minor modifications of the terminal chassis can facilitate the design of orthogonal multiple-input-multiple-output (MIMO) antennas with viable bandwidth at frequencies below 1 GHz. Herein, a new framework is proposed to further exploit TCM to enhance the performance of the orthogonal MIMO antennas. By correlating the characteristic currents and near fields of modes with high modal significance in a given frequency band, a single feed may be designed to excite multiple modes, leading to enlarged bandwidth. Similarly, the correlation of characteristic currents and near fields across different bands provides candidate modes that can be excited for multiband operation using a single feed. Moreover, the impedance matching of these modes can be improved by additional structural manipulation. As proof of concept, a dual-band (818-896 MHz, 1841-2067 MHz), dual-antenna prototype was designed on a 130 × 66-mm2 chassis for Long Term Evolution (LTE) operation. Full-wave simulation results were experimentally verified with a fabricated prototype.

A Method for the Evaluation of Radiation Q Based on Modal Approach

Abstract: A new formula for the evaluation of the modal radiation Q factor is derived. The total Q of selected structures is to be calculated from the set of eigenmodes with associated eigen-energies and eigen-powers. Thanks to the analytical expression of these quantities, the procedure is highly accurate, respecting arbitrary current densities flowing along the radiating device. The electric field integral equation, Delaunay triangulation, method of moments, Rao-Wilton-Glisson basis function and the theory of characteristic modes constitute the underlying theoretical background. In terms of the modal radiation Q, all necessary relations are presented and the essential points of implementation are discussed. Calculation of the modal energies and Q factors enable us to study the effect of the radiating shape separately to the feeding. This approach can be very helpful in antenna design. A few examples are given, including a thin-strip dipole, two coupled dipoles a bowtie antenna and an electrically small meander folded dipole. Results are compared with prior estimates and some observations are discussed. Good agreement is observed for different methods.

Characteristic Mode Analysis of a Class of Empirical Design Techniques for Probe-Fed, U-Slot Microstrip Patch Antennas

Abstract: In this paper, characteristic mode analysis (CMA) of three empirical design techniques for the probe-fed, symmetrically located, U-slot microstrip patch antenna, on a single-layer grounded substrate, is presented with supporting experimental data. The first method, resonant frequency (ResF), utilizes the existence of the four distinct ResFs, while the second one, dimensional invariance (DI), relies on the property of DI, for the design of the U-slot microstrip patch. In both these methods, the optimization of the probe location is necessary for further enhancement of the 10-dB return loss bandwidth. The third method, dimensionally invariant ResF, that optimally combines the features of the previous two is developed here and shown to yield better bandwidth performance with minimal or no probe location optimization, and hence is superior to the other two for rapid prototyping. CMA is carried out for critical parameters, such as substrate electrical thickness, slot width, probe radius, and feed location variations, to assess their dominant influence on the characteristics of the U-slot microstrip patch antenna.

Broadband Equivalent Circuit Models for Antenna Impedances and Fields Using Characteristic Modes

Abstract: An approach for modeling antenna impedances and radiation fields in terms of fundamental eigenmodes is presented. Our method utilizes the simple frequency behavior of the characteristic modes to develop fundamental building blocks that superimpose to create the total response. In this paper, we study the modes of a dipole, but the method may be applied to more complicated structures as the modes retain many of their characteristics. We show that the eigenmode-based approach results in a more accurate model for the same complexity compared to a typical series RLC resonator model. Higher order modes can be more accurately modeled with added circuit complexity, but we show that this may not always be necessary. Because this method is based on the physical behavior of the fundamental modes, it also accurately connects circuit models to radiation patterns and other field behavior. To demonstrate this, we show that far field patterns, gain, and beam width of a dipole can be accurately extrapolated over a decade of bandwidth using data at two frequency points.

Reconstruction of the Characteristic Modes on an Antenna Based on the Radiated Far Field

Abstract: In this paper, we present a method to reconstruct the modal current distribution on an antenna from the radiated far field and general knowledge about the modes involved. The method leads to good results if the radiation mechanism of the antenna can be approximated by the current distribution on a simplified structure. The current distribution of the simplified structure is decomposed into its characteristic modes and the related modal far field is calculated. Assuming that the far field of the actual antenna contains the same modes, their weighting coefficients are calculated by comparing the far field of the actual antenna to the modal far field of the simplified structure. It can be shown that the weighting coefficients of all significant modes can be reconstructed with good accuracy even for complex real structures such as mobile phones.