Pavel Hazdra

Czech Technical University in Prague | ČVUT · Department of Electromagnetic Field

We demonstrate design of fiber Fabry-Perot c avities based on large-core graded-index multimode fibers. Smallest full width at half maximum along with maximum transmission is reached for core diameters over 200 µ m core and reflectivity above 99%.

A compact three-element shared-aperture waveguide antenna array for the 24–28 GHz microwave-frequency band is presented as a proof-of-concept of an array with steerable directional beam suitable for 5G telecommunication systems. The array is intended for use in a microwave photonic link and is sufficiently steerable only with the progressively phas...

In this paper, design of a prime-focus feed for a deep reflector, Earth–Moon–Earth space communication system is described. The feed is based on a circular waveguide equipped with two chokes in order to minimise sidelobes and illuminate the deep dish with a high aperture efficiency of 70% . Based on sun noise measurements, it is estimated that the...

Characteristic mode (CM) theory has received a great deal of attention in the field of antenna engineering in recent years and is one of the best choices to gain thorough physical insight to explain antenna (generally scaterrer) operating mechanism. The antenna analysis, based on CM framework, provide a set of characteristic modes which are depende...

We present a hybrid radiofrequency and microwave photonic link at 25 GHz using the chromatic dispersion of an optical fiber to steer the beam of a three-element planar dipole-based phased antenna array (PAA). Our team has designed and developed an in-house built PAA, experimentally verified its parameters, and successfully demonstrated optically co...

There are many applications where the reception of global navigation satellite system signals is crucial. In such cases, the capability to reduce the interference (both unintentional or hostile) is critical. The proposed sector antenna offers a stable radiation pattern with no beam steering across the frequency band and good impedance matching. It...

With the emergence of the fifth generation and beyond mobile networks, both visible light communications (VLC) and radio frequency (RF) or millimetre wave (mmW) systems are expected to maintain the connectivity in various environments. In outdoor environments the link (VLC or RF) availability is paramount, which is affected by channel conditions. I...

The theory of superdirective antenna arrays was discussed. The procedure for finding the excitation currents of fixed-geometry arrays, which maximizes the directivity, termed as superdirectivity, for a given direction and polarization, was described. The procedure was based on the solution of an eigenvalue problem including the directivity and matr...

Course on Characteristic Modes: Theory and Applications Aimed at postgraduate research students and industrial engineers who want to acquire deep insight into the theory and applications of characteristic modes.

The concept of source currents of a radiating source can be employed to express its directivity in some particular cases analytically. For an antenna array, this concept can be extended to the concept of a generalized directivity based on self- and mutual radiation intensities, self- and mutual radiated powers and excitation currents of array eleme...

This paper describes the application of the theory of characteristic modes to excite a conducting cylinder representing the chassis of a rocket. Mode excitation is achieved by cutting H-shaped slots on the cylinder at specific locations where the maximum of modal current distribution occurs. The L-matching network is designed to match the impedance...

This article presents the design, simulations, and measured results of a dual-band coaxial feed for satellite communication in the 2.4 and 10.45 GHz bands. The feed is designed for communication with the geostationary satellite, Es'hail 2 (scheduled to be launched in late 2018), which will be equipped with a public amateur radio transponder coverin...

The theory of characteristic modes is used to analyze antenna arrays. In particular, to study arrays of thin-wire dipoles backed by an infinite electric ground plane. The proposed theory is based on an analytically prescribed current distribution on the dipoles where, when compared to the full Method of Moments solution, only a self- and mutual imp...

The concept of source currents of a radiating source can be employed to express directivity in some particular cases analytically. For an antenna array, this concept can be combined with concepts of mutual radiation intensity and the mutual power of array elements. Using these approaches, we treat the evaluation of the directivity for an elementary...

In classic antenna analysis, there exist several methods of calculating input impedance when the source distribution of an antenna is known. The well-known induced EMF method, based on spatially distributed currents, is typically applied for this purpose and, thereby, serves as a reference for this research. Conversely, the spectral domain method t...

Aspects of the theory of characteristic modes, based on their variational formulation, are presented and an explicit form of a related functional, involving only currents in a spatial domain, is derived. The new formulation leads to deeper insight into the modal behavior of radiating structures as demonstrated by a detailed analysis of three canoni...

The goal of this work is to design a dual-band, high efficiency feed for a reflector of the given size. To simplify feed design, configuration with a prime focus feed was prioritized.

Antenna parameters particularly relevant to electrically small antenna design are reviewed in this paper. Source current definitions are accentuated leading to the introduction of the source concept which advantageously utilize only spatially bounded quantities. The framework of the source concept incorporates powerful techniques such as structural...

Characteristic mode decomposition represents popular and powerful numerical method which offers deep physical insight into radiation mechanisms and an effective framework for small antenna design. The quality of resultant characteristic basis is strongly dependent on the properties of the impedance matrix but also on utilized factorization techniqu...

Aspects of the theory of characteristic modes, based on its variational formulation, are presented and an explicit form of a related functional, involving only currents in a spatial domain, is derived. The new formulation leads to deeper insight into the modal behavior of radiating structures as demonstrated by a detailed analysis of three canonica...

This study describes an analytical evaluation of the quality factor Q(Z) in a separable system in which the vector potential is known. The proposed method uses a potential definition of active and reactive power, implicitly avoiding infinite entire space integration and extraction of radiation energy. As a result, all the used quantities are finite...

A novel method for evaluation of the stored energy contained in a non-stationary electromagnetic field is presented in this paper. The method utilizes the classical definition of the radiated energy, which subtraction from the total electromagnetic energy is carried out in time domain during a transient state of the system under study.

This study describes an effective technique for calculating modal radiation efficiency calculation based on decomposition into characteristic modes. The key assumption is that the current distribution on the perfect electric conductor is almost the same as in the case of a very good conductor, for example, metals such as copper, aluminium and silve...

The functional relation between the fractional band-width and the quality factor of a radiating system is investigated in this note. Several widely used definitions of the quality factor are compared on two examples of RLC circuits that serve as a simplified model of a single resonant antenna tuned to its resonance. It is demonstrated that for a fi...

This paper describes an analytical evaluation of the measurable quality factor QZ of a system in which the vector potential is known. The method is presented on a canonical example of the currents flowing on a spherical shell, which leads to the analytical prescription for the lower bound of QZ.

New expressions for calculating of the quality factor QZ are presented. The resulting relations link QZ, based on the frequency change of the input impedance at the input port, with expressions based solely on the current distribution on a radiator. The derivation is based on electromagnetic potentials, automatically eliminating all divergent integ...

Closed-form equations are given for radiation quality factor of a thin-wire lambda/2 dipole above an infinite electric ground plane. Particular results of interest include a simple formula for a small separation between the dipole and the ground and for one dipole in free space.

This paper deals with practical aspects of mesh generation for the theory of characteristic modes. First, we describe a tool for surface-mesh generation in MATLAB. The tool is afterwards used for an analysis of relative convergence of modal results computed by an in-house modal analyzer in MATLAB. Different meshing scenarios are selected for a dipo...

This paper deals with practical aspects of mesh generation for the theory of characteristic modes. First, we describe a tool for surface-mesh generation in MATLAB. The tool is afterwards used for an analysis of relative convergence of modal results computed by an in-house modal analyzer in MATLAB. Different meshing scenarios are selected for a dipo...

This contribution describes our recent efforts in the research and design of special prime-focus feeds for reflector antennas intended for space communication using the Moon Bounce technique. Two contrasting structural designs are presented, illustrating the concept of multiband / multipolarization signal propagation. Besides space communication, t...

Radiation efficiency is an important parameter, especially for electrically small antennas. It can be computed directly from the method-of-moments impedance matrix, and also more generally by employing modal decomposition through characteristic modes. This advantageously enables us to study separately the effect of the radiating shape and the feedi...

This paper treats the old problem of defining and understanding stored electromagnetic energy. Three different concepts for evaluating the stored energy and the radiation Q factor of an antenna are introduced. The first two use time harmonic quantities and are based on the work of Vandenbosch and Yaghjian. The third concept is a time-domain method...

In an excellent paper [1], Prof. Vandenbosch derived rigorous equations for evaluating the radiated power and stored magnetic and electric energies explicit in terms of the source currents flowing on the radiating device. By integrating the radiated fields of an antenna it is easy to obtain the radiated power, but the evaluation of stored energies...

This paper describes an analytical evaluation of the radiation Q factor of any separable system in which the vector potential is known. The proposed method uses a potential definition of active and reactive power, implicitly avoiding infinite entire space integration and extraction of radiation energy. Furthermore, the proposed method uses solely m...

New expressions are derived to calculate the Q factor of a radiating device. The resulting relations link Q based on the frequency change of the input impedance at the input port (Qx, Qz) with expressions based solely on the current distribution on an radiating device. The question of which energies of a radiating system are observable is reviewed,...

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-decom...

Complex in-house tool for calculation of characteristic modes has been shortly introduced. Then some bottlenecks were identified and modified into parallel and distributive computing mode. One example has been completely adapted to GPU device. Preliminary tests show that practical parallel programing in Matlab is easy and very effective. Further de...

An active antenna based on a printed dipole directly connected to a differential amplifier is presented. The antenna covers the frequency band from 1.7-2.6GHz meaning the relative bandwidth of 41.86%. As the input impedance is mainly defined by the amplifier output, S11 < -10dB was obtained in the whole frequency range. By designing both the active...

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 alon...

We propose a novel, compact, prime-focus antenna feed for space communication. The feed requires full-wave simulator optimization for a given parabolic reflector and is designed to operate simultaneously on two bands, offering LHC/RHC polarizations for the 13 cm band and V/H polarizations for the 70 cm band. With performance results confirmed by me...

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 triang...

The chosen rectangular and fractal microstrip patch antennas above an infinite ground plane are analyzed by the Theory of characteristic modes. The resonant frequencies and radiation Q are evaluated. An method by G. Vandenbosch for rigorous evaluation of the radiation Q is employed for modal currents on a Rao-Wilton-Glisson (RWG) mesh. It is found...

The chosen rectangular and fractal microstrip patch antennas above an infinite ground plane are analyzed by the theory of characteristic modes. The resonant frequencies and radiation Q are evaluated. A novel method by Vandenbosch for rigorous evaluation of the radiation Q is employed for modal currents on a Rao-Wilton-Glisson (RWG) mesh. It is foun...

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...

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 intern...

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.

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 finite numerical accuracy and slight nonsymm...

In this paper we present an investigation into the radiation Q-factor of modal currents on a dipole antenna. First, we study the validity of the used thin-wire approximation with a reduced kernel. Different approaches of Q calculation are discussed and finally, the Q of coupled dipole antennas is evaluated. Good agreement between the assumed sinuso...

Modal methods are effectively used to design dual band fractal patch antenna. This contribution summarizes the workflow from generating fractal motif through choosing proper feeding to final antenna completion. As an antenna's feeding and matching structure, dual L-probe was proposed to widen its bandwidth. Moreover, the polarizations on operating...

In this letter, we present an investigation of the radia- tion -factors of two coupled thin dipole antennas with sinusoidal current distribution. The approach is based on novel rigorous equations for radiated power and stored energies recently derived by Vandenbosch. First, we study the validity of the used thin-wire approximation with a reduced ke...

In this contribution a novel configuration of high-directivity broadband antenna is presented. Its main operational principle is based on the so-called “short backfire” (SBF) concept, however, instead of conventional dipole, rectangular microstrip patch is used as feeder.

Paper describes usage of the IFS (Iterated Function System) fractals employed as a planar microstrip patch antennas. To generate the IFS fractals, versatile tool named IFSMaker has been evolved. Efficient design of patches will be shown. After fractal pre-design, one can start to optimize the IFS collage by using the PSO algorithm. This procedure i...

Two approaches, Virtual Reality Modeling Language (VRML) and graphic library OpenGL, are used for active stereoscopic vision of electromagnetic fields surrounding selected antenna or microwave elements. Input data are generated by analytical relations or acquired by electromagnetic field simulators and visualized in the form of vector fields and fi...

This paper shows the advantage of modal methods utilization in the area of microstrip patch antennas design. Namely, the Theory of Characteristic Modes (TCM) is developed starting from the Electric Field Integral Equation and formulating proper functional equation for stored and radiated power. Developed in-house TCM analyzer is presented and emplo...

In this paper, we demonstrate the possibility to strongly modify the radiated fields of a UMTS handset by using a phased two-element PIFA array. The structure is composed of a 100x40 mm2 metallic ground plane acting as the Printed Circuit Board (PCB) of the mobile phone. Two UMTS PIFAs are located at the top edge of this PCB. They are fed by a doub...

Radiation efficiency of two closely spaced metal sheets is studied by using the theory of characteristic modes (TCM). All modes of the structure in given frequency range are identified and their radiation efficiency is calculated. The overall radiation efficiency is computed as a combination of modal efficiencies. Radiation efficiency of the struct...

This paper describes an improved approach in an optimization of different UWB dipole antennas. The new procedure of tuning different optimization algorithms is presented. Fine-tuning of optimizing algorithm which is not elementary problem is discussed.