Pavel Hazdra

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

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.

The Measurable Q Factor and Observable Energies of Radiating Structures

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, and then the proposed Q factor as defined in this paper is physical. The derivation is based on potential theory rather than fields. This approach hence automatically eliminates all divergent integrals associated with electromagnetic energies in infinite space. The new formulas allow us to study the radiation Q factor for antennas without feeding (through e.g., characteristic modes) as well as fed by an arbitrary number of ports. The new technique can easily be implemented in any numerical software dealing with current densities. To present the merits of proposed technique, three canonical antennas are studied. Numerical examples show excellent agreement between the measurable QZ derived from input impedance and the new expressions.

Radiation

In this letter, we present an investigation of the radiation Q-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 kernel. Good agreement between the assumed sinusoidal current distribution and the real cylindrical antenna modeled with the full-wave method of moments (MoM) is observed. Then, radiation Q-factors are evaluated for half-wave side-by-side coupled dipole antennas with different feeding configurations. It is found that every such combination of studied coupled dipoles presents minimum Q for specific feeding arrangement and separation distance.

{Q}

The functional relation between the fractional bandwidth and the quality factor of a radiating system is investigated in this communication. Several widely used definitions of the quality factor are compared with 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 first-order system, only the quality factor based on differentiation of the input impedance has unique proportionality to the fractional bandwidth, whereas, e.g., the classical definition of the quality factor, i.e., the ratio of the stored energy to the lost energy per one cycle, is not uniquely proportional to the fractional bandwidth. In addition, it is shown that for higher order systems, the quality factor based on differentiation of the input impedance ceases to be uniquely related to the fractional bandwidth.

-Factors of Thin-Wire Dipole Arrangements

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 antennas 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 × 50 mm2, and the antenna operates at 1.25 and 2.1 GHz. The relative bandwidths are 4.18% and 11.4%, respectively.

On the Functional Relation Between Quality Factor and Fractional Bandwidth

A multibandband patch antenna design based on the Genetic Algorithm (GA) control of the pseudorandom generation of the patch topology in a grid of conductive cells is presented. GA operates on subdomains of the basic grid forming an original rectangular patch and creates meander edge notches to modify the radiator for excitation of higher order modes with the required radiation properties. Matlab/IE3D software environment has been used for the design of optimization loop. Results of 2.4/5.8 GHz dualband patch antenna design are presented. The principle of the multiband behavior is further explained via a description of vector surface current distribution of operational modes.

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

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.

Multiband patch antenna with perturbation elements generated by genetic algorithm

Abstract The implantation of 28Si+ ions at different substrate temperatures ranging from 120 to 820 K into shallow p+ n junction structures was used for the study of ion implantation defects in n-type Si. The stability of the created defects was investigated using isochronal furnace annealing in the temperature range 370–820 K. The results of DLTS measurements were compared with measured reverse I-V characteristics. The results show the dominant role of thermally stimulated dissociation and the production of secondary defects involving vacancies. These processes are significantly influenced both by implantation temperature and by the subsequent transient to room temperature.

Implementation of the Theory of Characteristic Modes in MATLAB

Electronic properties of radiation damage produced in 4H-SiC epilayer by proton and alpha particle irradiation were investigated and compared. 4H-SiC epilayers, which formed the low doped n-base of Schottky barrier power diodes, were irradiated to identical depth with 550 keV protons and 1.9 MeV alphas. Radiation defects were then characterized by capacitance deep-level transient spectroscopy and C-V measurements. Results show that both projectiles produce identical, strongly localized damage peaking at ion’s projected range. Radiation defects have a negligible effect on dynamic characteristic of irradiated 4H-SiC Schottky diodes, however acceptor character of introduced deep levels and their high introduction rates deteriorate diode’s ON-state resistance already at very low irradiation fluences.

The influence of implantation temperature and subsequent annealing on residual implantation defects in silicon

In this article, the effect of local radiation damage on the electrical characteristics of 1700 V 4H-SiC Merged-Pin Schottky (MPS) diode have been investigated. Radiation defects introduced by irradiation with 670 keV protons were placed into the low-doped n-type epi-layer and their influence on diode characteristics were characterized by capacitance DLTS, C-V profiling and I-V measurements. Simulation model accounting for the effect of proton irradiation was developed, calibrated and used for analysis of underlying effects and temperature dependencies. Results show that the forward voltage drop and breakdown voltage is insensitive to the position of the damage region when the defect peak is placed far away from the Schottky metal contact of the MPS diode. However, when the damage region approaches to the p+ regions, forward voltage drop degrades significantly. For fluences higher than 3.3×1010 cm - 2, the acceptor concentration in the peak region achieves donor doping level of the epi-layer and a sharp increase in the diode forward voltage drop is observed. Acceptor centers introduced by proton irradiation also slightly increase the breakdown voltage while decreasing the leakage current at voltages close to the MPS diode breakdown ( > 2000 V).