On the Modal Superposition Lying under the MoM Matrix Equations

This paper shows an interesting sight on the correspondence between total current solution obtained by the Method of Moments and by the Characteristic modes respectively. Derivation is based on representation of a matrix in its spectral form. Detailed study of dipole antenna fed under different conditions is presented demonstrating that modal decomposition of currents offers a nice physical insight into behavior of radiating structures

Dual-band Loop Feed with Enhanced Performance

This paper is aimed on specific problems of electrically small and deep dish parabolic antennas. Since these antennas may suffer with low efficiency authors describe design and optimization of simple dual-band loop prime-focus feed achieving good efficiency for these antennas

L-System Tool for Generating Fractal Antenna Structures with Ability to Export into EM Simulators

An L-System (Lindenmayer system) is a scheme primarily developed in the area of the computer science for simulating the development of biological structures. It has also been found very useful for generating the geometry of various fractal antennas. A Matlab environment has been used for both implementing an in-plane L-systems algorithm and for creating appropriate files for widely used EM simulators like the IE3D and the CST Microwave Studio. Finally, the performance of the developed script is demonstrated on two fractal microstrip patch antennas

Microwave Antennas and Circuits Modeling Using Electromagnetic Field Simulator

Electromagnetic field simulators have become a widely used tool in a design process of microwave circuits and systems. A proper usage of electromagnetic (EM) field simulators allows substantial reduction of the design time providing reliable results. In such case the required parameters of the designed circuit can be reached even at the first manufactured prototype in spite of high complexity of the structure. However, EM simulation as a numerical process suffers from systematic and random errors similar to measurement using real equipment. Thus the setting of the EM-field simulator such as a frequency range, mesh properties, usage of PEC and PMC walls etc. has to be done with the highest attention and the simulation results have to be always verified using well-established techniques. The aim of the paper is to demonstrate the selected capability of EM-field simulators with a few examples of antenna and circuit modeling. Also an issue of reliability and simulation errors will be discussed

Optical Characterisation of MOVPE Grown Vertically Correlated InAs/GaAs Quantum Dots

Structures with self-organised InAs quantum dots in a GaAs matrix were grown by the low pressure metal-organic vapour phase epitaxy (LP-MOVPE) technique. Photoluminescence in combination with photomodulated reflectance spectroscopy were used as the main characterisation methods for the growth optimisation. Results show that photoreflectance spectroscopy is an excellent tool for characterisation of QD structures wetting layers (thickness and composition) and for identification of spacers in vertically stacked QDs structures.Comment: Submitted on behalf of TIMA Editions (http://irevues.inist.fr/tima-editions

An Introduction to the Source Concept for Antennas

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 and modal decomposition, operator’s inversion and current optimization, thus opening new, challenging possibilities for antenna design, analysis and synthesis

Evaluation of the Input Impedance and Impedance Quality Factor of a Dipole in Spatial and Spectral Domains

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 takes the opposite approach for the input impedance and is evaluated using a far-field pattern. This paper compares the induced EMF method and the spectral domain method. Furthermore, the quality factor of the dipole antenna, based on the impedance variation with frequency, is calculated for both methods. This study shows that the induced EMF method and the spectral domain method are in close agreement

Two-Element PIFA Array Structure for Polarization Diversity in UMTS Mobile Phones

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 double Quasi-Lumped Coupler able to provide a 360° phase difference between its two outputs. By properly choosing the DC bias of the double QuasiLumped Coupler, we can set a specific phase difference between the two PIFAs. In this way the two-element array is able to radiate different electromagnetic fields. Simulated and measured radiation patterns in the two main planes of the chassis are presented for different phase differences. It is especially revealed that the novel twoantenna structure is able to radiate vertically-polarized electric fields in the azimuthal plane of the phone and horizontally-polarized electric fields in the same plane when changing the phase shift between the antennas from 0° to 180°. Potential applications are polarization-diversity techniques and Specific Absorption Rate reduction for handsets