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The use of the spiral modes-electromagnetically related to the orbital momentum of the photons- at microwave frequencies for imaging purposes is studied and some preliminary numerical and experimental results for basic canonical geometries are presented and discussed
In order to obtain a high resolution inverse synthetic aperture radar image, the kinematic parameters of the target must be estimated in order to focus the image. Entropy metrics have been a popular technique to achieve good estimates. For subsurface radar imagery, the parameter needed for focusing purposes is the permittivity of the medium. Unlike airborne radar, subsurface back scattering occurs...
The importance of differential satellite positioning has been intensively questioned in recent times, especially after ceasing of the selective availability (SA) in standard GPS positioning service. Almost without exception, experimental studies have confirmed the improvement in satellite positioning given by differential corrections still exists. In this article, the improvement of LBS positioning...
On the basis that academics, engineers and operators understand the technical aspects of GNSS but rarely consider institutional issues, this paper describes some of the political considerations associated with GPS, Galileo and Loran. It concludes that whilst Galileo will be a technical success, its financial viability is questionable
This paper presents an overview and analysis of a class of airborne radar systems that usually are named weather radars though traditionally they are multifunctional avionics systems. Functional, methodical, and technological aspects of airborne weather radar are considered. Significant contribution to the content of the paper is taken from the results of research and design works fulfilled with direct...
An analysis of long-term fading properties of 4times4 CW MIMO channels is presented in this paper. The main focus has been on the long-term variability of MIMO channels in urban cellular environments, with emphasis on the decorrelation distance over mid range distances along the mobile trajectory for different base station antenna heights. A model that characterizes the decorrelation distance at different...
The complexity in the evaluation of the radiation quality factor Q of small antenna lies in the calculation of the stored energy. Previous authors proposed several analytical expressions for simple antennas to obtain the Q which is of practical importance because of its relationship to the antenna bandwidth. This paper presents a simple method to calculate the Q using FDTD giving us accurate results...
The paper presents investigations into multiple input multiple output wireless communication systems, which are carried out from an electromagnetic perspective. The first part of the paper focuses on signal propagation models, which can be used for determining the MIMO system capacity or its performance when various space-time coding schemes are applied. Two types of models are considered. In the...
The paper describes an approach to teaching the digital TV technology at the Faculty of Electrical Engineering and Communication, Brno University of Technology (FEEC BTU). The main emphasis is given to description of laboratory education of practical exercises in an unique laboratory of digital TV technology. Sophisticated technical equipment of this laboratory, measuring workplaces and examples of...
The paper describes the possibilities of modern emotion recognition which can be also helpful for speaker verification systems. A proper choice of feature vectors is one of the most important tasks. Two important vectors have been chosen as the background for efficient system of emotion recognition: fundamental speaking frequency and time-energy distribution vector. The proposed method permits to...
This paper presents the design of novel conformal fractal loop antennas proposed for the rapidly developing RF identification (RFID) wireless technology. Two antennas, based on Koch and Hilbert fractal geometries, are designed and optimized for 0.953 GHz RFID band. Key design requirement has been maximizing the antenna gain and directivity that results in increasing the read range of RFID system....
In the present work a novel Gaussian beam antenna is presented. The antenna is based on a half of an open resonator structure with a metallic grid placed at the section of the resonating structure. A simple equivalent circuit to describe the antenna input impedance is derived. Results from full wave simulations will be presented and discussed
We demonstrate a novel, low-profile, compact antenna consisting of a rectangular dielectric resonator and a quasi-planar surface mounted horn. The proposed structure shows a gain of 8.5 dBi at 6.0 GHz, giving a 4.9 dB increase compared to the standard dielectric-resonator antenna (DRA) without a surface mounted horn. Total height of the fabricated structure is only 0.172 lambda0, or 8.61 mm at 6.0...
The principles of operation and equivalent circuit of a microstrip miniloop antenna are presented. Two possible uses hereof namely as a wake up and a communication antenna are discussed. An appraisal of performance parameters, the attainable effective height for the former and the path loss for the latter follows. To circumvent the difficulties involved in directly measuring these quantities, an alternative...
The purpose of this paper is evaluation of radiation pattern interaction and input impedance coupling between two adjacent ground station antennas in different frequency bands. Thus the antennas were simulated in different distances. Then a reliable relative distance for proper radiation performance, with acceptable characteristics degradation (in communication link), was defined. NEC-pro Software...
An efficient method for the optimization of multiband terminal antennas has been developed, and tested on a tree band antenna covering the GSM, DCS and UMTS bands. The method is based on genetic algorithms, refined with a procedure based on decision trees which allows preserving links between variables in the search domain. The electromagnetic simulation tool used in this procedure is a dedicated...
This paper presents the work carried out in the ACE Network of Excellence regarding technologies for small terminal antennas. The aim is to review the state of the art in this field, and identify the newest trends in antenna design for personal communications devices
This paper gives an overview of the different measurement procedures that have been developed the last five years for characterizing small antennas and complete wireless terminals that are intended for use in environments with Rayleigh fading. The measurements make use of a reverberation chamber which in principle is a resonant cavity, and they include measurements of the classical radiation efficiency...
A grounded dielectric slab covered with a metal strip grating in the form of an infinite linear array of microstrip lines constitutes a canonical structure for the realization of a variety of microwave components and antennas, including artificially hard and soft surfaces. In this contribution we review some recent theoretical and numerical results concerning surface and leaky waves supported by this...
The performance of thin-disk transducers made of PZT-5A ceramic using acoustic matching and air-backing is described using simplified 1-D model and experimental results. Several ultrasound transducers have been designed for studying influence of high power ultrasound energy on tissue. PZT-5A ceramic has been used as active element with thickness approximately lambda/2, depending on working frequency...
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