Analysis of Radiation Phenomena in a Wedge Ended Dielectric Slab Waveguide

Radiation phenomena observed in a wedge shape ended dielectric slab waveguide are analyzed using mode matching technique. The case of transverse electric polarization (TE) being parallel to dielectric slab waveguide is assumed. In order to describe the fields in the wedge region, a stack of dielectric plates is assumed and in each layer the fields are expanded in terms of the mixed spectrum of guided and radiated modes. A similar expansion is used in the constant thickness slab waveguide while in free space medium a continuous-radiation mode expansion is used. Then a mode matching approach is applied, incorporating the orthogonality properties of mixed spectrum modes, in order to compute the wave fields inside the dielectric slab waveguide and wedge medium. Mode matching is achieved by discretizing the continuous radiation mode spectrum leading into a numerically stable solution provided a sufficient large number of points are used to convert integrals into finite summations. Numerical computations are carried out for various wedge geometries and shapes including linear and exponential profiles.     

Millimeter wavelength radiation emission during dielectric aging

The current-voltage characteristic for a metal — thick insulator — metal structure has been investigated by applying high voltage impulses on a variety of industrial insulators. It appears that, in the high field regime (1MV/cm) S-type Negative Differential Conductance may occur, leading to self sustained conductivity oscillations possibly originating in field dependent carrier mobility. The phenomenon is associated with radiation emission during thermalization of hot electrons. Measurements have established the presence of millimeter wavelength radiation during prebreakdown and breakdown stages. The radiation emission intervals within a high-voltage pulse application and response have also been investigated.     

Advanced mode solver using an integral equation technique and entire domain plane wave basis functions

This work deals with the analysis and modelling of optical and millimetre-wave integrated circuits. The mathematical formulation is based on the method of integral equations, which are subsequently solved numerically by employing Galerkin's technique. The novel concept in this work lies with the development of a set of entire domain basis functions used to expand the unknown electric field in the waveguides' cross-sections. These functions have the simple form of plane waves and satisfy Maxwell's equations, therefore representing a proper expansion mechanism. As a demonstration of the developed computer code, configurations of single and coupled rectangular dielectric waveguides in a wide variety of open and closed substrate geometries are examined. The results presented, concerning the dispersion curves and the field patterns, give excellent agreement with published results of other methods. Furthermore, attenuation constants of lossy waveguides are numerically investigated. The main conclusion of the research presented in this contribution is that the entire domain plane wave basis functions (PWBFs) introduced provide a powerful tool for the unified modelling of a wide class of optical and millimetre-wave transmission lines. This revised version was published online in November 2006 with corrections to the Cover Date.     

A five port hybrid ring mixer design

The design, construction and measured experimental characteristics of a Ka-band balanced mixer based on microstrip technology, are presented. The mixer was realised using a configuration of a rat-race hybrid with five ports and two GaAs beam lead Schottky diodes. This type of balanced mixer is advantageous because it avoids via holes, airbridges and crossing transmission lines that deteriorate the performance of the circuit, and make its construction more difficult. The circuit was constructed in uniplanar microstrip configuration, so the circuits pattern was defined on one side of the substrate only, using thin film techniques. Performance characteristics of the mixer are presented as a function of RF and LO power, RF frequency and voltage bias of the Schottky diodes.     

Diffraction of guided waves by the end face of a dielectric slab waveguide terminated with a finite conductive strip

The diffraction of guided waves by the end face of a dielectric slab waveguide short circuited with a finite conductive strip is analyzed. An integral equation technique is employed to formulate the corresponding boundary problem. The unknown term in this integral equations is the electric field E(x) on the terminal plane of the waveguide. The homogeneous term is determined from the incident guided wave. A method of moments technique is employed to compute approximately the electric field E(x) by using Laguerre functions as describing and testing functions. The reflection coefficients of the guided waves are computed by using the approximate expression of the E(x) field. Numerical results are given for several guide and conductor plate dimensions.     

Gunn oscillator injection locking circuit at millimeter wave frequencies

Millimeter wave frequencies are proposed as carriers of microcell future mobile systems. High frequencies in the region of 60–62 Ghz are suggested. A serious difficulty in this context is the lack of sufficient gain in active devices. Both on receiver and transmitter units this difficulty is faced. Mixing, amplification, carrier recovery and modulation / demodulation subsytems are required to be operational at these higher frequencies. Presently the MMIC 's show also limited performance. In this report an alternative approach active processing technique is examined based on an injection locking in Gunn oscillator. A non-linear analysis is applied to determine the fundamental properties of injection locking in Gunn oscillator performance under the influence of an external signal. Details of waveguide action is taken into account by solving the corresponding boundary condition problem. Finally experimental results are presented for a 30GHz oscillator.     

Analysis of the coupling of two non-parallel dielectric rod waveguides

In this paper the coupling between two closely spaced single mode dielectric rod waveguides is investigated when the corresponding propagation axes are not in the same plane. An approximate analysis is presented by assuming only first order interaction between the guided waves. For a given incident HE₁₁ mode (in one of the rod waveguides) the coupled wave amplitudes are computed in the other waveguide for both propagation directions. Numerical results are presented for several coupling geometries.     

A Model for the Passive Infrared Detection of Naval Targets through FLIR: Model Description and Preliminary Results Applicable in the Eastern Mediterranean Sea

The maritime environment is a very unique system with respect to the environmental conditions that affect the transmission of electromagnetic energy, and especially the part of the spectrum that falls in the infrared band. This paper proposes an end-to-end model for the detection of ships at the environmental conditions of the eastern Mediterranean Sea, with the use of a Forward Looking Infrared (FLIR) system. The model: a) covers the issues regarding the detection and classification of simple model targets in various states of temperature conditions, by applying the Moser and O’Neill criteria, b) takes into account existing environmental conditions, by using data obtained from the Hellenic National Meteorological Service (HNMS) and the British Atmospheric Data Centre (BADC) for the years 2004–05, and c) uses the LOWTRAN 7 code for the calculation of the transmission through the maritime atmosphere. In the calculation of the atmospheric transmission, turbulence is taken into account through the introduction of a Modulation Transfer Function (MTF), to model the specific phenomenon. The FLIR system is also modeled as a series of MTF functions, with each one of those covering the characteristics of major subsystems of the detection device. Finally, the observer’s MTF is included in the model, and the probability of completing the specific task is calculated and presented for a range of observer to target distances. LOWTRAN computer model generated by the U.S. Air Force Geophysics Laboratory, is now in its 7th version and may be purchased in a PC version from the ONTAR Corporation, 9 Village Way North Andover 01845, Massachusetts. MATLAB and SIMULINK are registered trademarks of The Math Works Inc. 3 Apple Hill Drive, Natick 01760-2098 Massachusetts. S. E. Lagaras is currently pursuing the PhD degree in Electrical Engineering at the National Technical University of Athens.     

M/C2/c/K queuing model and optimization for a geriatric care center

Queuing systems with finite buffers are reasonable models for many manufacturing, telecommunication, and healthcare systems. Although some approximations exist, the exact analysis of multi‐server and finite‐buffer queues with general service time distribution is unknown. However, the phase‐type assumption for service time is a frequently used approach. Because the Cox distribution, a kind of phase‐type distribution, provides a good representation of data with great variability, it has a vast area of application in modeling service times. The research focus is twofold. First, a theoretical structure of a multi‐server and finite‐buffer queuing system in which the service time is modeled by the two‐phase Cox distribution is studied. It is focused on finding an efficient solution to the stationary probabilities using the matrix‐geometric method. It is shown that the stationary probability vector can be obtained with the matrix‐geometric method by using level‐dependent rate matrices, and the mean queue length is computed. Second, an empirical analysis of the model is presented. The proposed methodology is applied in a case study concerning the geriatric patients. Some numerical calculations and optimizations are performed by using geriatric data. Copyright © 2015 John Wiley & Sons, Ltd.