George A. Kyriacou

Bio: George A. Kyriacou is an academic researcher from Democritus University of Thrace. The author has contributed to research in topics: Finite element method & Microstrip antenna. The author has an hindex of 13, co-authored 140 publications receiving 735 citations.

Development of an Adaptive and a Switched Beam Smart Antenna System for Wireless Communications

Abstract: This study concentrates on the development of two separate Smart Antenna Systems for the 2.45 GHz ISM band. Both systems incorporate the RF-beamforming method. Each system has the ability to point the beam in a three dimensional space, both in azimuth and in elevation direction. The Switched Beam System adopts a passive network-based beamforming approach, using 2-D Butler matrix topologies. The Adaptive System utilizes the vector modulator method, but only in the azimuth direction, increasing beam-steering accuracy, whereas introducing complexity and cost. The system design is presented for both cases, along with some module design and testing examples. A comparison of the two systems will be also discussed.

A mode-matching technique for the study of circular and coaxial waveguide discontinuities based on closed-form coupling integrals

Abstract: A mode-matching scheme for the analysis of concentric circular and/or coaxial waveguide step discontinuities is proposed in this paper. An analytical evaluation of the involved coupling integrals for all possible discontinuities formed by any combination of a circular and a coaxial waveguide is performed. The originality mainly concerns the multimode excitation and scattering at a circular-to-coaxial waveguide step junction. Numerical results for a number of applications are compared against those of other techniques and/or measurements and are found to be in good agreement.

Design of True Time Delay Millimeter Wave Beamformers for 5G Multibeam Phased Arrays

Abstract: Millimeter wave (mm-Wave) technology is likely the key enabler of 5G and early 6G wireless systems. The high throughput, high capacity, and low latency that can be achieved, when mm-Waves are utilized, makes them the most promising backhaul as well as fronthaul solutions for the communication between small cells and base stations or between base stations and the gateway. Depending on the channel properties different communication systems (e.g., beamforming and MIMO) can accordingly offer the best solution. In this work, our goal is to design millimeter wave beamformers for switched beam phased arrays as hybrid beamforming stages. Specifically, three different analog beamforming techniques for the frequency range of 27–33 GHz are presented. First, a novel compact multilayer Blass matrix is proposed. Second, a modified dummy-ports free, highly efficient Rotman lens is introduced. Finally, a three-layer true-time-delay tree topology inspired by microwave photonics is presented.

A Cost-Effective Wideband Switched Beam Antenna System for a Small Cell Base Station

Abstract: A wideband switched beam antenna array system operating from 2 to 5 GHz is presented. It is comprised of a $4\times 1$ Vivaldi antenna elements and a $4\times 4$ Butler matrix beamformer driven by a digitally controlled double-pole four-throw RF switch. The Butler matrix is implemented on a multilayer structure, using 90° hybrid couplers and 45° phase shifters. For the design of the coupler and phase shifter, we propose a unified methodology applied, but not limited, to elliptically shaped geometries. The multilayer realization enables us to avoid microstrip crossing and supports wideband operation of the beamforming network. To realize the Butler matrix, we introduce a step-by-step and stage-by-stage design methodology that enables accurate balance of the output weights at the antenna ports to achieve a stable beamforming performance. In this paper, we use a Vivaldi antenna element in a linear four-element array, since such element supports wideband and wide-scan angle operation. A soft condition in the form of corrugations is implemented around the periphery of the array, in order to reduce the edge effects. This technique improved the gain, the sidelobes, and helped to obtain back radiation suppression. Finally, impedance loading was also utilized in the two edge elements of the array to improve the active impedance. The proposed system of the Butler matrix in conjunction with the constructed array can be utilized as a common RF front end in a wideband air interface for a small cell 5G application and beyond as it is capable to simultaneously cover all the commercial bands from 2 to 5 GHz.

Photonic crystals

Abstract: The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

Rfid Handbook Fundamentals And Applications In Contactless Smart Cards And Identification

Abstract: Thank you for reading rfid handbook fundamentals and applications in contactless smart cards and identification. As you may know, people have search numerous times for their chosen novels like this rfid handbook fundamentals and applications in contactless smart cards and identification, but end up in malicious downloads. Rather than reading a good book with a cup of coffee in the afternoon, instead they juggled with some malicious bugs inside their laptop.

Gain enhancement methods for printed circuit antennas

Abstract: Resonance conditions for a substrate-superstrate printed antenna geometry which allow for large antenna gain are presented. Asymptotic formulas for gain, beamwidth, and bandwidth are given, and the bandwidth limitation of the method is discussed. The method is extended to produce narrow patterns about the horizon, and directive patterns at two different angles.

Small microstrip patch antenna

Abstract: As stated in Chapter 1, one of the many advantages of microstrip patch technology over its competitors is its low profile and hence small volume. Another key advantage of this printed antenna is the relative ease in which it can be connected to the feed network, as was highlighted in Chapter 2. For these reasons antenna design engineers deduced that microstrip patch antennas could be utilized for applications requiring where there was very limited space to mount the antenna. One such global application is for wireless communication handset terminals.

Three-dimensional electrical impedance tomography based on the complete electrode model

Abstract: In electrical impedance tomography an approximation for the internal resistivity distribution is computed based on the knowledge of the injected currents and measured voltages on the surface of the body. It is often assumed that the injected currents are confined to the two-dimensional (2-D) electrode plane and the reconstruction is based on 2-D assumptions. However, the currents spread out in three dimensions and, therefore, off-plane structures have significant effect on the reconstructed images. In this paper we propose a finite element-based method for the reconstruction of three-dimensional resistivity distributions. The proposed method is based on the so-called complete electrode model that takes into account the presence of the electrodes and the contact impedances. Both the forward and the inverse problems are discussed and results from static and dynamic (difference) reconstructions with real measurement data are given. It is shown that in phantom experiments with accurate finite element computations it is possible to obtain static images that are comparable with difference images that are reconstructed from the same object with the empty (saline filled) tank as a reference.