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In this letter, a frequency-reconfigurable printed meandered monopole structure is presented. The antenna structure is composed of three radiating parts that are connected through two integrated PIN diodes. Such integration allows the antenna to reconfigure its operation within four frequency bands that correspond to various LTE, UMTS, and GSM channels. A graphical user interface (GUI) using Java is employed to control the states of the switches. The interface allows the control of a microcontroller to supply appropriate current to each of the two diodes. The GUI also simulates a cognitive radio environment where the activation of the corresponding PIN diodes is determined by the users’ activities. A prototype is fabricated and tested as a proof of concept where measured results agree with simulated data. [ABSTRACT FROM AUTHOR]

In this communication, a frequency and pattern reconfigurable V–shaped printed antenna is presented. The proposed structure operates at two different frequency bands. The variation in the frequency of operation is achieved by individually extending the length of each of the two antenna arms. The directional behavior of the proposed antenna structure is improved through the incorporation of a triangular parasitic element within the empty space between the two antenna arms. More specifically, the antenna is able to steer its gain pattern to either the left or right directions based on which arm of the V–shaped printed structure is fed. A prototype structure is fabricated and tested to validate the proposed approach in achieving directional behavior over two distinct frequency bands. [ABSTRACT FROM PUBLISHER]

An approach for calculating electromagnetic scattering, valid in the near- and far-field regions, from a homogeneous finite cylindrical vegetation sample at oblique incidence is presented and discussed. The proposed solution will help in taking into account multiple scattering effects due to plant structure. It does not require assumptions on the dimensions or electromagnetic properties of the vegetation cylinder. [ABSTRACT FROM PUBLISHER]

In this paper cognitive radio is described, discussed and compared with software defined radio (SDR). The two types of cognitive radio are presented and examples on both spectrum interweave and spectrum underlay cognitive radio antenna systems are detailed. Reconfigurable filtennas are proposed as communicating antennas in a MIMO setting for both cases of cognitive radio. The benefits of resorting to filtennas as well as to MIMO configuration is shown and discussed herein. The various antenna examples are designed, tested and compared with each other. Conclusions are drawn based on the presented results. [ABSTRACT FROM PUBLISHER]

This paper discusses the fundamental principles of a cognitive-radio RF system. The key points required to achieve a true cognitive-radio device are outlined. The operation of a cognitive-radio system is mainly divided into two tasks. In the first task, a cognitive-radio device searches and identifies any part of the spectrum that is not occupied. The second task consists of achieving an optimal mode of communication by allocating the appropriate channels to be used. In this paper, the RF requirements required to operate a cognitive-radio device are detailed. Such a device can adopt one of two scenarios of a cognitive-radio system: the ?interweave? or ?underlay? mode of operation. For both scenarios, a cognitive cycle is followed. This cycle consists of the following four steps: (1) observe, (2) decide, (3) act, and (4) learn. A cognitive-radio engine is responsible for managing and integrating these four functions together into a single cognitive-radio device. In this tutorial, the realization of the four functions of a cognitive-radio cycle are detailed for both types of cognitive radio, and various RF front-end examples are presented and discussed. [ABSTRACT FROM PUBLISHER]

Frequency-tunable microstrip antennas, for cognitive radio applications, are proposed herein. The approach is based on tuning the operating frequency of a bandpass filter that is incorporated into a wideband antenna. The integration of an open loop resonator-(OLR-) based adjustable bandpass filter into a wideband antenna to transform it into a tunable filter-antenna is presented. The same technique is employed to design a cognitive radio pattern diversity tunable filter-antenna. A good agreement between the simulated and measured results for the fabricated prototypes is obtained. The radiation characteristics of each designed tunable filter-antenna are included herein. [ABSTRACT FROM AUTHOR]

Volumetric left-handed metamaterials made up of an array of split-ring resonators (SRRs) and wires exhibit negative index of refraction in a very narrow bandwidth due to the resonant nature of SRRs. We investigate the possible bandwidth enhancement by adding resonances to the system using fractals. The operating bandwidth of the system is increased when the additional resonances are placed close enough to each other. The Sierpiński-carpet fractal pattern is chosen as the distribution for the SRRs. The principle is demonstrated through simulations, and prototypes are fabricated and tested to verify consistency with simulations. [ABSTRACT FROM AUTHOR]

The design of filter antennas with reconfigurable band stops is proposed. They are meant for employment in ultrawideband cognitive radio (UWB-CR) systems, where unlicensed users communicate using adaptive pulses that have nulls in the bands used by licensed users. Neural networks or circuits implementing the Parks-McClellan algorithm can generate such pulses. With filter antennas, reconfigurable bandstop filters are first designed, to induce adaptive nulls in UWB pulses, and are then integrated in the feed line of a UWB antenna. The advantages of this combination are discussed. The filters are based on split-ring resonators (SRRs) and complementary split-ring resonators (CSRRs). The relationship between the SRR and CSRR parameters and the stop band is also studied. [ABSTRACT FROM AUTHOR]

An analysis was carried out to determine the presence of enteroviruses and adenoviruses in public swimming pools in Cyprus. The effectiveness of the commonly implemented disinfection procedure of chlorination was confirmed by determination of bacteriological markers. Analysis of viral presence was carried out by sampling random swimming pools from the five major cities in Cyprus during a period of 21 months spanning from April 2007 to December 2008. A 10 l sample was taken from each swimming pool to be tested and was subsequently concentrated via membrane filtration using a new methodological approach for virus elution. Concentrated samples were analysed using of a Real Time Polymerase Chain Reaction (PCR) TaqMan® probe based approach to detect the presence of enteroviruses and adenoviruses. Over the period of 21 months a total of 126 swimming pools were sampled and analysed. In four swimming pools enteroviruses were detected, in one pool echovirus 18 was identified, in two pools echovirus 30 was identified and in one other pool poliovirus Sabin 1 was identified. Similarly, in four swimming pools adenoviruses were detected, in all four adenovirus 41 was identified. Bacteriological marker analysis showed that 98% of pools complied with Cyprus regulations. [ABSTRACT FROM AUTHOR]

This communication presents a new antenna system designed for cognitive radio applications. The antenna structure consists of a UWB antenna and a frequency reconfigurable antenna system. The UWB antenna scans the channel to discover “white space” frequency bands while tuning the reconfigurable section to communicate within these bands. The frequency agility is achieved via a rotational motion of the antenna patch. The rotation is controlled by a stepper motor mounted on the back of the antenna structure. The motor's rotational motion is controlled by LABVIEW on a computer connected to the motor through its parallel port. The computer's parallel port is connected to a NPN Darlington array that is used to drive the stepper motor. The antenna has been simulated with the driving motor being taken into consideration. A good agreement is found between the simulated and the measured antenna radiation properties. [ABSTRACT FROM AUTHOR]

The 32 papers in this special section focus on synthesis and optimization techniques in electromagnetics and antenna system design. The papers are briefly summarized here. [ABSTRACT FROM PUBLISHER]

We investigate the wave-propagation characteristics in urban environments as functions of the angle-of-arrival distribution, both in the azimuth and elevation planes. We also take into consideration the time delays for various base-station antenna elevations. We combine a statistical multi-parametric model, describing randomly distributed buildings, and a waveguide model, describing a grid of crossing streets with buildings lining the sides to create a new stochastic model. The joint probability of signal distributions in the azimuth-elevation, azimuth-time delay, and elevation-time delay planes are obtained and compared with high-resolution three-dimensional experiments carried out in urban areas in Helsinki, Finland. A good agreement between experimental and theoretical results is obtained. [ABSTRACT FROM AUTHOR]

A new multimode antenna consisting of a circular array of log periodic (LP) elements, suspended in dielectric material and placed in a circular cavity with a conical bottom, is presented and discussed. The conducting elements are contained within the dielectric. Far field patterns obtained using the method of moments (MoM) are compared to experimental measurements and show good agreement for both magnitude and phase. The effect of cavity cone angle on the antenna patterns is presented. Careful selection of the cone angle can result in significant suppression of undesirable higher order resonant modes on the LP elements. [ABSTRACT FROM AUTHOR]

The three-dimensional finite difference time domain (FDTD) algorithm is used to analyze finite-sized phased array antennas. Coaxially-fed, capacitively coupled stacked microstrip antennas are analyzed. A phase shift in the time domain is implemented to model the effects of scanning angle. A rigorous feed model, suitable for FDTD analysis with the perfectly matched layer (PML) is used. The S-parameters, from which input impedance and mutual coupling are evaluated, as well as other important indices are calculated and compared with measured results. [ABSTRACT FROM AUTHOR]

This paper presents a neural network approach for beamforming and interference cancellation. A three-layer radial basis function neural network is trained with input–output pairs. The results obtained from this network are in excellent agreement with the Wiener solution. It was found that networks implementing these functions are successful in tracking mobile users in real time as they move across the antenna's field of view. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 21: 451–455, 1999. [ABSTRACT FROM AUTHOR]

This article investigates the radiation characteristics of microstrip patch antennas located at arbitrary angular positions. The aperture method was employed to determine the radiated far field of the patch. A circular arrangement of the patch antennas was studied. The effect of the array configuration on the radiation characteristics are presented and analyzed. [ABSTRACT FROM AUTHOR]

A method-of-moments analysis shows that a practical, nonair dielectric may be used to reduce the separation and physical size required for optimal performance of a spiral antenna, backed by a ground plane. Microstrip transmission-line impedance equations are shown to be applicable in estimating the effective dimensions of such antennas. [ABSTRACT FROM AUTHOR]

This article presents a study of the ARTMAP neural network in designing cascaded gratings. A neural network can be trained to keep changing the dimensions of the metallic strips, their distance of separation, their width, the number of layers required in a multilayer structure, and the angle of wave incidence until the frequency response of the structure matches the desired one. In the past, the back-propagation (back-prop) learning algorithm was used in conjunction with an inversion algorithm for the design of frequency-selective surfaces. Unfortunately, both the back-prop algorithm and the inversion procedure are slow to converge. In this work the Fuzzy ARTMAP neural network is utilized. The fuzzy ARTMAP is faster to train than the back-prop, and it does hot require an inversion algorithm. Several results (frequency responses) from cascaded gratings for various angles of wave incidence, layer separation, width strips, and interstrip separation are presented and discussed. [ABSTRACT FROM AUTHOR]

This article presents a theoretical and experimental analysis of the focusing properties of metallic chirped gratings. These aperiodic gratings are designed to focus energy at a desired position by varying the strip width and strip spacing. The location of the individual strips, their width variation, distance of separation, and angle of incidence determine the focal point of the chirped grating. [ABSTRACT FROM AUTHOR]

The problem of scattering from a finite conductive cylinder with complex permittivity at arbitrary orientation is analyzed using a first-order approximation to an iterative technique developed by Shifrin. The classical Kerker solution for a simple infinite dielectric cylinder is extended to a more physically realistic solution accounting for a finite-length cylinder with frequency-dependent complex permittivity using a modified Drude conductivity approach. The polarization matrix of the cylinder is derived from the electrostatic solution for a finite cylinder in a uniform electric field, and it is given as a function of the length-to-diameter ratio (aspect ratio) and the permittivity of the cylinder. The electrostatic solution for a finite cylinder does not permit a closed solution: therefore the cylinder is approximated by an inscribed ellipsoid which provides a converging analytic expression. The effects of typical variations in the length, diameter, and bulk conductivity of the cylinder were analyzed for TE, TM, and TEM polarizations. [ABSTRACT FROM AUTHOR]

A uniformly illuminated square subarray of 16 circularly polarized patch elements is developed. It can be incorporated into a full-size direct broadcast satellite (DBS) receiver antenna. A stacked circular patch microstrip configuration is used to achieve increased bandwidth. Experimental results for the return loss, bandwidth, radiation pattern, and gain are presented. © 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 15, 68–72, 1997. [ABSTRACT FROM AUTHOR]

A low-cost, easy to fabricate waveguide-to-microstrip E-probe transition for the entire X band is introduced. Experimental data shows the E-probe transition to be broadband with low insertion loss. The design of a test fixture to characterize accurately a single waveguide-to-microstrip transition is also presented. [ABSTRACT FROM AUTHOR]

The insertion loss contribution of concatenated connectors in fiber-optic links is analyzed. A statistical approach, based on the loss distribution of single connectors with a method for numerical convolution is developed. The predicted insertion loss is less than the sum of the "worst case" connector loss values. An avionics short-haul fiber-optic example illustrates the new approach. [ABSTRACT FROM AUTHOR]