Antenna Excitation Research Articles

Boosting Local Field Enhancement by on-Chip Nanofocusing and Impedance-Matched Plasmonic Antennas.

Strongly confined surface plasmon-polariton modes can be used for efficiently delivering the electromagnetic energy to nanosized volumes by reducing the cross sections of propagating modes far beyond the diffraction limit, that is, by nanofocusing. This process results in significant local-field enhancement that can advantageously be exploited in modern optical nanotechnologies, including signal processing, biochemical sensing, imaging, and spectroscopy. Here, we propose, analyze, and experimentally demonstrate on-chip nanofocusing followed by impedance-matched nanowire antenna excitation in the end-fire geometry at telecom wavelengths. Numerical and experimental evidence of the efficient excitation of dipole and quadrupole (dark) antenna modes are provided, revealing underlying physical mechanisms and analogies with the operation of plane-wave Fabry-Pérot interferometers. The unique combination of efficient nanofocusing and nanoantenna resonant excitation realized in our experiments offers a major boost to the field intensity enhancement up to ∼12000, with the enhanced field being evenly distributed over the gap volume of 30 × 30 × 10 nm(3), and promises thereby a variety of useful on-chip functionalities within sensing, nonlinear spectroscopy and signal processing.

Dual-Polarized Reduction of Dipole Antenna Blockage Using Mantle Cloaks

We theoretically and experimentally explore the use of mantle covers to cloak dipole antennas and reduce their blockage on nearby antennas. The proposed structures allow reducing the observability in a given frequency range and overall scattering of conventional dipole antennas operating in a different frequency band, ideally suited to reduce the mutual influence among antennas placed in close proximity to each other. We prove this concept in the case of a low-band (LB) dipole antenna placed in close proximity to a high-band dipole antenna, and study several thin cover designs that are shown to be effective in reducing the LB blockage, without disrupting the performance of both antennas in terms of radiation pattern and impedance matching. An optimized cover is proposed to strongly reduce the interference and shadowing over a large bandwidth targeted for one polarization, and we also experimentally demonstrate the operation of dual-polarized covers for near-field horn and log-periodic antenna excitation.

Reflecting and Polarizing Properties of Conductive Fabrics in Ultra-High Frequency Range

The system based on ultra-wide band (UWB) signals was employed for qualitative estimation of attenuating, reflecting and polarizing properties of conductive fabrics, capable to prevent local static charge accumulation. Pulsed excitation of triangle monopole antenna of 6.5 cm height by rectangular electric pulses induced radiation of UWB signals with spectral density of power having maximum in ultra-high frequency (UHF) range. The same antenna was used for the radiated signal receiving. Filters and amplifiers of different passband were employed to divide UHF range into subranges of 0.3-0.55 GHz, 0.55-1 GHz, 1-2 GHz and 2-4 GHz bands. The free space method, when conductive fabric samples of 50x50 cm 2 were placed between transmitting and receiving antennas, was used to imitate a practical application. Received wideband signals corresponding to the defined range were detected by unbiased detectors. The fabrics made of two types of warps, containing different threads with conductive yarns, were investigated. It was estimated attenuation and reflective properties of the fabrics when electric field is collinear or perpendicular to thread direction. In the UHF range it was revealed good reflecting properties of the fabrics containing metallic component in the threads. The system has advantages but not without a certain shortcoming. Adapting it for specific tasks should lead to more effective usage, including yet unused properties of the UWB signals.

Opposition‐based BAT algorithm for optimal design of circular and concentric circular arrays with improved far‐field radiation characteristics

AbstractIn this paper, optimal designs of non‐uniform single‐ring circular antenna array (CAA) and non‐uniform three‐ring concentric circular antenna array (CCAA) have been dealt with, which gives rise to optimal improvement of far‐field radiation characteristics. An evolutionary optimization technique based on opposition‐based bat algorithm (OBA) is applied to determine an optimum set of current excitation weights and antenna inter‐element spacing for CAA of 8, 10, and 12 elements and optimal current excitation weights for CCAA, respectively. Two three‐ring CCAAs, one having the set of 4, 6, and 8 elements and the other having 8, 10, and 12 elements with and without center element, are considered. The results show a considerable reduction of side lobe level, 3‐dB beamwidth, and improved directivity of CAA and better side lobe level of CCAA, with respect to the results of some recent literature reported in this paper. The BAT is a metaheuristic algorithm, based on the echolocation behavior of bats. The capability of echolocation of microbats is fascinating as the bats can find their prey and discriminate different types of insects even in complete darkness. By idealizing the echolocation behavior of bats, BAT is recently introduced in the literature. In the present paper, opposition‐based learning is employed for population initialization and also for the generation jumping along with the original BAT for further improving the convergence performance of BAT. This new variant of BAT is termed as opposition‐based BAT. Copyright © 2015 John Wiley & Sons, Ltd.

Analysis of Wave Excitation of the Phase-Control ICRF Antennas with Three-Dimensional Full Wave Code on GAMMA 10

On the GAMMA 10 tandem mirror, divertor simulation experiments progress with high-temperature plasmas produced by waves in ion-cyclotron range of frequency (ICRF) and open magnetic fields. In these experiments, high-temperature and high-density plasmas are required to be produced and controlled. In order to enhance the ion heating in the anchor cell, phase-control experiments, which use two ICRF antennas installed in the central cell and the anchor cell, are introduced. In these experiments, ICRF waves in the same frequency (10 MHz) are excited. Ion heating in the anchor cell is performed more effectively with phase control. In order to analyze wave propagation in the phase-control experiments, a three-dimensional full wave code (TASK/WF), in which parallel processing has been implemented recently, is introduced. In this technical note, we discuss ICRF wave excitation and propagation in the phase-control experiments. It is clearly observed by the experiments and wave analysis that the enhancement of ion heating in the anchor cell is performed by phase-control experiments.

Magnetic antenna excitation of whistler modes. IV. Receiving antennas and reciprocity

Antenna radiation patterns are an important property of antennas. Reciprocity holds in free space and the radiation patterns for exciting and receiving antennas are the same. In anisotropic plasmas, radiation patterns are complicated by the fact that group and phase velocities differ and certain wave properties like helicity depend on the direction of wave propagation with respect to the background magnetic field B0. Interference and wave focusing effects are different than in free space. Reciprocity does not necessarily hold in a magnetized plasma. The present work considers the properties of various magnetic antennas used for receiving whistler modes. It is based on experimental data from exciting low frequency whistler modes in a large uniform laboratory plasma. By superposition of linear waves from different antennas, the radiation patterns of antenna arrays are derived. Plane waves are generated and used to determine receiving radiation patterns of different receiving antennas. Antenna arrays have radiation patterns with narrow lobes, whose angular position can be varied by physical rotation or electronic phase shifting. Reciprocity applies to broadside antenna arrays but not to end fire arrays which can have asymmetric lobes with respect to B0. The effect of a relative motion between an antenna and the plasma has been modeled by the propagation of a short wave packet moving along a linear antenna array. An antenna moving across B0 has a radiation pattern characterized by an oscillatory “whistler wing.” A receiving antenna in motion can detect any plane wave within the group velocity resonance cone. The radiation pattern also depends on loop size relative to the wavelength. Motional effects prevent reciprocity. The concept of the radiation pattern loses its significance for wave packets since the received signal does not only depend on the antenna but also on the properties of the wave packet. The present results are of fundamental interest and of relevance to loop antennas in space.

Magnetic antenna excitation of whistler modes. III. Group and phase velocities of wave packets

The properties of whistler modes excited by single and multiple magnetic loop antennas have been investigated in a large laboratory plasma. A single loop excites a wavepacket, but an array of loops across the ambient magnetic field B0 excites approximate plane whistler modes. The single loop data are measured. The array patterns are obtained by linear superposition of experimental data shifted in space and time, which is valid in a uniform plasma and magnetic field for small amplitude waves. Phasing the array changes the angle of wave propagation. The antennas are excited by an rf tone burst whose propagating envelope and oscillations yield group and phase velocities. A single loop antenna with dipole moment across B0 excites wave packets whose topology resembles m = 1 helicon modes, but without radial boundaries. The phase surfaces are conical with propagation characteristics of Gendrin modes. The cones form near the antenna with comparable parallel and perpendicular phase velocities. A physical model for the wave excitation is given. When a wave burst is applied to a phased antenna array, the wave front propagates both along the array and into the plasma forming a “whistler wing” at the front. These laboratory observations may be relevant for excitation and detection of whistler modes in space plasmas.

Semi-analytical formulation for a Unified Time and Frequency Antenna Characterization

The definition of parameters that characterize the radiation of electric and magnetic fields for antennas in the time and frequency domain on an unified representation is proposed. The formulation uses a straightforward semi-analytical formulation that can be subsequently applied on the analysis of excited antennas for an arbitrary source with temporal behavior. The effective height is a parameter for antenna analysis defined for quantities in far field region and can be used as a transfer function of the antenna. This transfer function can be described through the antenna singularities which can be obtained by singularity expansion. The Singularity Expansion Method (SEM) is capable to model an electromagnetic quantity with the singularities extracted by the current densities of an arbitrary object. This work proposes that the singularities are extracted by the Matrix Pencil method applied on the current densities. The current densities are obtained numerically through the method of the Finite Differences in the Time Domain (FDTD) for wired log-periodic antenna and, after the singularities are obtained, the formulation of the semi-analytical effective height equation is written. To validate the presented method, a formulation of the time-domain radiation pattern is presented and a corresponding frequency-domain radiation pattern is also presented using Parseval’s theorem.

An efficient synthesis approach for electromagnetic near‐ and far‐field contoured patterns using alternative narrow‐beam field functions transformed from the radiations of linearly excited array antennas with least computational complexity

AbstractThis paper presents an effective scheme to accelerate the computational efficiency in synthesizing the electromagnetic contoured patterns spanned by the radiations of phased array antennas, which is applicable to synthesize both the near‐ and far‐field patterns. The core concept is to adapt/create closed‐form and simple formulations with least computational unknowns to be used in the iterative synthesis procedure. The efficiency is assured by avoiding the cumbersome numerical integration/summation for the radiation fields in the synthesis procedure. Thus, the scheme first transforms the conventional field basis functions (FBFs) defined by the radiations of every array elements into a set of global FBFs arising from the radiations of a set of overlapped virtual arrays, where each of the virtual arrays is properly excited by a Gaussian taper to avoid the ray caustic problems encountered in the asymptotic evaluations. The new FBFs (NFBFs) created by this transformation have radiation fields focused in narrow spans in contrast to the wide patterns of conventional FBFs and may reduce the number of FBFs in the computation if a small coverage area is considered. Furthermore, the closed‐form formulations of global NFBFs are obtained by asymptotic evaluation and may dramatically reduce the computational time. This approach is implemented with the use of successive projection method, which also provides closed‐form formulations to update the excitations in each iterative step, to synthesize the near‐ and far‐field contoured patterns to demonstrate the feasibility and efficiency.

Radiation Characteristics of Floquet Mode over Two-Dimensional Infinite Near-Field Focusing Antenna with Focus Point in Complex Space

In this article, the near field of a two-dimensional infinite near-field focusing antenna with Gaussian taper excitation is determined. By Gabor representation, any slowly varying excitation of array antenna can be expanded to series of Gaussian taper excitation. To achieve the Gaussian taper excitation, the focus point of a two-dimensional infinite near-field focusing antenna is placed in complex space. By adopting the Poission sum formula, radiation fields of this type antenna are transferred to terms of Floquet modes. Asymptotic evaluation technique is utilized to calculate the Floquet mode integral in closed form. Results of asymptotic evaluation are compared with those obtained by direct numerical integral, and good agreement is achieved.

Identification of the Burial Depth of Radio Frequency Identification Transponders in Riverine Applications

AbstractRadio frequency identification (RFID) technology enables bidirectional, remote communication between a reader and a transponder (or tag) with a unique ID via an excitation antenna. This study provides a framework for estimating the burial depth of a transponder from a fixed location as a means of assessing scour depth or for other riverine applications. In doing so, a low frequency (LF), passive RFID system is used, which operates at a resonance frequency of 134.2 kHz and can penetrate through saturated sediments. The objective of this research is the development and validation of a semitheoretical expression that relates the decay of the received input voltage (VIN) at the reader with the transponder burial depth or detection distance, d, through a series of well-controlled experiments. This study examines the correspondence between VIN and d in air, as well as in water, gravel, and sand, and assesses the role of transponder orientation (perpendicular and parallel with respect to the excitation a...

Comparative Study of Circular and Hexagonal Antenna Array Synthesis Using Improved Particle Swarm Optimization

This paper describes the comparison of the performance of Circular array (CA) and Hexagonal Array (HA) of uniformly excited isotropic antennas which can generate directive beam with minimum relative Side Lobe Level (SLL). The Improved Particle Swarm Optimization (IPSO) method, which represents a novel approach for optimization problems in electromagnetic, is used in the optimization process. Two examples has been presented and solved. In first example, the IPSO is used to determine an optimal set of ‘ON-OFF’ elements in an 12 element thinned array, and in second example, IPSO is used to determine an optimal set of amplitude distributions in an 18 element array that provide a radiation pattern with maximum SLL reduction. This paper is basically concerned with the comparison of the performance of thinned CA and HA in terms of SLL by fixing the other array design variable. Numerical results for synthesizing two different array geometries demonstrated the superiority of Hexagonal Array over the Circular Array for both the examples.

OSCILLATORS WITH A NONUNIFORM DISTRIBUTION OF SURFACE IMPEDANCE NONLINEARITY

The results of investigations into nonlinear effects arising in the simplest radiating and scattering antennas are presented. It is shown that the uneven distribution of nonlinearity surface impedance (NSI) of the antenna or inclusion in the antenna quasi non-linear elements can significantly affect its performance. Varying the absolute values and the shape of the distribution of the NSI can change the shape of the current distribution on the antenna surface, and thus, change the shape of the radiation pattern. This concerns both the basic operating frequency of the antenna, and its higher harmonics. The type of the antenna excitation source is also important. The antenna characteristics on the harmonic frequencies depend on it to a significant extent.

Dispersion properties of plasma-filled metallic photonic crystal slow-wave structure

Plasma-filled slow-wave devices provide a new way to develop high efficiency and high power vacuum-electron microwave sources, but their theoretical analysis and simulation is difficult. This paper introduces the wheel spoke antenna to excite signals for analyzing the dispersion characteristics of resonant cavity with plasma-filled metallic photonic crystal slow-wave structure (SWS). Influences of parameters of the SWS and plasma density on dispersion characteristics of the SWS are studied. Results show that there is little difference in dispersion characteristics obtained by wheel spoke antenna excitation of signals and other methods without plasma filling. When plasma fills in the SWS, the frequency of zero mode is consistent with the previous results obtained by other methods. Hence, both the results with and without plasma filling demonstrate that the wheel spoke antenna signal-excitation method is effective. Moreover, decreasing the thickness of wheel spoke antenna properly and the distance between the antenna and reflection surface of the metal plate can reduce the wheel spoke antenna influence on the cavity resonance frequency. Furthermore, thicker antenna can excite the slow wave field easily, while thinner antenna can excite the resonant mode easily. Besides, the outer radius and thickness of the SWS plate have little influence on the dispersion characteristics, while the period length and the inner radius of the SWS plate have greater influence on the dispersion characteristics. In addition, the dispersion curves of frequency and phase velocity will move to higher frequency regions with the increase of plasma density. Further, the influence of plasma filling on low-order modes is greater than that on higher order modes. It is also found that the higher-order mode operation can reduce the size of cavity and the velocity of the electron beam.

Directional Radiation of Surface Plasmon Polaritons at Visible Wavelengths through a Nanohole Dimer Optical Antenna Milled in a Gold Film

The mechanism of optical interaction of two nanoholes, milled in an opaque gold film, by means of surface plasmon polariton (SPP) propagation is investigated. The interaction depends on the polarization direction of the incident light when the nanohole pair is illuminated through uniform single antenna excitations. It is shown that by illuminating one of the nanoholes, under single antenna excitation, the other nanohole can be excited indirectly via propagated SPPs from the excited nanohole. In addition, it is found that the spectrum of electromagnetic power above the surface of the metallic film at an arbitrary point along the axis of the nanohole pair presents two resonant peaks. These peaks are due to the optical interaction between nanoholes, where the short- and long-wavelength peaks can be assigned to in-phase and antiphase interactions of magnetic dipoles relative to each nanohole, respectively. The magnetic coupled dipole approximation (MCDA) method confirms the simulation results.

A new hybridized backtracking search optimization algorithm with differential evolution for sidelobe suppression of uniformly excited concentric circular antenna arrays

In this work, a hybridized combination of backtracking search algorithm (BSA) with differential evolution (DE) is proposed and applied on sidelobe suppression problem of uniformly excited concentric circular antenna arrays (CCAA). Each array is assumed to have isotropic elements and be placed on x-y plane and has one center element. A search for optimal setting of ring radius and number of elements in each ring is carried out so as to achieve low sidelobe performance on overall azimuth plane. Care has been taken so that directivity does not get degraded as far as possible. Before applying this algorithm to CCAA design problem, BSA and the hybridized algorithm BSA-DE are tested on five complex benchmark functions. Based on 30-independent runs for each benchmark function, Wilcoxon's pairwise signed ranks test is utilized to judge the relative search performance of these two algorithms. The hybridized algorithm proves its superiority on almost all the considered benchmark functions. For the CCAA design problem dealt with in this work, BSA-DE shows its superiority on one or both pattern parameters as well as structural parameters. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:262–268, 2015.

Synthesis of concentric ring antenna array for a wide isoflux pattern

AbstractThis research presents the synthesis of the concentric ring antenna arrays for a wide coverage pattern. The synthesis process is formulated as an optimization of the antenna excitations. Harmony search algorithm and particle swarm optimization are implemented for this optimization problem. The antenna array considers disk patches at the L‐band. First, the synthesis regards the behavior of the antenna array modeled by the cavity model. Second, the mutual coupling is included by using the full wave simulation. This synthesis could be very useful in satellites with terrestrial global coverage. The obtained antenna array provides a wide uniform power density and reduces considerably the hardware complexity for a satellite antenna system. Copyright © 2014 John Wiley & Sons, Ltd.

Numerical study of nanoparticle sensors based on the detection of the two-photon-induced luminescence of gold nanorod antennas

We investigate numerically the modification of the nonlinear optical properties of a nanoantenna in the trapping of nanoparticles (NPs) by using both the discrete dipole approximation method and the finite-difference time-domain technique. The nanoantenna, which is formed by two gold nanorods (GNRs) aligned end to end and separated by a small gap, can emit strong two-photon-induced luminescence (TPL) under the excitation of a femtosecond laser light which is resonant with its longitudinal surface plasmon resonance. In addition, the excited antenna can stably trap small NPs which in turn induce modifications in the emitted TPL. These two features make it a promising candidate for building highly sensitive detectors for NPs of different materials and sizes. It is demonstrated that sensors built with antennas possess higher sensitivities than those built with single GNRs and nanorod-based antennas are more sensitive than nanoprism-based antennas. In addition, it is found that the trapping probability for a second NP is significantly reduced for the antenna with a trapped NP, implying that trapping of NPs may occur sequentially. A relationship between the TPL of the system (antenna + NP) and the optical potential energy of the NP is established, enabling the extraction of the information on the optical potential energy and optical force by recording the TPL of the system. It is shown that the sequential trapping and releasing of NPs flowing in a microfluid channel can be realized by designing two different antennas arranged closely.

Estimation of Electrical Properties of Hidden Objects Using Microwave Signals

Pulsed excitation of a horn antenna for generating large B wideband electromagnetic pulses was used. The antenna was excited by electrical pulses with rise time of 200 ps and pulse voltage of 15 V. The spectral properties of the electromagnetic pulses were investigated using different wide band antennas and (0 – 18) GHz passband sampling oscilloscope. It was found that the signal spectra is wide and ranges from 0.3 GHz to higher than 12 GHz. Hollow cylinders made from opaque for visible light materials were used to hide other cylinders with certain electrical properties. To reveal their presence we employ the electromagnetic pulses. Transmitted through and reflected from investigated objects pulses were received by several antennas having different frequency ranges and detected to obtain needed information. The experiments show that analyzing this information leads to conclusions about the presence of the object and its electrical properties. This methodic supposedly can be employed to disclose electrical properties of objects having complex electrical properties if broadband amplifiers and digital oscilloscopes are used. DOI: http://dx.doi.org/10.5755/j01.ms.20.2.6331

Receiving and Detection of Ultra-Wideband Microwave Signals Radiated by Pulsed Excitation of Monopole Antennas

Pulsed excitation of small size monopole antennas for generating wideband electromagnetic pulses was used. The monopoles were excited by electrical pulses having rise times of 600 ps, 200 ps, 70 ps and voltages 100 V, 15 V, and 0.4 V respectively. Antennas spanning (0.3 – 26) GHz bandwidth, including broadband horns with coaxial outputs, were employed to receive signals, which were investigated using (0 – 26) GHz passband sampling oscilloscope. It was found that waveforms of signals, received by the antennas, mostly depend on the pulse rise time and on the details of geometry of monopoles. The electromagnetic pulses have relatively long duration of about 30 ns and spectral harmonics up to 22 GHz. Therefore they can be attributed to pulses with large base. The results show that the upper frequencies of the spectrum most probably are cut off by existing arrangement. Usage of such pulses can find wide practical application when they are received after transmission trough different media by a number of antennas having different operational frequency ranges, followed by digital signal processing. DOI: http://dx.doi.org/10.5755/j01.ms.20.2.6330