Antenna Excitation Research Articles

Magnetic Nanoparticle-Guided Blind Focusing of the Electric Field for Microwave Hyperthermia

This paper deals with microwave hyperthermia, presenting a novel way to achieve the blind focusing on the tumor of the electric field radiated by an array of antennas. As in a recently proposed approach, the idea is to determine the antenna excitations by measuring the variation of the electric field arising from a localized variation of the electromagnetic contrast, without requiring any a priori knowledge of the geometry and of the electric properties of the tissues wherein the electromagnetic field propagates (thus, the adjective “blind”). The first novelty of the new approach is the use of magnetic nanoparticles as contrast agents, which, in addition to being biocompatible, are appealing thanks to the possibility of changing their magnetic contrast, in a fast, remote, and reversible way, by applying an external magnetic field. This allows a reconfigurable focusing through a continuous tuning of the antenna excitations, thereby enabling one to counteract the possible loss of focusing that could occur during the treatment. However, the magnetic nature of the induced contrast variation requires the development of ad hoc strategies for the synthesis of the excitations, which represent the other novelty of the new approach. Its effectiveness has been thoroughly investigated with an exhaustive 2-D numerical analysis, considering as case study that of breast cancer, and further assessed through 3-D realistic numerical simulations.

Effect of distance between a magnet layer and an excitation antenna on the nonreciprocity of magnetostatic surface waves

We investigated the effect of the distance between a magnetic layer and an excitation antenna on the nonreciprocity of magnetostatic surface waves (MSSWs), using devices with various thicknesses of the SiO2 layer (tSiO2) to isolate an antenna from a permalloy layer. The nonreciprocity of MSSWs increases with increasing tSiO2. This increase in MSSW nonreciprocity is caused by an increase in the ratio of the MSSW excitation efficiency of the out-of-plane component of a microwave field to that of the in-plane component of a microwave field. Thus, we found that the nonreciprocity of MSSWs can be controlled by a very simple method.

Design Guidelines for the Excitation of Characteristic Modes in Slotted Planar Structures

This paper provides some design guidelines for the excitation of broadband slotted planar antennas, addressing key issues such as coupling, symmetries and multiple feeding. The theory of characteristic modes (CMs) is used to identify the collection of current modes that exists on these structures, dealing to a valuable understanding of the radiating mechanisms and allowing a more controlled design process. Modal analysis of a circular aperture cut on a finite square ground plane is presented in order to demonstrate that an optimum choice of the feeding mechanism can be made according to the current distribution of the desired modes. Based on the information yielded by this modal analysis, a capacitive-coupled dual-feed circular aperture antenna is presented. This antenna takes advantage of the symmetries of the characteristic currents by making use of multiple feeding, in order to excite only some particular modes. Usage of commonly-fed and differentially-fed configurations enables an increased control of the excitation of modes in the structure. CM analysis of the antenna including the feeding structures is presented, showing the influence of the feeding lines in the performance of this type of antennas. A prototype of the antenna has been fabricated and measured. Simulated and measured results are presented, being in good agreement.

Integration Multi-Objective Optimization Method of Airborne Radome System

To improve the characteristics of boresight error (BSE) and power transmission coefficient in a phased array antenna-radome system, an integration optimization method, adjusting radome structure and antenna excitation successively, is studied. A multi-objective fitness function is designed for the particle swarm optimization (PSO), which obtain the performance parameters by Aperture Integration-Surface Integration (AI-SI) method. The results obtained are compared with those achieved by pure radome optimization, showing the effectiveness of the proposed method.

Plasmon-Enhanced Second Harmonic Generation: from Individual Antennas to Extended Arrays

We analyze the emission yield of the second harmonic generation (SHG) from dense ordered arrays of L-shaped Au nanoantennas within a well-defined collection angle and compare it to that of the isolated nanostructures designed with the same geometrical parameters. Thanks to the high antenna surface density, arrays display one order of magnitude higher SHG yield per unit surface with respect to isolated nanoantennas. The difference in the collected nonlinear signals becomes even more pronounced by reducing the collection angle, because of the efficient angular filtering that can be attained in dense arrays around the zero order. Albeit this key-enabling feature allows envisioning application of these platforms to nonlinear sensing, a normalization of the SHG yield to the number of excited antennas in the array reveals a reduced nonlinear emission from each individual antenna element. We explain this potential drawback in terms of resonance broadening, commonly observed in densely packed arrays, and angular filtering of the single antenna emission pattern provided by the array 0th order.

A Novel Wideband Magneto-Electric Dipole Antenna with Improved Feeding Structure

A novel feeding structure in magneto-electric dipole antenna is proposed and analyzed, which is simpler and better in performance than previous designs, involving differential feeding. Due to this improved feeding structure, the antenna has achieved an impedance bandwidth of 133.3% ( 0.5 GHz – 2.5 GHz, resulting into an ultra-wide band antenna. The maximum broadside gain 7.5dBi with unidirectional radiation pattern has also been reported for the entire the range of operation. Symmetry in E-plane and H-plane radiation patterns has been observed due to the symmetry in structure and excitation of antenna. The antenna has also been able to achieve cross polarization levels.

Synthesis and photophysical characterization of luminescent lanthanide complexes of nucleotide-functionalized cyclen- and dipicolinate-based ligands

Luminescent Eu(III)- and Tb(III)-complexes based on functionalized tetraazamacrocycle (cyclen) or dipicolinic acid (dpa) metal binding sites, and carrying 2′- or 5′-linked uridine moieties were prepared. The light-harvesting antennae were either a coumarin (in the cyclen-based architectures) or the dpa-moiety itself. Antenna excitation resulted in metal-centered emission for all complexes. The presence of the uridine resulted in less intense lanthanide emission compared to non-nucleotide-modified reference compounds. Nd(III)-complexes of cyclen ligands carrying a uridine but without a sensitizing antenna were also synthesized; these are envisioned as energy transfer acceptors to the Eu(III)-complexes. The possibility for Eu-to-Nd energy transfer was probed. The reported complexes are models for oligonucleotide-attached lanthanide probes.

Performance Evaluation of Smart Antennas Employing Adaptive Elliptical and Hexagonal Arrays using Particle Swarm Optimization and Genetic Algorithm

Background: With the advent of smart antennas, there has been a phenomenal technological development in wireless communications industry. They paved path to number of new inventions that gave a boost to mobile industry. In this paper a comparison on elliptical array and hexagonal array of uniformly excited isotropic antennas are studied. Methods: The configurations generate maximum directive beam with reduced side lobe level. Two optimization techniques were used, particle swarm optimization and genetic algorithm. Both the arrays are evaluated in terms of efficient null placing and side lobe levels reduction using the algorithms taken into consideration. Findings: Hexagonal array using particle swarm optimization has better beam forming capabilities with reduced side lobe levels when compared elliptical array configuration. Applications: Smart antennas combat signal fading and suppress interfering signals from unwanted directions and thereby increase the capacity of wireless systems.

Remote plasmon-induced heat transfer probed by the electronic transport of a gold nanowire

We show in this paper that the heat generated by the optical excitation of resonant plasmonic antennas and diffusing along a simple glass/air interface disturbs the electron transport of a nearby conductive element. By probing the temperature-dependent resistance of a gold nanowire $R_{\rm nw}(T)$, we quantitatively analyze the impact of a resonant absorption of the laser by the antennas. We find that the temperature rise at the nanowire induced by the laser absorption of a distant nanoparticle may exceed that of a direct illumination of the nanowire itself. We also find that a global temperature calibration underestimates the heat generated locally by the laser. The temperature deduced from resistance variations are verified by numerical simulations with a very satisfactory agreement.

Multifrequency and multidirection optimizations of antenna arrays using heuristic algorithms and the multilevel fast multipole algorithm

AbstractWe consider fast and efficient optimizations of arrays involving three‐dimensional antennas with arbitrary shapes and geometries. Heuristic algorithms, particularly genetic algorithms, are used for optimizations, while the required solutions are carried out accurately and efficiently via the multilevel fast multipole algorithm (MLFMA). The superposition principle is employed to reduce the number of MLFMA solutions to the number of array elements per frequency. The developed mechanism is used to optimize arrays for multifrequency and/or multidirection operations, i.e., to find the most suitable set of antenna excitations for desired radiation characteristics simultaneously at different frequencies and/or directions. The capabilities of the optimization environment are demonstrated on arrays of bowtie and Vivaldi antennas.

Optimization of the transmitter pulse duration by the criterion of the radiation spectrum maximization at a given frequency

The possibility of achieving the maximum level of the probe pulse spectrum at a fixed frequency when selecting the optimal duration of the excitation pulse of the radar with pulse excitation antenna has been investigated.

Conceptual study of an ICRH traveling-wave antenna system for low-coupling conditions as expected in DEMO

For the central heating of a fusion reactor ion cyclotron radio frequency heating (ICRH) is the first choice method as it is able to couple RF power to the ions without density limit. The drawback of this heating method is the problem of excitation of the magneto-sonic wave through the plasma boundary layer from the antenna located along the wall, without exceeding its voltage standoff. The amount of coupling depends on the antenna excitation and the surface admittance at the antenna output due to the plasma profile. The paper deals with the optimization of the antenna excitation by the use of sections of traveling-wave antennas (TWAs) distributed all along the reactor wall between the blanket modules. They are mounted and fed in resonant ring system(s). First, the physics of the coupling of a strap array is studied by simple models and the coupling code ANTITER II. Then, after the study of the basic properties of a TWA section, its feeding problem is solved by hybrids driving them in resonant ring circuit(s). The complete modeling is obtained from the matrices of the TWA sections connected to one of the feeding hybrid(s). The solution is iterated with the coupling code to determine the loading for a reference low-coupling ITER plasma profile. The resulting wave pattern up to the plasma bulk is derived. The proposed system is totally load resilient and allows us to obtain a very selective exciting wave spectrum. A discussion of some practical implementation problems is added.

Analysis of a Uniform Linear Broadside Dipole Antenna Array Operating at 1.8 GHz for Use in GSM Application.

A uniform broadside array antenna is the arrangement of equally spaced and equal
 current amplitude excitation of identical antennas, which are placed along the axis
 perpendicular to the direction of maximum radiation. The overall radiation pattern of an
 array is determined by array factor combined with the radiation pattern of the antenna
 element. The number of the elements and their spacing may produce the diverse radiation
 properties. In this work the impact of these two factors on the radiation characteristics of
 a uniform linear broadside dipole array were analyzed using the 4NEC2 simulation
 software. The spacing between the elements varied from 0.1λ to 2λ in steps of 0.02λ for
 a number of elements up to 10 elements. For GSM application at 1.8GHz frequency the
 best configuration to achieve the required gain of 13.8dBi was 7-elements with 0.88λ
 spacing.

Antenna-assisted picosecond control of nanoscale phase transition in vanadium dioxide.

Nanoscale devices in which the interaction with light can be configured using external control signals hold great interest for next-generation optoelectronic circuits. Materials exhibiting a structural or electronic phase transition offer a large modulation contrast with multi-level optical switching and memory functionalities. In addition, plasmonic nanoantennas can provide an efficient enhancement mechanism for both the optically induced excitation and the readout of materials strategically positioned in their local environment. Here, we demonstrate picosecond all-optical switching of the local phase transition in plasmonic antenna-vanadium dioxide (VO2) hybrids, exploiting strong resonant field enhancement and selective optical pumping in plasmonic hotspots. Polarization- and wavelength-dependent pump–probe spectroscopy of multifrequency crossed antenna arrays shows that nanoscale optical switching in plasmonic hotspots does not affect neighboring antennas placed within 100 nm of the excited antennas. The antenna-assisted pumping mechanism is confirmed by numerical model calculations of the resonant, antenna-mediated local heating on a picosecond time scale. The hybrid, nanoscale excitation mechanism results in 20 times reduced switching energies and 5 times faster recovery times than a VO2 film without antennas, enabling fully reversible switching at over two million cycles per second and at local switching energies in the picojoule range. The hybrid solution of antennas and VO2 provides a conceptual framework to merge the field localization and phase-transition response, enabling precise, nanoscale optical memory functionalities.

Approach to axial ratio improvement for circularly polarised microstrip patch antennas excited via two inputs

A novel approach to enhance a quality of circular polarisation of microstrip patch antennas is presented. It is applicable to microstrip antennas with square as well as circular patches which are excited through two inputs with a 90° phase shift. In this approach, an analytical model based on a superposition of the antenna far fields is used. This model leads to the closed-form formulas for correcting the axial ratio at the operating frequency by a proper amplitude and phase excitation of the patch antenna. The formulas use the simulated far fields of the patch antenna with only one input being active while the other one connected to the absorbing load. It is shown by numerical examples that this approach is particularly suitable for microstrip patch antennas excited with the through-substrate probes of coaxial connectors. Furthermore, it is illustrated by numerical examples that the excitation with a proper amplitude and 90° phase shift may be sufficient – from practical point of view – to ensure a high-quality circular polarisation. The proposed correction procedure enhances both the right- and the left-hand polarisations of the microstrip patch antenna of interest.

A cavity-backed quad-slot antenna with novel aperture-coupled feed for circular polarization

This article describes a novel aperture-coupled feed, for the excitation of a cavity-backed quad-slot antenna with circular polarization. Firstly, a quad-slot cavity-backed antenna with linear polarization (LP) is proposed. Then, a novel aperture-coupled feed, which is composed of a cross-shaped coupling aperture and a T-shaped feeding microstrip line, will be applied to this LP antenna. By differing the lengths of the four radiation slots together with the novel aperture-coupled feed, 90° phase difference and equal magnitude between the radiations from the two pairs of slots can be generated. As a result, a good performance of axial ratio will be achieved for the proposed antenna. A prototype is fabricated at Ka band for a demonstration. Investigations show that the antenna can present a minimum axial ratio (AR) of only about 0.37 dB, as well as a fractional AR bandwidth of about 0.94%. A relative high gain of 6.9 dBic at 32.1 GHz is also achieved for the prototype. The proposed substrate integrated cavity backed antenna with circularly polarization has great potential to be integrated into millimeter-wave transceiver modules. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:588–594, 2016.

Nanoantenna-controlled radiation pattern of the third-harmonic emission

We present the third-harmonic emission pattern of single and multiple gold nanoantennas excited by few-cycle infrared laser pulses. The angular distribution of the nonlinear emission is measured by back focal plane imaging with a high-numerical-aperture objective lens. The third-harmonic emission of a single-rod antenna has a dipole-like radiation pattern modified at the air–glass interface. Simultaneous excitation of multiple antennas under the same laser focus results in interferences of the far-field third-harmonic radiation, which can be well explained using a dipole model.

Gyrokinetic particle simulation of beta-induced Alfven-acoustic eigenmode

The beta-induced Alfven-acoustic eigenmode (BAAE) in toroidal plasmas is verified and studied by global gyrokinetic particle simulations. When ion temperature is much lower than electron temperature, the existence of the weakly damped BAAE is verified in the simulations using initial perturbation, antenna excitation, and energetic particle excitation, respectively. When the ion temperature is comparable to the electron temperature, the unstable BAAE can be excited by realistic energetic particle density gradient, even though the stable BAAE (in the absence of energetic particles) is heavily damped by the thermal ions. In the simulations with reversed magnetic shear, BAAE frequency sweeping is observed and poloidal mode structure has a triangle shape with a poloidal direction similar to that observed in tokamak experiments. The triangle shape changes the poloidal direction, and no frequency sweeping is found in the simulations with normal magnetic shear.

A Wideband Circularly Polarized Cubic Dielectric Resonator Antenna Excited With Modified Microstrip Feed

A wideband circularly polarized cubic-shaped dielectric resonator antenna (DRA) was excited with a new question-mark-shaped microstrip feed, which provides two orthogonal modes with a quadrature phase difference, hence generating circular polarization. The proposed antenna offers measured - 10-dB impedance bandwidth of 35.35% (at center frequency 3.14 GHz) and measured 3-dB axial-ratio bandwidth of 20.62% (centered on 3.29 GHz) in the broadside direction. The proposed DRA shows the maximum gain and radiation efficiency of 1.51 dB and 90.65%, respectively, in the operating band. It was observed that the proposed antenna is left-hand circular polarized. This antenna is useful for WiMAX (3.3-3.7 GHz) applications.

Array Pattern Synthesis of Real Antennas Using the Infinite-Array Approach and Linear Programming

This work proposes an efficient optimization methodology of antenna array excitations accounting for the effects of mutual couplings and real radiating patterns of array elements with complex geometry. The method is formulated as a linear programming problem providing multibeam patterns with specified beamwidths, constraints on sidelobe and cross-polar levels, and null pointing directions. A matrix formulation is used to integrate the optimization procedure and a finite-array analysis based on the infinite-array approach, in which the periodic radiating element is characterized by a full-wave and hybrid procedure, combining the domain decomposition technique, the finite-element method, and modal analysis. Numerical examples of arrays of open-ended waveguides, microstrip antennas, and dielectric resonator antennas are presented.