Symmetric Dipole Research Articles

Research and Modeling of Digital Antenna Arrays with Directional Elements on Azimuth-Elevation in VHF Terrain and Vegetation Multipath Propagation Situations

In the paper the problem of using digital antenna arrays equipped with dipole and directive elements simultaneously in the azimuthal and elevation planes is discussed. In particular, they are investigated for communication channels of the VHF range below 1 GHz. This range is characterized by the fact that it has found wide distribution. However, its application is fraught with many difficulties, such as attenuation, reflection from rough surfaces, etc. One of the solutions to these problems can be azimuth-elevation digital beamforming. The paper presents the simulation results for the propagation of signals in the VHF range in free space, two-ray ground-reflection and foliage models. It is assumed that a symmetrical dipole is used on the transmitting side, and a directional Yagi antenna on the receiving digital antenna array (DAA) also equipped with a dipole. The circular (CAA) and hemi-dodecahedron shapes of the arrangement of elements of the receiving digital antenna array are simulated. The bit error rates (BER) depending on the distance between the transmitter and the receiver are estimated for the three above mentioned cases.

Nearly spherical ablation zone with minimally invasive microwave ablation: Analysis and experimental characterization of a tapered-tip symmetric dipole antenna

Microwave ablation (MWA) is a widely used technology for tumors treatments. The reported asymmetric dipole antennas were not ideal in ablation zone. Although some methods were proposed to improve the ablation performance, other important characteristics were still not satisfactory enough, such as poor impedance matching, increased invasion diameter, or additional insertion devices. In this paper, a minimally invasive antenna with a nearly spherical ablation zone for microwave ablation is presented by a tapered-tip symmetric dipole structure with a sleeve. The tapered-tip symmetric dipole, fed by a coaxial line, are composed of a tapered-tip cylinder arm and a hollow cylinder arm. Both of the lengths of the two arms are approximately equal to a quarter of wavelength. The proposed antenna provides good matching at resonating frequency without any extra impedance matching network. Moreover, the tapered-tip structure enables the proposed MWA antenna be inserted into the tissues directly without an additional needle-shape catheter. Furthermore, the sleeve structure, electrically isolated from the dipole and the coaxial feed line, is employed to prevent the current and thermal from flowing along the feed line. A minimally invasive antenna with a diameter of only 1.9 mm working at 2.45 GHz is designed and fabricated for verification, in which different input power and heating time are taken into account. The temperature evolution in four locations of the liver tissue is recorded by using a 4-channel temperature monitoring system. The comparison with a commercial MWA antenna of the same diameter is also included. Simulation and experiment results show that the proposed MWA antenna create nearly spherical ablation zones. The proposed MWA antenna would be promising for minimally invasive medical applications.

Low-Profile Wideband Millimeter-Wave Circularly Polarized Antenna With Hexagonal Parasitic Patches

A low-profile wideband circularly polarized (CP) millimeter-wave (mm-Wave) L-shaped dipole antenna with hexagonal parasitic patches is presented in this letter. Two types of hexagonal parasitic patches are placed round the rotationally symmetrical L-shaped dipole to enhance the impedance and axial ratio (AR) bandwidth. Based on this antenna element, a substrate integrated waveguide-fed 2 × 2 subarray with sequential rotate feeding technique is designed to further improve AR bandwidth. Finally, a 4 × 4 CP array is designed to further enhance the gain. The measurement shows the proposed array can achieve the impedance bandwidth of 27.7%, the AR bandwidth of 28.5%, and the peak gain of 17.85 dBic while maintaining a lower profile. Therefore, the design scheme will be suitable for 5G mm-Wave communications and satellite communication systems.

Scattering of partially coherent vortex beams by a $\mathcal {PT}$-symmetric dipole.

We investigated the statistical properties of partially coherent optical vortex beams scattered by a $\mathcal {PT}$ dipole, consisting of a pair of point particles having balanced gain and loss. The formalism of second-order classical coherence theory is adopted, together with the first Born approximation, to obtain the cross-spectral density of the scattered field. It is shown that the radiated pattern depends strongly on the coherence properties of the incident beam and on the non-Hermitian properties of the dipole. The spectral density for the scattered radiation is ruled by two terms, one associated to the vortex structure and the other independent of the topological charge, and the competition between these terms dictates the directional properties of the scattered radiation. When they have same order of magnitude, the scattered profile resembles that of an incoherent system, with radiation being emitted in all directions in the three-dimensional space, regardless of the dipole's gain and loss properties. Depending on the gain and loss present in the dipole, the system may scatter light in some preferable directions. All of these effects are accompanied by a change in the spectral degree of coherence of the scattered field.

A Broadband High-Gain Printed Antenna Array Using Dipole and Loop Patches for 5G Communication Systems

A broadband and high-gain printed antenna array is presented in this paper. Its single antenna element consists of a loop and two symmetric dipole patches, making the element exhibiting broad impedance bandwidth and improved gain at the targeted frequency, which is 28 GHz, one of the 5G mm-wave band, for this design. An 8×3 antenna array fed by a microstrip line feed network was designed and simulated. With a compact size of 98×32.5 mm2 , the array presents a broad -10 dB impedance bandwidth of 6.8 GHz (24.3%) and a high gain of 18 dBi at 28 GHz. Besides, the single-layered array also features low profile, simple geometry, and low cost, making it a good candidate for 5G communication systems.

PT -symmetric Helmholtz resonator dipoles for sound directivity

Parity-time ($\mathcal{PT}$)-symmetric or, more generally, non-Hermitian systems have opened a new area for unconventional management of waves, with significant applications, especially in optics. However, fewer proposals are found in acoustics, possibly due to the lack of a simple mechanism for coherent gain. In this paper, we propose a composite non-Hermitian system in acoustics consisting of assemblies of $\mathcal{PT}$-symmetric Helmholtz resonator (HR) dipoles. Like meta-atoms are used as building elements in metamaterials, we propose $\mathcal{PT}$-symmetric dipoles to design non-Hermitian systems intended to engineer complicated directivity fields. We theoretically analyze, numerically confirm, and experimentally show the symmetry breaking in a two-dimensional space of non-Hermitian dipoles consisting of a pair of Helmholtz resonators with different levels of gain and loss. In particular, we explore, as an application, a metastructure to concentrate the sound pressure inside the circular array formed by $\mathcal{PT}$-symmetric dipoles. The proposed HR dipoles may be a convenient composite element for smart control of sound.

Экспериментальное измерение импульсных характеристик сверхширокополосных излучателей.

This work presents the results of experimental measurements of the impulse response of ultra-wideband emitters: a biconical antenna and a symmetrical dipole. A measurement technique was presented. The channel impulse response is calculated using Tikhonov’s regularization. It is shown that the measured signal corresponds to calculated.

Theoretical Simulation of the Near-Field Probe for Non-Invasive Measurements on Planar Layers with Biological Characteristics.

The article presents the design of the near-field probe, which is a combined emitter (a combination of a symmetric dipole and an annular frame). The design of the probe allows forming a prolonged zone of the near-field. This effect can be used for in-depth penetration of the field in media with high absorption, without loss of information. Particular attention in this article is given to a detailed study of the interaction of the field created by this probe on plane-layered biological media. A theoretical analysis of the interaction of the electromagnetic field was carried out in a wide frequency band with a model plane-layer biological medium containing blood vessels of shallow depth using the proposed probe design. Conclusions are drawn about the depth of penetration of a useful signal into different media-analogs of biological tissue. This study is necessary to consider the possibility of using this probe for non-invasive measurements of blood glucose concentration. The studies were carried out using numerical simulation in the CST (Computer Simulation Technology) Microwave Studio environment. All biological tissues were simulated over a wide frequency range from 10 MHz to 10 GHz.

Retroreflection from a single layer of electromagnetic Helmholtz cavities based on magnetic symmetric dipole modes.

We demonstrate a new electromagnetic mode which is formed by the dynamic interaction between a magnetic quadrupole mode and an electric monopole mode in a two-dimensional electromagnetic Helmholtz cavity. It is termed a magnetic symmetric dipole mode since it shares similarity with a magnetic dipole mode in the sense that their radiation is both overwhelmingly dominant in the forward and backward directions with respect to the incident wave. However, the phase distribution in the two radiation directions is symmetric, in stark contrast to the antisymmetry of magnetic dipole modes. When the Helmholtz cavities are arranged in a line, the incident wave will be reflected back to the source, in other words, retroreflection occurs because of the peculiar properties of magnetic symmetric dipole modes. We show that the retroreflection is quite robust against the disorder of the orientation angle of Helmholtz cavities and there exists a wide tolerance for wavelength and the outer radius of the cavity. With low fabrication demands, this might offer a feasible solution for the design of ultrathin retroreflectors towards device miniaturization and the realization of multiplexing holography.

Generation and Intensification of Mesoscale Anticyclones by Orographic Wind Jets: The Case of Ierapetra Eddies Forced by the Etesians

AbstractMotivated by the recurrent formation and intensification of the Ierapetra anticyclones in the southeast of Crete, we investigated with a reduced gravity model the response of the oceanic surface layer to a seasonal wind jet that varies slowly (over several weeks or months) and mimics the Etesian winds. Our study answers why the oceanic response to such forcing is mainly a large and intense anticyclone. We build a dimensionless parameter that integrates in time the Ekman pumping and quantifies the relative amplitude of the isopycnal displacement induced by the local wind stress curl. According to the range of the wind forcing parameter, the oceanic response to a symmetric wind jet could be a symmetric dipole or a strongly asymmetric structure dominated by an intense and robust anticyclone. This intrinsic asymmetry is driven by the finite isopycnal displacements that occur when the wind forcing parameter reaches unity. Since the anticyclonic wind shear for the Etesian wind jet is 2 times larger than the cyclonic one, the asymmetry of the oceanic response is enhanced. Several weeks after the wind forcing has stopped, an intense mesoscale anticyclone which satisfies the cyclogeostrophic balance remains. Moreover, if a similar wind jet blows on a preexisting anticyclone, the latter remains robust and coherent and gets reintensified in agreement with the previous analysis of remote sensing observations. Hence, this paper is the first numerical study which provides a dynamical understanding for the formation of the single Ierapetra anticyclones and explains their intensification 1 year after formation.

Interference properties of a trapped atom interferometer in two asymmetric optical dipole traps* *Project supported by the Postdoctoral Applied Research Program of Qingdao (Grant No. 62350079311135), the National Natural Science Foundation of China (Grant Nos. 11704053 and 11947057), and the Science and Technology Project Affiliated to the Education Department of Chongqing Municipality (Grant No. KJQN201800629).

We investigate interference properties of a trapped atom interferometer where two symmetric optical dipole traps (ODTs) act as the atomic wave-packets splitter and combiner with internal state labelling. After the preparation of initial superposition states, the atomic wave-packet is adiabatically split and moves into two spatially separate asymmetric ODTs. The atomic wave-packets in two ODTs are then adiabatically recombined after a duration of free evolving in traps, completing the interference cycle of this atom interferometer. We show that the interferogram exhibits a series of periodic revivals in interference visibility. Furthermore, the revival period decreases as the asymmetry of two dipole potentials increases. By introducing an echo sequence to the interferometer, we show that while the echo effect is not influenced by the asymmetry of the two ODTs, the onset of periodic revivals changes by the echo sequence. Our study provides an effective method to cancel or compensate the phase shift caused by position and time correlated force.

Electric Symmetric Dipole Modes Enabling Retroreflection from an Array Consisting of Homogeneous Isotropic Linear Dielectric Rods

AbstractLinear‐dielectric‐based in‐plane optical design is attractive yet challenging in nano‐optical technologies when combined with the compatibility with complementary metal‐oxide‐semiconductor technology. Here, by exciting an electric symmetric dipole mode (ESDM), exploiting the interplay between an electric quadrupole mode and a magnetic dipole mode in a homogeneous isotropic linear dielectric rod, an in‐plane retroreflector is successfully realized in the case of no dependence on asymmetry arising from anisotropic/bianisotropic materials, complex unit cell, or asymmetric environments. The ESDM is analogous to an electric dipole (ED) in the sense that its radiation is overwhelmingly dominant in the forward and backward directions, while its phase symmetry is in stark contrast to the antisymmetry of ED modes. The studies herein show symmetric dipole modes are one of general mechanisms for retroreflection. Such a retroreflector combines many other outstanding advantages such as low loss, unitary efficiency, and simple configuration with low fabrication demands. The in‐plane manipulation for waves makes it an appealing platform for manipulating particles and developing on‐chip optical cavities, light sources in integrated optical circuits, optical parametric oscillators, and interferometers.

Equatorial aurora: the aurora-like airglow in the negative magnetic anomaly.

The most fantastic optical phenomena in the Earth's upper atmosphere are the auroras. They are highly informative indicators of solar activity, geomagnetic activity, upper atmospheric structures and dynamics, and magnetospheric energetic particles. An area where the geomagnetic field differs significantly from the expected symmetric dipole, such as at the South Atlantic Anomaly, where the magnetic field intensity is low, gives rise to stronger precipitation of energetic particles into the upper atmosphere. Impact excitation and the subsequent airglow emissions exhibit aurora-like dynamic signatures. Nomenclatures of nonpolar aurora or equatorial auroras are similar to those used with the polar auroras owing to their similar excitation mechanisms. This paper provides an overview of the knowledge and the challenges concerning auroral activity at the South Atlantic Anomaly, or more generally, at the negative magnetic anomaly. We emphasize systematic investigation of the equatorial auroras to reveal the temporal and spatial evolution of the magnetic anomaly and the behaviour of energetic particles in near-Earth space.

High-efficiency antenna-to-antenna polarization converters for customized polarization angle deflection

AbstractIn this paper, an antenna-to-antenna method to design high-efficiency polarization converters was proposed. Two in-linked split ring resonators (SRRs) were used as the fundamental unit cell, which can effectively make the original linear polarization angle deflected into a customized one (include but not limited to 90°). The same as the process of energy reception and transmitting of microstrip symmetric dipole antennas, the top SRR plays the role of a receiving antenna and the bottom one acts as a transmitting antenna. Under normal illumination, the strong coupling between electric resonance and magnetic resonance can result in high transmission and broad bandwidth. Since the two SRRs act as two independently polarization selective components, the polarization angle of transmitted waves can be easily controlled by rotating the transmitting SRRs around the center. The proposed concept and the design method are validated using numerical simulations, as well as experimental results of three examples for 45, 60 and 90° polarization angle rotation, the polarization conversion ratio of which is about 92.2, 88.9 and 91.9% from 7.5 to 10 GHz.

Broadband printed MIMO dipole antenna for 2.4 GHz WLAN applications

Broadband printed dipole antenna with elliptical-arms and integrated balun for multiple-input-multiple-output (MIMO) antennas at 2.4 GHz frequency is designed and presented. The MIMO structure is composed of four symmetrical dipole elements and a circular ground plane. To enhance the isolation between contiguous elements, they are placed in a perpendicular direction. Isolation of parallel dipoles with identical polarization is guaranteed by a suitable distance. Outstanding impedance matching, good isolation, high-gain, and stable directional radiation pattern are advantages of this design. Structural simplicity is achieved by printing dipole arms, balun structure, and the ground plane on FR4 substrates. The proposed MIMO antenna is manufactured and tested in the anechoic chamber. The empirical results have a proper discrepancy with the simulation outcomes.

Conductive coupling for efficient generation of multiple Fano resonances in multiple two-split-ring-resonators and its application in refractive index sensor

The properties of two and three two-split-ring-resonators (TSRRs) are investigated in this paper, which shows a remarkable Fano resonance in the microwave frequency. In two TSRRs, the Fano resonance results from the interference between two TSRRs by conductive coupling, both experiments and numerical simulations are in good agreement. The structure shows strong magnetic dipole at the intersection of two TSRRs. In three TSRRs, the double Fano resonances can be excited and double magnetic dipoles produce at two intersections. Because of the interaction between two magnetic dipole, symmetric magnetic dipole and anti-symmetric magnetic dipole (toroidal dipole) modes are presented, respectively. An almost doubled Q factor is observed in the three TSRRs compared to the two TSRRs. In addition, we experimentally demonstrate that the double Fano resonances are sensitivity to the refractive index of background. The sensitivity changes with the change of position of detected material. The highly sensitive areas of double Fano resonances locate at two intersections. This study paves the way to excite the multiple Fano resonances. Such Fano resonance can be applied to the sensors.

Integral equation of a horizontal dipole located near the interface of media

In the article the output of integral equations symmetric cylindrical dipole antenna of superconductive material. The antenna is located parallel to the interface between the two media. An example of calculating the current distribution over the antenna depending on the parameters of the medium is given.

Atomistic simulations of dipole tilt wall stability in thin films

In this work, we use molecular statics to study the stability of a pair of symmetric dipole tilt walls in Cu thin films. Two geometric wall parameters, the dislocation spacing and wall separation distance, are varied in the calculations. We find that even closely spaced dipole walls can be stabilized in a thin film under no applied strain, and with this insight, develop a stability map that identifies the regime of maximum dislocation spacing and minimum wall separation for which dipole walls can reside in the film. In addition, we show that a critical in-plane tensile strain exists that can destabilize the dipole walls and transition the film to a wall-free state. The simulations reveal that the wall recovery process occurs by sequentially annihilating alternating pairs of dipole dislocations rather than sudden, simultaneous annihilation of an entire wall. Dipole wall stability is rationalized based on a substantial enhancement in the Peierls barrier of the wall dislocations due to the reorientation of the lattice between the walls and narrowing of their intrinsic stacking faults, two effects that have atomic-scale origins.

Plasmonic Properties of Close-Packed Metallic Nanoparticle Mono- and Bilayers

The self-assembly of metallic nanoparticles is a promising route to metasurfaces with unique properties for many optical applications, such as surface-enhanced spectroscopy, light manipulation, and sensing. We present an in-depth theoretical study of the optical properties of mono- and bilayers assembled from gold and silver nanoparticles. With finite-difference time-domain simulations, we predict the occurrence of two plasmon modes, a bright and a dark mode, which exhibit symmetric and antisymmetric dipole configurations between the layers, respectively. The dark mode resonance energy depends sensitively on the size of the particles and the interparticle gaps. Hotspots with a nearfield intensity enhancement of up to 3000 are expected, which, together with the fact that the dark mode is roughly four times narrower than the bright mode, reveals how promising these materials are for spectroscopy purposes.

An umbrella‐shaped broadband circularly polarized antenna with wide beamwidth for global navigation satellite systems applications

AbstractA novel umbrella‐shaped wideband circular polarization (CP) antenna with a wide half‐power beamwidth (HPBW) and a wide axial ratio (AR) bandwidth is proposed in this article. Two pairs of symmetrical patch dipoles are attached to the surface of an umbrella‐shaped substrate to broaden both the impedance bandwidth (IBW) and the HPBW. A parasitic metallic ring is located immediately above the umbrella substrate to provide further enhancement of the HPBW. Each patch dipole is excited via a coaxial line, while a conductor balun with length of λ0/4 (where λ0 is the wavelength of the center frequency) is introduced to obtain a feeding balance. Measurement results indicate that the proposed antenna has a −10 dB IBW of 71.3% (from 1.03 to 2.17 GHz), and a 3 dB AR bandwidth of 55.6% (from 1.13 to 2.0 GHz). Additionally, an HPBW of more than 110° is obtained over the whole CP bandwidth, 48.2% of which has an HPBW of more than 120°. The antenna has dimensions of 100 × 100 × 28 mm3, which corresponds to (0.52 × 0.52 × 0.14)λ03.