Antenna Mode Research Articles

Unidirectional Dielectric Resonator Antennas Employing Electric and Magnetic Dipole Moments

Through symmetry breaking, an electric dipole moment is generated out of the fundamental magnetic dipole mode of dielectric resonator antennas (DRAs). Unidirectional radiation is then achieved based on the concept of complementary antennas by disturbing the modal field distribution. The eigenmode method and Cartesian multipole analysis are utilized to analyze the modified DRA and quantitatively monitor the amplitude and phase of the dipole moments. The characteristic mode analysis and scattering spectrum method are also applied for further validation. It is found that the unidirectional radiation pattern is obtained by a modified eigenmode instead of the superposition of two adjacent ones. Based on the proposed mechanism, several different design examples are presented. High front-to-back ratios (FBRs) are observed.

Accurate Sub-Structure Characteristic Mode Analysis of Dielectric Resonator Antennas With Finite Ground Plan

In this communication, we develop a surface integral equation-based sub-structure characteristic mode (CM) formulation to accurately analyze the resonant modes of dielectric resonator antennas (DRAs) with finite ground plane (GP). Two numerical examples of practical DRAs with finite GP are presented to compare the differences between the modal results obtained from the conventional full-structure and the proposed sub-structure CM formulations. It is found that the full-structure CM formulation leads to some resonant modes of the finite GP, which are undesirable modes for the DRA design. On the contrary, the proposed sub-structure CM formulation can suppress the undesirable modes. Thus, the sub-structure CMs are more suitable for the modal analysis of the resonant behavior of the DRAs than the full-structure CMs.

Brightening single-photon emitters by combining an ultrathin metallic antenna and a silicon quasi-BIC antenna

Bright single-photon emitters (SPEs) are fundamental components in many quantum applications. However, it is difficult to simultaneously get large Purcell enhancements and quantum yields in metallic nanostructures because of the huge losses in the metallic nanostructures. Herein, we propose to combine an ultrathin metallic bowtie antenna with a silicon antenna above a metallic substrate to simultaneously get large Purcell enhancements, quantum yields, and collection efficiencies. As a result, the brightness of SPEs in the hybrid nanostructure is greatly increased. Due to the deep subwavelength field confinement (mode size < 10 nm) of surface plasmons in the ultrathin metallic film (thickness < 4 nm), the Purcell enhancement of the metallic bowtie antenna improves by more than 25 times when the metal thickness decreases from 20 nm to 2 nm. In the hybrid nanostructures by combining an ultrathin metallic bowtie antenna with a silicon antenna, the Purcell enhancement (Fp≈2.6 × 106) in the hybrid nanostructures is 63 times greater than those (≤ 4.1 × 104) in the previous metallic and hybrid nanostructures. Because of the reduced ratio of electromagnetic fields in the ultrathin metallic bowtie antenna when the high-index silicon antenna is under the quasi-BIC state, a high quantum yield (QY ≈ 0.70) is obtained. Moreover, the good radiation directivity of the quasi-BIC (bound state in the continuum) mode of the silicon antenna and the reflection of the metallic substrate result in a high collection efficiency (CE ≈ 0.71). Consequently, the overall enhancement factor of brightness of a SPE in the hybrid nanostructure is EF* ≈ Fp × QY × CE ≈ 1.3 × 106, which is 5.6 × 102 times greater than those (EF* ≤ 2.2 × 103) in the previous metallic and hybrid nanostructures.

Emission Manipulation by DNA Origami‐Assisted Plasmonic Nanoantennas

AbstractPlasmonic nanoantennas mediate far and near optical fields and confine the light to subwavelength dimensions. The spatial organization of nanoantenna elements is critical as it affects the interelement coupling and determines the resultant antenna mode. To couple quantum emitters to optical antennas, high precision on the order of a few nm with respect to the antenna is necessary. As an emerging nanofabrication technique, DNA origami has proven itself to be a robust nanobreadboard to obtain sub‐5 nm positioning precision for a diverse range of materials. Eliminating the need for expensive state‐of‐the‐art top‐down fabrication facilities, DNA origami enables cost‐efficient implementation of nanoscale architectures, including novel nanoantennas. The ability of DNA origami to deterministically position single quantum emitters into nanoscale hotspots further boosts the efficiency of light–matter interaction controlled via optical antennas. This review recapitulates the recent progress in plasmonic nanoantennas assisted by DNA origami and focuses on their various configurations. How those nanoantennas act on the emission and absorption properties of quantum emitters positioned in the hotspots is explicitly discussed. In the end, open challenges are outlined and future possibilities lying ahead are pointed out for this powerful triad of biotechnology, nanooptics, and photophysics.

Coupled and Characteristic Modes of a Wideband Slot Antenna Using FEKO

Coupled Mode Theory (CMT) is a classic model that addresses many diverse problems in physics and electrical engineering. Although CMT is well-established in areas such as directional coupler design, its significance in antenna engineering is less well-recognized. Recently, Characteristic Mode Analysis (CMA) has shown how CMT quantitatively models a wide variety of multi-mode patch structures. In this paper, we extend these ideas to a double-tuned slot antenna utilizing some unique features of the method of moments code FEKO. The modeled slot antenna has a stable radiation pattern throughout its 50% impedance bandwidth. CMA decomposition indicates the antenna consists of two resonators: the slot and a lumped LC resonator that represents the feed probe. The two are electromagnetically coupled to produce broad impedance bandwidth. An equivalent circuit whose values are derived directly from the CMA results is given.

Investigation of the Leaky-Wave Characteristics of a Cylindrical Dielectric Rod Using the Coefficient Matrix of the System of Characteristic Equations and Davidenko’s Method

An open dielectric waveguide includes both guided propagating modes within the waveguide and radiating and evanescent modes that propagate transversely outside the waveguide. In this study, the leaky-wave characteristics of a cylindrical dielectric rod are investigated using the coefficient matrix of the system of characteristic equations and Davidenko’s method. Using the coefficient matrix of the system of characteristic equations simplified the derivative(s) required to use Davidenko’s method. The results obtained for a 10-mm radius structure with a relative dielectric constant of 4 showed that a second antenna mode region existed for higher-order hybrid HE modes and lower-order transverse magnetic (TM) modes. However, it did not exist for transverse electric (TE) modes. Additionally, the hybrid HE modes had larger leaky-wave spectrum and antenna mode regions than both the TE and TM modes. This demonstrates that for antenna applications, hybrid HE modes supply a wider frequency spectrum.

Bright Optical Eigenmode of 1 nm^{3} Mode Volume.

We report on the discovery and rationale to devise bright single optical eigenmodes that feature quantum-optical mode volumes of about 1 nm^{3}. Our findings rely on the development and application of a quasinormal mode theory that self-consistently treats fields and electron nonlocality, spill-out, and Landau damping around atomistic protrusions on a metallic nanoantenna. By outpacing Landau damping with radiation via properly designed antenna modes, the extremely localized modes become bright with radiation efficiencies reaching 30% and could provide up to 4×10^{7} times intensity enhancement.

Online Learning-Based Reconfigurable Antenna Mode Selection Exploiting Channel Correlation

Reconfigurable antennas (RAs) emerged as a promising technology that can deal with channel variations and enhance the capacity and reliability of the wireless channel. To fully exploit the advantage of RAs, optimal antenna modes need to be selected in an online manner. However, the channel statistics are unknown a priori. Multi-armed bandit-based online learning algorithms were proposed to address this challenge, but the main drawback of existing approaches are that their regret scales linearly with the number of antenna modes, which converges slowly when the latter is large. To improve the scalability, we first apply an existing algorithm: Thompson sampling via Gaussian process (TS-GP), and propose two new algorithms for antenna mode selection: upper confidence bound with channel prediction (UCB-CP) and Thompson Sampling with channel prediction (TS-CP). TS-GP uses Gaussian prior to model the reward distribution of each antenna mode, as well as the correlation among them. UCB-CP and TS-CP exploit channel modeling to predict the channel conditions of unexplored antenna modes at each time step, by relating the correlation between different channel states to the underlying antenna modes. We prove the finite-time regret bound of UCB-CP and show that it is independent from the number of arms, when the expected channel estimation errors are small enough. We also extend the algorithms to the mobile setting. Both simulation results and real-world experiments show that all of our proposed learning algorithms can significantly improve the convergence rate and yield much lower regret (thus higher throughput) than existing schemes.

Which plasmonic nano-antenna is best for free-space out-coupling of single photon emission from a hyperbolic metamaterial resonator?

Recently, hyperbolic metamaterials (HMMs) have shown large emission-rate/Purcell enhancement for emitters coupled to them. However, due to the large momentum ($ k $) mismatch between the high-k hyperbolic modes of HMMs and free-space modes, the far-field out-coupling of the emission is limited and requires an antenna. In this work, we present an in-depth theoretical study of the performance of some commonly known plasmonic antennas-cylindrical, cuboid, crossed, and bow-tie-when coupled to a HMM. Of all these antennas, the cylindrical antenna was observed to be the best for out-coupling to the high-$ k $ HMM modes with the Purcell factor and collection efficiencies reaching 1000 and 0.5, respectively. The hyperbolic HMM modes are observed to be efficiently coupled to the resonance modes of the cylindrical antenna, with the antenna modes getting effectively out-coupled into free space. These values are expected to result in two to three orders of fluorescence enhancement from a solid-state single photon source. For other antennas, the greater momentum mismatch between the hyperbolic HMM modes and the antenna modes resulted in relatively much weaker free-space out-coupling.

An analysis of leaky hybrid modes depending on structural parameters in a circular dielectric rod

Abstract Open dielectric waveguides are structures used to guide electromagnetic energy in integrated circuits above the cutoff or as leaky wave antennas propagating the energy transversely out of the waveguide in a narrow region below the cutoff. In this study, the related operating regions for the hybrid EH modes of a cylindrical dielectric rod were obtained analytically. Analyses of the leaky wave characteristics of the hybrid EH modes for various radii of the rod and various dielectric constant values were performed. The guided modes existing above the cutoff with a pure real propagation constant, and the leaky wave modes existing below the cutoff with a complex propagation constant, were obtained from the coefficient matrix of the characteristic equations system of the structure using the bisection method and Davidenko’s method, respectively. Additionally, the guided modes of the structure were obtained and designated in the light of previous studies in the literature. The results show that the frequency spectrum of the antenna mode region increases as the value of the dielectric constant and the radius of the dielectric rod decrease. In addition, a circular dielectric with a smaller radius and dielectric constant had a larger frequency spectrum in the leaky wave antenna applications.

Frequency-Spectra-Based High Coding Capacity Chipless RFID Using an UWB-IR Approach.

A novel methodology is proposed to reliably predict the resonant characteristics of a multipatch backscatter-based radio frequency identification (RFID) chipless tag. An ultra-wideband impulsion radio (UWB-IR)-based reader interrogates the chipless tag with a UWB pulse, and analyzes the obtained backscatter in the time domain. The RFID system consists of a radar cross-section (RCS)-based chipless tag containing a square microstrip patch antenna array in which the chipless tag is interrogated with a UWB pulse by an UWB-IR-based reader. The main components of the backscattered signal, the structural mode, and the antenna mode were identified and their spectral quality was evaluated. The study revealed that the antenna-mode backscatter includes signal carrying information, while the structural mode backscatter does not include any tag information. The simulation findings were confirmed by experimental measurements obtained in an anechoic chamber environment using a 6-bit multipatch chipless RFID tag. Finally, the novel technique does not use calibration tags and can freely orient tags with respect to the reader.

Interaction between filaments and ICRF in the plasma edge

• Recent progresses in understanding of interaction between filaments and ICRF in the plasma edge are summarized. • RF induced convective cells can poloidally distort, stretch and break up filaments and influence the local plasma transport in the SOL. • The mutual influence of multiple filaments induces poloidally distributed and radially extended stripe structures in the wave fields and causes wave scattering. • Filaments redirect part of the RF power from the perpendicular direction to the parallel direction as a result of rectification of antenna power spectrum and mode conversion of fast wave to slow wave. Ion Cyclotron Range of Frequencies (ICRF) heating is a standard heating method for magnetic confinement fusion devices. ICRF waves can interact with filaments in the scrape-off layer (SOL) and induces a series of important phenomena. Understanding their interaction and the related physics is essential to the success of ICRF heating and plasma confinement. This paper is a review paper summarizing the recent progress in understanding of interaction between filaments and ICRF in the plasma edge and presents some key experimental and simulation results. In particular, the influence of RF convective cells on filament transport and the influence of filament on RF wave scattering, energy spectrum density, power redirection and wave mode conversion are discussed in detail. Most results shown in the paper make use of the published work, and some new results about mode conversion are also present.

A Dual-Mode Medium Access Control Mechanism for UAV-Enabled Intelligent Transportation System

With the exponential growth in technologies for the vehicular Internet of things applications and high demands for autonomous road vehicles, future transportation systems are projected to be revolutionized on a global scale. This new landscape requires a stable, flexible, and business-friendly base of connectivity, networking, and computing technology, in which Unmanned Aerial Vehicles (UAVs) can play an important role. A UAV-enabled Intelligent Transportation System (ITS) can provide a cost-effective communication solution to improve the safety and efficiency of the transportation system, particularly if the data traffic is nonhomogeneous and nonstationary. Typically, wireless is the communication medium between vehicles and UAVs in an ITS setting, which is based on the IEEE802.11p MAC protocol adopted by car manufactures. However, the IEEE 802.11p MAC protocol is modified solely for omnidirectional antennas, which restricts network coverage, delay, and throughput. In comparison, the directional antenna has greater network coverage, spatial reuse, and bandwidth. In addition, a multiaccess edge computing (MEC) facility at the backhaul link will provide ultralow latency and high bandwidth services to meet the increasingly growing demand for latency-sensitive vehicle applications such as vehicular video data analytics, autonomous driving, and intelligent navigation. Therefore, this article aims to propose a novel dual-mode MAC protocol that can work in two antenna modes, i.e., directional and omnidirectional. For modeling and simulation purposes, we use the Optimized Network Engineering Tool (OPNET) and aim to seek an evaluation with respect to throughput, media access delay, and retransmission attempts. The results obtained demonstrate the effectiveness of the proposed scheme.

An ultra-thin double-functional metasurface patch antenna for UHF RFID applications

An ultra-thin double-functional metasurface patch antenna (MPA) was proposed, where it can operate not only in the antenna mode but also can simultaneously act as perfect absorber for normal incident waves, suitable for RFID applications in the 868 MHz band. The MPA structure consists of a typical coaxially-fed patch antenna merged, for the first time, with a metasurface absorber acting as artificial ground. A methodology for the unit-cell design of the metasurface is proposed followed by an equivalent circuit model analysis, which makes it possible to transform a low-loss (tandelta =0.0015) unit-cell with highly-reflective characteristics to a perfect absorber for normal incident waves. It is based on modifying the critical external coupling by properly introducing slits on the unit-cell, allowing to design an ultra-thin (lambda _0/225 at 868 MHz) and a very compact structure in comparison to previously developed designs. For validation purposes, the MPA was fabricated and its performances in both functional modes were characterized numerically and experimentally. It is demonstrated that merging the absorber with the patch not only allows obtaining a well-matched (|S_{11}|<-30 dB) antenna with an enhanced gain (by 175.6% compared to a typical patch) at the desired frequency but also leads to an overall thickness of only 2.5 mm (lambda _0/138.1 at 868 MHz). With an absorber size limited to the MPA dimensions, a reasonable 1.3 dB reduction in powers reflected by the MPA was achieved compared to a similar size metallic sheet. Whilst having the lowest profile among the so far reported RFID readers, the proposed MPA can be conveniently fitted for example within the required volume of smart shelf RFID readers or used in portable RFID readers while being capable of mitigating multipath reflection issues and incorrect reading of RFID.

Capacity of Vehicular Ad Hoc Networks Based on Multibeam Directional Transmission

The development of multibeam directional transmission technology used in vehicular ad hoc networks is drawing much more attention in recent years due to its wider coverage ability than omnidirectional transmission. In this paper, we analyse the transport capacity of the vehicular network using different antenna modes in the transmitter and receiver end, respectively. We first construct the cross‐layer model comprising the characteristic of the directional antenna model, arbitrary network model, and interference model. Then, based on scaling laws, we calculate the upper and lower bound of the network capacity with and without the directional multibeam transmission technology. In order to reduce the capacity lower bound computation complexity, several topology frameworks are constructed while taking various interferences into account included in the actual project. Finally, we analyse the capacity under changes of different parameters and also evaluate the law of capacity changes to discover how much improvement multibeam transmission technology can bring to the network performance. Analysis shows that compared with DTOR and OTDR mode, DTDR mode can continue to increase network capacity by 2 to 3 times on the basis of the above two modes.

EMC Chamber Quiet Zone Qualification for Applications Above 1 GHz Using Frequency Domain Mode Filtering

Anechoic chambers used for electromagnetic compatibility (EMC) measurements above 1 GHz are qualified based on the site voltage standing wave ratio (SVSWR) method as per the international standard CISPR 16-1-4. With one antenna at the fixed position, some distance away from the quiet zone (QZ), the SVSWR is acquired by moving a dipole-like antenna along several linear paths that are located at the edge of the QZ. To reduce test burden, the SVSWR method under-samples the measurement by design, in that only six discrete points along each 40 cm linear travel path are measured. As a result, the test results are generally overly optimistic. In this article, we propose to use a novel cylindrical mode coefficient (CMC)-based frequency domain mode filtering techniques to obtain the VSWR. Here, we measure the vector pattern cut of the dipole-like test antenna with an offset placement at the outer edge of QZ. The antenna is then mathematically translated to the rotation center, whereupon a bandpass filter that tightly encloses the test antenna mode spectrum is applied. Two approaches are studied herein for translating the rotation center. One is by applying a path length correction to both magnitude and phase, and the other is by performing a cylindrical far-field transformation on the quasi-far-field data. The difference between the mode filtered antenna pattern and the original perturbed pattern is used to derive the chamber SVSWR. In contrast to the conventional technique, the proposed, novel method does not suffer from positional under-sampling, so it is well-placed to be applied at microwave frequencies and above.

TanDEM-X: 10 Years of Formation Flying Bistatic SAR Interferometry

On June 21, 2010, the TanDEM-X mission was launched and opened a new era in spaceborne radar remote sensing. The first formation flying radar system was built by extending the TerraSAR-X synthetic aperture radar (SAR) mission by a second, TerraSAR-X-like satellite TanDEM-X. The resulting large single-pass SAR interferometer features flexible baseline selection, enabling the acquisition of highly accurate cross-track interferograms not impacted by temporal decorrelation and atmospheric disturbances. The primary objective of the mission was the generation of a global Digital Elevation Model (DEM) with unprecedented accuracy (12-m horizontal resolution and 2-m relative height accuracy). The main mission phase for DEM data acquisition has been finished in 2014; the processing of the global TanDEM-X DEM was concluded in September 2016. The final DEM product is well within specifications and features an extremely low percentage of void areas. It is of fundamental importance for a wide range of commercial and scientific applications. But the scientific exploitation of TanDEM-X is not limited to the DEM. TanDEM-X has unique capabilities, including along-track interferometry, and new bistatic and multistatic SAR techniques, that support numerous secondary mission objectives. Indeed, some of these experiments were directly performed during the DEM acquisition phase, when suitable satellite formation geometries were available. Moreover, regular acquisitions over selected super test sites enabled multitemporal analyses. A dedicated science phase after the DEM acquisitions included up to 4 km cross-track baselines, operation in the so-called Dual-Receive Antenna mode, as well as a period in pursuit monostatic flight formation. Comparisons of the TanDEM-X DEM with that of SRTM, or among multitemporal TanDEM-X data, revealed dramatic, ongoing, changes in Earth's topography, especially over ice and forests. In the last 3.5 years the mission has further acquired data for a global change layer showing the height changes relative to the first global DEM dataset. The so-called “Change DEM” is planned for release in 2021. Despite being well beyond their design lifetime, both satellites are still fully functional and have enough consumables for several additional years. Therefore, bistatic operations continue with a focus on changes in the cryosphere, biosphere, and densely populated urban areas.

Phase-retrieval Fourier microscopy of partially temporally coherent nanoantenna radiation patterns.

We report an experimental technique for determining phase-resolved radiation patterns of single nanoantennas by phase-retrieval defocused imaging. A key property of nanoantennas is their ability to imprint spatial coherence, for instance, on fluorescent sources. Yet, measuring emitted wavefronts in absence of a reference field is difficult. We realize a defocused back focal plane microscope to measure phase even for partially temporally coherent light and benchmark the method using plasmonic bullseye antenna scattering. We outline the limitations of defocused imaging which are set by spectral bandwidth and antenna mode structure. This work is a first step to resolve wavefronts from fluorescence controlled by nanoantennas.

A novel high-power waveguide phase shifter with continuous linear phase adjustment.

A novel all-metal phase shifter with continuous linear phase adjustment for high-power microwave applications is presented and tested in this paper. The phase adjustment is achieved through the rotation of a phase reverser for a circularly polarized wave, and the output phase accomplishes a phase adjustment range of 360° by rotating the phase reverser for 180°. Due to the symmetrical characteristics, its position after rotating 180° is the same as the initial position, which can achieve continuous phase adjustment and avoid phase mutation. Simulation results indicate that the phase shifter achieves the transmission efficiency greater than 99.90% at a center frequency of 8.4 GHz, and the bandwidth of transmission efficiency greater than 98.00% is up to 50 MHz. Experiments are carried out and the measured results are in good agreement with simulation. To sum up, the power capacity of this phase shifter is estimated to be more than 80 MW under vacuum conditions (<10-3 Pa), and it can be applied to fast continuous high-power beam-steerable antenna arrays or mode conversion systems.

Chipless RFID Reading Method Insensitive to Tag Orientation

This article presents a new reading method which is able to decode the backscattered signal of a chipless tag without any assumption on its orientation. The method is analytically justified by a model and can be applied to any known scatterers or chipless tags composed of multiple resonators. The presented approach is based on two orthogonal measurements in co-polarization on the reader part and can be optionally combined with time gating. Finally, read range is not reduced with this method since the entire energy of the chipless tag's antenna mode is exploited by the reader.