Antenna Response Research Articles

3D Printed Active Origami Dielectrics for Frequency Tunable Antennas Through Mechanical Actuation

The possibility of using a reconfigurable metamaterial structure based on high permittivity dielectric elements in a flexible origami framework to control the electromagnetic response of a suspended patch antenna is investigated. Two different modular origami-inspired dielectric structures are fabricated by additive manufacturing and their insertion in the air gap of a suspended patch antenna is shown to modify the patch resonant frequency, originally designed to operate at approximately 1 GHz. Fused filament fabrication is used to manufacture dielectric origami using a ABS-30 vol% BaTiO₃ filament with a dielectric permittivity of ~11 to produce dielectric elements that are then connected by flexible hinges. A second structure is composed of a flexible, polymeric origami lattice manufactured by stereolithography containing inserted dielectric elements of ABS-60 vol% CaTiO₃ manufactured by field assisted sintering and with permittivity of ~18. Tunablity is achieved by different configurations of the dielectric origami, actuated by hand or mechanically, which varies the density of the dielectric origami and thus its effective permittivity and the patch resonant frequency. The dielectric origami structures provide a tunable range up to ~14% in good agreement with numerical simulations. Simulations were also used to show how a broader tunability range can be achieved easily, for example, by optimizing the size of the dielectric elements. Overall, the results from the preliminary dielectric origami structures shown here, enabled by advances in multi-material additive manufacture, suggest that the approach offers a wide design space with the potential to realise novel antenna functionality and flexibility.

Imaging sensitivity of a linear interferometer array on lunar orbit

ABSTRACT Ground-based observation at frequencies below 30 MHz is hindered by the ionosphere of the Earth and radio frequency interference. To map the sky at these low frequencies, we have proposed the Discovering the Sky at the Longest wavelength mission (DSL, also known as the ‘Hongmeng’ mission, which means ‘Primordial Universe’ in Chinese) concept, which employs a linear array of micro-satellites orbiting the Moon. Such an array can make interferometric observations achieving good angular resolutions despite the small size of the antennas. However, it differs from the conventional ground-based interferometer array or even the previous orbital interferometers in many aspects, new data-processing methods need to be developed. In this work, we make a series of simulations to assess the imaging quality and sensitivity of such an array. We start with an input sky model and a simple orbit model, generate mock interferometric visibilities, and then reconstruct the sky map. We consider various observational effects and practical issues, such as the system noise, antenna response, and Moon blockage. Based on the quality of the recovered image, we quantify the imaging capability of the array for different satellite numbers and array configurations. For the first time, we make practical estimates of the point source sensitivity for such a lunar orbit array, and predict the expected number of detectable sources for the mission. Depending on the radio source number distribution which is still very uncertain at these frequencies, the proposed mission can detect 102–104 sources during its operation.

Reversible Tuning of Mie Resonances in the Visible Spectrum.

Dielectric optical nanoantennas are promising as fundamental building blocks in next generation color displays, metasurface holograms, and wavefront shaping optical devices. Due to the high refractive index of the nanoantenna material, they support geometry-dependent Mie resonances in the visible spectrum. Although phase change materials, such as the germanium-antimony-tellurium alloys, and post-transition metal oxides, such as ITO, have been used to tune antennas in the near-infrared spectrum, reversibly tuning the response of dielectric antennas in the visible spectrum remains challenging. In this paper, we designed and experimentally demonstrated dielectric nanodisc arrays exhibiting reversible tunability of Mie resonances in the visible spectrum. We achieved tunability by exploiting phase transitions in Sb2S3 nanodiscs. Mie resonances within the nanodisc give rise to structural colors in the reflection mode. Crystallization and laser-induced amorphization of these Sb2S3 resonators allow the colors to be switched back and forth. These tunable Sb2S3 nanoantenna arrays could enable the next generation of high-resolution color displays, holographic displays, and miniature LiDAR systems.

Numerical simulation of the frequency response and phase response of combined UWB antennas in the receiving-transmitting mode

Results of a simulation and experimental study of a combined ultra-wideband antenna, which is a combination of electric and magnetic dipoles, are presented. The input signal recovery of the transceiver path of combined antennas made by the MathCad code and the experimental one were compared. The reconstruction took place according to the frequency and phase responses of the transceiver path of these antennas.

Substrate integrated waveguide omnidirectional filtering antenna with a controllable radiation null for 5.8 GHz WiFi application

A filtering antenna composed of a monopole and two stacked circular substrates integrated waveguide (SIW) cavity for 5.8 GHz WiFi application is proposed in this letter. Cross-coupling between the feeding probe and the second SIW cavity resonator is utilized to generate a radiation null at the frequency above the working band. By properly designing the location of the feeding probe and the size of the coupling slot between the two SIW resonators, the frequency of the radiation null can be adjusted. Experimental results of the fabricated filtering antenna show good agreement with the simulated performance. The measured filtering antenna response has a return loss greater than 10 dB with a fractional bandwidth of 16.4% centered at 5.48 GHz while there is a radiation null at 6.85 GHz. Omnidirectional patterns are achieved in horizontal plane with a maximum gain of 1.1 dBi. The proposed filtering antenna has the merits of compact size and good stopband radiation suppression.

An ELC meta-resonator inspired wideband wearable MIMO antenna system for biotelemetry applications

A compact wideband multiple-input multiple-output (MIMO) antenna for body-centric communication is presented in this article. Initially, an electric field-driven LC metamaterial resonator inspired monopole antenna is developed that exhibits 122.19 % (1.28–5.30 GHz) bandwidth covering 2.4 GHz WLAN and 3.5 GHz WiMAX application bands. Thereafter, the MIMO antenna is proposed, and a pair of meander line structure as a wideband decoupling network is introduced on the ground plane to reduce the inter-element coupling. The proposed antenna holds a reduced mutual coupling and low envelope correlation coefficient over the wideband. To explain the wideband antenna response and its decoupling mechanism, a circuit model analysis is incorporated. Moreover, the proposed antenna demonstrates a robust performance under complex bending and crumpling conditions with an acceptable specific absorption rate (SAR <1.6) during the on-body conditions. Besides, a high data rate link-margin analysis makes the antenna suitable for wireless biotelemetry.

Response of a Polarimetric Antenna to Ionospherically Propagated Signals

The Earth’s magnetic field causes the ionosphere to be birefringent at radio frequencies, which means that any system using ionospherically propagated radio waves, such as long-distance broadcasting, high-frequency (HF) skywave communications, over-the-horizon radar, and oblique incidence sounders (OIS) will receive pairs of waves with different polarizations. In this article, we develop a model for the polarization of ionospherically propagated radio waves; the polarization is dependent only upon the strength and direction of the magnetic field at the location where the radio wave exits the ionosphere. This leads to the hemisphere of possible incoming directions of arrival to any particular receiver being divided into three distinct regions. We then use this model to predict the response of a polarimetric antenna to a transmitted OIS signal and validate the model against real ionograms, including cases where all three polarization regions can be clearly observed.

Fast and reliable knowledge-based design closure of antennas by means of iterative prediction-correction scheme

PurposeA novel framework for expedited antenna optimization with an iterative prediction-correction scheme is proposed. The methodology is comprehensively validated using three real-world antenna structures: narrow-band, dual-band and wideband, optimized under various design scenarios.Design/methodology/approachThe keystone of the proposed approach is to reuse designs pre-optimized for various sets of performance specifications and to encode them into metamodels that render good initial designs, as well as an initial estimate of the antenna response sensitivities. Subsequent design refinement is realized using an iterative prediction-correction loop accommodating the discrepancies between the actual and target design specifications.FindingsThe presented framework is capable of yielding optimized antenna designs at the cost of just a few full-wave electromagnetic simulations. The practical importance of the iterative correction procedure has been corroborated by benchmarking against gradient-only refinement. It has been found that the incorporation of problem-specific knowledge into the optimization framework greatly facilitates parameter adjustment and improves its reliability.Research limitations/implicationsThe proposed approach can be a viable tool for antenna optimization whenever a certain number of previously obtained designs are available or the designer finds the initial effort of their gathering justifiable by intended re-use of the procedure. The future work will incorporate response features technology for improving the accuracy of the initial approximation of antenna response sensitivities.Originality/valueThe proposed optimization framework has been proved to be a viable tool for cost-efficient and reliable antenna optimization. To the knowledge, this approach to antenna optimization goes beyond the capabilities of available methods, especially in terms of efficient utilization of the existing knowledge, thus enabling reliable parameter tuning over broad ranges of both operating conditions and material parameters of the structure of interest.

Dielectric permittivity effects in the detection of tree roots using ground-penetrating radar

The use of GPR as a method to estimate root biomass has been studied in recent decades as an alternative to avoid traditional methods that are destructive and repetitive. Biomass estimation with GPR is usually done by estimating the volume of roots or other calculated indexes imaged in the radargram and then converting to biomass using correlation methods. The volume estimation varies with the antenna's response, which depends on physical factors of soil moisture, and root properties such as diameter, orientation, depth, and water retention. In this work, we study how the dielectric permittivity variation of roots affects the GPR-derived root diameter estimates. We show that the relationship between dielectric permittivity and the amount of water present in each root affects the imaged diameter. We calculate the dielectric permittivity for roots samples with different moisture content. We acquired sections through a 2 m diameter sandbox, and compared our results with synthetic models.We noticed a correlation between the analyzed indices and the relative dielectric permittivity (εr) in the synthetic data that indicates the diameter estimate may vary widely with roots moisture. We observed that the indexes extracted from the radargrams did not correlate with our independent estimates of dielectric permittivity. To estimate the roots' diameter, we used 40% of the image amplitude generated after the Hilbert transform as a parameter, which resulted in an average error equal to 8%. We also propose a correction factor to eliminate the effects of the amount of water on the diameter estimation. This processing step reduced the diameter estimation error on synthetic models.

Tuning the optical response of Nano dipole antenna by using plasmonic materials as a load in the gap

Possibility of tuning the optical response of a Nano dipole antenna by using various plasmonic based materials is demonstrated. By incorporating various load geometry in Nano dipole antenna’s gap, different optical characteristics of Nano dipole antennas, e.g. extinction cross section (ECS), input impedance, scattering cross section (SCS), has been numerically investigated. It is shown that by properly design, based on desired goal, tunable and broadband absorption cross section can be achieved. In addition, a graphene based load is also incorporated, and multiple peaks for ESC at THz band was showed.

Digital Uncoupling of Coupled Multi-Beam Arrays

Antenna arrays consisting of up to thousands of elements are required in a plethora of applications, such as wireless communications, microwave imaging, radio astronomy, and radar. The electromagnetic fields surrounding the antenna elements are mutually coupled; this means that an excitation of a given element also causes voltages to be induced in the terminals of the neighboring elements. Such coupling causes deviation of the expected antenna array beam response unless mitigation of the mutually-coupled fields available within the beamforming scheme. Antenna mutual coupling also causes LNA noise coupling, which can severely degenerate the noise performance of an array receiver. The mutual coupling between elements can be quantified by measuring the scattering parameters across the array using a vector network analyzer. This paper proposes a low-complexity and real-time capable algorithm that will furnish the uncoupling of mutually coupled elements in the digital signal processing back-end using a fast inversion algorithm for tridiagonal toeplitz matrices.

Field-resolved detection of the temporal response of a single plasmonic antenna in the mid-infrared

Unveiling the spatial and temporal dynamics of a light pulse interacting with nanosized objects is of extreme importance to widen our understanding of how photons interact with matter at the nanoscale and trigger physical and photochemical phenomena. An ideal platform to study light–matter interactions with an unprecedented spatial resolution is represented by plasmonics, which enables an extreme confinement of optical energy into sub-wavelength volumes. The ability to resolve and control the dynamics of this energy confinement on the time scale of a single optical cycle is at the ultimate frontier towards a full control of nanoscale phenomena. Here, we resolve in the time domain the linear behavior of a single germanium plasmonic antenna in the mid-infrared by measuring the complex optical field response in amplitude and phase with sub-optical-cycle precision, with the promise to extend the observation of light–matter interactions in the time domain to single quantum objects. Accessing this fundamental information opens a plethora of opportunities in a variety of research areas based on plasmon-mediated photonic processes and their coherent control, such as plasmon-enhanced chemical reactions and energy harvesting.

Global EM-driven optimization of multi-band antennas using knowledge-based inverse response-feature surrogates

Electromagnetic simulation tools have been playing an increasing role in the design of contemporary antenna structures. The employment of electromagnetic analysis ensures reliability of evaluating antenna characteristics but also incurs considerable computational expenses whenever massive simulations are involved (e.g., parametric optimization, uncertainty quantification). This high cost is the most serious bottleneck of simulation-driven design procedures, and may be troublesome even for local tuning of geometry parameters, let alone global optimization. On the one hand, globalized search is often necessary because the design problem might be multimodal (i.e., the objective function features multiple local optima) or a reasonably good initial design may not be available. On the other hand, the computational efficiency of popular algorithmic approaches, primarily, nature-inspired population-based algorithms, is generally poor. Combining metaheuristics procedures with surrogate modelling techniques and sequential sampling methods alleviates the problem to a certain extent but modelling of nonlinear antenna responses over broad frequency ranges is extremely challenging, and the aforementioned solutions are normally limited to rather simple structures described by a few parameters. This paper proposes a novel approach to global optimization of multi-band antennas. The major component of the presented framework is the knowledge-based inverse surrogate constructed at the level of response features (e.g., frequency and level locations of the antenna resonances). The surrogate facilitates decision-making process of inexpensive identification of the most promising regions of the parameter space, and a rendition of the good-quality initial design for further local tuning. Our methodology is validated using three examples of dual- and triple-band antennas. The average optimization cost is only 150 full-wave antenna analyses while ensuring precise allocation of the antenna resonances at the target frequencies. This performance is demonstrated superior over both local optimizers and population-based metaheuristics.

Rapid prototyping of a bispectral terahertz-to-infrared converter.

Conversion of terahertz radiation into thermal radiation is a promising approach for the development of low cost terahertz instruments. Here, we experimentally demonstrate bispectral terahertz-to-infrared conversion using metamaterials fabricated using a rapid prototyping technique. The converter unit cell is composed of two metal-insulator-metal (MIM) antennas absorbing independently the terahertz radiation at 96 and 130 GHz and a thin carbon nanotubes (CNT) layer used as a thermal emitter. The converter unit cell has a typical λ/100 thickness and sub-wavelength lateral dimensions. The terahertz absorption of the converter was observed by monitoring its thermal emission using an infrared camera. Within the first hundred milliseconds of the terahertz pulse, thermal radiation from the CNTs only increases at the location of the MIM antennas, thus allowing to record the terahertz response of each MIM antenna independently. Beyond 100 ms, thermal diffusion causes significant cross-talk between the pixels, so the spectral information is more difficult to extract. In a steady state regime, the minimum terahertz power that can be detected is 5.8 µW at 130 GHz. We conclude that the converter provides a suitable low-cost solution for fast multi-spectral terahertz imaging with resolution near the diffraction limit, using an infrared camera in combination with a tunable source.

Statistical analysis comparison of HEMP transient response of monopole antenna from facility and burst views

The existing literatures, concentrating on the statistical analysis of transient response of antennas, radiated by high-altitude electromagnetic pulse, always choose an area-based method to calculate the statistics from the perspective of explosion. However, it may be more suitable to analyze from the view of the affected facility position. In this paper, we demonstrate a statistical analysis comparison of multiple norms of the transient response from both viewpoints. Distinguished from the burst view, the location of the affected facility is set as the observer location, and the formulas of uncertain factors, involved in the HEMP coupling calculation of monopole antenna, are derived. An efficient statistical method, based on Polynomial Chaos and Moment of Method, is applied to compute the statistical results of monopole antenna in a finite conductive plane. The statistical comparison reveals several primarily interesting conclusions in the end, which will be beneficial for system-level HEMP vulnerability assessment.

Tunable terahertz circularly polarized dielectric resonator antenna

A circularly polarized (CP) dielectric resonator (DR) antenna (DRA) is implemented and numerically analyzed for terahertz (THz) applications. A composite of different deformed geometries silicon based DRs is utilized for obtaining the orthogonal modes required for achieving the CP response in THz frequency range. A rectangular slab of silicon is kept at the top of the annular circular silicon DR rotated at around 45° for generating the orthogonal degenerate modes. The proposed THz CPDRA provides the 4.67% (3.97-4.16) axial ratio and 3.72% 3.95-4.1 THz impedance bandwidth. The top surface of annular DR is coated by the graphene material for obtaining the tunability in frequency response of antenna. In addition, the proposed antenna provides high gain and radiation efficiency in the THz frequencies.

Semi-insulating GaAs surface modifications and their influence in the response of THz devices

In this work, we use the Metal-Assisted Chemical Etching (MACE) technique together with an NH3 plasma treatment using a Remote Plasma-Enhanced Chemical Vapor Deposition (RPECVD) equipment to modify the surface of semi-insulating GaAs (SI-GaAs) substrates. Using our modified SI-GaAs, we fabricate photoconductive antennas for THz emission to study the modification's influence on the optical and electrical antenna response. We found substantial gaps in the frequency-domain spectra of the devices, whose origin could reside in a change of the substrate's optical absorption due to: (a) a surficial chemical change or (b) a substrate topographic modification or a combination of both. We showed experimentally that slight and reproducible substrate surface modifications could lead to significant variations in the electrical behavior and THz response of SI-GaAs devices.

A unified calibration framework for 21 cm cosmology

ABSTRACT Calibration precision is currently a limiting systematic in 21 cm cosmology experiments. While there are innumerable calibration approaches, most can be categorized as either ‘sky-based,’ relying on an extremely accurate model of astronomical foreground emission, or ‘redundant,’ requiring a precisely regular array with near-identical antenna response patterns. Both of these classes of calibration are inflexible to the realities of interferometric measurement. In practice, errors in the foreground model, antenna position offsets, and beam response inhomogeneities degrade calibration performance and contaminate the cosmological signal. Here, we show that sky-based and redundant calibration can be unified into a highly general and physically motivated calibration framework based on a Bayesian statistical formalism. Our new framework includes sky-based and redundant calibration as special cases but can additionally support relaxing the rigid assumptions implicit in those approaches. We present simulation results demonstrating that, in a simple case, working in an intermediate regime between sky-based and redundant calibration improves calibration performance. Our framework is highly general and encompasses novel calibration approaches including techniques for calibrating compact non-redundant arrays, calibrating to incomplete sky models, and constraining calibration solutions across frequency.

SIW Cavity-Fed Filtennas for 5G Millimeter-Wave Applications

In this article, novel millimeter-wave (mmWave) filtennas (filtering antennas) are proposed to realize compact size and low insertion loss for 5G applications. It is achieved by employing eighth-mode substrate-integrated waveguide (EMSIW) cavities fully shielded by metallized vias and cover as resonators, which are named as fully shielded EMSIW (FSD-EMSIW) cavities. Interdigital coupling between cavities is introduced in order to obtain higher coupling strength for wideband operation. The proposed single-polarized antenna consists of a feeding stripline, two FSD-EMSIW cavities, and two stacked square patches, generating the four-order filtering antenna response. Furthermore, this design has been extended to realize a dual-polarized filtenna by employing double sets of feeding network. For demonstration, single-/dual-polarized filtenna prototypes were fabricated and measured, the measured results show that the 5G mmWave band (24.25-29.5 GHz) can be covered with average gains of 4.5 dBi. Good bandpass filtering response is also observed. Finally, to validate the proposed idea in array applications, a 16-element filtenna array is designed and measured with good performance.

Flexible passive LC resonator for wireless measurement during curing of thermosets

Monitoring of fibre composites is an important task to spread the application of fibre composites. Cure monitoring of the polymer matrix of fibre composites during the fabrication can be realized with interdigital sensors. The measured impedance can be directly related to the curing process. However wiring the sensor may disrupt the material, therefore sensing should be done wireless. As many fibre composites are processed under high temperature and high pressure conditions no electronics can be used inside the material. Here we present the design, fabrication, and characterization of a wireless sensory system using a chipless strategy for online cure monitoring. For this purpose, different combinations of sensors and readers are designed, consisting of a planar inductor-capacitor (LC) resonator, where capacitance is an interdigital capacitor, and an inductor as antenna operating wirelessly through inductive coupling. The designs are realized onto flexible polyimide substrate using microfabrication technology. To characterize the coupling effect, the response of the reader antenna has been carried out when sensor is placed in its vicinity. Furthermore, the curing process of adhesive is demonstrated and results are discussed. It is shown that the curing process of a thermoset polymer can be monitored by a flexible chipless LC resonator wirelessly.