Aperture Field Research Articles

Multibeam Forming With Arbitrary Radiation Power Ratios Based on a Conformal Amplitude–Phase-Controlled Metasurface

In this communication, we present a novel amplitude–phase-controlled metasurface (APCMS), which features a full <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\pi $ </tex-math></inline-formula> phase coverage and amplitude variation from 0 to 1 for transmissive waves. By alternately cascading three ultrathin printed circuit boards (PCBs) and two curved 3-D-printed substrates, the proposed APCMS is designed to be a cambered surface and can be applied to certain space-constrained scenarios. Different from phase-only controlled metasurfaces (MSs), with the ability to impart a new degree of freedom, we use the APCMS to construct a spatial power divider by superimposing multiple aperture fields assigned to amplitude weighting coefficients. As a proof-of-concept example, two quarter-cylindrical APCMS-based spatial power dividers are designed to generate equal-power and unequal-power triple-beam radiation patterns at different and same elevation angles, respectively. A prototype of an equal-power divider is fabricated and measured to verify the proposed strategy. The results show that upon illumination of a feed horn, the maximum difference among the realized gains of the three beams is less than 0.9 dB at 12 GHz. Their 3 dB gain bandwidths are 26.7%, 19.5%, and 23.3%. Our study holds potential applications in multibeam shaping and multiple target tracking systems.

Comparative Analysis of Imaging and Measurements of Micrometer-Scale Fracture Aperture Fields Within a Heterogeneous Rock Using PET and X-ray CT

Comparative Analysis of Imaging and Measurements of Micrometer-Scale Fracture Aperture Fields Within a Heterogeneous Rock Using PET and X-ray CT

Ray-Tracing Model for Generalized Geodesic-Lens Multiple-Beam Antennas

geodesic-lenses are a compelling alternative to traditional planar dielectric lens antennas, as they are low loss and can be manufactured with a simple mechanical design. However, a general approach for the design and analysis of more advanced geodesic-lens antennas has been elusive, limiting the available tools to rotationally symmetric surfaces. In this article, we present a fast and efficient implementation built on geometrical optics and scalar diffraction theory. A numerical calculation of the shortest ray path (geodesic) using an open-source library helps quantify the phase of the electric field in the lens aperture, while the amplitude is evaluated by applying ray-tube power conservation theory. The Kirchhoff-Fresnel diffraction formula is then employed to compute the far field of the lens antenna. This approach is validated by comparing the radiation patterns of a transversely compressed geodesic Luneburg lens (elliptical base instead of circular) with the ones computed using commercial full-wave simulators, demonstrating a substantial reduction in computational resources. The proposed method is then used in combination with an optimization procedure to study possible compact alternatives of the geodesic Luneburg lens with size reduction in both the transverse and vertical directions.

Inference of geostatistical hyperparameters with the correlated pseudo-marginal method

We consider non-linear Bayesian inversion problems targeting the geostatistical hyperparameters of a random field describing hydrogeological or geophysical properties given hydrogeological or geophysical data. This problem is of particular importance in the non-ergodic setting as there are no analytical upscaling relationships linking the data to the hyperparameters, such as, mean, standard deviation, and integral scales. Full inversion of the hyperparameters and the local properties of the field (typically involving many thousands of unknowns) brings substantial computational challenges, such that simplifying model assumptions (e.g., homogeneity or ergodicity) are typically made. To prevent the errors resulting from such simplified assumptions while also circumventing the burden of high-dimensional full inversions, we use a pseudo-marginal Metropolis–Hastings algorithm that treats the random field as latent variables. In this random effects model, the intractable likelihood of observing the data given the hyperparameters is estimated by Monte Carlo averaging over realizations of the random field. To increase the efficiency of the method, low-variance approximations of the likelihood ratio are obtained by using importance sampling and by correlating the samples used in the proposed and current steps of the Markov chain. We assess the performance of this correlated pseudo-marginal method by considering two representative inversion problems involving diffusion-based and wave-based physics, respectively, in which we infer the hyperparameters of (1) hydraulic conductivity fields using apparent hydraulic conductivity data in a data-poor setting and (2) fracture aperture fields using borehole ground-penetrating radar (GPR) reflection data in a more data-rich setting. For the first test case, we find that the correlated pseudo-marginal method generates similar estimates of the geostatistical mean as classical rejection sampling, while an inversion assuming ergodicity provides biased estimates. For the second test case, we find that the correlated pseudo-marginal method estimates the hyperparameters well, while rejection sampling is computationally unfeasible and a simplified model assuming homogeneity leads to biased estimates.

Circular Airy-like beams through leaky-wave antennas

A planar nonuniform radially periodic leaky-wave antenna is proposed for the generation of circular, azimuthally symmetric Airy beams. The design is compact and low cost, and it is excited by an integrated coaxial cable. An annular metal strip grating is considered as background structure, designed to support a fast, backward, radially propagating space harmonic, which is capable of generating nondiffracting fields. The period and slots width are then properly modulated to synthesize the relevant Airy-like aperture-field distribution. An approximate formula is proposed to describe the aperture field, which is then used to retrieve the pattern of the annular strips. The near field produced by the structure is evaluated through the radiation integral, and validated by means of numerical full-wave simulations.

Leaky-Wave Analysis of TM-, TE-, and Hybrid-Polarized Aperture-Fed Bessel-Beam Launchers for Wireless-Power-Transfer Links

Bessel beams (BBs) can be generated at microwave frequencies by means of compact, planar devices based on Fabry–Perot cavity leaky-wave resonators. Most designs are based on the excitation of a single transverse magnetic/transverse electric (TM/TE) leaky mode by means of a vertical electric/magnetic dipole source. In this work, we analyze the important case of a horizontal magnetic dipole, which excites both TM and TE modes, developing an original theoretical framework suitable for resonant radiators. Analytical expressions are provided for the dominant leaky-wave aperture field. The near-field distribution is then evaluated through an accurate numerical integration of the radiating currents and validated through full-wave simulations for the relevant case of a BB launcher when excited by a waveguide-fed slot. Different designs are presented and analyzed in order to obtain TM, TE, and hybrid polarizations, finding in all cases an excellent agreement between simulations and theoretical results. Finally, we evaluate and compare the wireless-power-transfer efficiency of two coupled TM-, TE-, or hybrid-polarized BB launchers when a wireless link is established in the radiative near-field region. Interestingly, full-wave results demonstrate the superior performance of resonant BB launchers in TM or TE polarization with respect to the nonresonant hybrid case.

Analysis of Cross-Polarized Field by Panel Misalignment Errors in a Deployable Reflector Antenna

This paper analyzes the generation mechanism of a cross-polarized field resulting from panel misalignment errors in a solid-surface deployable antenna. Misalignment of the panel in a deployable antenna results in path length error and rotation of the unit normal vector on the reflector surface. However, in terms of the analysis of cross-polarization (cross-pol) generation, rotational error is a more significant factor. In the aperture field, the distributions of cross-pol components are calculated to identify the polarization characteristics of the radiated field. For uniform misalignment, the peak-to-cross polarization (XPOL) is found to be smaller than -50 dB for misalignment angles less than 3°. Furthermore, when the panels are non-uniformly misaligned with a sinusoidal distribution, the cross-pol level depends on the angular position of the maximum misalignment.

Independent Manipulation of Aperture and Radiation Fields in a Transmission‐Reflection Integrated Complex‐Amplitude Metasurface

AbstractMetasurfaces have superior performance in flexible wave manipulation used for various multifunctional devices. However, they remain challenging for the completely spatial manipulation of electromagnetic waves including wave propagation direction and distance degrees of freedom. Here, a novel strategy of multiplexing metasurface with a non‐interleaved meta‐atoms array is introduced. The design fully explores wave propagation direction and distance degrees of freedom by combining irregular complex‐amplitude encoding method and transmission‐reflection selective meta‐atom. Therein, by limiting effective meta‐atoms to a specific geometry and encoding highly selective phase sequences for wavefront shaping to these meta‐atoms, the distance multiplexing properties of aperture and radiation fields can be designed to suit application needs. Also, the transmission‐reflection integrated meta‐atoms is further engineered to increase the propagation direction degrees of freedom in electromagnetic manipulation. As proof of concept, a six‐channel metasurface operating in one transmitted mode and two reflected modes are experimentally generated, enabling us to reconstruct an aperture‐field printing image and a radiation‐field holographic image for each mode simultaneously. This strategy may have an alternative route for potential applications such as data storage, image encryption, and information communication systems.

Heat extraction performance of fractured geothermal reservoirs considering aperture variability

It is still a challenging task to explain the uncertainty of the production of fractured geothermal reservoirs by using a parallel plate model without considering the variable aperture. Hence, we incorporated a heterogeneous aperture field with contact obstacles into a discrete fracture network (DFN) with different connection paths and densities and executed a medium-scale fluid flow and heat transfer simulation. The results show that severe flow channelization occurs in fracture systems with variable apertures, and the effective flow area is less than 40%. The increase in correlation length and contact obstacles leads to a decrease in the flow rate. The flow topology network reveals the reselection of dominant flow channels in the DFN. The effective flow intensity is independent of the fracture density and connection path length but has a negative correlation with the correlation length. The production temperature and cumulative heat energy production of the DFN model show a linear relationship with the correlation length. Finally, the strong correlation between cumulative heat production and the effective flow area emphasizes the critical role of flow channelization in the heat extraction of complex fracture systems. This study provides useful help for understanding how the micro heterogeneous aperture impacts macro production.

Reconfigurable Bidirectional Beam-Steering Aperture With Transmitarray, Reflectarray, and Transmit-Reflect-Array Modes Switching

The design and experiment of an electronically reconfigurable bidirectional spatially-fed array are presented, which combines the functionalities of reconfigurable transmitarray (TA), reflectarray (RA), and transmit-reflect array (TRA). First, we demonstrate a novel bidirectional unit cell composed of a tunable resonant layer between a pair of orthogonally oriented metal gratings. Two positive-intrinsic-negative (PIN) diodes are integrated into the tunable resonant layer to achieve the 1-bit phase resolution in either transmission or reflection mode. Based on the proposed unit cell, a 16 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times16$ </tex-math></inline-formula> -element array arranged in a square grid, which can be controlled independently by a field programmable gate array (FPGA)-based digital control circuit, is excited by a linearly-polarized horn to show the beam steering ability of reconfigurable TA and RA. To realize TRA function integration with the bidirectional beam independent steering simultaneously, the method based on superposition of the aperture fields (SAF) on the aperture is used. In SAF design, the entire aperture is divided into transmission and reflection modes co-existing, and the arrangement and phase distribution are optimized by particle swarm optimization (PSO) algorithm to achieve minimum sidelobe levels (SLLs) and peak gain of bidirectional beam. The measured results of the prototype demonstrate that the antenna can steer bidirectional beam both in simultaneous and time division operating modes, which is not reported to the best of the authors’ knowledge. Our proposed method opens a new avenue for the design of high-performance multifunctional reconfigurable antenna systems.

Analysis of Field Propagation inside A Waveguide Diplexer using Cavity Model Analysis

This paper presents a numerical analysis of field propagation inside a waveguide diplexer network. To do the analysis the diplexer network has been modeled using multiple cavities and then solved using a method of moments. Field propagation inside the network has been demonstrated in terms of aperture field distributions at various transverse planes of the network at the two-channel frequencies and a stopband frequency. To validate the numerical analysis, the frequency responses of the diplexer have been compared with literature available data.

Analytical approach for calculation of aperture efficiency enhancement of horn antennas using a thin metal cylinder

AbstractThis study aims to increase horn antenna gain and aperture efficiency in a way that are compatible with aperture electric field distribution similar to TE10 rectangular waveguide mode using analytical calculation method. The proposed analytical approach can be useful to calculate the performance of a horn antenna design with thin (r«λ) perfect electric conductor (PEC) cylinder placed on the antenna aperture dividing H‐plane. In the analytical solution, the aperture field distribution is obtained by solving the electromagnetic scattering from an infinitely long cylinder placed in front of the aperture. This structure not only improves the aperture electric field amplitude distribution but also corrects phase errors in the horn antenna. An X‐band pyramid horn antenna is manufactured by using three‐dimensional (3‐D) printer and coated with aluminum tape. The measurement results of the 3‐D printed antenna are also compared with the simulation results. The antenna gain is measured with and without the PEC cylinder on the aperture. It is found that, the antenna gain is increased by 1 dB. The results of the proposed analytical calculation method are compared with the simulation and measurement results and justified.

Parallel-mode-channel approach to multimode Gaussian state estimation

The imaging process and its corresponding state estimation are treated as parallel mode channels and two estimation subproblems, respectively. In the two subproblems, the displacement vector and covariance matrix of the object field are estimated independently from the measured ones of the aperture field by minimizing their respective cost functions defined quantum mechanically. The measurement scheme is also briefly discussed. As an application, the location estimation of a point feature of a disk object is studied analytically and numerically. The results show that the estimation that uses only the displacement vector does not enhance the resolution of the amplitude image to a large extent. On the contrary, the quantum Cram\'er-Rao bound of spatial resolution can be pushed down toward the uncertainty relation. Furthermore, the high quantum fidelities verify the effectiveness of the estimation and the broad applicability to arbitrary multimode Gaussian states.

Upper bounds on focusing efficiency.

Upper bounds on the focusing efficiency of aperture fields and lens systems are formulated using integral equation representations of Maxwell's equations and Lagrangian duality. Two forms of focusing efficiency are considered based on lens exit plane fields and optimal polarization currents within lens design regions of prescribed shape and available materials. Bounds are compared against the performance of classical prescriptions of ideal lens aperture fields, hyperbolic lens designs, and lenses produced by inverse design. Results demonstrate that, without regularization, focusing efficiency based solely on lens exit plane fields is unbounded, similar to the problem of unbounded antenna directivity. Additionally, results considering extruded two-dimensional dielectric geometries driven by out-of-plane electric fields for the calculation of bounds and inverse design demonstrate that aperture fields based on time-reversal do not necessarily yield optimal lens focusing efficiency, particularly in the case of near-field (high numerical aperture) focusing.

Sidelobe Suppression for Leaky-Wave Antennas Using a Complementary Paired Configuration

In this letter, an effective method is proposed to suppress the overall sidelobes for period-modulated leaky-wave antennas (PM-LWAs). The radiation mechanism of the high sidelobes in PM-LWAs is thoroughly investigated by space harmonic (SH) analysis of the aperture field. It is found that the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n = 0$</tex-math></inline-formula> SH in PM-LWAs occupies a larger proportion of power than that in periodic LWAs (P-LWAs), resulting in a higher sidelobe level (SLL) in PM-LWAs than that in P-LWAs. An SLL suppression method for PM-LWAs is proposed based on even SH cancellation, which is realized by aligning inversed period modulations in a pair of PM-LWAs. Exciting the PM-LWA pair with equal amplitudes and reversed phases, all radiations from the even SHs are cancelled out and hence the overall sidelobes including the first sidelobe and grating lobe are efficiently suppressed. Prototypes are designed, simulated, fabricated, and experimentally measured. Measured results agree well with simulations, which verify the theoretical predictions. The overall sidelobes are suppressed by more than 10 dB in almost the entire forward region. The radiation of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n = - 2$</tex-math></inline-formula> SH (grating lobe) and the first sidelobe is reduced by more than 20 and 3.4 dB, respectively.

Customizable landmark-based field aperture design for automated whole-brain radiotherapy treatment planning.

To develop and evaluate an automated whole-brain radiotherapy (WBRT) treatment planning pipeline with a deep learning-based auto-contouring and customizable landmark-based field aperture design. The pipeline consisted of the following steps: (1) Auto-contour normal structures on computed tomography scans and digitally reconstructed radiographs using deep learning techniques, (2) locate the landmark structures using the beam's-eye-view, (3) generate field apertures based on eight different landmark rules addressing different clinical purposes and physician preferences. Two parallel approaches for generating field apertures were developed for quality control. The performance of the generated field shapes and dose distributions were compared with the original clinical plans. The clinical acceptability of the plans was assessed by five radiation oncologists from four hospitals. The performance of the generated field apertures was evaluated by the Hausdorff distance (HD) and mean surface distance (MSD) from 182 patients' field apertures used in the clinic. The average HD and MSD for the generated field apertures were 16±7 and 7±3mm for the first approach, respectively, and 17±7 and 7±3mm, respectively, for the second approach. The differences regarding HD and MSD between the first and the second approaches were 1±2 and 1±3mm, respectively. A clinical review of the field aperture design, conducted using 30 patients, achieved a 100% acceptance rate for both the first and second approaches, and the plan review achieved a 100% acceptance rate for the first approach and a 93% acceptance rate for the second approach. The average acceptance rate for meeting lens dosimetric recommendations was 80% (left lens) and 77% (right lens) for the first approach, and 70% (both left and right lenses) for the second approach, compared with 50% (left lens) and 53% (right lens) for the clinical plans. This study provided an automated pipeline with two field aperture generation approaches to automatically generate WBRT treatment plans. Both quantitative and qualitative evaluations demonstrated that our novel pipeline was comparable with the original clinical plans.

Electrically large aperture horn array antenna with low side lobe level for Ku‐band frequency

AbstractUsing electrically large antennas for array applications may cause grating lobes and this can change the array pattern. To achieve a low side lobe level for boresight pattern for linear or planar array antennas, in the literature it is seen that the common method is the use of feeding each antenna with some amplitude distribution and keeping the distance between the antennas less than a wavelength. However, in this study the distance between the antennas is chosen to be greater than a wavelength. Therefore, the common methods cannot be used. To achieve a low side lob level in the radiation pattern for an array of antennas composed of antennas with a distance greater than one wavelength. The aperture length of each antenna is chosen to be variable and an analytical solution method is used to calculate the amplitude of each aperture field of the horn antennas. Thus, the determination of unit horns' optimal aperture lengths Li can be considered a multivariable optimization problem. This challenging problem was achieved using a novel meta‐heuristic optimization algorithm called the differential evolutionary algorithm (DEA), where the aperture lengths of each array element are taken as inputs to find the optimal side lobe level (SLL). Based on the obtained solutions, a 4 × 1 horn array antenna design alongside its feed network was designed for Ku‐band applications. The design of the array is simulated in CST simulation software, and the obtained simulated results had been compared with experimental results and counterpart designs in the literature.

Internal Solitary Waves in the White Sea: Hot-Spots, Structure, and Kinematics from Multi-Sensor Observations

A detailed picture of internal solitary waves (ISWs) in the White Sea is presented based on an analysis of historical spaceborne synthetic aperture radar (SAR) data and field measurements. The major hot-spot of ISW generation locates in the southwestern (SW) Gorlo Strait (GS), characterized by the presence of strong tides, complex topography, and two distinct fronts. Here, pronounced high-frequency isopycnal depressions of 5–8 m were regularly observed during flood and flood/ebb slackening. Other regions of pronounced ISW activity are found near Solovetsky Islands and in the northwestern Onega Bay. The spatial and kinematic properties of the observed ISWs are linked to water depth, with larger wave trains and higher propagation speeds being observed over the deep regions. Direct estimates of ISW propagation speeds from sequential and single SAR images agree well, while theoretical ones obtained using a two-layer model overestimate the observed values by 2–3 times. This is explained by the effective modulation of ISW propagation speed during the tidal cycle by background currents that are not accounted for in the model. Enhanced values of diapycnic diffusion coefficient in the pycnocline layer were registered near the frontal zones, where intense 14–17 m high ISWs were regularly observed.

Generalized Sequential Rotation Arrays With Full Control of Dual-Circularly-Polarized Aperture-Field Distribution Based on Elliptically-Polarized Elements

In this article, the theory, design, and experimental validation of wideband generalized sequential rotation arrays (GSRAs) are reported. In particular, the GSRA has the ability to provide dual-circularly polarized (dual-CP) beams with different handedness using a single feeding network, whose aperture amplitude and phase distributions can both be independently controlled. Such functionality is achieved by jointly utilizing the dynamic phase and Berry phase, as well as exploiting elliptically polarized (EP) array elements with different axial ratio (AR) values. The proposed technique and the design methodology are verified by two proof-of-concept microstrip GSRAs consisting of an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times8$ </tex-math></inline-formula> array of EP stacked-patch elements operating in the K-band. The first prototype exhibits a 3 dB gain difference between the two CP beams, while the other offers a 6 dB gain difference and different sidelobe levels (SLLs) for the generated dual-CP beams. Both arrays are fabricated and measured, experimentally achieving a joint <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{11} &lt; -10$ </tex-math></inline-formula> dB, AR < 3 dB, and 3 dB gain bandwidth of more than 28.4% and 20.1% with a beam squinting of less than 3°. In addition, the two GSRAs enable a bandwidth of about 19% and 3% within which the gain difference between the two CP beams of different handedness deviates from the targeted value by less than 1 dB. With the large degree of freedom in aperture field control, the proposed GSRAs could be potential candidates for use in satellite communications, point-to-multipoint communications, and so on.

Understanding intrinsic healing process in cementitious cracks through modeling and experiments

This study aims to understand the intrinsic healing process along crack depth in cementitious materials with various physical and chemical parameters. A new, coupled transport-thermodynamics model was formulated to predict crack wall profile change with time due to healing. The model considers the time-dependent interaction among ions transport through crack depth, healing products precipitation along crack walls, and local alteration of crack transport properties. The model was validated by controlled experiments quantifying the 3D crack aperture field before and after healing. Using X-ray computed microtomography, scanning electron microscopy and chemical analysis, the experiments uncovered and quantified the non-homogenous healing ratios and chemical compositions along crack depth. Parametric studies further elucidated how different physical (crack width, geometry, flow rate) or chemical (unhydrated cement ratio, ion concentration) parameters affect the healing profile change with time. The results shed light on the intrinsic healing mechanisms and robustness in cementitious materials.