Array Aperture Research Articles

Research on Direction Finding Method under Impulsive Noise Based on Nonuniform Linear Array

Direction of arrival (DOA) estimation under impulsive noise has always been an important research area in array signal processing. The traditional methods under impulsive noise mostly rely on prior parameters and have high computational complexity. Based on the filtering theory, we present an effective pretreatment filtering technology to cut out the impulse mixed in the array received data and employ the nonuniform linear array to improve the estimation performance further. First, according to the amplitude characteristics of impulse noise, the pretreatment filtering technology is proposed to cut out the impulse based on the median filter and sliding average filter, which is valid for both strong and weak impulsive noise. Second, the minimum redundant array is adopted to carry out array virtual expansion so that the array aperture can be increased and the estimation performance can be improved. Finally, based on the idea of matrix reconstruction, we propose the improved estimation of signal parameters via rotational invariance techniques algorithm and an improved root multiple signal classification algorithm for DOA estimation. Theoretical analysis and simulation results show that the proposed method has a simple processing process, small calculation load, good array expansion ability, and excellent noise adaptability. Moreover, the proposed methods greatly improve the direction-finding performance under the condition of low signal-to-noise ratio and strong impulsive noise.

Triad-Displaced ULAs Configuration for Non-Circular Sources with Larger Continuous Virtual Aperture and Enhanced Degrees of Freedom

Non-uniform linear array (NULA) configurations are well renowned due to their structural ability for providing increased degrees of freedom (DOF) and wider array aperture than uniform linear arrays (ULAs). These characteristics play a significant role in improving the direction-of-arrival (DOA) estimation accuracy. However, most of the existing NULA geometries are primarily applicable to circular sources (CSs), while they limitedly improve the DOF and continuous virtual aperture for non-circular sources (NCSs). Toward this purpose, we present a triad-displaced ULAs (Tdis-ULAs) configuration for NCS. The Tdis-ULAs structure generally consists of three ULAs, which are appropriately placed. The proposed antenna array approach fully exploits the non-circular characteristics of the sources. Given the same number of elements, the Tdis-ULAs design achieves more DOF and larger hole-free co-array aperture than its sparse array competitors. Advantageously, the number of uniform DOF, optimal distribution of elements among the ULAs, and precise element positions are uniquely determined by the closed-form expressions. Moreover, the proposed array also produces a filled resulting co-array. Numerical simulations are conducted to show the performance advantages of the proposed Tdis-ULAs configuration over its counterpart designs.

Resolution improvement in aerial imaging by a retroreflector using micro aperture arrays.

For a floating display system using a prism- or bead-type retroreflector, non-retroreflected light is the key cause of the deterioration in image resolution. In the present study, a micro aperture array was used to enhance the image resolution of aerial imaging displays based on prism and bead retroreflectors. The effects of different micro aperture parameters on the divergence angle of the retroreflector were experimentally studied, and the modulation of the point spread function of different retroreflectors was also explored in detail. The experimental results showed that by properly arranging the micro aperture array, the divergence angle of the retroreflective light could be effectively reduced. Moreover, the full width at half maximum of the point spread function of the retroreflector was effectively narrowed. Finally, after the modulation of the micro aperture array, the imaging resolution was increased by 115%-150% compared to the original resolution. The proposed micro array is low cost, easy to process, and flexible and can be applied to a retroreflector-based aerial imaging system to provide high image quality.

Mainlobe and sidelobe jamming suppression method based on distributed array radar with eigen‐projection matrix processing and null constraints

AbstractThe jamming in electronic warfare environment significantly degrades the performance of the radar system, especially the mainlobe jamming. The distributed array radar can suppress the mainlobe jamming by increasing the array aperture with auxiliary arrays. However, when the aperture of an auxiliary array is smaller than that of the main array, it results in residual jamming in auxiliary arrays after beamforming and affects the performance of the radar system. To tackle this issue, a mainlobe and sidelobe jamming joint suppression method with eigen‐projection matrix processing (EMP) and null constraints is proposed. In the proposed method, firstly, the adaptive beamforming with EMP is performed in main and auxiliary arrays to suppress the sidelobe jamming with mainlobe maintenance. Then, the null constraints based on the Capon spectrum of main array are applied to suppress the residual jamming in auxiliary arrays. Finally, the minimum mean square error (MMSE) beamforming is utilised to cancel the mainlobe jamming. Simulation results demonstrate the jamming suppression performance of the proposed method.

Migrated coprime array with low mutual coupling for space limited aperture

It is well established that sparse sensor array can estimate more sources than number of sensors exploiting difference coarray. However, the array aperture size is restricted in space limited scenarios and all sensor elements are distributed in limited space. This could raise potential problems due to the mutual coupling effect. To address this issue, a migrated coprime based sparse array configuration is designed considering the following schemes. Enhancing the length of consecutive part in difference coarray while introducing no extra sensor. The mutual coupling level is reduced as low as possible, and the array aperture is also limited to acceptable level to allow possible applications in space limited scenarios. Simulation results elaborate the superiority of proposed strategy from the above aspects.

Retrieval of Interior Structure of Asteroids with the Low-Frequency Telescope DART

Understanding the internal structure of asteroids is crucial for deciphering their formation and establishing defenses against potential hazards. The Daocheng Radio Telescope (DART), a recently constructed interferometric array designed for low-frequency Sun imaging, presents a promising tool for probing asteroid interiors. With a substantial 1-km array aperture and an equivalent receiving area of approximately 8,850 m 2 , DART plays a vital role in diagnosing asteroid internal structures. This study introduces an electromagnetic wave scattering model tailored to asteroids within DART’s operational frequency range (150 to 450 MHz). Ground-based radar detection can unveil multiple facets of these celestial bodies by leveraging low-frequency waves’ penetrating capabilities and capitalizing on asteroids’ rotational dynamics. Through simulations capturing the characteristics of low-frequency waves traversing a layered model and interacting with internal structures, we propose an electromagnetic scattering model of asteroids. Our results underscore DART’s potential as a crucial instrument for discerning the internal structure of near-Earth objects. We first formulate an asteroid model through celestial impact models, dimensional analysis, and data fitting to achieve this. Subsequently, we derive an electromagnetic scattering model using geometric optics and a propagation model for lossy mediums. Simulations demonstrate that morphology and internal structure dictate the distribution of scattered waves, with forward and backscattered waves providing comprehensive internal structure information over a rotation cycle. Furthermore, we observe that alterations in electromagnetic wave frequency induce changes in the scattering characteristics, prompting the convenience of employing multiple frequencies for retrieving detailed information about an asteroid’s internal medium and structure. This multidimensional approach positions DART as a promising asset in advancing our understanding of asteroid interiors, offering valuable insights for scientific inquiry and hazard mitigation strategies.

Use of the Sub Array From Microstrip Elements in Dielectric Layers Before the Aperture of Phased Antenna Array for Impedance Matching at Scanning

The solution of an electrodynamics’ problem of radiation of the Phased antenna array (PAR), representing the infinite periodic structure generated from the open ends of waveguides is offered. Before an aerial aperture sub array from strip (tape) elements in the dielectric layers is installed. The array in the dielectric layers f organizes of strip-geometry elements artificial medium. The problem is reduced to system of the integrated equations of 1-st sort which is decided concerning unknown fields in the aperture of the open ends of waveguides and currents on stripe-geometry elements. In a wide frequency band the numerical analysis of radiation parameters artificial dielectric medium on PAR electrodynamics’ characteristics at beam steering.

Planar antenna array synthesis for wireless power transmission based on brain storm optimization algorithm

AbstractThis study investigates the synthesis of a two‐dimensional transmitting planar antenna array for a wireless power transmission system. The antenna synthesis problem is transformed into an optimization problem under multiple constraints. Accordingly, a brainstorming optimization algorithm is utilized to optimize the element position of the planar antenna arrays under the constraints of aperture size, array spacing, and side lobe level. A numerical simulation of the beam collection efficiency is conducted under different receiving region shapes. The simulation results confirm the effectiveness of the proposed method in optimizing the two‐dimensional transmitting planar antenna array for wireless power transmission systems.

A high-resolution angle estimation method for distributed aperture arrays

A high-resolution angle estimation method for distributed aperture arrays

Performance Analysis of Multiple Interference Suppression of One Small Four Elements Array Antenna used in Satellite Navigation System

background: The anti-interference requirements of miniaturized satellite navigation arrays is increasing, the anti-interference ability reducing of small aperture arrays caused by large mutual coupling, large main lobe width, may be solved through adopting quad-arrays antenna. objective: Research of multiple interference suppression method is the aim of the paper, and it makes the research of small four element satellite navigation array antenna method: In the paper, it focuses on the structural design of low coupling polarized array antennas, and makes analysis of mutual coupling between array elements, the compensation technology based on auxiliary sources is proposed. result: Experimental analysis of antenna narrowband interference suppression are made. Relevant anti-interference results on four element antenna are also obtained. The anti-interference ability of four element antenna is summarized. conclusion: The anti-interference ability of four element antenna is analyzed and summarized in the paper, related results show that small four element satellite navigation array antenna can be used in the multiple interference suppression, in the satelliate navigation system.

Probing magneto-ionic microstructure towards the Vela pulsar using a prototype SKA-Low station

Abstract The Vela pulsar (J0835 $-$ 4510) is known to exhibit variations in Faraday rotation and dispersion on multi-decade timescales due to the changing sightline through the surrounding Vela supernova remnant and the Gum Nebula. Until now, variations in Faraday rotation towards Vela have not been studied on timescales less than around a decade. We present the results of a high-cadence observing campaign carried out with the Aperture Array Verification System 2 (AAVS2), a prototype SKA-Low station, which received a significant bandwidth upgrade in 2022. We collected observations of the Vela pulsar and PSR J0630 $-$ 2834 (a nearby pulsar located outside the Gum Nebula), spanning $\sim$ 1 and $\sim$ 0.3 yr, respectively, and searched for linear trends in the rotation measure (RM) as a function of time. We do not detect any significant trends on this timescale ( $\sim$ months) for either pulsar, but the constraints could be greatly improved with more accurate ionospheric models. For the Vela pulsar, the combination of our data and historical data from the published literature have enabled us to model long-term correlated trends in RM and dispersion measure (DM) over the past two decades. We detect a change in DM of $\sim$ 0.3 $\mathrm{cm}^{-3}\,\mathrm{pc}$ which corresponds to a change in electron density of $\sim$ $10^5\,\mathrm{cm}^{-3}$ on a transverse length scale of $\sim$ 1–2 au. The apparent magnetic field strength in the time-varying region changes from $240^{+30}_{-20}\,\mu\mathrm{G}$ to $-6.2^{+0.7}_{-0.9}\,\mu\mathrm{G}$ over the time span of the dataset. As well as providing an important validation of polarimetry, this work highlights the pulsar monitoring capabilities of SKA-Low stations, and the niche science opportunities they offer for high-precision polarimetry and probing the microstructure of the magneto-ionic interstellar medium.

Calibration of an SKA‐Low Prototype Station Using Holographic Techniques

AbstractPerformance of digitally beamformed phased arrays relies on accurate calibration of the array by obtaining gains of each antenna in the array. The stations of the Square Kilometer Array‐Low (SKA‐Low) are such digital arrays, where the station calibration is currently performed using conventional interferometric techniques. An alternative calibration technique similar to holography of dish based telescopes has been suggested in the past. In this paper, we develop a novel mathematical framework for holography employing tensors, which are multi‐way data structures. Self‐holography using a reference beam formed with the station under test itself and cross‐holography using a different station to obtain the reference beam are unified under the same formalism. Besides, the relation between the two apparently distinct holographic approaches in the literature for phased arrays is shown, and we show that under certain conditions the two methods yield the same results. We test the various holographic techniques on an SKA‐Low prototype station Aperture Array Verification System 2 (AAVS2) with the Sun as the calibrator. We perform self‐holography of AAVS2 and cross‐holography with simultaneous observations carried out with another station Engineering Development Array 2. We find the results from the holographic techniques to be consistent among themselves as well as with a more conventional calibration technique.

Improving Transmission Efficiency in Optical Wireless Networks with IR Radiative Element Clusters and Phased Array Apertures

Improving Transmission Efficiency in Optical Wireless Networks with IR Radiative Element Clusters and Phased Array Apertures

Ambit-Process-Based Spatial-Wideband MIMO Channel Model for Sub-THz Urban Microcellular Communication

The design and development of sub-Terahertz (sub-THz) cellular systems entail the need for new channel models that can precisely predict channel characteristics beyond 100 GHz in outdoor and dynamic environments. This work proposes a novel multiple-input and multiple-output (MIMO) channel model for cellular communication, developed within the framework of a class of spatio-temporal stochastic processes called ambit-process. The modeling methodology effectively captures the typicalities of sub-THz propagation like molecular absorption and scattering of the evolving multipaths while accounting for the propagation delay of electromagnetic waves across large array apertures deployed at the transmitter and the receiver. This allows for an accurate characterization of the spatial-wideband effect along with other relevant spatio-temporal attributes of the channel. Numerical simulations indicate a good level of agreement between the spectral efficiency and spatio-temporal correlation of the proposed model against a state-of-the-art stochastic Terahertz (THz) channel model and measurements reported in the literature.

Influence of Transceiver Array Aperture Size on Electromagnetic Linear Inverse Scattering From 2-D Objects Embedded in Planarly Multilayered Media

Influence of Transceiver Array Aperture Size on Electromagnetic Linear Inverse Scattering From 2-D Objects Embedded in Planarly Multilayered Media

Influence of 2-D Transceiver Array Aperture Size and Polarization on 3-D Microwave Imaging of Subsurface Objects Under Born Approximation

Influence of 2-D Transceiver Array Aperture Size and Polarization on 3-D Microwave Imaging of Subsurface Objects Under Born Approximation

Extremely Large Aperture Arrays Simulator for Calculating the IRF in Practical Scenarios for Massive MIMO Systems

Extremely Large Aperture Arrays Simulator for Calculating the IRF in Practical Scenarios for Massive MIMO Systems

Coherent signals direction estimation using high-order quantities in the acoustic field

To meet the demands of underwater remote detection technology, the receiving array must be extended to low frequencies by increasing the array aperture required for detection. Furthermore, the base array aperture must be increased owing to the loss of effective array aperture in coherent targets detection using most decoherent algorithms; however, this prevents its use on small platforms, such as autonomous underwater platforms. Thus, reducing the array aperture while ensuring high resolution is required. In this article, high-order quantities in the acoustic field are utilized to construct a full rank covariance matrix to Multiple Signal Classification Method (MUSIC), which achieves high-resolution results for small aperture arrays with small incident angular intervals in low-frequency coherent targets. The correlated noise of each sensor is considered in the small aperture arrays and the gain of each element in the new matrix is derived. The theoretical analysis, numerical simulations, and experimental verifications show the validity of the method.

An off-grid direction-of-arrival estimator based on sparse Bayesian learning with three-stage hierarchical Laplace priors

For direction-of-arrival (DOA) estimation problems, sparse Bayesian learning (SBL) has achieved excellent estimation performance, especially in sparse arrays. However, numerous SBL-based methods with hyperparameters assigned to Gaussian priors cannot enhance sparsity well, and mainly focus on the nested array (NA) or the co-prime array (CPA) that cause relatively large degree of freedom (DOF) losses. Based on this, we propose a novel method with a Bayesian framework containing three-stage hierarchical Laplace priors that significantly promote sparsity. Moreover, the proposed method is based on the minimum hole array (MHA) that retains a larger array aperture than NA or CPA after redundancy removal, which is required and achieved simultaneously by a denoising operation. In addition, to correct the intractable off-grid model errors caused by grid mismatch, a new refinement operation is developed. And, the refinement empirically outperforms others based on Taylor expansion. Extensive simulations are presented to confirm the superiority of the proposed method beyond state-of-the-art methods.

Altitude measurement method of VHF radar based on spatial smoothing of correlation matrix

For very high frequency (VHF) phased array radar, the key problem to be solved in altitude measurement is the super-resolution spatial spectrum estimation under the condition of coherent sources. The spatial smoothing algorithm is a kind of decorrelation algorithm with excellent properties, but the decorrelation process is at the expense of the effective array aperture. Because it only uses the autocorrelation information of the subspace, its performance is significantly reduced, when the positions of the coherent sources are very close. In order to solve the above problems, this paper proposes an altitude measurement method of VHF radar based on the space smoothing of autocorrelation and cross-correlation matrix, which is used to realize the correlation and super-resolution processing of echo signals and multipath signals. The proposed method does not need to construct a weighting matrix, and can make full use of the received data, enhance the signal components in the equivalent spatial smoothing matrix, reduce the impact of noise, and improve the resolution of coherent sources. The simulation results show that the weighted spatial smoothing method proposed in this paper is correct and effective.