Linear Array Configuration Research Articles

Spectroscopy Detection and Imaging System Based on Line Array Single Photon Detectors

Abstract. Single-photon detectors, with their exceptional sensitivity, provide a reliable means for single-photon-level detection, demonstrating significant advantages in detecting weak signals in complex environments compared to traditional detectors. With the continuous advancement in semiconductor manufacturing technology, single-photon detectors based on linear array configurations have emerged and rapidly developed. This study utilizes a linear array single-photon detector in free-running mode combined with a scanning mechanism to design and implement a spectral detection and imaging system. Through the spectral scanning unit, this system successfully achieves precise spectral detection in the 890 nm to 1710 nm range, with a spectral resolution better than 2 nm. Utilizing the imaging scanning unit, the system effectively performs target spectral imaging under single and multiple wavelength conditions at 1064 nm, 1310 nm, and 1520 nm. By optimizing algorithms for data processing, the system can achieve rapid and accurate spectral detection and imaging even under low-light conditions where the average photon count per pixel is less than 3. The results of this study are expected to provide strong technical support for the application of spectral imaging technology in the field of high-speed detection and imaging.

Simulation-Based Enhancement of SNR in Drone Communication through Uniform Linear Array Configurations

Simulation-Based Enhancement of SNR in Drone Communication through Uniform Linear Array Configurations

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.

Decoupling and Cloaking of Rectangular and Circular Patch Antennas and Interleaved Antenna Arrays with Planar Coated Metasurfaces at C-Band Frequencies-Design and Simulation Study.

An electromagnetic cloaking approach is employed with the intention to curb the destructive effects of mutual interference for rectangular and circularly shaped patch antennas situated in a tight spacing. Primarily, we show that by coating the top surface of each patch with an appropriately designed metasurface, the mutual coupling is considerably reduced between the antennas. Furthermore, the cloak construct is extended to a tightly spaced, interleaved linear patch antenna array configuration and it is shown that the coated metasurfaces successfully enhance the performance of each array in terms of their matching characteristics, total efficiencies and far-field realized gain patterns for a broad range of beam-scan angles. For rectangular patches, the cloaked Array I and II achieve corresponding peak total efficiencies of 93% and 90%, in contrast to the total efficiencies of 57% and 21% for uncloaked Array I and II, respectively, at their operating frequencies. Moreover, cloaked rectangular Array I and II exhibit main lobe gains of 13.2 dB and 13.8 dB, whereas uncloaked Array I and II only accomplish main lobe gains of 10 dB and 5.5 dB, respectively. Likewise, for the cloaked circular patches, corresponding total efficiencies of 91% and 89% are recorded for Array I and II, at their operating frequencies (uncloaked Array I and II show peak efficiencies of 71% and 55%, respectively). The main lobe gain for each cloaked circular patch array is approximately 14.2 dB, whereas the uncloaked Array I and II only achieve maximum gains of 10.5 dB and 7.5 dB, respectively.

Broadband All-Metal Vivaldi Array Antenna with Pyramidal-Shaped Wings for LEO Satellite Applications

In this paper, we propose an all-metal Vivaldi antenna with pyramidal-shaped conductive wings for use in satellite signal intelligence applications. The inner metal Vivaldi antenna consists of radiating flares and a transition part between the feeder and the flares. The curvature of the inner flares is optimized, while the outer edges of the radiating flares are connected to the pyramidal-shaped wings to obtain a higher antenna gain over the entire operating frequency band. To verify the antenna’s feasibility, performance aspects such as the reflection coefficient, the radiation patterns, and the boresight gain are measured in a full anechoic chamber. The fractional bandwidth of the proposed antenna is 54%, while the boresight gain is greater than 7.3 dBi in the frequency range from 8 GHz to 12 GHz. To examine array performance aspects such as the total gain and beam steering, the proposed Vivaldi antenna is extended to a 4 × 1 linear array configuration. When the main beam is steered from 0° to 15°, the maximum gain is varied from 14.5 dBi to 13.7 dBi, while the side lobe level is decreased from 11.2 dB to 6.3 dB.

A Novel Application of Polynomial Solvers in mmWave Analog Radio Beamforming

Beamforming is a signal processing technique where an array of antenna elements can be steered to transmit and receive radio signals in a specific direction. The usage of millimeter wave (mmWave) frequencies and multiple input multiple output (MIMO) beamforming are considered as the key innovations of 5 th Generation (5G) and beyond communication systems. The mmWave radio waves enable high capacity and directive communication, but suffer from many challenges such as rapid channel variation, blockage effects, atmospheric attenuations, etc. The technique initially performs beam alignment procedure, followed by data transfer in the aligned directions between the transmitter and the receiver [1]. Traditionally, beam alignment involves periodical and exhaustive beam sweeping at both transmitter and the receiver, which is a slow process causing extra communication overhead with MIMO and massive MIMO radio units. In applications such as beam tracking, angular velocity, beam steering etc. [2], beam alignment procedure is optimized by estimating the beam directions using first order polynomial approximations. Recent learning-based SOTA strategies [3] for fast mmWave beam alignment also require exploration over exhaustive beam pairs during the training procedure, causing overhead to learning strategies for higher antenna configurations. Therefore, our goal is to optimize the beam alignment cost functions e.g. , data rate, to reduce the beam sweeping overhead by applying polynomial approximations of its partial derivatives which can then be solved as a system of polynomial equations. Specifically, we aim to reduce the beam search space by estimating approximate beam directions using the polynomial solvers. Here, we assume both transmitter (TX) and receiver (RX) to be equipped with uniform linear array (ULA) configuration, each having only one degree of freedom (d.o.f.) with N t and N r antennas, respectively.

Forward-Looking Passive Radar With Non-Uniform Linear Array for Automotive Applications

With the rapid and growing spread of automotive radar systems in modern vehicles, the problem of their mutual interference is becoming a major safety concern. This paper considers the use of receive-only sensors onboard the vehicles, which exploit an external illumination source to provide automotive radar functionalities. The passive radar paradigm would solve the problem of mutual interference, allowing different systems to share the same transmitted signal. A preliminary analysis of the feasibility of this concept is carried out, exploiting real-world transmitters of opportunity. The potentialities offered by both satellite and ground-based illuminators are investigated and the expected performance is evaluated in terms of achievable coverage and spatial resolution. Aiming to enable a practical implementation of the proposed concept, an appropriate signal processing scheme is proposed to obtain maps of the observed scene. A Doppler beam sharpening approach is adopted to discriminate and localize stationary scatterers in azimuth based on the differences in their relative Doppler shift. The problem of left/right ambiguity arising from the forward-looking geometry is tackled by exploiting an array of few antenna elements on receive. Specifically, an ambiguity removal approach is proposed, based on digital beam pattern adaptation, designed to maximise the response in the desired direction and suppress unwanted echoes from the corresponding ambiguous one. The effectiveness of this approach is further improved by cascading an apodization technique that prevents the undesirable increase in the noise level. Moreover, some criteria are introduced for the design of the antenna layout, resorting to non-uniform linear array configurations. The proposed system is tested against a simulated environment, where the multi-channel signal processing, combined with a properly designed array layout, is shown to provide an unambiguous mapping of the observed scene over wide angular sectors, even operating with few antenna elements on receive.

A simple NULA design strategy for target detection and DoA estimation in mobile passive radar

This paper explores the advantages of Non-Uniform Linear Array (NULA) configurations for target detection and Direction of Arrival (DoA) estimation in mobile passive radar space-time adaptive processing (STAP). The limited number of receiving channels and the low directivity of antennas, typical of passive radar systems, may limit the moving target detection and angular localization capabilities. Therefore, the use of non-uniform distributions of antennas is encouraged, aimed at making the most of the available channels, by leveraging on spatial diversity. However, selecting a suitable NULA configuration represents a difficult task, being characterized by competing requirements. On the one hand, maximizing the array total length shrinks the clutter notch and reduces the DoA estimation error. On the other hand, increasing the inter-element spacings may lead to the appearance of statistical ambiguities, associated to sidelobes of the array beampattern, resulting in large estimation errors, as well as detection performance degradations. We propose a simple strategy for the selection of suitable NULA configurations, based on a requirement on the maximum peak-to-sidelobe ratio, which guarantee satisfactory performances in terms of both target detection and DoA estimation. The resulting array configuration are tested, via numerical analysis, addressing the case of a mobile passive radar exploiting DVB-T as a signal of opportunity.

Nonreciprocal Electromagnetically Induced Unidirectional Absorption Based on the Quasi-Periodic Metastructure and Its Application for Permittivity Sensing

Nonreciprocal unidirectional absorption, as a critical feature in both applications of military and civilian, has always been a challenging research topic. Here, we introduce a linear incremental arrangement into the formation of the electromagnetically induced absorption (EIA) in a single metastructure unit, creating an asymmetry spatial modulation for the nonreciprocal electromagnetic responses. A unidirectional EIA peak with a high absorption reaching 87.87% is observed for the forward case, and nearly all the incident energy is reflected in the backward case. The maximum isolation ratio (IR) between the forward and backward absorptions is 10.79 dB. To obtain a higher forward absorption and enlarge the IR, an improved nonreciprocal metastructure array is proposed and experimentally demonstrated by applying a linear quasi-periodic array configuration. The forward electromagnetically induced unidirectional absorption is enhanced to 99.53% with an IR of 12.73 dB. The near-perfect absorption provides a promising platform for permittivity sensing, and the measurement of common microwave plates with different relative permittivity shows an excellent linear regression. Such an implementation innovatively combines the asymmetric spatial modulation with EIA to form unidirectional absorption, offering a new guideline for novel nonreciprocal devices, and possessing considerable practical applications in the wireless communication system, ultrasensitive sensing, one-way invisibility, and absorptive switching.

Triple-Structured Compressive Sensing-Based Channel Estimation for RIS-Aided MU-MIMO Systems

Reconfigurable intelligent surface (RIS) has been recognized as a potential technology for 5G beyond and attracted tremendous research attention. However, channel estimation for RIS-aided systems is still a critical challenge due to the excessive amount of parameters in the cascaded channel. The existing compressive sensing (CS)-based RIS estimation schemes only adopt incomplete sparsity, which induces redundant pilot consumption. In this paper, we analyze and exploit the specific triple-structured sparsity of the cascaded channel, i.e., the common column sparsity, structured row sparsity after offset compensation and the common offsets among all users. Furthermore, a novel on-grid Multi-user Triple-Structured-Compressive-Sensing simultaneous orthogonal matching pursuit (MTSCS-SOMP) algorithm along with an enhanced super-resolution (gridless) generalized iterative reweighted (MTSCS-IR) scheme are successively proposed. The former is practical and can be easily employed with low computational complexity, and the latter is further proposed to handle the severe power leakage problem encountered in mmWave channel estimations. Besides, we extend the sparsity property and algorithms from uniform linear array (ULA) configuration to uniform planar array (UPA), by transforming cascaded channel from matrix to tensor. Simulation results show that our approaches can significantly reduce pilot overhead over 50% and achieve enhanced performance on estimation accuracy.

Extended Nested Array Configuration with Increased Degrees of Freedom for DOA Estimation

Abstract: In this paper, a new linear array configuration inspired by the two-level Nested Array concept has been proposed. The proposed geometry comprises of two Uniform Linear Arrays (ULAs) with different spacings and an additional element, this geometry results in a hole-free Difference Co-Array (DCA). In comparison to most of the existing sparse array configurations, the proposed geometry has simple closed-form expressions for the element positions and Degrees of Freedom (DoFs), also providing consecutive DoFs hence, avoiding the need for spatial interpolation. Spatially Smoothed MUltiple SIgnal Classification (SS-MUSIC) algorithm has been deployed for Direction of Arrival (DOA) estimation. Numerical simulations using MATLAB are performed to exhibit the superior performance of the proposed geometry. Keywords: DOA estimation, Co-array Processing, Spatial Smoothing, Degrees of Freedom, Non-Uniform Linear Arrays

A New Beamforming Approach Using 60 GHz Antenna Arrays for Multi-Beams 5G Applications

Recent studies and research have centred on new solutions in different elements and stages to the increasing energy and data rate demands for the fifth generation and beyond (B5G). Based on a new-efficient digital beamforming approach for 5G wireless communication networks, this work offers a compact-size circular patch antenna operating at 60 GHz and covering a 4 GHz spectrum bandwidth. Massive Multiple Input Multiple Output (M–MIMO) and beamforming technology build and simulate an active multiple beams antenna system. Thirty-two linear and sixty-four planar antenna array configurations are modelled and constructed to work as base stations for 5G mobile communication networks. Furthermore, a new beamforming approach called Projection Noise Correlation Matrix (PNCM) is presented to compute and optimise the fed weights of the array elements. The key idea of the PNCM method is to sample a portion of the measured noise correlation matrix uniformly in order to provide the best representation of the entire measured matrix. The sampled data will then be utilised to build a projected matrix using the pseudoinverse approach in order to determine the best fit solution for a system and prevent any potential singularities caused by the matrix inversion process. The PNCM is a low-complexity method since it avoids eigenvalue decomposition and computing the entire matrix inversion procedure and does not require including signal and interference correlation matrices in the weight optimisation process. The suggested approach is compared to three standard beamforming methods based on an intensive Monte Carlo simulation to demonstrate its advantage. The experiment results reveal that the proposed method delivers the best Signal to Interference Ratio (SIR) augmentation among the compared beamformers.

An unambiguous DOA estimation method for coprime array with displaced subarrays

In this paper, the direction-of-arrival (DOA) estimation using a coprime array with displaced subarrays (CADiS) is researched. Mostly, subspace-based methods have been studied for DOA estimation with CADiS. However, the subspace-based methods suffer from the problem of directional matrix ambiguity. It occurs due to the non-uniform linear array configuration of CADiS, whereby there always exists a set of DOAs with linearly dependent directional vectors. As a consequence, the directional vectors that are not associated with true DOAs also lie in the signal subspace and result in an estimate of true and ambiguous DOAs. In the proposed method, the true DOAs are distinguished from ambiguous estimates using the estimated power of the transmitted signals. Here, the source covariance function is derived based on the signal subspace eigenvalues and its associated eigenvectors to estimate the power of the transmitted signals. The proposed method successfully detects the true DOAs and eliminates ambiguous estimates. The performances of the proposed method are validated through simulation studies for reliability and accuracy of the estimation.

Critical Review of Basic Methods on DoA Estimation of EM Waves Impinging a Spherical Antenna Array

Direction-of-arrival (DoA) estimation of electromagnetic (EM) waves impinging on a spherical antenna array in short time windows is examined in this paper. Reflected EM signals due to non-line-of-sight propagation measured with a spherical antenna array can be coherent and/or highly correlated in a snapshot. This makes spectral-based methods inefficient. Spectral methods, such as maximum likelihood (ML) methods, multiple signal classification (MUSIC), and beamforming methods, are theoretically and systematically investigated in this study. MUSIC is an approach used for frequency estimation and radio direction finding, ML is a technique used for estimating the parameters of an assumed probability distribution for given observed data, and PWD applies a Fourier transform to the capture response and produces them in the frequency domain. Although they have been previously adapted and used to estimate DoA of EM signals impinging on linear and planar antenna array configurations, this paper investigates their suitability and effectiveness for a spherical antenna array. Various computer simulations were conducted, and plots of root-mean-square error (RMSE) against the square root of the Cramér–Rao lower bound (CRLB) were generated and used to evaluate the performance of each method. Numerical experiments and results from measured data show the degree of appropriateness and efficiency of each method. For instance, the techniques exhibit identical performance to that in the wideband scenario when the frequency f = 8 GHz, f = 16 GHz, and f = 32 GHz, but f = 16 GHz performs best. This indicates that the difference between the covariance matrix of the signal is coherent and that the steering vectors of signals impinging from that angle are small. MUSIC and PWD share the same problems in the single-frequency scenario as in the wideband scenario when the delay sample d = 0. Consequently, the DoA estimation obtained with ML techniques is more suitable, less biased, and more robust against noise than beamforming and MUSIC techniques. In addition, deterministic ML (DML) and weighted subspace fitting (WSF) techniques show better DoA estimation performance than the stochastic ML (SML) technique. For a large number of snapshots, WSF is a better choice because it is more computationally efficient than DML. Finally, the results obtained indicate that WSF and ML methods perform better than MUSIC and PWD for the coherent or partially correlated signals studied.

Helix Inspired 28 GHz Broadband Antenna with End-Fire Radiation Pattern

This paper presents the design and characterization of a via free planar single turn helix for 28 GHz broadband applications. The proposed antenna is designed using ROGERS RO4003 material, having a simple structure and end-fire radiation pattern. The antenna comprises of a compact dimension of 1.36 λ0 × 0.9 λ0 with a thickness of 0.0189 λ0 (where λ0 is the free-space wavelength at the central frequency of 28 GHz). Parametric study has been carried out to investigate the impact of key design parameters and to achieve an optimum design. Results show a good agreement between the simulated and measured results. A single turn helical inspired antenna covers −10 dB impedance bandwidth of 26.25–30.14 GHz having a peak gain of 5.83 dB and radiation efficiency up to 85%. Moreover, linear array configurations with 2 and 4 elements have been analyzed for applications with higher gain and space constraints. Presented array configurations are suitable for applications having space constraints in one dimension. Results show that peak gain up to 8.2 dB and 11.1 dB can be achieved with 2 and 4 elements, respectively. Due to its simple planar and via free structure, this antenna is suitable for 5G communications and for sensing, imaging, IoT and tracking applications at 28 GHz band spectrum.

Dual-Slot Cavity Antenna for mm-Wave Beamforming Array

A cavity-fed, dual-slot element and its 4-element linear array configurations for beam-steering applications at 28 GHz are described. The element cavity is formed from rectangular substrate integrated waveguide (SIW), perturbed at one of its corners to excite dual slots for increasing the impedance bandwidth. With a mobile terminal in mind, we look to both classical array principles and to the available theories for finite arrays with mutual coupling, to help guide the design. The impact of the finite ground-plane required to support the slot elements and array is investigated by simulation, including the impact on the patterns of using a cellphone chassis as a platform. A chassis-born 4-element (8 slots) configuration, suitable for beamforming in 28 GHz 5G networks is demonstrated for both linear polarizations. The simulation results are supported by pattern measurements of prototypes, a challenging task at 28 GHz.

Iteratively reweighted super-resolution channel estimation in hardware-impaired hybrid-precoded MM-wave massive MIMO systems using dual SVD and Marquardt's global search

In this paper, a three-dimensional geometric channel model characterized by channel gain, angle of arrival, and departure (AoA/AoD) is used to develop a non-ideal and more realistic system representation that accounts for additional signal perturbations other than additive white Gaussian noise (AWGN). Hinged on this, compressive sensing (CS) based channel estimation technique is proposed for millimeter-wave (MM-Wave) massive multiple-input multiple-output (MIMO) systems with inherent challenges due to hardware impairment (HI). The proposed estimator named dual singular value decomposition (SVD) and Marquardt, abbreviated as DSM estimator aims at tolerating complexity and improving channel estimation accuracy at reasonable trade-offs in the system. The normalized mean square error (NMSE) performance of the proposed channel estimation scheme, with modified Marquardt's global minimum search, achieves higher accuracy at below 0 dB (LoS)/-3 dB (NLoS) signal-to-noise ratio (SNR) for uniform linear array (ULA) configuration and performs better for uniform planar array (UPA) configuration. A low-rank range of unit difference is adopted for matrix decomposition twice (dual SVD) per SNR in ULA/UPA setting. The proposed estimator's result shows early convergence during the simulation and a linearly scaled complexity in comparison with one of the earlier proposed schemes in literature in particular the super-resolution channel estimation with gradient descent optimization.

Mutual Coupling Evaluation and Radiation Pattern Performance for Coplanar Vivaldi Antenna Array

This study has aimed to examine the mutual coupling evaluation and the radiation pattern performance of the Coplanar Vivaldi Antenna (CVA) array. Generally, the mutual coupling evaluation is determined based on the calculation of two antenna elements in the E-plane and the mutual scattering assessment of several linear and planar array configurations. The calculation is analyzed by multiplying the radiation pattern modeling of its element and the flux pointing vector. There has been a significant difference between the simulation and the modeling results of the radiation pattern element and mutual coupling of the Coplanar Vivaldi antenna. The mutual scattering has been determined in the contour plot with different array configurations in the E and in the H-plane. Coplanar Vivaldi Antenna with Exponential Corrugated Slot (CVA-ECT) has showed a better return loss and gain performance than CVA with No Slot (CVA-NS) in the E-plane, which is different in the H-plane. With the same volume size of an array, the smaller the width of the element is, the better the performance in radiation pattern than the wider ones is. The planar array shows that at 7 GHz, the 3×2 array gains up to 13.69 dB while 2×2 CVA-NS attains 8.9 dB in the same volume.

Investigating the accuracy of co-registered ionoacoustic and ultrasound images in pulsed proton beams

The sharp spatial and temporal dose gradients of pulsed ion beams result in an acoustic emission (ionoacoustics), which can be used to reconstruct the dose distribution from measurements at different positions. The accuracy of range verification from ionoacoustic images measured with an ultrasound linear array configuration is investigated both theoretically and experimentally for monoenergetic proton beams at energies relevant for pre-clinical studies (20 and 22 MeV). The influence of the linear sensor array arrangement (length up to 4 cm and number of elements from 5 to 200) and medium properties on the range estimation accuracy are assessed using time-reversal reconstruction. We show that for an ideal homogeneous case, the ionoacoustic images enable a range verification with a relative error lower than 0.1%, however, with limited lateral dose accuracy. Similar results were obtained experimentally by irradiating a water phantom and taking into account the spatial impulse response (geometry) of the acoustic detector during the reconstruction of pressures obtained by moving laterally a single-element transducer to mimic a linear array configuration. Finally, co-registered ionoacoustic and ultrasound images were investigated using silicone inserts immersed in the water phantom across the proton beam axis. By accounting for the sensor response and speed of sound variations (deduced from co-registration with ultrasound images) the accuracy is improved to a few tens of micrometers (relative error less than to 0.5%), confirming the promise of ongoing developments for ionoacoustic range verification in pre-clinical and clinical proton therapy applications.

Determination of the Azimuthal Extent of Coherent E‐Region Scatter Using the ICEBEAR Linear Receiver Array

AbstractThe Ionospheric Continuous‐wave E‐region Bistatic Experimental Auroral Radar (ICEBEAR) is a VHF coherent scatter radar that operates with a field‐of‐view centered on 58°N, 106°W and measures characteristics of ionospheric E‐region plasma density irregularities. The initial operations of ICEBEAR utilized a wavelength‐spaced linear receiving array to determine the angle of arrival of the ionospheric scatter at the receiver site. Initially only the shortest baselines were used to determine the angle of arrival of the scatter. This publication uses this linear antenna array configuration and expands on the initial angle of arrival determination by including all the cross‐spectra available from the antenna array to determine both the azimuthal angle of arrival and the azimuthal extent of the incoming ionospheric scatter. This is accomplished by fitting Gaussian distributions to the complex coherence of the signal between different antennas and deriving the azimuthal angle and extent based on the best fit. Fourteen hours of data during an active ionospheric period (March 10, 2018, 0–14 UT) were analyzed to investigate the Gaussian fitting procedure and determine its feasibility for implementation with ICEBEAR. A comparison between mapped scatter, both neglecting azimuthal extent and including azimuthal extent is presented. It demonstrates that the azimuthal extent of the ionospheric E‐region scatter is very important for accurately portraying and analyzing the ICEBEAR measurements.