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In this paper, we formulate a recently proposed qualitative imaging approach named near-field orthogonality sampling method (NOSM) for a general measurement configuration. In the very first version, the NOSM was basically a backpropagation method, which analytically transforms the scattered fields, which is obtained with some specific multiview–multistatic measurement configurations (circular or linear), to reduced scattered electric fields on the sampling domain, which encapsulates the targets. The contributions of this paper are: 1) physical meaning of the reduced scattered field of the NOSM is explained by showing how it approximates the contrast source values in the sampling domain for different generic and limited aperture configurations; 2) the application of the NOSM is generalized to a generic configuration and some comments are made how to reduce the computational complexity and source requirements; 3) the reciprocity of the data is accounted for to improve the performance for limited aperture measurement scenarios; and 4) finally, a useful modified indicator is obtained by relying on the physical meaning of the indicator. The accuracy and stability of the proposed formulations are corroborated with numerical examples for which the excitation-measurement configuration is of limited aperture. [ABSTRACT FROM AUTHOR]

Synthetic aperture sonar and synthetic aperture radar involve the creation of high-resolution images of a scene via scattered signals recorded at different locations. Each pixel of the reconstructed image includes information obtained from multiple aspects due to the changing position of the sources/receivers. In this paper, the aspect-dependent scattering at each pixel is exploited to provide additional information about the scene; this paper presents a framework for converting and utilizing multiaspect data, as well as several examples. For sonar data, as is presented here, the aspect dependence may be leveraged to separate objects of interest from the background, to understand the local bathymetry, or for visualizing acoustic shadowing in full circular synthetic aperture sonar images. Several examples of images of the seafloor containing objects of interest are presented for both circular and linear apertures. In addition, the aspect dependence of low-frequency elastic scattering from objects may be used to understand the underlying scattering physics, which is of potential use in fields such as target recognition and nondestructive testing; a laboratory example is presented. [ABSTRACT FROM AUTHOR]

This paper proposes a wideband and low direct-coupling tapered slot antenna (TSA) using electromagnetic bandgap (EBG) structure. We name this antenna the EBG-TSA. In some near field imaging systems including ground penetrating radars, a number of TSAs are arranged into an array with very small spacing in order to realize high-resolution imaging without synthetic aperture processing. Then, the direct coupling among TSA elements is nonnegligible and harmful. In this paper, we show that the EBG structure is effective in reducing the direct coupling with its stopband, which prevents an electromagnetic wave from propagating in a specific frequency band. Our EBG-TSA reduces its direct coupling by 3 dB or more in a wide band. We also find that the tapered EBG structure area assists the radiation by guiding the fin current flow two-dimensionally along the tapered slot so that the boresight gain increases. The EBG structure contributes to both the direct coupling reduction and the boresight gain enhancement. [ABSTRACT FROM AUTHOR]

This paper describes a new pulse sequence design and estimation approach, which can increase the maximum detectable velocity in synthetic-aperture (SA) velocity imaging. In SA, $N$ spherical or plane waves are emitted, and the sequence is repeated continuously. The $N$ emissions are combined to form a high-resolution image (HRI). Correlation of HRIs is employed to estimate velocity, and the combination of $N$ emissions lowers the effective pulse repetition frequency by $N$. Interleaving emission sequences can increase the effective pulse repetition frequency to the actual pulse repetition frequency, thereby increasing the maximum detectable velocity by a factor of $N$. This makes it possible to use longer sequences with better focusing properties. It can also increase the possible interrogation depth for vessels with large velocities. A new cross-correlation vector flow estimator is also presented, which can further increase the maximum detectable velocity by a factor of 3. It is based on transverse oscillation (TO), a preprocessing stage, and cross-correlation of signals beamformed orthogonal to the ultrasound propagation direction. The estimator is self-calibrating without estimating the lateral TO wavelength. This paper develops the theory behind the two methods. The performance is demonstrated in the accompanying paper for convex and phased array probes connected to the synthetic aperture real-time ultrasound system scanner for parabolic flow for both conventional and SA imaging. [ABSTRACT FROM AUTHOR]

This paper presents a generalized analytical expression for directivity of phased array antennas (PAAs). It includes important design consideration of PAAs such as arbitrary element type and array geometry, complex excitations, mutual coupling, scan angle, and embedded element pattern. We also present an approximate expression of directivity, helpful for quick analysis of large PAAs overcoming computing time constraints of analytical expressions. It provides a quick PAA design tool for predicting accurate locations of blind spots in desired scan volume due to the chosen array geometry. This paper also presents the study on wide scan characteristics of periodic sparse PAAs using the proposed expressions. [ABSTRACT FROM AUTHOR]

This paper demonstrates a novel nanofabrication technology for producing high-density gated molybdenum (Mo) field-emitter array (FEA) based on modified nanosphere lithography (NSL). The arc-shaped side wall of gate apertures introduced by the conventional NSL process put obstacles in the formation of sharp cone-type emitters. In this paper, a two-method solution was employed to facilitate the realization of gate apertures with sharper cutting side wall which are beneficial for the formation of sharper gated Mo emitters. One method was softening nanosphere to enlarge the contact area between nanosphere and substrate. The other was optimizing gate film deposition conditions to dramatically reduce the diffraction effects. Due to the improvements in the geometrical shape of gated Mo emitters, a low-voltage working high-density gated Mo FEA was demonstrated in this paper. This is the first observation of remarkable electron emission from high-density gated Mo FEA fabricated using such as low-cost, high-throughput, and high-efficiency technique which is expected to substantially overcome the challenges in the traditional fabrication process and promotes the low-cost and large-area application of high-density gated field-emitter devices. In addition, the novel nanofabricating method is expected to offer a simple and scalable route which allows fabrication of many gated field-emission devices. [ABSTRACT FROM AUTHOR]

In order to improve the breaking capacity of contacts, it is very important to find a better contact material. In this paper, the triggering experiments of plate contact with different materials are studied to investigate the characteristics of vacuum arc. The current range is from 1 to 9 kA (rms). The gap distance is selected as 3 and 5 mm. The arc appearance and the behavior of cathode spots are captured by high-speed camera with an exposure time of $2~\mu \text{s}$. The surface topography of contacts after experiments is evaluated by scanning electron microscope. The arc current and arc voltage are measured at the same time by Rogowski coil and high-voltage probe. The diameter of the contact is 25 mm. There are seven kinds of materials (CuCr10, CuCr25, CuCr30, CuCr40, WCu10, WCu30, and CuW–WC) conducted in this paper. Compared with the experimental results, the arc of WCu alloy distributes more evenly on the contact plane with many bright cathode spots. The small gap distance makes the burning point more fixed. The arc of CuW–WC is unstable. During the arc trigger moment to the arc stable burning stage, the radial diffusion velocity of WCu10 cathode spot is the lowest with about 25% of CuCr10. CuCr10 alloy has the worst melting resistance. WCu alloy has good melting resistance and bad toughness. The toughness of CuW–WC is even worse. Under the low current, CuCr30 might be preferred for vacuum interrupters from the cathode spots’ radial diffusion speed, arc appearance, and erosion result. When the current increasing, the arc can easily spread to the entire surface of WCu contact, and WCu10 would be the prefer material with the diffusion arc and good erosion resistance. [ABSTRACT FROM AUTHOR]

This paper offers a new approach for far-field high-resolution imaging of conducting obstacles based on arrays of frequency-multiplexed subwavelength resonant elements. Each resonator is a circular aperture in a metallic screen that is strongly miniaturized by means of loading by a thin epsilon-negative and near-zero metamaterial (MTM) liner. Each MTM-lined aperture exhibits a fano-shape transmission profile, i.e., a peak followed by a minimum, and the resonance frequencies of different apertures are chosen such that the resonance of one lies within/very close to the antiresonance of the other to ensure strong decoupling. This paper shows that blocking an aperture using a conducting disc removes the corresponding resonance peak/minimum from the transmission/far-field amplitude spectrum, enabling far-field detection of any distribution of such obstacles with a spatial resolution determined by the aperture sizes, which measure less than one-sixth of free-space wavelength at their respective resonance frequencies. The proposed imaging mechanism is verified through full-wave HFSS simulations as well as far-field measurements. Some challenges associated with this approach are then discussed. [ABSTRACT FROM AUTHOR]

In this paper, the impairments of free-space optical (FSO) communication systems caused by angular fluctuations including beam misalignment and angle-of-arrival (AOA) fluctuations are modeled in the presence of both atmospheric turbulence and transceiver vibrations. In particular, assuming FSO receivers with a limited field-of-view (FOV), the fading caused by AOA fluctuations is studied. The outage probability expressions for both coherent and direct detections are derived in both shot-noise-limited and thermal-noise-limited regimes. For direct detection, the optimal receiver FOV that achieves the minimum outage probability is considered. Furthermore, the issue of imperfect phasefront tracking in practical coherent receivers is investigated. [ABSTRACT FROM PUBLISHER]

In this paper, extremely subwavelength evanescent Bessel beam launchers are designed, simulated, and experimentally tested to generate nondiffracting beams. The launching apertures consist of several concentric coils strategically positioned to spatially filter the fields of a single actively fed radiating coil. The geometrical properties of each coil element of the aperture were obtained through a procedure based on the orthogonal matching pursuit algorithm in order to maximize the quality of the launched beam while minimizing manufacturing complexity. Two apertures with outer diameters of 64 and 48 mm were fabricated and the generated field distributions were measured at the operating frequencies of 13.66 and 13.86 MHz, respectively. Desired and measured field distributions exhibited correlations above 0.9 even as the distance from the aperture was increased, demonstrating the ability of the apertures to approximate the field distribution and harmonic content of a Bessel beam. This paper furthers the study and practical implementation of Bessel beams and other types of beams in extremely subwavelength applications such as focusing, wireless power transfer, magnetic stimulation, and microwave ablation. [ABSTRACT FROM PUBLISHER]

To solve the low spatial and/or temporal resolution problem which the conventional hyperspectral cameras often suffer from, coded hyperspectral imaging systems have attracted more attention recently. Recovering a hyperspectral image (HSI) from its corresponding coded image is an ill-posed inverse problem, and learning accurate prior of HSI is essential to solve this inverse problem. In this paper, we present an effective convolutional neural network (CNN) based method for coded HSI reconstruction, which learns the deep prior from the external dataset as well as the internal information of input coded image with spatial-spectral constraint. Specifically, we first develop a CNN-based channel attention reconstruction network to effectively exploit the spatial-spectral correlation of the HSI. Then, the reconstruction network is learned by leveraging an arbitrary external hyperspectral dataset to exploit the general spatial-spectral correlation under adversarial loss. Finally, we customize the network by internal learning with spatial-spectral constraint and total variation regularization for each coded image, which can make use of the internal imaging model to learn specific prior for current desirable image and effectively avoids overfitting. Experimental results using both synthetic data and real images show that our method outperforms the state-of-the-art methods on several popular coded hyperspectral imaging systems under both comprehensive quantitative metrics and perceptive quality. [ABSTRACT FROM AUTHOR]

In this paper, we propose a relative pose estimation algorithm for micro-lens array (MLA)-based conventional light field (LF) cameras. First, by employing the matched LF-point pairs, we establish the LF-point-LF-point correspondence model to represent the correlation between LF features of the same 3D scene point in a pair of LFs. Then, we employ the proposed correspondence model to estimate the relative camera pose, which includes a linear solution and a non-linear optimization on manifold. Unlike prior related algorithms, which estimated relative poses based on the recovered depths of scene points, we adopt the estimated disparities to avoid the inaccuracy in recovering depths due to the ultra-small baseline between sub-aperture images of LF cameras. Experimental results on both simulated and real scene data have demonstrated the effectiveness of the proposed algorithm compared with classical as well as state-of-art relative pose estimation algorithms. [ABSTRACT FROM AUTHOR]

The growing need for high-performance imaging tools for terrorist threat detection and medical diagnosis has led to the development of new active architectures in the microwave and millimeter range. Notably, multiple-input multiple-output systems can meet the resolution constraints imposed by these applications by creating large, synthetic radiating apertures with a limited number of antennas used independently in transmitting and receiving signals. However, the implementation of such systems is coupled with strong constraints in the software layer, requiring the development of reconstruction techniques capable of interrogating the observed scene by optimizing both the resolution of images reconstructed in two or three dimensions and the associated computation times. In this paper, we first review the formalisms and constraints associated with each application by taking stock of efficient processing techniques based on spectral decompositions, and then, we present a new technique called the transverse spectrum deconvolution range migration algorithm allowing us to carry out reconstructions that are both faster and more accurate than with conventional Fourier domain processing techniques. This paper is particularly relevant to the development of new computational imaging tools that require, even more pronouncedly than in the case of conventional architectures, fast image computing techniques despite a very large number of radiating elements interrogating the scene to be imaged. [ABSTRACT FROM AUTHOR]

This paper utilizes sparse array motion to increase the numbers of achievable both degrees of freedom (DOFs) and consecutive lags in direction-of-arrival (DOA) estimation problems. We use commonly employed environment-independent sparse array configurations. The design of these arrays is not dependent on the sources in the field of view, but rather aims at achieving desirable difference co-arrays. They include structured coprime and nested arrays, minimum redundancy array (MRA), minimum hole array (MHA), and sparse uniform linear array (SULA). Array motion can fill the holes in the spatial autocorrelation lags associated with a fixed platform and, therefore, increases the number of sources detectable by the same number of array sensors. Quasi-stationarity of the environment is assumed where the source locations and waveforms are considered invariant over array motion of half wavelength. Closed-form expressions of the number of DOFs and consecutive spatial correlation lags for coprime and nested arrays as well as SULA, due to array translation motion, are derived. The number of DOFs and consecutive lags for the specific cases of MRA an 5 avaluated. We show the respective DOA estimation performance based on sparse reconstruction techniques. [ABSTRACT FROM AUTHOR]

In this paper, a novel concept for visible light positioning is introduced, which employs a liquid crystal display as a dynamic optical filter in front of a photodetector. By electronically switching dedicated pixel areas in transparent or blocking mode, respectively, the angle of arrival is estimated. The measurement principle is supported by a mathematical model. Finally, an experimental setup is presented and measurement results are compared to the theoretical findings. [ABSTRACT FROM AUTHOR]

Molecular communication via diffusion (MCvD) is a method of achieving nano- and micro-scale connectivity by utilizing the free diffusion mechanism of information molecules. The randomness in diffusive propagation is the main cause of inter-symbol interfe-rence (ISI) and the limiting factor of high data rate MCvD applications. In this paper, an apertured plane is considered between the transmitter and the receiver of an MCvD link. Either after being artificially placed or occurring naturally, surfaces or volumes that resemble an apertured plane only allow a fraction of the molecules to pass. Contrary to intuition, it is observed that such topology may improve communication performance, given the molecules that can pass through the aperture are the ones that take more directed paths towards the receiver. Furthermore, through both computer simulations and a theoretical signal evaluation metric named signal-to-interference and noise amplitude ratio (SINAR), it is found that the size of the aperture imposes a trade-off between the received signal power and the ISI combating capability of an MCvD system, hinting to an optimal aperture size that minimizes the bit error rate (BER). It is observed that the trend of BER is accurately mirrored by SINAR, suggesting the proposed metric’s applicability to optimization tasks in MCvD systems, including finding the optimal aperture size of an apertured plane. In addition, computer simulations and SINAR show that said optimal aperture size is affected by the location of the aperture and the bit rate. Lastly, the paper analyzes the effects of radial and angular offsets in the placement of the apertured plane, and finds that a reduction in BER is still in effect up to certain offset values. Overall, our results imply that apertured plane-like surfaces may actually help communication efficiency, even though they reduce the received signal power. [ABSTRACT FROM AUTHOR]

A microsphere lens on top of a photodetector sensor increases its sensitivity and reduces its Noise-to-Signal Ratio (NSR), as shown in our previous work. This paper discusses a methodology to determine the optimal sphere-sensor ratio, in terms of increased current sensitivity, for microsphere-lens-enhanced photodetectors, using computational analysis including a modeling, with an experimentally derived photo-detector sensor responsivity and simulation setup that emulates conditions generally found within cameras and telescopes. In particular, we study and analyze the effect that several variables have on such ratios. We focus on variables such as microsphere material type, photodetector hardware technology type, light source temperature, and in the case of reflective telescopes, central obscurations from a secondary mirror. Results of the effect of microsphere-sensor misalignment on such ratios are also presented. As we show in this paper, since the optimized ratio is dependent on a given wavenumber considered, therefore the proposed methodology uses an integral optimization over a given spectral band to derive the optimized ratio over that band. Some of our findings show, for the first time, that the optimal ratio is virtually independent of a given central obscuration. Finally, we demonstrate here the flexibility of the proposed methodology in showing performances of microsphere-enhanced photodetector sensors. [ABSTRACT FROM AUTHOR]

This paper presents a method based on frequency shift feedback for living cell manipulation and in situ nanoinjection with a cantilevered micropipette probe (CMP). This method can detect tip–cell interactive forces at the piconewton level by measuring the frequency shift of the rigid CMP oscillated in the first bending eigenmode (amplitude: ~10 nm). Different interaction states throughout the process of manipulation and injection, including the contact, gripping, detaching, and cell (nuclear) membrane penetration, can be well detected and thereby controlled. In addition, the cell adhesion can be quantified by the integral of the frequency shift during the detachment process. Manipulation and nanoinjection are automatically performed using two types of CMPs with different apex aperture diameters (manipulation: Ø $4~\mu \text{m}$ ; nanoinjection: Ø200 nm), under the control of the dynamic force and microscope vision feedback. The proposed method can control the contact force of ~ 300 pn for nondestructive cell manipulation and can detect cell membrane (~250 pn) and nuclear membrane (~400 pn) penetration forces in nanoinjection. The versatility and robustness of the proposed method are further demonstrated by quantifying the cell-substrate adhesion, the building of cell patterns, and automated cell nanoinjection. Note to Practitioners—Cell manipulation and injection are the essential processes for most cell-based bioengineering applications. Cell manipulation enables not only cell transport and pattern building but also adhesion measurement both between cells and the external matrix. On the other hand, in situ cell injection is a significant process for cell-based medicine development and genetics research. Automated force-controlled cell manipulation and injection will greatly reduce the requirements of the user’s experience and increase the efficiency and consistency of the experiment. This paper introduces a method based on frequency shift feedback for obtaining highly accurate monitoring of the interactions (at the piconewton level) between cells and developing tools for automated and nondestructive manipulation and injection. The research outcome provides a unique solution to achieve high-precision cell manipulation and in situ nanoinjection. [ABSTRACT FROM AUTHOR]

Sampling plays a critical role in remote sensing and signal analysis. In conventional sampling theory, the signal is sampled at a uniform rate at a minimum of twice the signal bandwidth. Sampling with an aperture function requires a fixed-aperture function, which can be removed by deconvolution after signal reconstruction. However, in some cases, the signal samples are available only at irregular positions, and different samples use different aperture functions. In this paper, the theory of finite-length signal reconstruction with irregular samples and variable apertures in one and two dimensions is considered. In the 1-D case, a band-limited discrete signal can be exactly reconstructed from a finite number of arbitrarily spaced samples with few restrictions on the aperture functions. Exact reconstruction in the 2-D case requires the sampling matrix be invertable, and is not always possible. Variable aperture functions, while complicating the process, can enable reconstruction for a broader range of sample locations. Practical issues are discussed, and numerical examples are provided. Variable aperture reconstruction has application in a variety of remote sensing problems. In this paper, reconstruction from 2-D irregular sampling with variable apertures is illustrated using Special Sensor Microwave/Imager radiometer observations. [ABSTRACT FROM PUBLISHER]

Compared with frequency-domain algorithms, time-domain algorithms (TDAs) can achieve image focusing under the conditions of arbitrary trajectories and large integration angles. However, the interpolations in both range and bearing angle directions are required in the coordinate transformation of fast TDAs, which inevitably increases the computational load and introduces interpolation errors. In this paper, a fast time-domain imaging and corresponding autofocus method based on the hybrid coordinate (HC) system is proposed. First, the interpolation operation is optimized in the process of fast TDAs. It transforms the 2-D interpolation into 1-D interpolation only in the bearing angle direction, which improves the execution efficiency and reduces the interpolation error. Next, a 3-D trajectory deviation estimation method based on Gauss–Newton iteration is investigated for the motion compensation in the HC system. By iterative optimization, the 3-D motion errors during the flight are estimated accurately, and the space-variant phase error is compensated precisely. This method has good robustness and universality. Simulation results and real data processing demonstrate the effectiveness and the practicability of the method presented in this paper. [ABSTRACT FROM AUTHOR]

In this paper, a design of reflector antennas to produce near-field focused (NFF) radiation is presented. Instead of focusing the radiation at a single focal point, which results in an ellipsoidal reflector, this new reflector antenna application concept designates a finite zone, especially a finite curved surface, for NFF illumination. This finite zone may consist of several subzones for multi-NFF radiation. The design concept employs equal path lengths of wave propagation from the feed’s phase center toward the focal zone via reflections from the reflector’s surface in a one-to-one correspondence, which results in a confluence of reflection points found from a set of ellipsoidal surfaces. Based on a definition of the mapping mechanism to extract the reflection points to form the reflector, the field can be properly focused in the target zone by the concept of geometric optics (GO). In this paper, the basic theoretical concept is first summarized with a design equation developed for easy implementation. The focus property is demonstrated by a time-domain physical optics (TD-PO) analysis of spherical wave illumination with a transient-step field behavior to show the focusing responses of electromagnetic scattering from the reflector. The focusing characteristics of the frequency domain (FD) are also shown by PO simulation at 20 GHz. [ABSTRACT FROM AUTHOR]

In the massive multiple-input multiple-output systems, the antennas should have the ability of beamforming. Under this requirement, the sliding aperture technique is adopted. In this paper, the principle of the sliding aperture technique is first demonstrated. This technique refers to the customization of each beam by part of the aperture, resulting in low scan loss over a wide angular range. Then, with the help of II-shaped transmit element, a linear multibeam transmitarray antenna based on the sliding aperture technique is designed. To the best of the authors’ knowledge, the linear transmitarray is reported for the first time. The fabricated prototype shows that the proposed antenna can generate eight beams simultaneously covering the ±42° azimuth area with low scan loss and the beam intersection level better than −4 dB. The proposed antenna has been simulated, fabricated, and measured, and the experimental results are in good agreement with the simulation results. [ABSTRACT FROM AUTHOR]

Combining the advantages of lens antenna and array techniques, transmitarrays have been widespreadly concerned in recent years. In the first part of this paper, a wideband four-layer transmitarray operating at 13 GHz fed by a horn with a focus-to-diameter ratio (F/D) of unity is proposed. The employed elements composed of dual-resonance double hexagonal rings are closely arranged in the honeycomb lattice. The simulated results show that the transmitarray can achieve a 53.34% peak aperture efficiency and a 19.23% bandwidth for 1 dB gain drop, respectively. The factors with strong influences on the measured results are analyzed. In the second part, an improved feed mechanism, which is aimed at reducing the transmitarray profile, is discussed in detail. The conjugate field matching technology is utilized to realize an ideal compensation. The small-scale antenna array, which has a nearly identical aperture size to the feed horn applied in the first design, can effectively excite the transmitarray with a profile reduction of 64.5%. These prototypes confirm the feasibility of designing a wideband transmitarray and a low-profile array-fed transmitarray. [ABSTRACT FROM AUTHOR]

The capacity of the intensity modulation direct detection multiple-input-multiple-output channel is studied. Therein, the nonnegativity constraint of the transmit signal limits the applicability of classical schemes, including precoding. Thus, new ways are required for deriving capacity bounds for this channel. To this end, capacity lower bounds are developed in this paper by deriving the achievable rates of two precoding-free schemes: channel inversion and orthogonal-upper triangular matrix product decomposition. The achievable rate of a dc-offset singular-value decomposition-based scheme is also derived as a benchmark. Then, capacity upper bounds are derived and compared against the lower bounds. As a result, the capacity at high signal-to-noise ratio (SNR) is characterized for the case where the number of transmit apertures is not larger than the number of receive apertures, and is shown to be achievable by the QR decomposition scheme. This is shown for a channel with average intensity or peak intensity constraints. Under both constraints, the high-SNR capacity is approximated within a small gap. Extensions to a channel with more transmit apertures than receive apertures are discussed, and capacity bounds for this case are derived. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel design approach for a filtering antenna, which contains an array of 4 by 2 waveguide aperture radiation elements. Coupling matrix theory is introduced in this paper to synthesize the multiple coupled-resonators circuit. Unequal amplitude excitation is applied to the 4 \times 2 elements so as to obtain a low sidelobe level. To demonstrate the concept, an X-band antenna array is designed and fabricated using a three-layer waveguide structure. Measured results show that the filtering antenna array can achieve a gain of more than 15.58 dBi and a radiation efficiency of higher than 90% over the passband (9.91–10.1 GHz). The sidelobe level is −18.3 dB in the {H} -plane and −21.1 dB in the {E}$ -plane. [ABSTRACT FROM AUTHOR]

The benefits of terahertz (THz) radiation have increased its use, especially in imaging systems. Recently, the use of a linear sparse periodic array (SPA) has been proposed as an effective solution for two-dimensional (2D) scanning in THz imaging systems. However, the special multistatic structure of the SPA is such that it is not possible to apply fast Fourier transform-based techniques directly in the near-field (NF). Therefore, in this paper, a fast processing approach based on two Fourier techniques compatible with linear SPA is presented for NF THz imaging. In this approach, we first employ a multistatic-to-monostatic conversion to reduce phase errors due to NF multistatic imaging. Then, to improve the quality of the results, we mathematically derive an interpolation formula to counteract the non-uniform spacing of the virtual array. The modified data is then processed by three rapid techniques (fast Fourier transform (FFT)-inverse fast Fourier transform, matched filtering and a novel 1D FFT-based technique with low computational complexity) to obtain reconstructed images of the scene. Numerical and experimental results confirm the satisfactory performance of the proposed approach in terms of both the computational time and the quality of the reconstructed images. [ABSTRACT FROM AUTHOR]

One of the main problems faced by communication systems is the presence of skip-zones in the targeted areas. With the deployment of the fifth-generation mobile network, solutions are proposed to solve the signal loss due to obstruction by buildings, mountains, and atmospheric or weather conditions. Among these solutions, reconfigurable intelligent surfaces (RIS), which are newly proposed modules, may be exploited to reflect the incident signal in the direction of dead zones, increase communication coverage, and make the channel smarter and controllable. This paper tackles the skip-zone problem in terrestrial free-space optical (T-FSO) systems using a single-element RIS. Considering link distances and jitter ratios at the RIS position, we carry out a performance analysis of RIS-aided T-FSO links affected by turbulence and pointing errors, for both heterodyne detection and intensity modulation-direct detection techniques. Turbulence is modeled using the Gamma-Gamma distribution. We analyze the model and provide exact closed-form expressions of the probability density function, cumulative distribution function, and moment generating function of the end-to-end signal-to-noise ratio. Capitalizing on these statistics, we evaluate the system performance through the outage probability, ergodic channel capacity, and average bit error rate for selected binary modulation schemes. Numerical results, validated through simulations, obtained for different RIS positions and link distances ratio values, reveal that RIS-based T-FSO performs better when the RIS module is located near the transmitter. [ABSTRACT FROM AUTHOR]

In this paper, new methodologies for the estimation of the depth of a target with unknown dimensions, based on depth from focus strategies, are proposed. The measurements are extracted from images acquired with a single camera, resorting to the minimization of a new functional, deeply rooted on the optical characteristics of the lens system. The analysis and synthesis of two complementary filters and a linear parametrically varying observer are discussed in detail. These estimators use information present on the boundary of the target, which is assumed to be on a plane parallel to the camera sensor, and whose dimensions are considered to remain constant over time. This paper complements a single pan and tilt camera-based indoor positioning and tracking system. To assess the performance of the proposed solutions, a series of indoor experimental tests for a range of operation of up to ten meters, which included tracking and localizing a small unmanned aerial vehicle with unknown dimensions, was carried out. Depth estimates with accuracies on the order of a few centimeters were obtained. [ABSTRACT FROM PUBLISHER]

This paper targets the performance analysis of multiple-input-multiple-output (MIMO) point-to-point single-aperture relay-assisted and MIMO relay-assisted free-space optical (FSO) communications. The objective of the paper is to compare the different FSO diversity methods via an outage probability analysis over gamma-gamma turbulence channels in the case of independent fading among the different apertures of the communicating nodes. Through a well-tailored calculation method, we approximate the gamma-gamma distribution and the gamma-gamma sum-distribution by appropriate gamma distributions. This method resulted in simple closed-form outage probability expressions that are accurate for average-to-large values of the signal-to-noise ratio (SNR) and in asymptotic expressions that are useful for evaluating the diversity gains and coding gains. In particular, we derived the diversity gains of MIMO repetition coding (RC), MIMO transmit laser selection (TLS), MIMO all-active relaying (AR) and MIMO selective-relaying (SR). We prove that MIMO-RC and MIMO-TLS, on one hand, and MIMO-AR and MIMO-SR, on the second hand, achieve the same diversity gain and we evaluate the coding gain of TLS with respect to RC and of SR with respect to AR. By comparing the MIMO and cooperative methods with point receivers, we reach the central result that it is always better, from a diversity gain point of view, to add more apertures to the source and destination rather than adding more relays in their vicinity despite the fact that the fading variance along FSO links decreases with the distance. For receivers that implement aperture averaging, we derive conditions under which MIMO techniques are unconditionally better than cooperative techniques with any network topology. [ABSTRACT FROM PUBLISHER]

This paper presents design and analysis methods for planar antennas based on modulated metasurfaces (MTSs). These antennas operate on an interaction between a cylindrical surface-wave (SW) excited by an isotropic TM radiator, and an MTS having a spatially modulated equivalent impedance. The MTS is realized by using sub-wavelength patches printed on a grounded slab, thus resulting in a structure with light weight and compact volume. Both features are appealing characteristics for space applications. This paper introduces for the first time an impedance-based amplitude synthesis of the aperture field distribution and shows several new examples of antennas for space applications obtained in recent research projects financed by the European Space Agency. [ABSTRACT FROM PUBLISHER]

In this paper, a radar demonstrator system with real-time capability operating at W -band is presented. It operates at 90–100 GHz and provides 3-D information about the illuminated scene. The system uses frequency modulated continuous wave signals to extract range information whereupon long-range applications are aimed at. It consists of a sparse array of 22 transmitting and 22 receiving antennas and makes use of the multiple input multiple output (MIMO) principle. A back-propagation algorithm provides cross-range information. With the help of simulations and a simulated annealing algorithm, the geometry of the sparse array is optimized to meet application requirements using the available hardware. In this paper, the demonstrator system is described and the imaging theory is shortly reviewed. Measurements are presented to verify simulation results as well as 3-D imaging and long-range capability. [ABSTRACT FROM AUTHOR]

Light field (LF) acquisition faces the challenge of extremely bulky data. Available hardware solutions usually compromise the sensor resource between spatial and angular resolutions. In this paper, a compressed sensing framework is proposed for the sampling and reconstruction of a high-resolution LF based on a coded aperture camera. First, an LF dictionary based on perspective shifting is proposed for the sparse representation of the highly correlated LF. Then, two separate methods, i.e., subaperture scan and normalized fluctuation, are proposed to acquire/calculate the scene disparity, which will be used during the LF reconstruction with the proposed disparity-aware dictionary. At last, a hardware implementation of the proposed LF acquisition/reconstruction scheme is carried out. Both quantitative and qualitative evaluation show that the proposed methods produce the state-of-the-art performance in both reconstruction quality and computation efficiency. [ABSTRACT FROM PUBLISHER]

A normally OFF trench current aperture vertical electron transistor (CAVET) was designed and successfully fabricated with Mg-doped p-GaN current blocking layers. The buried Mg-doped GaN was activated using a postregrowth annealing process. The source-to-drain body diode showed an excellent p-n junction characteristics, blocking over 1 kV, sustaining a maximum blocking electric field of 3.8 MV/cm. Three-terminal breakdown voltages of trench-CAVETs, measured up to 225 V, were limited by dielectric breakdown. This paper highlights the achievement of the well-behaved buried p-n junction that has been a formidable challenge in the success of vertical GaN devices. [ABSTRACT FROM AUTHOR]

A digital fractional- N subsampling multiplying delay-locked loop is proposed in this paper. A zero phase-offset latch-based aperture phase detector is introduced in a reference spur cancellation loop to precisely cancel any static phase offset (SPO) between the injected reference and the digitally controlled oscillator (DCO) phases. An in situ detection scheme is employed to directly measure this phase offset accurately by obviating the requirement of a high-speed off-chip measurement setup. Moreover, a mathematical expression is derived for the calculation of reference spur generated from a given SPO. A uniformly distributed switched capacitor-based DCO frequency tuning achieves highly linear gain. The chip prototype is fabricated in a 1.2-V supply, 65-nm LP CMOS technology and covers an output frequency range of 0.2–1.45 GHz while occupying a core area of 0.054 mm2. Measured phase noise at 1.4175 GHz is −95 dBc/Hz at 100-kHz offset, which is 9 dB lower than in phase-locked loop mode of operation. [ABSTRACT FROM PUBLISHER]

In the last few years, interest in multicircular synthetic aperture radar (SAR) acquisitions has arisen as a consequence of the potential achievement of full 3-D reconstructions at very high resolution over 360° azimuth angle variation. In particular, SAR systems at low frequencies are sensitive to volumetric backscattering of semi-transparent media, and they allow the imaging of internal structures, such as forests. To achieve a full 3-D reconstruction, a 2-D synthetic aperture is required, consisting of a circular (azimuthal) and a vertical component. This 3-D capability can be understood as the result of the combination of holographic and tomographic techniques. In this paper, both techniques will be presented to establish the concept of holographic SAR tomography (HoloSAR). As a further investigation, this paper also presents an analytical expression of the 3-D impulse response function (IRF) of targets in and off the center of the illuminated area. The IRF is characterized by its spatial resolution and sidelobe power, both being a function of the radar resolution capabilities and the geometric acquisition. The second part of this paper presents a polarimetric analysis of HoloSAR tomograms. In particular, the polarimetric signature of scatterers in forested areas is investigated for three different focusing approaches, namely coherent imaging, incoherent imaging, and the generalized likelihood ratio test (GLRT). The three algorithms use the fast-factorized back-projection (FFBP) for individual circular trajectories, and the latter two use in addition compressive sensing (CS) to retrieve the complex reflectivity in elevation. The IRF is validated using a polarimetric L-band HoloSAR survey, which consists of 19 circular passes conducted by the German Aerospace Center's airborne F-SAR sensor over a test site in Kaufbeuren, Germany. The same data set is used for the analysis of the backscattering of forests. Results show a significant horizontal resolution improvement for distributed targets with the coherent imaging approach, whereas a better sidelobe suppression in the direction perpendicular to the line of sight is achieved for the incoherent imaging and the GLRT. [ABSTRACT FROM AUTHOR]

Conventional stereoscopic displays suffer from vergence-accommodation conflict and cause visual fatigue. Integral-imaging-based displays resolve the problem by directly projecting the sub-aperture views of a light field into the eyes using a microlens array or a similar structure. However, such displays have an inherent trade-off between angular and spatial resolutions. In this paper, we propose a novel coded time-division multiplexing technique that projects encoded sub-aperture views to the eyes of a viewer with correct cues for vergence-accommodation reflex. Given sparse light field sub-aperture views, our pipeline can provide a perception of high-resolution refocused images with minimal aliasing by jointly optimizing the sub-aperture views for display and the coded aperture pattern. This is achieved via deep learning in an end-to-end fashion by simulating light transport and image formation with Fourier optics. To our knowledge, this work is among the first that optimize the light field display pipeline with deep learning. We verify our idea with objective image quality metrics (PSNR, SSIM, and LPIPS) and perform an extensive study on various customizable design variables in our display pipeline. Experimental results show that light fields displayed using the proposed technique indeed have higher quality than that of baseline display designs. [ABSTRACT FROM AUTHOR]

Using low-frequency (UHF to L-band) ultrawideband synthetic aperture radar (SAR) technology for detecting buried and obscured targets, e.g., bomb or mine, has been successfully demonstrated recently. Despite promising recent progress, a significant open challenge is to distinguish obscured targets from other (natural and manmade) clutter sources in the scene. The problem becomes exacerbated in the presence of noisy responses from rough ground surfaces. In this paper, we present three novel sparsity-driven techniques, which not only exploit the subtle features of raw captured data, but also take advantage of the polarization diversity and the aspect angle dependence information from multichannel SAR data. First, the traditional sparse representation-based classification is generalized to exploit shared information of classes and various sparsity structures of tensor coefficients for multichannel data. Corresponding tensor dictionary learning models are consequently proposed to enhance classification accuracy. Finally, a new tensor sparsity model is proposed to model responses from multiple consecutive looks of objects, which is a unique characteristic of the data set we consider. Extensive experimental results on a high-fidelity electromagnetic simulated data set and radar data collected from the U.S. Army Research Laboratory side-looking SAR demonstrate the advantages of proposed tensor sparsity models. [ABSTRACT FROM AUTHOR]

This paper reports the development of a wideband resonant cavity antenna (RCA). The RCA device was obtained by using an optimized aperture-coupled coplanar waveguide fed wideband patch antenna and a metamaterial-based superstrate design. The wideband behavior is based on the effects of Fabry–Perot cavity on either side of the resonant frequency of the metamaterial superstrate and the finite size of the superstrate to obtain enhanced gain around this frequency. In addition, the metamaterial superstrate in this paper contains two identical layers of a frequency selective surface (FSS) based on a 2-D patch array rather than dissimilar arrays as used in the previous studies. Two such FSS layers are assembled using a laser micromachined polymethyl methacrylate rim and an SU8-based bonding method. The air spacer based metamaterial design offers better performance by minimizing the dielectric loss between the metallic patch arrays and also offers flexibility in the control of the separation between the two FSS layers as well as resulting in a lightweight RCA device. The RCA device was designed to operate in the X-band. The dimensions of the compact RCA device are $45\times 45\times24$ mm3. The gain of the device was measured to be ~13 dBi with a 3-dB bandwidth of 46% and a corresponding 1-dBi-ripple bandwidth as wide as 40%. The measured impedance bandwidth was 44%. [ABSTRACT FROM AUTHOR]

An essential question in understanding how to develop and build collaborative immersive virtual environments (IVEs) is recognizing how people perform actions together. Many actions in the real world require that people act without prior planning, and these actions are executed quite successfully. In this paper, we study the common action of two people passing through an aperture together in both the real world (Experiment 1) and in a distributed, collaborative IVE (Experiment 2). The aperture's width is varied from too narrow to be passable to so wide as to be easily passable by both participants together simultaneously. We do this in the real world for all possible gender-based pairings. In virtual reality, however, there is potential for the gender of the participant and the gender of the self-avatar to be different. We also investigate the joint action for all possible gender-based pairings in the distributed IVE. Results indicated that, in the real world, social dynamics between gendered pairings emerged; male-male pairings refused to concede to one another until absolutely necessary while other pairings did not. Male-female pairings were most likely to provide ample space to one another during passage. These behaviors seemed not to appear in the IVE, and avatar gender across all pairings generated no significant behavioral differences. In addition, participants tended to require wider gaps to allow for passage in the IVE. These findings establish base knowledge of social dynamics and affordance behaviors within multi-user IVEs. [ABSTRACT FROM AUTHOR]

This paper addresses the use of the $Z$ transform to synthesize radiation patterns with prescribed nulls from a phased array of electronically reconfigurable leaky-wave antennas (LWAs). This approach provides the relationship between such antennas and linear and time invariant (LTI) systems. Using this signal processing perspective, the proper locations of the poles and zeros of the $Z$ transform of the associated LTI system provide a radiation pattern with prescribed specifications (mainly main lobes’ directions and surrounding radiation nulls). Then, these poles and zeros’ positions can be transformed into particular values of the LWA array control coefficients. The effectiveness of the proposed technique is demonstrated with the synthesis of various radiation patterns, with application to reconfigurable smart antennas. A comparison with more conventional uniform linear array architecture is also performed to evaluate the synthesis flexibility and system complexity of the proposed approach. [ABSTRACT FROM AUTHOR]

This paper presents a new approach to describe the scattering of an electrically large slot aperture between half-space and a rectangular cavity. The developed method generalizes known theories for the scattering of electrically small apertures and presents a general and understandable formalism for correctly calculating the induced scattering moments. The theory is first developed and validated for the electrically long thin wire in free space. Then, it is applied to describe the scattering of an electrically large thin slot in an infinite screen and backed by a rectangular cavity. The results can be used to determine the effects of external excitation, e.g., a high-power and wideband electromagnetic pulse, on the internal and external fields caused by the scattering slot. The external fields can also be analyzed for the internal resonances of the cavity. [ABSTRACT FROM AUTHOR]

This paper leads a discussion on how to form a Synthetic Aperture Radar (SAR) image without knowing the relative track. That is, within the scope of factorized geometrical autofocus (FGA). The FGA algorithm is a base-2 fast factorized back-projection (FFBP) formulation with six free geometry parameters (per subaperture pair). These are tuned step by step until a sharp image is obtained. This innovative autofocus concept can compensate completely for an erroneous geometry. The FGA algorithm has been applied successfully on two ultrawideband (UWB) data sets, acquired by the CARABAS II system at very high frequency (VHF)-band. The relative tracks are known (measured accurately). We, however, adopt and modify a basic geometry model. A linear equidistant track at fixed altitude is initially assumed. Apart from deviations due to linearization, a ~2.5-m/s along-track velocity error is also introduced. Resulting FGA images are compared to reference images and verified to be focused. This indicates that it is feasible to form a wavelength-resolution SAR image at VHF-band without support from a motion measurement system. The execution time for the examples in this paper is about five times longer with autofocus than without. Hence, the FGA algorithm is now fit for use on a regular basis. [ABSTRACT FROM AUTHOR]

Acoustic-resolution photoacoustic microscopy (AR-PAM) is a promising technology for vascular or tumor-targeted molecular imaging. Unique advantages of AR-PM are its non-invasive, non-ionizing real-time, and deeper imaging depth. AR-PAM typically uses an ultrasound transducer with a high acoustic numerical aperture (NA) to enable deeper imaging depth. While high NA achieves good lateral resolution in the focal plane but significantly degrades the lateral resolution in the out-of-focus region. Synthetic aperture focusing technique (SAFT) has been introduced to overcome this out-of-focus degradation by synthesizing the correlated signals. Several 2-D SAFTs have been also reported to improve degraded resolution in all directions. However, the resolution enhancement of the previously reported 2-D SAFTs are suboptimal and are not equivalent to the 1-D SAFT performance under an ideal condition with the sample orientation perpendicular to the synthetic aperture direction. In this paper, we present a new 2-D SAFT called 2-D directional SAFT that improves the lateral resolution significantly and we compare our results against 1-D SAFT under ideal condition. We applied this algorithm to phantom and in vivo images to show the improvement in image quality. We also implement this algorithm in a graphical processing unit to achieve high performance to show the practicality of implementing this new algorithm in a system. [ABSTRACT FROM AUTHOR]

Pseudospark-sourced electron beam with high energy can be produced by the pseudospark device. In this paper, the breakdown voltages of the hollow cathode discharge with the pseudospark geometry influenced by electrode geometry and the gas have been studied and analyzed. In the wide range of pressure and gap, the breakdown voltage increases with the increase in the pressure and the gap distance. There is a pressure threshold and a gap distance threshold, below which the discharge mode will change. The product of the pressure threshold and the gap distance threshold is about 65 Pa $\cdot$ mm. The breakdown voltage is affected by the aperture diameter and the gap distance together. When the ratio of the gap distance to the aperture diameter is greater than 4, the electric field inside the small hole is almost zero and the discharge is converted to the plate electrode discharge. When the ratio is in the range of 0.67–4, the breakdown voltage decreases with the increase in the aperture diameter. When the ratio is less than 0.67, the breakdown voltage hardly changes with the aperture diameter. [ABSTRACT FROM AUTHOR]

This paper presents the first demonstrator of a portable, multiview, high-resolution, 3-D, and real-time microwave imaging system. The system is based on a recently developed real-time 3-D microwave camera, which performs quasi-monostatic acquisitions, equipped with an optical depth camera, providing target surface profile information. In addition, the entire system can be arbitrarily moved along the target performing microwave and depth camera synchronized acquisitions from different views with a twofold purpose, namely: 1) enabling a coverage area much larger than that possible with a static imaging system and b) allowing for incorporation of several tilt angles (or views) to enhance capturing specular reflection imaging data to improve the overall image quality. At each scanning position, the imaging data from the microwave camera are processed to build a local 3-D microwave image. The information is then merged, using recently proposed techniques for multiview synthetic aperture imaging, to compose the global image. The synchronized optical camera depth acquisitions enable tracking the entire imager movements so that the position and attitude are known. Moreover, the data acquired by the depth camera are also use to build a complementary 3-D outer surface profile model of the target, producing a combined and realistic image of the internal and external geometries of the target. Finally, the performance of the combined system is evaluated using several examples related to hidden contraband covered by clothing (i.e., people screening). [ABSTRACT FROM AUTHOR]

The erosion of the accelerator grid affects the life of the ion thruster. One of the most important reasons for accelerator grid erosion is the bombardment of charge exchange (CEX) ions to the accelerator grid. There are two types of erosions caused by CEX ions: barrel erosion and pits and grooves erosion. The erosion mechanism of pits and grooves erosion is the CEX ion back flowed from the downstream of the optics. However, there is no unified conclusion on the erosion mechanism of barrel erosion since the erosion mechanism of barrel erosion developed in most of the current research is only applicable to the specific conditions set up in each research. In this paper, the 3-D IFE-PIC-MCC algorithm is used to simulate the beam ion motion, the CEX collision, and the erosion of CEX ion on the accelerator grid under different operation conditions. The erosion mechanism of barrel erosion under different operation conditions is studied. The results indicate that the main production areas of CEX ions which cause the barrel erosion are different under different operation conditions. [ABSTRACT FROM AUTHOR]

This paper presents a CMOS image sensor with the in-pixel aperture technique for single-chip 2-D and 3-D imaging. In conventional image sensors, the aperture is located at the camera lens. However, in the proposed image sensor, the aperture is integrated on the CMOS image sensor chip and is formed at a metal layer of the CMOS image sensor (CIS) process. A pixel array of the image sensor is composed of the W, R, B, and PA pixels (W pixel with integrated metal aperture) for extracting color and depth information. While the image of the W pixel becomes blurred with increasing distance from a focused object, the image of the PA pixel maintains the sharpness. Therefore, the depth image can be obtained using the depth from the defocus method. The size of the pixel, which is based on a four-transistor active pixel sensor with pinned photodiode, is $2.8 \,\,\mu {\mathrm{ m}} \times 2.8\,\,\mu \text{m}$. A prototype of the proposed image sensor was fabricated using the 0.11- $\mu \text{m}$ CIS process and its performance was evaluated. [ABSTRACT FROM AUTHOR]

A novel cylindrical millimeter-wave holography regime using a multi-input-multi-output (MIMO) array is first introduced. More importantly, an accurate and fast 3-D imaging algorithm is developed for this regime. Although many efficient imaging algorithms for synthetic aperture radar (SAR) or circular SAR have been developed, they can hardly be used for this new regime due to the compound effects of a spherical wavefront, MIMO geometry, and cylindrical observation aperture. In this paper, we develop an efficient algorithm mainly based on the ideas of a spherical wave decomposition, circular convolution, and nonuniform fast Fourier transform. The proposed algorithm achieves similar imaging quality with the golden-standard back-projection algorithm (BPA) while costs much less time. Compared with the BPA, the proposed algorithm belongs to a kind of the frequency-domain method built upon range migration techniques. Detailed derivations are first presented. Then, several important issues including resolutions, sampling criteria, and computational complexities are analyzed. Finally, a series of simulations and experiments are carried out, and all the results verify the effectiveness of the proposed algorithm on both accuracy and efficiency. [ABSTRACT FROM AUTHOR]

A passive compressive device (PCD), which works at millimeter waves, is proposed in this paper. In a passive manner, the device allows to compress the signals from multiple separate channels into a single or a reduced number of channels. This permits a simplification of the transmitter or receiver chains for radar imaging applications. The PCD is a 3-D cavity that ensures each channel to be decorrelated with each other. If the transfer functions are known, the compressed signals are decompressed in postprocessing. This paper proposes a suitable method to estimate simultaneously the transfer functions of the PCD. This is validated by measurements in a multiple-input-multiple-output (MIMO) configuration to produce a complex synthetic aperture radar image. Measurements revealed that the point spread function generated by the MIMO configuration with the use of the PCD leads to almost similar results, in terms of spatial resolution and sidelobe level ratio, as those of a single-input-multiple-output configuration (uniform amplitude), with a fewer receiving elements. [ABSTRACT FROM AUTHOR]

Conventional transmit subarray partitioning schemes of phased-MIMO radar will cause several problems, the reduction of array aperture, the increase of feeding network complexity and optimization algorithms time cost. Focus on the problems above, this paper proposes a deep learning-based interleaved sparse transmit subarray partitioning method. Firstly, the training data is generated by phased-MIMO array manifold matrix. Secondly, a dimensionality reduction method for radar data is introduced to reduce the dimensionality of the sample data while minimizing information loss. Then, a lightweight convolutional neural network is constructed for training and the optimal array structures is selected by classification. Finally, linear and plane arrays experiment results show that our proposed method can achieve 97.95% classification accuracy, better than other conventional dimensionality reduction methods and neural networks; compared with the traditional SCP partitioning method, our proposed method has similar beampattern sidelobe level and DOA estimation accuracy, but the time cost is greatly reduced. [ABSTRACT FROM AUTHOR]