Array Element Spacing Research Articles

A Dual‐Polarized Wide‐Angle Scanning Linear Phased Array Antenna With Simple Decoupling Structure

ABSTRACTA dual‐polarization linear phased array with a simple decoupling structure is designed for wide scanning in this letter. The suggested antenna is made up of two printed dipole antennas that are orthogonally arranged and have a high cross‐polarized isolation. Metal sheets cladding on antenna substrates serve as a decoupling structure, with an array element spacing of 0.48 . A linear phased array of seven elements is fabricated and measured to ensure that the planned array is feasible. The simulated and measured results demonstrate that the phased array can scan its main beam up to ±75° in dual‐polarized excitations at 5.6–6.4 GHz. The co‐polarized mutual coupling is below −28 dB, and the active reflection coefficient of the element is less than −15 dB.

Sidelobes and sideband minimization in time-modulated array antenna based on chaotic exchange nonlinear dandelion optimization algorithm

Time-modulated array antenna (TMAA) is a new type of array antenna based on time modulation technology. By introducing "time" as the fourth dimensional design freedom into the design of conventional array antennas in three-dimensional space, the array antenna has time modulation characteristics, which better controls the radiation characteristics of the array antenna and achieves the best far-field radiation pattern synthesis. This paper designs a Time-modulated linear array (TMLA) with low sidelobe level (SLL) and low sideband level (SBL) based on the chaotic exchange nonlinear dandelion optimization (CENDO) algorithm. Three optimization methods are studied: firstly, determining the optimal on-time (τnn) for each array element; The second is to determine the optimal on-time (τnn) and optimal uniform array element spacing (d) for each array element; The third is to determine the optimal opening time (ton), closing time (toff), and optimal uniform array element spacing (d) for each array element. To achieve simultaneous reduction of sidelobe level and suppression of harmonic interference. The same array model contains different harmonic frequency radiation. In this article, we only considered two harmonic frequencies, namely the first sideband frequency and the second sideband frequency. Because the harmonic of other sideband frequencies has a very small impact on the radiation of the fundamental wave, it can be ignored. To demonstrate the stronger ability of the CENDO algorithm in optimizing Time-modulated array antennas, and in line with the principle of fairness and impartiality, this paper also simulates different Time-modulated array models and compares the results of the CENDO algorithm with other published literature. It is concluded that this study shows lower SLL and lower SBL in different models. This provides a more scientific and accurate explanation of the superiority of the CENDO algorithm compared to other algorithms in the field of antenna optimization in electromagnetics. At the same time, this also provides great research value and fundamental support for designing high-performance Time-modulated array antennas in subsequent engineering applications.

Optimizing Elliptical Cylindrical Antenna Array for Improved Wireless Communication Using Novel PSO Algorithm

This paper presents a novel approach to optimize the thinning of an elliptical cylindrical array (ECA) composed of uniformly stimulated, isotropic antennas with the objective of achieving a directed beam characterized by a significantly reduced relative Sidelobe Level (SLL). The optimization process employs the Novel Particle Swarm Optimization (NPSO) method, which offers a fresh perspective on addressing electromagnetic optimization challenges by its ability to effectively explore solution spaces. By employing the NPSO algorithm, which emulates the collective behavior of swarming particles to search for optimal solutions, this study addresses complex optimization challenges inherent in antenna array design. This study focuses on identifying the optimal combination of ON–OFF components (use the minimum number of ON antenna elements) within the antenna array to produce a radiation pattern exhibiting the greatest decrease in SLL. Additionally, the First Null Beam Width (FNBW) is targeted for optimization without predefined values. The optimization approach also considers the effect of thinned array element spacing on the overall performance metrics. Out of total 36 elements, only 15 elements are switched ON and the remaining of the elements are OFF, so the total reduction or thinning of ECAA is 41.66%. Simulation results demonstrate that the proposed methodology enables a simultaneous reduction of more than half of the antenna array elements while achieving superior SLL minimization. This significant reduction in antenna elements not only contributes to simplifying the array design, but also enhances the array’s beamforming capabilities.

Intercoupling Suppression of Very Closely Spaced MIMO Antenna Based on Current Cancellation Method

Herein, a high isolation multiple-input–multiple-output (MIMO) antenna with a very close array element spacing, is proposed. By loading a pair of L-shaped parasitic stubs on the antenna feeder, the impedance matching bandwidth of the antenna is significantly improved. Furthermore, since the λ / 2 microstrip line can make the signal through it produce 180°phase transformation at the resonant frequency. A dielectric wall decoupling structure withλ / 2metal microstrip lines etched on both sides of the substrate is designed, and its profile height is 1.3 mm ( 0.022λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ).When the antenna element edge-to-edge distance is only 1mm ( 0.017λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ), the isolation of the MIMO antenna at the resonant frequency of 5.37 GHz is improved by 51.5 dB by introducing the dielectric wall decoupling structure. Finally, the close-spacing MIMO antennas using current cancellation method are compared, and the results show that the proposed decoupling structure is simple and has great versatility and extensibility.

Efficient DOA-polarization estimation for 2-D mirrored array based on the hybrid aperture expansion

At present, there are fewer studies on the polarization-sensitive mirrored array (PS-MA). Meantime, the estimation accuracy will decrease when the array element spacing is lower than half wavelength. This paper focuses on the aperture expansion of the PS-MA to improve the estimation accuracy. To this end, we establish the received signal model of the 2-D PS-MA with two perpendicular reflectors. Unlike the existing virtual array without polarization information, a novel model of the polarization-sensitive virtual array (PS-VA) is suggested based on the hybrid coarray technique. Additionally, the spatial smoothing (SS) technique is used to recover the rank of the covariance matrix, and the modulus value boundedness (MVB) of the polarization vector is used to reduce the dimension of the polarization-spatial spectrum. Then, the MVB-MA-SS algorithm is proposed for polarization-DOA estimation, which is much more efficient than the standard group-lasso algorithm used in the 1-D PS-MA. Numerical experiments show that the proposed algorithm can provide satisfactory estimation accuracy with significantly reduced computational complexity.

Analysis of Focusing Performance in Phased Array Probe Using COMSOL

To improve the detection ability of ultrasonic phased array detection for hydrogen storage vessel, COMSOL was used to simulate the main parameters of phased array probes. The influence of the number of array elements, array element spacing and excitation frequency on the sound propagation characteristics was analysed. The results showed that the number of array elements has a significant effect on the focused sound field. When the number of array elements is 8, effective focus cannot be formed at the pre-set focus position, and the maximum sound pressure value does not change significantly at the three pre-set focus depths. At a focus depth of 30mm, the maximum sound pressure in the 32-element mode is more than twice that in the 8-element mode. The relationship between excitation frequency and focal sound pressure is non-linear. In addition, as the array element spacing increases, the length of the focal column decreases. And the smaller the array element spacing, the higher the sound pressure at a deeper depth.

Study on Directivity of Underwater Circular Transducer Array

At present, in the detection and identification of underwater noise sources, one of the most commonly used transducer arrays is the circumferential transducer array. The circumferential transducer array is symmetrical in space and has high withstand voltage capability and small sound pressure fluctuation in the horizontal beam. Its directivity is an important index that affects the performance of the array. This paper focuses on the directivity maps of circular arrays with different sizes and numbers of elements. From the graph, it is concluded that the undulation of the directivity graph of the circular array is directly related to the array element spacing. The smaller the array element spacing is, the smaller the undulation is, and vice versa. The directivity formula and law can provide technical guidance for the design of a uniform circular transducer array.

New precision electroforming process for the simultaneous improvement of thickness uniformity and microstructure homogeneity of wafer-scale nanotwinned copper arrays

Nanotwinned (nt) Cu has received much attention because of its superior mechanical and electrical properties, but only a few production processes can yield nt-Cu parts with uniform thickness and a homogeneous microstructure on the wafer scale. To solve this problem, a new precision electroforming process is proposed that combines auxiliary cathodes with pulse reverse current (PRC) electroforming, which provides a synergistic effect to increase the homogeneity of the thickness and a nanoscale twin structure. As a practical example of the proposed process, 4-inch nt-Cu lamina arrays were fabricated and numerically modeled to probe into the synergistic mechanisms. The intrinsic correlations among the array element spacing, current waveform, and main forms of thickness nonuniformity were determined. In addition, the effects of the processing parameters on the microstructural evolution and microhardness of the nt-Cu arrays were analyzed. The results indicated that such a significant improvement in thickness uniformity and microstructure homogeneity were due to the auxiliary-cathode/PRC combination, which enables maximization of the PRC leveling efficiency by inducing a uniform current distribution; this effectively ensures that the microstructures are uniform across all laminae on the wafer scale. Additionally, thick nt-Cu deposited on the current-crowding regions was preferentially stripped during the application of reverse current. This alleviates the adverse effects of the current redistribution resulting from the auxiliary cathode on the thickness uniformity of the laminae and offers additional possibilities for homogeneous growth of nt-Cu. The new precision electroforming process has significant potential to produce wafer-scale components with uniform thickness and specific microstructures.

Design, Array, and Test of Super-Low-Frequency Mechanical Antenna Based on Permanent Magnet

As a new type of super-low-frequency (SLF, 30–300 Hz) magnetic antenna, the permanent magnetic mechanical antenna (PMMA) has great potential for applications in underwater communication, underground communication, and earthquake prediction. PMMAs use large-volume permanent magnets to enhance the signal, posing a significant challenge to power consumption of the mechanical drive structure. We optimize the permanent magnets in terms of magnetization structure, magnetic material, and form factor to determine the optimal permanent magnet structure. We establish an analytical model of the magnetic torque of the array elements and the radiated field of the array to determine the optimal array form. Based on the analytical model, we analyze the effects of the array element spacing, the phase difference of the array elements, and the number of array elements on the radiated time-varying magnetic field. Finally, a 3-D array prototype operating in the frequency band of 75–125 Hz is developed for testing. The test results show that when the phase difference is less than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm{26}^{\circ} $ </tex-math></inline-formula> , the effect on the radiation intensity of the array is negligible. When the array element spacing is 0.15 m, the motor cannot drive the mechanical structure, and when the array element spacing increases to 0.3 m, it can operate normally. Communication experiments were conducted, and the transmission rate could reach 2 bps.

Aperture Synthesis With Digital Array Radars and Covariant Change of Wavenumber Variables

Attributes of digital array radars are leveraged in enhancements of wideband frequency-wavenumber (omega-k) methods to achieve 1) single-pulse, short-range imaging from a stationary array; 2) single-pulse, all-range, high-density, digital beamforming-on-receive from a stationary array; 3) multiple-pulse aperture synthesis for short-range imaging with sensor movement; and 4) multiple-pulse inverse aperture synthesis for long-range imaging with tracked object movement. Modifications to conventional omega-k algorithms used in synthetic aperture radar are introduced to accommodate antenna element level data, real array element spacing, large scene size and small array size (compared to scene size). Large scene size with k-space processing is handled by a novel Huygens-Fresnel transfer function that does not fully rely on zero-padding to resolve array and scene size mismatch. Aperture synthesis with generalized pulse-to-pulse sensor-step operations is supported. Connections between omega-k wavenumber migration and a covariant change of variables transform associated with Dirac's spectral models of free and scattered electromagnetic fields are established.

Design of Miniaturized Wideband Beam Deflection Conformal Array Antenna

Antenna beam deflection, along with miniaturization and wideband of the antenna is in demand for practical applications. In this paper, a cylindrical conformal array antenna with a small-tilt forward beam was designed. The microstrip antenna unit was loaded with the artificial electromagnetic structure, which reduced the size of the antenna unit. As a result, the center spacing of the array elements can be shortened with the same array element spacing. The beam deflection angle can be increased in this way without increasing the coupling effect between the parts. Changing the number of line array elements and the number of line arrays can regulate the beam width of E-field and H-field, respectively. The bandwidth of the antenna can be significantly extended by slotting the ground plane. This work implemented a cylindrical conformal array of the antenna's forward beam with a small dip angle using a cylindrical carrier as an example. The measurement results showed that the angle between the main beam and the carrier axis of the conformal antenna was less than 30°, the bandwidth was more than 30%, and the antenna volume decreased by 40.4%.

Unambiguous broadband direction of arrival estimation based on improved extended frequency-difference method.

In this paper, we consider the problem of bearing ambiguity in the direction of arrival (DOA) estimation due to spatial aliasing when the minimum wavelength of the processing broadband signal is less than the element spacing of a uniform linear array (ULA). First, an extended frequency-difference (FD) method is presented. Unlike the existing FD methods, the extended FD signal is constructed by conjugate multiplying a diagonal matrix consisting of steering vectors at high frequency and pre-processing direction with the array sampled signal matrix at low frequency. Then, this paper establishes a decision criterion for distinguishing the aliasing component that varies linearly with frequency in the extended FD space. Finally, an unambiguous broadband DOA estimation method is achieved by suppressing spatial aliasing in the extended FD space. The simulation results show the effectiveness of the proposed method in low signal-to-noise ratio, low signal-to-interference ratio, and multi-interference conditions. The unambiguous processing ability of the proposed method is further verified in the South China Sea using ship signals in the frequency band of 200 to 700 Hz and a 10-element ULA with a 6.25 m spacing deployed on the seabed.

The Limited Aperture Sparse Array for DOA Estimation of Coherent Signals: A Mutual-Coupling-Optimized Array and Coherent DOA Estimation Algorithm

The paper investigates DOA estimation of coherent Signals with the limited aperture sparse array. Mutual coupling between the sensors of the array cannot be ignored in practical radar with a limited aperture of array sensors, which will result in a degradation in the performance of Direction of Arrival (DOA) estimation. This paper proposes a Mutual-coupling-optimized array (MCOA) with a limited aperture in this scenario to reduce the mutual coupling effect. Firstly, we prove the sparse uniform linear array (SULA) has the smallest mutual coupling leakage when the array aperture and the number of sensors is determined. Secondly, we modify the spacing of the array sensors in SULA to make sure that the spacing between all array sensors and the reference sensor are coprime aiming to estimate DOA without spatial aliasing. Thirdly, we give an expression for the array element spacing arrangement with reduced mutual coupling leakage. Finally, the coherent signals are well resolved by the Sparse Bayesian Learning (SBL) algorithm. Numerous simulations are conducted to validate the advantages of the proposed array compared to several sparse arrays for estimating coherent signals in the presence of mutual coupling.

Research on factors affecting ultrasonic phased array detection imaging quality for curved component

An in-depth analysis on the beam directivity of ultrasonic phased arrays has been made to solve the problems of low image quality and identification difficulties caused by a suboptimal configuration of array elements. The influence on the number and spacing of array elements on the imaging quality of curved components was studied. The simulation and experimental verification of the phased array sound field for curved components were carried out. The rules governing the influence of phased array transducer parameters on imaging quality were obtained, and an approach to the optimization of parameters was proposed. The results of this study have important significance for transducer design and the phased array detection of curved components.

Convex Array With Variable Spacings (CAVS) for Ultrafast Ultrasound Diverging-Wave Imaging

The synthetic focusing of coherent plane-wave compounding (CPWC) has gradually developed from ultrasound linear array to convex array. The field of view (FOV) has been expanded compared to that of the linear array. However, the existing technology does not make the most of the convex structural advantages and FOV is greatly limited by the element number of a convex array. In this paper, based on the convex array of diverging wave (DW) imaging theory and the special structure design principles, the elements of the convex array probe are unequally spaced for better imaging quality and wider FOV. Firstly, the sound field pattern was simulated for sidelobe comparison. Then, DW imaging of the new convex array was simulated and the experiment was carried out on the tissue-mimicking ultrasound phantom using the commercial probe. Comparisons of lateral and axial variations illustrated that the convex array with variable spacings (CAVS) does improve the imaging quality when compared to the given convex array with uniform spacings. Finally, we conclude that CAVS can further extend the FOV of DW imaging by taking advantage of the structure of convex array and variable element spacings.

Three-dimensional localization of gas leakage using acoustic holography

Gas leakage localization is essential to prevent accidents from gas transportation or storage failures. There have been extensive studies on one-dimensional (1D) and two-dimensional (2D) gas leakage localization problem. This paper is the first to report the demonstration of a three-dimensional (3D) localization of gas leaks using far-field acoustic holography. This approach simultaneously provides 2D sound field imaging and depth position information regarding the leakage source. A virtual phased array composed of only two sensors collects the needed data, resulting in improved accuracy, enhanced feasibility and reduced cost. Various parameters, including the number of sensors, the spacing of array elements and the distance to the leakage source, are analyzed by a simulation of leakage sound field reconstruction. A series of experiments validated the effectiveness and accuracy of the proposed approach. Our results demonstrate that the proposed method achieves 3D localization and high-resolution imaging recognition of gas leaks.

Adaptive Transmit Beamspace Optimization Design based on RD-log-FDA Radar

Because of the range-angle dependency in random log frequency diverse array (RD-log-FDA) radar, a method for designing beamspace transformation matrix in angle and range based on the receive signal has been proposed. It is demonstrated that the designed beamspace transformation matrix basically meets the requirements of beam gain. However, there are some problems in the transformation matrix designed, such as unstable beam gain and high sidelobe. Hence, we propose an optimization method by adjusting array element spacing and random number in frequency offset to get the optimum beam gain. Therefore, particle swarm optimization (PSO) is used to find the optimal solution. The beam gain comparison before and after the optimization is obtained by simulation, and the results show that the optimized array after beamspace preprocessing has more stable beam gain, lower sidelobe, and higher resolution in parameter estimation. In conclusion, the RD-log-FDA is capable of forming desired beam gain in angle and distance through beamspace preprocessing, and suppressing interference signals in other areas.

Unmanned Aerial Vehicles Swarm-Based Distributed Phased Arrays for Grating Lobe Mitigation and Collision Avoidance

Distributed phased arrays based on unmanned aerial vehicle (UAV) swarm with small antenna elements on each micro-UAV are expected to achieve much better performance than the traditional phased arrays due to a large amount of swarm mobile individuals and deployment flexibility. To avoid the possible collisions of the flying UAVs, a large separation distance between UAVs is required, but grating lobes can appear when the array element spacing is larger than one-half wavelength. To solve this issue, array antennas with aperiodic element placement are normally used to mitigate the grating lobes, while suffering from a high collision risk for UAVs due to the reduced array element separation in the aperiodic array. This paper proposes a novel 3-D aperiodic array design by adding an additional degree of freedom in the optimization of array configuration. The sidelobe levels can be largely reduced from the planar periodic arrays. In addition, the collision risk for UAVs represented by the minimum separation distance between array elements can be largely decreased from the planar aperiodic arrays. This work provides a feasible strategy for the design and optimization of the UAV swarm-based phased arrays for practical applications.

DOA Estimation of Underwater Acoustic Targets Based on Bayesian Compressed Sensing

Aiming at the performance degradation or even failure of existing underwater acoustic target direction of arrial (DOA) estimation methods under the conditions of low signal-to-noise ratio and low snapshot, a underwater acoustic target DOA estimation method based on sparse Bayesian compressed sensing theory is studied, and simulation experiments are carried out by MATLAB to verify the feasibility and effectiveness of the proposed method. Simulation results show that compared with CBF , MUSIC and OMP algorithms, the proposed method can improve the estimation accuracy in the case of lower snapshot number, lower number of array elements and smaller array element spacing, and can achieve high resolution DOA estimation in the case of low signal-to-noise ratio and close position of multiple target signals.

Modeling of spatial correlation characteristics of broadband ocean ambient noise vector field

The signal-to-noise ratio gain of the array is closely related to the spatial characteristics of the noise field. The modeling of the spatial characteristics of marine environmental noise is always a hot spot. For sonar with different functions, the working frequency band and bandwidth are usually different. Therefore, the spatial correlation coefficient of the noise field in arbitrary frequency band has important reference value for designing sonar systems. According to the process of generating the marine environmental noise field under the high frequency approximation condition, a noise field time-domain modeling method is proposed, and the integral expression of the time-domain sound pressure and particle vibration velocity of marine environmental noise in a horizontally layered medium is given. This lays the foundation for establishing a broadband model of the noise vector field. In particular, the analytical expression of the spatial correlation coefficient of the broadband white noise vector field in the vertical direction under specific condition is also given. Following the spectral structure of wind-generated noise, the spatial correlation coefficients of noise fields with different frequency bands and different spectral slopes are numerically calculated, revealing the influence of bandwidth and spectral structure on the spatial characteristics of marine environmental noise, and the principle behind the result is explained through theoretical derivation. With the increase of the array element spacing and bandwidth, the number of oscillation periods and the oscillation amplitude of the spatial correlation coefficient of each component of the noise vector field gradually decrease, which is caused by the frequency domain average of the noise field correlation coefficient. When the spectral slope is less than zero, the low-frequency noise plays a major role, causing the spatial correlation radius of the broadband noise field to be larger than that of the narrowband noise field. The result of the experiment conducted in South China Sea shows that the measured vertical spatial correlation coefficient of the sound pressure field of marine environmental noise is in good agreement with the theoretical result. The model has potential application prospects for the research of transducer array technology and the inversion of environmental parameters.