Narrow Beamwidth Research Articles

Synthesis of Thinned Planar Arrays Based on Precoded Subarray Structures

A thinning method based on precoded subarray structures is proposed for planar arrays. It introduces the matrix descriptions, including the subarray structure matrix <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> and the coefficient vector <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> , and transforms the thinning of a planar array into the arrangement of predetermined subarrays with specified thinning rates. This process effectively leads to order reduction and achieves fast optimization. We apply the evolutionary algorithm to accomplish the ideal radiation performance iteratively. The dependence of the array performance on <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> is also investigated. For demonstration, the 10×20- and 23×23-element arrays are optimized. By comparing with the traditional thinning methods, it is verified that the proposed method not only provides us with lower sidelobes and narrower beamwidth but also avoids the random element arrangement. In addition, the introduction of precoded subarrays may further reduce production and maintenance costs, especially from engineering implementation and mass production perspectives.

Near-Field Terahertz Communications: Model-Based and Model-Free Channel Estimation

Terahertz (THz) band is expected to be one of the key enabling technologies of the sixth generation (6G) wireless networks because of its abundant available bandwidth and very narrow beamwidth. Due to high frequency operations, electrically small array apertures are employed, and the signal wavefront becomes spherical in the near-field. Therefore, near-field signal model should be considered for channel acquisition in THz systems. Unlike prior works which mostly ignore the impact of near-field beam-squint (NB) and consider either narrowband scenario or far-field models, this paper introduces both a model-based and a model-free techniques for wideband THz channel estimation in the presence of NB. The model-based approach is based on orthogonal matching pursuit (OMP) algorithm, for which we design an NB-aware dictionary. The key idea is to exploit the angular and range deviations due to the NB. We then employ the OMP algorithm, which accounts for the deviations thereby ipso facto mitigating the effect of NB. We further introduce a federated learning (FL)-based approach as a model-free solution for channel estimation in a multi-user scenario to achieve reduced complexity and training overhead. Through numerical simulations, we demonstrate the effectiveness of the proposed channel estimation techniques for wideband THz systems in comparison with the existing state-of-the-art techniques.

Microwave Imaging With Novel Time-Domain Clutter Removal Algorithm Using High Gain Antennas for Concealed Object Detections

This paper presents a novel time-domain clutter removal algorithm for microwave imaging of concealed objects using a new high gain ultra-wideband (UWB) antipodal antenna. Bistatic antenna setup is employed to image the objects like a gun prototype, knife and blade using UWB Gaussian modulated pulses. A synthetic aperture radar (SAR) beamforming algorithm with a new clutter removal method is adopted for microwave imaging of the objects inside and outside the anechoic chamber. The proposed algorithm successfully removes the unwanted clutter from the measured scanning data, with only single scanning of the target area. The proposed method along with windowing, envelope detection and finally image reconstruction results in effective reconstruction of the concealed target as compared to the existing methods in the literature. An UWB high gain antipodal antenna is designed for the proposed imaging setup with a peak gain of 26 dBi at 8.4 GHz, which is the highest among previously reported UWB antennas. The proposed antenna achieves a wide gain bandwidth over 6 – 14 GHz (80%) with a gain of > 18 dBi. Simulation and measured results validate the design principle of the antenna with characteristics like high front to back ratio, narrow half-power beam width, and low cross-polarization. In the opinion of the authors, the proposed clutter removal algorithm is the simplest and effective method for single-time scanning of the concealed targets, in a realistic scenario.

Fast Beam Discovery and Adaptive Transmission Under Frequency Selective Attenuations in Sub-Terahertz Bands

Sub-THz-based communication needs ultra-large antenna arrays to generate pencil-like beams under the stringent requirements of line-of-sight (LoS) to overcome the effect of the rapid attenuation of signal strength, including atmospheric attenuation. In addition, the complexity of attaining narrower beamwidth, which also requires fast and perfect alignment between the TX-RX pair, makes the sector sweeping-based beam discovery approach no longer suitable. To solve these challenging problems, in this paper we propose a leaky waveguide (LWG)-assisted, high-resolution codebook-based beam discovery, precoding, and combining scheme together with an adaptive frequency hopping spread spectrum (FHSS) for a network with relays and small base stations (SBS). The proposed method can help the transmitter quickly determine a suitable beam pattern for an LoS path requiring only limited feedback information. In the beam discovery phase, we use LWG to attain valuable information about the angle of departure (AoD) and angle of arrival (AoA). LWG has also been used to identify frequency selective attenuated regions, which can change from time to time depending on the local atmospheric moisture conditions. To mitigate the impact of such attenuations, we opt for an adaptive Frequency Hopping Spread Spectrum (FHSS). The simulation results indicate that our beam discovery and FHSS based method can achieve a much higher performance than baseline methods.

Far-Field Wireless Power Transfer for the Internet of Things

A complete end-to-end far-field wireless power transfer (WPT) is proposed and studied in this paper for the application of the Internet of Things (IoT) at the industrial, scientific, and medical (ISM) band of 2.4 GHz. The radiative WPT has achieved a remarkable attraction for the capability to transfer power in the long range. We propose two approaches. In the first approach, a 2×4 microstrip patch transmitter antenna array with a high gain and a narrow beamwidth is proposed that is rotated toward the IoT device using a small stepper motor. The performance of the rectifier in the receiving circuit was separately analyzed, and 17.54% efficiency was achieved with a load of 0.6 kΩ for the circuit, while the input power was 10 dBm. The overall system test was performed and the targeted result was investigated considering the distance between the transmitter and the receiver, and an input radio frequency (RF) power of 5 dBm to 15 dBm at 2.4 GHz. The second approach uses a 1×4 transmitter antenna array fed through a Butler matrix to provide four individual beams with a 22.5∘ angular separation, and 90∘ total angular coverage. The goal was to focus the power into four angular locations and to reduce the power waste in other directions. A mobile app was developed to control the direction of the beam. A system efficiency of as much as 19% was measured for an input RF power of 0 dBm and a resistive load of 62 kΩ.

Obtaining Feasible Minimum Side Lobe Level for Narrow Beam Width Using Convex Optimization in Linear, Planar, and Random Antenna Arrays

In many applications, the radiating elements of the used antenna may be configured in the form of a one-dimensional linear array, or two-dimensional planar array or even random array. In such applications, a simple optimization algorithm is highly needed to optimally determine the excitation amplitudes and phases of the array elements to maximize the system’s performance. This paper uses a convex optimization instead of other complex global stochastic optimizations to synthesize a linear, planar, and random array patterns under pre-specified constraint conditions. These constraints could be either fixed beam width with the lowest possible sidelobe levels or fixed sidelobe level with narrower possible beam width. Two approaches for array pattern optimization have been considered. The first one deals with the problem of obtaining a feasible minimum sidelobe level for a given beam width, while the second one tries to obtain a feasible minimum beam width pattern for a given sidelobe level. Both optimization approaches were applied to the linear, planar, and random arrays. Simulation results verified the effectiveness of both optimization approaches and for all considered array configurations.

Remote acoustic sizing of tethered fish using broadband acoustics

Remote fish sizing is desirable in fisheries (e.g., pre-catch) and research (e.g., platforms without biological sampling capacity) applications. In those contexts, the high spatial resolution of pulse compressed broadband echoes combined with narrow beamwidth transducers makes it feasible to resolve the scattering from different parts of the fish body and hence can be used to measure the body size. A motorized apparatus was used to suspend individual fish in the acoustic beam of two laterally oriented transducers (45–90 kHz, 160–260 kHz, 12.2 m range) with precise control of rotation angle. Broadband scattering was measured from tethered Atlantic mackerel (Scomber scombrus), saithe (Pollachius virens), and pollack (Pollachius pollachius) ranging in standard length from 239 to 491 mm as a function of orientation angle to validate sizing based on the acoustic resolution of fish body parts. Under these controlled conditions, fish size was underestimated by 11–19 mm, varying with broadband pulse characteristics, orientation angle, species, and fish size. The best remote acoustic sizing results were obtained using 160–260 kHz pulses with a slow rise and fall of pulse amplitude (aka, taper).

High-Efficiency 2-D Multibeam Rectenna Based on Gain Enhanced Patch Array

Wireless power transfer (WPT) is a promising technique used in many applications, like smart terminals, IoT equipment, etc. For WPT systems based on RF rectifying, working in very low power density situation, high-gain rectenna system is of great essential. According to the antenna theory, for the same physical size, higher gain means higher aperture efficiency, which means more power will be received by the antenna instead of being scattered. However, high-gain rectenna usually means narrow beam width and high directivity, which is contradictory to a power harvesting system that need to have wide spatial coverage. In order to realize high aperture efficiency and wide spatial coverage at the same time, a two-dimensional (2-D) multibeam rectenna based on gain enhanced patches and hybrid coupler is proposed, which can improve the 2-D spatial coverage and achieve the maximum 81.5% power receiving efficiency. Simulation and experimental results indicate that the power receiving efficiency is more than 50% with 100° coverage in main beam cutting plane, 70° in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> -plane, and 90° in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> -plane. The practicality of this letter is fully verified, which can help to provide a guidance for the design of rectenna.

Integrated Module Antenna for Automotive UWB Application

In this paper, an integrated module antenna for automotive UWB application is proposed. The target applications of the proposed antenna are for UWB localization and rear passenger detection. The purpose of this work is to design an antenna with a wide and narrow beamwidth that can be attached to the exterior/interior of a vehicle for simultaneous UWB localization and a rear passenger detection sensor with a single-module substrate in a limited space. For UWB localization, the wide beam coverage is required so the antenna receives the signal from any incident angle in horizontal plane. Meanwhile, the rear passenger detection sensor requires a relatively narrower beamwidth than the localization antenna for accurate detection within the vehicle. To integrate two different antennas into a single compact module substrate, modified ground stubs and parasitic radiators are applied. The size of the entire antenna structure is 35 mm × 65 mm × 1.156 mm. The proposed antenna designed on the multi-layered FR-4 substrate with a dielectric constant of 4.3. The bandwidth of the monopole is 6.14~8.24 GHz, and the patch array is 6.95~8.47 GHz. The isolation between the monopole and the patch array is less than −23 dBi in the target band. The performance of the proposed antenna is verified with simulation and measurement. In addition, a simulation of the proposed antenna with the real vehicle model is also conducted to verify the feasibility on actual vehicle. Based on this work, the proposed antenna can be applied to multi-function antenna for automotive application with low cost.

Design of Sparse Uniform Linear Array Beamformer using Modified FRM Structure for Varied Applications

This paper presents a method to generate antenna patterns for a Uniform Linear Array (ULA) having narrow beamwidth and low sidelobe levels (SLL) using the recently proposed Modified FRM (ModFRM) architecture. This allows it to direct the beams to specific ground cells for communications while mitigating inter-cell interference. The sharpness of the beam pattern defines the spatial discriminating performance of a ULA beamformer, while the SLL dictates the interference and noise suppression capabilities. Typically, a conventional ULA beamforming will demand high computational complexity and a large number of sensors to satisfy these requirements. Hence to reduce the system cost, using the ModFRM technique a sparse array is developed. With this strategy, the total number of sensors is drastically reduced compared to conventional ULA beamformers. The designed beamformers can be used in applications with stringent requirements where cost and size are concerned.

Effective half-wavelength pitch optical phased array design for aliasing-free 2D beam steering.

We present a method to design an optical phased array (OPA) simultaneously realizing both narrow beam width and aliasing-free 2D beam steering without the need to arrange the antennas at actual half-wavelength pitch. The method realizes an effective half-wavelength pitch in one direction formed by location projection of the antennas. The distances between the antennas in the other direction can be sufficiently large to form an effective large aperture realizing narrow beam width without needing a long grating. The presented method is proven by both theory and numerical simulations to achieve an equivalent grating-lobe-free far field of an ordinary half-wavelength pitch design. One design example exhibits 180° steering with a minimal beam width of 0.4°*0.032° and a sidelobe suppression ratio of >13d B.

A hemispherical near‐field focusing antenna for non‐metallic delamination detection

This paper proposes a novel hemispherical near-field focusing radial line slot array (RLSA) antenna to detect delamination within non-metallic composites. By adjusting the positions and dimensions of the antenna slots, the near-field focusing antenna produced a radiation pattern with a narrow beamwidth and a low side lobe level of the normal component of the electric field. Since the electromagnetic (EM) field of the near-field focusing antenna can be focused on the material under test (MUT), delamination within it will significantly affect the reflected information of the antenna. Simulation and measurement have shown the good focusing characteristics of the novel RLSA antenna, a low side lobe level (−19 dB) and a narrow beamwidth (6 mm) were attained. Taking glass fiber reinforced polymer (GFRP) sheets as MUTs, delamination with different thicknesses are detected using a set of mechanical scanning experimental devices. The results show that delamination as thin as 30 μm can be detected. The proposed near-field focusing antenna can detect thinner delamination inside non-metallic composites at a lower cost and in a simpler way than other microwave non-destructive testing (NDT) methods.

Frequency reconfigurable dielectric lens antenna with graphene nano-antenna feed for THz applications

This paper proposes a frequency reconfigurable dielectric lens antenna (DLA) to compensate high attenuation due to atmospheric losses in the THz region. An aperture coupled graphene plasmonic nanoantenna has been designed and used to feed DLA. Frequency tuning has been introduced by varying the chemical potential of graphene. A lumped elements equivalent circuit for graphene-based feed antenna has also been proposed. The values of the lumped elements are obtained using the vector fitting algorithm. The proposed DLA has high gain, narrow beamwidth, broadside radiation pattern and stable input impedance. Directivity achieved through simulation is up to 7.3 dBi with radiation efficiency of 70 % and 21.2 dBi with radiation efficiency of 65 % for feed antenna and DLA respectively. The performance of DLA has also been studied as the function of feed element, relative permittivity of lens material, radius of lens and off-axis displacement tolerances.

Synthesizing of concentric circular antenna arrays by using a combination of ant lion optimizer and sequential quadratic programming

AbstractAntenna array synthesis is quite a popular topic in electromagnetics and finding suitable array parameter values is a challenging nonlinear engineering problem in this field. In recent years, it has been realized that optimization algorithms can be used to achieve desired solutions in this area. Besides, improvements in the optimization algorithms make it possible to perform synthesis processes on different array structures and to obtain better results. In this paper, a method based on a combination of ant lion optimizer (ALO) and sequential quadratic programming (SQP) is proposed for the concentric circular antenna array (CCAA) synthesis. Excitation amplitudes of array elements are optimized for CCAAs with low maximum sidelobe level (MSL), narrow first null beamwidth (FNBW), and low dynamic range ratio (DRR). The results of proposed ALO‐SQP method are compared with those of 11 different algorithms: ALO, moth flame optimizer (MFO), SQP, symbiotic organisms search (SOS), biogeography based optimization (BBO), opposition‐based gravitational search algorithm (OGSA), cat swarm optimization (CSO), firefly algorithm (FA), evolutionary programming (EP), backtracking search optimization algorithm (BSA), and seeker optimization algorithm (SOA). The comparisons indicate that the CCAAs synthesis using the proposed method presents good MSLs, FNBWs, and DRRs.

Auxiliary antenna design for anti‐interference of satellite communication earth station

AbstractIn this study, a novel elliptical widebeam auxiliary antenna is proposed for anti‐interference of satellite communication earth station. The wide beam width of about 180° in horizontal plane (H‐plane) is achieved by increasing the width of the substrate, reducing the size of the ground plane and adding a V‐shaped aluminum frame. And the narrow beam width of about 30° in elevational plane (E‐plane) is achieved by designing a binary element array. Only two auxiliary antennas are needed for sampling to cover interference from any azimuth direction in H‐plane. The antenna is fabricated and measured, and the results are in good agreement with simulation. The corresponding −10 dB impedance bandwidth is about 17% with maximum gain of 6.5 dBi. The 3 dB beam widths are respectively 33° and 178° in E‐plane and H‐plane. Furthermore, simulation and experiment of the proposed auxiliary antenna in interference cancelation system verify its anti‐interference performance. According to sidelobe canceler, an average interference cancelation ratio of about 27 dB is achieved.

Design of a Planar Antenna Array with Wide Bandwidth and Narrow Beamwidth for IR-UWB Radar Applications

This paper presents the design of an H-band planar antenna array with broad bandwidth and narrow beam width for an IR-UWB radar application. The basic single wideband microstrip antenna is achieved by adding slots and the inset-fed technique. Then, we proposed a planar antenna array on a limited area that obtains an essential narrow beamwidth for the radar of a Non-Contact Human Vital Signs Detection application. The experimental and simulated results of the microstrip antenna array are in good agreement. The measured results show that the proposed antenna array exhibits a wide impedance bandwidth of 10.7% at around 7.5 GHz and a narrow beamwidth of 40 degrees vertically and 50 degrees horizontally, respectively.

Implementation of continuously steerable beam patterns for a uniform circular projector array.

A continuously steerable super-cardioid beam pattern (SCBP) has advantages such as controllable direction, narrower beam width, and higher gain. It is generally implemented with a uniform circular array (UCA). Here, an implementation method of continuously steerable SCBPs is proposed for a projector array. The synthesis and the implementation of the continuously steerable SCBP are studied and analyzed based on a UCA model composed of omnidirectional sources. An improved version of the common method is proposed. It requires fewer array elements and the massive power amplifiers matched to each array element, which reduces the cost and the installation space. Subsequently, a continuously steerable SCBP is implemented with a uniform circular projector array (UCPA). This system is composed of single-sided radiation flextensional transducers and is studied and analyzed with a finite element method, which verified that the proposed method is suitable for the underwater acoustic projector array. Finally, UCPA prototypes were fabricated. The tests demonstrated that the proposed implementation method is a flexible way for the application of the continuously steerable SCBP in the low-frequency emission field.

Sidelobe level suppression for elliptical antenna arrays using modified SALP swarm algorithm

Abstract In this study, a modified version of salp swarm algorithm (MSSA) is used to synthesize elliptical antenna arrays (EAAs). The original salp swarm algorithm (SSA) is an optimization algorithm inspired by the behavior of salps in nature, which is used to solve engineering problems. The main purpose of the synthesis in this study is to obtain an EAA pattern with low maximum sidelobe levels (MSLs) for a fixed narrow first null beamwidth (FNBW). For different examples, the amplitude and angular position values of the antenna array elements are considered as optimization parameters. To show the effectiveness of the MSSA, eight examples of EAAs with 8, 12, and 20 elements are given. The results obtained with MSSA are compared with those of the antlion optimization, symbiotic organizations search, flower pollination algorithm, and accelerated particle swarm optimization from the literature. It is clear from the numerical results that MSSA outperforms the other algorithms in terms of the suppression of MSL.

Two-dimensional single-lobe Si photonic optical phased array with minimal antennas using a non-uniform large spacing array design.

We report a two-dimensional Si photonic optical phased array (OPA) optimized for a large optical aperture with a minimal number of antennas while maintaining single-lobe far field. The OPA chip has an optical aperture of ∼200µm by 150 µm comprising a 9×9 antenna array. The two-dimensional spacings between these antennas are much larger than the wavelength and are highly non-uniform optimized by the genetic deep learning algorithm. The phase of each antenna is independently tunable by a thermo-optical phase shifter. The experimental results validate the design and exhibit a 0.39∘×0.41∘ beamwidth within the 3 dB steering range of 14∘×11∘ limited by the numerical aperture of the far-field camera system. The method can be easily extended to a larger aperture for narrower beamwidth and wider steering range.

Accelerated Deconvolved Imaging Algorithm for 2D Multibeam Synthetic Aperture Sonar.

High-accuracy level underwater acoustical surveying plays an important role in ocean engineering applications, such as subaqueous tunnel construction, oil and gas exploration, and resources prospecting. This novel imaging method is eager to break through the existing theory to achieve a higher accuracy level of surveying. Multibeam Synthetic Aperture Sonar (MBSAS) is a kind of underwater acoustical imaging theory that can achieve 3D high-resolution detecting and overcome the disadvantages of traditional imaging methods, such as Multibeam Echo Sounder (MBES) and Synthetic Aperture Sonar (SAS). However, the resolution in the across-track direction inevitably decreases with increasing range, limited by the beamwidth of the transducer array of MBES. Furthermore, the sidelobe problem is also a significant interference of imaging sonar that introduces image noise and false peaks, which reduces the accuracy of the underwater images. Therefore, we proposed an accelerated deconvolved MBSAS beamforming method that introduces exponential acceleration and vector extrapolation to improve the convergence velocity of the classical Richardson-Lucy (R-L) iteration. The method proposed achieves a narrow beamwidth with a high sidelobe ratio in a few iterations. It can be applied to actual engineering applications, which breaks through the limitation of the actual transducer array scale. Simulations, tank, and field experiments also demonstrate the feasibility and advantages of the method proposed. 3D high-accuracy level underwater acoustical surveying can be achieved through this 2D MBES transducer array system, which can be widely promoted in the field of underwater acoustical remote sensing.