Antenna Array Configuration Research Articles

Towards Practical Antenna Selection Based on Multilabel CNN for Large‐Scale MIMO System in an Indoor Scenario

ABSTRACTLarge‐scale multiple input multiple output (MIMO), also known as massive MIMO, serves as a transformative technology that effectively addresses the surging need for data‐intensive applications in the realm of 5G mobile networks and beyond. With a multitude of antennas at its disposal, a large‐scale MIMO base station possesses the capability to concurrently improve by orders of magnitude system spectral and energy efficiencies. Nevertheless, hardware cost and power consumption arise as serious challenge. To circumvent this latter, we investigate the potential of multilabel convolutional neural network (ML‐CNN) to develop an antenna selection (AS) model that based on the available channel state information (CSI) at the transmitter, it dynamically selects the optimal subset of antennas in real‐time. We evaluate the model performance using real indoor channel measurements under three different antenna array configurations. The obtained results demonstrate that the proposed ML‐CNN approach performs similarly to the convex relaxation‐based method, a mathematical technique often used for AS problems that provides optimal solutions with high computation cost, with the advantage of significantly reduced computation time. Moreover, it exhibits strong resilience across various antenna array configurations. Additionally, assessing the ML‐CNN's performance in scenario with imperfect channel estimation confirms its robustness.

Innovative K-band slot antenna array for radar applications

This article introduces a novel microstrip slot antenna array (SAA) configuration for radar applications. The proposed antenna is specifically designed for operation in the K-band, spanning from 23 to 24.3 GHz. The antenna structure comprises two substrates: the feed network and ground plane are on the bottom substrate, and the radiating slots are on the top layer of the first substrate. The incorporation of a unique grid feed configuration, featuring 50 Ohm center excitation for the first time, improves the feed mechanism of the microstrip SAA. This innovation contributes to achieving a compact size and high gain. To enhance the side lobe level, the design incorporates a substrate-integrated waveguide-backed cavity, which significantly reduces surface waves. The SAA consists of 25 radiating elements with a gain of 14 dBi. In the elevation and azimuth planes, the half-power beamwidths are measured at 12.1° and 69.1°, respectively. The proposed antenna array’s measured impedance bandwidth ranges from 23.15 to 24.75 GHz, guaranteeing a reflection coefficient (S11) of less than − 10 dB. The suggested antenna's applicability for automotive multi-input multi-output radar has been validated.

High isolation MIMO antenna array for multiband terahertz applications

The advancement of future technology seeks to create wireless systems capable of achieving faster data transfer rates. One solution to confront this challenge is by employing Multiple-Input Multiple-Output (MIMO) systems. Nonetheless, the primary obstacle in assessing MIMO performance revolves around the size and spacing of the antennas to maintain isolation among the ports. Consequently, it is essential to devise an approach to tackle these challenges, with the utilization of a DGS as a viable and promising approach. Hence, in this study, we developed a dual-frequency MIMO system featuring two linear array antennas with two elements each and configured to function at 128 GHz and 178 GHz. Initially, this design is conceived as a single-element structure before evolving into a two-element MIMO antenna array configuration. The antenna's physical dimensions are 2.7 × 3.65 × 0.15 mm3, and it consists of two linear array nodes positioned at a separation distance of 0.18 mm. Additionally, the antenna delivers peak gains of 5.16 dB and 6.24 dB at frequencies of 128 GHz and 178 GHz, respectively. The values of various MIMO performance indicators meet stringent standards with ECC values below 0.012 and a DG of approximately 10 dB. Furthermore, the TARC remains below 0 dB. The aim of this research is to create a novel design for a THz antenna that can achieve a wide bandwidth and a high gain while maintaining the standard compact antenna size necessary for THz applications.

Detection of breast tumor with a frequency selective surface loaded ultra-wide band antenna system

Breast tumors are a significant cause to the global death rate among women. However, the fatality rate can be lowered through early detection. This paper presents an ultra-wideband, modified patch antenna of a compact size that can be used for microwave-sensing biomedical applications in the detection of breast cancer. A partial ground plane and slots are implemented in a transformed patch antenna to enhance the impedance bandwidth. The antenna is backed by a uniform frequency selective surface of 5 × 5 unit cells to achieve the necessary antenna characteristics, specifically directivity and gain, for microwave detection applications. Through optimization and fabrication, the final design maintained (|S11|< −10 dB) over the entire frequency band of 11.6 GHz (3.1–14.7 GHz) and achieved an average gain of over 5 dBi. Other metrics, such as group delay and the fidelity factor in different setups, are also simulated to observe the expected performance in the required frequency range. Finally, based on simulation, a model is suggested that comprises various configurations of antenna arrays, including one Tx antenna and one to seven Rx antennas. Further, breast phantom with different tumor sizes and locations were used in the simulation. The simulation results successfully validated the detection of breast cancer cells. We believe these technologies can open possibilities in healthcare applications for identifying tumors.

High-resolution 2D-DoA sequential algorithm of azimuth and elevation estimation in automotive distributed system of coherent MIMO radars

Objectives. One of the main tasks of radiolocation involves the problem of increasing spatial resolution of the targets in the case of limited aperture of the radar antenna array and short length of time samples (snapshots). Algorithms must be developed to provide high angular resolution and low computational complexity. In order to conform with the existing Advanced Driver Assistance Systems requirements, modern cars are equipped with more than one radar having a common signal processing scheme to improve performance during target detection, positioning, and recognition as compared to a single radar. The present study aims to develop a two-dimensional Direction-of-Arrival algorithm with low computation complexity as part of distributed coherent automotive radar system for cases involving short time samples (snapshots).Methods. A virtual antenna array formation algorithm is formulated according to the two-dimensional Capon method. A proposed modification of two-dimensional Capon algorithm is based on sequentially estimating the directions of arrival for the distributed radar system. The Monte Carlo method is used to compare the effectiveness of the considered algorithms.Results. The 2D-DoA sequential algorithm of azimuth and elevation estimation is proposed. The comparative analysis results for the developed algorithm and classical 2D Capon method based on numerical simulation using Monte Carlo method are presented. The proposed scheme of DoA estimation for coherent signal processing of distributed radars is shown to lead to an improvement of the main considered metrics representing the probability of correctly estimating the number of targets, mean square error, and square error compared to a single radar system. The proposed low-computational algorithm shows the gain in complexity compared to full 2D Capon algorithm.Conclusions. The proposed two-stage algorithm for estimating the directions of arrival of signals in azimuth and elevation planes can be applied to the distributed system of coherent radars with several receiving and transmitting antennas representing multiple input multiple output (MIMO) radars. The algorithm is based on sequentially estimating the directions of arrival, implying estimation in the azimuthal plane at the first stage and estimation in the vertical plane at the second stage. The performance of a coherent radar system with limited antenna array configuration of separate radar is close in characteristics to a high-performance 4D-radar with a large antenna array system.

3D Antenna array for multi-user massive MIMO system to minimize unfavorable propagation

Unfavorable propagation in massive multiple input multiple output (MIMO) systems is an underlying channel condition that reduces the gains offered by the system in terms of parallel channels. This paper presents a study on different types of antenna array configurations at base station (BS) to minimize unfavorable propagation conditions. Unfavorable propagation results in increased correlation between channel vectors of two or more mobile terminals (MTs) which arises when the signals from two or more MTs have small angular separation and small angular spread. The study starts with the investigation of the conventional uniform linear array (ULA) under different propagation conditions using a geometrical channel model based on a single cluster of scatterers per MT to quantify the performance degradation in unfavorable propagation. Subsequently, the performance of other types of array geometries is investigated. A custom cluster-based geometrical channel model is used in this study which includes practical propagation aspects like multipath fading, shadow fading, and the effect of BS height. Further, the study considers two cases: micro-cell and macro-cell. Under space constraint settings in terms of the maximum dimension of the array, the proposed technique uses randomized antenna locations in the array to minimize the effect of unfavorable propagation. Based on the results on performance parameters like user correlation and capacity, the study reveals that an antenna array configuration comprising of elements distributed random-homogeneously in a spherical shell outperforms other configurations.

Extended Kalman Filter-Based Vehicle Tracking Using Uniform Planar Array for Vehicle Platoon Systems.

We develop an extended Kalman filter-based vehicle tracking algorithm, specifically designed for uniform planar array layouts and vehicle platoon scenarios. We first propose an antenna placement strategy to design the optimal antenna array configuration for precise vehicle tracking in vehicle-to-infrastructure networks. Furthermore, a vehicle tracking algorithm is proposed to improve the position estimation performance by specifically considering the characteristics of the state evolution model for vehicles in the platoon. The proposed algorithm enables the sharing of corrected error transition vectors among platoon vehicles, for the purpose of enhancing the tracking performance for vehicles in unfavorable positions. Lastly, we propose an array partitioning algorithm that effectively divides the entire antenna array into sub-arrays for vehicles in the platoon, aiming to maximize the average tracking performance. Numerical studies verify that the proposed tracking and array partitioning algorithms improve the position estimation performance.

Design method of a focusing dielectric lens antenna and temperature increment measurement at the focusing spot

In radio wave hyperthermia therapy, array antenna configuration was mainly studied to generate a small spot at the diseased part. Array antennas have the flexibility in controlling radiation performance, such as spot positions, by using their numerous radiating elements. However, the flexibility is achieved at the expense of antenna structure complexity. On the other hand, a lens antenna can concentrate radio waves into a small spot by forming a lens shape. The simplicity of a lens antenna structure lends itself to easy handling in a practical application. Moreover, the frequency independence of the lens antenna allows for a more flexible selection of hyperthermia therapy frequencies. Therefore, the lens antenna is selected as a focusing antenna in this paper. The lens shaping method and the temperature increment measurement are the main contents of this paper. The designed lens has a diameter of 30 cm, a focusing distance of 30 cm, and a working frequency of 2.45 GHz. A thin lens design method is applied to reduce lens weight. Firstly, the focusing ability of the designed lens is ensured by comparing the spot size results of electromagnetic (EM) simulation with its theoretical value. A spot size of 1.77 cm is obtained in both cases. Next, the temperature increment is examined by EM simulations. The temperature at the 2 cm tumor was increased to 41 °C from the human body temperature of 37 °C by an input power of 10 Watts (W). For the temperature increment measurement, a tumor within human body phantom is utilized and the available input power is reduced to 4 W. The tumor temperature increased from 21.5 °C of room temperature to 24.4 °C, which was captured by a thermal imaging camera. As a result, the functionality of the lens antenna for hyperthermia therapy is verified.

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

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

Study of the accuracy characteristics of a GNSS receiver with an antenna array

The article presents the results of experimental studies of the accuracy of measuring navigation parameters by a receiver of global navigation satellite systems (GNSS receiver) equipped with an antenna array. The use of ring antenna arrays in GNSS receivers is substantiated. The main advantage of such antenna arrays is their invariance to the direction of the main lobe of the radiation pattern in the azimuthal plane. However, ring antenna arrays have some disadvantages. The use of the minimum required number of radiators in such antenna arrays to form a beam of a given width leads to a simultaneous increase in the level of side lobes. However, when using ring antenna arrays in GNSS receivers, this drawback can be neglected, since the level of side lobes significantly affects the quality of navigation signal reception only with powerful signal re- reflections. The structure of the hardware- software complex for research is given and the principle of its operation is described. Its main parts are a 24-channel beam- forming GNSS receiver and an 8-element ring antenna array. The software and hardware complex allows the study of various configurations of antenna arrays – two, four and eight elements. The technique of carrying out the experiment is given. A eature of the technique is the use of differences in measured pseudoranges using a single antenna and various configurations of antenna arrays. The results of measurements of code and phase pseudorange are presented.

RAU-Net-Based Imaging Method for Spatial-Variant Correction and Denoising in Multiple-Input Multiple-Output Radar

The conventional back projection (BP) algorithm is an accurate time-domain algorithm widely used for multiple-input multiple-output (MIMO) radar imaging, owing to its independence of antenna array configuration. The time-delay curve correction back projection (TCC-BP) algorithm greatly reduces the computational complexity of BP but suffers from spatial-variant correction, sidelobe interference and background noise due to the use of coherent superposition of echo time-delay curves. In this article, a residual attention U-Net-based (RAU-Net) MIMO radar imaging method that adapts complex noisy scenarios with spatial variation and sidelobe interference is proposed. On the basis of the U-Net underlying structure, we develop the RAU-Net with two modules: a residual unit with identity mapping and a dual attention module to obtain resolution spatial-variant correction and denoising on real-world MIMO radar images. The network realizes MIMO radar imaging based on the TCC-BP algorithm and substantially reduces the total computational time of the BP algorithm on the basis of improving the imaging resolution and denoising capability. Extensive experiments on the simulated and measured data demonstrate that the proposed method outperforms both the traditional methods and learning-imaging methods in terms of spatial-variant correction, denoising and computational complexity.

An Improved Performance Radar Sensor for K-Band Automotive Radars.

This paper presents a new radar sensor configuration of a planar grid antenna array (PGAA) for automotive ultra-wideband (UWB) radar applications. For system realisation, the MIMO concept is adopted. The proposed antenna is designed to operate over the 24 GHz frequency band. It is based on split-ring resonator (SRR) elements to enhance the operating bandwidth and increase the antenna gain, leading to a better-performing radar system. The PGAA consists of thirty-one radiating elements, in which each element excitation is obtained using a common transmission line centre fed by a 50 Ω coaxial probe. By introducing a superstrate dielectric layer at a distance of λ/2 from the top of the antenna array, the PGAA gain and impedance bandwidth are further improved. The gain is improved by 2.7 dB to reach 16.5 dBi at 24 GHz, and the impedance bandwidth is enhanced to 9.3 GHz (37.7%). The measured impedance bandwidth of the proposed antenna array ranges from 20 GHz to 29.3 GHz for a reflection coefficient (S11) of less than -10 dB. The proposed antenna is validated for automotive applications.

Measurements and Characteristics Analysis of 6G Ultra-Massive MIMO Wireless Channels With Different Antenna Configurations and Scenarios

In this paper, ultra-massive multiple-input multiple-output (MIMO) channel measurements at 5.3 GHz are conducted, including different antenna array configurations and different measurement scenarios. The antenna array configurations include uniform linear array (ULA) and distributed uniform linear array (DULA). The measurement scenarios include single-user fixed-to-fixed (F2F), multi-user F2F, and single-user fixed-to-mobile (F2M) measurement scenarios. The statistical properties of ultra-massive MIMO channels are studied, including delay power spectral density (DPSD), space cross-correlation function (SCCF), angle cross-correlation function (ACCF), frequency correlation function (FCF), root mean square (RMS) delay spread (DS), RMS angle spread (AS), singular value spread (SVS), scalar product (SP), level crossing rate (LCR), average fading duration (AFD), Doppler power spectral density (PSD), etc. The specific ultra-massive MIMO channel characteristics are investigated and validated by channel measurements, including spatial non-stationarity, spherical wavefront behavior, channel hardening, and sparse properties in the angle domain. In addition, channel capacities are investigated. The channel measurement results will be a great importance for ultra-massive MIMO communication system deployments.

Generations of Multiple Orbital Angular Momentum Modes by 2-D Fisheye-Lens-Based Beamformer Excited Antenna Arrays in a Spiral Configuration

This paper presents the generations of multiple orbital angular momentum (OAM) modes in a spiral antenna array configuration. The feeds to the antenna elements are produced from a Fisheye-lens-based beamforming circuit (FL-BFC), where relatively linear phase variations of different slopes are generated. By selecting proper slope values, the feeding to planar circular arrays results in orthogonal OAM modes. Besides, selecting proper output port positions on the circumference of the FL-BFN may produce phases to excite the antenna array in various configurations to reduce the nulling regions of radiation by different OAM modes. This paper presents the characteristics of FL-BFC in its implementation to excite a planar array of antennas for OAM mode radiations. The orthogonality characteristics are quantized using an envelope correlation coefficient (ECC) for accounting for the mutual interaction. An orthogonalization procedure is also examined to obtain the orthogonal OAM modes. The radiation characteristics are compared to demonstrate the feasibility. Both full-wave simulation and measurement results are shown to validate the design concept.

Design and Simulation of Microstrip Antenna Array Operating at S-band for Wireless Communication System

In this article, different design configurations of rectangular microstrip patch antenna (RMSA) array operating at S-band frequency are presented. The substrate material utilized in the designs is Rogers-RT-5800 with dielectric permittivity (Ԑr= 2.2), thickness of (h=1.6 mm), and loss tangent of (δ = 0.009). The performances of a single element, (1×2), (2×2) and (1×4) array elements operating at (3.6 GHz) are investigated using the CST and HFSS numerical techniques. The simulation results indicates that the antenna gain of (8.68, 10.35, 10.43 and 10.52) dB, VSWR (1.045, 1.325, 1.095 and 1.945), return loss (-34.91, -17.15, -27.42 and -12.26) dB, and bandwidth (85.00, 200.00, 215 and 106.4) MHz are achieved with the implementation of HFSS for advanced single element, (1×2), (2×2) and (1×4) array elements, respectively. Besides, the corresponding antenna parameter values provided by CST are, gain (7.36, 9.8, 9.87 and 10.30) dB, VSWR (1.011, 1.304, 1.305 and 1.579), return loss (-44.97, -17.58, -17.55 and -14.01) dB, and bandwidth (92.28, 204, 229.49 and 129.12) MHz, respectively. The results also reveals that the higher gain and wider bandwidth are, respectively, achieved with (1×4) and (2×2) array configuration arrangement and with both simulation techniques. Additionally, a good agreement and an advancement between the obtained results with the ones previously studied for the same array types operating at S-band frequencies are also observed.

Low-cost thin film patch antennas and antenna arrays with various background wall materials for indoor wireless communications

The present study introduces an inkjet-printed flexible coplanar waveguide patch antenna array concept. Single antenna and four-element antenna arrays were characterized, which were attached to a subminiature version A connector via an innovative solderless, 3D-printed ‘plug-and-play-type’ tightener. Furthermore, indoor wireless communication and Internet of Things scenarios with commonly used wall materials including gypsum and plywood boards, on which patch antennas and antenna arrays can be attached, were also presented. In order to validate the concept, design and fabrication iterations in parallel with numerical and experimental investigations were executed. To elaborate, single antenna and antenna array configurations without and with wall materials were characterized to see their functionality at 2.4 GHz resonance frequency and beyond 300 MHz bandwidth, respectively. The results demonstrate that the investigated configurations fulfill short-range radio transmission and can be utilized, e.g., for indoor backscattering-type communications and wireless sensing applications, as an affordable and versatile alternative to their conventional counterparts. Being attached to their corresponding background materials, single-antenna specimens were measured to have return losses beyond 18 dB and peak gains around 1 dBi, while higher peak gains above 6 dBi were detected for antenna arrays. Moreover, the antenna arrays can enable multiple-input and multiple-output communication. The proposed arrays had diversity performance in terms of return losses higher than 15 dB, isolation of more than 20 dB, envelope correlation coefficient , diversity gain dB, mean effective gain dB, power ratio factor dB, and channel capacity loss bits/s/Hz.

Towards a full design of a super-wide band slotted antenna array using graphene material for future 6G applications

Sixth-generation (6G) wireless communication systems have been developed in response to the growing demand for higher data rates and ultra-high-speed communication. It is expected to emerge around the year 2030. In order to fulfill this need, the 6G wireless communication system will exploit the terahertz (THz) frequency spectrum (0.1–10 THz). In the same framework, the current study seeks to design and analyze various antenna and antenna array configurations across the whole THz range. Initially, by integrating graphene material into various patch and feedline combinations for a single antenna. The return loss, VSWR (Voltage Standing Wave Ratio), gain, and directivity of the antenna were the four key features that were analyzed. Furthermore, a parametric investigation of substrate thicknesses was carried out for three distinct materials: Rogers RT5880, silicon, and polymide. In order to increase the directivity and gain of the optimized graphene antenna, we used five different antenna array architectures (1*2, 1*4, 2*2, 2*4, and 4*2) in both serial and parallel configurations. Finally, a further enhancement of the structure—a sixteen-antenna array (2*8 array)—was implemented by doubling the arrays' structural dimensions to meet the requirements of the sixth generation of telecommunication systems in terms of gain and directivity.

Impact of antenna directivity on compressed sensing-based DOA estimation employing UCA antenna

This letter investigates the impact of the antenna element directivity on compressed sensing (CS)-based direction of arrival (DOA) estimation employing the uniform circular array (UCA) antenna. In the CS-based approach, the reconstruction accuracy of sparse signals is determined by a sensing matrix, which depends on the array antenna configuration in the DOA estimation. In our study, we analyze the cross-correlation between column vectors of the sensing matrix and clarify the estimation accuracy for various antenna element radiation patterns.

Sequential Rotation of Antenna Array Elements – Rotation Angle for Optimum Array Polarization

Abstract. The principle of sequential rotation, a well-known method to arrange the radiating elements of antenna arrays, is briefly described, and the impact on the polarization of different antenna array configurations is presented. The influence of the number of rotations and rotation angles is investigated, and arrangements for optimized polarization quality of antenna arrays are shown, which are of significant importance for current and future communications systems.

Classification of flying object based on radar data using hybrid Convolutional Neural Network-Memetic Algorithm

In the last decade, the low cost and easy availability of Unmanned Aerial Vehicles (UAVs) have led to their enormous use in modern society, which leads to privacy and security issues. To keep an eye on the intruder UAV in the restricted area, it needs to classify the other flying objects, such as helicopters, birds, etc. Hence, this work is taken up by considering the Micro-Doppler Signature (MDS) of the flying objects from the different configurations of radar antenna array such as Uniform Linear Array (ULA) and Uniform Rectangular Array (URA). In order to obtain the MDS from the intruder UAV, proper positioning or configuration of the radar antenna array is needed to avoid performance degradation due to the large Angle of Arrival (AoA) of the received signal. A novel Hybrid Convolutional Neural Network-Memetic algorithm is proposed to classify the flying object, which is evaluated for both MDS data collected from the HB100 radar set-up by varying configurations and Real Doppler RAD-DAR (RDRD) existing dataset.