Array Beamforming Research Articles

Effect of Target Motion on Equivalent Transmit Beamforming for the Frequency Diverse Array

Conventional antenna-array beamforming along a selected direction cannot discriminate between different far-field subranges. To select a particular subrange in the far-field, a distance-specific multi-antenna transmission architecture known as the frequency diverse array along with a matching receiver architecture known as equivalent transmit beamforming (ETB) has been recently proposed. However, these breakthroughs have not explicitly addressed the effects of target motion, which is ubiquitous in radar applications. These effects are analyzed in this paper, leading to the conception of a range-direction-Doppler version of the “direction cosine” which is used to develop analytical formulas for the ETB beampattern characteristics in terms of the ETB system parameters along with insights for system design.

Redundancy-Reduced Sparsity-Based Adaptive Beamforming for Polarization-Sensitive Arrays

Redundancy-Reduced Sparsity-Based Adaptive Beamforming for Polarization-Sensitive Arrays

Sound power estimation method based on dual arrays sound intensity scaling and sound pressure superposition

The sound intensity scaling method can be used to calculate the source sound power from the array beamforming results. The distance between the sound source and the array and the environmental noise during the test process will affect the accuracy of the sound source intensity measurement. A sound power level solution method for sound intensity scaling suitable for complex environments is verified in this paper. The depth of the sound source is determined by dual arrays. The sound wave propagation and superposition characteristics are used to establish an optimized objective function, to optimize the strength of the target sound source and remove the noise components. Finally, the sound power level of the sound sources after noise reductions are calculated by the sound intensity scaling method. In the semi-anechoic room, white noise signal and impact signal are used as interference noise in the experiments. The results show that this method can effectively reduce the noise of the signal in the noisy environment and improve the calculation accuracy of the sound power level of the sound source. The error of the sound power level calculation results under the influence of white noise and impact noise has been greatly reduced after optimization. The calculation error of sound power level decreased from 3.2 dB–12.2 dB to 0.2 dB–5dB.

Near-Field Calibration Methods for Integrated Analog Beamforming Arrays and Focal Plane Array Feeds

Near-Field Calibration Methods for Integrated Analog Beamforming Arrays and Focal Plane Array Feeds

Efficient Initialization for the Adaptive LMS Beamforming Algorithm

In spite of the great progress in research work related to the smart antenna field, obtaining an efficient beamforming technique with low complexity, fast converge, and better other performance remains the preferred objective of most researchers. The present work proposes a new version of least mean square (LMS) approach for the beamforming of smart antenna array. The novelty of the proposed algorithm versus its basic version is focalized in its dependence on a new initialization technique, whose aim is to accelerate convergence speed and maintain, at the same time, the algorithm simplicity. The central idea of the proposed technique, which is named new initialized LMS (NI-LMS), is to compute an initial weight vector using only a diagonal matrix extracted from the spatial auto-covariance matrix. Simulation examples are carried out on linear antenna array to demonstrate and validate the effectiveness of the new method. In addition, the computational complexity of the new proposition is analyzed and compared to that of the conventional LMS beamforming approach.

Covert mmWave Communication When the Warden Locates in the Beam Direction

In this letter, the beamforming scheme based on random frequency diverse array (RFDA) is newly investigated to enhance the performance of covert mmWave communications. First, the closed-form expressions of covertness constraint are derived for the RFDA and the conventional phase array (PA) beamforming schemes, respectively. Then, the optimal transmit power and blocklength maximizing the average effective covert throughput (AECT) are derived for both beamforming schemes. Considering the pessimistic scenarios that Willie locates in its desired direction as Bob (but different distances), our examination shows the enhancement of maximum AECT by adopting the RFDA beamforming scheme. Besides, in this case, the maximum AECT for the RFDA beamforming scheme can be improved while that for the PA beamforming scheme remains unchanged as the number of antennas enlarges. Furthermore, it is revealed that the superior performance of the RFDA beamforming scheme is influenced by Willie’s location, and the range of Willie in which the RFDA beamforming scheme outperforms the PA beamforming scheme is obtained.

An efficient beamformer for uniform rectangular arrays

An efficient beamformer for uniform rectangular arrays

DNN Beamforming for LEO Satellite Communication at Sub-THz Bands

The 6G communication system will be designed at sub-THz frequencies due to increasing demand in data rates, emerging new applications and advanced communication technologies. These high-performing systems will heavily rely on artificial intelligence (AI) for efficient and robust design of transceivers. In this work, we propose a deep neural network (DNN) beamformer that will replace the use of phase shifters for a massive array of antenna elements employed at the ground station for wideband LEO satellite communication at sub-THz bands. We show that the signal processing algorithm employed using DNN is capable to match the performance of a true-time delay beamformer as the angle of arrival of the received wideband signal at the ground station is changing due to rapid movement of the LEO satellite. The implementation of DNN beamformer will be able to reduce the cost of receiver and provide a way for the efficient and compact design of the massive array beamforming for wideband LEO satellite applications.

Hybrid Beamforming for Terahertz Wireless Communications with Beam Squint: A Survey

Benefiting from the ultra-wide bandwidth, terahertz (THz) communication is considered one of the core technologies of the 6G mobile communication. However, high path loss is a severe issue for THz band, which needs to be solved by the ultra-massive multiple-input multiple-output (MIMO) technology. For the sake of reducing the hardware cost and power comsumption, the hybrid beamforming technology is required, which has been adopted in the 5G communication. In the hybrid beamforming for the THz wideband system, the enormous antenna and ultra-wide bandwidth cause the spatial- and frequency-wideband effect, resulting in acute beam squint. Eliminating beam squint is the key to the engineering realization of ultra massive MIMO for the THz band. To circumvent this issue, this paper presents a comprehensive overview of the hybrid beamforming technology including the channel model, the traditional phase shifter based and the true time delay based architectures, the 3D hybrid beamforming for the uniform planar array. Finally, multiple significant open issues and potential challenges are pointed out and elaborated.

Hybrid OTA Chamber for Multidirectional Testing of Wireless Devices: Plane Wave Spectrum Generator Design and Experimental Demonstration

This article investigates practical implementation aspects of a novel hybrid chamber concept that has been recently introduced for over-the-air (OTA) testing of wireless devices. The chamber allows to synthesize a spectrum of plane waves (PWs) incident on a device under test (DUT) from a wide range of angles of arrival (AoAs) through exploiting multiple field scattering inside the overmoded waveguide (WG) chamber. An optimal design approach for the plane wave spectrum generator (PWSG) array inside the chamber is presented considering: 1) array antenna impedance matching for the desired test zone (TZ) quality and AoAs’ range; 2) an operational frequency bandwidth of the test environment and an instantaneous signal bandwidth; and 3) the impact of PWSG excitation errors. A robust linearly constrained minimum variance (LCMV) beamformer is formulated to realize the desired test environment over a wide frequency band, while accounting for the varying number of the WG propagating modes as excited by PWSG array. Numerical simulations and measurements with the first prototype of the hybrid chamber for FR1 frequency band (~3.5 GHz) are presented. This prototype includes a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${7\times 7}$ </tex-math></inline-formula> bowtie antenna element PWSG array, a 1.00 m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times1.25$ </tex-math></inline-formula> m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times1.75$ </tex-math></inline-formula> m metal WG chamber, an off-line optimal array beamforming setup, and a planar scanner for TZ characterization.

Optimal beamformer design in spherical sector harmonics domain

Beamforming using spherical microphone arrays (SMAs) with processing in spherical harmonics (SH) domain is widely being studied. This is due to the ease of array processing in SH domain with no spatial ambiguity. Despite the widespread applications of SMA in beamforming, its size makes it inconvenient for practical or commercial use. Building of SMA over a rigid sphere is also a challenging task. Additionally, use of the entire sphere comes at the cost of more microphones and signals to process. Hence, it is uneconomic to use full SMA when sources are only present in restricted regions of the environment. Attempts have been made in literature to use hemispherical microphone array for beamforming. Acoustic image principle was utilized to enable application of SH but with greater computational complexity. In this paper, the use of a spherical sector microphone array is proposed for beamforming. An orthonormal spherical sector harmonics (S2H) basis function is used for data model development. An ideal direction-invariant beampattern using S2H basis function is utilized. Subsequently, to make the beamformer robust against sensor noise with a sharp directivity pattern at the direction of arrival and zero elsewhere, a new maximum directivity and white noise gain (MD-WNG) beamformer is designed for a spherical sector microphone array. Performance analysis of the proposed beamformer is presented using various experiments on directivity pattern and array gain. The proposed method is additionally compared with several existing beamforming techniques. The comparison reveals that the S2H based beamforming provides reasonably better results compared to the existing methods.

A 4 × 4 Steerable 14-dBm EIRP Array on CMOS at 0.41 THz With a 2-D Distributed Oscillator Network

Terahertz (THz) beamforming arrays are critical to address emerging applications in wireless communication, sensing, and imaging. Enabling such architectures, particularly with respect to synchronization of distributed radiating THz sources, is very challenging due to the sensitivity of such synchronizations to variations of process, voltage, temperature (PVT), and device mismatches. In this article, we propose and demonstrate a multi-layer THz array architecture to address robust frequency synthesis, optimal harmonic THz power generation, and scalable phase generation for THz beamforming. The bottom-most layer of this multi-layer network consists of a scalable 2-D negative transconductance (−Gm) cells that collectively oscillates at the center frequency of 69.3 GHz, thereby establishing a robust frequency and phase distribution across the entire chip. By eliminating independent oscillation capability of each node and merging resonator and coupling structures into one single network, the 2-D mesh removes the possibility of moving out of synchronization due to PVT variations or device mismatches and forms the underlying frequency synthesis layer. Local frequency multiplication and radiating elements are placed across the 2-D THz array, and beamforming is enabled through varactor control in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-G_{m}$ </tex-math></inline-formula> cells. We demonstrate the proposed architecture in a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\,\times \,4$ </tex-math></inline-formula> array with effective isotropic radiation power (EIRP) of +14 dBm at 0.416 THz in a lensless setup using a 65-nm CMOS process with the beamforming capability of ±30° in both <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}$ </tex-math></inline-formula> - and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${H}$ </tex-math></inline-formula> -planes.

Semi-blind calibration for orbital angular momentum generating system using maximal likelihood estimation.

Generating a high quality vortex beam carrying orbital angular momentum (OAM) is of importance in the application of the OAM to target detections or communications. This paper presents a semi-blind method to calibrate the uniform circle array (UCA) OAM generating system by using a virtual receiving sensor array without knowing the precise position of this auxiliary array. A low computational complexity algorithm is proposed to solve the maximum likelihood estimate (MLE) for the amplitude and phase errors of the transducers of the UCA based on the separation of parameters to be estimated. Moreover, this MLE is proved to be related to the beamforming of the virtual array. Simulations indicate that this method can estimate the mismatch parameters of the UCA effectively, and experiments in an anechoic tank show that the OAM generating system can generate a desirable vortex beam after we compensate each transducer of the UCA.

IN-ME Position Error Compensation Algorithm for the Near-Field Beamforming of UAVs

The target of an unmanned aerial vehicle swarm will present near-field characteristics when it is integrated as an array, and the existence of the unmanned aerial vehicle swarm motion error will greatly deteriorate the beam pattern formed by the array. To solve these problems, a near-field array beamforming model with array element position error is constructed, and the Taylor expansion of the phase difference function is used to approximately simplify the model. The improved Newton maximum entropy algorithm is proposed to estimate and compensate for the phase errors. The maximum entropy objective function is established, and the Newton iterative algorithm is used to estimate the phase error iteratively. To select the proper Newton iteration initial value, based on a single reference source signal, the initial value of the phase error is estimated through the phase gradient information of the received array signal. Beamforming is carried out after phase error compensation regarding the array. In order to assess the mismatch of the phase error compensation function based on the proposed method, when the beam is scanning, the effectively compensated spatial area of the array beamforming is divided, which lays a foundation for subsequent spatial region division and unmanned aerial vehicle swarm path planning. The simulation results show that the beam formed by the method proposed in this paper has a lower sidelobe level, and as the signal-to-noise ratio changes, the robustness of the proposed method is better validated. The proposed algorithm can effectively suppress the adverse influence of array element position error on array beamforming, and when the beam is scanning, the effectively compensated area of the phase error compensation function is divided, based on the proposed method.

W-Band Binary Phase-Controlled Multibeam Antenna Array Based on Gap Waveguide Magic-Tee

In this article, a compact 94 GHz multibeam antenna array based on the binary phase-controlled concept is proposed. The feeding network is composed of four unconnected layers, and the ridge or groove gap waveguides are adopted as the guided wave structures. A key planar gap waveguide Magic-Tee is designed to obtain 0° and 180° phase states and then integrates with an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\,\times \,8$ </tex-math></inline-formula> slot antenna array to achieve multibeam operation for the first time. Compared with the traditional phased array and passive beamforming networks (BFNs), the feeding design is simple in construction, consisting of only Magic-Tees and cascaded power dividers without any phase shifters. Benefiting from the gap waveguide technology, the antenna array does not require electrical contact among the metal layers, so it is simple and low cost to manufacture. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times8$ </tex-math></inline-formula> slot antenna array can easily switch among one-beam and three different dual-beam states that point to ±7°, ±17°, and ±38°. The measurement results of 6.6% bandwidth from 91.7 to 98 GHz for both reflection coefficients <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&lt; -10$ </tex-math></inline-formula> dB and isolations >25 dB are achieved. The proposed multibeam antenna array would be an attractive candidate for millimeter-wave multiuser communication where it requires multiple beams simultaneously.

A Directly Connected OTA Measurement for Performance Evaluation of 5G Adaptive Beamforming Terminals

Spatially beamformed communication, which is achieved by antenna array and multiple-input and multiple-output (MIMO) technologies, has become the most critical technology to drastically increase spectrum utilization rate of 5G. To guarantee the successful deployment of 5G, different aspects of device design, particularly those related to radio-frequency front end and antenna array for enabling beamformed communication, have to be accurately verified. It is more cost effective to identify design imperfections through lab testing rather than using field testing-based trial and error approaches, especially for the explosive growth of 5G-enabled Internet of Things devices. In this article, a directly connected over-the-air (OTA) test solution for 5G MIMO OTA evaluations with the focus on dynamic beamforming devices is proposed. The proposed solution can mathematically achieve constructions among the S ports of base station (BS) and U ports of the receiving antenna array, which makes it possible for measuring the throughput of terminal with an adaptive beamforming array in an OTA way. All system parameters are emulated, including S elements BS antenna gain, U elements of receiving terminal performance, and 3-D <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S{\times }U$ </tex-math></inline-formula> propagation channel characteristics. To further validate the theoretical analysis and test procedure, a newly developed 4 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\times }$ </tex-math></inline-formula> 4 5G MIMO device is measured in terms of its throughput. The results exactly reflect the true performance of the proposed solution under realistic operational conditions.

Noise Shaping for Phased Array Beamforming

Quantization of phase and/or amplitude has far-reaching effects on the radiation characteristics of the phased array (PA), including gain, minor lobe level, and point deviation. Traditionally, one common method to address such a nonlinear distortion is using random-phasing to interrupt the error periodicity. Here, we show that the distortion due to the quantization can be better remediated by spectrally shaping the error compared to the random-phasing (dithering) approaches. We adapted the method for phase-only and amplitude-phase synthesis of planar array designed based on analog beamforming (ABF). To do that, for the first time, 2-D real- and complex-coefficient minimum-phase digital finite impulse response (FIR) filters are designed based on the discrete Hilbert transform (DHT) method. In particular, the digital filter design for phase-only synthesis is comprehensively investigated, respecting the error spectra in the beamspace domain. It is shown that by pushing the error out of the so-called visible region, the decrease of antenna directivity due to the quantization can be compensated to some extent, which provides a quite advantage over the uniform distribution of error. For some cases, pushing the error out of the visible region might be impossible. For such cases, we proposed using the spaced-notches filter. It is also shown that the method is on maximum efficacy when both phase and amplitude of the excitation signal are controllable. Thus, complex-valued noise shaping (CV-NS) can be exploited for the phase-amplitude synthesis of the PA, showing quite promising performance.

Analysis and Linearization of Frequency-Multiplier-Based RF Beamforming Transmitters Over a Wide Steering Range

This article first analyzes the nonlinear behavior of frequency-multiplier (FM)-based radio frequency (RF) beamforming transmitters TXs) over a wide range of steering angles. Then, based on this analysis, a digital predistortion (DPD) scheme is proposed to linearize FM-based TX arrays. Specifically, a dual-input behavioral model of FM-based TX arrays is derived. This dual-input model is then transformed into an angle-dependent single-input–single-output (SISO) model. Next, the effect of load modulation on FM nonlinearity is studied using a circuit-inspired behavioral model, and a very distinctive feature is revealed. Notably, it is shown that FM-based RF beamforming arrays have reduced sensitivity to load modulation when compared to last-stage power-amplifier (PA)-based arrays. This is first validated in simulation using a frequency doubler and PA terminated with load impedances extracted from an 8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 8 electromagnetically simulated array. Furthermore, experimental results are obtained using a 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 2 planar frequency-doubler-based RF beamforming TX operated at 28 GHz and driven with up to 400-MHz-wide orthogonal frequency-division multiplexing (OFDM) signals where the subcarriers are modulated using up to 256-QAM. It is experimentally demonstrated that a single set of SISO DPD coefficients can significantly improve the adjacent channel power ratio (ACPR) and error vector magnitude (EVM) over a wide steering range. Specifically, for the case of a 100-MHz signal, the ACPR and EVM improved from 20 dBc and 23% to, at worst, 48 dBc and 1%, respectively, when the array is steered from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-40^\circ $ </tex-math></inline-formula> to 40° and measured along the main beam direction. In light of the FM-based arrays reduced sensitivity to load modulation, this article also investigates different TX observation receiver (TOR) methods for DPD function training, namely, far-field-based TOR, coupler-based TOR, and single-element-based TOR, and their impacts on the linearizability of the FM-based RF beamforming TXs.

Digital Predistortion of Millimeter-Wave Arrays Using Near-Field Based Transmitter Observation Receivers

This article proposes a novel method to train the digital predistortion (DPD) function in a radio frequency (RF) beamforming array using feedback signals acquired from a near-field-based transmitter observation receiver (NF-TOR). Accordingly, the proposed DPD training method relies only on information/signals available at the transmitter side and does not require the deployment of a far-field (FF)-based TOR. The method starts by first identifying the coefficients of the propagation channels between the radiating antennas and the NF probes. These NF channel coefficients are then used to estimate the forward model of each power amplifier in the array and to train the DPD function. Proof-of-concept validation experiments were conduthis article, the complex basebandcted on a 16-element 29-GHz RF beamforming array with four embedded NF probes. When driven by 400-MHz orthogonal frequency-division multiplexing signals with subcarriers modulated using 256-QAM, the DPD trained using the NF-TOR allowed for an improvement in the adjacent channel power ratio and error vector magnitude (EVM) from &#x2212;29.66 to &#x2212;40.49 dB and 8.29&#x0025; to 2.40&#x0025;, respectively, in the main beam direction. Furthermore, the application of the NF-TOR trained DPD allowed the effective isotropic radiated power to increase from 28.3 to 33.3 dBm while maintaining an EVM below 3.5&#x0025;. These results, obtained using the proposed NF-TOR training method, are similar to those obtained with a DPD function trained using an FF TOR method.

Slow Light Mode at the Degenerate Band Edge for True Time Delay Applications

Tuneable true time delay device is designed at the degenerate band edge (DBE) by using two coupled periodic silicon ridge waveguides. The holes of the two ridge waveguides are well-tuned to let four modes couple and degenerate at the bandgap providing a slow light mode (the DBE mode). Transfer matrix method is utilized to trace and verify the slow light mode in the device. A 25-unit cell device ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10~ \boldsymbol {\mu m}$ </tex-math></inline-formula> length device) is constructed to realize the slow mode at the DBE with 70% transmission and 42.5 ps signal delay over 130 GHz dispersion free bandwidth. Liquid crystal cladding layer is incorporated to provide continuous control of the slow mode velocity around the DBE resonance for UWB antenna array beamforming applications.