Phased Array Beamforming Research Articles

FPGA realisation-based architecture for direction-of-arrival in wireless communication

A signal processing technique used in sensor arrays for directional signal transmission or reception is known as beamforming. By combining elements in a phased array beamforming is achieved. This is done in such a way that, signals at particular angles experience constructive interference while others experience destructive interference. To detect and calculate the signal-of-interest at the output of a sensor array by means of the most desirable spatial filtering and interference rejection, adaptive beamforming is used. But, before beamforming technique, the directions of desired users and undesired users or interferes must be prevailed using a direction-of-arrival (DOA) estimation algorithm. This paper presents FPGA realisation-based design of a smart antenna system based on DOA estimation algorithm using Xilinx system generator (XSG). MUSIC algorithm is considered in this paper to identify the DOA of the input signals incident on the sensor array comprising the smart antenna system. The MUSIC algorithm is a simple and effective eigen structure method of DOA estimation. With this approach, the results of proposed simulated FPGA design of a smart antenna system shows effective hardware utilisation.

FPGA realisation-based architecture for direction-of-arrival in wireless communication

A signal processing technique used in sensor arrays for directional signal transmission or reception is known as beamforming. By combining elements in a phased array beamforming is achieved. This is done in such a way that, signals at particular angles experience constructive interference while others experience destructive interference. To detect and calculate the signal-of-interest at the output of a sensor array by means of the most desirable spatial filtering and interference rejection, adaptive beamforming is used. But, before beamforming technique, the directions of desired users and undesired users or interferes must be prevailed using a direction-of-arrival (DOA) estimation algorithm. This paper presents FPGA realisation-based design of a smart antenna system based on DOA estimation algorithm using Xilinx system generator (XSG). MUSIC algorithm is considered in this paper to identify the DOA of the input signals incident on the sensor array comprising the smart antenna system. The MUSIC algorithm is a simple and effective eigen structure method of DOA estimation. With this approach, the results of proposed simulated FPGA design of a smart antenna system shows effective hardware utilisation.

A Sub-Nyquist, Variable Sampling, High-Frequency Phased Array Beamformer.

A digital receive beamformer implementing a "one sample per pixel" variable sampling technique is described. The sampling method reduces the required sampling rates by a factor of 3, and reduces the data capture rate by a factor of 2, in comparison with the previous systems based on variable sampling. The sampling method is capable of estimating broadband pulse envelopes accurate for bandwidths up to 83.0%. This beamforming method has been implemented on a field-programmable gate array with maximum transmit and receive delay errors measured to be less than ±1.0 ns. The beamformer was tested and verified on a previously described 45-MHz 64-element phased array. The system generates images with 128 lines, 512 pixels per RF line, and 2 transmit focal zones. The system generates images with approximately 55 dB of dynamic range and was tested by imaging wire targets submersed in a water bath, wire targets embedded in a tissue phantom, and real-time in vivo imaging of a human wrist.

A variable gain CMOS phase shifter for phased array antenna applications

ABSTRACTThis letter presents for the first time the development of a variable gain CMOS phase shifter using 0.18 µm CMOS process in the S‐band frequencies to be integrated with conformal phased array beamforming antenna for smart communication radar applications. The vector modulator based phase shifter has an integrated variable gain amplifier codesigned with the phase shifter circuitry in order to be capable of controlling both phase and gain simultaneously which is necessary to recover the degraded radiation pattern due to the conformal shaping of the phased array antenna. The phase shifter achieves measured continuous phase shift of 303° along with measured 7 dB gain control range over 2–2.60 GHz and an insertion loss of 7.12 dB at 2.2 GHz. The measured DC power consumption of the phase shifter is 34.2 mW from a 2 V supply with a smaller chip area of 1.12 mm2 including all pads. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:324–328, 2017

Structural health monitoring of wind turbine blades using acoustic microphone array

This article proposes a non-contacting measurement technique based on acoustic monitoring to detect cracks or damage within a structure by observing sound radiation using a single microphone or a beamforming array. The technique works by mounting an audio speaker inside a hollow structure, such as a wind turbine blade, and observing the sound radiated from the blade to identify damage. The primary hypothesis for this structural damage detection technique is that the structural damage (cracks, edge splits, holes, etc.) on the surface results in changes in the sound radiation characteristics of the structure. Preliminary measurements to validate the methodology were carried out on a section of a wind turbine blade containing different sized holes and cracks. An acoustic microphone array with 62 microphones was used to measure the sound radiated from the structure when an audio speaker generating random noise was placed inside a cavity emulating a wind turbine blade. A phased array beamforming technique and CLEAN-based subtraction of point spread function from a reference were employed to locate the different damage types on the test structures. The same experiment was repeated using a commercially available 48-channel acoustic ring array to compare the test results. It was shown that both the acoustic beamforming and the CLEAN-based subtraction of point spread function from reference techniques can identify the damage in the test structures with sufficiently high fidelity.

Rapid guided wave delamination detection and quantification in composites using global-local sensing

This paper presents a rapid guided ultrasonic wave inspection approach through global inspection by phased array beamforming and local damage evaluation via wavenumber analysis. The global-local approach uses a hybrid system consisting of a PZT wafer and a non-contact laser vibrometer. The overall inspection is performed in two steps. First, a phased array configured by a small number of measurements performs beamforming and beamsteering over the entire plate in order to detect and locate the presence of the damage. A local area is identified as target damage area for the second step. Then a high density wavefield measurement is taken over the target damage area and a spatial wavenumber imaging is performed to quantitatively evaluate the damage. The two-step inspection has been applied to locate and quantify impact-induced delamination damage in a carbon fiber reinforced polymer composite plate. The detected delamination location, size and shape agree well with those of an ultrasonic C-scan. For the test case studied in this work the global-local approach reduced the total composite inspection (damage detection and characterization) time by ∼97% compared to using a full scan approach.

Photonic True-Time Delay Beamforming Using a Switch-Controlled Wavelength-Dependent Recirculating Loop

A photonic true-time delay beamforming network to provide tunable progressive time delays for phased array beamforming is proposed and demonstrated. In the proposed system, a microwave signal is modulated on multiwavelength optical carriers and sent to an optical dispersive recirculating loop that contains a linearly chirped fiber Bragg grating (LCFBG) to provide a wavelength-dependent round trip time. As the microwave-modulated optical signals recirculate in the loop, the microwave signals carried by different wavelengths will experience different time delays at the output of the loop. By controlling the number of round trips, tunable progressive true-time delays are achieved, which are required for true-time delay phased array beamforming. The proposed true time delay beamforming network is experimentally evaluated. Two dispersive loops that can introduce a single-round-trip true-time delay difference of 2.5 ns and 160 ps are designed, which are implemented by using two LCFBGs with two different dispersion coefficients of 2500 and 200 ps/nm. The progressive time delays for beam steering achieved by the two dispersive loops can cover a beam scanning range from –60° to 60°.

Applications of RF aperture-array spatially-bandpass 2-D IIR filters in sub-Nyquist spectrum sensing, wideband doppler radar and radio astronomy beamforming

The application of two-dimensional (2-D) infinite impulse response (IIR) spatially-bandpass (SBP) filters as a digital beamformer for a wide spectrum of practical applications spanning wireless cognitive radio communications, doppler radar, and radio astronomy instrumentation is discussed. The paper starts with an introduction of the recently proposed 2-D SBP filter. The first application is a spectrum sensing scheme for dynamic spectrum access based cognitive radios. A 2-D IIR SBP filter is used in conjunction with a sub-Nyquist wideband signal reconstruction technique to achieve aperture-array directional spectrum sensing using sub-Nyquist sparse sampling based on the recently reported Eldar algorithm. The second application is related to wideband pulse and continuous-wave frequency modulated Doppler radar sensing. The SBP filter is integrated with a wideband radar back-end connected to an electronically-steerable aperture antenna. A a low-complexity directional localization algorithm is presented, which estimates the range and angle of a target scatterer with a signal to interference ratio improvement of 10 dB. We also present applications of 2-D IIR SBP in the fields of classification and remote sensing of unmanned aerial vehicles. Finally, a digital aperture-array wideband beamforming model using the 2-D IIR SBP filters is presented for radio telescope systems based on dense aperture arrays and time-domain beamforming. A well-known example is the study of pulsar astrophysics using a highly-directional aperture antenna system. The 2-D IIR SBP beamformer is simulated as the digital backend of the time-domain beamforming system with array signals synthesized using measured time-domain signatures from the Crab pulsar obtained from the GAVRT. The SBP filter shows a gain of 12.3 dB with an order of magnitude lower circuit complexity compared to traditional phased-array digital beamformers. To obtain comparable levels of SINR improvement, the wideband phased-array beamformers require 48-point FFTs per antenna. Assuming the optimum three real-multiplications per complex multiplication for the Gauss algorithm, it is discovered that the proposed 2-D IIR SBP beamformers are more than 97 % lower in digital multiplier complexity compared to traditional FIR phased-array FFT-beamformers.

Tunable Multiwavelength Fiber Laser Source for Continuous True-Time-Delay Beamforming

We present a novel approach of a true-time-delay (TTD) laser source for continuous phased-array beamforming employing a semiconductor optical amplifier (SOA) and a tunable Fabry–Perot filter (FPF). The wavelength tuning is achieved by tuning the cavity length of the filter, to which an SOA that generates the $C$ -band optical signal is applied. A five-channel TTD system based on a linear chirped fiber grating (LCFG) has been constructed and experimented using the proposed laser source. The signal-to-noise ratio of the obtained multiwavelength signal can be more than 35 dB. Thanks to the high position resolution of the translation stage, the time delay responses can be continuously controlled by changing the cavity length of the FPF.

Low latency digital beamforming radar using aperture coding

A binary phase shift keying, space time coding approach to digital beamforming radar is considered for low latency estimation of range, velocity, and bearing angles of scatterers. Scattering information from all angles within the field of view is gathered during a single range/velocity acquisition and subsequent processing produces a range/velocity matrix for each beam direction. This coded aperture radar (CAR) approach provides range, velocity, and bearing angle estimates with low latency and requires only a single transceiver. These advantages are accompanied by a decrease in SNR as compared to conventional phased array and digital beamforming radars due to the fact that CAR receives less total energy. Furthermore, obtaining a sufficient number of measurements within an acquisition period to provide unambiguous estimation for a large number of bins may be impractical. Utilizing a reduced measurement set gives rise to residual ambiguity, whose level is shown to be proportional to total received energy.

IBUS: An Integrated Beamformer and Uplink Scheduler for OFDMA Small Cells

Beamforming is a signal processing technique with numerous benefits in wireless communication. Unlike traditional omnidirectional communication, it focuses the energy of the transmitted and/or the received signal in a particular direction. Although beamforming has been extensively studied on conventional systems such as WiFi, little is known about its practical impact on performance in orthogonal frequency-domain multiple access (OFDMA) small-cell deployments. Since OFDMA schedules multiple clients (users) in the same frame in contrast to WiFi, designing intelligent scheduling mechanisms and at the same time leveraging beamforming is a challenging task. Unlike downlink, we show that the integration of beamforming with uplink scheduling projects an interesting tradeoff between beamforming gain on the one hand, and the power-pooling gain resulting from joint multiuser scheduling on the other hand. This, in turn, makes the uplink scheduling problem even hard to approximate. To address this, we propose algorithms that are simple to implement, yet provably efficient with a worst-case guarantee of 1/2. We implement our algorithms on a real WiMAX small-cell platform integrated with an eight-element phased-array beamforming antenna. Evaluations from both prototype implementation and trace-driven simulations show that the algorithms deliver throughput gains of over 40% compared to an omnidirectional scheme.

An applicable 5.8 GHz wireless power transmission system with rough beamforming to Project Loon

Abstract In recent, Google proposed the Project Loon being developed with the mission of providing internet access to rural and remote areas using high-altitude balloons. In this paper, we describe an applicable prototype of 5.8 GHz wireless power transmission system with rough beamforming method to Project Loon. From the measurement results, transmit beamforming phased array antenna can transmit power more efficiently compared to a horn antenna and array antenna without beamforming with increasing the transmission distance. For the transmission distance of 1000 mm, transmit beamforming phased array antenna can obtain higher received power about 1.46 times compared to array antenna without transmit beamforming.

Guided wave phased array beamforming and imaging in composite plates

This paper describes phased array beamforming using guided waves in anisotropic composite plates. A generic phased array algorithm is presented, in which direction dependent guided wave parameters and the energy skew effect are considered. This beamforming at an angular direction is achieved based on the classic delay-and-sum principle by applying phase delays to signals received at array elements and adding up the delayed signals. The phase delays are determined with the goal to maximize the array output at the desired direction and minimize it otherwise. For array characterization, the beam pattern of rectangular grid arrays in composite plates is derived. In addition to the beam pattern, the beamforming factor in terms of wavenumber distribution is defined to provide intrinsic explanations for phased array beamforming. The beamforming and damage detection in a composite plate are demonstrated using rectangular grid arrays made by a non-contact scanning laser Doppler vibrometer. Detection images of the composite plate with multiple surface defects at various directions are obtained. The results show that the guided wave phased array method is a potential effective method for rapid inspection of large composite structures.

Ultra-Wideband and Adaptive Photonic Signal Processing of Microwave Signals

Microwave photonic techniques are attractive for processing high bandwidth signals, overcoming inherent electronic limitations. These processors provide new capabilities for realizing adaptive processing over extremely wide microwave frequency ranges, ultra-wideband operation, and electromagnetic interference immunity. In-fiber signal processors are inherently compatible with fiber-wireless systems, and can provide connectivity with in-built signal conditioning. Recent new methods in wideband microwave photonic processing are presented, including ultra-wideband phase shifters and true time delays for phased array beamforming, widely tunable single passband filters, switchable microwave photonic filters, wideband photonic mixers, high-resolution multiple frequency microwave photonic measurement systems, and photonic RF memory structures.

Advances in High-speed and Adaptive Microwave Photonic Signal Processing

Photonic signal processing, using photonic approaches to condition wideband microwave signals, is attractive due to the inherent advantages of high time-bandwidth product and immunity to electromagnetic interference. In this keynote paper, we describe recent advances in wideband microwave photonic signal processing. This includes programmable microwave photonic phase shifters and true-time delay elements for phased array beamforming, and single bandpass tunable filtering approaches that overcome spectral periodicity. We also present optoelectronic oscillators with wideband frequency operating range, high-resolution multiple frequency microwave photonic measurement systems, and photonic RF memory structures that can realise a long reconfigurable storage time with wide instantaneous bandwidth.

Capacity Enhancement of Ad Hoc Networks Using a New Single-RF Compact Beamforming Scheme

This paper proposes a new single-radio-frequency (RF) compact beamforming scheme that forms the beam by adjusting variable loads. In a conventional phased-array beamformer, half-wavelength antenna spacing is required in order to achieve a reasonable performance without taking into account the mutual coupling. On the other hand, a conventional electronically steerable parasitic array radiator (ESPAR) system requires smaller antenna spacing, but it provides a lower beamforming performance compared to the phased-array beamformer. The proposed method delivers a beamforming performance close to that of a phased array, without having any constraints on the antenna spacing. In the proposed structure, the RF front-end is connected to each antenna via a tunable load, whereas all antenna elements are also terminated by other tunable reactive loads. Simulation results confirm that the proposed scheme provides better interference suppression and achieves more average capacity compared to ESPAR technique. To further validate the beamforming ability of the proposed method, a testbed with 1/20 of the wavelength antenna spacing was fabricated. A good agreement is observed between the measurement and simulation results.

Beamforming Investigation of Dominant Counter-Rotating Open Rotor Tonal and Broadband Noise Sources

Phased array microphone measurements and beamforming technology have been applied in the investigation of counter-rotating open rotors in an attempt to better understand their noise sources. It has already been presented in the literature that the beamforming results of rotating coherent noise sources, typical tonal noise sources for counter-rotating open rotors, will be localized to their respective Mach radii rather than their true noise source locations. Building on these results, the present beamforming investigation provides an approach for identifying tonal and broadband noise sources of counter-rotating open rotors. The methods provide a means for localizing noise sources and identifying noise source mechanisms truly responsible for given components of tonal and broadband noise. Groups of interaction tones that can have the greatest impact on the sound field of counter-rotating open rotors are singled out, and the most dominant noise sources of broadband noise are determined.

Wind turbine blade health monitoring using acoustic beamforming techniques

Wind turbines operate autonomously and can possess reliability issues attributed to manufacturing defects, fatigue failure, or extreme weather events. In particular, wind turbine blades can suffer from leading and trailing edge splits, holes, or cracks that can lead to blade failure and loss of energy revenue generation. In order to help identify damage, several approaches have been used to detect cracks in wind turbine blades; however, most of these methods require transducers to be mounted on the turbine blades, are not effective, or require visual inspection. This paper will propose a new methodology of the wind turbine non-contact health monitoring using the acoustic beamforming techniques. By mounting an audio speaker inside of the wind turbine blade, it may be possible to detect cracks or damage within the structure by observing the sound radiated from the blade. Within this work, a phased array beamforming technique is used to process acoustic data for the purpose of damage detection. Several algorithms are evaluated including the CLEAN-based Subtraction of Point spread function from a Reference (CLSPR) on a composite panel and a section of a wind turbine blade in the laboratory.

2-D-IIR Time-Delay-Sum Linear Aperture Arrays

A uniform linear array (ULA) digital beamformer with enhanced selectivity (interference rejection) over conventional true-time delay-sum (TTDS) beamforming is proposed for scanned aperture applications. Conventional TTDS transfer function, which contains only zero-manifolds, is modified by introducing complex pole-manifolds based on 2-D infinite impulse response (IIR) digital beam filters, thereby achieving enhanced selectivity for the same number of antennas in the ULA. For a ULA of 64 antennas, desired direction of arrival (DOA) 30° and interference DOA -60° from array broadside, a relative improvement in signal-to-interference ratio (SIR) of 7 dB is verified. For 128-element ULA, interference DOA -10°, a relative improvement in SIR of 5-10 dB is obtained for the desired DOA in the range 10°-90°. The projected improvements are independent of the weights of the conventional phased-array, TTDS, or filter-sum beamformer used because the method does not change the zero-manifolds of the original array pattern.

Microwave photonic signal processing

Photonic signal processing offers the advantages of large time-bandwidth capabilities to overcome inherent electronic limitations. In-fibre signal processors are inherently compatible with fibre optic microwave systems that can integrate with wireless antennas, and can provide connectivity with in-built signal conditioning and electromagnetic interference immunity. Recent methods in wideband and adaptive signal processing, which address the challenge of realising programmable microwave photonic phase shifters and true-time delay elements for phased array beamforming; ultra-wideband Hilbert transformers; single passband, widely tunable, and switchable microwave photonic filters; and ultra-wideband microwave photonic mixers, are described. In addition, a new microwave photonic mixer structure is presented, which is based on using the inherent frequency selectivity of the stimulated Brillouin scattering loss spectrum to suppress the carrier of a dual-phase modulated optical signal. Results for the new microwave photonic mixer demonstrate an extremely wide bandwidth operation of 0.2 to 20 GHz and a large conversion efficiency improvement compared to the conventional microwave photonic mixer.