Showing papers on "Phased array published in 2002"

Fractal antennas: a novel antenna miniaturization technique, and applications

Abstract: Fractal geometry involves a recursive generating methodology that results in contours with infinitely intricate fine structures. This geometry, which has been used to model complex objects found in nature such as clouds and coastlines, has space-filling properties that can be utilized to miniaturize antennas. These contours are able to add more electrical length in less volume. In this article, we look at miniaturizing wire and patch antennas using fractals. Fractals are profoundly intricate shapes that are easy to define. It is seen that even though the mathematical foundations call for an infinitely complex structure, the complexity that is not discernible for the particular application can be truncated. For antennas, this means that we can reap the rewards of miniaturizing an antenna using fractals without paying the price of having to manufacture an infinitely complex radiator. In fact, it is shown that the required number of generating iterations, each of which adds a layer of intricacy, is only a few. A primer on the mathematical bases of fractal geometry is also given, focusing especially on the mathematical properties that apply to the analysis of antennas. Also presented is an application of these miniaturized antennas to phased arrays. It is shown how these fractal antennas can be used in tightly packed linear arrays, resulting in phased arrays that can scan to wider angles while avoiding grating lobes.

Capacitive micromachined ultrasonic transducers: next-generation arrays for acoustic imaging?

Abstract: Piezoelectric materials have dominated the ultrasonic transducer technology. Recently, capacitive micromachined ultrasonic transducers (CMUTs) have emerged as an alternative technology offering advantages such as wide bandwidth, ease of fabricating large arrays, and potential for integration with electronics. The aim of this paper is to demonstrate the viability of CMUTs for ultrasound imaging. We present the first pulse-echo phased array B-scan sector images using a 128-element, one-dimensional (1-D) linear CMUT array. We fabricated 64- and 128-element 1-D CMUT arrays with 100% yield and uniform element response across the arrays. These arrays have been operated in immersion with no failure or degradation in performance over the time. For imaging experiments, we built a resolution test phantom roughly mimicking the attenuation properties of soft tissue. We used a PC-based experimental system, including custom-designed electronic circuits to acquire the complete set of 128/spl times/128 RF A-scans from all transmit-receive element combinations. We obtained the pulse-echo frequency response by analyzing the echo signals from wire targets. These echo signals presented an 80% fractional bandwidth around 3 MHz, including the effect of attenuation in the propagating medium. We reconstructed the B-scan images with a sector angle of 90 degrees and an image depth of 210 mm through offline processing by using RF beamforming and synthetic phased array approaches. The measured 6-dB lateral and axial resolutions at 135 mm depth were 0.0144 radians and 0.3 mm, respectively. The electronic noise floor of the image was more than 50 dB below the maximum mainlobe magnitude. We also performed preliminary investigations on the effects of crosstalk among array elements on the image quality. In the near field, some artifacts were observable extending out from the array to a depth of 2 cm. A tail also was observed in the point spread function (PSF) in the axial direction, indicating the existence of crosstalk. The relative amplitude of this tail with respect to the mainlobe was less than -20 dB.

Phased arrays - part 1: theory and architectures

Abstract: An overview of electronically scanned array technology with a brief introduction of the basic theory and array architectures are presented. Implementations, current state-of-the-art, and future trends are briefly reviewed in Part II of this paper.

Optimization of thinned aperiodic linear phased arrays using genetic algorithms to reduce grating lobes during scanning

Abstract: The scan volume of a thinned periodic linear phased array is proportional to the spacing between array elements. As the spacing between elements increases beyond a half wavelength, the scan range of the array will be significantly reduced due to the appearance of grating lobes. This paper investigates a method of creating thinned aperiodic linear phased arrays through the application of genetic algorithms that will suppress the grating lobes with increased steering angles. In addition, the genetic algorithm will place restrictions on the driving-point impedance of each element so that they are well behaved during scanning. A genetic algorithm approach is also introduced for the purpose of evolving an optimal set of matching networks. Finally, an efficient technique for evaluating the directivity of an aperiodic array of half-wave dipoles is developed for use in conjunction with genetic algorithms.

Sparse 2-D arrays for 3-D phased array imaging - design methods

Abstract: One of the most promising techniques for limiting complexity for real-time 3-D ultrasound systems is to use sparse 2-D layouts. For a given number of channels, optimization of performance is desirable to ensure high quality volume images. To find optimal layouts, several approaches have been followed with varying success. The most promising designs proposed are Vernier arrays, but also these suffer from high peaks in the sidelobe region compared with a dense array. In this work, we propose new methods based on the principles of suppression of grating lobes to form symmetric and non-symmetric regular sparse periodic and radially periodic designs. The proposed methods extend the concept of sparse periodic layouts by exploiting either an increased number of symmetry axes or radial symmetry. We also introduce two new strategies to form designs with nonoverlapping elements. The performance of the new layouts range from the performance of Vernier arrays to almost that of dense arrays. Our designs have simplicity in construction, flexibility in the number of active elements, and the possibility of trade off sidelobe peaks against sidelobe energy.

Coupling and decoupling theory and its application to the MRI phased array

Abstract: In classical MRI phased-array design, optimal coil overlapping is used to minimize coupling between nearest-neighbor coils, and low input impedance preamplifiers are used to isolate the relatively weak coupling between non-nearest neighbors. However, to make the complex sensitivities of phased-array coils sufficiently distinct in parallel spatially-encoded MRI, it is desirable to have no overlapping between coils. Also, if phased arrays are used as transmit coils in MRI, one can no longer rely on the low input impedance of the preamplifiers for decoupling. Here a coupling and decoupling theory is introduced to provide a better understanding of the relations between coupled and uncoupled signals in the MRI phased array, and to offer a new method for decoupling phased-array coils without overlapping the nearest coil pairs. The new decoupling method is based on the assumption that any n-element phased array can be decoupled by a 2n-port interface system between phased array and preamplifiers. The detailed analysis and the experimental results show that a four-port interface can be used to decouple a two-element phased array. Furthermore, the four-port interfaces can serve as building blocks to construct a 2n-port decoupling interface. This new method allows one to place the coil elements anywhere that could optimize parallel spatial encoding without concern for coupling between the coils. The method can also be used for phased-array transmit coils.

Farfield calibration method used for phased array antennas containing tunable phase shifters

Abstract: A method for calibrating a phased array antenna and the calibrated phased array antenna are described herein. In the preferred embodiment of the present invention, the method for calibrating a phased array antenna containing a plurality of electronically tunable phase shifters each of which is coupled to a column of radiating elements includes the steps of: (a) characterizing each of the electronically tunable phase shifters; (b) calculating phase offsets for each column of radiating elements using a nearfield antenna range and the characterized data for each of the electronically tunable phase shifters; and (c) using the calculated phase offsets in a calibration table to adjust the tuning voltage of each of the electronically tunable phase shifters to cause the columns of radiating elements to yield a uniform beam.

Beamforming In Acoustic Testing

Abstract: Non-intrusive measurements of wind tunnel model noise can be made in non-acoustic, hardwall wind tunnels, as well as free jets and other challenging settings, by using beamforming techniques with sparse, wide-band phased arrays of microphones The process, which was developed for this application at Boeing in the last few years, begins by measuring a full array cross-spectral matrix for each frequency of interest A grid of potential source locations in the test section is defined A complex array steering vector is computed for each grid point with non-uniform flow, microphone imperfections, and installation effects taken into account Beamforming combines the cross-spectral matrices and the steering vectors to produce maps of the wind tunnel model’s acoustic source distribution Several beamforming algorithms are described with intuitive motivation and expected performance Practical details of steering vector construction are presented Techniques for removing various types of interference are detailed

Phased array beamformer module driving two elements

Abstract: A modular beamformer system for providing signals to at least two radiating elements of a phased array antenna is provided. The system includes a right-hand circular polarization beamformer module and a left-hand circular polarization beamformer module. The left and right circular polarization beamformer modules are coupled to two radiating elements. Each beamformer module includes two groups of beamforming circuitry, one per radiating element. At least one feeder line extends from each beamforming circuitry and is coupled to one of the radiating elements to transmit an output of each beamforming circuitry.

Antenna-Integrated printed wiring board assembly for a phased array antenna system

Abstract: A phased array antenna system including a plurality of metal, column-like elements formed adjacent the RF probes for improving the electrical performance of the system. In one embodiment a hole is formed in a multi-layer, probe-integrated printed wiring board of the system and metal material is plated thereon to fill the hole. The metal, column-like elements are each disposed generally in between associated pairs of the RF probes. The metal, column-like elements essentially form metal pins that improve the return loss bandwidth, probe-to-probe isolation, insertion loss bandwidth, higher order mode suppression and cross-polarization generation.

Ultrasound transducer array

Abstract: This invention relates to an ultrasonic transducer array for non-destructive imaging and inspection of materials, suitable for applications such as bio-medical imaging. According to the invention, the transducer has at least one electrode comprising an array of electrode elements, wherein the elements are not separated by a grooves or kerfs. The grooveless transducer design simplifies transducer construction and permits very high operating frequencies, and hence very high resolution. In one embodiment suitable for producing real-time high resolution 3-dimension images, the invention provides a hybrid transducer comprising two opposed electrodes, one electrode being a grooveless linear array and the second electrode being a grooved linear phased array.

Aeroacoustic Phased Array Testing in Low Speed Wind Tunnels

Abstract: This chapter on Aeroacoustic Phased Array Testing in Low Speed Wind Tunnels provides comprehensive coverage of practical aspects for successfully deploying acoustic phased array measurement capability in low-speed wind tunnels. Non-intrusive requirements for acoustic measurement during aerodynamic testing are discussed including array design, construction, and installation. Instrumentation, data acquisition system, and data reduction system requirements are presented. Operational aspects that bring tractability to the demanding challenge of high-channel-count phased array acoustic measurements including calibration techniques, data visibility, and data management are also covered. The author’s broad experience in successfully deploying acoustic phased array measurement technology in several venues including multiple High-Reynolds-Number Wind Tunnels provides proven insights for practicing engineers and advanced students interested in conducting aeroacoustic tests.

Continuous true-time-delay beamforming for phased array antenna using a tunable chirped fiber grating delay line

Abstract: In this letter, we demonstrate a new five-element true-time-delay (TTD) system that uses only a single tunable linear chirped fiber grating (TLCFG) delay line for continuous TTD beamforming. The system avoids the complicated wavelength tuning and synchronal control of the tunable lasers as well as the tunable bandpass filters. Different time delays are achieved by tuning the chirp rate of the TLCFG, to which a multiwavelength laser source that carries the RF signal is applied. The time delay responses of the TTD system are measured experimentally, which agree well with the theoretical analysis. The beampointing angle can be controlled continuously by changing the chirp rate of the TLCFG. The minimum time delay step can be much smaller than 1 ps thanks to the high position resolution of the actuator.

Monopole phased array thermotherapy applicator for deep tumor therapy

Abstract: A monopole phased array thermotherapy applicator radiating radiofrequency energy for inducing a temperature rise in a target within a body includes a plurality of monopole elements each for transmitting electric-field radiation; a metallic waveguide with an RF reflecting ground plane surface with a plurality of circular holes for mounting the monopole elements where the metallic waveguide forms an aperture for receiving a body to be treated; a waveform generator providing a source of electric field coupled to each monopole radiating element through a respective phase and power weighting network; at least one electric field probe positioned on a skin surface of the body for detecting electric field radiation from the plurality of monopole elements; and a controller circuit coupled to the electric field probe received feedback signals to adjust the phase and power delivered to the plurality of monopole elements so that one or more adaptive nulls are formed on the surface of the body and a focus is formed at the target tissue to be treated with thermotherapy

Angular-profile tuning of guided waves in hollow cylinders using a circumferential phased array

Abstract: Angular-profile tuning of guided waves in hollow cylinders is implemented by using partial loading of the elements in a circumferentially placed phased array. Each partial loading element generates nonaxisymmetric guided waves in a pipe. In earlier work, numerical calculations and experiments have shown that, for nonaxisymmetric guided waves, circumferential distribution of particle displacements (i.e., the angular profile) changes with propagation distance, frequency, and mode. To change the angular profile at a certain distance, either frequency or mode has to be changed for a single partial loading element. This is not the case, however, for a circumferential phased array. The total angular profile of a circumferential array is the superposition of contributions from all elements. If given the knowledge of the angular profile for a single element, the total guided wave angular profile can be controlled and thus focused at any specific circumferential location by a circumferentially placed phased array with adjustable voltage level and phase inputs. This angular profile tuning technique can be used for implementing a circumferential scan with focused, guided wave beams, which leads to the detection of smaller defects as a result of stronger focused beams. Algorithms and specific nondestructive evaluation (NDE) applications for pipe inspection using this technique are discussed.

On the size requirement for finite phased-array models

Abstract: The question considered is how large an array model must be in order to capture approximately the characteristics of both the interior and the edge elements of a large multi-octave phased array. Arrays with tapered slot elements and with top-loaded dipoles are analyzed at element spacings as small as 0.1/spl lambda/ and it is concluded that at any frequency, a finite array model with this type of element should be at least 5/spl lambda//spl times/5/spl lambda/ in size. This suggests the generalization of the 10/spl times/10 element model often used as an engineering "rule of thumb" in the normal narrow-band case with 0.5/spl lambda/ element spacing. An array model with a 5:1 bandwidth thus needs about 25 times more elements than a narrow-band model. The array feed impedance is considered and it is found that the array active reflection coefficient in finite arrays but not in infinite arrays is dependent on the matching condition at the feed. The finite-difference time-domain (FDTD) technique is used to analyze arrays up to 49/spl times/49 elements, demonstrating that computer power now makes feasible the full wave solution for large phased arrays with complex geometry.

Determination of absolute levels from phased array measurements using spatial source coherence

Abstract: ¶The phased array technique is a valuable tool in acoustic testing for its capability to distinguish between different source locations. However, the interpretation of phased array measurements is still difficult due to the simultaneous occurrence of several effects: the size and level of a spot in a conventional acoustic 'source plot' may be affected by a combination of (1) the limited resolution of the array (2) coherence loss during propagation to the array (3) the spatial extent of the source region. This ambiguity complicates the determination of absolute source levels from phased array measurements. The current paper addresses this problem for a noise source that is extended mainly in one direction, i.e. trailing-edge noise. Simulations are done for a line source, and the influence of array resolution and source coherence length on the array output is investigated. Furthermore, an array processing technique is presented which determines the coherence level between different sources in the scan plane. As a first application, the technique is used to identify mirror sources in a closed wind tunnel. The new method is then applied to trailing-edge noise measurements in NLR's Small Anechoic Wind Tunnel, in order to estimate the spanwise coherence length. In conjunction with the simulations this enables an improved determination of absolute trailing-edge noise from phased array measurements.

A fully packaged true time delay module for a K-band phased array antenna system demonstration

Abstract: A 1-to-64 [6-bit(2/sup 6/)] optical true-time delay module is designed, fabricated, and packaged for squint-free beam steering in phased array antennas, providing linear time delays ranging from 0 to 443.03 ps. The phases versus RF frequencies are measured to verify that the time delay is independent of RF frequencies. The optical true-time delay module is integrated into a K-band (18-26.5 GHz) phased-array antenna system. Far-field patterns at different frequencies over the entire K-band are measured and compared with simulated results to verify the system's wide instantaneous RF bandwidth. The Q factor is measured to be 10.20 of the true-time delay optical link transmitting 2.5-Gb/s random digital signal.

Phases array communication system utilizing variable frequency oscillator and delay line network for phase shift compensation

Abstract: An improved receiving phased array communication system supplies oscillating waveform signals with different phase delays to downconverting mixers in the processing channels of the receiving phased array communication system to compensate for phase difference in the received signal over the antenna elements therein. Similarly, an improved transmitting phased array communication system supplies oscillating waveform signals with different phase delays to the upconverting mixers in the processing channels of the transmitting phased array communication system to introduce phase difference in the transmit signal for transmission over the antenna elements therein. The oscillating waveform signals with different phase delays are preferably derived from a local oscillator that generates a local oscillating signal, and a delay line network having a plurality of fixed delay lines arranged in a serial manner to introduce increasing fixed phase delays in the local oscillating signal.

Beamformer for multi-beam broadcast antenna

Abstract: A phased array antenna system operative to broadcast multiple beams that each include coded data for specific users located within the coverage area of the corresponding beam. An appropriate receiver then receives and decodes a particular beam to extract the specific data for a corresponding user. Multiple users may be assigned to each beam using frequency division or orthogonal code multiplexing, and the user data may be encoded into the beams using frequency shift key or phase shift key encoding. For each coding technique, the encoded antenna control signals are combined into a total gain and total phase shift control signal, which drives a single phase and gain control device for each antenna element. In addition, a single data modulator generates the coding parameters for the entire communication system.

A subspace-tracking approach to interference nulling for phased array-based radio telescopes

Abstract: Several next-generation radio telescopes, now in the planning stages, are based on phased-array technology. One reason for this is to make use of adaptive nulling techniques to combat radio frequency interference, which is a growing problem for radio astronomy. This paper presents a low-complexity approach to interference nulling which is suitable for use in such systems. The approach uses subspace-tracking to identify interference, followed by spatial projections to place deep nulls in the directions of interferers. This technique overcomes two limitations of power-minimization algorithms (e.g., "minimum variance"), namely power inversion and pattern rumble, which create serious problems for radio astronomy. Furthermore, this technique imposes a lower computational burden and provides side information which is useful in later stages of data processing. Performance results from a phased array demonstrator system and a simulation are presented.

1.5-D high intensity focused ultrasound array for non-invasive prostate cancer surgery

Abstract: The aim of this study is to demonstrate the feasibility of a new spherically curved 1.5-D phased array for the treatment of localized prostatic cancer. The device is designed to conform to the Ablatherm(R) machine (EDAP-Technomed. France), a commercially available machine in which high intensity focused ultrasound (HIFU) treatment for prostate cancer is administered transrectally. It uses high intensity electronically focused ultrasound to steer a beam along two axes, allowing enough depth to be reached to treat large prostates and eliminating two degrees of mechanical movement. Through computer simulation, it was determined that a curved 1.5-D configuration offered the optimal design. Two configurations were then proposed, and their ability to steer a beam within a target volume centered on the geometric focus of the transducer was simulated. An eight-element prototype was constructed to test the piezo-composite material and its electro-acoustical efficiency. Then, an array was constructed, and a multichannel amplifier and control system were added, to permit remote operation. Acoustical and electrical measurements were made to verify performance. Finally, the 1.5-D array was tested in vitro on samples of pig liver to confirm the ability to induce lesions.

Multiband phased array antenna utilizing a unit cell

Abstract: A multi-band phased array antenna for radiating low frequency band signals and high frequency band signals. The multiband phased array antenna is formed from unit cells having waveguides for radiating high frequency band signals and end-fire radiating elements for radiating low frequency band signals. The unit cells have four walls with an open input end and an open radiating end. End-fire radiating elements are disposed on inner surfaces and outer surfaces of the four walls and radiate out the radiating end. Four waveguides are disposed together to radiate into the input end of the low frequency assembly.

Beamformer for multi-beam receive antenna

Abstract: A phased array antenna system that is operative to simultaneously form multiple beams without requiring an undue amount of hardware. The system collects propagating energy with a number of antenna elements to form multiple beams, encodes the beams as the energy is collected, combines the encoded beams, and then decodes the combined signal to separate the beams. In this way, the beams can be formed with a single set of antenna hardware instead of requiring a multiplicity of antenna hardware, one for each beam. Frequency coding may be implemented by repeatedly applying a Doppler phase shift to each beam, and then using a Doppler filter to separate the beams. Alternatively, a code division multiplexing technique may be implemented by using a CDMA code generator to apply a code to each beam, and then using a CDMA filter to separate the beams.

Modified constant modulus algorithm for digital signal processing adaptive antennas with microwave analog beamforming

Abstract: This paper proposes a novel algorithm, called modified constant modulus algorithm (M-CMA), which is able to give adaptability to microwave beamforming phased array antennas. Since microwave analog beamformers basically require much fewer RF devices than digital beamformers, microwave analog beamformers based on M-CMA, that is, adaptive microwave beamformers, can be cheaply fabricated. Therefore, they are very suitable for mobile communication systems where both miniaturization and low cost are required for the mobile terminals. M-CMA obtains a gradient vector by a combination of analytical calculation and perturbation of the microwave beamforming control voltage. Though M-CMA is implemented with a digital signal processor, M-CMA controls the microwave analog beamformer by utilizing the gradient vector. The microwave analog beamformer based on M-CMA is analyzed to have the following characteristics: (1) the beamformer can point its main beam to the desired direction in additive white Gaussian noise (AWGN) channels; (2) although the beamformer may possibly fail in ill solutions in cochannel interference (CCI) channels, M-CMA can converge to the optimum solution when the desired direction is roughly a priori known.

Phased array radars-past, present and future

Abstract: This is a survey paper summarizing the developments and future trends in passive, active bipolar and monolithic microwave integrated circuitry (MMIC) phased array radars for ground, ship, air, and space applications. Covered is the DD(X) ship radar suite; THAAD (formerly GBR); European COBRA; Israel BMD radar antennas; Dutch shipboard APAR; airborne US F-22, JSF and F-18 radars, European AMSAR, Swedish AESA, Japan FSX and Israel Phalcon; Iridium. (66 satellites in orbit for total of 198 antennas) and Globalstar MMIC spaceborne active array systems (these last two are communications but the technology is the same as used by radar systems, in fact the Iridium T/R module technology derives from technology developed for a space based radar); Thales (formerly Thomson-CSF) 4 inch MMIC wafer 94 GHz seeker antenna; digital beamforming; ferroelectric row-column scanning; optical electronic scanning for communications and radar; the MMIC C-band to Ku-band Advanced Shared Aperture Program (ASAP) and AMRFS antenna systems for shared use for communications, radar, electronics countermeasures (ECM) and ESM; and continuous transverse stub (CTS) voltage-variable dielectric (VVD) antenna.

Method and structure for phased array antenna interconnect using an array of substrate slats

Abstract: A phased array antenna is formed from an array of apertures having walls containing phase shifter devices for phase shifting and beam steering a radiated beam of the phased array antenna. The phase shifter devices are interconnected with an interconnect structure formed from substrate slats that form the walls of the apertures. The substrate slats may be thin film circuitized column slats having a metal substrate, dielectric layers, metal bias/control circuitry, a shielding layer, and circuit terminations to connect to a phase shifter device attached to the substrate slat.