Showing papers on "Phased array published in 1979"

Ultrasonic imaging using arrays

Abstract: An analysis is presented of the two general types of arrays-the direct imaging array and the phased array. These are analyzed over three levels of approximation: geometric optics, steady-state sinusoidal diffraction, and wide-band diffraction. Systems are studied which provide electronic deflection and focusing. In addition, systems are considered which exhibit high resolution in both lateral dimensions.

Imaging reflector arrangements to form a scanning beam using a small array

Abstract: To obtain the performance of a large aperture phased array, a small phased array is combined with a large main reflector and an imaging arrangement of smaller reflectors to form a large image of the small array over the main reflector. An electronically scanable antenna with a large aperture is thus obtained, using a small array. An attractive feature of the imaging arrangement is that the main reflector need not be fabricated accurately, since small imperfections can be corrected efficiently by the array. As an application, a 4.2-m diameter antenna is discussed for a 12–14 GHz satellite with a field of view of 3 degrees by 6 degrees required for coverage of the continental United States.

Phased array radar

Abstract: In a phased array radar system with the radiating elements of the antenna are connected to associated r.f. transmitter-receiver modules. Each of the modules receives a transmitter signal and a local oscillator signal and delivers, upon reception of an echo signal via the antenna an i.f. signal. Furthermore a system of fiber optical waveguides is incorporated to distribute to the modules the transmitter signal and the local oscillator signal, both of which signals being modulated on carriers, which are frequency-matched to the system of fiber optical waveguides. Each of the modules comprises a demodulator to procure the transmitter signal and the local oscillator signal from the applied modulated signals.

Charge transfer device phased array beamsteering and multibeam beamformer

Abstract: A phased array radar system is disclosed, capable of simultaneously transmitting beams in different directions as well as simultaneous multiple beam beamforming with both linear and planar arrays. The system employs charge transfer device complex matrix multipliers to generate the phase weights necessary to produce and steer one or more transmit beams, and applies these phase weights to control directly the phasing of distributed transmitters individual to the antenna elements of the array. Similar matrix multipliers are employed to generate the phase weights necessary for beamforming on receive.

On the gain-versus-scan trade-offs and the phase gradient synthesis for a cylindrical dome antenna

Abstract: Gain-versus-scan trade-offs for a circular cylindrical dome antenna are considered. A theorem by Stangel [1] is generalized, and it is shown that the scan angle limitations of the feed array and of the dome result in an upper bound on the average dynamic gain (scan dependent gain function) and in an upper bound on the gain in any particular scan direction. For specified scan limits, the former bound is determined essentially by the feed array, the latter by the dome size. These bounds are useful in posing realistic performance requirements for dome antennas and have been verified in a few specific examples. Subsequently, the synthesis problem is addressed; an optimization scheme is employed to arrive at a dome insertion phase distribution that produces a desired gain-versus-scan variation. Illustrative examples are given.

Scan independent phased arrays

Abstract: This paper discusses a derivation of the scan impedance for a phased array consisting of arbitrarily oriented planar elements with arbitrary current distribution located in a general stratified media. It is shown that the scan impedance will remain scan independent if and only if the product of the element power pattern and the transformation function for the stratified dielectric media varies as the cosine to the scan angle. An entire class of scan independent phased arrays is defined in this fashion. As simple examples of this class, we discuss arrays of slots or dipoles bounded by a single dielectric slab with ϵ = 1.3. The scan impedance has VSWR < 1.5 for scan angles up to ±80° in both principal planes, and further improvements appear possible. These designs are quite different and superior to earlier phased array designs (Magill and Wheeler, 1966; Campbell and Popovich, 1972; Chen, 1973).

Angular Response of Piezoelectric Elements in Phased Array Ultrasound Scanners

Abstract: Abstruct-In the design of phased linear array sector scanners for medical applications, it is important to preserve uniform response at each angle throughout the sector scan of k45". Examination of Linear array transducers showed reduced transmit pressure and receive sensitivity a t angles beyond * 20" by individual array elements. The angular response of piezoelectric elements, many wavelengths long and approximately one wavelength or less in width, do not agree with the predictions of simple diffraction theory for plane apertures. Continuous wave (CW) angular response measurements using the RCA Ultrasonovision of individual piezoelectric elements 0.6 h t o 2 h wide indicated this behavior was independent of inter-element coupling and pulse excitation effects within a linear array transducer. Spectral analysis of isolated elements showed a significant amount of energy coupled into the transverse mode due to the small aspect ratio of width to thickness dimensions of the piezoelectric elements. A fist-order hvo-dimensional numerical model, based on thickness mode and transverse mode vibrations, resulted in angular response functions which agree well with experimental measurements.

Optical phase measurement in real time

Abstract: A method has been developed for the real-time measurement of optical phase. The optical wave whose phase is to be measured is interfered with a spatially coherent plane-wave reference on the face of a photodetector array. The irradiance is measured simultaneously at all array elements for each of three specific phase shifts of the reference, and the phase and magnitude at each array element are calculated from the three measured irradiances by a simple algorithm. The method can be used for hybrid optical-digital analog computation of 2-D Fourier transforms: information is introduced coherently into the front focal plane of a lens with a spatial light modulator, and the phase and magnitude are measured in the back focal plane. Experimental results of the Fourier transform technique are described.

Stand alone collision avoidance system

Abstract: A stand alone collision avoidance system is disclosed for mounting to a large passenger jet especially to avoid the collision problem common to such large jets colliding with small propeller driven aircraft. A bistatic radar antenna system is disclosed having a frequency in the range of 40 Giga Hertz (hereafter GHz). Paired bistatic antennas are used with each couplet of bistatic transmitting and receiving antennas searching one quadrant of a total forward hemisphere of search in the direction of plane travel. Paired transmitter antennas, one for each quadrant, are typically located above and below the nose located weather radar and are mechanically scanned side to side in the typical "beaver tail" scan with the beaver tail occupying 100° of elevation and 0.71° of beam width. Paired receiving antennas, again one for each quadrant, are located with one such antenna on the leading edge of the vertical stabilizer or tail and the other antenna on a special mast lowered in a position where landing gear shadow does not obscure forward view. Each receiving antenna is mechanically scanned side to side synchronously with its transmitter antenna and consists of a phased array with a vertical scan generated from about 500 discrete linearly disposed receiving elements for vertical resolution of up to 0.21°. The antenna is responsive only to radar return signals approaching the antenna in a narrow vertical angular range, at some desired, and variable, vertical angle.

Phased array antenna arrangement with filtering to reduce grating lobes

Abstract: The present invention relates to a method for reducing the grating lobes associated with phased array antenna arrangements. The present invention, which may be employed with any phased array antenna arrangement, consists of disposing a filtering means capable of blocking the grating lobes at any real focal point in the focal plane of the antenna arrangement. The size of the central region of the filter is determined by the desired field of view at the far-field, and may be adjusted so as to reduce the grating lobes to an admissible level with minimal gain degradation of the main beam.

Design of array and line-source antennas for Taylor patterns with a null

Abstract: An antenna pattern design technique which results in a generalized Taylor pattern, except in a narrow region where a deep null is formed, centered at a preassigned position is presented. It is shown how this technique can be applied effectively to both linear arrays and line sources. The approach is direct so that the technique does not use either iterative sampling or a perturbation procedure. It is particularly useful in the design of a large array with a prescribed deep null. Numerical results indicate that to steer such a null, adjustment of the excitation is necessary near the edges only.

Scannable beam forming interferometer antenna array system

Abstract: An antenna array comprising at least three interferometer pairs of antenna elements with selected spacings made to form a single beam which is readily scannable. All spatial frequencies generated by a signal and intercepted by the array are derived from a signal processing technique applied to the array. The array samples space in the spatial frequency domain while the signal processing technique utilizes real time convolution of functions in the spectral frequency domain. Summation of the appropriate spatial frequencies is equivalent to a Fourier transform operation, yielding the location of the signal source in space. Resolution and freedom from interference of the interferometer system is equal to that of a fully filled array of the same aperture size containing element spacings of one-half wavelength. An antenna array system comprising four antenna elements forming six interferometer pairs with a resolution equal to that of a sixteen element array with spacings of one-half wavelength is described, as well as other multiples of one-quarter wavelength or partial multiples of a wave length.

A Simplified Ultrasound Phased Array Sector Scanner

Abstract: The phased array principle was introduced into medical ultrasound by Somer (1) and is now mainly used in two-dimensional echocardiography. In a phased array the ultrasound beam is rotated around the transducer and a sector scan is performed. The transducer typically has a width of 1–2 cm and consists of many elements, usually about 30. The rotation of the ultrasound beam is achieved by emitting the ultrasound pulses from the different elements at different instants and subjecting the received echo signals to delays, which are different for each element of the array. The principles of the ultrasound phased array are well known by now (see e.g. (1). (2)). The difference in delay τk between adjacent elements is given by $$\tau_{\rm k}=\rm x_k \cdot (sin\ \alpha)/c$$ where xk is the distance between elements, α is the deflection angle and c is the sound velocity.

A novel radar array and its imaging properties

Abstract: A novel radar array providing resolution superior to any other antenna configuration with the same physical aperture is described. Application of the new array to a localized imaging system suitable for real-time operation is simulated, and its resolution and depth of field properties ate compared with those of a crossed array and the conventional filled array antenna. Substantial savings in weight, cost, and complexity are offered by the proposed configuration.

Scanning beam antenna arrangement

Abstract: The present invention relates to an antenna arrangement capable of generating one or more linearly scanning spot beams which are scanned over separate strip portions of the entire field of view of the antenna. The antenna arrangement comprises an optical system comprising an aperture and a focal plane, and a novel feed arrangement. The feed arrangement comprises a separate linear phased array disposed within a separate rectangular waveguide section for each linear scanning beam desired. An offset curved reflector, disposed in each waveguide section, converts a linearly scanning planar wavefront generated by an array into a converging beam forming a linearly moving point source on the antenna's focal plane with the principle ray of each instantaneous wavefront being directed at the center of an image of the aperture of the optical system as seen by the feed arrangement.

First experimental results from the Valley Forge radio camera program

Abstract: An X-band high angular resolution imaging radar experiment using a broadly distributed antenna array has been conducted. The experimental resolving power is 5.2 × 10-4rad. Adaptive beam-forming is employed to compensate for the distortion in the aperture.

Broadband Chirp Transducers for Integrated Optics Spectrum Analyzers

Abstract: A broadband integrated optic spectrum analyzer IOSA requires a SAW transducer with a large bandwidth and low insertion loss. Several approaches have been investigated for this application including composite transducers made up of several transducers with staggered synchronous frequencies, phased array transducers, as well as chirp type transducers. A novel modification of the chirp transducer was employed in this study. In this design the electrode spacings and the electrode tilt angles are varied smoothly over a range of values that is synchronous with the range of frequencies in the desired response. By varying the tilt angle the Bragg condition can be met at all frequencies. As a result the Bmgg acousto-optic bandwidth is independent of the acoustic aperture. There are several additional advantages which result from using a chirp type transducer. The total number of electrodes can be selected primarily to satisfy impedance matching conditions to achieve low insertion loss instead of being determined by the required bandwidth, and using larger numbers of electrodes reduces electrode resistance effects. Also the chirp transducer can handle larger peak power levels which is particularly important for the IOSA.

Analysis of a dual-frequency array technique

Abstract: This paper describes the radiating properties of a new element for a dual-frequency phased array that operates over two frequency bands separated by about an octave. The analysis considers the array element excited by two waveguides for high-frequency operation, and includes an evaluation of the element radiation properties at both frequency bands. The analysis of radiation is carried out for the case of H -plane scan, which is expected to be the most severe test of the element's scanning behavior. Computed results indicate that the structure radiates efficiently within the two bands and operates free from anomalous behavior over substantial scan angles. These results demonstrate the feasibility and practicality of the basic concept.

Ultrasonic material fault detector using sector-shaped scanning beam - which is provided by phased array and measuring characteristic of max. echo amplitude curve

Abstract: The fault detector uses ultrasonic waves provided by a phase-controlled array, with differing radiation angles relative to the tested material. The combined radiated beam covers an angular secotr of 90 deg., with the returned echo signals synchronously displayed on a viewing screen. This provides a spread out sector image, with the periodic position variation of the defect echo used to obtain the fault parameters. Pref. the max. signal amplitude (Ux) is determined for different points (x) along the scanned sector, with the highest point of the curve displaying the max. signal amplitude occuring directly above the fault, where the length of the wave propagation path is least. The sharpness of the curve gradient either side of the highest point is measured to obtain the angle at which the flow lies relative to the material surface etc.

Position-modulated phased array-space factor considerations

Abstract: The space factor of an element position-modulated array is expressed as an Anger function series for a general amplitude distribution. The behavior of the main lobe and the diffraction sidelobes for uniform excitation are presented in the form of universal curves. It is found that the nulls near the main lobe disappear for the modulation index above a critical value. The peak level of the grating plateaus and their shapes are given in terms of approximate expressions and are exactly determined computationally. The nature of the curves suitable for design of such arrays for a given scan range and permissible peak sidelobe level is given. An example shows that a high resolution beam may be obtained with a comparatively smaller number of elements than required by a uniformly illuminated periodic array. An exact-series summation formula for the directivity of nonuniformly spaced antenna arrays of isotropic elements is given. The directivity of the modulated array computed by this formula shows a smooth variation at the ends of the scan range in contrast to the sudden fall in the case of the periodic array.

Admittance analysis of nonuniformly spaced phased arrays of waveguide apertures in a ground plane

Abstract: A general formulation for the analysis of a phased array of waveguide apertures in a common ground plane has been given for finite number of elements and nonuniform spacings based on network representation of the system. The analysis yields the radiation pattern, reflection coefficient, and aperture field in each waveguide. The pattern of an array of physically identical elements is expressed as superposition of patterns of infinite number of arrays. The formulation, when applied to single and two aperture cases, confirms the known results. It is then applied to investigate the properties of the element position modulated phased array of 15 rectangular waveguide apertures excited by uniform incident waves. Uniformly spaced arrays are also analyzed for comparison. The dominant mode and one higher order evanescent mode are included in the computations. The results show that the overall power reflection coefficient of the nonuniform array does not undergo any peaks over a wide scan range. It is concluded that the advantages of nonuniformly spaced arrays in suppressing grating lobes and eliminating blind spots are physically realizable.

Factors Affecting the Performance of Adaptive Antenna Systems and Some Evaluation Techniques.

Abstract: : The basic performance of an adaptive antenna system is influenced somewhat independently by two sub-systems: the antenna and the adaptive processor. Choice of the antenna type (multiple beam antenna or phased array) and the design of the adaptive processor (which is used to control the weighting at each antenna feed port) depends strongly on the specific requirement of a particular system. To date, much has been published on the ideal performance characteristics of adaptive nulling antenna systems. However, little has been published on the effects of hardware component imperfections on system performance. To characterize these effects is the purpose of this note. We present methods for categorizing, analyzing and measuring the effects of a few of the key components which are common to the majority of adaptive systems implemented to date. Some examples we will discuss are those effects due to antenna type, antenna tolerance errors, channel tracking errors, weighting circuits, hard-limiters, correlators and base-band components. We analyze these from the viewpoint of the degree of cancellation achievable by the adaptive processor and also their impact on loop dynamics (where appropriate). In order to illustrate the various effects, measured performance results obtained using an experimental Applebaum-Howell type adaptive processor will be presented. (Author)

Currents on generalized yagi structures

Abstract: Characteristics of currents produced on an infinite linear array of parasitic radiators when one of the radiators is excited are found. Yagi antennas use arrays of electric dipoles; detailed analyses and results are given for a generalized Yagi structure in which the dipoles are inclined at an arbitrary, angle to the array axis. These results suggest a simple mechanical means for broadbanding. Calculations are carried out within a network formulation. The integral solution obtained from this formulation is used to demonstrate the interrelation between the properties of the array of radiators excited parasitically or excited as a phased array. The solution simplifies remarkably when the angle of inclination of the dipoles is 54.74\deg . The surface-wave components and the (feed) correction currents are then explicitly evaluated. Although for conventional Yagi structures surface-wave solutions have been found only for capacitive dipoles, for sufficiently small angles of inclination surface waves can exist on arrays of inductive dipoles.

Phased array antenna system

Abstract: PURPOSE:To increase the scanning velocity by performing the scan within the horizontal plane in an electronic way and the scan within the vertical plane in a mechanical way respectively, and thus to form an economical radar antenna.

Near-Field Theory and Techniques for Wideband Radiating Systems at In-Band and Out-of-Band Frequencies.

Abstract: : Theoretical and numerical analyses were performed to study the application of near-field theory and techniques to characterize the radiation and coupling characteristics of wideband, in-band and out-of-band pulsed or cw radiating systems Specifically, theory and equations were developed for characterizing the radiation patterns of wideband cw or pulsed antennas over both in-band and out-of-band frequency intervals from measured data collected via near-field measurement techniques The results are applicable to either phased array or reflector antennas Three analytical techniques for analyzing the in-band and out-of-band coupling between pairs of cosited antennas were studied The three techniques are (1) the Plane Wave Spectrum (PWS), (2) the Spherical Wave Spectrum (SWS), and Geometrical Theory of Diffraction (GTD) The existing theory and equations that are applicable to selected common waveguide components under normal in-band operation were extended to describe wideband out-of-band responses Also, the theory and equations were formulated for computing the higher-order mode coefficients at the aperture of a waveguide radiating element from a knowledge of the measured far-field electric field of the radiating element when surrounded by a large conducting ground plane