Showing papers on "Phased array published in 1981"

Phased array theory and technology

Abstract: This review of array antennas highlights those elements of theory and hardware that are a part of the present rapid technological growth. The growth and change in array antennas include increased emphasis on "special-purpose" array techniques such as conformal and printed circuit arrays, wide angle scanning arrays, techniques for limited sector coverage, and antennas with dramatically increased pattern control features such as low sidelobe, adaptively controlled patterns. These new topics have substantially replaced large radar arrays in the literature and constitute a major change in the technology. The paper presents a tutorial review of theoretical developments emphasizing techniques appropriate to finite arrays, but indicating parallel developments in infinite array theory, which has become the useful tool for analysis of large arrays. A brief review of the theory of ideal arrays is followed by a generalized formulation of array theory including mutual coupling effects, and is appropriate to finite or infinite arrays of arbitrary wire elements or apertures in the presence of a conducting ground screen. Some results of array tolerance theory are summarized from the literature and retained as reference throughout discussions of array component requirements and device tolerance for low sidelobe arrays. Examples from present technology include conformal and hemispherical coverage arrays, lightweight printed circuit arrays, systems for use with reflectors and lenses in limited sector coverage applications, and wide-band array techniques.

Conceptual Performance of a Satellite Borne, Wide Swath Synthetic Aperture Radar

Abstract: A satellite borne synthetic aperture radar can image a wide swath in the order of 700 km with one-look 100-m resolution. If the design meets the ambiguity constraints at the far edge of the swath, the maximum swath width is independent of both radar wavelength and shape of the physical antenna aperture. The antenna pattern can be a pencil beam scanned in the elevation plane, or a fan beam formed by a long antenna. The scanning pencil beam antenna may be a phased array or multiple-feed reflector which may be more practical than a long antenna to image a wide swath. Design performance trade computations are presented involving resolution, swath width, antenna area, average transmitter power and digital data rate.

Phased array antenna employing linear scan for wide angle orbital arc coverage

Abstract: The present invention relates to phased array antenna arrangements which comprise a linear array of feed elements where the array has an aperture which is out at a bias angle along the minor axis of the array to produce a fixed linear phase taper along the minor axis by all elements Then by linearly scanning the array along the major axis of the aperture of the array, a beam is scanned along an arc which can be made to correspond to an orbital arc segment around a celestial body and within the field of view of the antenna arrangement when the bias angle is properly chosen The feed elements can comprise long feedhorns or horn antenna configurations which can be used in a separate array or disposed in an array on a conjugate plane of a main cylindrical reflector when used in multiple reflector phased array antenna arrangements

Scanning capabilities of large parabolic cylinder reflector antennas with phased-array feeds

Abstract: Two methods of scanning large parabolic cylinder antennas are examined: one method moves a small array across the focal plane to form a scanning beam; the other method employs a larger stationary array which is capable of electronically scanning the beam. With conventional single-element feeds, the maximum possible scan angle decreases with increasing reflector size. With array feeds, however, the scan limits are shown to be independent of reflector size and antenna gain. Antennas with movable array feeds are found to have high performance (high gain and low sidelobes) even when scanned more than ten degrees off axis; antennas with stationary array feeds degrade rapidly beyond about one degree of scan because of aperture blockage. Off-axis designs which eliminate the aperture blockage are shown to extend the coverage of antennas with stationary feeds to about \pm 5 degrees.

Non-Ideal Radiators in Phased Array Transducers

Abstract: One dimensional arrays for medical acoustic imaging are a group of point radiators. The individual r adiators (transducer elements) are modeled as single mode, piston v ibrators w ith negligible cross-coupling. It is straightforward to calculate the acoustic beam response -- steering, focusing, and resolution -- from such a model. In "real world" arrays with high element density the situation becomes more complex. Cross-coupling between elements and multi-moding of the individual elements become the dominant problems. The beam response then departs from the ideal. This paper will discuss the sources of cross-coupling and explore suppression techniques. The mass-spring mode will be reviewed, and novel suppression techniques will be presented. Vibration modes in a single element will be explored, in particular, the relation between the non-ideal behavior of the array elements and the resulting beam response deficiencies.

Distributed beam steering computer

Abstract: A distributive beam steering computer network for a radar phased array antenna is disclosed which provides direct drive for individual antenna phase shifter elements using a plurality of microcomputers co-located with each phase shifter. The microcomputers calculate the phase shift based on constants stored in a ROM which is located in each microcomputer and phase shift data comprising sin α, sin β, and 1/λ signals are distributed to all microcomputers over a single serial data line. The constants required for each shifter are different, and therefore, the ROM in each microcomputer is programmed for a specific location in an array antenna. A phase shift steering command for each element of the phased array antenna is calculated using a shift-and-add multiplication algorithm which is hard-wired into each microcomputer.

Cavity/microstrip multi-mode antenna

Abstract: A microstrip backfire antenna configuration combining the microstrip type tenna element with a waveguide cavity which provides control over the radiation pattern and obviates the need for a more expensive phased array antenna system; the microstrip element is placed in a waveguide cavity so as to excite both the microstrip element and the waveguide cavity in a predetermined manner.

Delay Quantization Error in Phased Array Images

Abstract: Time quantization errors in phased array systems can cause increased sidelobe amplitude, thereby limiting the dynamic range of the ultrasound system. A simulation program predicting the position and amplitude of these anomalous quantization error grating lobes has been developed to study the effects of transmitted pulse length on the ampli- tude of these anomalous lobes. Three parallel processing techniques for decreasing these sidelobe amplitudes while smoothing the speckle pat- tern are investigated.

Phased array system to produce, steer and stabilize non-circularly-symmetric beams

Abstract: A phased array antenna system for eliminating antenna induced errors and distortions comprising an antenna array consisting of orthogonal rows and columns of antenna elements in which each row of elements is supplied signal power by a single beam forming network. Each input port of the beam forming network corresponds to an element of only one of a number of composite beam constituents which, when combined, form the complete composite beam. The beam constituents are adjusted in position to correct the composite beam shape as necessary by means of plurality of phase shifters, each of which is placed in series with only one input port of the beam forming networks. This unique positioning of the phase shifters in the antenna distribution system reduces the total number of phase shifters required to control the beam, permits the forming of a shaped beam such as a fan beam without the need for amplitude control and simplifies the complexity of the phased array control system.

Target simulation system

Abstract: The target simulation system includes a reflector 18 located within a closed and shielded room 10. An array 30 of transmitting elements is located within an opening 22 of the room so that the array is centered at a first focal point F1 of an ellipsoidal reflecting surface 18A of the reflector, and a receiving element of the target seeker 34 to be tested is located within an opening 24 so that the receiving element is centered at a second focal point F2 of the ellipsoidal reflecting surface. Phased array control system 32 causes the array to simultaneously and independently transmit a plurality of beams of radiation toward the reflector and each transmitted beam results in a corresponding reflected beam whose beam axis passes through the second focal point of the array so that each reflected beam simulates radiation coming from a distinct target. In the case where the radiation is electromagnetic radiation in the MMW range, the phased array control system (FIGS. 2 and 3) performs all phasing and modulation that is required for the steering and focusing of each beam and for the simulation of target range, target characteristics and target seeker characteristics at an intermediate frequency.

Modeling Wavefronts from Acoustic Phased Arrays by Computer

Abstract: A computer simulator is described which allows the study in the near field of acoustic pressure waves generated by a linear phased array excited with short pulses. The simulator provides two-dimensional (2-D) and three-dimensional (3-D) representations of acoustic wavefronts and receiver sensitivity patterns generated by a pulsed phased array. Using the computer simulator, several phased arrays are studied to investigate transient effects in an area covering the near field of the corresponding unfocused arrays. Weak and strong focusing are compared. An algorithm for the optimal quantization of time delays, acoustic beampatterns and the structure of sidelobes and grating lobes are analyzed.

Ultrasonic diagnostic equipment

Abstract: In an ultrasonic diagnostic equipment which irradiates a subject with ultrasonic waves and receives reflected waves responsive thereto so as to provide a tomogram of the subject on the basis of the received signals, two tap-changing type phased arrays having different focal sections are alternately operated during a period of the reception of the reflected waves, and while one of the phased arrays is being operated, the tap changing of the other phased array for altering the focal section is made. In spite of reduced numbers of high-class switches and phased arrays used, spike noise due to the changes-over of switches during the dynamic focusing are prevented.

An extremely lightweight fuselage-integrated phased array for airborne applications

Abstract: A design of a lightweight low volume electronically scanned antenna is described. This antenna, besides being the radiating aperture, serves as a load-sharing fuselage panel in a small weight-sensitive remotely piloted vehicle (RPV). A demonstration array incorporating the microstrip radiating elements, stripline feed circuit, and microstrip-line p-i-n diode phase shifters was assembled to evaluate the electrical characteristics and scanning capabilities of the array. The demonstration array was tested on the antenna range and operated successfully as part of a radar/communication subsystem demonstration. An eight-element lightweight section of the demonstration array was subsequently designed and fabricated in a modern production facility utilizing numerically controlled machines and state-of-the-art printed circuit board etching and plating equipment. Successful operation of this lightweight section sufficiently demonstrated that a lightweight and low volume electronically steerable phase-array antenna can be fabricated and integrated into a structural panel in production quantities.

Electronically Variable Surface Acoustic Wave Time Delay Using a Biasing Electric Field

Abstract: Experimental Results The influence of a biasing electric field on the propagation of surface acoustic waves in LiNbO?, LiTaOg, and PbTi03 ceramic substrates is experimentally investigated. The 128" rotated Y- cut, X-propagating orientation of LiNb03 shows a linear and fairly large variation of time delay with the biasing field. Fractional time delay changes greater than 9xlO* have been obtained, and values upto 0.16 percent appear possible in SAW devices fabricated on this material. These changes in time delay are adequate to make the technique useful for several applications. Possible applications of this effect for beam steering in phased array antennas, measurement of high voltages, and temperature compensation in SAW devices are discussed.

Signal processing for target detection in experimental phased-array radar ELRA

Abstract: The concept and some experimental results of the phased-array system ELRA are presented, with emphasis on signal processing for target search. Multiple beams together with a variable number of pulses in each beam position are used for sequential detection and also for search in clutter by applying a recursive filter against stationary target echoes. New considerations concerning the practical application of sequential detection for multiple range elements, even in cluttered areas, are discussed.

An antenna beam steering technique comprised of constant-phase array elements

Abstract: Beam steering is normally achieved by the use of phase shifters at each element of an array. The phase taper thereby produced causes a shift of the far-field pattern in sin θ space. An alternate approach to beam steering is presented in which a pair of interleaved arrays are employed. One array of the pair is fed entirely by currents of zero phase, while the other array is fed entirely by currents of quadrature phase. Beam steering is done by control of amplitude at each element. An example of this technique is presented and discussed.

Phased array antennas using frequency multiplication for reduced numbers of phase shifters

Abstract: The present invention relates to a phased array antenna system which, in the transmission mode, forms a directional planar wavefront (20) including a signal at a first frequency at a first array (18 1 -18 m ) which is a sub-multiple of the frequency to be ultimately transmitted. By sending the wavefront through a lens or reflector, an image of the first array is formed on an image plane. A second array (26 1 -26 n ) disposed at the image plane intercepts the wavefront and the received signal's frequency and phase is then harmonically multiplied by a predetermined number to permit reradiation of the resultant signal by a third array (32 1 -32 n ) in the same direction as the original wavefront. The second and third arrays include corresponding elements and configurations with more elements than the first array. In the receive mode, the sequence is complementary to the transmit mode.

Directive antenna system employing a paraboloidal main dish and ellipsoidal subdish

Abstract: Directive antenna or radio telescope systems in which a large aperture objective directs incident electromagnetic energy onto a relatively much smaller field element which in turn directs it upon a small directive feed such as a phased array.

Tracking radar system

Abstract: A tracking radar system which includes a variable frequency oscillator for supplying to a vertical antenna array an oscillation frequency which is changed for each of a number of pulses transmitted from the antenna array. The antenna array transmits an electric wave toward a target at a low altitude and receives an echo from the target. An electronic computer estimates an elevation angle of the target from the echo received by the antenna array according to array aperture sampling technique for each pulse. An averaging circuit averages those estimated elevation angles of the target to provide its elevation angle. Alternatively, the oscillation frequency may change for each of finite time intervals.

Synthetic-Aperture Radar Based on Nonsinusoidal Functions: X-Array Gain, Planar Arrays, Multiple Signals

Abstract: Beam forming based on a line array of sensors and radio signals with a triangular autocorrelation function was discussed in Part IX of this series. The resolution angle e was shown to vary like 1/?P/PN with the signal-to-noise ratio P/PN, which puts a premium on getting the best possible signal-to-noise ratio. This paper shows that the signal-to-noise ratio holding for one sensor can be replaced by the signal-to-noise ratio holding for the whole array, which usually is referred to as making use of the array gain. The result is generalized from the one-dimensional line array to the two-dimensional planar array. Furthermore, the method of beam forming is extended from signals returned by point-like scatterers or reflectors to structures composed of several point-like scatterers; the utilization of the array gain has not yet been investigated for this case.

Principles of real-time two-dimensional B-scan ultrasonic imaging

Abstract: This review gives a brief outline of the situation that lead to the development of real-time 2-dimensional B-scanners followed by a discussion of the fundamental principles underlying real-time ultrasonic B-scanning and how they determine the performance ultimately achievable. The various types of scanner, linear array, phased array and mechanical, that have been developed and their salient features and modes of operation are reviewed together with their limitations.

Phased array signal processing

Abstract: A phased array radar system, such as may be used in a low-angle tracking radar or direction finding equipment, includes a multi-channel digital filter to remove unwanted multipath signals. The R.F. signals from the array are first converted to zero I.F. and digitized. After n-channel Doppler filtering (13) the digital signals are subjected to filtering (14) either to effect band-pass spatial filtering, thereby attenuating generally all signals arriving outside preset angular limits, or notch filtering which heavily attenuates signals arriving from one particular angle. In one embodiment spatial filtering is followed by notch filtering. The filtered signals are then beam-formed (15) before being applied to further digital processing, such as beam peak tracking (16).

Nulling performance of null-steering arrays with digital phase-only weights

Abstract: After a brief description of various application capabilities offered by phased array techniques, a simulated analysis is presented of null-steering arrays using microwave digital phase-only weights, i.e. in the presence of phase quantisation errors. It is shown that sufficiently good nulling performances requires only a small number of bits.

Wide Deterministic Nulling by Means of Multiplicative Array Techniques

Abstract: A method is proposed for suppressing extended clutter in "a priori" known region of space (e.g. along horizon) by means of an additional attenuation of antenna sidelobes. The reduction of antenna sidelobes is obtained through the non-linear control of a certain number of array elements. The method derives from multiplicative array theory. The system performance has been assessed by comparing the signal-to-noise power ratio of the multiplicative array with that obtained with an additive array followed by a square-law detector. Moreover, the clutter attenuation has been evaluated. The problem of cross-product terms in a complex multitarget environment is briefly revised. Finally, the random aperture errors and the multipliction accuracy are considered in the performance evaluation.

Non-resonant ultrasonic transducer array for a phased array imaging system using1/4 λ piezo elements

Abstract: A phased array transducer is disclosed for transducing ultrasound of a predetermined frequency. The transducer includes a number of piezoelectric elements, all having the same natural frequency, and having two surfaces located opposite to each other, each provided with an electrode. The distance between the two surfaces of each element is one quarter of the wavelength of the ultrasound produced by the transducer within the piezoelectric material.

Applications of a phased array antenna in a multiple maneuvering target environment

Abstract: The phased array antenna has the ability to perform adaptive sampling by directing the radar beam without inertia in any direction. This property has the potential for significant performance improvements in many aspects of the multiple maneuvering target tracking problem. This paper begins by outlining a general method by which several of the recently developed approaches to the multiple target tracking problem will be combined in a system using a phased array type antenna. The general approach is to use gating and other tests to define the tracking environment and then to choose the appropriate tracking methods and sampling interval. Detailed methods and results are presented for two specific areas. These are the application of a phased array antenna to the detection and tracking of maneuvering targets and to the initiation of separate tracks on two closely spaced targets.

Non-dispersive array antenna and electronically scanning antenna comprising same

Abstract: Non-dispersive array antenna of the prism array type in which the primary dispersive input array and the secondary output array include an acute angle α between each other, made of a piling up of non-dispersive, monodimensional array antennas, in each of which the propagation between said arrays is guided. Application to electronic scanning antennas of the prism array type.

Digital control system for ultrasonic phased array - uses interruptions of clock signal to control intermediates storage via CCD delay lines

Abstract: The control system uses CCD delay lines. The transmission or reception signals to be delayed are temporarily stored in CCD delay lines of equal length by interruptions of a common clock frequency. These interruptions are each controlled by the output of a respective counter coupled to a start-stop logic. The interruptions may correspond to the time taken for the counter to count backwards to zero from an initial value. A required scan angle can be obtained by a preset linear increase in the counter states, while a quadratic increase is used to obtain variable or parabolic focussing of the sound beam. The direction of the latter is varied by adjusting the clock frequency. The phased array is used for workpiece flaw detection or analysis or for ultrasonic medical diagnostic appts.

A Thinned Cylindrical Array for Focused Microwave Hyperthermia

Abstract: A phased array configuration for microwave induced hyperthermia in cancer treatment is proposed with the objective of heating tumors deep within the body. The computer simulation consists of an elliptic cylinder representing the human thorax partially surrounded by a semi-circular array of radiators and a short linear array of radiators parallel to the main axis of the cylinder. This configuration of only 17 elements yields sufficient energy concentration at the desired location without excessive surface heating. Modification of the array illumination function allows a certain degree of control over the heated volume. The arrangement would be attractive in clinical practice since it neither requires contact nor close proximity to a patient as with radiation treatment in current practice.