Showing papers on "Antenna array published in 1990"

The performance enhancement of multibeam adaptive base-station antennas for cellular land mobile radio systems

Abstract: The problem of meeting the proliferating demands for mobile telephony within the confinement of the limited radio spectrum allocated to these services is addressed. A multiple-beam adaptive base-station antenna is proposed as a major system component in an attempt to solve this problem. The approach is demonstrated by employing an antenna array capable of resolving the angular distribution of the mobile users as seen at the base-station site, and then using this information to direct beams toward either lone mobiles, or groupings of mobiles, for both transmit and receive modes of operation. The energy associated with each mobile is thus confined within the addressed volume, greatly reducing the amount of cochannel interference experienced from and by neighboring cochannel cells. To ascertain the benefits of such an antenna, the conventional and proposed antenna systems are modeled in a typical mobile radio environment. For a given performance criterion, the theoretical results indicate that a significant increase in the spectral efficiency, or capacity, of the network is obtainable with the proposed antenna. >

Mutual coupling compensation in small array antennas

Abstract: A technique to compensate for mutual coupling in a small array is developed and experimentally verified. Mathematically, the compensation consists of a matrix multiplication performed on the received-signal vector. This, in effect, restores the signals as received by the isolated elements in the absence of mutual coupling. This technique is most practical for digital beamforming antennas where the matrix operation can be readily implemented. >

Spectral self-coherence restoral: a new approach to blind adaptive signal extraction using antenna arrays

Abstract: A new approach to blind adaptive signal extraction using narrowband antenna arrays is presented. The approach has the capability to extract communication signals from cochannel interference environments using only known spectral correlation properties of those signals, i.e. without using knowledge of the content or direction of arrival of the transmitted signal, or the array manifold or background noise covariance of the receiver, to train the antenna array. The class of spectral self-coherence restoral (SCORE) objective functions is introduced, and algorithms for adapting antenna arrays to optimize these objective functions are developed. Using the theory of spectral correlation, it is shown by analysis and simulation that these algorithms maximize the signal-to-interference-and-noise ratio at the output of the narrowband antenna array when a single communication signal with spectral self-coherence at a known value of frequency separation, along with an arbitrary number of interferers without spectral self-coherence at that frequency separation, are impinging on the array. >

Combinations of an adaptive array antenna and a canceller of interference for direct-sequence spread-spectrum multiple-access system

Abstract: In the realization of code-division multiple access based on a spread-spectrum communication system, i.e. spread-spectrum multiple access (SSMA), reduction of cochannel interference is an important problem. An adaptive array antenna system is proposed that includes a cancellor of cochannel interference, which can improve performance by a combination of temporal and spatial filtering. While the adaptive array suppresses interference sources with arrival angles different from those of the desired user, the adaptive digital filter-canceller rejects those whose arrival angles are the same as those of the desired user. The proposed system can achieve stable acquisition and low error rate of demodulated data even in a heavy-interference channel where a conventional array antenna system cannot achieve satisfactory acquisition. >

Intersection approach to array pattern synthesis

Abstract: The array synthesis problem is of utmost importance and therefore a large number of papers have been devoted to it. A new synthesis method based on the intersection approach is presented: the synthesis is viewed as the problem of finding the intersection of sets. This is a more natural, flexible and effective formulation of the problem but despite this it has not previously received much attention. The search for a point belonging to the intersection of two sets allows a very effective solution procedure, based on the projector concept and on a suitable choice of the starting point of the iteration. A number of one and two dimensional examples are presented to highlight the various aspects of the method. Emphasis is put on constrained array synthesis which is important when the practical realisation of the synthesised array is of concern. The method permits the synthesis of constrained patterns without appreciable degradation of the pattern desired.

A numerical pattern synthesis algorithm for arrays

Abstract: A numerical technique for pattern synthesis in arrays is presented. For a given set of elements, the technique allows one to find a set of array coefficients that steer the main beam in a given direction and yield sidelobes meeting a specified criterion, if such a set of array coefficients exists. If the pattern specifications cannot be met with the given elements, the algorithm finds the best attainable pattern. The advantage of this technique is that it can be used with an arbitrary set of array elements. Different elements in the array can have different element patterns, and the array can have arbitrary nonuniform spacing between elements. The synthesis technique is based on adaptive array theory. The given array elements are assumed to be used as the elements of an adaptive array. The main beam is pointed in the proper direction by choosing the steering vector for that direction, and the sidelobes are controlled by introducing a large number of interfering signals at many angles throughout the sidelobe region. The algorithm iterates on the interference powers until a suitable pattern is obtained. >

Monolithic millimeter-wave two-dimensional horn imaging arrays

Abstract: A monolithic two-dimensional horn imaging array has been fabricated for millimeter wavelengths. In this configuration, a dipole is suspended in an etched pyramidal cavity on a 1- mu m silicon-oxynitride membrane. This approach leaves room for low-frequency connections and processing electronics. The theoretical pattern is calculated by approximating the horn structure by a cascade of rectangular-waveguide sections. The boundary conditions are matched at each of the waveguide sections and at the aperture of the horn. Patterns at 93 and 242 GHz agree well with theory. Horn aperture efficiencies of 44+or-4%, including mismatch and resistive losses, have been measured. A detailed breakdown of the losses is presented. The coupling efficiency to various f-number imaging systems is investigated, and a coupling efficiency of 24% for an f0.7 imaging system (including spillover, taper, mismatch and resistive losses) has been measured. Possible application areas include imaging arrays for remote sensing, plasma diagnostics, radiometry and superconducting tunnel-junction receivers for radio astronomy. >

Phased array for millimeter wave frequencies

Abstract: A phased array is presented at a frequency of 70 GHz, consisting of a corporate feed, ferrite phase shifters and dielectric rod antennas. Metal waveguides were utilized to construct the feed network, whereas a special dielectric waveguide structure was employed for the ferrite phase shifter and dielectric rod antenna. Beam scanning can be performed electronically controlled in the horizontal plane.

Design considerations for low sidelobe microstrip arrays

Abstract: The factors affecting the realizable sidelobe performance of microstrip arrays are discussed and quantified. These include excitation amplitude and phase accuracies, mutual coupling, diffraction effects, positioning errors, and errors due to imperfect element matching and feed network isolation. It is shown that low-sidelobe microstrip arrays require a very tight tolerance on the resonant frequencies of the elements, and the elimination of spurious radiation from the feed network. Cross-polarization and surface wave effects are discussed. An experimental 16-element microstrip array prototype incorporated these considerations into the design, and achieved a -35 dB relative sidelobe level. >

Linear antenna array pattern synthesis with prescribed broad nulls

Abstract: A technique of synthesizing an antenna array pattern with prescribed broad nulls is presented. The array pattern synthesis problem is formulated as a least-square null constrained optimization problem. Numerical techniques based on the matrix factorization method are developed for reducing the computational complexity of determining the optimal weight vector. Subsequently, a set of eigenvector constraints are used to approximate the effect of the quadratic constraint. Numerical results are presented to illustrate the performance achievable. >

A photonic variable RF delay line for phased array antennas

Abstract: It is shown that by applying spatial frequency-dependent phase compensation in an optical heterodyne process a variable RF delay line can be synthesized over a prescribed frequency band. Experimental results which demonstrate the performance of the delay line with regard to both maximum delay and resolution over a broad bandwidth are presented. A spatially integrated optical system is proposed for control of phased array antennas. The integrated system provides mechanical stability essentially eliminates the drift problems associated with freespace optical systems, and can provide high-packing density. The approach uses a class of spatial light modulator known as a deformable mirror device and leads to a steerable arbitrary antenna radiation pattern of the true time-delay type. >

Convergence of the SMI and the diagonally loaded SMI algorithms with weak interference (adaptive array)

Abstract: Approximations for the power levels at the output of an adaptive array that uses the diagonally loaded sample matrix inversion (SMI) algorithm are derived. Diagonal loading is a technique where the diagonal of the covariance matrix is augmented with a positive or negative constant prior to inversion. The authors examine how the signal-to-interference-plus-noise ratio (SINR) and signal-to-interference ratio (SIR) at the array output vary with the number of samples taken when the input signals are continuous wave. It is shown that positive loading produces more rapid convergence with a reduction in output SIR. Negative loading provides an improved SIR level, but it is shown that positive loading produces more rapid convergence with a reduction in output SIR. Negative loading provides an improved SIR level, but it is shown that the output power levels are erratic and slow to converge. Simulation results which verify the theoretical procedure are given. >

Performance of phased array antennas with mechanical errors

Abstract: The performance of planar phase-array antennas with mechanical errors is investigated. Errors in array element positions as a result of structural distortions are considered as deterministic and predictable. Detailed calculations for two assumed modes of distortion reveal that their effects on antenna performance are the loss of peak response in the scan direction and the broadening of the mainlobe, while the far-out sidelobe structure remains relatively intact. For large antennas, performance improvement can be expected by suitable phase compensation. Performance of antennas with random errors in their element positions must be treated statistically. Expressions of average directivity and sidelobe level corresponding to arbitrary error magnitudes in element position, amplitude and phase of excitation as well as finite rate of failure of element modules were derived and verified by direct numerical calculations from the antenna directivity patterns. For a planar phased-array antenna typical for space-based radars, the standard deviation of element position errors must not exceed 1% of the operating wavelength in order to maintain a -10 dBi sidelobe level. >

Apparatus for locating concealed electrical conductors

Abstract: An apparatus and method for determining the location of a concealed conductive object. The method includes the steps of determining the lateral position of the object by using an antenna array to detect a signal propagating on the object. The antenna array is comprised of at least one center antenna positioned perpendicular to a surface concealing the object and at least two antennas symmetrically positioned about the center antenna at angles not equal to ninety degrees. The depth of the concealed object is determined by using a bottom sensor to detect the signal propagating on the object as a first signal. A vertically displaced top sensor then detects the signal as a second signal which is amplified by a variable gain amplifier until it equals the first signal. The depth of the object is calculated from the gain increase required to achieve equality between the first and second signals. The variable gain amplifier comprises a plurality of iteratively connected amplifiers whose gains are set by digital commands from an up/down counter. The gain increase is determined by a direct current, digital-to-analog converter amplifier which receives the same digital commands as the variable gain amplifier. The lateral direction to the object is determined by comparing the phase of the signal generated by the antenna array to a reference phase.

A systolic array processor for MVDR beamforming

Abstract: The authors describe a novel systolic array which can efficiently compute the minimum variance distortionless response (MVDR) from an array of antenna receiver elements in a rapidly changing signal environment. The MVDR beamforming problem amounts to minimising, in a least squares sense, the combined output from an antenna array subject to K independent linear equality constraints each of which corresponds to a chosen 'look direction' The constraints are independent in the sense that, for each new vector of received data samples, it is necessary to compute the minimum array output subject to each constraint in turn. This involves the solution of K independent, but closely related, least squares minimisation problems.

Monopulse phased array antenna with plural transmit-receive module phase shifters

Abstract: A monopulse antenna array arrangement includes a transmit-receive processor (TR Proc) associated with each antenna element. Each TR Proc has a port associated with the radiating element and at least two further ports, one for a sum beamformer and another for a difference beamformer. Within each TR Proc, a switching arrangement allows transmitter signal to flow through a phase shifter and transmit amp during transmission, and allows received signal to flow through a low-noise amp and the same phase shifter on reception. Each TR Proc includes a coupling arrangement with a second phase shifter and a second output port, adapted to be coupled to a difference beamformer during reception.

Analysis of slot coupling in a radial line slot antenna for DBS reception

Abstract: A radial line slot antenna (RLSA) is a nonresonant multimode waveguide slotted array. The slot coupling to the radial waveguide in this antenna is analysed. A parallel plate waveguide with a periodic boundary condition is used to simulate a sectral region of the circular aperture in a RLSA. A set of integral equations for the fields in the slot is derived, based on the field equivalence theorem, and is solved numerically by Galerkin's method. Theoretical results effectively express the measured effects of the various antenna design parameters on the slot coupling.

Low impedance printed circuit radiating element

Abstract: A printed circuit radiating element comprises a geometrically symmetric planar area of a conducting material separated from a ground plane by a dielectric medium. The driving point of the radiating element is at the base of a notch in one side thereof so that the driving impedance is reduced from that obtained when the element is driven at its edge. Symmetrically disposed on opposite sides of an axis of symmetry of the element along which the driving point lies are two notches which restore the electrical symmetry of the radiating element thereby to suppress higher order modes. The suppression of these higher order modes results in a radiation pattern with minimal cross-polarized energy in the principal planes and high port-to-port isolation which could not be achieved with an asymmetrical element. Two driving points may be employed with the radiating element to produce a dual linearly polarized antenna and a reactive combiner or hybrid may be employed to obtain circularly-polarized radiations. The shape of the radiating element may be square, rectangular or circular, for example, in accordance with the desired characteristics. A plurality of radiating elements may be interconnected via appropriate transmission paths to form an antenna array.

Asymmetric ridge waveguide radiating element for a scanned planar array

Abstract: A novel linear array radiating element for use in a large low-sidelobe, planar slot array electronically scanned in azimuth is described. The planar array consists of many vertical resonant linear array elements; i.e. single ridge waveguides with broadwall shunt slots, closely spaced to avoid array grating lobes when the array is scanned in azimuth. Traditional linear broadwall slot arrays require alternating slot displacement from the waveguide centerline, which generates undesirable secondary beams in skewed directions during electronic scan. To eliminate the secondary beams, a design has been devised in which all slots are exactly collinear and lie on the waveguide centerline. The methods considered to achieve the required waveguide asymmetry, the design procedure used in the successful approach, and the experimental results obtained with a demonstration model are presented. >

A unified approach to the design of robust narrow-band antenna array processors

Abstract: A unified approach to the design of robust narrowband antenna array processors is presented. The approach is based on the idea of minimizing the weighted mean-square-deviation between the desired response and the response of the processor over variations in parameters. Three specific examples of robust design are considered: robustness against directional mismatch, robustness against array geometry errors, and robustness against channel phase errors. Initially, a general quadratic constraint on the weights is developed. However, it is then shown that the quadratic constraint can be replaced by linear constraints or at most linear constraints plus norm constraint. These latter constraints are no more complex than those required for designs which do not incorporate robustness features explicitly. Numerical results show that the proposed approach appears to offer a unified treatment for directly designing narrowband processors which are robust against various types of errors and mismatches between signal model and actual scenario. >

High‐power radiating facility at the HIPAS Observatory

Abstract: UCLA's radio frequency ionospheric heater, 25 miles (40 km) east of Fairbanks, Alaska, is described. The heater consists of eight crossed dipole antennas arranged in a circular pattern to give a gain of 18.4 dB over isotropic at 2.85 MHz (˜ 2nd electron cyclotron harmonic). At 1.2 MW total radiated power the array has a calculated equivalent radiating power of 84 MW. Each antenna is driven by a 150-KW transmitter, originally from the Platteville heater. The eight transmitter antennas are managed by a personal computer which controls power, modulation, and beam steering. Methods of tuning the antennas, to achieve either right (O mode) or left (X mode) circular polarized radiated beams, are described. The heater is powered by two 1500-horsepower diesel electric generators. It can be operated throughout the year over −30°C to 40°C ambient temperature extremes. Future improvements include the construction of an even larger 840 × 840 m (24 × 24 antenna) array with a gain of 37.5 dBi.

Beamforming in the presence of correlated arrivals using structured correlation matrix

Abstract: Expressions are derived for the SNR (signal-to-noise-ratio) at the output of two antenna array processors in the presence of correlated arrivals, and the effect on the output SNR of the magnitude and the phase of the correlation, the number of elements in the array, the direction of the level of the interference source, and the level of the uncorrelated noise is investigated. The two processes considered are the optimal element space processor (ESP) and the optimal postbeamformer interference canceller (PIC). The PIC processes the signal by forming two beams and adjusting the weights of one beam, in contrast to the ESP where the signals from all the elements are weighted and all the weights are adjusted. A method is proposed for decorrelating the correlated sources, and an analytical expression is derived to show the decorrelation effect of the proposed technique for a line array of equispaced elements. Numerical examples are included. >

Matching slot pair for a circularly-polarised slotted waveguide array

Abstract: A matching slot pair which radiates all the incident power in a circularly-polarised wave is proposed and analysed for use as a terminal in a leaky-wave slotted waveguide array. The position and size of the slots are numerically optimised to suppress reflection and to realise a desired polarisation in the tilted beam direction, which contributes to improving the antenna efficiency. It is verified experimentally that the return loss is below -15 dB over 0.1 GHz at the 4 GHz band and the 3 dB axial ratio bandwidth is about 5% in the tilted beam direction. >

Beam steering module

Abstract: A beam steering module for rapidly applying control signals to a plurality of digital phase shifters in a phased array antenna system. The module can receive and store a plurality of phase shift commands for a plurality of phase shifters. The commands may be quickly applied to the phase shifters to rapidly steer the beam from the antenna array.

Active patch antenna element for array applications

Abstract: A packaged microwave FET has been integrated directly onto a rectangular patch antenna, forming an active radiating element for array applications. The FET is mounted across a narrow slot in the patch, and operates in a single bias, common-source configuration. A total radiated power of approximately 6 mW was measured at 8.2 GHz.

Evaluation of adaptive phased array antenna, far-field nulling performance in the near-field region

Abstract: A theory for analyzing the behavior of adaptive phased array antennas illuminated by a near-field interference test source is presented. Conventional phased array near-field focusing is used to produce an equivalent far-field antenna pattern at a range distance of one to two aperture diameters from the adaptive antenna under test. The antenna is assumed to be a linear array of isotropic receive elements. The interferer is assumed to be a bandlimited noise source radiating from an isotropic antenna. The theory is developed for both partially and fully adaptive arrays. Results are presented for the fully adaptive array case with single and multiple interferers. The results indicate that near-field and far-field adaptive nulling can be equivalent. The adaptive nulling characteristics studied in detail are the array radiation patterns, adaptive cancellation, covariance matrix eigenvalues, and adaptive array weights. >

A deformable mirror-based optical beamforming system for phased array antennas

Abstract: Microwave carrier generation along with the signal processing required for dynamic beamsteering of a high-resolution phased array antenna with an arbitrary radiation pattern is accomplished using optical components. It is shown that a deformable mirror type spatial light modulator can establish a truly arbitrary continuous optical phasefront which is directly converted to spatial RF phase information by an optical heterodyne system. Experimental results simulating the performance of the actual system are presented. A spatially integrated optical implementation providing mechanical stability and essentially eliminating the drift problems usually encountered in free space systems is presented. >

Improved adaptive-beamforming target for self-calibrating a distorted phased array

Abstract: An improved adaptive beamforming procedure is presented for self-calibrating a distorted phased array. The multiple scatterer algorithm (MSA) combines the echoes from several range bins to synthesize a beamformer that is less perturbed by clutter than the basic dominant scatterer algorithm (DSA). It was tested using experimental microwave echoes from industrial sites near Phoenixville, PA. It was found that the MSA can synthesize a nearly ideal beamformer using the echoes from three range bins having good beamformers, and that it can improve the image quality using the echoes from three bad beamformers, each of which is incapable of phase cohering the array by itself. >

Characterization of tapered slot antenna feeds and feed arrays

Abstract: A class of feed antennas and feed antenna arrays used in the focal plane of paraboloid reflectors and exhibiting higher than normal levels of cross-polarized radiation in the diagonal planes is addressed. A model which allows prediction of element gain and aperture efficiency of the feed/reflector system is presented. The predictions are in good agreement with experimental results. Tapered slot antenna (TSA) elements are used as an example of an element of this type. It is shown that TSA arrays used in multibeam systems with small beam spacings are competitive in terms of aperture efficiency with other, more standard types of arrays incorporating waveguide type elements. >

Modular transmitter and antenna array system

Abstract: A module for constructing a modular transmitter is disclosed. The module contains antenna elements along the front edge of a base. RF circuitry is fabricated on both the top and the bottom sides of the base. The base contains heat pipes to carry heat away from RF circuitry. The base is made to be plugged into a mounting block which provides electrical signals to the module and acts as a sink for the heat removed by the heat pipes.