Showing papers on "Antenna array published in 1984"

Scan blindness in infinite phased arrays of printed dipoles

Abstract: A comprehensive study of infinite phased arrays of printed dipole antennas is presented, with emphasis on the scan blindness phenomenon. A rigorus and efficient moment method procedure is used to calculate the array impedance versus scan angle. Data are presented for the input reflection coefficient for various element spacings and substrate parameters. A simple theory, based on coupling from Floquet modes to surface wave modes on the substrate, is shown to predict the occurrence of scan blindness. Measurements from a waveguide simulator of a blindness condition confirm the theory.

Analysis of inifinite phased arrays of printed dipoles

Abstract: The problem of a finite array of printed dipoles is treated, and results are presented in the form of reflection coefficient magnitudes, element patterns, and efficiency (based on power lost to surface waves). Various sized arrays are considered, and are compared with infinite array solutions. The excitation of surface waves is discussed in relation to the scan blindness phenomenon and the transition to an infinite array. Techniques for computational efficiency are also presented.

Finite periodic structure approach to large scanning array problems

Abstract: There are two conventional techniques dealing with mutual coupling problems for antenna arrays. The "element-by-element" method is useful for small to moderate size arrays. The "infinite periodic structure" method deals with one cell of infinite periodic structures, including all the mutual coupling effects. It cannot, however, include edge effects, current tapers, and nonuniform spacings. A new technique called the "finite periodic structure" method, is presented and applied to represent the active impedance of an array, it involves two operations. The first is to convert the discrete array problem into a series of continuous aperture problems by the use of Poisson's sum formula. The second is to use spatial Fourier transforms to represent the impedance in a form similar to the infinite periodic structure approach. The active impedance is then given by a convolution integral involving the infinite periodic structure solution and the Fourier transform of the equivalent aperture distribution of the current over the entire area of the array. The formulation is particularly useful for large finite arrays, and edge effects, current tapers, and nonuniform spacings can also be included in the general formulation. Although the general formulation is valid for both the free and forced modes of excitation, the forced excitation problem is discussed to illustrate the method.

Circular log-periodic direction-finder array

Abstract: A circular frequency-independent antenna array (10) includes a plurality of radially extending log-periodic subarrays (12, 14, 16, 18, 20, and 22) of slot radiators (26) provided in a ground-plane conductor (28). Associated with each slot is a cavity (34) into which the slot opens. A traveling-wave element in the form of a wire (30) cooperates with a ground-plane conductor (28) in which the slots are provided to support propagation of an electromagnetic signal. The signal is radiated upon encountering a slot that resonates at a frequency near that of the signal, and the depths of the cavities are adjusted so that the phase relationships between the radiation from the slots and the signal propagated along the traveling-wave element results in an antenna pattern that launches radiation in a direction away from the center of the array. Direction-finding errors are reduced because interference between the several subarrays is kept to a minimum.

Nulling a symmetric pattern location with phase-only weight control

Abstract: Sidelobe nulling at symmetric locations in linear array patterns can be accomplished with phase-only weight control if no restriction is placed on the magnitude of the phase perturbations. Nonlinear programming techniques can be used to calculate the required phases. Several examples are presented.

The mobile SOUSY Doppler radar: Technical design and first results

Abstract: On the basis of the experience obtained with the stationary SOUSY radar in the Harz mountains, a mobile VHF Doppler system was developed during the last two years. The electronic part is installed in a 20-foot container and was tested for the first time during a joint experiment at the Arecibo Observatory (Puerto Rico) using a special log-periodic aerial to illuminate the 300-m dish. In 1982 this system was extended by designing a mobile phased antenna array with 576 Yagi elements. The grouping of the single Yagis, the feeding network, the phase shifters, the power splitters, and the transmit receive switch are described. A summary of results obtained during the first two campaigns is presented as well as a survey of future programs demonstrating the flexibility of this mobile system.

Simultaneous nulling in the sum and difference patterns of a monopulse antenna

Abstract: Most adaptive array research has not directly addressed the problem of nulling in a monopulse antenna. Placing a null in the sum does not automatically place a null in the difference pattern and vice versa. Nulls may be placed in the two patterns with the use of separate adaptive weights and controls for the sum and difference channels. However, this requires two sets of adaptive hardware for one antenna. A technique for simultaneous hulling in the sum and difference channels of a monopulse phased array using one set of adaptive weights shared by both channels is described. First, the technique is described for amplitude and phase nulling, then for phase only hulling. In each case, the ability to simultaneously null in both channels with one set of variable weights is theoretically demonstrated.

Method of null steering without using phase shifters

Abstract: Null steering without using phase shifters is achieved by forcing the zeros of the array factor to occur in conjugate pairs on the unit circle in the complex plane. It is shown that if the number of jammers is much smaller than half the total number of elements in the array, it is possible to optimise the pattern as well as suppressing the jammers. Alternatively, wide nulls in the radiation pattern can be easily approximated.

Direction finding systems

Abstract: A DF system using a circular array of three to eight antennas, analyses the received signals digitally by first calculating at (8) the Fourier transform of the received signals to obtain frequency information and deriving at (10) from the Fourier transform the relative phases of the received signals at each of a number of spaced sample frequencies. This phase information is then fed to a stage (12) which takes the spatial Fourier series of the phases from which the required bearing information is derived as π/2 minus the arctan of the ratio of the real and imaginary parts of the Fourier series taken to suitable moduli. For a four antenna array the diameter of the circular array is constrained to be less than half of the wavelength at the highest frequency of interest. For a three antenna array, the diameter is constrained to be less than one third the wavelength at the highest frequency of interest in order that the analysis should yield accurate and unambiguous bearing outputs.

NMR antenna and method for designing the same

Abstract: An antenna system for nuclear magnetic resonance (NMR) imaging or spectroscopy devices which produce a uniform magnetic field in an object under examination includes transmit and receive antenna arrays each comprising a group of loop antennas. A signal generating circuit produces a set of input antenna signals which are applied to the loop antennas of the transmit array which transmits RF signals of a frequency that perturbs the magnetic moment of nuclei in a volume of the object. The receiving antenna array is responsive to NMR signals produced by the relaxation of perturbed nuclei in said volume for producing a set of output antenna that are applied to a signal processing circuit. A control circuit selectively controls the relative phases and amplitudes of at least one set of antenna signals to control the size and location of the region of the volume in which excitation of nuclei occurs, or from which NMR signals are processed. The relative phases and amplitudes can be controlled in such a way that nuclei in only a preselected region of the volume are excited, and that NMR signals from nuclei in only a preselected region of the volume are processed.

Guidance apparatus with dual mode sensor

Abstract: Guidance apparatus for a tactical guided missile uses a dual-mode sensor having both active millimeter wavelength RF sensing capability and passive infrared sensing capability within a single aperture. A dual reflector-antenna assembly is formed by chemical vapor deposition of dielectric material transparent to infrared and RF radiation. Embedded within the reflector assembly is an RF microstrip antenna array, formed by thin-film metalization techniques, which defines an antenna beam axis. A surface of the reflector assembly is ground, optically polished, and coated with infrared reflective material to form a primary reflecting surface of a Cassegrainian optical system, which also includes a secondary mirror, for defining an infrared detection beam axis coincident with the antenna beam axis. Infrared radiation from a target is concentrated by the Cassegrainian optical system onto an infrared detector to produce a first guidance signal. RF energy is supplied to the antenna array to be transmitted to and reflected from a target. Reflected RF radiation from the target is received by the antenna array to produce a second guidance signal.

Adaptive nulling in monopulse antennas

Abstract: Theoretical and experimental results are presented for phase-only nulling in low-sidelobe monopulse antennas. Both results are based on a gradient search algorithm that simultaneously searches for a minimum in the sum and difference channel output powers. The array's beam steering phase shifters double as the adaptive weights. Each element in the gradient is found by changing phase shifter setting by Delta Psi (the phase shifter stepsize) and measuring the change in output power. Then the phase shifter is restored to its original value, and the process repeated for all the remaining array phase shifters. The algorithm iterates as long as each new adaptive weight setting reduces the total output power. If the output does not go down, then Delta Psi is decremented by one setting and the iteration is started again. The algorithm stops when Delta Psi =0. The adaptive weights act as random perturbations to the phase taper of the array. Consequently, the sidelobe level is proportional to the size of the phase perturbations and inversely related to the number of elements. By keeping the adaptive phase shifts small, the average sidelobe level and the main beam gain do not drastically change. >

Borehole antenna array for determining radar incidence direction

Abstract: An antenna arrangement for use in a bore hole to receive radar signals and produce electrical signals from which the incidence direction of the radar signals can be determined includes a cross coil arrangement with two coils having elongated sides mounted adjacent the outer surface of a cylindrical insulative probe body. In one embodiment, one cross coil assembly is used in conjunction with an omnidirectional antenna and an evaluation circuit. In another embodiment two axially aligned cross coil assemblies are connected to also be usable as an omnidirectional antenna.

A Local Field Study of a Water-Immersed Microwave Antenna Array for Medical Imagery and Therapy

Abstract: A water-immersed microwave array system for medical imaging is described, and a theoretical analysis of its Iocal field pattern is presented. The theoretical study also applies to similar systems for medical therapy purposes. It is shown that, using a technique of phase and amplitude conjugations, a satisfactory three-dimensional focusing for targets located in the neighborhood of the array may be achieved. The focusing resolutions for transverse and Iongitudinal directions are approximately lambda/2 and lambda , respectively, where lambda is the wavelength in the dielectric. By increasing the element spacing of the array, the resolutions can be as good as 5.3 and 11.7 mm, respectively, at the operating frequency of 3 GHz.

The design of a slot array in nonradiating dielectric waveguide, part II: Experiment

Abstract: Measurement procedures for obtaining the self-impedance of an isolated inclined radiating slot in the metal wall of a nonradiating dielectric (NRD) waveguide are discussed. The design procedure for an antenna array fed by NRD-waveguide and making use of this information is described. As an example, the design, construction and evaluation of a ten-element input-matched broadside linear array is described.

Intruder detection radar system and automatic nulling antenna array

Abstract: A bistatic VHF Doppler radar is utilized to detect and track one or more intruders crossing a large annular ring surveilance zone surrounding a central high security installation. A central omni-directional transmitter radiates the surveillance zone with a continuous wave (CW) signal. Predetermined ones of a plurality of receiver antennas circumferentially spaced around the surveillance zone receive a portion of the signal which is reflected by an intruder crossing the surveillance zone and a portion of the signal which is directly radiated from the transmitter antenna. The reflected signal portion may be received by antenna arrays each of which is controlled to form a null in its pattern toward the transmitter antenna to overcome direct signal overload. The direct signal portion may be received by stub antennas. Each antenna array and each stub antenna is connected to a separate channel of a dual channel receiver. An intruder moving across the surveillance zone causes signals representative of Doppler cycles of phase change to be generated. The outputs of the two separate channels are compared and their relative phase changes measured. A detected intruder causes an alarm signal at a central processing station and the Doppler information is processed to generate tracking data which is shown on a display device. An automatic null control circuit may also be utilized to accommodate multipath conditions and static clutter due to environmental factors.

On the constrained synthesis of array patterns with applications to circular and arc arrays

Abstract: Synthesis of array patterns involving optimization with linear and nonlinear constraints is considered. The general solution for the composite weight vector can be decomposed into a part which satisfies the linear constraints and another lying orthogonal to it. This decomposition is shown to yield simple solutions to several beam optimization problems including some with nonlinear constraints. A geometrical derivation of this result is presented which also provides new insights into the mechanism of null-steering via linear constraints. Application of this approach in conjunction with some search algorithms to the synthesis of optimum array patterns with prescribed narrow or broad nulls is shown to yield interesting and useful solutions. The results are illustrated by considering the design of "circular" and "arc" arrays.

Extension of projection method to nonuniformly linear antenna arrays

Abstract: The study of linear arrays has been developed in different regions. The computerized techniques that appeared in this century motivated the researchers to find a new techniques that save time. In this work the method of succesive projection is used in solving the nonuniform space and phase arrays. This technique was used before to solve the nonuniform current arrays. The main concept of this method is to find a common point of many different sets. This point will have the best solution to satisfy all conditions. In this technique the solution of the set of inequalities is the main scope. The addition of one or more constraints to the array is only as adding one more set to the group of sets we have. This means that the solution of constrained arrays also is available. Several illustrations are discussed and compared with different other techniques. A simple program is available and easy to establish. In this work, the broadside direction pattern is divided into 180\deg that represent 180 sets. At each set the synthesized pattern must satisfy the desired pattern.

A proof of the odd-symmetry of the phases for minimum weight perturbation phase-only null synthesis

Abstract: It is proved that if phase-only weight control is used to impose nulls in a real pattern of a linear array of isotropic equispaced elements while minimizing the sum of the squares of the absolute weight perturbations then the phase perturbations are odd-symmetric with respect to a phase reference at the array center. Equivalently, the perturbed pattern is real.

Microstrip patch array antenna

Abstract: A microstrip array with mutual coupled rectangular patch radiators is described. By the avoidance of a corporate feeding network, advantages in the antenna performance and design are realisable. Experimental results are presented for both linearly and circularly polarised antennas which demonstrate the usefulness of this special antenna configuration.

Normalized relationship among errors and sidelobe levels

Abstract: This paper examines the effect of errors on the peak sidelobe level of a phased array. The sidelobe level distribution of the radiation pattern for both linear and planar arrays is seen to be Rician. A set of constant probability curves is presented which relates the allowable phase and amplitude errors with the allowable sidelobe level deterioration. Examples are presented to demonstrate how these curves can be used to design a low sidelobe array with a better tolerance of error. These curves, or extensions of them, provide a useful tool for the engineer designing an array antenna. For a planar array with correlated errors the total variance σ is the root-sum-square of the error in each element σμ (including both correlated and uncorrelated errors) and the contribution of correlated error in a subarray σc. Both σμ and σc are functions of the errors and the illuminations, but σc is also a function of the pattern of the subarray in which the errors are correlated.

On eigenvalues, SINR, and element patterns in adaptive arrays

Abstract: A simple relationship between the output signal-to-interference-plus-noise ratio (SINR) of an adaptive array and the eigenvalues of the associate signal covariance matrix is pointed out. For two simple cases involving continuous wave (CW) signals, it is shown that the eigenvalue associated with the desired signal is equal to the SINR plus one. This relationship is useful for understanding the effects of element patterns and spacings on eigenvalue behavior in adaptive arrays.

Method and apparatus for four-beam radar

Abstract: A method and apparatus for producing remote profiling beams pointing altetely to the north, east, west or south by ordered distribution of phase shifts to elements of a square antenna array. Elements within a given group of four array elements share a related group of four phase shift means. Elements in a group trade phase shift means intragroup but there is no intergroup trading. The arrangement permits four-beam capability without unduly increasing the cost or complexity of the radar assembly over prior art assemblies. Also disclosed is a system for "tipping" the array either virtually or physically to obtain a vertical beam.

Dipole ring array antenna for circularly polarized pattern

Abstract: A NAVSTAR satellite has a navigation antenna array beamed toward the earth. A communications antenna array for communicating with other satellites requires a pattern null near the axis and high gain to the sides with minimum losses. This is achieved with a dipole ring array comprising eight elements surrounding the navigation array. The ring has a diameter of 1.1 wavelength, and is fed with equal amplitudes and a third mode phase progression, which produces good circular polarization in the far field. For a different sized dipole ring, there will still be an optimum phase distribution which will give good circularly polarized patterns.

Phased antenna array for wind profiling applications

Abstract: A diagonal phased antenna array for use as a wind profiler by means of Doer shift measurements comprises a plurality of Yagi-Uda antennas which are oriented in a predetermined direction such that Yagi-Uda antennas have a polarization 45° offset from the principal planes of operation of the antenna array resulting in similar radiation patterns subject to a geometric taper in the array aperture with respect to the principal planes.

A formula for efficient computation of radiation from a current source in proximity to cylindrical scatterers

Abstract: A systematic and efficient two-dimensional method is presented for calculation of the three-dimensional radiation field from current sources which are located in proximity to long cylindrical scatterers. The method is applied to the calculation of the isolated-element pattern of a linear array of crossed dipoles (i.e., current sources) mounted above a long and narrow ground plane. Computed and measured results are given. The results are subsequently applied to the problem of prediction of the radiation characteristics of a cylindrical reflector antenna fed by such a linear array.

Borehole logging tool utilizing electromagnetic energy in the determination of dip of subsurface formations surrounding a borehole

Abstract: An electromagnetic borehole logging tool has at least two antenna arrays positioned at spaced-apart locations along the longitudinal axis of the borehole tool. Each antenna array has at least three sub arrays spaced approximately equally around the longitudinal axis of the tool. Each sub array has at least one antenna for transmitting and receiving electromagnetic energy. The three sub arrays of the first of the two antenna arrays are respectively located at approximately the same circumferential positions around the longitudinal axis of the tool as the three sub arrays of the second of the two antenna arrays. Each of the sub arrays transmits electromagnetic energy into the formations surrounding the borehole and receives electromagnetic energy upon its return to the borehole from such formations.

Self and mutual admittance between two concentric, coplanar, circular radiating current sources

Abstract: Radiation admittance for an annular ring microstrip antenna has been determined using the magnetic current model and the variational technique. The results obtained for self conductance of a ring source have been verified with those available in the literature. The expression obtained for mutual admittance can also be used to describe mutual coupling effects in an array of annular rings.

Electronic antenna array for a cellular radio telephone network with fixed base stations, and with mobile and portable units

Abstract: 1. An electronic antenna system for a cellular radio telephone network associating stationary stations to mobile or portable stations, this system comprising - reception antennas performing a sectorisation of the space to be covered, - at least one antenna access cable (20a ), - and reception circuits, characterized in that it comprises : - at least one array of reception antennas (1a ...8a ), - and, close to the antennas, at least one frequency transposition and multiplexing circuit (100) for transposing the signals received by the different antennas of the array in the radio frequency subbands, and for combining them, the antenna access cable (20a ) connecting the output of the transposition and multiplexing circuit (100) to these reception circuits, - and, in these reception circuits, a set of receivers (ERl ... ERm ) associated to the different reception frequencies in the radio frequency band Fj , j=l to m, a measuring receiver Ro , at least one demultiplexing and transposition circuit (200) connecting the terminal of the cable to the inputs of the receivers, at least one control circuit (300) for the selection of the transposed subband in which the signal has the highest level, on the basis of the values measured by the measuring receiver Ro and for each reception frequency Fj , each receiver being further connected to the output of the demultiplexing and transposition circuit (200) supplying a signal coming from the corresponding subband for transposing and processing it.