Showing papers on "Antenna array published in 1977"

Antenna array for a cellular RF communications system

Abstract: An array of antennas for a cellular RF communications system for providing communications to randomly placed transceivers in a given area. The antenna array includes a plurality of antenna sites located in the centers of cells. Each antenna site has a plurality of sectored antennas for providing a plurality of communication channels. A predetermined number of sites are used to constitute a subarray of cells to provide a set of communication channels and channel allocations are repeated from subarray to subarray. Channels are also so allocated as to minimize channel interference and optimize channel utilization. An omnidirectional antenna may be provided for each antenna site for signalling purposes.

Design of a stripline log-periodic dipole antenna

Abstract: A procedure is given for designing a two-layer stripline log-periodic dipole (LPD) antenna array. Measured input impedance and far-field characteristics are demonstrated for a 12-element array for 1-2 GHz operation that are in good agreement with design specifications.

Phased power switching system for scanning antenna array

Abstract: A system for a phased array antenna including a set of power amplifiers for amplifying the power of a signal to be transmitted by radiating elements of the antenna. A set of hybrid couplers are connected between the power amplifiers and the radiating elements with individual ones of the hybrid couplers being cross-connected for sharing the power of each amplifier among a set of radiating elements. The coupling of power is selectively varied between the amplifiers and the radiating elements by shifting the phase of the signal applied to each power amplifier.

Phase conjugation method and apparatus for an active retrodirective antenna array

Abstract: An active retrodirective antenna array wherein a reference array element is used to generate a phase reference which is replicated at succeeding elements of the array. Each element of the array is associated with a phase regeneration circuit and the phase conjugation circuitry of an adjacent element. In one implementation, the phase reference circuit operates on the input signal at the reference element, a voltage controlled oscillator (VCO) output signal and the input pilot signal at the next array element received from a transmission line. By proper filtering and mixing, a phase component may be produced to which the VCO may be locked to produce the phase conjugate of the pilot signal at the next array element plus a transmission line delay. The same phase conjugation process occurs at the next element where the proper phase reference is regenerated by mixing samples of the input pilot and transmitted signal. In another implementation, particularly suited for large arrays in space, two different input pilot frequencies are employed. Their difference is the phase reference of the system, and a local oscillator is used in obtaining this difference, which is in the IF range. The two pilot frequencies are selected in accordance with particular criteria to insure proper phase addition and elimination of local oscillator components. Appropriate mixing and filtering is performed to achieve phase conjugation and phase reference replication.

Principles and Applications of Adaptive Filters: A Tutorial Review,

Abstract: : This report reviews the characteristics of a class of adaptive filters useful in signal processing and other applications where the properties of the signal are unknown or variable with time. The basic element of these filters is the adpative linear combiner, which weights (adjusts the gain of) and sums a set of input signals to form a single output signal. The weighting process is governed by a recursive algorithm that seeks to minimize the mean square of the difference between the combiner's output and a 'desired response' (training signal). It is shown that for statistically stationary inputs the mean-square difference is a quadratic function of the weight values, allowing the minimum to be sought by gradient estimation and other similar techniques. Expressions are given that define the relationship between rate of adaptation and deviation from optimal performance due to noise in the gradient estimation process for the Widrow-Hoff LMS algorithm. Methods of deriving the inputs to the combiner are described, including the use of a tapped delay line to form an adaptive transversal filter. Experimental results obtained by computer simulation are presented that show the ability of the adaptive transversal filter to model an unknown network or physical system; to reduce or eliminate intersymbol interference in multipath communication channels; to reduce or eliminate periodic interference in electrocardiography and broadband interference in the sidelobes of an antenna array; and to separate periodic and broadband signals and detect very low level periodic signals. (Author)

Impedance-match and element-pattern constraints for finite arrays

Abstract: It is shown how an N -element antenna array may in principle be impedance matched by means of a specially designed interconnecting feed network to N real generators (for arbitrary excitation of these generators). The resulting element patterns for a single excited element (a single generator) in the terminated-array environment are then calculated. It is shown that for closely spaced regular arrays a condition of partial match, as contrasted with perfect match for all excitations, is the more appropriate design objective. The theory is illustrated through application to a uniform array of line sources. Element patterns obtained with an appropriately matched finite array are compared with those from the corresponding matched infinite-array model, the latter patterns having been obtained previously by an independent technique. The range of finite-array parameters to which the infinite-array model approximately applies is discussed.

Light-controlled semiconductor waveguide antenna

Abstract: A rectangular dielectric waveguide of intrinsic semiconductor material has been investigated for an application in the 30–40 GHz range The resistivity of the semiconductor material has locally been changed by GaAs-laser-beam illumination Depending on the pattern and intensity of the light spot, the generated waveguide inhomogeneity behaves essentially as a termination, a short circuit or an antenna element This effect can be controlled in position and time Hence the optically controlled waveguide can be used either as an antenna for fast aperture scanning or as a simple optoelectronically tuned antenna array

Radio frequency lens

Abstract: The inventive lens focuses a plurality of radio frequency signals received by a multi-element antenna array into a coherent signal. A circular transmission cavity has probe sites located therein. The probe sites are located on radii of the circular cavity approximately one quarter wavelength of the radio frequency of interest from the cavity's perimeter. A probe pair is positioned at each probe site. The signal from each antenna element is coupled through a three port circulator to a particular probe pair via a 180° coupler. Incoherent images received at the probe pair are dumped in a load resistor, whereas the focused image of the received signal is routed through the circulator and to a receiver.

Inconspicuous antenna system employing the airframe as an antenna

Abstract: of the Disclosure A phase front homing system airborne antenna array which employs portions of the airframe as two antenna elements and wherein each antenna element includes a coaxial sleeve coupler.

Antenna array with printed circuit lens in coupling network

Abstract: A radiated signal, received by each one of a plurality of spatially separated antennas, forming a directive array, is coherently recovered by the lens. The lens is comprised of a plurality of vertically standing and circularly arranged printed circuit panels, each of which includes a conductive strip connected at one end to each antenna. A plurality of semi-elliptical circuit panels are affixed to the vertical panels at a predetermined angle with respect thereto. Plated on the semi-elliptical panels are metal strips of predetermined length to provide the desired time delay to the antenna signals. A combining strip couples to the time delay strips and provides a combined output signal at one end of the semi-elliptical panel. The angle at which the semi-elliptical boards are affixed to the vertical boards corrects for time delay distortion caused by the placement of the combining strip.

Scanning beam navigational beacon with transmitted coherence reference signal and thinned two-dimensional phased array

Abstract: A scanning beam navigational beacon for transmission to a remote station (aircraft, for example) which measures a navigational angle therefrom. A thinned, two-dimensional main antenna array and linear reference array are provided. A single antenna element is provided at each vertical level of the array. Reference radiations are based on main array phase to allow coherent signal processing at the remote station. Azimuth frequency diversity is provided by grouping of the excited main elements and reference array elements at different frequencies, all features cooperating to minimize the effects of azimuthally displaced multipath signals which may fall inside the far-beam of elevation guidance. Thus, the effective array aperture exhibits a distributed frequency pattern in the azimuth plane.

A Constrained Adaptive Beamformer Tolerant of Array Gain and Phase Errors

Abstract: This paper describes a new method of constrained adaptive beamforming whose performance is relatively unaffected by array gain and phase errors. The method consists of setting certain of the adaptive parameters of a conventional adaptive beamformer to zero. It provides a means of rejecting large signals incident on the side lobes of an antenna array while preserving small broadband and narrowband and large broadband signals incident in the steering direction. In exchange for error tolerance broadband superdirectivity and large narrowband signal reception are lost.

Drive arrangement for an instrument landing system glidepath antenna

Abstract: A drive arrangement for an instrument landing system (ILS) glidepath antenna array, the drive system providing for a shorter image ground than is required by the known null reference, sideband reference or M-array systems. The drive system is applicable to an antenna array structure which is similar to an M-array structure, but the drive signals are fundamentally different from the M-array drives and the resultant field pattern does not have the "scooped portion" characteristically associated with the M-array system. A three element array structure is employed, with SBO signals driving each of the elements and CSB signals driving also two of the elements.

Doppler navigation system with enhanced multi-path discrimination capability

Abstract: A radio navigation system of the simulated Doppler type, including a ground beacon having a multi-element linear antenna array, the elements of which are energized discretely and, in turn, to provide digitized scanning. A remote receiver, in an aircraft on landing approach, for example, derives a beat signal relating to a navigational angle. The remote receiver has a bandpass filter covering the range of Doppler beat frequencies of directly received signals and also detects the start of each ground beacon commutation cycle. A unique combination of inhibiting circuits for eliminating filter transients during at least part of its transient response time and filter cut-off characteristics affords discrimination between direct and multi-path signals when the angular separation of the paths of those signals is at a minimum.

Airborne antenna system employing the airframe as an antenna

Abstract: A phase front homing system airborne antenna array employing portions of airframe as two antenna elements.

Instrument landing system glidepath antenna array and drive therefor

Abstract: An instrument landing system (ILS) glidepath antenna array and drive therefor which provides for lower susceptibility to above-ground interference and higher stability than the known M-array system. The antenna array also provides for a shorter image ground requirement than the known null reference and sideband reference systems. The antenna array comprises a four-element structure, two of which are driven with CBS only signals having relatively different amplitude and phase, and the other two elements of which are driven with SBO only signals having relatively different amplitude and phase.

Radiating slot opening antenna array

Abstract: Radio frequency antenna arrays of radiating slot apertures serially connected along a predetermined path transverse to the radiating slot apertures In the exemplary embodiments, the radiating slot apertures are formed by parallel edges of conductive radiator surfaces where the edges are spaced apart by substantially one-half wavelength at the anticipated antenna operating frequency Such radiator surfaces are, in some embodiments, dimensioned in a direction parallel to the apertures in relation to the relative proportion of radio frequency energy which is to be radiated to/from the slot apertures associated therewith to thus determine the total array aperture amplitude taper while the spacing between the radiator surfaces determines the phase taper across the total array aperture Other exemplary embodiments utilize internal reflections in an array to determine the array amplitude taper and still other exemplary embodiments combine a plurality of such arrays to form two-dimensional special purpose arrays

A Solution for a Wide Aperture Reactively Loaded Antenna Array.

Abstract: : This report considers an array of wide aperture reactively loaded antennas, specifically, an N element array of closely-spaced waveguide-backed rectangular slots radiating into a half-space region. Only the center slot is fed and the other slots are parasitically excited. The parasitic slots are reactively loaded by short-circuit waveguides. By varying the positions of the short circuits, a directive beam can be steered through 180 deg in space. The solution uses the moment method applied to the integral equation for the equivalent magnetic current in the aperture region and a numerical integration technique. Solutions for seven, nine, and fifteen element aperture arrays are given. A computer subroutine which generates the aperture halfspace admittance matrix is described and listed. (Author)

Network parameter measurements of antenna arrays

Abstract: A new method is developed for determining the admittance or the scattering parameters of an antenna array considered as a multiport network. The technique requires the use of a hybrid junction to provide two different modes of excitation at the antenna ports taken in pairs. It is shown that by measuring the reflection coefficients at each port, for both modes of excitation, the desired parameters can be obtained. The inherent errors of the method are analyzed and discussed. Experimental results are presented which illustrate the theory and demonstrate the practicality of the procedure.