Showing papers on "Antenna array published in 1979"

Superresolution of uncorrelated interference sources by using adaptive array techniques

Abstract: By using adaptive techniques an antenna array can achieve an angular resolution of uncorrelated interference sources substantially greater than the aperture of diffraction limit. The antenna beam is scanned over the interference source locations, and for each scan condition the adaptive processor is allowed to reach its steady state. It is shown that for realistic ratios of interference strengths to system thermal noise, resolutions in excess of 0.25 times the Rayleigh limit can be achieved.

Beam forming network for butler matrix fed circular array

Abstract: A circular multimode antenna array having N radiating elements, an NXN Butler matrix and N-1 phase shifters includes feed networks comprising a back fill-in network, a sum pattern power divider network, a difference pattern power divider network and a sum-difference combiner network. The various networks are used either alone or in simultaneous combination to provide sum and difference circular antenna patterns having omnidirectional side lobes.

Baseband signal combiner for large aperture antenna array

Abstract: A method and apparatus for combining baseband signals from a large aperture antenna array in which none of the individual baseband signals has a sufficiently high signal-to-noise ratio to be used as a correlation or reference signal for phase adjusting the remaining baseband signals. More specifically, the invention provides a means whereby the baseband output signals of all but one of the receivers associated with each of the antennas are summed and used as a correlation reference for the baseband signal not contained in the summed signal, thereby providing a plurality of correlation or alignment loops, each having an output signal related to the phase difference between its input baseband signal and the summed signal. The invention further provides a means for subtracting an output or error signal generated in one of the correlation loops whose baseband signal has a predetermined phase delay from all the other alignment loops, thereby avoiding interaction and reflection effects in the signal combiner. A variable phase delay means for each of the other baseband signals is controlled by its corresponding correlation loop. The invention discloses how a plurality of loops operating in the above manner provides a means for adjusting the phase of each baseband signal so that they will all be in phase with each other and can thus be added to provide a composite signal output having a higher signal-to-noise ratio than any of the individual baseband signals.

Edge slotted waveguide antenna array with selectable radiation direction

Abstract: An antenna array consists of one or more slotted-waveguide, linear subarrays. Slots for radiation are cut in both narrow walls of each such waveguides, and PIN diodes across the slots are selectably forward and backward biased to effectively open the slots along one waveguide narrow wall while the others are closed and, alternatively, vice verse.

Method and apparatus for electrically scanning an antenna array in a monopulse DF radar system

Abstract: From an antenna array of a plurality of fixed, narrow beamwidth antennas, geographically oriented to provide omnidirectional coverage, first and second sets of antennas are selected in sequence. The first selected set includes several pairs of oppositely oriented antennas. The signals received by the antennas in each pair of the first selected set are combined and each of the combined signals is connected to a different one of a number of matched receiver channels. If the logarithmic video output signals from the receiver channels meet certain rules of acceptance, the monopulse ratio, formed by subtracting the outputs of the channels receiving the strongest and next strongest signals, is digitized and stored. This ratio represents the angular difference between the direction of the received signal and the direction of one of the antennas in the pair of the first set generating the strongest signal. However, it cannot be determined which of the antennas in the pair has the forelobe response and, thus, the ratio contains a 180° ambiguity. To resolve the ambiguity, a second antenna set is selected to include only the pair of the first selected set which were connected to the channel receiving the strongest signal. Each antenna in the second set is connected to the input of a different channel, the outputs of which are compared. The stronger signal is considered to be the forelobe response, and information relating to the sector of the antenna with the stronger signal is used to resolve the ambiguity present in the stored ratio.

A Circularly Polarized Traveling-Wave Chain Antenna

Abstract: A novel traveling-wave antenna array with bent conductors as elements can give circularly polarized radiation. An expression for the far-field has been derived, from which the lengths and bending angle of the conductors can be calculated for circular polarization. A useful application would be printed circuit microwave antenna for different purposes. Antennas have been made and work well over reasonable large bandwidths. They can also function on their broadside frequency.

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.

Anastigmatic three-dimensional bootlace lens

Abstract: A three-dimensional bootlace lens with minimum possible focusing aberrati, minimum possible focusing size and minimum possible dielectric loading. The feed and lens surfaces are in the shape of a spherical cap and covered by contiguous arrays of radiators. The region between the inner surfaces of the lens is filled with a nonuniform dielectric material with an index of refraction which constantly changes from the center line outwardly. Lens ports are connected to a radiating antenna array by means of coaxial transmission lines all of which have the same length. The axial feed point has a focusing performance which is perfect. For all other points the lens is free of all first-order aberrations except coma. The outputs of the lens can be used to feed a planar radiating antenna array so as to produce a multiple directive beam in one angular dimension or to feed a circular array so as to make it amenable to scanning or multibeam feed systems that are used with linear arrays.

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.

Around-the-mast rotary annular antenna feed coupler

Abstract: An annular rotary antenna feed coupler especially for around-the-mast use, as on shipboard. A housing in the general shape of a cylinder with a central axial opening essentially concentric with the axial center line of the housing contains a circumferential distribution of a number of fixed axially elongated, conductive loops each with a feed port. Radially spaced therefrom, a second, group of elongated conductive loops circumferentially distributed about a circle of different radius as compared to the aforementioned fixed loops is rotatably mounted. A corresponding plurality of ports, one for each rotating loop, is also provided, and input and output combiner/divider devices, one for the fixed and another for the rotating sub-assemblies serve to combine all ports into a single fixed and a single rotating port. Mechanically, the rotating combiner/divider rotates with the antenna array with which it operates.

Improvements in or relating to stripline antennae

Abstract: A travelling wave stripline antenna array adapted for use as a frequency-swept antenna, comprising a pattern of conducting material 4,5 on an insulating substrate 2 with a conducting backing 3, the pattern comprising a feeder strip 5 and a plurality of radiating antenna elements 4, each in the form of a strip attached to and extending transversely away from the feeder strip, and having an open circuit termination at its free end At least some, and preferably all, of the strips 4 are formed with a longitudinal slot 6 extending from the opposite side of the feeder strip and terminating before the open circuit end of the strip, so that each slotted strip behaves as a phase shifter as well as a resonant radiating antenna element

Directional location of periodically repeated pulsed signals - using circular antenna array with sequential scanning and single amplifier

Abstract: A direction finding method is for periodically repeated pulsed signals. It depends upon a number of antennas equi-distantly spaced around a circular arc and with single direction lobes radiating from the circle or arc centre. Adjacent lobes touch or overlap slightly. Antenna output voltages are summed vectorially to enable total vector direction measurement w.e.t a reference direction. Antenna related digital storage accessing and signal processing provide economical elimination of noise signals. The antenna voltages are sequentially scanned, amplified, after frequency conversion if necessary, in a single amplifier channel, rectified, and stored.

Direction determining apparatus responsive to electromagnetic radiation

Abstract: An antenna array for directional determination comprises two pairs of elongated end-firing log-periodic antenna elements, each pair fixed symmetrically to a reference plane and preferably forwardly convergent to it. The two antenna elements of one pair converge forwardly at an angle b, those of the other pair converge at a preferred angle a=1.5 b. In one embodiment each pair is connected with a 90°--hybrid, and from the detected and amplified signals across individual elements of each pair there is obtained a difference signal designated L 1 for the b-angle pair, L 2 for the a-angle pair. A third difference signal L 3 is obtained from L 2 -L 1 . The magnitude of each difference signal depends upon value of an angle V between a symmetry line in the plane of symmetry, symmetrical to the antenna elements, and the projection in that plane of a line through the array and a detected radiation source. An indication of V is taken on the basis of L 1 if L 1 , L 2 and L 3 are on the same side of zero. A more precise indication of V is then taken on the basis of L 2 by comparing absolute value of L 2 with the absolute value of an adjustably variable reference signal. Other signal processing arrangements are disclosed that produce the same effective lobe sharpening.

Quasi-linear antenna array

Abstract: An antenna array suitable for mounting at a selected height above a target plane, which provides for excellent resolution along a line in said plane extending through the vertical projection of the center of said array and perpendicular to a plane including said array. The array may comprise a plurality of radiators, each having a phase center along a support. The support is constrained to describe a segment of a circle in a vertical plane whose center lies on said line. As a result, the distance from any arbitrary point on the line in the target plane to any element of the array is equal.

A UHF Test Simulator for an Antenna Nulling System.

Abstract: : A UHF Test Simulator designed for use in testing adaptive antenna array nulling systems is described. The simulator consists of two major components: a Jammer Simulator and an Antenna Array Simulator. The Jammer Simulator can simulate up to eight independent jammers. The Array Simulator can simulate an array of eight elements in a four jammer environment. Operating details of both these simulators is discussed. (Author)

Effect of reflector and exciter size on the radiation of circular-loop Yagi arrays

Abstract: Both gain and bandwidth of circular-loop Yagi arrays are investigated for various reflector and exciter sizes. It is shown that these array characteristics can be optimised by increasing the size of the reflector and the exciter. The required increases are found to be within about 20% of the director size.

An intrusive slotted cylinder antenna array for subsurface moisture profiling

Abstract: Theoretical analysis and measured performance of an intrusive microwave probe for sensing the distribution of soil moisture from near surface to root zone depths (1-2 m) are presented. The probe consists of a linear array of slot antennas mounted along the axis of a metal cylinder and is intended for borehole installation. Measurements of self and mutual slot antenna admittances are used to derive a discrete depth profile of the soil’s complex permittivity. The moisture distribution is then deduced from this permittivity profile by empirical relations.