Showing papers on "Reflective array antenna published in 1982"

Imaging antenna arrays

Abstract: Many millimeter and far-infrared imaging systems are limited in sensitivity and speed because they depend on a single scanned element. Because of recent advances in planar detectors such as Schottky diodes, superconducting tunnel junctions, and micro-boiometers, an attractive approach to this problem is a planar antenna array with integrated detectors. A planar line antenna array and optical system for imaging has been developed by the authors. The significant advances are a "reverse-microscope" optical configuration and a modified bow-tie antenna design. In the "reverse-microscope" configuration, a lens is attached to the bottom of the substrate containing the antennas. Imaging is done through the substrate. This configuration eliminates the troublesome effects of substrate surface waves. The substrate lens has only a single refracting surface, making possible a virtually aplanatic system, with little spherical aberration or coma. The array is characterized by an optical transfer function that is easily measured. An array with 19 dB crosstalk levels between adjacent antennas has been tested and it was found that the array captured 50 percent of the available power. This imaging system was diffraction limited.

Calculation of Site Attenuation from Antenna Factors

Abstract: A site-attenuation model expressed in terms of the antenna factors of the transmit and receive antennas is presented. Both horizontal and vertical polarizations are included, as are the effects of mutual coupling between closely spaced horizontal antennas. Expressing site attenuation in terms of antenna factors allows the use of broad-band antennas with their attendant advantages over tunable dipoles. Measured and calculated results for a variety of sites, antennas, and geometries are compared in the frequency range of 30 MHz to 1 GHz.

The synthesis of shaped patterns with series-fed microstrip patch arrays

Abstract: A method of designing series-fed microstrip patch arrays to produce a shaped pattern is described. The technique is based on a circuit representation of the patches in the array environment with experimentally determined parameters. The positions and widths of the patches are derived from the amplitudes and phases of the elements of a uniform array, which produces the desired pattern and which has the same extent as the patch array. For the array to have high efficiency, the amplitude distribution mast not be strongly peaked. An algorithm for obtaining an approximation to the desired far-field amplitude distribution while retaining control over the amplitude of excitatian is presented. Very close agreement has been obtained between calculated and measured performance of such arrays.

A high-frequency analysis of radome-induced radar pointing error

Abstract: An analysis is presented of the effect of a tangent ogive radome on the pointing accuracy of a monopulse radar employing an aperture antenna. The radar is assumed to be operating in the receive mode, and the incident fields at the antenna are found by a ray tracing procedure. Rays entering the antenna aperture by direct transmission through the radome and by single reflection from the radome interior are considered. The radome wall is treated as being locally planar. The antenna can be scanned in two angular directions, and two orthogonal polarization states which produce an arbitrarily polarized incident field are considered. Numerical results are presented for both in-plane and cross-plane errors as a function of scan angle and polarization.

Wide angle phased array dome lens antenna with a reflection/transmission switch

Abstract: An antenna assembly configured by the combination of the high forward gain of a conventional planar phased array antenna with the wide angle scanning capability of a dome antenna. The invention includes an optically fed phased array, which may be structurally configured similar to a conventional lens array, but comprises a reflection/transmission switch and an electronic phase shifter at each radiating element. The switches facilitate operation of the phased array in two distinct modes; when the switches are set for the transmission mode, the phased array operates substantially as a conventional lens array to scan a ±60° conical sector; when the switches are set for the reflection mode, the phased array behaves like a reflect array to scan an additional ±60° to ±120° sector.

Properties of phase synchronizing sources for a radio camera

Abstract: A distorted phased array can be made to operate as a diffraction-limited aperture if a compensating time delay and/or phase shift is added in each antenna element channel. When the distortion is not known a priori the correction mast be based upon phasefront measurements of the radiation from a source external to the array. The ideal adaptive synchronizing source is a point source radiating in free space. The phasefrouts of realistic sources are perturbed, however. Three types of practical sources and calculations of the conditions under which their radiation fields are acceptable for adaptive beamforming are discussed. The sources are the passive reflector, the active beacon, and radar ground clutter.

Low sidelobe phased array antenna system

Abstract: In a pulse radar system, wide angle sidelobes are reduced considerably in a phased array antenna by advancing each digital phase shifter by one bit just before each radar pulse is transmitted. This advance maintains the linear phase slope of the antenna elements as the difference in phase between adjacent elements is uniform, thereby having little effect on the antenna's main beam. However, the radar return signals from the sidelobes are reduced in comparison to the main beam return due to the radar receiver's integration process.

Planar Millimeter Wave Antennas With Application To Monolithic Receivers

Abstract: A number of applications of millimeter waves can benefit from development of low-cost, planar antenna elements, which can be combined into either phased arrays or arrays with imaging properties. Such applications range from communication, navigation and battle-field passive and active systems to remote sensing and space science instrumentation. This paper discusses the general requirements on such planar antenna elements, with specific data for three examples: (i) the Vivaldi (tapered slot) antenna, (ii) printed dipole arrays, and (iii) planar slot arrays. It is shown that such elements can be used for both prime-focus paraboloids and Cassegrain systems, with excellent aperture efficiency and beam efficiency, with the potential number of elements in the hundreds. In order to be optimally useful, planar antennas should be suitable for integration with receiver elements, i.e. mixer diodes and IF-amplifiers. It seems feasible to construct monolithic versions of these arrays in the future.

Low and medium gain microwave antennas

Abstract: The isolated and relatively small microwave antenna is the topic in this chapter. Array elements and large antennas are covered in other chapters. The basis for the selection has been novelty, either in design or in theory of operation. Most of the material in this chapter has not appeared in previous antenna design books, which date back 10 to 15 years, although of course some overlap is unavoidable. An understanding of the physical principles, in network theory or wave propagation, is the underlying philosophy, since this seems to be the basis for new, innovative design. The mathematics has been kept to a minimum, but the references will carry the reader on to greater details.

A dual-band TEM lens for a multiple beam antenna system

Abstract: A three-dimensional electromagnetic (TEM) lens is made of many printed circuit cards for future satellite multiple beam antenna applications. To obtain a low scan aberration lens combined with cross-polarization suppression, the lens array faces have a nonuniform distribution of element rotational orientations, making the array faces electrically nonuniform as to mutual coupling. An experimental procedure is presented for developing dual-band active impedance matched lens elements. Using such elements, a lens is built and tested to verify the adequacy of the design procedure.

Resonance phenomena on non-skewed H-plane multiple-Yagi arrays

Abstract: Theoretical and experimental swept-frequency radiation and impedance characteristics of several multiple-Yagi arrays indicate that, in addition to the resonance phenomena associated with the dipole cutoff region of the single Yagi, other resonances are also present on the multiple-Yagi configuration These resonances are dependent not only with the individual Yagi parameters but also upon the relative orientation and spacing of the array antennas Substantial variations are also observed in the array gain, bandwidth, and front-to-back ratio with the antenna spacing and position

Feed system design and experimental results in the uhf model study for the proposed Urbana phased array

Abstract: The effects of atmospheric turbulence and the basis for the coherent scatter radar techniques are discussed. The reasons are given for upgrading the Radar system to a larger steerable array. Phase array theory pertinent to the system design is reviewed, along with approximations for maximum directive gain and blind angles due to mutual coupling. The methods and construction techniques employed in the UHF model study are explained. The antenna range is described, with a block diagram for the mode of operation used.

A circular array configuration for simplifying multiplexing in radiocommunication antennas

Abstract: This paper describes a novel application of a circular array for the central antenna of base/repeater stations in mobile radio communication systems. The antenna is fed from a multiple port feed network which offers a number of omnidirectional coverage patterns which remain electrically independent. This provides isolation between multiple transmitters and receivers. The experimental results presented suggest at least 30dB isolation can be achieved over an octave bandwidth.

A note on utilizing far-field phase information

Abstract: The far-field phase information available from an antenna pattern is discarded in most system applications. Making use of such information for an angle-of-arrival estimation application across a relatively wide region of space is discussed in this note. The far-field phase difference response from two simultaneous shaped beam receive patterns generated by a linear array antenna is shown to provide an appropriate relative phase property for making unambiguous angle determinations.

Exact gain measurement of large aperture antennas using celestial radio sources

Abstract: The correction factors for angular extension of celestial radio sources, Cassiopeia A (Cas A), Taurus A (Tau A), and Cygnus A (Cyg A) were calculated based on the detailed contour maps of brightness temperature. Examinations of the flux densities of those radio sources were made using the published data. The gain of antennas of several sizes measured by using the three radio sources was determined by applying the newly obtained parameters. It was found that the gain of large aperture antennas at 4- and 6-GHz bands could be determined to the accuracy of better than \pm0.45 dB (3\sigma) by use of the three radio sources.

Radiating elements for hemispherically scanned arrays

Abstract: The problem of obtaining hemispherical coverage using an electronically steered antenna beam is considered Radiating elements consisting of combinations of slots, parasitic dipoles, and surface wave structures were investigated for this application Both planar and cylindrical supporting structures were used It was found that such elements showed enhanced radiation near the horizon in both the E -plane and the H -plane Patterns were measured on an eight-element linear array of slots covered by a surface wave structure When the beam was scanned electronically to endfire, the pattern was enhanced by several dB over that obtained from the array without the surface wave structure

A novel leaky-wave antenna for millimeter waves based on the groove guide

Abstract: Abstract : Leaky wave antennas for millimeter waves face two main problems. The first relates to the small wavelengths involved, which require small waveguide dimensions and pose fabrication difficulties. The second problem is higher metal loss. In the new leaky wave antenna described and analyzed here, we overcome the first of these problems by choosing a structure with a longitudinally continuous aperture, and the second by basing the antenna on a low-loss waveguide, the groove guide. The groove guide is an open waveguide, but its dominant mode is purely bound by virtue of structural symmetry. By placing a longitudinal asymmetric metal strip along the guide, the symmetry is distributed and a new TEM-like mode is produced in the transverse direction that propagates to the open end and leaks power away. An accurate theoretical analysis is presented for the performance properties of this antenna structure. The cross section is represented by a transverse equivalent network that contains some subtle features. All of the elements of this transverse network are obtained in closed form, so that the dispersion relation for the propagation characteristics is likewise in closed form.

Resolution of monochromatic signal sources using a simple receiving antenna array

Abstract: A simple method to isolate the amplitude and the direction of m incident rays on a linear antenna array of 2m elements is described. This method differs from other similar proposals by its ease of hardware implementation at microwave frequency.

Spatial digital processing: Application to radar antennas

Abstract: Recent improvements of fast processors and microwave components, and their expected applications in the radar domain, open the way to the realization of digital beam forming antennas. A lot of advantages can be expected from the use of that kind of antenna. Many needs and requirements of radar systems are satisfied : jamming cancellation, environmental adaptivity, beam shaping...Our research about digital beam forming is aimed at estimating the performances of such equipment and designing architecture and element specifications.