Showing papers on "Reflective array antenna published in 1979"

Water-Immersed Microwave Antennas and Their Application to Microwave Interrogation of Biological Targets

Abstract: This paper describes a method of significantly improving the resolution of systems used for interrogating the spatial variation of permittivity of biosystems at S band. The basic principle employed is to contract the wavelength of the interrogating radiation and to reduce the physical aperture of the interrogating probes by immersing the transmitting antenna, receiving antenna, and the target into a material with a high dielectric constant, namely water. The antenna design is described, and line scans employing transmitted and reflected energy are presented.

On the gain-versus-scan trade-offs and the phase gradient synthesis for a cylindrical dome antenna

Abstract: Gain-versus-scan trade-offs for a circular cylindrical dome antenna are considered. A theorem by Stangel [1] is generalized, and it is shown that the scan angle limitations of the feed array and of the dome result in an upper bound on the average dynamic gain (scan dependent gain function) and in an upper bound on the gain in any particular scan direction. For specified scan limits, the former bound is determined essentially by the feed array, the latter by the dome size. These bounds are useful in posing realistic performance requirements for dome antennas and have been verified in a few specific examples. Subsequently, the synthesis problem is addressed; an optimization scheme is employed to arrive at a dome insertion phase distribution that produces a desired gain-versus-scan variation. Illustrative examples are given.

Aircraft television antenna receiving system

Abstract: An omnidirectional VHF television antenna system for an aircraft which includes one pair of slot antennas on each side of the aircraft vertical fin. Each pair of antennas includes a VHF high band slot antenna and a VHF low band slot antenna. Due to co-channel interference the antenna system includes a left, right or omnidirectional azimuth response characteristic selectable by a cabin attendant through control of the antenna system antenna pattern select switch. The VHF low band slot antennas are tilted from the vertical by about 24° and the VHF high band slot antennas are disposed vertically. Signal processing circuit means coupled between the slot antennas and the antenna system output terminal includes solid state switches to select antenna coverage omnidirectional and azimuth, or to the left or right of the aircraft to minimize ghosts or co-channel interference.

Design of array and line-source antennas for Taylor patterns with a null

Abstract: An antenna pattern design technique which results in a generalized Taylor pattern, except in a narrow region where a deep null is formed, centered at a preassigned position is presented. It is shown how this technique can be applied effectively to both linear arrays and line sources. The approach is direct so that the technique does not use either iterative sampling or a perturbation procedure. It is particularly useful in the design of a large array with a prescribed deep null. Numerical results indicate that to steer such a null, adjustment of the excitation is necessary near the edges only.

A novel radar array and its imaging properties

Abstract: A novel radar array providing resolution superior to any other antenna configuration with the same physical aperture is described. Application of the new array to a localized imaging system suitable for real-time operation is simulated, and its resolution and depth of field properties ate compared with those of a crossed array and the conventional filled array antenna. Substantial savings in weight, cost, and complexity are offered by the proposed configuration.

Radiation characteristics of dielectric tube antennas

Abstract: A study of the radiation characteristics of dielectric tube antennas is made with a possibility of its application in communications satellites. It has been shown through a systematic analysis that a multimoded dielectric tube shows a dip in the boresight region which is suitable for satellite antennas.

Conformal dielectric-filled edge-slot antennas with inductive-post tuning

Abstract: A class of circumferential-slot antennas, called edge-slot antennas, that are ideally suited for conformal mounting on conducting bodies of revolution has been developed. The simplest form of the antenna is a disk of dielectric substrate that is copper-plated on both sides and mounted between two parts of the conducting body so that the aperture coincides with the surface. The antenna is excited by a single coaxial stub at the center and is tuned for proper operating frequency by inductive posts that connect the two copper-plated sides of the disk. By varying the number and location of the inductive posts the operating frequency of a disk can be tuned over a 6:1 range. Instantaneous bandwidths of three percent are typical. In practice, plated-through holes are used as inductive posts to provide mounting and access holes. The single coaxial feed excites azimuthally symmetric fields that are not significantly distorted by the symmetrically placed inductive posts. Therefore, radiation patterns of edge-slot excited bodies display a high degree of azimuthal symmetry. The small size, light weight, and inexpensive fabrication procedure make the edge-slot antenna attractive for many applications.

IEE Electronics Division: Chairman's address. Some recent advances in microwave reflector antennas

Abstract: The paper presents a review of some recent advances in microwave reflector antennas, and places emphasis on the work of the Electromagnetics Applications Group at Queen Mary College (QMC). After a brief historical review, the following classes of antenna are considered: pencil beam, shaped beam, beam scanning and multiple beam. The operation of these antennas is described in nonmathematical terms and their performance constraints are identified. Many new antennas and feeds are illustrated and their operation discussed. In nearly all cases, they have resulted from innovation coupled with computer-aided design methods. The latter development distinguishes antenna developments of the last decade from those of the past. It is expected that this feature of antenna design will be exploited still more in the future.

The influence of aperture shape on the radiation patterns of horn-reflector antennas

Abstract: The role of aperture shape in influencing the far-zone radiation pattern in the vicinity of the main beam of horn-reflector antennas is examined. The three major types of horn-reflector antennas are considered-pyramidal, diagonal, and conical-and the influence of their aperture shape on the spatial character of antenna radiation is assessed.

Minimum Directive Gain of Hopped-Beam Antennas.

Abstract: : The optimum parameters of an antenna whose beam is hopped to uniformly spaced directions within a circular coverage are derived for a phased array and for a multifeed lens antenna. The minimum directive gain, GMIN , within the coverage is the parameter optimized. The analysis shows that, for small bandwidth-diameter products, the two antenna configurations exhibit about the same GMIN, but the optimum aperture diameter is about 30% smaller with the phased array. However, as the bandwidth-diameter product increases, the GMIN of the lens antenna becomes progressively greater than that of the phased array.

Effective Sidelobe Levels Due to Scatterers

Abstract: The far-field radiation patterns of radar antennas when installed aboard ships may differ substantially from their free-space or theoretical design radiation patterns. We obtain some estimates for the effective sidelobe levels generated by scatterers in the main beam of the antenna by 1) ships and other discrete scatterers in the far field; 2) the sea in the far field; and 3) the ship's own superstructure in the Fresnel region.

Evanescent-wave tracking: new approach to the analysis of large reflector and aperture antennas

Abstract: A new method based on local evanescent-wave tracking is proposed for the analysis of large reflector and aperture antennas.

Lossy-feed networks in multiple-beam arrays

Abstract: Using a lossy-feed network in a multiple-beam array antenna, particularly a receiving system without active amplifying components embedded in the network, has generally been avoided. Attention is called to certain antenna pattern characteristics that should be evaluated with respect to the system application involved. Lossless-feed networks often possess one or more of these pattern characteristics which can possibly be enchanced when the capabilities of a lossy network are properly traded off. Maximizing available antenna gain at the beam crossover points, for example, is shown to be one possible advantage for employing a lossy network instead of a lossless design. Near-in sidelobe levels can readily be controlled with a lossy network.