Showing papers on "Conformal antenna published in 1971"

Omnidirectional loop antenna array

Abstract: An antenna array for use with a system for receiving signals from a radio capsule disposed within a patient''s gastrointestinal tract. The array of antennas comprises three mutually perpendicular loop antennas, two of which are ferrite-core loop antennas disposed near the center of the array, the third being a loop antenna surrounding the two ferrite-core antennas. The antenna array includes means for matching the impedance of the loop antennas to transmission lines to which they are to be connected.

Antenna spacing requirement for a mobile Radio base-station diversity

Abstract: The minimum required antenna spacing between two base-station antennas in order to take advantage of spatial diversity technique was investigated. The measurements were made for two cases: (i) the incoming radio signal was perpendicular to the axis of two base-station antennas (the broadside case), and (ii) the signal was in-line with the axis of two base-station antennas (the in-line case). The correlation of signals received from two separated antennas at the base station was found to be much higher for the in-line case than for the broadside case with any given antenna spacing. For correlation up to 0.7, from which most of the advantage of two-branch diversity can still be obtained, we found the minimum required antenna spacing is around 70λ–80λ for the in-line case and 15λ–20λ for the broadside case. In order to achieve a correlation always less than 0.7 between two base-station signals regardless of the arrival direction of the incoming signal, a triangular configuration with a three-antenna array used with a three-branch diversity receiver is proposed, requiring less antenna spacing in the array than for a two-antenna setup.

Possibilities of dimensioning doubly curved reflectors for azimuth-search radar antennas

Abstract: To produce directional antenna patterns having a shaped beam in one plane such as is required, for instance, in the case of rotating-search radar antennas having a vertical radiation pattern of cosecant-squared shape, doubly curved reflectors are used as a rule. Besides the well-known composition of such reflectors from a stack of strips of parabolic shape, the paper delineates possibilities of an assembly from strips of elliptic shape that are also segments of parabolic dishes. With reflectors assembled in this way certain antenna characteristics such as directivity, sidelobe suppression, etc., can be modified and improved, depending on the type of strip configuration proposed. Experimental results gained with two different reflectors (width 12.5\lambda , height 5.6\lambda ) assembled from strips of elliptic shape are discussed. One of the strip configurations devised turns out particularly favorable for small reflectors.

Satellite communications to mobile platforms

Abstract: This paper describes a program carried out by the M.I.T. Lincoln Laboratory to demonstrate the feasibility of satellite communications to mobile platforms, particularly aircraft. The VHF/UHF 225-400-MHz band was selected to permit the use of simple, hemispherical coverage aircraft antennas. Experiments were carried out in 1965-1966 to establish initial feasibility by measuring the electromagnetic noise environment in this band and the nature of the multipath occurring on the link between a satellite and a nondirectional aircraft antenna. A satellite, LES-3, was orbited in 1965 to provide a propagation signal source for the latter measurements. Two satellites, LES-5 and LES-6, were orbited in 1967 and 1968, respectively, to serve as UHF repeaters for communications experiments. A multiple-access modulation system, TATS, was developed and tested in ground and aircraft environments with these satellites. In addition, a flush-mounted, crossed-slot aircraft antenna with good coverage properties was developed.

Note on transistor-fed active-array antennas

Abstract: The feed requirements for an active radiating array in which each element is independently excited by a transistor are shown to be less dependent on the elemental mutual coupling effects than in the corresponding passive case. Using a simple transistor equivalent network, it is predicted that as the limit of ideal transistors is approached the input impedance of the active array should exhibit less variation with frequency.

Compatible double precision doppler omnidirectional bearing system

Abstract: A circular antenna array has a first antenna and second and third antennas or a first antenna and two pairs of antennas arranged around the first antenna on a circular perimeter of which the first antenna is the center of the circular array. A frequency modulation is generated in the signals associated with the second and third antennas or the two pairs of antennas characteristic of a rotational condition of the second and third antennas or the two pairs of antennas on the perimeter at a low frequency in a manner whereby the second and third antennas or two pairs of antennas are rotated in opposite directions around the perimeter to provide a phase difference in electrical degrees in the modulation of the signals which are radiated which is double the actual displacement in azimuth degrees. A signal radiated from the center antenna is used as a reference to eliminate the 180* ambiguity.

Empirical Optimization of Antenna Arrays.

Abstract: : The report describes a technique developed to optimize the performance of antenna arrays under realistic, on the vehicle conditions. This technique permits free choice of optimality criteria and design parameters and is applicable to both planar and nonplanar arrays with geometric constraints. The need for an improved Airborne Early Warning (AEW) airplane, the improvement being that of an airborne antenna system with reduced side lobes, was the main impetus for this investigation. The work reported grew from an initial study of the antenna array problem under the assumption of idealized free-space conditions. An experimental-computational approach to the solution of this problem has been formulated in which powerful n-dimensional optimum search methods (i.e., the Davidon algorithm) are applied to experimental data obtained from carefully scaled models of the vehicle and antenna array configuration. The optimization algorithm provides a new design for the antenna array that is then used in the scale model, and the process develops in an iterative fashion. The necessary laboratory setup and data processing techniques used to test the feasibility of this approach are discussed. Experimental results showing encouraging improvements have been obtained on an array of eight elements both with and without an aircraft model. These results indicate that the algorithmic procedure is both stable and convergent. (Author)

Circularly symmetric retrodirective antenna system

Abstract: A method is described by which automatically retrodirective performance may be obtained from circular arrays and circularly continuous aperture antennas. The method is also directly applicable to cylindrical antennas for two-dimensional retrodirectivity and is generalized to include a method for obtaining three-dimensional retrodirectivity. Both passive and active systems are possible, and control of the reradiated beam characteristics may be provided.

Correlating antenna array

Abstract: A set of arbitrarily located receiving antenna elements, each connected with an appropriate network, can be used to construct a matched filter where the antenna array response results in an autocorrelation of a specified desired signal, correlating over time and space coordinates simultaneously. A receiving system using such a signal processing antenna can discard interferences which do not have the same spectral characteristics as the desired signal, or which do not originate from the same point as the desired signal source. Examples of correlating antenna arrays for various arbitrary intelligence modulations of the desired signal are discussed in this communication.