Showing papers on "Reflective array 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.

A study of the antenna array configuration of an M-branch diversity combining mobile radio receiver

Abstract: The theoretical analysis in this paper is based on the assumption that the angles of signal arrival on the mobile receiver are uniformly distributed. From the analysis and experimental studies, we find that if the antenna spacing between two adjacent antennas in a space diversity array is greater than 0.5λ the array configuration does not affect the cumulative distribution curves nor the shapes of the level-crossing-rate (LCR) curves, and only slightly affects the signal level at which the maximum LCR occurs. Hence a three-element array with a triangular shape or a four-element array with a rectangular shape can be considered a good arrangement, provided each side (antenna spacing) is greater than 0.5λ. Two slightly better arrangements than those we just mentioned for improving the signal fading are also proposed for three-branch and four-branch diversity signals, respectively.

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.

Phased array of six log-periodic dipoles

Abstract: A direction finding antenna for accurate direction finding over broad conuous frequency spectrums, independently of polarization, comprising a phased array of six log-periodic dipole antennas with loaded elements.

Radiation resistance of antennas in lossy media

Abstract: Using the concept of modified power density, expressions are derived for the radiation resistance and efficiency of antennas in a dissipative medium.

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.

Phased Array Antennas

Abstract: The theory of array antenna design has matured such that the tools are now available to design elements with predictable performance and to verify this performance with high confidence. The antenna feed is of equal importance to the antenna element. Multiple reflections in a poorly designed feed may generate spurious responses in the array antenna pattern. Space feeds offer economy and simplicity but tend to be limited in instantaneous bandwidth, flexibility of amplitude tapers, and ability to form clusters of beams. The near field off-set fed Gregorian reflector system appears to eliminate much of the inflexibility of the more conventional space-fed systems. This system is an attractive potential feed for the all-solid-state, phased-array radar. The all solid-state phased array radar typically will have a larger aperture relative to its vacuum tube counterpart. This large aperture increases the likelihood of the need for time-delay steering and clusters of simultaneous receive beams.

Realizable method of pattern synthesis for array antenna

Abstract: The problem of realization of an arbitrary current distribution on an broadside array antenna derived from the theory of pattern synthesis is treated and some practical methods are proposed. In these methods, the input voltage of each antenna is transformed by a reactive transformer to take the required value. In one of the methods, experiments to yield Chebyshev patterns were performed and satisfactory results were obtained.

Excitation of surface wave on circular-loop array

Abstract: A method is presented of analyzing surface-wave excitation to an infinite periodic linear array in which only one element is excited and all others are parasitic. The approach taken in the analysis is based on the properties of the periodic structure. A formal solution for the current distribution on the array element is obtained, and the propagation constant of the surface wave is also found. In the case where the array consists of loop antennas, the surface wave can propagate only when the separation of the array element is less than one-half wavelength and the circumference of the loop is less than one wavelength. Calculated values of the propagation constant of an array are in good agreement with the measured results.

A 7-25 MHz high-power ten-element electronically scanned array for ionospheric backscatter measurements

Abstract: A ten-element array of log-periodic monopole antennas with a power gain of about 20 dB is described. The individual elements are designed for input continuous wave (or peak) powers of 200 kW and differ somewhat from previous monopole configurations. The array element spacing is adjusted so that when it is electronically scanned in synchronism with the associated receiving array all side and grating lobes of the two-way pattern are down at least 20 dB. Element, array, and ground screen designs are discussed, as well as the model array mutual coupling measurements, electronic scanning systems and the associated coaxial transmission lines.

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.

Monopulse Antenna Performance When Receiving Nonuniform Waves

Abstract: Variations in apparent target direction, or glint, as sensed by an amplitude monopulse tracking antenna are analyzed for several cases when a nonuniform wave is incident on the antenna. Results are given for a target consisting of two isotropic scatterers, and compared with results previously obtained for the case of a locally uniform wave incident on the antenna.

A signal detectability approach to optimization of the geometry of distributed aperture (array) receivers

Abstract: A technique which allows the analytical specification of optimal array geometry that enhances array reception is developed. The technique is illustrated for small antenna arrays of up to four elements in two classes of interference fields, with and without spatial constraints. The analytical treatment is predicated upon signal detectability and employs error-free arrays of noninteracting nondirectional elements. The interference fields considered are those due to isotropic sources (case I) and sources uniformly distributed on an unbounded plane (case II). The optimality criterion is minimization of the signal detection error probability. For a phased receiving array, this is equivalent to maximizing the array detectability gain function, which has the effect of maximizing the predetection signal-to-noise ratio (SNR). The optimal array configuration is found to be two-dimensional in both cases (circular configuration in case I and elliptical configuration in case II, with the antennas equally spaced in angle along the periphery of the configuration). Numerical results are given which indicate that practical increases in predetection SNR of as much as 10 to 15 dB can be achieved by employing the array configuration most appropriate for the space-time correlation structure of the interference fields.

Electric field bounds over a phased array aperture

Abstract: In the following, a bound on the electric field magnitude existing over a phased array antenna is presented. Use of this bound in predicting the power handling capability of the array is discussed. It is shown that, although the overall array is large with respect to wavelength, the narrow beamwidth often required significantly affects the near field over the aperture and just outside the antenna. The result is compared to a previously existing bound obtained for a single rectangular aperture.

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.