Showing papers on "Reflective array antenna published in 1978"

Reactively controlled directive arrays

Abstract: The radiation characteristics of an N -port antenna system can be controlled by impedance loading the ports and feeding only one or several of the ports. Reactive loads can be used to resonate a real port current to give a radiation pattern of high directivity. The theory of resonance is extended to include complex port currents and impedance loads. The initial design of an array is obtained by resonating a desired port current vector, which is then improved by an optimum seeking univariate search method. The direction of maximum gain can be controlled by varying the load reactances. Several numerical examples are given for a circular array of seven dipole elements.

Superdirective receiving arrays

Abstract: Some of the characteristics of arrays designed for maximum directive gain subject to a tolerance constraint are described. Numerical data are presented which illustrate trade-offs between array size, directive gain, SNR, efficiency, bandwidth, tolerances, and farfield patterns. The results of an experimental study are found to be in good agreement with theoretical predictions.

Design of arrays for acoustic sounder antennas

Abstract: The use of an array of loudspeaker elements for an acoustic sounder antenna is discussed. The effect of variations between the phase and amplitude of individual elements in the array is investigated and measurements are compared with the predicted radiation patterns for both a 6*6 square array and a 2*12 rectangular array of re-entrant horn loudspeakers.

The performance of an iris-loaded planar phased-array antenna of rectangular waveguides with an external dielectric sheet

Abstract: A new method for calculating the performance of an iris-loaded planar phased-array antenna of rectangular waveguides is presented. The method is based upon the expansion of the tangential electric aperture field in terms of judiciously chosen functions. Also, the influence of a dielectric sheet in front of an antenna the apertures of which are loaded with inductive irises is investigated. In the experiments, a sheet with a low relative permittivity ( \epsilon_{r} = 2.3 or \epsilon_{r} = 3.5 ) is spaced in front of a space-fed planar antenna of some 850 radiating elements, and the total transmitted power of the antenna is measured as a function of frequency and scan angle. The results indicate, that both in theory and in practice, an excellent match can be achieved with a polythene sheet ( \epsilon_{r} = 2.3 ) or a Perspex sheet ( \epsilon_{r} = 3.5 ).

Survey of design techniques for flat profile microwave antennas and arrays

Abstract: The increasing compactness of modern microwave communication and radar equipment commonly demands that the associated antennas have flat profiles; this paper surveys the various planar antenna design techniques that are available. After summarizing the well-established methods using slotted waveguide arrays, the more recent stripline and cavity backed printed antennas are surveyed; finally the latest techniques using microstrip arrays are introduced and state-of-the-art designs discussed. Outline design and explanatory details are given for each antenna and any special characteristics, advantages and disadvantages are noted; ample references are given throughout the text. Several conclusions are reached about ways of improving the various individual designs but the need to improve the control of both mechanical and electrical tolerances and also more accurately predict the sidelobe behaviour of arrays are seen as important general requirements for further research.

Transmission and Reception with Embedded Antennas

Abstract: Electromagnetic problems relating to biomedical telemetry are reviewed. The reciprocal theorem is used with the previously determined receiving properties of embedded bare and insulated dipoles and two-element arrays to obtain the ratio of the voltage across the load in a receiving dipole or Yagi array in air to the voltages driving various embedded transmitting antennas. The solution of the electro-magnetic problem of the transponder at vrious depths in a body of skin is thus completed.

VLF loop array antenna

Abstract: A directional loop array antenna for very low frequency (VLF) reception. array comprises four closely spaced loop antennas forming a unidirectional reception pattern with a main beam of less than 43° between half power points. The array combines two double loop coaxial antennas dispersed with their axis parallel along 45° lines. The signal from one double loop array is delayed sufficiently such that a unidirectional reception pattern is formed.

Highly decoupled colinear antennas

Abstract: The mutual coupling of two independently fed antennas has been minimized over a broad frequency range by mounting them colinearly and by incorporating an "isolator section" in the feedline of the upper antenna which effectively reduces the coupling due to currents on the transmission line outer surface. An isolation greater than 35 decibels has been realized in the frequency range from 225 to 400 MHz between a pair of broadband colinear dipole antennas at a spacing of 1.5 meters.

Feed network for dual beam reflector antennas

Abstract: A primary feed network for doubly curved shaped-beam reflector antennas is described which allows simultaneous signal reception on two distinct elevation plane patterns such that the underside falloff separation between a fixed lower beam and a higher beam can be substantially varied in a lossless manner. A three-element feed array is employed wherein two elements of the array are interconnected by means of a sum-difference hybrid. The sum port generates the fixed low beam while the difference port generates an orthogonal beam pattern suitable for RF combining with an independent high beam generated by the third array element. Adjustment of the combining amplitude and phase relationships permits the variation of the underside falloff separation. The fixed low beam is, of course, also used for transmission at high power. Design parameters for a typical surveillance radar application axe discussed for a linearly polarized case. Calculated antenna patterns and free-space coverage diagrams are presented. The complexities of extending the feed network concept to handle switchable linear/circular polarization cases and an integral directional beacon pattern for L band systems are indicated.

Antenna system with several individual units - consists of set of antennae between which further units for smaller frequency range are inserted

Abstract: Individual antennas are mounted in a plane and can be connected as required. In order to widen the antenna frequency range without increasing secondary lobes of its directional characteristic and without unwanted couplings between adjacent individual antennas, the packing density of antennas is increased by insertion between each two wide band antennas for the full antenna system frequency range, of a similar antenna for a part of the total frequency range. Alternatively two or more individual antennas of the same or similar type for the same or for different parts of the total frequency range may be inserted.

Electronic scanning antenna using a nonuniformly-spaced planar array

Abstract: In a uniformly-spaced planar-array antenna, when the main beam electronically scans a wide angle, the sidelobe near the secondary mainlobe, and even the secondary mainlobe, may emerge from imaginary space to real space. In this paper, a new method for calculating the separation between the elements of a planar array is presented. The employment of this method not only reduces the above wide-angle-scanning problem, it also can result in a reduction of sidelobes as compared with a uniformly-spaced array. Two cases with uniform and nonuniform excitation for a uniformly-spaced planar array with 20 × 20 elements are shown. In both cases, the uniformly-spaced planar array is used as a base from which the related nonuniformly-spaced array is obtained. A comparison of sidelobes, beam broadening and numbers of elements have been done while the main beam moved in elevation between ±50° or ±60°, depending on weightings, and in azimuth from zero to 90°. A sidelobe reduction of about 6.8 dB for an unweighted planar array and about 3.3 dB for a weighted array, as compared with the uniform spacing, between the above angles, have been obtained. These results have been accomplished by increasing the halfbeam broadening by about 1.17, as compared to a uniformly-spaced array scanned through the same region.

P-Band loop antennas in radial array

Abstract: A P-band uniform loop antenna system simulating the small uniform in-phaseurrent loop by using a number of smaller radiating elements that are connected in phase so that each current in each element is in phase. Thus, a small uniform loop radiation pattern is simulated, but the loop elements are arranged on a radius that is not small compared to a wavelength, and are located around a cylinder.

Control of small phased-array antennas

Abstract: Series of reports, patent descriptions, calculator programs, and other literature describes antenna control and steering apparatus for seven-element phased array. Though series contains information specific to particular system, it illustrates methods that can be applied to antennas with greater or fewer numbers of elements. Included are programs for calculating beam parameters and design functions and information to interfacing digital controller to beam-steering apparatus.

The Measurement of Echo Direction in a Phased-Array Radar

Abstract: For a planar-array antenna with a monopulse feed horn, this study describes a simple algorithm for the determination of the direction of target echoes. Antenna pattern measurements of the array indicate that the direction sines of a received wavefront can be independently obtained with one simple relation between a normalized difference channel output and a direction sine. This paper determines the accuracy of the algorithm.

Dipole Array on a Transmission Line.

Abstract: : Gain and pattern calculations have been made for an end-fire array of dipoles on a transmission line. For uniform dipole separation it is found that the array gain is a function of the line characteristic impedance and it attains a maximum value for a certain characteristic impedance. Two principal gain maxima are found to exist and the first one corresponding to a shorter uniform interdipole distance has a higher value and it is generally sharper than the other. An array with even number of dipoles has zero gain for the uniform interdipole distance of about half a wavelength. On the other hand, arrays with odd number of dipoles show a small relative maximum at the same interdipole distance. For a given line, the uniform dipole separation corresponding to the gain maxima appears to be independent of the termination. When the end-fire array gain is maximized by varying the interdipole distances and individual dipole lengths, the maximum array gain and the beam width seem to be more or less independent of the transmission line impedance and the termination. The maximum array gain is about N squared, where N is the number of dipoles in the array. (Author)