Showing papers in "IEEE Transactions on Antennas and Propagation in 1964"
TL;DR: In this paper, a method is presented for evaluating the Q of an antenna, where the Q is defined as in conventional network theory, and the method consists of subtracting the energy density associated with the power flow from the total energy density, thus enabling the magnetic and electric reactive energy to be computed.
Abstract: A method is presented for evaluating the Q of an antenna, where the Q is defined as in conventional network theory. The method consists of subtracting the energy density associated with the power flow from the total energy density, thus enabling the magnetic and electric reactive energy to be computed. Specific application of the method is made to the evaluation of the Q of spherical and cylindrical modes. It is verified that the Q becomes very large when the order of the mode exceeds k_{0}a where a is the radius of the sphere or cylinder on which the sources are located.
479Â citations
TL;DR: In this article, it was shown that the required number of elements is closely related to the desired sidelobe level and is almost independent of the aperture dimension, and the resolution or the beamwidth depends mainly on the aperture dimensions.
Abstract: Various probabilistic properties of a large antenna array with randomly spaced elements have been studied. It is found that for almost all cases of practical interest the required number of elements is closely related to the desired sidelobe level and is almost independent of the aperture dimension, the resolution (or the beamwidth) depends mainly on the aperture dimension, and the directive gain is proportional to the number of elements used if the average spacing is large. As a consequence the number of elements required is considerably less than that with uniform spacings. Starting with a given number of elements and a given aperture size, it is possible to improve the resolution by a factor of ten, a hundred, or more by spreading these elements over a larger aperture with little risk in obtaining a much higher sidelobe level and a lower directive gain. In fact, this method offers a solution which is optimum in a certain statistical sense, i.e., all sidelobes are of equal level with equal probability. In addition, this analysis also gives a simple estimate of the sidelobe level of most nonuniformly spaced antenna arrays. In a number of such arrays studied by various investigators with high speed computers, the agreement found is remarkable.
330Â citations
TL;DR: A retrodirective array using a single microwave mixer to accomplish conjugate phase shift in each element is described in this paper, which has an advantage over the Van Atta array in that the elements are not restricted to being located on a plane surface.
Abstract: A retrodirective array using a single microwave mixer to accomplish conjugate phase shift in each element is described. Reradiated patterns were measured for a four-element array to substantiate the predicted performance. This array has an advantage over the Van Atta array in that the elements are not restricted to being located on a plane surface. It is more efficient than the previously used method of employing two mixers to provide conjugate phase shift because of the reduction in converison loss and LO (local oscillator) power.
312Â citations
TL;DR: The application of the optimization technique known as dynamic programming to the design of "thinned" arrays with unequally-spaced elements is described and the results obtained compare favorably with similar results found by other design techniques.
Abstract: The application of the optimization technique known as dynamic programming to the design of "thinned" arrays with unequally-spaced elements is described. Dynamic programming is a systematic procedure for efficiently utilizing the capabilities of modern high-speed digital computing machines to find solutions to problems not computationally feasible by conventional means. In this paper it is applied to the design of linear arrays of 25 elements spaced within a 50 wavelength aperture. The results obtained compare favorably with similar results found by other design techniques. The effect on the sidelobes of varying the angular region of optimization and the spacing-quantization is also explored.
224Â citations
TL;DR: In this article, it was shown that in a large planar array with a very large number of regularly-spaced radiating elements, perfect impedance match for all scan angles can be postulated for every typical element without encountering any real discrepancy in the determination of element gain.
Abstract: In a phased-array antenna with a very large number of regularly-spaced radiating elements, the gain realized at the beam peak is equal to the number of elements times the gain realized in the same direction when only one typical element is excited. The ideal radiation pattern of one such element in a large planar array has a cosine variation of gain with angle when the elements are closely spaced, and has a peak value of gain equal to 4\pi A/\lambda^{2} where A is the area allotted to each element. The active impedance of each element in a practical phased array varies with scan angle, because of mutual coupling between the elements. The associated mismatch causes power to be returned to the generators, thereby reducing the gain realized by the array and by the element. The element pattern, measured in the proper environment of surrounding elements, deviates from the ideal pattern in proportion to this effect. Mutual coupling is inherently unavoidable in a closely-spaced infinite array of elements; for example, in a square array with less than \lambda/\sqrt{2} spacing. There is a loss of element efficiency caused by the coupling, and since coupling increases with closer spacing, this accounts for the lower gain expected from ideal elements with reduced allotted area. Grating lobes can exist when the elements are not closely spaced; for example, in a square array with more than \lambda/2 spacing. In this case, the ideal pattern is truncated to discriminate against grating lobes; this gives the higher gain expected from ideal elements with larger allotted area. It is concluded that in a phased-array antenna having a very large number of regularly-spaced radiating elements, perfect impedance match for all scan angles can be postulated for every typical element without encountering any real discrepancy in the determination of element gain. In the absence of grating lobes, such an antenna would realize the greatest possible gain for all scan angles.
204Â citations
TL;DR: In this article, the authors considered the design of "thinned" planar array antennas in which the density of elements located within the aperture is made proportional to the amplitude of the aperture illumination of a conventional "filled" array.
Abstract: The design of "thinned" planar array antennas is considered in which the density of elements located within the aperture is made proportional to the amplitude of the aperture illumination of a conventional "filled" array. Density tapering permits good sidelobe performance from arrays of equally radiating elements. The selection of the element locations is performed statistically by utilizing the amplitude taper as the probability density function for specifying the location of elements. The statistical design procedures and the theoretical prediction of performance are given. Application to a 50 wavelength diameter planar aperture is discussed and the results compared to conventional amplitude-taper designs. Examples of computed patterns are shown for density tapers modeled after 25, 30, 35, and 40 db circular Taylor distributions. The properties of a planar array of 10,000 elements are examined for "natural" thinning and for 70 per cent and 90 per cent of the elements removed. The sidelobes are determined more by the number of remaining elements than by the model amplitude taper. Statistically designed density-tapered arrays are useful when the number of elements is large and when it is not practical to employ an amplitude taper to achieve low sidelobes.
173Â citations
150Â citations
TL;DR: In this paper, the properties of circular and square loop antennas as probes for measuring the magnetic field were investigated and the response of an electrically small loop to the magnetic and the electric components of a given electromagnetic field was determined theoretically for singly-and doubly-loaded loops in terms of suitably defined constants.
Abstract: The properties of circular and square loop antennas as probes for measuring the magnetic field are investigated. The response of an electrically small loop to the magnetic and the electric components of a given electromagnetic field is determined theoretically for singly- and doubly-loaded loops in terms of suitably defined constants. A system error ratio is defined as a measure of the ability of a given probe to discriminate against the effects of the electric field. An experimental procedure for measuring loop sensitivities in the elliptically polarized near field of a quarter-wave monopole is described. Experimental and theoretical results are compared. It is concluded that very large errors are possible when a singly-loaded loop is used to measure magnetic fields unless its diameter is less than 0.01\lambda . The doubly-loaded probe may be used with comparable accuracy when its diameter is as large as 0.15\lambda .
147Â citations
TL;DR: In this article, a grid or mesh structure is described for a linearly polarized traveling-wave antenna with the main lobe of radiation in a backward angle-fire direction, where the direction of the beam is a function of the frequency.
Abstract: A new type of array is described which consists of a grid or mesh structure situated parallel and close to a flat conducting sheet. It operates as a linearly polarized traveling-wave antenna with the main lobe of radiation in a backward angle-fire direction. The direction of the beam is a function of the frequency. Operation of the antenna is analyzed by simple array theory and comparisons are made between calculated and measured performance. An application of the array as a radio telescope antenna is mentioned.
138Â citations
TL;DR: In this article, the integral equations for scattering by a set of parallel metallic cylinders, each cylinder of arbitrary cross section, are solved directly by means of a digital computer program giving the current distribution induced on the scatterer surfaces, the scattering cross section vs azimuthal angle, and the induced field ratio (IFR) for both parallel and perpendicularly polarized incident waves.
Abstract: The integral equations for scattering by a set of parallel metallic cylinders, each cylinder of arbitrary cross section, are solved directly by means of a digital computer program giving the current distribution induced on the scatterer surfaces, the scattering cross section vs azimuthal angle, and the induced field ratio (IFR) for both parallel and perpendicularly polarized incident waves. The present program is suitable for cylinders up to 25\lambda to 40\lambda circumference. The validity of the computer program has been verified by comparing results 1) with exact calculations for circular cylinders, 2) with measured values for more than 40 rectangles and rectangles with feathered and rounded faces, and 3) by interchanging the direction of incidence and the direction of observation, whereby, according to the reciprocity theorem, the observed scattered field must remain the same.
134Â citations
TL;DR: In this article, the optimum directivity of various types of uniformly spaced broadside arrays of dipoles is investigated theoretically and the formulation is processed with the aid of an array matrix.
Abstract: The optimum directivity of various types of uniformly spaced broadside arrays of dipoles is investigated theoretically in this paper. The formulation is processed with the aid of an array matrix. The expression for the optimum directivity and the corresponding excitation are expressed directly in terms of the elements of the array matrix. The computed values are assembled in several sets of curves, and the results are compared with the directivity of uniformly excited arrays.
TL;DR: In this paper, a self-phasing array antenna is described which operates on the incident wavefront in such a manner that when it is retransmitted it returns whence it came as a coherent wavefront irrespective of the original phase distribution incident on the array.
Abstract: A self-phasing array antenna is described which operates on the incident wavefront in such a manner that when it is retransmitted it returns whence it came as a coherent wavefront irrespective of the original phase distribution incident on the array. Self-phasing is useful where a two-way propagation path is available and where a conventional antenna cannot operate efficiently because of an unknown phase distribution in the incident wavefront. The operation of a self-phasing array, its properties, its relation to other antenna design techniques and its potential applications are discussed.
TL;DR: In this article, the authors considered the scattering of electromagnetic waves by an infinitely long anisotropic plasma-coated conducting cylinder and obtained complete expressions for the scattered electric and magnetic fields.
Abstract: This paper considers the scattering of electromagnetic waves by an infinitely long anisotropic plasma-coated conducting cylinder. The source is assumed to be a magnetic current filament which gives rise to an incident magnetic field with only an axial component. Complete expressions for the scattered electric and magnetic fields are obtained. Scattering by an anisotropic plasma column and that by an isotropic plasma-coated conducting cylinder are special cases of the present problem.
TL;DR: In this article, a theoretical and experimental study of the minimization of the back scattering by a thin cylinder by central loading is presented, where the induced current on a centrally loaded cylinder illuminated by a plane wave at normal incidence was determined theoretically and experimentally.
Abstract: A theoretical and experimental study of the minimization of the back scattering by a thin cylinder by central loading is presented. The induced current on a centrally loaded cylinder illuminated by a plane wave at normal incidence was determined theoretically and experimentally. The magnitude and phase of the induced current can be greatly changed by a central impedance. The optimum loading to achieve zero back scatter in the broadside direction from a thin cylinder shorter than two wavelengths and the optimum central impedance for the purpose of minimizing the broadside back scattering from a thin cylinder over a wide range of frequencies has been determined.
TL;DR: In this paper, the inherent spherical aberration of a spherical reflector antenna is corrected by using an auxiliary Gregorian reflector feed system that rotates about the center of curvature of the reflector.
Abstract: The inherent spherical aberration of a spherical reflector antenna is corrected by using an auxiliary Gregorian reflector feed system that rotates about the center of curvature of the reflector. Tests at both X - and K -band frequencies demonstrate feasibility of the design for wide-angle scanning.
TL;DR: In this paper, the impedance of a finite electric dipole immersed in a homogeneous, anisotropic, magneto-ionic medium with parameters appropriate to "whistler" frequencies in the ionosphere was evaluated.
Abstract: This paper evaluates the impedance of a finite electric dipole immersed in a homogeneous, anisotropic, magneto-ionic medium with parameters appropriate to "whistler" frequencies in the ionosphere, i.e., X > Y^{2} \gg 1 . Although the basic formulation is also valid when collision frequency is taken into account, the computations presented here were made under the assumption that the collision frequency is zero. Under this assumption, all the matrices involved are Hermitian and the computations are simplified considerably. It is pointed out that in the ionosphere the VLF point dipole will have an infinite resistance as well as reactance even when neglecting losses in the medium. This "infinity catastrophe" cannot be removed by assuming small losses in the medium. It can be removed only by considering the finite dimensions of the antenna. A physical explanation of this phenomenon is presented, and some results for both resistance and reactance are given as a function of antenna dimensions, orientation and ionospheric parameters. A discussion of the far-field antenna pattern is also presented.
TL;DR: In this paper, a series of rigorous numerical calculations of the backscatter cross section of a conducting sphere with a thin lossless dielectric coating were carried out, and curves of the results are presented which indicate that the back scatter cross-section of a coated sphere may be increased by as much as a factor of ten over that of an uncoated sphere of the same size, and, due to interference effects, an even greater decrease may be obtained.
Abstract: Several series of rigorous numerical calculations of the backscatter cross section of a conducting sphere with a thin lossless dielectric coating were carried out. The ratio of the radius to wavelength was varied from about 0.02 to 10.0; the dielectric constant of the coating was taken to be 2.56, 4.0, or 6.0; and the thickness of the coating was 0.1 or 0.05 times the outer radius of the coated sphere. Curves of the results are presented which indicate that the backscatter cross section of a coated sphere may be increased by as much as a factor of ten over that of an uncoated sphere of the same size, and, due to interference effects, an even greater decrease may be obtained. Further, small changes (less than one per cent) in the thickness or dielectric constant of the coating, or in the wavelength, may bring about large changes in the cross section. The numerical results are also compared with some experimental measurements, and with predictions of a "creeping-wave" type of analysis carried out by Helstrom.
TL;DR: In this paper, the concept and design of an active retrodirective array, resulting from the specialized requirements and constraints of space/earth communications, is presented. And the advantages of employing active microwave gain are discussed.
Abstract: The concept and design of an active retrodirective array, resulting from the specialized requirements and constraints of space/earth communications, is presented. The advantages of employing active microwave gain are discussed. The attendant problem of instability is defined and several aspects of the solution, namely frequency offsetting and polarization isolation, are detailed. The latter technique makes use of orthogonally polarized "subarrays" -one for receiving and one for transmitting-intermeshed on a common aperture surface. A discussion of tolerable phase errors and the effect of element failure on the system reliability is presented. Techniques for realizing the active circuitry required for the functions of RF amplification, frequency conversion and modulation are described. An experimental model, employing strip transmission line techniques throughout, was fabricated and tested. All results, including those of array gain, retrodirectivity and simultaneous retrodirectivity from several sources at different frequencies, and effects of element removal, corresponded closely to their calculated predictions.
TL;DR: In this article, the general problem of the insulated antenna in an isotropic homogeneous medium of infinite extent is reviewed under the assumption that the medium is sufficiently conducting to permit the application of coaxial line theory.
Abstract: The general problem of the insulated antenna in an isotropic homogeneous medium of infinite extent is reviewed under the assumption that the medium is sufficiently conducting to permit the application of coaxial line theory. The currents and associated electromagnetic fields for the completely insulated antenna are obtained and the directional properties of the latter explained by comparison with a collinear array. An antenna in which only a central portion is insulated, while the ends are bare, is analyzed in terms of the theories of the insulated and bare antenna, both when the structure is driven by generators at the junctions of the bare and insulated sections and when it is driven by an internal coaxial feeder in the manner of a sleeve dipole. Finally, the center-driven insulated antenna with bare ends is investigated and its field is compared with that of the antenna driven at the junctions of the bare and insulated sections.
Journal Article•
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TL;DR: In this paper, a four-element broadside array of antenna-amplifier arrays is described in which the gain of each element is varied by controlling the base bias, and the resulting measured and calculated patterns, half-power beamwidths, gain over a half-wavelength dipole, and noise temperatures are presented.
Abstract: The integrated transistorized dipole antennafier (antenna-amplifier) is ideally suited for use in array systems. The advantages include ease of amplitude-distribution control, low noise, high gain, high reliability and simplicity. The integration is achieved by using the antenna as a circuit element of the transistorized amplifier, thus eliminating the tuned input circuits and transmission lines commonly used. A four-element broadside array of antennafiers is described in which the gain of each element is varied by controlling the base bias. Binomial, uniform, edge and Dolph-Chebyshev distributions were chosen to show the wide variation of beam control possible; the resulting measured and calculated patterns, half-power beamwidths, gain over a half-wavelength dipole, and noise temperatures are presented. A method of experimentally evaluating the noise performance, based on a theoretical development, is also described.
TL;DR: The linear aperture synthesis method of Woodward and Levinson is extended to a circular distribution in this article, which includes circularly symmetric and nonsymmetric radiation patterns, and the results are applicable to the design of reflector feeds and to electronically scanned arrays where a prescribed radiation pattern is desired.
Abstract: The linear aperture synthesis method of Woodward and Levinson is extended to a circular distribution. The extension includes circularly symmetric and nonsymmetric radiation patterns. The results are applicable to the design of reflector feeds and to electronically scanned arrays where a prescribed radiation pattern is desired.
TL;DR: In this article, simplified expressions for the electromagnetic fields produced by a vertical or horizontal magnetic dipole (loop antenna) located in air above the sea were derived for the quasi-near range.
Abstract: Simplified expressions are derived for the electromagnetic fields produced by a vertical or horizontal magnetic dipole (loop antenna) located in air above the sea. The expressions hold over the quasi-near range in both media subject to certain mild restrictions. The solutions are obtained by first applying the boundary conditions to determine the magnetic Hertz potential \bar{\pi}^{\ast} in the form of Sommerfeld integrals, and then relating these to two auxiliary integrals U, V and their derivatives, asymptotic series for which are obtained by extending the work of Banos and Wesley. The horizontal magnetic dipole (loop in the vertical plane) is found to be superior to the vertically-oriented dipole of the same size and excitation from the point of view of field strength induced in the sea at large distances from the source. A comparison with previously published results for the electric dipole shows the magnetic dipole to be better, provided the number of turns in the loop exceeds a certain minimum. An approximate analysis on the basis of equal powers also shows the magnetic dipole to be better except for points near the outer rim of the quasi-near range, where the two types of dipoles are equivalent.
TL;DR: In this article, the normalized input admittance of thin bare circular loop antennas has been evaluated from the theory of T. T. Wu in the case of air and in an infinite homogeneous isotropic dissipative medium.
Abstract: The normalized input admittance of thin bare circular loop antennas has been evaluated from the theory of T. T. Wu. Computations have been made for loops in air and in an infinite homogeneous isotropic dissipative medium. A comparison is also made with Storer's theory of the loop. Numerical results are given in the form of graphs for several wire sizes and for loops up to two and one-half wavelengths in circumference. The properties of the medium are represented by the ratio \alpha/\beta in the range from zero (perfect dielectric) to one (good conductor); \alpha and \beta are the imaginary and real parts of the complex propagation constant k=\beta-j\alpha = \omega\sqrt{\mu(\epsilon-j\sigma/\omega)} where \mu is the permeability, \epsilon the dielectric constant, and \sigma the conductivity of the medium.
TL;DR: In this paper, the authors describe the design and performance of annular slot planar arrays which generate pencil beams and monopulse tracking beams in both principal planes, which can be fabricated inexpensively.
Abstract: This paper describes the design and performance of annular slot planar arrays which generate pencil beams and monopulse tracking beams in both principal planes. These planar arrays consist of a transmission line in the form of a radial waveguide whose upper plate contains annular groups of linear slots. Monopulse operation is obtained by dividing the transmission line into four independently excited quadrants, each of which is propagating a field configuration identical to the dominant H_{01} radial waveguide mode. The antennas radiate linear polarization. In contrast with many other types of two-dimensional waveguide slot arrays, these antennas can be fabricated inexpensively. Small diameter versions possess the following electrical and mechanical advantages when compared to a dish antenna of comparable size: 1) comparable gain, 2) improved backlobe suppression, and 3) more compact size and lower weight. Designs have been developed at X band.
TL;DR: The basic principles of operation of active adaptive receiving and transmitting antenna arrangements, including performance analyses in the presence of noise, are presented in this paper to demonstrate the usefulness of such antennas.
Abstract: Electronically adaptive receiving and transmitting antenna systems which can be employed for ground tracking stations and satellite and space vehicles are discussed. The receiving antenna systems described herein contain active elements which, unlike in passive antenna arrays, automatically adjust the electrical phases of the signals received by the array elements to obtain antenna directivity. The self-focusing feature of these receiving antenna systems is achieved by a set of phase-locked loops, which permit phase adjustments of signals received by various antenna elements continuously regardless of the direction of the transmitting source. For a transmitting antenna, the self-focusing feature is provided by a pilot signal from the receiving station which enables the transmitting antenna beam to point in the direction of the receiving station automatically. The basic principles of operation of active adaptive receiving and transmitting antenna arrangements, including performance analyses in the presence of noise, are presented in this paper to demonstrate the usefulness of such antennas.
TL;DR: In this paper, the surface integral of the fields over the slot plane and over the surface of the plasma layer is derived from the free space Green's function by the method of images, which leads to an integral equation that is reduced to a form suitable for machine computations.
Abstract: The rectangular cavity or waveguide backed slot is covered by a plasma layer of finite thickness. The longitudinal variation of the voltage across the slot is obtained from the variational solution of an integral equation. The solution for plasma layer of finite thickness is obtained from the free space Green's function by the method of images. The fields outside the slot depend on the surface integral of the fields over the slot plane and over the surface of the plasma layer. If the thickness of the plasma layer is large compared with the wavelength, the fields on the surface of the plasma may be related to the voltage distribution along the slot by plane wave reflection coefficients. This leads to an integral equation that is reduced to a form suitable for machine computations. These calculations show the slot admittance to remain almost constant for plasma layers of various thicknesses h . The slot conductance tends to increase for h/ \lambda . The presence of a plasma layer affects the voltage distribution along the slot for a center excited slot. The field distribution along the waveguide excited slot differs only slightly from the principal mode field distribution in the guide.
TL;DR: In this article, the authors made experimental measurements of the nose-on backscattering radar cross section over a range of diameters from 0.05 to 1.0 wavelengths of a series of ogives with total included nose angles of 40\deg, 75\deg, and 120\deg.
Abstract: Experimental measurements have been made of the nose-on backscattering radar cross section over a range of diameters from 0.05 to 1.0 wavelengths of a series of ogives with total included nose angles of 40\deg , 75\deg , and 120\deg ; of cone spheres with nose angles of 15\deg , 30\deg , 40\deg 60\deg and 120\deg ; of double-rounded cones with nose angles of 15\deg , 40\deg , and 75\deg ; and of double-backed cones with nose angles of 40\deg . Further, a series of ogives of approximately the same diameter and with nose angles of 25\deg , 40\deg , 60\deg , 75\deg , 95\deg , 120\deg , 160\deg and 180\deg have also been measured. All the present results have been obtained using two monostatic phase-locked CW balanced-bridge model measurement radars operating at frequencies of 9 Gc and 35 Gc. For targets with maximum dimensions less than two inches, cross sections of less than 10^{-7} square meters at 9Gc and 10^{-6} square meters at 35 Gc can be measured with an accuracy of \pm0.5 db. The experimental data is sufficiently comprehensive to provide qualitative explanations of the scattering mechanism in the Rayleigh and resonance regions, and to make rigorous tests of the various theoretical predictions. An extension of the physical optics theory of Adachi was found to predict accurately the echo area of the ogive, the double-rounded cone, and double-backed cone in the resonance region. The Rayleigh theory was found to be generally accurate for all the models considered. The impulse analysis of Kennaugh and Moffatt was found to be accurate for the cone sphere.