Showing papers in "IEEE Transactions on Antennas and Propagation in 1972"

First-order theory and analysis of MF/HF/VHF scatter from the sea

Abstract: Scatter from the sea near grazing from MF through VHF is analyzed in this paper. Results based on the compensation theorem show that the dependence upon the grazing angles, as well as upon frequency, range, and the effective surface impedance, can be removed for vertical polarization as the familiar "Norton attenuation factors." Time variation of the surface is included, and results are derived for both the average received power and its spectral density. The first-order dispersion relationship for gravity waves is used to show that the received spectrum from a patch of sea consists of two discrete Doppler shifts above and below the carrier, predictable from simple Bragg diffraction considerations. Using the Phillips wind-wave model as an upper limit for wave heights, estimates for \sigma^{0} (radar cross section per unit area) of - 17 dB are obtained near grazing. Both the magnitude of \sigma_{\upsilon u}^{0} predicted from theory and the nature of the received spectrum are compared with measurements, and the agreement supports the theory on both counts. Finally, the use of MF/HF radars for measuring sea state is suggested and discussed.

Delay Doppler characteristics of multipath propagation at 910 MHz in a suburban mobile radio environment

Abstract: Statistical descriptions of the time delays and Doppler shifts associated with multipath propagation in a suburban mobile radio environment obtained from bandpass impulse response measurements are presented. The measuring equipment which has 0.1 \mu s resolution in time delay and a data output bandwidth of less than 5 kHz is also described. For the first time small scale statistics of the multipath propagation for vehicle travel distances on the order of 30 m along streets are presented in the following forms: 1) average power-delay profiles made up of over 200 individual profiles, 2) cumulative distributions of signal amplitude at fixed delays, and 3) radio frequency Doppler spectra at fixed delays. Delay spreads for typical suburban streets are on the order of 0.25 \mu s. Extreme cases have paths with significant amplitudes at excess delays of 5 to 7 \mu s and the square root of the second central moment delay spreads up to about 2 \mu s. Often the signal at fixed delays has a Rayleigh distributed amplitude but large departures from the Rayleigh distribution also occur. RF Doppler spectra at fixed delays indicate that some of the multipath is from one relatively discrete scattering center while at other delays several scattering centers distributed widely in angle are involved. The observed RF Doppler spectra are consistent with the cumulative amplitude distributions at the same delays.

Characteristic modes for dielectric and magnetic bodies

Abstract: A theory of characteristic modes for material bodies, both with and without losses, is developed. For loss-free bodies, the modes consist of a set of real characteristic sources which diagonalize the generalized network matrix for the body, and a set of characteristic fields which diagonalize the scattering matrix. Most of the properties of these modes remain the same as those of the corresponding modes for perfectly conducting bodies. For lossy bodies, the corresponding modes have complex characteristic sources. However, in the lossy case there also exists a set of real characteristic sources which diagonalize the generalized network matrix, but their fields do not diagonalize the scattering matrix.

Control of radar scattering by reactive loading

Abstract: A method for obtaining a desired radar scattering pattern by reactively loading a conducting body is given. The theory uses the concept of characteristic modes of a loaded body. Any desired real current can be resonated by reactive loads to make it the dominant mode current of that body. If no other mode is near resonance, the radar scattering pattern becomes nearly the same as the radiation pattern of the resonated current. A quality factor Q is defined as a measure of the broadband behavior of a scatterer. Procedures for computing the real currents having minimum Q and maximum gain-quality ratio are given. A pattern synthesis procedure is developed for obtaining the real current whose radiation field pattern is the least mean-square approximation to a desired field pattern. Numerical examples are given for each procedure discussed.

Spatial sampling and filtering in near-field measurements

Abstract: A sample spacing criterion and a data minimization technique for measurements made over the surface of a plane in the near field of an antenna are presented. The sample spacing is shown to depend on the distance from the antenna to the measurement plane, and on the extent to which evanescent waves can be neglected. The near-field data minimization technique utilizes two-dimensional spatial filtering to effect a significant reduction in computational effort required to calculate selected portions of the far-field pattern. Far-field patterns of an X band antenna calculated from near-field measurements are presented and compared with those measured on a standard far-field range. The far-field calculations are repeated for several near-field sample spacings and for various post-filter sample rates.

The peak sidelobe of the phased array having randomly located elements

Abstract: A formula is derived for the peak sidelobe level of a phased array in which the elements are randomly located. The parameters of the formula are the number and size of the array elements, size of the array, wavelength, beamsteering angle, and signal bandwidth. The theory is tested by measurement of the peak sidelobe of several hundred computer-simulated random arrays. Unlike the case for the conventional array the effect of spatial taper (nonuniform density of element location) upon the peak sidelobe level is minor. The peak sidelobe of the two-dimensional planar array is approximately 3 dB higher than that of the linear array of the same length and same number of elements.

A numerical solution for the near and far fields of an annular ring of magnetic current

Abstract: A simple method for calculating the near and far zone fields from an annular ring of circumferentially directed magnetic current which may be used to represent coaxial apertures is presented. Near-field contours are given for two ring sizes. The utility of the method has been illustrated by its application in several practical antenna problems where the magnetic ring current serves as the primary source. Among these are the analysis of dipole antennas mounted on a conducting sphere or cylinder, the impedance of a coaxially fed Yagi-Uda antenna, a coaxially driven wire loop, and the radiation from a coaxial aperture at the base of a cone.

Temporal frequency spectra of multifrequency waves in turbulent atmosphere

Abstract: General formulations for temporal frequency spectra of the fluctuations of plane, spherical, and beam waves operating at two frequencies are given based on weak turbulence and frozen-in assumptions. The cross spectra and the coherence are obtained for the amplitude at two frequencies, the phase at two frequencies, and the amplitude at one frequency and the phase at another frequency. The results are examined in detail for plane and spherical waves. For the spectrum of the index of refraction \kappa^{-n} in the inertial subrange, the amplitude spectrum behaves as k^{(5-n)/2} for \omega \rightarrow 0 and k^{2}\omega^{1-n} for \omega \rightarrow \infty . The phase spectrum for \omega\rightarrow 0 and for \omega\rightarrow\infty behaves as k^{2}\omega^{1-n} with different constants. These results agree well with the experimental work of Janes et al. [11] at 9.6 and 34.5 GHz, and explains the ratio of the spectra at two frequencies. Also noted is the experimental slope of -2.6 as and for \omega \rightarrow \infty which may be compared with 1-n = -2.66 using the Kolmogorov spectrum of n = 11/3 . The amplitude and phase coherence are calculated, and the results agree well with the experimental data. This agreement is indicative of the general validity of the theory for frequencies as low as 10\sim30 GHz and the path length as long as 60 km. It is also shown that using the preceding theory, the wind velocity and the structure constant C_{n} can be deduced from the experimental data. Theoretical wind velocity of 15.6 knots obtained from the propagation data compares favorably with the meteorologically measured value of 14 knots, and two values of C_{n} obtained independently from the amplitude and phase measurements closely agree with each other.

Antenna synthesis and solution of inverse problems by regularization methods

Abstract: Antenna pattern synthesis is discussed as an example of "improperly posed" problems. This serves the purpose of introducing a concept that is useful in many other applications: remote sensing, inverse scattering, etc. It also suggests that regulation methods that have been devised to "solve" improperly posed problems can be applied to antenna synthesis and the aforementioned problems. This gives systematic methods for solving the pattern synthesis problem even when the element patterns are arbitrary.

A portable coaxial collinear antenna

Abstract: A novel collinear antenna constructed of coaxial cable with inner- and outer-conductors interchanged at half-wavelength intervals is described. A 26-element antenna of this type has been constructed and evaluated. Design criteria presented allow extension to the use of coaxial cable of different types in a variety of radio/radar arrays.

A new numerical approach to the calculation of electromagnetic scattering properties of two-dimensional bodies of arbitrary cross section

Abstract: A new method is introduced for formulating the scattering problem in which the scattered fields (and the interior fields in the case of a dielectric scatterer) are represented in an expansion in terms of free-space modal wave functions in cylindrical coordinates, the coefficients of which are the unknowns. The boundary conditions are satisfied using either an analytic continuation procedure, in which the far-field pattern (in Fourier series form) is continued into the near field and the boundary conditions are applied at the surface of the scatterer; or the completeness of the modal wave functions, to approximately represent the fields in the interior and exterior regions of the scatterer directly. The methods were applied to the scattering of two-dimensional cylindrical scatterers of arbitrary cross section and only the TM polarization of the excitation is considered. The solution for the coefficients of the modal wave functions are obtained by inversion of a matrix which depends only on the shape and material of the scatterer. The methods are illustrated using perfectly conducting square and elliptic cylinders and elliptic dielectric cylinders. A solution to the problem of multiple scattering by two conducting scatterers is also obtained using only the matrices characterizing each of the single scatterers. As an example, the method is illustrated by application to a two-body configuration.

An experimental study of a balun-fed open-sleeve dipole in front of a metallic reflector

Abstract: The characteristics of a balun-fed open-sleeve dipole mounted in front of a metallic reflector for operation in the 225 to 409 MHz band are investigated. A parametric study is made of the VSWR response as a function of dipole and sleeve diameter, sleeve length, and sleeve-to-dipole spacing. It is shown that an open-sleeve dipole can be operated over a bandwidth of 1.8:1 as compared with an operating bandwidth of approximately 1.25:1 for a conventional cylindrical dipole with the same diameter. Pattern and gain data are presented for an open-sleeve dipole mounted in front of a flat metallic reflector. Preliminary results on mutual coupling effects are also discussed.

Mutual coupling in phased arrays of randomly spaced antennas

Abstract: Mutual coupling effects in phased arrays with randomly located elements are studied. The network formulation of antenna arrays is found to be a convenient and useful approximation. Two main effects of coupling are separately considered. The first is the increase in the sidelobe level. A new solution for the distribution of sidelobe level has been obtained which is applicable even for small arrays. It is found that the increase in sidelobe level is noticeable only for small average spacing (e.g., less than 2.5 wavelengths). The second effect of coupling is that it causes the fluctuation of main-beam amplitude as a function of the scan angle. The probabilistic properties of these fluctuations are studied. In the uniformly spaced arrays the accumulation of coupling effects may cause "blind angles". In random arrays this accumulation is highly improbable. This method of removing blind angles is further illustrated by an experiment on diffraction gratings where Wood's anomalies and blind angles are recognized as identical phenomena. Finally, an important contribution of this investigation is the analysis by various methods of the radiation pattern of random array. The results obtained by these methods agree remarkably well with the Monte Carlo simulations.

Formulation of echelon dipole mutual impedance for computer

Abstract: A concise formula suitable for computer calculations is given for mutual impedance of two dipoles with sinusoidal current in echelon. It is a rearrangement of that of King [2].

Aperture efficiency enhancement in dielectrically loaded horns

Abstract: The effect of symmetrically loading a horn aperture with E -plane dielectric slabs is examined both theoretically and experimentally. It is shown that aperture efficiencies of the order of 92-96 percent may be obtained easily and inexpensively. The technique, which was demonstrated experimentally for a small horn aperture, might find application in limited scan arrays.

The Toeplitz matrix: Its occurrence in antenna problems and a rapid inversion algorithm

Abstract: A special form of the Toeplitz matrix which frequently occurs in the numerical solution of antenna analysis and synthesis problems is discussed. Specific examples are presented illustrating its occurrence in the solution of the integral equation for a thin cylindrical antenna and in the theory of arrays. A matrix inversion algorithm is presented which, by exploiting the unique symmetry properties of the Toeplitz matrix, specifies the inverse matrix elements in terms of recurrence relationships. In this way computational time is proportional to the square of the matrix order rather than the cube as is the case with a general algorithm.

VLF/ELF input impedance of an arbitrarily oriented loop antenna in a cold collisionless multicomponent magnetoplasma

Abstract: A study is made of the input impedance Z of a small strip-loop antenna with arbitrary orientation in a cold collisionless uniform multicomponent magnetoplasma. Assuming a uniform current distribution, an integral expression for Z is derived which is valid for arbitrary values of driving frequency, plasma composition and density, loop orientation angle \phi_{0} , and static magnetic field strength. The integral expression is evaluated numerically for the VLF/ELF range in a plasma modeled upon the inner magnetosphere. Approximate closed-form expressions for Z are also developed. It is found that the loop VLF/ELF input reactance is essentially identical to its free space self inductance. Also the loop radiation resistance is found to be a strong function of \phi_{0} for frequencies near the lower-hybrid-resonance frequency or below the proton gyrofrequency. In addition it is found that for small loops a second-order quasi-static theory correctly predicts Z over much of the VLF/ELF range.

Satellite altimetry using ocean backscatter

Abstract: A model for the signal received when satellite altimetry pulses are scattered back by the ocean's surface is postulated and analyzed. The second-order statistics of the complex nonstationary random process appearing at the detector input are graphically and analytically displayed as a function of the sea state. The standard deviation of various altitude estimates derived by subsequent operations on the detector output are computed, too. The analysis applies both to ordinary short-pulse altimeters and to systems that employ pulse compression.

Radiation efficiency of electrically small multiturn loop antennas

Abstract: The radiation efficiency of electrically small multiturn loop antennas is calculated using an ohmic resistance which includes both the normal skin effect and the additional loss due to the proximity effect.

The extended boundary condition solution of the dipole antenna of revolution

Abstract: By applying Waterman's extended boundary condition a general formulation is developed for the dipole antenna of revolution. Both transmission and scattering from the antenna are considered with no formal restrictions on the antenna dimensions. As examples, the prolate-spheroidal and solid-cylindrical geometries are considered.

A modal analysis of the dielectric rod antenna excited by the HE 11 mode

Abstract: A hybrid modal solution is developed for the circular semi-infinite dielectric rod antenna excited in the HE_{11} hybrid mode. Numerical results for the near-zone and far-zone fields, as well as the gain, beamwidth, and percentage of power radiated, are determined for three rods of different diameter and dielectric constant by enclosing the rods with a concentric metal pipe and allowing the radius of the pipe to become large. Comparison is made between these results and previous approximate methods of solution that have been applied to the dielectric rod antenna.

Comparison of radio transmission at X-band frequencies in suburban and urban areas

Abstract: Measurements were made at a frequency of 11.2 GHz of the signal strength received by a fixed-base station from a mobile transmitter. Distributions of the instantaneous and rms signal levels are compared for data taken in New York City and suburban New Providence, N. J.

Numerical analysis of electromagnetic radiation properties of smooth conducting bodies of arbitrary shape

Abstract: A numerical-theoretical technique is described for determining the surface current density distribution and subsequently the near- and far-zone fields of an arbitrarily shaped perfectly conducting body excited by an arbitrary primary source. The arbitrary surface is described by dividing it into a number of connected cells which are mathematically described as quadric surfaces. The "arbitrary body" formulation is applied to two configurations; namely the radial dipole above a conducting cylinder of finite length and a quarter-wavelength monopole mounted atop the fuselage of a CH-47 helicopter. The numerical results are compared with those obtained through an experimental program as well as those obtained by alternate numerical means and good agreement is noted.

The diffraction matrix for a discontinuity in curvature

Abstract: To enlarge the scope of the geometrical theory of diffraction, the diffraction matrix for a surface singularity where the curvature but not the slope is discontinuous is rigorously derived. The model that is employed consists of two parabolic cylinders of different latus recta joined together at the front, thereby creating a line discontinuity of the required form. For each of the two principal polarizations, asymptotic developments of the surface fields in the vicinity of the join are calculated, from which the diffraction coefficients are then obtained by integration. The results differ significantly from the physical optics estimates and are analogous to those for a wedge-like singularity. This analogy permits a trivial deduction of the complete diffraction matrix.

The monopole slot: A small broad-band unidirectional antenna

Abstract: A small radiating structure has been developed which, operating on a large ground plane, maintains stable input impedance and a unidirectional-beam pattern over bandwidths of 10 to 1 or more. Impedance stability and directivity are obtained from this small antenna at the cost of frequency-dependent efficiency. Useable bandwidth, being determined by factors other than impedance match, may therefore exceed that for other small antennas with fixed matching networks.

Scattering of waves with normal amplitude distribution from cylinders

Abstract: The scattering of waves with a Gaussian amplitude distribution from perfectly conducting and radially inhomogeneous dielectric cylinders is presented. The plane wave scattering solution is obtained as the limiting case when the radius of the scatterer is much smaller than the size of the wave. The scattering of beam waves from spherically symmetric particles was considered recently by Morita et al. [1]. In this communication the case of scattering of waves with a Gaussian amplitude distribution from cylindrically symmetric and infinitely long targets is considered. In a future contribution the scattering of beam waves at normal and oblique incidence from cylindrically symmetric fibers will be reported.

Kirchhoff theory: Scalar, vector, or dyadic?

Abstract: The superior nature of the Franz formula as compared to that of Stratton and Chu is pointed out. A connection between the two distinct formulas is shown. The compactness of the dyadic version of Franz' formula is emphasized.

Dielectric-loaded horn antenna

Abstract: A wide-band dual-mode horn, which has a rotationally symmetric beam and extremely low sidelobe levels, can be obtained by loading a dielectric band inside the horn antenna. Measured radiation characteristics of such antennas, including the so-called shaped-beam antenna, are shown.

Subsurface electromagnetic fields of a circular loop of current located above ground

Abstract: The electromagnetic fields produced by a circular loop of current is considered for a homogeneous half-space model of the earth. The integral representations for the subsurface field are evaluated numerically and presented in graphical form.

The effect of the thin-wire approximation and the source gap model on the high-frequency integral equation solution of radiating antennas

Abstract: The effect of using the thin-wire approximation in the integral equation solution of radiating antennas is discussed in this communication. In addition, the effect of having a source region which varies with the number of matching points used for solving the integral equation is considered. It is found that these effects can cause large errors in the solution at high frequencies and may cause appreciable error in the time domain response of the antenna if it is calculated by Fourier inversion.