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Phased-array radar systems using wide-band linear-FM pulses suffer from array dispersion. This causes a loss in signal-to-noise (S/N) ratio and in radar range resolution (a broadening of the compressed-pulse width). Depending on the choice of the receiver matched filter (MF) and weighting filter (WF) one or the other of these effects may be minimized. The effects of dispersion in a square planar array with either a parallel feed or a center-fed series feed are studied. Loss in S/N ratio and in range resolution are determined for typical cases, and general curves are given for arrays with arbitrary size, scan range, and signal bandwidth. It is shown that there is an optimum or maximum-useful signal bandwidth for each array, for which the minimum S/N-loss MF-WF design is the same as the ideal-compressed-pulse-shape MF-WF design. For pulses having greater signal bandwidths, time delay steering should be used in the array.

The effect of soil moisture on the radar backscattering coefficient was investigated by measuring the 4-8 GHz spectral response from two types of bare-soil fields: slightly rough and very rough, in terms of the wavelength. An FM-CW radar system mounted atop a 75-ft truck-mounted boom was used to measure the return at 10 frequency points across the 4-8 GHz band, at 8 different look angles ( 0\deg through 70\deg ), and for all polarization combinations. A total of 17 sets of data were collected covering the range 4-36 percent soil moisture content by weight. The results indicate that the radar response to soil moisture content is highly dependent on the surface roughness, microwave frequency, and look angle. The response seems to be linear, however, over the range 15-30 percent moisture content for all angles, frequencies, polarizations, and surface conditions.

The design and construction of an electronic-scan phased-array antenna system for use with a clutter-mapping radar system is described. The phased array is capable of \pm-20\deg of electronic beam steerng and full hemispheric mechanical steerability. It is composed of 780 short-backfire radiators with a total gain of 36 dB. It is vertically polarized and has phase-monopulse-tracking ability. The electronic beamforming and steering is controlled by a digital system using a PDP-11/20 general-purpose computer system. The same computer is used to control the digital clutter-mapping system, which is composed of an A/D converter, multiplexer, digital tape recorder, high-speed disk storage, and an intensity-modulated graphic recorder.

A detailed analysis is made of a laterally displaced interrogator sidelobe suppression (SLS) radar beacon antenna system. This method is recommended as a very economical solution to the FAA requirement for installing interrogator SLS capability at operating beacon systems where no provision had been made for interrogator SLS. The analysis was verified by an actual field test at a joint use (Department of Defense/Federal Aviation Agency) radar site at Sault Ste. Marie, Mich. Sidelobe suppression was practically complete and neither time displacement nor blockage was discernible as predicted by the analysis.

We assume that the backscattered electromagnetic far-field of a perfectly conducting scatterer is known for all aspects and for frequencies greater in magnitude than some positive number m . Then using standard integral equation techniques, we show how numerical instability enters into the Bojarski-Lewis inverse scattering method. Since the assumed knowledge of the backscattered field is even more complete than can be expected with radar, these results show that for radar applications the Bojarski-Lewis method is numerically unstable. Moreover we show, as expected, that the degree of instability depends directly upon m . The more low frequency information we haves (i.e, the smaller m is), the more stable the method is. In the concluding remarks is noted a recent constrained Bojarski-Lewis method that overcomes much of the instability of the original unconstrained method studied here.

The identification and classification of radar targets is facilitated by a newly developed technique based on measurements of the differential phase shift of the target scattering obtained at harmonic phase-locked frequencies. These phase differences are independent of target range and relative motion. It is mathematically proved that for a smooth conducting body in the Rayleigh region the copolarized terms of the scattering matrix have zero phase shift. Based on this, the absolute target phase can be measured. The differential phase shift between two harmonic frequencies has been measured for various types of targets. The experimental results indicate that the differential phase shift is a useful parameter for classifying or identifying targets, and one that can be readily measured in practical radars.

The mechanism by which electromagnetic waves are scattered from the sea surface is studied herein. Principal applications for such studies occur in over-water communication channels and radar. Predictions based on rigorous formulations for diffraction from a (moving) time-space periodic surface are correlated with the experimental results of other authors. Such predictions explain the existence of strong coherent scattering from the sea surface in nonspecular directions (grating lobes) and also anticipate the appearance of well-defined, harmonically related, frequency shifts (time-space harmonics) in scattered signals observed in these experiments. On the basis of such manifestations of the periodic nature of the sea surface, a model is formulated for use in calculation of the angular power spectrum of scattered electromagnetic waves. This model, accounting for spatial coherence effects, assumes for the fluctuation of heights on the water surface a Gaussian distribution with a narrow band-pass (nearly sinusoidal) spatial spectrum. Calculations of the angular, scattered spectrum due to this model show strong predominantly coherent wave summation in directions corresponding precisely to the grating lobes of a purely periodic structure of period equal to the center period of the band-pass spectrum. Spectral (angular) spreading increases with increased bandwidth of the spatial spectrum of the surface. Calculations for the present study are made on the basis of a perfectly reflecting boundary and hence do not display the proper distinction of polarization expected for a completely realistic model. The results, however, display the spectral charactral characteristics necessary to explain strong scattering in nonspecular directions by a random surface.

By carefully accounting for the effects of Faraday rotation, certain of the polarization properties of radar echoes from the moon at 25 MHz could be estimated even though only a single-fixed linearly polarized antenna was used. The combination of Faraday rotation and antenna response sinusoidally modulates the linear FM signals used. This "Faraday modulation" does not appreciably affect the range resolution (which was about 20 \mu S) but strongly affects the proportions of the cross-polarized components of the echoes. The measured frequency and phase of the Faraday modulation on each echo allows the determination of the proportions and, hence, the separate estimation of the components. Because the data reduction primarily involved digital spectral analysis, the effects of the modulation are interpreted in terms appropriate to power spectral estimation. The techniques used, but not the results, are discussed here.

Variation of the apparent angular location of a radar target, or glint, is a form of backscattered wave-interference phenomenon. The resulting error can be of such magnitude as to indicate the reflecting object to be many times the target span beyond the actual target extent. A survey of the literature dealing with glint is presented. This review reveals no analytical model which is adequate in describing glint for a complex target, and yet simple enough to permit reasonable implementation for evaluating diversity improvements. A model is developed which uses the concept of computing the total backscattered field by coherent summation of the field contributions from nonisotropic scattering complexes. The glint error is determined by use of a simple geometric construction, together with values of total field phase in the region of the tracking aperture. A technique of synthesizing nonisotropic amplitude and phase patterns for scattering complexes is described. The results, having used a synthesized target and applying frequency and space diversity in a computer analysis, are presented. These indicate considerable tracking improvement by using the simple scheme of choosing the tracking-error signal which corresponds to the diversity return having the largest signal amplitude.

Electromagnetic waves are launched and collected by the same directive radar antenna located on a reentry vehicle. The scattering obstacle is the fireball resulting from a nuclear detonation. The objective of this communication is to determine approximately the incoherent power scattered from the rough surface of the sphere available at the source at a specified time. The received power depends on many factors including the scattering cross section per unit area of the sphere and the area illuminated. The area illuminated is determined by the intersection of the sphere with a volume of space that is a function of the radar pulsewidth and the time of interest.

The backscattering characteristics of various types of insects found in the lower atmosphere were measured and the results are reported in this paper. The magnitudes of the insect cross sections and the effects of incident electromagnetic energy polarization are presented along with physical characteristics of the insects. The measuring equipment is described and its capability discussed.

This paper discusses the design and construction of a branch-fed, variable-phase, 20 to 55 Mc array of 48 log-periodic elements. Phasing to control-beam direction is described and the correction necessary for ionospheric refraction is presented in terms of vertical incidence critical frequency. The array gain as measured by moon-bounce techniques is found to be in good agreement with the theoretical value.

A theory on the minimization of the end-fire radar echo of a long, thin body by an impedance loading technique is presented. When a long, thin body is illuminated by a plane wave in the region of longitudinal incidence, a large backscatter is observed. This backscatter is due to the induced traveling wave which is reflected from the rear end of the body. By an appropriate impedance loading, this backscatter can be minimized. In this paper, the induced current on a long, thin and loaded cylinder is studied. The optimum impedance loading which minimizes the end-fire radar echo is explicitly obtained. Theoretical results are compared with the experimental data and an excellent agreement is obtained.

An investigation has been made of the vertical-plane dual-beam properties of a doubly curved shaped-beam reflector to provide design information relative to possible modifications for a large class of surveillance antennas (in particular, the cosecant-squared family) in order to improve their performance when working in the presence of serious ground clutter problems. Experimental results obtained with an X -band model reflector utilizing various dual-feedhorn geometries are presented. Measured secondary patterns demonstrating several important performance characteristics are shown for a linearly polarized situation. Measured primary patterns for the feeds which generate these results are included, Two-way radar coverage diagrams for one set of dual-beam patterns are examined in detail. These plots make it clear that for many ground clutter minimizing applications it appears desirable to mix at RF the signals received by both feedhorns.

Prolate spheroidal wave functions may be used to obtain an estimate of a distributed source that has been observed from an aperture of finite size. An estimate of the source distribution can also be obtained by the use of the truncated inverse Fourier transform. A quantitative measure is obtained of the reductions in the mean-squared error in the estimates which are produced by the data processing techniques. The relative merits of the two processing techniques depend upon the aperture size and the signal-to-noise ratio. The processing of data by means of the wave functions is found to be more advantageous for small apertures and for large signal-to-noise ratios. The processing techniques are also compared as to the ability to reconstruct the detail in an isolated target or source distribution of limited size. The wave functions are shown to be useful for the processing of data obtained from a large aperture that is used to observe a small target.

Some preliminary work relating to the pulse radar return from ionized media, such as fireballs resulting from nuclear explosions and the wakes of high-speed reentry vehicles, is reported. In all cases the objective is to retrieve the envelope of the backscattered signal correctly related in time to the transmitted pulse.

In many monostatic configurations, the effective scattering volume is defined longitudinally by the radar gating and transversely by either the antenna beamwidth or the extent of the scattering region. Often the radar signal must traverse fluctuating transmission regions on its way to and from the range cell. Consequently, the return signal is perturbed not only by events within the range cell but contains statistical characteristics ascribable to the fluctuating transmission path as well. The limit of large-scale fluctuations (which is of interest in the current context) is dominated by strong incoherent small angle scattering. A systematic analytic sequence resembling that pursued by Bremmer [1] (though significantly complicated by the three dimensionality and temporal dependence of the fluctuations) constitutes the main subject matter of this study. The proposed iterative scheme, while properly accounting for multiple small angle scatter, orders successive iterates by the number of large angle scattering events they represent. While the discussion is carried within the physical framework of an electromagnetic (radar) application, an extension to the acoustical (sonar) analog is simple. Furthermore, the extension of the presently investigated monostatic configuration to bistatic ones is possible but is by no means trivial. The reported work has initially been motivated by an attempt to interpret on board radar cross section and spectre measurements associated with an ionized wake.

The major contributors to the random component of the instrument limited angular measurement errors in electronically scanned phased array radars are reviewed and formulas are developed for statistical modeling of these error sources. The error model employed is applicable to space-fed and certain types of corporate-fed arrays. A comprehensive computer program, embodying this analysis, has been developed for determining these array measurement errors and their spatial correlation statistics, in two angle variables. This program is used to evaluate the statistical behavior of angular errors for some typical situations of interest. The use of angle, frequency, and phase "dithering" for improving the correlation statistics of these arrays is examined. The phase dithering technique is shown to be at least as effective as angle and frequency dithering and has the virtue of being readily implemented in the beam steering computer.

This work presents preliminary results on attempts to map winds of a storm at long range (500 to 1000 nmi) over a large area ( 10^{5} mi2) in the North Atlantic from the U. S. Naval Research Laboratory, HF radar research facilities at Chesapeake Beach, Md. [1] It appears that the short time response of the sea surface to local winds can be mapped by the analysis of a matrix of range-azimuth records containing frequency power spectra of HF radar signals backscattered from the sea surface via the ionosphere. This paper presents such a map based upon the ratio of the strengths of the first-order contributions to the backscatter spectrum (the approach-recede first-order Bragg lines) and is compared qualitatively with a U. S. Weather Bureau map of the area.

A mathematical model for microwave backscatter from the sea at near-vertical incidence is presented. The model, which is formulated in terms of Huygens principle, expresses the backscatter in terms of an "expected transfer function" of the round-trip path between the antenna and the surface of the sea. In its present form, the model is restricted to describing the case in which the microwave-illuminated area of the sea is large enough for the distribution of illuminated sea-surface area in elevation to be accurately known. It differs from other models in that it does not make the assumption that the incident electromagnetic field is plane or that the antenna is located in the Fraunhofer zone of the scattering surface. The analysis is carried out in terms of a general probability-density function of sea-surface elevation. However, an approximately Gaussian probability-density function is assumed for the purpose of working out a detailed example. The most interesting feature of the model is that it indicates that values of average radar cross sections per unit area of the sea ( \sigma \deg ), when measured at near-vertical incidence, cease to be independent of range and of antenna gain. Needed extensions of the model should treat the case in which the illuminated area size is small, and the problem of mathematically describing the boundaries between the large and small illuminated area cases. A number of experiments are recommended for verifying predictions of the model.

Users of extended range HF (3 to 30 MHz) radar and communication systems employing the ionosphere desire signal reception at incidence angles near-grazing to the local earth tangent. For vertical polarization, the vanishing received fields at low incidence angles over dielectric earth may be increased by using large ground screens. In this paper a ground-screen formulation based on scattering techniques is developed. The ground screen is viewed as a scatterer in free space, excited by a plane wave. A Fresnel image wave is added to establish the air-earth interface. Formulations are developed for the semi-infinite screen and for the circular-cylinder surface segment screen. The semi-infinite screen is representative in performance to a round screen of radius equal to the distance from the edge of the semi-infinite screen at which the field is computed or measured. For a ground screen on a hill the cylindrical segment is appropriate. Computations for a simulated earth were made and corroborated by experimental simulation with scale models. Improvements in field strength of 7 to 14 dB or more can be achieved with large screens over no screen. "Relatively small" tilted or raised flat screens, and cylindrical segment screens, can give improvements equal to very large flat screens on the earth.

A technique is developed for measuring the rms wave height averaged over an area of the sea that is much greater than any horizontal scale of the surface waves. The method involves a nadir looking radar which transmits and receives two monochromatic signals simultaneously. Signal processing at the receiver involves the computation of the correlation between the two returning signals as a function of theft variable frequency separation. The cross correlation between the amplitude and phase functions of the individual returning carriers depends on the distribution of discrete scatterers along the direction of propagation. This information can be used to determine the rms surface elevation (about the mean); it does not depend on the temporal or spatial frequency spectrum of the wave height or slope. Under conditions which are typical for a microwave signal being normally incident and reflected by the sea, the two frequency correlation function R(\Delta k) is seen to be equal to the characteristic function of the surface elevation of specular points. Laboratory measurements have been conducted on wind driven waves, and the measured correlation function compares favorably with the theory developed here.

From theoretical considerations, it is possible to calculate attenuation through rain at several wavelengths. It is shown that attenuation is a linear function of rain rate for a 0.86- cm wavelength. This property is independent of the distribution spectra of drop radius within a ten-percent precision. This later property has been tested experimentally in two different ways. 1) Measurements through rain have been made with a radar at 0.86 cm. Results are reported. They show quite important differences between theoretical and experimental results. 2) Experiments have been conducted in rainfall to measure fall speeds and diameter spectra of drops. The apparatus used for this purpose is briefly described. With the results obtained it is possible to calculate the propagation properties of rainfall at several wavelengths, particularly at 0.86 cm. We hope to be able to compare the results obtained with those observed by radar in the future. The interest in short wavelengths for radiolocation or radio communication is well known, but when using shorter wavelengths we encounter greater attenuation in the atmosphere. We know that for wavelengths between 1 and 10 cm, attenuation by atmospheric gases may be neglected (except near 1.25 cm). At millimetric wavelengths, propagation is only possible in certain bands. At 0.86 cm, attenuation by oxygen and water vapor is not negligible, but can be considered constant. At the wavelengths of 0.4 cm and 0.20 cm, attenuation is dependent upon the concentration of water vapor, that is to says upon meteorological conditions. The effect of atmospheric particles is more important with shorter wavelengths. Practically negligible at 10 cm, attenuation by precipitation begins to be important at 3 cm and 5.5 cm and is strong at 0.86 cm and other milllmetric wavelengths. The purpose of the present work is to study theoretically effects of rainfall at several wavelengths.

A theory is presented for the analysis and optimization of systems which process electromagnetic fields carrying information. The theory is thus intended for use primarily by communications and radar engineers. The definitions are motivated by a fundamental requirement that the input-output space-time mutual information transfer be a maximum. The theory can be applied to problems involving nonstationary and nonergodic processes in space and time. The technique proposed is particularly useful in the analysis and optimization of controlled systems carrying man-made information, such as radar and communications. System optimization is carried out by maximization of the trans-correlation function with respect to the variable parameters of the system. The transcorrelation function is a space- and time-averaged correlation function between the desired and the actual system outputs. The optimization technique is applied to the problem of an antenna embedded in a nonstationary medium, such as a hot plasma. The amplitude and phase shading of the array are the variable parameters chosen for optimization of the system, and medium effects, background (object) noise, receiver noise, etc., are considered.

High-resolution radar becomes limited by the feeding mechanism in traveling wave antennas, forcing the design to some form of corporate feed. A spectral method of solving this problem is introduced which conveniently handles any transmitter pulse shape or receiver bandpass. The equivalence between this approach and an older transient solution is established. The method is applied to a uniform and a cosine illuminated aperture for both one- and two-way transmission through the antenna. It is shown that as a rule of thumb, the traveling wave feed should be less than half the spacial length of the transmitter pulse in the feed ( L/V_{g}T ). Antennas exceeding this length must be divided into several sections, each of which must be corporately fed.

In attempting to estimate the radar cross section of airborne vehicles, it is often only necessary to consider average values of the radar returns. A method of providing a quick estimate of the average bistatic radar cross section of the vehicle components would be useful. Ray optics provides a method of predicting the radar cross section of electrically large, perfectly conducting, simply curved, convex bodies such as spheres, ogives, ellipsoids, etc. This paper extends the method of ray optics to the case of an arbitrary body, which may be concave and/or convex, on which doable reflection and depolarization can occur. The incident radiation on the scattering body is represented by a large number (10^{5}-10^{6}) of rays. The rays reflected in a given direction with a given polarization are collected at infinity and combined by phasor addition. For the bodies investigated, this method yields results within \pm2 dB of measured results except in small angular regions where trapped waves contribute significantly to the radar return.

The use of satellite differential Doppler measurements to study latitudinal variations of F -region electron density is described. It is shown that the ambiguity in the total phase path length may be resolved employing either incoherent scatter radar measurements or vertical-incidence ionosonde data, together with some assumptions concerning east-west gradients at the latitude of the observing station. Sample results are given showing the location of the midlatitude trough of electron density observed at Millstone Hill through observations of the U.S. Navy Navigation Series satellites.

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.

A method is proposed for improving the azimuthal resolution of HF radar several times beyond the limitation due to ionospheric scattering. Azimuthal resolution improves directly with array size, in accordance with standard array theory, until the beamwidth shrinks to a few degrees. Further increase in array size does not produce a dependable resolution improvement. In radio parlance, the signal is said to be decorrelated across the aperture. This "decorrelation" is due to scattering by the nonhomogeneous ionosphere. The scattered energy accounts for only a portion of the received wave. The remainder, an almost specular component, not only has a very much narrower angular distribution of its energy, but appears to have a much longer (perhaps 100 times) time constant of fluctuation. This difference in fluctuation rate permits separation of the two components by filtering the received radar echo. The decorrelating component is thus reduced, and the available azimuthal resolution, i.e., the resolution limitation due to scatter, correspondingly increases. When literature data are applied to the theory, a several-fold increase in available azimuthal resolution is predicted.

This paper describes a method for measuring the backscattering cross section of an arbitrary target using FM radar techniques. This method has a merit that it does not require a nonreflecting background behind the target, by the use of a high selective amplifier in the FM radar. The principles of this measuring method and the results of the measurements are described.

The standing-wave method of measuring radar cross sections has been adapted for use at 26 MHz. A target in the middle of a large flat field was illuminated by a transmitter 300 feet away, and a probe was moved along the transmitter-target line to measure the amplitude and position of the standing wave due to the target. Aluminum dipoles of different lengths were first used as targets. Both the target cross section and the phase of the scattered radiation varied with the target length in the same way as predicted from previous microwave measurements. The results demonstrate the validity of extrapolating microwave measurements to the high-frequency part of the spectrum. Calibration of the system was achieved by using the known cross section of a half-wave dipole. The technique was used to measure cross sections of trees, street lights, and vehicles. With vertical polarization, oak trees had cross sections between 30 m2and 70 m2, indicating that trees can be an important source of ground backscatter. A street light had a cross section of 240 m2, and vehicles had cross sections ranging from 0.7 m2to 28 m2, depending on aspect.

Compact range techniques for measuring the gain patterns of full-size microwave antennas and for making radar reflectivity measurements are described. The basic principle of this technique is the use of a large collimating device to generate a uniform plane wave across the aperture of a target or antenna without requiring the normal far-field separation. Two different collimating devices were used in the investigation, a paraboloid with a point-source feed and a parabolic cylinder with a line-source feed generated by a large hoghorn. Pattern and gain measurements were made on both compact ranges using a 30-inch paraboloidal test antenna, and the measurements were compared with similar ones made on conventional outdoor ranges. Radar cross-section patterns as a function of aspect angle were measured for various size standard targets and compared with theoretically calculable radar cross-section patterns. The results which have been achieved are very encouraging. They demonstrate that the performance of compact ranges at the X -band is comparable to that of outdoor ranges.

When array antennas are used for wide-frequency operation a difficulty with grating lobes is encountered at the upper frequency end of the operating band. This paper points out that the use of arrays for transmission and reception with different interelement spacings can be used to extend the operating frequency band in a radar system. The principle of transmitting-receiving arrays with different illuminations was used by Mattingly [2] to lower the sidelobe level of a radar array antenna. Birge [3] used it to reduce the number of elements in an array while preserving the resolution. The same principle is used in this paper to extend the operating frequency bandwidth of a radar antenna system. Relationships for an optimized radar array antenna system are derived. The criterion for optimization is the maximum bandwidth with a given total number of elements. It is shown that in an optimized system the number of elements in one array antenna is one greater than in the other, and the ratio of interelement spacings is inversely proportional to the square of the number of elements in the respective arrays. Based on these conditions, a function k is computed and tabulated. This function determines the number of grating lobes permissible in the specified angular sector, without overlap, as a function of the number of elements in the two arrays. An application to a high frequency (HF) ionospheric radar antenna system, now under construction, is used as an illustration of the principles outlined in the paper.

An antenna capable of high resolution can be synthesized by moving a side-looking radar a long distance and treating positions along the path as the positions of elements in an actual physical array. Important characteristics of such synthetic-aperture radar systems and the effect of target motion on their resolution have been considered. If the motion of the target is known, a transformation can he made in which the target appears stationary, and the relative motion between target and radar determines the effective synthetic aperture. However, if the assumed velocity of the target differs from its actual velocity, the velocity error will cause an apparent displacement of the target and a degradation of the performance of the radar. The effect of velocity errors was considered.

With sinusoidal bases and Galerkin's method, the tumble-average radar backscatter is computed for parallel wires, crossed wires, a planar tripod, and a regular quadripod. This communicalion presents calculated and measured results. One of the configurations, the quadripod, demonstrates attractive tumble-average properties for use as a chaff element.

The radar backscatter of natural snow surfaces was measured at 10 GHz and 35 GHz and at grazing angles from 1\deg to 0.3\deg . For horizontal polarized radiation the terrain clutter per unit area (m2) at 10 GHz of a flat snow terrain decreases from -50 dB at 1\deg to -70 dB at 0.4\deg . The return is approximately 10 dB lower for vertical polarized radiation. The terrain clutter was found to depend on the free water content of the snow. The radar cross sections of ice blocks placed on the snow surface is roughly proportional to the square of the area of the ice block facing the radar at 10 and 35 GHz and is approximately 20 dBsm below the return expected for a perfectly reflecting plane surface. At 95 GHz the ice blocks become diffuse reflectors.

Previous work indicates that although accurate predictions are generally obtained from the geometrical theory of diffraction for cylinders and frustums, scattering from the rear edges of these bodies is sometimes poorly predicted. A new formulation provides satisfactory results for a cylinder, but conical bodies require further work.

An expression is derived for the average backscattering cross section of an obstacle for arbitrary transmitter and receiver antenna polarizations. Results are given for straight wires, circular loops, and one-turn helices.

Describes a simple mechanical way of moving a model target during laboratory measurements of radar cross section to simulate the precession motion of a satellite or reentry vehicle. The value of the simulation lies in the speed with which it can be accomplished and in its use as a diagnostic tool to aid the analysis of typical signature data

A class of circuits is described that can be used with a phased-array antenna in order to allow a given array feed system to provide phase control for a phased array with many more elements. Alternatively, certain variations of these circuits can be used alone to provide phase control for small arrays while using only a single phase shifter for each direction of scan.

Utilizing time discrimination techniques, atmospheric layers have been resolved with bistatic and monostatic radars over common regions. The results also indicate the importance of time resolution in bistatic probes to distinguish main beam common volume scattering from that due to sidelobes.

A detailed investigation of the differences between the upwind and downwind Doppler spectra of the radar sea echo has been made, utilizing P- , L- , and C -band data obtained with the Naval Research Laboratory's Four-Frequency Radar System. The results indicate that while the Doppler bandwidth is nearly independent of wind direction, the differential Doppler looking upwind is nearly twice that for the downwind case.

The bistatic scattering cross section of a reentry vehicle with wake of nonuniform axial conductivity is investigated using a simple model. For some typical physical parameters normalized radar cross sections are presented in tabular form for a reentry vehicle with wake of exponentially decreasing axial conductivity.

An effort recently undertaken to compute radar cross sections of thin metallic disks for frequencies near resonance is described. All calculations are based upon an ideal disk scattering problem in which each disk is assumed to be perfectly conducting and infinitely thin and the incident field is assumed to be an electromagnetic plane wave. A good agreement between the values of the backscattered fields for the ideal disk scattering problem and the thin metallic disk scattering problem for large values of ka is found, but may become poor for ka less than or equal to 1.0.

Introduces computer programs (FORTRAN IV) designed for field calculation from conducting bodies of revolution. A set of four programs which calculate the generalised impedance matrix and admittance matrix for triangular expansion functions, bistatic radar scattering for an axially incident plane wave, radiation from rotationally symmetric aperture antennas, and radar backscattering for an obliquely incident plane wave, are presented. Results for a number of examples are summarised and discussed. The accuracy of computation depends on the smoothness of the body and of the excitation

A calculation of back scattering from a rough surface using Huygen's principle is carried out along the lines introduced by Davies. Davies original equation is extended to include a contribution from the component of the surface normal which is parallel to the average surface. The effect of this component is to multiply the usual expression for incoherent backscatter by a factor of 1/ \cos^{4} \Psi where \Psi is the angle between the radar line of sight and the normal to the average surface.

High-frequency scattering by a finite perfectly conducting right-circular cone is analyzed by modifying geometrical diffraction theory for application at and near nose-on aspects. Formulas appropriate for predicting principal-polarization radar cross sections as functions of frequency and aspect angle are presented. Calculations on a cone are in very good agreement with monostatic measurement data in the limited aspect interval 0 \leq \phi \leq \gamma , where \gamma , is the half-angle of the cone.