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An instrument that has been developed for measuring the deformations in shape that result from the movement of a radio telescope reflector is described. A radar technique is used to measure distances from near the focal point of the reflector to selected points on the reflector surface. The short term accuracy of the instrument is ±0.003 in) and when used on the 140-ft telescope in Green Bank, W.Va., good agreement was found between calculated and measured deformations.

The theory of linear statistical models is implemented to obtain an algorithm which accurately locates radar sites. True bearing and navigation data are used as input. The linear model developed is adaptable and allows removal of bearing errors that are nonrandom, or systematic. The model may be written in recursive form and used for real-time applications.

The evolution and state of development of the radars used in the Ground-Controlled Approach (GCA) systems of the U.S. Air Force is described. Emphasis is placed on the radar requirements of this application and the evolution made possible by the advances in component technology. We first review the concept of GCA operation and show how this leads to the requirements of the two radars in the system. Next we discuss the early history of GCA and the AN/MPN-1, the first operational system. The evolution of the GCA radars since the AN/MPN-1 is then summarized. Finally, we describe in more detail the AN/TPN-19. This is the most recent GCA system to be developed, and it makes effective use of array technology, frequency diversity, monopulse, pulse compression, and computer control.

This paper surveys the field of automotive radar and represents an expansion of a previous paper, "Automotive Radar-Problems and Promises" [1]. Both the roadside environment in which the car and driver operate and on-board physical environments in which the electronics must function are treated. Applications involving speed sensing, predictive crash sensing, obstacle detection, braking, and station keeping are addressed. Current radar system state of the art is reviewed. Considerations relating to target discrimination, weather penetration, and basic radar system parameters are covered. Modulation techniques for range determination are examined, and radar system configurations are discussed in an effort to identify the advantages and disadvantages of each. It is concluded that although considerable development work remains before radar becomes a practical automotive system, significant progress has been made.

High angular resolution is a desirable property of mapping and reconnaissance radar systems. The synthetic-aperture principle reduced the beamwidth of airborne radar by as much as two orders of magnitude. Notwithstanding the long interest in the subject, a quantitative relationship is lacking between beamwidth and resolution. This paper is an attempt to overcome this deficiency. Among its several results, it is shown that the angular resolution of synthetic-aperture radar can be considerably poorer than expected. It is also shown that a modest tapering of the synthetic aperture in those cases offers significant improvement.

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.

This paper studies the application of Kalman filtering to single-target track systems in airborne radar. An angle channel Kalman filter is configured which incorporates measures of range, range rate, and on-board dynamics. Theoretical performance results are given and a discussion of methods for reducing the complexity of the Kalman gain computation is presented. A suboptimal antenna controller which operates on the outputs of the angle Kalman filter is also described. In addition, methodological improvements are shown to exist in the design of range and range-rate trackers using the Kalman filter configuration.

Radio scattering measurements have been made of a region of the ionosphere above the Institute for Telecommunication Sciences' ionospheric heating facility at Platteville, Colorado. Strong scattering was observed at frequencies in the HF and VHF bands. The scattering has been shown to originate from electron density fluctuations that are highly elongated in the direction of the geomagnetic field. Radar scattering cross sections of 70 to 80 dbsm are measured in the HF and low VHF bands. The scattering cross section decreases at a rate of 20 to 30 db per octave at the high end of the VHF band. The scattering irregularities are produced by operation of the heating facility with o-mode polarization at frequencies that reflect within the ionosphere. The strength of the scattered energy decreases at a rate of at least 10 db per degree for observation geometries that do not match the geometry for specular reflections from long cylinders aligned with the geomagnetic field. The spatial distribution of irregularities has been estimated for both E- and F-region heating. The temporal properties of the scattering have also been determined including the frequency spectrum of the scattered signals. The processes by which ionospheric heating produces these irregularities are not yet fully explained. Several potentially useful applications of radio scattering from such irregularities are discussed.

The paper presents a model for radio wave scattering from the ionospheric irregularities generated by the intense radio wave transmissions from the Platteville heater. The model is based upon the HF-UHF radar backscatter observations for a physical description of the scattering medium and upon the theory of weak scattering (Born approximation) from anisotropic irregularities for mathematical development. According to the model, the electron density fluctuations responsible for radio wave scattering having an rms value of 1 to 1.5% are aligned along the earth's magnetic field and are distributed in a diffuse pancake-shaped volume of 15 km gaussian thickness vertically and of the size of the heater beam which is 100 km in gaussian diameter horizontally. At radio frequencies the irregularities within the disturbed volume are highly aspect sensitive and consequently only those scatterers which lie on the surface of specularity where a radar views transverse to the magnetic field count in contributing to the received signal. Model computations have been made of the scattering cross sections for monostatic as well as bistatic radar configurations and they are found to be in good agreement with the observations. The radar cross section at a given frequency for bistatic geometry is substantially greater than that for monostatic geometry, all else being equal. Finally, it is shown that the width of the scatter-illuminated bands on the ground is set primarily by the finite dimensions of the scattering volume rather than by the finite aspect sensitivity of the individual scatterers.

a unique aspect of the San Francisco Experimental Vessel Traffic System has been its extensive use of real time automatic processing technology. Automatic detection and tracking of vessels in radar coverage areas has successfully been accomplished even in the presence of clutter. Vessel movement information has been extracted, presented to operators on computer-animated displays, and traffic analyzed both automatically and at the request of operators. But these demonstrated capabilities should be employed only as a guide to the design of future systems and not interpreted as a literal prototype configuration. Future system designs should assume traffic will be controlled, rather than advised. Risk analysis based upon port geometry, traffic levels, and minimum turning radius can contribute to assessing deployment priorities. Vessel routing should be constrained to follow narrow tracks rather than broad lanes. A minimum configuration would be based upon a computerized Vessel Movement Reporting (VMR) system. Data entry and retrieval terminals could be available within the maritime community. Information, including guidance, could be selectively distributed to active ships via a novel multiplexed television transmission. All radar configurations would include automatic detection and tracking equipment. Finally, area navigation systems could be integrated with VTS. The opinions expressed in this document are those of the author, presented in the interest of stimulating discussion, and they do not necessarily reflect the views of either the Applied Physics Laboratory or the United States Coast Guard.

In radars that achieve a high subclutter visibility by coherent processing over several pulses, a serious problem appears in the form of blind Dopplers, or "speeds," at which target detection is impossible. Of the possible methods of eliminating these blind speeds, the most basic one that is employed when the performance requirements are high involves the use of several PRF's. These PRF's are chosen so that coverage is obtained at any Doppler with at least one PRF. The problem faced by the radar designer is to select the set of PRF's and the pulse numbers for each PRF so that the search frame time is minimized. This paper evolves a systematic method for the design of the blind-speed elimination scheme. A formalized approach is offered that shows the possible combinations of wavelength, PRF, and pulse number and the tradeoffs involved, without introducing the confusion ordinarily associated with multiparameter choices.

The developmental activities pertaining to the RF RATIOMETER was necessitated by the need for the continuous monitoring of VSWR in MEDIUM RANGE TRACKING RADAR being developed at Thumba Equatorial Rocket Launching Station, Trivandrum, and give warning when the VSWR reaches a value at which arcing is likely to occur. Since it is not possible to use the slotted line techniques at such a high power level as 1 MW, RF RATIOMETER becomes imperative.This equipment is coupled to the Tracking Radar in such a way as to trip it off when the VSWR exceeds a safe value. This equipment has the capability of measuring the VSWR over the complete frequency band of 10 MHz to 10 GHz.

The National Maritime Research Center, Kings Point, N.Y., is conducting projects dealing with the “new technology” in the field of navigation. This paper consists of a survey of this area of activity of the Center. The intent is not only to disseminate information to the wide community of navigators but also to structure a mutually beneficial communications link between the NMRC and the Institute of Navigation. The paper will cover the following projects, some innovative, others extensions of previous programs: —RAPS (Radar Automatic Plotting System) —MASS (MarAd Anti-Stranding Sonar) —TRANSIM (Simplified Transit) —MARINE RADAR TRANSPONDER —MARSCAN (Maritime Satellites Communication and Navigation System) —INTEGRATED CONNING SYSTEM

The problems of low-angle tracking over the earth's surface are explored in the light of rough-surface scattering theory. A detailed model of diffuse scattering is constructed which agrees with available test data and which permits the power distributions in radar coordinates to be estimated. Using this model, the potential performance of various techniques proposed for avoidance of multi-path is evaluated, Several are found effective in maintaining tracks of reasonable accuracy down to one-fourth beamwidth above the horizon, but no generally practical solution to height measurement below that angle appears available.

Advances in the design, development, and fabrication of key microwave components along with those in electronics have resulted in growing optimism about the application of radar technology to solving the automotive highway collision problem. However, before an automotive radar system can be fully realized, a major effort will be required to define the environment in which the system must operate, and to obtain a fundamental understanding of the influence of these RF parameters. One such parameter which will have a considerable effect on the design of automobile radars is that due to the presence of natural and man-made surfaces within the beamwidth of the antenna. Generally, the presence of such a surface will result in incident RF energy being reflected off the surface in a forward direction and some portion being scattered in a backward direction. This paper presents the results of a program which was designed to measure this type of reflectivity characteristic for common road surfaces. Measured data are presented along with a theoretical study demonstrating the influence that this phenomenon can have on highway collision radar systems.

Enhancements of various features of the incoherent scatter spectrum are observed when the ionosphere is illuminated with powerful, high frequency radio waves. The radio waves excite plasma instabilities producing lines or more complex spectral features near the local plasma frequency, at the local ion acoustic frequency, near the local gyrofrequency, and near twice the gyrofrequency. The enhancements occur in a thin slab as observed by the incoherent scatter radar and at both upshifted and downshifted frequencies with respect to the probing radar frequency. The enhancements are observed to vary with time when the excitation is held constant and is turned on or off. The high power radio waves are produced by a 160 kw transmitter feeding a log-periodic pair of curtains mounted at the focus of the 1000-ft reflector and covering the frequency range from 5 to 12 MHz. The effects are observed with the incoherent scatter radar using the same reflector and with ionosondes and photometers. The frequencies of the enhanced plasma line and the ion line and their relation to the pump (high frequency radio wave) frequency are predictable from available parametric instability theory. Other spectral features are being explained as the theory develops with the help of the observations. There remain some discrepancies, in particular the asymmetries in intensity, width, and fluctuations of the upshifted compared to the downshifted plasma lines.

RF pulses are used in radar and sonar to detect and locate targets in extended media. Short RF pulses (and impulses) can be used to find buried objects or voids by echo sounding, or can be used to probe snow fields or the depths of the earth. Although similar to radar in principle, there are important differences in these applications that can lead to significant variations in the design approach. A novel system is described, with a computer-programmed tunable RF source, that tunes rapidly through all the frequencies of a nanosecond pulse spectrum, makes individual "CW" measurements, stores them, and finally computes a synthetic echo. Target signatures can be "recognized" by calculating correlation functions. Experimental results are presented.

The complex indicated angle technique, applicable to monopulse radars, is being investigated as a means of overcoming the serious degradation of elevation measurement caused by multipath when the target is within a beamwidth or so of the horizon. This technique makes use of the quadrature-phase component of the normalized difference signal, as well as the in-phase component. Results of analysis and computer simulation have been published previously. This paper reports results of a test program using a slightly modified AN/FPS-16 monopulse tracking radar and a simulated target. The results to date indicate a potential for high accuracy, though there are limitations as to the applications for which the technique appears feasible. A computer program has been developed to perform the elevation estimate and to resolve ambiguities.

Three microwave garnet phase-shifter designs are used in the AEGIS weapons system. The microwave design is straight-forward except that the toroid assembly is potted with silicone rubber to increase its power-handling capability and the magnetizing wires are shielded with a spiral-wrapped wire to prevent the propagation of higher order modes. The driver circuit uses a new "flux-feedback" concept for improved accuracy and employs monolithic circuits, hybrid circuits, and discrete components. Mechanical and electrical design of the interfaces with mating components are important cost considerations and the chosen designs are described in detail. Several techniques for improving production yield are discussed and a table of production statistics is provided. Performance histograms and data averages as a function of time and operating frequency are also presented.

Various shortcomings of modulated subcarrier attenuator calibrators are discussed. Very precise attenuation measurements on short lengths of waveguide have been obtained by inserting into the subcarrier channel a tuned reflectometer system which contains a waveguide switch for setting the zero. Using this technique, total spreads of less than 0.0013 dB have been obtained at 4 GHz in 10 completely independent measurements on the same unknown. The full theory of this method is given in the Appendix. The total range of a modulated subcarrier system has been extended to over 100 dB by using a 1-W microwave oscillator and placing in the subcarrier channel a rotary attenuator with very good resettability and a fully matched two-path configuration that contains two waveguide switches and the unknown.

The possible use of multiple wavelength radar systems to determine raindrop size distributions is examined. Pairs of radars at 1, 3, and 10 cm, respectively, are considered; the method involves measurements of rain reflectivities at two wavelength and at two range intervals separated by about one km. Assuming a general exponential form for the drop distribution, equations are derived relating the distribution parameters to the measurements. From these analytical forms the sensitivities of these parameters to radar inaccuracies are examined. The results show that one needs combined 2-radar accuracies of 1 dB to get even marginal drop distribution accuracies. Such accuracies are considered impractical at present. Other impractical constraints implicit in the results are the assumed uniformity of reflectivity over distances of approximately 1 km, and the requirement to average as many as 104 independent power samples.

The quality of coherent radar images is affected by several factors inherent in the target scattering phenomenon and in the radar system. Certain of these factors, such as resolution, image fluctuation, assumed amplitude cell statistics, noncoherent smoothing, background noise, and the film response, are investigated in detail. Simple statistical models of an extend target are constructed in order to simulate images and to show how these effects are related. It is shown that resolution is the dominant factor that affects image quality. The relative importance of all other factors is highly dependent on resolution.

The UK incoherent scatter system operates in two modes. The monostatic pulsed system has been in operation since 1968, and a summary of the results obtained in this mode is given. The full multistatic CW system has been operating since September 1972 and among the preliminary results are measurements of the total vector of velocity drift.

A series of experiments was conducted with HF and VHF radars at White Sands, New Mexico, during the months of October 1970 and June 1971 to search for direct RF backscatter from ionospheric irregularities produced by the Platteville heater. The observations were made from White Sands because radars at this location view the heated volume normal to the earth's magnetic field lines. Direct echoes from the heated volume were unquestionably observed. Returns were obtained at frequencies up to the highest available at the HF radar site: 30 MHz during the first series of observations and 54 MHz during the second. The echoes were observed only after sunset, at times when the local plasma frequency over Platteville was of the order of 5 MHz at the layer maximum. The total radar scattering cross section of the heated volume was found to decrease with increasing frequency and to vary from less than 104 m2 (the minimum detectable cross section) to 109 m2, depending on frequency and time of day. The Doppler spectrum of the returns indicated that the drift velocity of the scatterers through the heated volume was greater than the relative velocity between scatterers and comparable to the drift velocity of natural irregularities at midlatitudes.

The paper describes a special combination of high resolution, high accuracy, solid-state radar equipment with a sophisticated computer operated automatic acquisition automatic plot collision avoidance indicator. Technical characteristics and special features that make this equipment particularly suitable for the newer higher speed Merchant Marine vessels are described. A description is given of the separate displaying of high resolution radar and automatic navigational data. Information is also presented concerning application and performance features that make it particularly well suited for service aboard ships.

In the course of the past year or so, several papers have been presented here and abroad dealing with the utilization of transponders in ship's navigation. Multiple usage transponder systems are available as aids for both navigation and target recognition by Radar. Extensive research for additional uses of transponders is continuing on a broad scale in the United States and similarly in Great Britain and Holland. A simple system is needed which can operate on present day ships, now-today-with today's personnel. This system must be commercially feasible, in cost and maintenance, and be compatible with presently used instrumentation on board the average ship. The year by year rising losses in life and ships caused by collisions demand it. One proposed system is presented here.

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.

A new large incoherent scatter radar system has been proposed as the principal element in a binational center for studies of the upper atmosphere. The radar has been designed to yield a sensitivity comparable to the best now available and yet provide a latitude coverage of the F region of ±13°. The radar shall comprise a 100-m diameter parabolic reflector antenna that can be tilted in the magnetic meridian plane by ±85° from the zenith. This antenna will be coupled to a UHF pulse transmitter with a peak power of 10 Mw, and will serve for both transmitting and receiving. Two auxiliary fully steerable antennas will be located northeast and northwest of the main antenna and will also receive the signals. This will enable the velocity of the ion drift to be studied, permitting measurements of neutral winds, electric fields, and fluxes of ions into or from the magnetosphere. The auxiliary antennas will form 10 coplanar pencil beams, so that these drift measurements may be made at 10 heights simultaneously. The paper describes how the above concept was developed and the work of selecting a site for the radar. By locating the main station near L = 4, and the auxiliary stations about 550 km distant, it will be possible to measure the electric fields in the F region over the range 3 ≤ L ≤ 8 to an accuracy of ±2 mv m−1. Thus, the radar should be able to map the electric fields produced by substorms at auroral and subauroral latitudes. In addition, the properties of the ionosphere and many parameters of the atmosphere will be determined over the altitude range 100 to 1000 km.

A multipulse correlator system for the Chatanika, Alaska, incoherent scatter radar is described. The system utilizes a hardware correlator unit that can deliver as many as 40 8-bit by 8-bit lagged products every 20 μsec. The particular lags at which products are computed are patch-wire programmable, and the range gates at which data are taken are set arbitrarily under computer control. The system operates with a fixed bandwidth of 50 kHz, so that the maximum range resolution is 6 km. To obtain sufficient lag resolution for operation at 1290 MHz, we compute lagged products at other than the nominal subpulse spacing. An example of the correlator operation is given.

HF radar signatures have been synthesized from a time-dependent Gaussian ion cloud using a three-dimensional ray-tracing progam that can take into account both electron collisions and the earth's magnetic field. The ion cloud model is based on the theory of ambipolar diffusion and the model parameters are based upon the observations made during a barium cloud test conducted at White Sands, New Mexico. Ray-tracing results have been generated for both ordinary (O) and extraordinary(X) modes as well as for the “no-field” case. The results, presented in the form of a time-history of the Doppler shift and the scattering cross section, are found to be quite similar for all three cases. Relative to the O mode, the X-mode variations lag in time and obtain a maximum cross section which is greater only by about 2 db. The variations for the no-field case fall in between that of the O and X, but closer to the O mode. The results show that the cloud is extremely defocussing with an estimated defocussing factor (relative to free space) for the X mode increasing from 7.6 × 103 to 1.85 × 107 over the interval 5 to 190 sec of cloud's life. The ray-tracing signatures are compared to those synthesized by means of a hard expanding ellipsoid method with a view to evaluating the importance of underlying ionization. The effects are found to be such as to introduce a significant time lag in Doppler history and to cause a cross section reduction by a factor that builds up with time from 5 db to more than 30 db. A comparison drawn between the observed and the ray-tracing signatures leads to the conclusion that good agreement between the two can be expected only when the clouds experience either slow or no deformation and striation but not otherwise.

Solid-state array radar is of gyeat current interest because of the inherent reliability of solid-state devices and the concomitant promise for improvement in system reliability. However, no extensive reliability base has been established for solid-state devices employed under radar operating requirements. In this paper some of the important factors bearing a device reliability are treated. Accelerated life tests under RF conditions are presented for L-band power transistors. Preliminary life-test and failure-analysis data are also presented with recommendations on how the information can be used by the radar systems designer.

A technique to reduce radar pointing errors due to glint using frequency agility and amplitude weighting is presented. The reduction in rms tracking error is developed into an equation dependent upon the original glint tracking error, ?g, and the number of returns weighted, N. The rms tracking error is thereby reduced approximately by a factor of N. Finally, the equation formulated allows one to evaluate the reduction in glint error versus the number of frequencies chosen for frequency agility.

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.

A systematic, thick refraction medium approach to calculating ionospheric radar refractive effects by means of propagation-related integrals yields equations valid to second order in the tangent of the propagation angle with respect to the straight line between source and target. Significant differences are found from more intuitive developments currently used. When more than one propagation path exists between source and target, alternate propagation paths cannot be located reliably by the propagation integral method. However, inclusion of the higher-order terms responsible for the alternate solutions does significantly improve the accuracy of the primary path solution when those terms can be estimated accurately in a strong refraction situation.

the vector analog computer (vac) is a new radio navigational instrument which enables a pilot (1) to fly a rectilinear course either on or off the Victor airways with no appreciable lateral displacement, (2) proceed directly to any given latitude and longitude with exact positional information at all times, (3) navigate directly to any specified holding point and then hold the pattern precisely, (4) make the transition to an ILS approach with extreme versatility, and (5) assist radar traffic controllers by providing more precise information about his aircratt's position in the traffic picture than radar can provide. VAC offers continuous readings of position, bearing, distance, and ground speed with signal reception from only one VORTAC station at a time. After proceeding beyond the range of the VORTAC transmitter it can still navigate for relatively long distances on mechanical memory. It is a superior anti-collision device, is readily adaptable to all aircraft from helicopters to jets, and is capable of directing an automatic pilot independently of the magnetic directional information normally required in beam guidance systems. This paper discusses the limitations of present radio navigation systems, offers a list of criteria for an airborne navigational director with the simplicity and accuracy of visual reference, and then explains the principles of design and operation of the Vector Analog Computer.

The measurement of the radar cross section of full-size targets in flight presents some unique problems. The techniques employed to maintain the dynamic range of the signal, facilitate data handling, and control the target aspect, all contribute to the efficiency with which the requisite data may be gathered and reduced. The approaches taken in solving these problems are discussed in connection with the U. S. Naval Research Laboratory (NRL) dynamic measurement radar. This system is specially designed for simultaneous pulse-by-pulse measurements at L, S, and X bands permitting a high degree of polarization flexibility. Data reduced from film records, when combined with program-derived aspect information, enables a graphical description of radar cross section to be plotted as a function of target aspect. Data from measurements of a C-54 aircraft have been plotted in this manner and show the variation of σVV, σHH at L and S bands, and σVV, σHH, σVH, σHV, σRR, σLL, σRL, σLR at X band. Operating experience with this system indicates the practicability of performing dynamic measurements.

The scattering matrix of a target generalizes the scattering properties to include a description of their dependence upon radar polarization. The matrix may be determined directly through two successive transmissions at orthogonal polarizations, with reception of each at both of the polarizations. In the laboratory, it is possible to eliminate the requirement for phase measurement by an indirect technique using successive measurements at six polarizations (five of which may be linear). In the case where results are to be applied to linearly polarized radars, it is sufficient to determine the "linear restricted matrix" by six linear measurements. Analysis is provided and measurement technology described and evaluated for both classes of indirect measurement.

This paper reports on progress in signal design that has led to improvedresolution capability in radar and communication systems without theuse of complicated signal-processing techniques.Two approaches to the problem of improving resolution capabilityare made. The first approach emphasizes the need to produce sharplypeaked autocorrelation functions. The optimum signal amplitude infrequency is specified to accomplish this, and the spectral density ofthe deterministic signal is shown to satisfy a homogeneous Wiener-Hopfequation. The second approach emphasizes the need to producelow and flattened cross-correlation functions, in order to distinguishthem (since they correspond to error outputs) from the sharply peakedautocorrelation functions. With the use of stationary phase integration,a detailed method for producing any desired cross-correlationamplitude is presented. In particular, the techniques necessary to producesinusoidally modulated cross-correlation functions are discussed.These tools are applied to a realistic N-signal processing system,and the resulting optimum signals are shown to be amplitude-modulatedchirped sinusoids. Detailed examples for physically justifiablesystem parameters are included.

A maneuvering synthetic aperture radar in squint mode, during a loosely piloted maneuver, is simulated with presence of various navigation system errors. The error sources investigated place emphasis on short-term effects, involving platform servo transients, noise and quantization in accelerometers, interaction of angle pickoff uncertainty with the displacement from platform to radar antenna, and uncertainty in this displacement itself. Simulation results are accompained by interpretive discussion, and followed by suggested areas for further study.

Progress in coordinating the design of airborne radar equipment with the airframe is discussed, emphasizing such basic design characteristics as accessibility, form factor, heat dissipation, altitude, shock, vibration. R-F noise and primary power supply. A review of the scope of present-day installation problems follows, giving specific examples of coordinated design. Suggestions for improving current design practices include an early exchange of information among all agencies concerned, close liaison as the design unfolds, and throughout, an appreciative understanding of each others problems.

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.

A new technique is described which provides for precision angle tracking of celestial radio sources with a conventional monopulse antenna receiving system. It is shown that this technique is readily adapted to angle tracking radars. The features of conventional monopulse operation are preserved while permitting precise angle tracking of noise sources when signal to noise ratios are much less than unity. Measurements, using a four-horn monopulse feed with a 28-foot parabolic reflector and a "monopulse radiometer" produced the characteristic monopulse angle detection functions when using the sun, the moon, and Cassiopeia A as boresight reference sources. Precision measurements were made to 8 arc second under varying weather conditions using 28-foot radio astronomy antennas. The accuracy of the measurements were limited by the antenna angle encoders, consequently no conclusions are drawn with regard to the absolute accuracy of the measurements. The celestial coordinates of four discrete radio sources and the equations for coordinate transformation to local elevation and azimuth are contained in the Appendixes.

This paper presents results of an early study of the influence of parameters of a pulse radar system on its sensitivity. More specifically, it describes an experimental determination of the absolute value of minimum pulse signal visually detectable through random noise with a probability of 50 per cent for a wide range of the following parameters: pulse-repetition rate r, pulse length t, intermediate-frequency bandwidth B, and video bandwidth b. The following empirical formula expresses the results of the investigation with considerable accuracy: 1/ 1 \/ 1670\ 1/ 6 Vmin =-E. B112I1 +-1 ) 2 \ tB/ r/ where V min is the minimum detectable pulse voltage and E n is the noise voltage per unit intermediate-frequency bandwidth of the receiver. The application of the results to the design of search radar systems is briefly discussed.

A method is discussed for tracking the radar cross-section centroid of an ensemble of scatterers, using a raster scan observation technique. Estimation of the mean-squared dimensions of the ensemble is also considered. A maximum permissible beam separation is defined for the scan. Expressions for the bias and variance of the centroid estimates are given. Advantages of the approach are that individual scatterers need not be resolvable, and that the number of beams is independent of the number of scatterers.

Some factors that influence radar target detectability on a cathode-ray tube at high ambient light levels, such as occur in fighter airplanes, have been investigated. The signals considered are those that are intensity-modulated, as in B scopes and PPI. The problem is considered to consist of three parts that should be investigated separately: 1) the ambient brightness at which the indicator shall produce detectable signals, 2) the target spot brightness or intensity required for detection in this surround, and 3) the conversion of electrical signals into visual signals in the CRT. In this paper only 2) and 3) are discussed. It is found that with an intensity-modulated display, target detectability is determined by the spot intensity rather than by the spot brightness. The brightness of a conventional CRT shows an early saturation, but the intensity increases uniformly. Neither brightness nor intensity is a linear function of the radar parameters.

To realize full benefit from a radar, the analyzed echoes must be strong and sharp. Two options are available: Either the transmitted burst must be an intense, short pulse (often not a propitious arrangement) or the onus can be put on the receiver to process the echo into something more than it appears to be. One method for ``upgrading'' the received signal beyond a feeble echo from a not-too-powerful transmitted beam is acoustooptical processing, in which the reflected radar beam is converted to an acoustic wave that is used to modulate a light source. Then with the appropriate operation on the modulated light, the radar echo input is correlated against an optical filter. Of the two acoustooptic correlator classes described here, one works well below 150 MHz and the other is appropriate for frequencies above 150 MHz.

A recent work calculated the probabilities of detection and false alarm for the mean and median detectors for the log-normal and contaminated-normal descriptions of sea clutter. This correspondence extends the previous work by first calculating the performance of the trimmed-mean detector and then calculating the detection performance of all three detectors when the target exhibits Rayleigh fluctuations. Finally, a simple example is used to show that the optimal beamwidth of a radar need not be the smallest obtainable beamwidth.

The development of an unambiguous unit-distance code configuration for automatic altitude reporting via the ATC Radar Beacon System is described. This code provides for compatible altitude reporting in increments of 100, 250, and 500 feet within one common system. The code is developed by using Karnaugh mapping techniques. Some assumptions and requirements are set forth to provide guidance for the determination of the most desirable code. A brief presentation of a developmental code in use in the United Kingdom is also given. It is concluded that the flexibility of the unit-distance code affords a satisfactory compromise which can satisfy the objectives of the various users.

An effective forward step in terminal area air traffic control has been accomplished by development and installation of Radar Approach Control (RAPCON) Center and control tower prototype facilities described. Esoteric complexes detailed provide airport and approach controllers with radar and communication implementation of manual aids to jet and propeller driven traffic control procedures and techniques. Equipment reported also serves as manual backup and override facilities capable of eventual expansion to fully automatic air traffic control system operation dictated by high-speed jet performance characteristics.