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Interference in the form of multipath or uncooperative targets can seriously degrade the angle-of-arrival estimation accuracy of mutiplebeam processors. In this paper, the generalized likelihood ratio test is used to derive a test to detect the presence of interference for multiple beam processors. The detector performance is then analyzed in detail with respect to its dependence on signal-to-noise ratio (SNR), signal-to-interference ration (SIR), and on the relative phase between the target and interfering signals. It is shown that good detection performance can be obtained unless the phase difference between the target and interference signals is either in or out of phase.

The usefulness of radar as an automotive obstacle detection system is currently being investigated. Possible applications of such a system presently are automatic braking and air bag actuation and eventually the totally automatic highway. One type of radar having possible potential for these short range applications is diplex Doppler radar. The microwave and electronic circuits basic to a diplex Doppler radar obstacle detection system are described in this paper. The system provides Analog outputs proportional to range, velocity, and time to impact relative to an obstacle, as well as indicating whether the velocity is opening or closing.

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 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.

An experiment is described by which the ephemeris of a near-synchronous satellite was determined from passive range observations. The data consist of the measured times of reception at ground tracking stations of electromagnetic signals which are radiated from the satellite at regular intervals. A comparison of the ephemeris to one obtained from Doppler tracking indicates an accuracy of better than 4.9 mrad rms.

The antenna elevation control signal and the associated staticequilibrium equations are analyzed for the case of tracking of lowaltitude targets for both monopulse and conical-scanning radar. Three possible equilibrium positions of the radar antenna under static operating conditions are ascertained. The static solutions suggest certain dynamic solutions that are likely to arise under practical conditions. The extreme values of the pointing error are shown in graphical form.

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.

Coherent high-resolution synthetic-aperture radar systems achieve their range resolution by pulse compression and azimuth resolution by compression of naturally generated FM coding due to Doppler shifts as the aircraft flies by the target. If the data is left unprocessed, it is, in effect, a defocused map of the terrain. As such, it should exhibit less dynamic range than if the data is compressed. This paper describes an experimental study to verify the above conjecture. The results of this study indicate that if dynamic range of the data link is a problem, the radar data should be transmitted in its unprocessed form. This might very well be the case for planetary mapping by means of satellites.

Recent developments in airborne Doppler and ground mapping navigation radars and ground and satellite based radio systems are described. Simultaneous lobing and slope tracking techniques can remove the well-known Doppler sea bias error in fast and slowly moving vehicles. Doppler velocity information can be extracted from coherent forward-looking mapping radars, and high position fixing accuracy can be achieved by synthetic aperture radars. In radio navigation systems, such as Loran, Omega, and satellite systems, direct-ranging and differential techniques greatly reduce the geometric dilution and propagation effects which have plagued conventional radio navigation systems. The advantages gained by mixing of the data from these and other navigation sensors in a digital multisensor system are discussed and approaches for processing these data are suggested.

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 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

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.

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.

The modified generalized sign test processor is a nonparametric, adaptive detector for 2-D search radars. The detector ranks a sample under test with its neighboring samples and integrates (on a pulse-to-pulse basis) the ranks with a two-pole filter. A target is declared when the integrated output exceeds two thresholds. The first threshold is fixed and yields a 10-6 probability of false alarm when the neighboring samples are independent and identically distributed. The second threshold is adaptive and maintains a low false-alarm rate when the integrated neighboring samples are correlated and when there are nonhomogeneities, such as extraneous targets, in the neighboring cells. Using Monte Carlo techniques, probability of false-alarm results, probability of detection curves, and angular accuracy curves have been generated for this detector. The detector was built and PPI photographs are used to indicate the detector's performance when the radar is operated over land clutter.

In this paper an exact closed-form expression for the radar detection probability is derived and results are plotted for a frequency diversity radar receiver. The receiver model performs post-detection integration on all received pulses in all diversity channels. The target model assumed is the slow fluctuating Rayleigh-distributed (Swerling case I target) scatterer. Each of the M frequency diverse channels receives N amplitude-correlated returns to give a total of NM post square-law detection integrations. The tabulated data falls between the two extreme cases, that for which all the returns are amplitude-correlated and that for which each return is independent. The plotted results fall close to the figures obtained through simple empirical relationships.

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 mathematical model to study target image return frequency spectrums in Doppler radars is described. The model includes the effects of eclipsing, sea surface slope distribution, and surface reflectivity characteristics. The procedure of calculations has been computerized and the analytical results are compared to flight-test values obtained from flights over the ocean. The calculated values of amplitude-frequency spectrums of target image returns correspond reasonably well with the respective recorded flight-test data.

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.

Lacking Compass, sextant, chronometer, radio, radar and inertial navigation aids, “ancient mariners” relied on an observed knowledge of the prevailing winds, tides, and currents; the habits of birds, particularly sea birds; the discontinuities that exist where the sea meets the land; and the stars (1,2). A particularly well developed use of the “natural means” of the Marshallese (3, 4, 5). These Micronesian navigators devised an aid, artistic in execution, but near scientific in design and based primarily on water surface conditions.

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.

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.

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.

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.

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.

This paper presents a method of greatly simplifying the processing of received signals from antenna arrays through the use of a coherent optical system for signal processing. It is shown that a coherent optical system is ideally suited for carrying out beamforming operations. Several other advantages of coherent optics for this application are also discussed. A major result is a technique for forming several unambiguous beams simultaneously by correlating the signals from two linear arrays. The coherent optics technique permits this operation to be carried out with extreme simplicity.

Rocket vehicles are being used to expel passive wind sensors in the altitude range of 100,000 to 300,000 feet. The sensors are tracked with S-band and X-band radars to determine wind direction and velocity. Both chaff and metalized parachutes serve as wind sensors and AGC voltage recordings made on both X-band and S-band radars during tracking periods are presented. The recordings are calibrated in decibels above the radar minimum discernible signal and plotted vs slant range. A short discussion of the effects of chaff dispersion is included. Although chaff dispersion deteriorates the effectiveness of the target at a rate of about 20 db/hour, it is concluded that the effective radar target size of the sensors and the slant ranges over which they are employed are quite compatible when AN/MPQ-12 and AN/MPQ-18 radars are utilized.

This paper describes some of the early developments in the synthetic aperture technique for radar application. The basic principle and later extensions to the theory are described. The results of the first experimental verification at the University of Illinois are given as well as the results of subsequent experiments. The paper also includes a section comparing some of the important features of real and synthetic aperture systems.

A simple Markov process model of binary, digitized radar clutter returns is assumed. Probability distributions for the number of hits in n observations are developed for small n with a binary parameter describing the process derived for Rayleigh distributed clutter. Tables of distributions are included, along with an example to show the effects of correlation on the false-alarm probabilities of a sliding-window detector.

One of the more difficult requirements to meet in the design of radars is that of accurate angular measurement. In tracking radars the azimuth and elevation of a target can be measured to a high degree of accuracy by a nulling method. Two of the most practical methods for obtaining angular accuracy in search radars are discussed in this paper. The first method is an interferometer technique employing either two receiving antennas for each dimension of angular measurement with two frequencies of transmission for the resolution of ambiguities, or three receiving antennas positioned relative to one another so that the equivalent effect is achieved with only one-frequency transmission. The second method is a combination amplitude comparison and interferometer technique in which the ambiguities are resolved by the amplitude comparison system. An analysis of each of these systems has been made using a statistical approach in which equations are developed relating the probability of error for a specified angular accuracy to SNR power in the receiver. Curves are presented which show this relationship for a 100 to 1 beam-splitting ratio.

This paper is concerned with the navigation of a manned space vehicle during its powered deboost phase of flight prior to landing on the moon. An inertial measurement unit (IMU), which operates continuously, is provided on board the vehicle along with an altimeter and a doppler radar. The basic problem of interest is to determine the best way to navigate the vehicle with these instruments, considering factors such as equipment operating ranges, data rates, random and bias measurement errors, terrain anomalies, and computational complexity. The navigation systems presented are based on the least-squares estimation techniques developed by Kalman and Battin. Up-to-date estimates of the vehicle's state are obtained by comparing altimeter or doppler-radar measurements with IMU-derived estimates of the same physical quantity. The key to the estimation process is the determination of the best weighting to use on these measurement differences in the updating procedure. Several different sets of weighting factors for use in the deboost phase are developed in the paper, using minimization of mean-squared estimation errors as the basic performance criterion. Bias errors in the IMU measurements, uncertainties in the knowledge of the orientation of the radar antennas relative to the IMU, and anomalies of the lunar terrain are assumed to be the predominant navigation-system error sources. The major differences between the weighting factors result from the particular model employed for the navigation sensors, the model used for the lunar terrain, and the methods used to account for measurement bias errors in the weighting-factor computations.

Propagation errors along paths between an array radar and a distribution of targets cause degradations in angle measurements and detection range. The overall objective of the research described in this paper was to analyze and demonstrate the use of conjugate reflections for compensating adverse effects of path errors. The effect of reflecting the conjugate of an incident wave is described mathematically and is demonstrated by computer simulation. Repeated conjugate reflections are shown to result in the formation of a single beam usually focussed on a target highlight. Echoes from this spatial reference, or "beacon" are shown to provide the means by which aperture phase errors may be effectively compensated. Results of radar simulations include two-way patterns computed for an example involving a distribution of three-point targets and half-wave-length Gaussian aperture errors. Without compensation a gain loss of 12 dB is computed; with error correction, based on echoes from an adaptively focussed beam, the two-way pattern is within a small fraction of a dB of the ideal pattern. The effect of noise on adaptive beacon forming was considered for a case involving one target. Repeated conjugate reflections improve signal-to-noise ratio as long as the effect of noise is less than the effect of aperture dephasing on the power reflected back to the target. An example is presented in which signal-to-noise ratio at the output of the receiver combining network is increased from 4 to 11.8 dB.

The equivalence of the vector addition, cross-correlation, and filtering approaches to deriving synthetic array patterns and analyzing processing techniques is demonstrated here. A mathematical model is defined which establishes a geometry, a transmitted and received signal, and a general synthetic array weighting function. A preliminary analysis of this model derives the signals received at the flight-path points where radar pulse transmission and reception occurred, and the effects at these flight-path points of the synthetic array weighting function. The weighted, received signal expression is then summed over the array, and the resultant shown to be a vector addition, a cross-correlation integral, or a filtering operation depending on the changes of variable and formal manipulations employed.

Noncoherent Doppler permits determination of the ground course as the azimuth of a null in the clutter Doppler returns and, therefore, can be a frequency insensitive adjunct to a pilotage search radar, especially where weight and/or power is at a premium. This stands in contrast to the customary coherent Doppler navigators which relate the frequency changes upon reflection, fore and aft, to the drift angle. An X-band self-coherent Doppler implementation developed that 88 per cent of the drift-angle measurement was within ± 1° of a concurrent optical measurement.

The use of a two-lobe monopulse radar for measuring slant range to the surface of the earth in the absence of discrete targets is analyzed. It is shown that tracking dispersion can be considered as the resultant of two components. One component is independent of range and results from the finite pulse length and gate length and the random nature of the return signals. The other component is due to receiver noise and increases as the signal-to-noise ratio decreases. The dispersion component independent of range is shown to be proportional to the pulse length and tracking gate length. The variable dispersion is shown to be proportional to the five halves power of the range and the three halves power of the cotangent of the depression angle of the antenna boresight axis. Performance calculations for a specific radar are carried out and compared with experimental data.

Techniques are presented for the approximate calculation of optimum midcourse fixed- and variable-time-of-arrival velocity-correction schedules. The theoretical results are compared to those of a simulation program which utilizes Earth-based radar and onboard sextant tracking data processed with a Kalman filter for two typical interplanetary transfets. It is shown that the agreement between theory and simulation improves as the amount of radar data processed is increased and that the theoretical optimum timing equations provide an accurate first estimate for generating interplanetary midcourse velocity-correction schedules.

Orbiting passive communication satellites cannot exploit radar target structures, for the reflected energy must cover the entire globe. Each orbital altitude dictates its maximum tolerable gain. Structures with large plane surfaces have too narrow beams and intolerable scintillations. Only spheres studded with several thousand retrodirective elements of wide scan angle eliminate scintillations and are tolerable in weight. Investigations of corner reflectors as retrodirective elements revealed, only small (3?) three dimensional right angle corners are feasible. The overall efficiency in a spherical arrangement is limited by sidescattering to about 12 db.

The problem of designing finite-pulse-train radar signals and receivers to maximize the detectability of targets masked by thermal noise and clutter returns is considered in this paper. A practical constraint is introduced: the amplitude of each subpulse in the transmit waveform is taken to be fixed. The need for such a constraint is dictated in most radar applications, because the transmitter is most efficiently utilized by saturating its amplifying tube. An algorithm for generating optimal waveforms subject to this new constraint is presented, and the performance of the resulting waveforms is compared with those obtained using existing optimization techniques.

A method is described whereby a conventional non-Doppler radar may be used in the measurement and detection of atmospheric turbulence. The technique involves the measurement of the average echo power and the variance of the fluctuation spectrum in each of two separated pulse volumes, and corresponding measure ments of echo power and variance of the detected signals in a channel representing the predetection sum of the signals from those two volumes. It is shown that the variance of the sum channel is the power-weighted sum of the variances in the independent channels plus a term dependent upon the difference in mean radial velocity of the associated pulse volumes. Accordingly, the difference in mean radial velocity can be measured. When the spacing of the sampled volumes is adjusted to represent distance along an aircraft flight plan, the measurement is a measure of the turbulence to be experienced in traversing the space between those volumes. Specific systems for accomplishing the measure ment are discussed.

The Dynamic Target and Countermeasures Simulator described herein was developed at the U. S. Army Signal Missile Support Agency Laboratories, White Sands Missile Range, Las Cruces, N. M., by a group of Signal Corps engineers and technicians, utilizing components from scrapped radars and standard RF test equipment. This versatile simulator can be used to test existing radars for signal saturation and electronic counter-countermeasures techniques, such as regulating RF and video gain, contrast, etc. Provision is made to simulate antenna patterns and to vary the size of the target from 0.1 to 100 square meters. The expense involved in training radar operators to cope with raids involving hundreds of aircraft has led to the development of various target simulators. As the state-of-the-art in electronic countermeasures (ECM) improved, it became apparent that ECM simulation was also necessary to train radar operators under the conditions that would prevail when aircraft would be radiating thousands of watts of jamming power. Most of the simulators developed used IF or video injection of target signals in the simulator and did not provide the realism desired or allow the radar operator to exercise electronic counter-countermeasures (ECCM) techniques effectively. The problem then became one of realistic simulation of both target and jamming signals. Field experience at White Sands Missile Range (WSMR) had demonstrated that simulation could be accomplished most effectively at the RF level. This finding, by WSMR engineers, led to the design and development of the Dynamic Target and Countermeasures Simulator.

An analytical technique is proposed for investigating the effect of antenna pattern shape on reentry vehicle radar altimeter performance. Initially, a method is presented that computes the average performance under all roll positions. This method is then extended to allow performance to be determined at each roll position. Some numerical results are included that show roll effects for a typical antenna pattern.

A technique is described for the measurement of power spectra which is designed to distinguish the spectrum of a weak signal which is masked by strong background noise. The method was applied during the Jet Propulsion Laboratory Venus radar experiment to study spectral characteristics of the echo. An analysis is given which describes the performance of the system in such an application.

Uniform coherent pulse trains offer a practical solution to the problem of designing a radar signal possessing both high range and range-rate resolution. The Doppler sensitivity provides some rejection of off-Doppler (clutter) returns in the matched filter receiver. This paper considers the use of a processor in which members of the received pulse train are selectively weighted in amplitude and phase to improve clutter suppression. The techniques described are particularly suitable for rejecting interference entering the processor through ambiguous responses (range sidelobes) of the signal. The complex weights which are derived are optimum in the sense that they produce the maximum clutter suppression for a given detection efficiency. In determining these weights, it is assumed that the distribution of clutter in range and range rate relative to targets of interest is known. Thus, clutter suppression is achieved by reducing the sidelobe levels in specified regions of the receiver response. These techniques are directly applicable to array antennas; the analogous antenna problem would be to reduce sidelobe levels in a particular sector while preserving gain. Complex weighting is most successful when the clutter is limited in both range and velocity.

The number of transmitted pulses associated with the Doppler histories of a side-looking radar may greatly exceed the desired azimuth compression ratio of the system. This discrepancy is taxing if the storage required for the azimuth processing is provided by cores, magnetic drums, and the like. Thus, as a practical matter, one considers presumming of the data prior to correlation in an attempt to achieve the desired performance with a minimum amount of digital storage. In this paper, the optimum (in terms of resolution) presummer is derived, along with the optimum apportionment of the available storage capacity between the presumming and correlation operations. Under the condition (or generally pessimistic approximation) that the illumination pattern of the antenna uniformly illuminates a Doppler bandwidth equal to the PRF of the radar, the optimum presumming coefficients are the first Np Fourier coefficients of a function which is one of the Doppler bandwidth to be correlated and zero on the remainder of the PRF bandwidth, where Np is the number of transmitted radar pulses over which presumming is provided. Increasing Np reduces the degradation due to presumming, but may leave inadequate storage for correlation. Hence, we optimize the apportionment between the two operations and present the obtainable resolution as a function of total storage and the number of transmitted pulses in the received Doppler history.

Moving targets submerged in clutter can be more readily detected by range-gated filtering techniques. Range-gated filtering is a two-dimensional process in which target Doppler frequency and range are desired output quantities. Optical data processing techniques are inherently multidimentsional. An experimental system using a He-Ne laser source and film transparencies representing radar echoes gave output patterns in agreement with theoretical predictions. Major advantages of an optical filter are simplicity and relatively small size.