Search

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.

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.

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.

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.

This paper contains a brief summary of the Signal Corps' contribution to the antenna art. Emphasis is on the post World War II period and on microwave antennas. Only developments which have had reasonably wide application are discussed.

A new monopulse radar signal processing technique is described, which requires only a single IF amplifer channel to instantaneously process the returns from all targets within a beamwidth. The basic signal processor consists of a wide-band amplifier-hard limiter, followed by appropriate band-pass filtering. The mathematical basis for its operation is developed and corroborating experimental results are given. Angle accuracy curves for a sum and difference monopulse system are derived as a function of input SNR.

This paper explains the present methods of simulating the earth's topography and their uses, the difficulty and time consumed in making some of these simulations, and the limitations of their uses. It then explains the need for some better method because of the greater volume of topographic information required in greater detail because of the needs of cold war, national defense, industry, road expansion, seaway expansion, airport construction, radar site construction?all to be done in a great hurry. It leads up to the automatic terrain model system. It explains quickly the several systems that were considered and why the printed circuit system was chosen. It mentions the fact that the information is stored on magnetic tape and utilized to carve a three-dimensional terrain model, and then goes into detail as to the greater information that this particular system can provide automatically that cannot be done except through extensive hand calculation with the other systems.

Based on precalculated data for the position and velocity vector of the injection points for the Explorers I through V, orbital elements are derived and compared with the actual orbital elements at injection time, calculated from position and velocity data obtained from radar measurements. Calculations are also made for the different orbital periods of a satellite perturbed by the Earth's oblateness. For Explorer I, it is shown that the actual orbital elements derived from tracking observations agree well with the actual elements derived from early astronomical observations.

An account is given of the development of the AN/UPD-1 (XPM-1) system. This airborne mapping radar, by synthesizing an extremely long antenna which expands in length in direct proportion to radar range, provides a linear resolution in the azimuth direction that is constant for all radar ranges.

This paper describes a method of simulating the radar displays of an airborne radar system. The simulator employs a scan-programmed vidicon tube and a low-power light source in conjunction with a three-dimensional terrain model to simulate radar return from land-mass formations, cultural areas, and target complexes. All effects of a moving aircraft, including velocity, heading, altitude, position, and attitude, are included in the simulation. This device will produce the displays for ground mapping, contour mapping and terrain clearance radar systems. It may be employed with an operational flight simulator or as a self-contained radar mission trainer for radar navigation and blind bombing operations.

A circuit theory model is derived for coherent radar, communication, sonar and antenna systems. The model involves linear time invariant operators and hence can be thought of as cascaded filters. The model provides insight for such systems not previously available, and it provides a unified approach to the analysis of all the above systems. The analysis is concerned with continuously distributed target fields and point targets, perturbed by both additive noise and random phase errors. The model in general consists of two filters, a pre-filter and a post-filter. For radar, sonar, and antenna systems the input is the reflectivity of the target field to be sensed. For the radar and sonar case the impulse response of the pre-filter is the transmitted pulse while for antenna systems the impulse response is the current distribution. For communications, radar, and sonar the post-filter is the receiver while for antennas the post-filter is a combination of the receiver and the receiving antenna. Additive receiver noise is accounted for at the input of the post-filter. Lack of perfect coherence or phase errors can be due to many causes, e.g., atmosphere or ocean inhomogeneities. To account for the various sources of phase errors, one must consider both the pre-filter and post-filter as random parameter systems and include a multiplicative error at the input of the post-filter. This also accounts for fading. Optimum detection has been considered extensively in the literature; in this report we emphasize two other related criteria, namely resolution and mean-square error.

One of the limitations of FM/CW radars, often quoted in the literature, is in their inability to handle multiple targets. Several variations of a comparatively simple Range/Range Rate Display, capable of handling and resolving a large number of targets when used in conjunction with an FM/CW radar, are presented. The FM/CW plane and means for resolving target ambiguities are discussed, as well as system features, which, when used in conjunction with the displays, enable multiple target range and velocity information to be obtained and utilized simultaneously.

Practical experience is now available with the Electron Beam Parametric Amplifier (EBPA) used as a low-noise preamplifier in radar systems. Principles of operation of the EBPA are briefly recapitulated. Among its desirable characteristics are unilateral behavior, high stable gain and a double-channel noise figure (NF) of 1 db or less; its bandwidth, input and output impedance remain constant as gain is adjusted. An L-band amplifier is described in detail. A discussion of various ways of handling the idler channel follows. The technique of in-pass-band pumping achieves an effective NF of 2.5 db or better in radars with conventional detection. Complications arise with Moving Target Indicator (MTI) systems; remedies are described. The paper reports on field tests in which these techniques were used, including a few flight tests. The results show substantial improvements in sensitivity and range. They also spotlight the ability of the EBPA to tolerate high overload and to act somewhat like a TR switch.

This paper presents an analysis of the problem of the resolvability of two radar targets which are located close together, in the sense that any parameters of the targets being measured (e.g., range, range rate, range acceleration, azimuth, azimuth rate, etc.) are close together. Arbitrary sets of parameters are allowed, and it is assumed there is additive noise of arbitrary but known spectral shape. A criterion of resolvability is formulated, and in terms of this criterion equations are derived for the general case to show whether neighboring targets are resolvable. The results are specialized for the case of white-noise interference and the measurement of range and range rate.

Data obtained on high-power traveling-wave tubes at S and C band indicate performance suitable for the final amplifier in a wide bandwidth phase coherent radar transmitter. Static phase measurements demonstrate the capability of parallel operation of tubes and the feasibility of use in pulse compression systems. Gain and power output data show that for the most efficient operation a programmed drive is needed. Data taken at constant drive power displays a compressed gain variation and a somewhat lower output. An extrapolation of present data indicates the feasibility of obtaining 25- to 30-per cent bandwidth in high-power traveling-wave tubes with other improved characteristics.

The background for the present safety system is outlined in a review of the original Air Force plans and installations and subsequent Navy-Air Force agreements for the coordinated use of the Pacific Missile Range, considering the expanded scope of operations in the area. A description is given of the ground stations in the unified acquisition and tracking system for range safety as well as the auxiliary equipment for missile monitoring during early parts of its flight trajectory. A review is made of the associated data transmission and processing equipment including operational direct voice circuits. The corresponding safety equipment in different types of missiles is discussed in connection with both command, tracking, and telemetry functions. The implementation of the flight termination command requirements is outlined in the main transmitting station and missile checkout apparatus. The support areas of status reporting, telemetry, timing, and communications are discussed in detail. Finally, new requirements for precise downrange impact prediction and vehicle thrust termination are described.

This paper describes a Radar Track Simulator which generates the track of thirty-two aircraft in x, y, and h coordinates accurate to one-hundreth of a mile and produces video accurate to one-hundreth of a mile in range, one milliradian in azimuth and two milliradians in elevation. The output video signals are modified by the radar beam pattern, aircraft scintillation noise, radar receiver noise, fading of video signal with range, and blip-scan effects to produce a realistic display.

The U. S. Army Signal Research and Development Laboratory has developed several types of radar equipment to fulfill the combat requirements of the Field Army. To aid in obtaining an all-weather continuous surveillance capability, the AN/PPS-4 and AN/TPS-25 ground radar sets were developed. To extend and supplement their coverage of the combat zone, the AN/APS-94 airborne radar was developed. Locating weapons of interest is another important function of combat surveillance. The AN/MPQ-4 mortar locator was developed for this purpose.

One of the major recent advances in radar technology has been in the processing of the received signals. Several techniques have been developed to enhance the desired signals (aircraft) relative to ground clutter, sea clutter, rain, interference from other radars, and active countermeasures. The following techniques are discussed: MTI, Sweep Integration, and Blanking and Switching. A signal processing system utilizing these techniques is described.

A model range-channel pulse-compression system is postulated and the problem of suppressing sidelobes in the compressed pulse is discussed. It is concluded that amplitude-weighting in the time domain (at IF) is a convenient method of suppressing sidelobes. An integration loss factor is defined which characterizes the decrease in signal-to-noise ratio (SNR) resulting from the inclusion of weighting. For a radar system which is peak-power-limited, it is shown that the integration loss is less if the amplitude-weighting is accomplished entirely at the receiver while ``mismatching'' the system, rather than weighting at both transmitter and receiver while preserving a ``matched'' system. Some common amplitude-weighting functions are compared in terms of integration loss, main-lobe broadening, and sidelobe structure. The Hamming weighting is shown to be a good compromise among the above factors and, in addition, it is relatively easy to implement. The effect of a time-mismatch between the Hamming amplitude-weighting function and an echo pulse is considered for the special case of linear-frequency modulation.

This paper traces the development of the various techniques used to generate synthetic land mass or terrain radar signals for radar training devices. The survey begins with a description and assessment of the Ultrasonic System and concludes with a discussion of the more flexible Two-Transparency System now under development by the Navy.

The theory of optimum linear prediction and filtering is applied to determine the optimum system response of pulse (noncoherent) and pulse-Doppler (coherent) radars for target motions consisting of 1) random steps of velocity, and 2) random steps of acceleration. The rms error in velocity data is calculated for each system, and the improvement factor of pulse-Doppler over pulse radar is obtained. The improvement factor is considerably greater in the case of random steps of acceleration, demonstrating that the relative accuracy of the two systems depends on the nature of the target motion, as well as on the radar parameters. Although the errors in both systems are reduced somewhat by allowing large delays in output data, the relative accuracy is found to be unchanged.

A procedure for radar range calculation is described, reflecting current knowledge of the effects of external natural noise sources, atmospheric-absorption losses, and the refractive effect of the normal atmosphere. The range equation is presented in terms of explicitly defined and readily evaluated quantities. Curves and equations are given for evaluating the quantities that are not ordinarily known by direct measurement. Some conventions are proposed for use in general radar range calculation, including an antenna-noise-temperature curve, minimum-detectable signal-to-noise ratio (``visibility factor'') curves, and a formula for the reflection coefficient of a rough sea. A noise-temperature table and a work-sheet for range calculation are included in the Appendix.

Coverage patterns for trans-horizon radar systems can be predicted both analytically and empirically. Empirical methods are preferred because of their rapid application and lack of need for elaborate computing facilities. In addition, the coverage techniques introduced may be used eventually to determine the slant range, absorption, and effective noise temperature of trans-horizon radar systems. Some of the fundamental considerations which influence the prediction of coverage, such as geographical location, and the diurnal, seasonal, and anomalous behavior of the ionosphere, are discussed qualitatively. In spite of these factors, however, it is shown how HF radar systems overcome the line-of-sight limitations imposed upon conventional microwave radar systems and theoretically permit up to four or five times the range for a single hop.

Phase monopulse, amplitude monopulse, and phase-amplitude monopulse are compared. The latter uses only two antenna feeds and by controlling the aperture illumination from these feeds has a separation of the illumination phase centers in one axis and opposed tilts of the phase fronts, or squint, in the other axis. It is described as more fundamental or less redundant than four-horn or other multihorn monopulse designs. In lacking redundancy it is less complex, but has fewer degrees of freedom to optimize performance. The earliest example of phase-amplitude monopulse, the AN/APG-25 (XN-2), is described and its performance given.

Recognition and application of fundamental signal-gain relationships inherent to monopulse radars provide the means for determining the angle offset pattern and hence, angular position of all targets within the beam of a monopulse radar. With this method some 20 to 40 targets can be tracked with dynamic accuracies that approach the static accuracy of the radar, thus permitting precise determinations of their individual trajectories and cross sections. These determinations can be made in real or nonreal time, as desired, by using a small portion of the storage capacity of the digital computer normally utilized with range instrumentation systems to calibrate, store and process information in accordance with the data operations described herein. The main advantage of this digital data processing scheme lies in the elimination of a number of complications which characterized earlier methods.

A practical AFC system for both X-band and Ku-band magnetron radar transmitters has been developed. This system meets the needs of three radar systems currently in production. Frequency stabilization is accomplished by electronically controlling the magnetron load impedance. Therefore, the magnetron ``pulling figure'' is put to use. The closed loop AFC system maintains frequency stability to better than ±2 Mc at Ku-band and ±1.5 Mc at X-band frequencies over wide environmental conditions. The system dynamically compensates for deviations in frequency due to temperature, vibration, shock, changes in duty cycle, drift with life, and poor voltage regulation. The response time of the AFC system is such that, starting at the limits of thle capture range, ``on frequency'' response is Obtained within the first five pulses of the magnetron. One of the radar systems requires a considerable delay between groups of pulses. For this radar, the AFC system provides a memory to hold the conditions for ``on frequency'' response during the delay periods. A qualitative analysis of the closed-loop system is made with reference to the Rieke Diagram. It is shown how a single magnetron has been used to meet two different sets of system performance requirements. System operation and hardware are discussed with reference to practical difficulties.

Consideration is given to the direction of future microwave device research and development based on requirements for space communication, tracking, search and surveillance, and interference and countermeasures. The crucial element in two-way communication with a space vehicle is the vehicle-borne transmitter. The large values of one-way transmission loss associated with interplanetary distances will require great improvements in these transmitters. Radar involves two-way transmission loss, so even more improvement will be required for tracking and search radars. Solution of interference problems will require increased instantaneous bandwidths. Accordingly, it is suggested that much additional microwave device research and development work is needed. Average power and efficiency of microwave tubes must be increased, with the longer centimeter wavelengths to be used for earth-based radars and 1-30 millimeter wavelengths to be used for radars to be borne in space vehicles. This work should concentrate mainly on traveling-wave tubes. Solid-state low-noise receiving devices and low-noise traveling-wave tubes must be extended to higher frequencies and broader bandwidths. Means of generating microwave power through the use of plasmas must be investigated. All types of microwave election devices must be adapted to the space environment.

This paper is a study of the ultimate attainable accuracy in the radar measurement of range, range rate, and range acceleration. It is assumed that these quantities are to be measured by a coherent radar with a large output signal-to-noise ratio. The approach is entirely theoretical, and the accuracy evaluated is the accuracy that would be attained with an ideal receiver which performs maximum-likelihood estimates of the unknown parameters. The transmitted waveformn is fixed and arbitrary, and the error variances and covariances are evaluated in detail in termns of the amplitude and frequency modulation of the transmitted wave. Specific results are also given for constant amplitude pulses carrying arbitrary combinations of linear and quadratic frequency modulation.

A brief introduction to coherent radar applications is given by discussing some basic pulse and CW systems. Comments on the historical development of these systems are followed by a general discussion of coherent radar parameter variations as they relate to the accuracy, resolution and ambiguity of target position or speed measurements.

Usually in a radar signal-processing scheme, the primary consideration is the geometrical resolution of the system, or, if a particular measurement is desired, the accuracy of the system. Thus a given signal-to-noise ratio may be sought in order to meet a simple detection requirement or a desired accuracy. Usually, beyond these simple criteria, the matter of signal amplitude fidelity is not particularly stressed. In many processes, however, signal fidelity can be an important consideration in evaluating the over-all effect on the observer. In this paper the loss of information caused by signal interference in correlation or matched filter techniques is evaluated in an approximate manner. This is related to the invariance of the total integral of the Woodward ambiguity function. Degradation of the desired signal due to the statistical fluctuation of the signal itself is also considered. The distinction between pre-detection integration, which is involved in the correlation process, and post-detection integration is made. How these fluctuations can be reduced by post-detection integration is discussed and the resulting probability distributions of the signal are evaluated. Finally some brief comments are made on the philosophy of providing adequate gray-level rendition in radar displays. Attention is given to reconciling the dynamic ranges of the display and the signal, and to the number of resolvable gray levels available in the signal. A good example of these principles is the problem of recognition of objects in maps obtained from high-resolution radars.

This paper is intended to provide the systems engineer with a practical introduction to the use of solid-state maser amplifiers in radars. Various environmental problems involved in the successful application of masers are discussed. An elementary survey of reflection-cavity and traveling-wave masers, together with some experimental results are presented. Another section treats the problem of saturation in masers and discusses some of the methods available for protecting masers from the TR leak-through pulses in radar. Progress made in the development of open-and closed-cycle liquid helium cryogenic systems suitable for masers is described. The authors' personal evaluations of the state of the art of ruby masers and closed-cycle helium refrigerators are given in appendixes.

Signal processing distortion degrades radar performance with respect to target data accuracy, ambiguity and resolution. A measure of the loss in performance is obtained by the development of a modified radar ``uncertainty function'' which results from the presence of time- and frequency-domain distortions in the system. Losses due to the major sources of distortion are evaluated and several compensation techniques discussed.

The present status (1959-1960) of the ABMA Early Orbit Determination scheme for the Juno space vehicle is described, The design of the scheme was essentially influenced by three factors: 1) its origin centered around post flight vehicle analysis; 2) the flexibility required for accepting varied kinds of data; and 3) the potential of high speed computers concentrated in the ABMA Computation Laboratory. The scheme is outlined and the evaluation techniques used for the various steps of the orbit determination are discussed in detail.

It is the purpose of this paper to show that optical accuracies can be reached with electronic tracking if the refractive index is known at the site of the radar, as well as at the site of the target. This is the case in tracking space vehicles with microwaves. The index can be measured at the tracking site and it is unity beyond the denser atmosphere. Ionospheric influences can be neglected in the higher kilomegacycle range. It is also shown that the uncertainty of the course of any particular profile between the surface of the earth and the target has only minute effects on range and angular errors. Accuracy limits are determined and presented numerically. The inherent high precision of modern electronic tracking systems can be fully utilized under these conditions; this is not the case in tracking vehicles flying in the atmosphere.

This paper summarizes problems which confront engineers who are responsible for the design of radar beacons and beacon antennas used in IRBM and ICBM test vehicles. The most important factors which affect compatibility between the beacon and tracking radars at the test range are enumerated. Cited also are several design areas which should be correlated with the test range prior to finalization of beacon design criteria.

This article tells the missile radar-beacon story from the beginning of V-2 missile firing in America until today. It compares the weight, dimensions, characteristics, and uses of former beacons with those used today. It also describes briefly new beacons under development, and tells how some of the future missiles and satellites may use these beacons.

This paper describes a semi-active radar system in which the transmitter is carried in a satellite. The satellite transmits a randomly modulated signal. On the ground the radar has two antennas and receivers. One antenna points at the satellite, the other at the target. The signal from the satellite-oriented receiver is delayed and correlated with the satellite signal reflected from the target. The delay corresponding to the peak of the correlation function is used to determine range. It is planned to test this system with various communications satellites.