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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.

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.

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.

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.

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.

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.

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.

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.

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.

The CV35 klystron, one of a number of English radar tubes made in Australia during the war, is described and an outline given of the techniques and equipment used in its manufacture. described and an outline given of the techniques and equipment used in its manufacture.A modification which improved the control characteristics of the later production is discussed, and a short method of estimating the transit time in non-linear fields is described

The paper discusses the design of special radar circuits for use where reduced weight and enhanced reliability are desired. It is concluded that in such instances the circuits form the core around which the rest of the design must be framed. Some of the problems which face the circuit designer are elaborated, the use of pulse ratings, tropic-proofed materials and miniature valves being particularly noted. Circuits are given which illustrate methods of material and dissipative economy. Mention is made of ancillary gear and of the importance attached to careful choice of the source of power, and its precise nature.

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.

This paper describes the use of frequency-modulated radar techniques for accurate location of faults on power transmission lines. It includes the design of a prototype frequency-modulated fault location system. Test results of this system operating on a simulated transmission line are also included.

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 common problem in radar, navigation systems or pulse-time modulation systems is that of determination of the delay or time of arrival of a pulse or other distinctive modulation form. while considerable effort has been directed toward the optimization in various senses of the signal-to-noise ratios for such signals, the problem of the most accurate determination of time delay of signals in noise bas, with a few noteworthy exceptions, been taken for granted. It is of interest to examine this problem for its own sake, not only as indicative of optimum circuit practice, but, more important, in order to make clear the fundamental accuracy limitations and the manner in which these limitations depend upon signal and noise parameters. The consideration of this paper is limited to the case where there is no doubt as to the existence nor approximate position of a pulse but where the accuracy of determination of pulse position is limited by noise. This case is therefore more representative of the problems of high accuracy systems such as Loran or shoran than of radar.

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.

This paper outlines the work currently being carried out at the Royal Radar Establishment (RRE) in the RF and Microwave National Standards Division of the British Calibration Service, on both hot and cold noise standards and comparator systems. The design of three cryogenic noise sources for use in WG15 are described in detail along with the theoretical calculation of their output noise power spectral density. A noise-adding radiometer is analyzed, and finally the sources of uncertainty involved in a recent calibration are discussed.

The elementary electronics circuits familiar to radar men are not limited to one field, as is shown by this description of a typical industrial electronics application. Ultrahigh frequency techniques are described as used for register control in the printing and paper industries.

An extension of the principle of space-frequency equivalence to increase the directivity of a two-element antenna array is described. A method to utilize this idea for improving the accuracy of tracking radar is suggested.

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.

Previous work on optimum gain control is extended to an important class of diversity receivers used for digital data transmission through fading media and for radar. As in the single diversity case the optimum gain (which yields minimum average cost of receiver saturation) is extremely insensitive to relative costs of saturation at the upper and lower dynamic range bounds. The sensitivity to relative cost decreases as the order of diversity increases. Optimum gain and performance characteristics are given from which dynamic range requirements for diversity receivers can be deduced.

Needs for nondispersive microwave variable delay devices exist in RADAR, communication, ECM, and test systems. Methods which have been investigated to satisfy these needs are reviewed in this paper. Techniques that employ solid-state microwave acoustic interactions and that have promise of satisfying some of the microwave variable delay requirements are described in detail, and their present capabilities and potential capabilities are discussed. One technique employing magnetoelastic waves is particularly promising and the state of the art of this technique is analyzed thoroughly.

Digiplot is a marine radar aid for automatic anti-collision navigation which processes signals from conventional radar and presents computed information on a separate screen to give at-a-glance situation appreciation. The company's origin is touched on and conception and design are described as they evolved to meet operational requirements.The majority of sophisticated radar equipments and devices available today have evolved from successive shipborne radar developments over a considerable period of years. With Digiplot it is otherwise. The Iotron Corporation was established in 1969 by a few men whose background had been information technology in the realms of fire control and navigational systems for submarines, aircraft, missiles and spacecraft, and reconnaissance systems using electronic and optical techniques; in all these systems digital electronics played a key role. The choice of the navigational functions of marine radar as the most appropriate subject for attention by the group was made after a general study of the commercial field, because of the revolution apparent in ships, their equipment and their operations.

General considerations pertaining to the parameters of a tracking radar are discussed and an optimum set of the system parameters for long range capability are arrived at. A concise description of the radar microwave transmit/receive chains designed and developed here and the measured performance on various subsystems are given and this data is then compared with the requirements arrived at in the above context.

The 120-foot diameter Haystack antenna operates at X-band and is used for satellite communications, radio astronomy, and radar astronomy. Haystack is used to study stars, planets, the sun, the moon, and earth satellites. In order to point the antenna to within 1/10 beamwidth (22 seconds of arc) and to provide flexible control and data processing for diverse users, a digital computer is tightly integrated into the control system. The parameters of an experiment and computer control are arranged via simple operator discourse through a keyboard/printer. The computer system can simultaneously direct the antenna, process receiver signal data, drive convenient operator displays, and permit operator discourse. Thus, processed signal data can be observed in real time, and experiment modifications rapidly implemented. The computer control system is in full operation.

Ground-Controlled Approach (GCA) was developed to meet military requirements for a "universal" blind-landing system, needing no additional airborne equipment or pilot indoctrination beyond short-range voice radio and basic instrument training. The talk-down principle, previously discredited in favor of beam-approach systems, was proved feasible when accurate information was available. The requirements of rapid radar scanning, at low angles to the horizon, with a high degree of accuracy at short range, were met by linear dipole arrays at 3-cm wavelength, with mechanical variation of waveguide width varying the angle of radiated power to the array. Half-power beamwidth for the elevation antenna was 0.1°; for the azimuth antenna, 0.8°. To translate range/angle data into a linear relationship of range vs deviation in feet from a selected approach path, a new type of indication was developed, i.e., Expanded Partial PPI Indicator (EPI). This permitted direct interpretation and immediate transmission of the data to the pilot by the controller. GCA's wartime service record, beginning late in 1944, proved its effectiveness under all conditions and led to further modifications and simplification for postwar commercial as well as military use.

A brief discussion of several types of CW radar will be given. Emphasis will be directed toward the function of the tube in each of the various radar systems. A detailed discussion of the requirements placed on the CW oscillator for each of the radar systems will be made. Tube characteristics which limit radar performance will be discussed. Some measuring techniques for evaluating magnetrons and klystrons will be discussed.

This paper describes the function and practical design of high-power pulse transformers as applied to radar pulse transmitters.The effects of pulse-transformer constants on the load pulse-shape are analysed and optimum values for the various relationships derived.The characteristics of magnetic core-materials under conditions of pulse magnetization and practical and theoretical methods of measuring and estimating them are discussed. Apparatus for measuring pulsemagnetization characteristics is described.

A seven-hop 295-mile combined microwave and tropospheric forward-scatter communications system is being installed for carrying voice, timing, telemetering, radar data, and controls for the Eglin Gulf Testing Range. System design of the frequency-diversity 7000-mc microwave system is reviewed, as well as the design of the four-fold diversity 2000-mc scatter system. Problems of special interest on transmission of timing signals, telemetry, and radar digital data are discussed and solutions indicated. Considerations for reliability, flexibility and ease of maintenance are indicated. Integration of the range operations by use of the commnnications system is described.

This paper describes a system which permits a substantial reduction in the amount of equipment required for the detection of narrow-band radar returns which may fall into any part of a wide, noisy Doppler band. The system utilizes a two-step process; the first providing a coarse, high false-alarm indication of range and Doppler, and the second providing high-quality detection and parameter estimation. The basic principles are discussed, followed by a description of an experimental prototype system. Experimental results are presented.

Certain sequential tests of statistical hypotheses known as sequential probability ratio tests (SPRT) possess an optimum property that they can accelerate, on the average, the termination of the test or alternately execute the test in the same time with less error, or with the same error but on less distinguishable hypotheses than a fixed sample-size test. These properties are of practical importance when applied to the radar problem, but in the application of sequential methods to radar surveillance some modification of an SPRT is frequently necessary. In particular, design problems relating to phased array radars are considered. This paper reviews the problem of angle search constraints, existence of multiple resolution elements in range and velocity, possibility of a flexible allocation of pulses, and fluctuations of radar cross sections of targets. Representative numerical results are included to indicate what performance can be expected with the use of sequential methods. An attempt is made to present an integrated theoretical and practical picture. Key references are listed.

The principles of f.m. radar are outlined and a comparison is made between pulse and f.m. techniques, particularly with respect to the requirements of the merchant service. It is concluded that multi-gate f.m. radars are too complex for this application and methods are outlined for overcoming the inherently low scanning rate of single sweeping-gate systems. Equipment is described which has an aerial beamwidth of 1.7° and a rotation rate of 10 r.p.m. with a fractional range resolution of 1/30.The future of f.m. radar for mercantile marine use is critically examined, the conclusion being that it will be most useful where very-short-range high-resolution pictures are required. Before such equipment is economically available further developments in transmitting valves must take place.

To achieve optimum performance from a microwave receiver that uses a balanced crystal mixer, matched pairs of crystals should be used. However depending on the reason for choosing the balanced mixer for a particular receiver, the crystal characteristics that should be matched and the degree of balance that is required vary considerably. The three principal reasons for using balanced mixers are: 1. To minimize noise figure by suppressing local-oscillator noise. 2. To suppress local-oscillator power radiation. 3. To reduce receiver sensitivity to certain spurious responses. For radar receivers, the first reason is the only important one, and fortunately it places the least stringent requirement on the degree of balance.

Based on the experience gained during two years of simulation and flight testing of the air traffic control (atc) radar beacon system, this paper outlines the desired functional characteristics of an expanded beacon system for air traffic control and explains the operational factors involved. The expanded system would utilize recent developments in altitude transducers and multichannel activereadout decoding techniques, to provide the air traffic controller with a filtered display incorporating a positive cross reference between aircraft position, identification, and altitude data.

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.

The paper describes a transistorized digital system for improving the signal/noise ratio of a search radar, by correlating the responses from several successive transmitted radar pulses. The main emphasis in the paper is on the circuit techniques employed. The radar information is first quantized into 2 levels of amplitude (`0? and `1?) and then into 1024 range elements each of ? nautical mile, i.e. 3.09 microsec. The correlation is achieved by counting the `1?s stored at each range for a number of consecutive radar p.r.f. periods and deciding whether or not the results are significant. The criteria chosen for this should enable the system to have an overall bearing accuracy somewhat better than the aerial beamwidth. Four separate correlation circuits are used, each handling every 4th range quantum. Thus the clock period is 12.4 microsec, which allows the use of standard magnetic-core-storage techniques. The machine is entirely transistorized and among the circuits described are (a) a precision 323 kc/s triggered LC oscillator, (b) highspeed logical circuits using transistors and diodes, (c) a high-speed reversible counter and (d) parts of the storage system.

A single-tube control circuit has been devised which had important application in delay circuits for radar use. This article, in which the circuit is described, was awarded the AIEE Student Branch paper prize for the academic year 1946–1947.

The performance of some basic integration systems is analysed, and the effect of beam pattern on their performance is considered. A new system is described employing two delay loops which, in general, will give a small improvement in threshold detection and furthermore has a number of practical advantages

A new radar technique has been developed that provides a solution for the conflicting requirements of simultaneous long-range and high-resolution performance in radar systems. This technique, called Chirp at Bell Telephone Laboratories, recognizes that resolution depends on the transmitted pulse bandwidth. A long high-duty-factor transmitted pulse, with suitable modulation (linear frequency modulation in the case of Chirp), which covers a frequency interval many times the inherent bandwidth of the envelope, is employed. The receiver is designed to make optimum use of the additional signal bandwidth. This paper contains many of the important analytical methods required for the design of a Chirp radar system. The details of two signal generation methods are considered and the resulting signal waveforms and power spectra are calculated. The required receiver characteristics are derived and the receiver output waveforms are presented. The time-bandwidth product is introduced and related to the effective increase in the performance of Chirp systems. The concept of a matched filler is presented and used as a reference standard in receiver design. The effect of amplitude and phase distortion is analyzed by the method of paired echoes. One consequence of the signal design is the presence of time side lobes on the receiver output pulse analogous to the spatial side lobes in antenna theory. A method to reduce the time side lobes by weighting the pulse energy spectrum is explained in terms of paired echoes. The weighting process is described, and calculated pulse envelopes, weighting network characteristics and dele-???

In this paper different techniques used for determining doppler shift in carrier frequency due to a moving target have been described. The first technique, basically a swept receiver which has a CRT display, is commercially available and commonly used in tracking radars. The other two techniques employing synchronous demodulator along with band-pass filters and autocorrelation method are used for sophisticated type of experiments. The system based on the autocorrelation techniques is under development for the back scatter radar operating at 54·95 MHz.

The advantages to be gained in the operation of radar systems at very high frequencies have led to the use of frequencies of several thousand megacycles. Operation at these frequencies has imposed serious problems in obtaining suitable tube behavior. Because of the difficulty in obtaining amplification at the transmission frequency, the r.f. section of the usual radar receiver consists of a crystal converter driven by a beating oscillator and operating directly into an i.f. amplifier. Since the midband frequency of the latter has commonly been either 30 or 60 Mc., it has been necessary to provide beating oscillators operating at frequencies differing from those of the transmitter by only a few per cent. For radar systems intended to operate at approximately 3000 Mc., which were under development in the early days of the war, it was found that triodes then available gave unsatisfactory performance. Attention shifted to the possibility of using velocity-modulated tubes, and the particular form known as the reflex oscillator came into general use. In this paper the requirements on beating-oscillator tubes for radar systems will be discussed, and the design features which have made the reflex oscillator eminently satisfactory in this application will be pointed out. Problems encountered in such oscillators will be outlined, and the solution in a number of cases is indicated. In some instances military requirements and expediency were in conflict with the optimum performance, and hence certain compromises were necessary.

The PRSD detector improves radar performance by controlling the distribution of energy in space, thus making a radar adaptive to its environment. An increase in performance over classical detectors may be realized in any of several ways: 1) greater maximum range; 2) smaller minimum detectable targets; 3) higher data rates; 4) lower average transmitted power, which allows smaller size and weight of equipment. The model of the PRSD detector described herein was tested with a semi-agile beam radar, and gave measured field performance improvement (for this particular radar) equivalent to an S/N increase ranging from 5 to 22 dB with a mean of 9.5 dB. This increase is greater than the 5-dB improvement predicted for the system in a white noise environment because many of the field tests were at locations subjected to heavy interference. The PRSD detector was extremely effective reducing the interference. In this paper, we will briefly review the theory of operation, describe the equipment and the method of test, and present experimental data. The data presented here are essential to a complete understanding of sequential detection since a rigorous theory encompassing multiple range bin radar has not been developed at this time. Finally, an extensive bibliography is appended.

A distribution-free detection procedure for a multiplerange-bin radar is described. This procedure is based on the ranks of observations, but does not require elaborate equipment for rapidly ranking large amounts of data. Proposed equipment is described and analysis and results are given comparing this new procedure with certain practical (nondistribution-free) procedures. Comparisons with some "best" theoretical procedures are also given.

Experimental data and discussion are presented which show the desirability of using thick punch-through PIN diode for high-power limiting. The slower speed of response sets an upper limit on thickness. Data are presented on the maximum thickness allowable as a function of frequency. Results are given for a high-peak-power narrow-pulsewidth receiver protector, and for a high-average-power wide-pulsewidth balanced duplexer. These devices are compared to conventional gas T-R tubes and results suggest that the use of multiple PIN diodes in limiters and duplexers can offer significant improvements in some RADAR applications.

A Doppler navigation radar for space applications must be at least 30 db more sensitive than present Doppler sensors but still maintain the same (or better) error tolerances. Yet, solution of the problem (if at all attainable) by conventional approaches is severely hampered by the prohibitive space and power limitations of present spacecraft. This paper will show that proper frequency modulation of the microwave transmitter can code the ground scatterer return in such a way that considerable signal bandwidth reduction (40-50 times) can be effected [referenced to the normal continuous-wave (CW) bandwidth] with an attendant increase in peak spectral power and a reduction of certain critical error sources.

A new analysis of the problem of continuously recovering periodically sampled data is given which starts with the assumption that the waveform being sampled is a stationary random function of time. The popular idealization of a band-limited frequency spectrum is not made; results obtained apply to all types of spectra and for any sampling frequency. In addition to such things as telemetering, radar, and data storage systems, for which the solution of this problem is of direct interest, the analytic techniques used may also be applied in the design and analysis of closed-loop control systems which utilize some digital elements.

The fundamental limits to radar performance in search and tracking can be expressed on three charts, in terms of products involving transmitted power, antenna gain, and effective aperture area. Locations of past and present radar systems on these charts disclose evolutionary trends in system design and indicate regions of practical and economic balance between transmitter and antenna complexity, in terms of ratios of power to gain and aperture. The basis of choice for operating frequency is clarified for different applications of radar, such as air surveillance, precision tracking, weapon control, and combinations of these tasks. It is suggested that these historical trends, derived from a large sample of successful radar systems, will furnish a better guide to economic optimization than will empirical cost equations. They are also helpful in comparing diverse approaches to radar system design, and in estimating the dependence of proposed systems upon new component and technique developments. The examples used in this paper are drawn primarily from ground-based radar systems, and serve to clarify the relationships between conventional and phased-array radar systems used for aircraft and missile detection, tracking, and weapon control.