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Trunk, Naval Research Laboratory (CHAPTER 8) T. A. Weil, Equipment Division, Raytheon Company (CHAPTER 4) Lewis B. |
They are often so large that they might not be completely removed by MTI. Thus it is not uncommon for MTI radar to have at its output many fixed point-scatterers that must be recognized so as not to be confused with desired targets. Probability density function for land clutter. |
Skolnik, M. L: An Analysis of Bistatic Radar, IRE Trans., vol. ANE-8, pp. |
NUMBERED COEFFICIENTS ARE USED TO RESPECTIVELY CREATE ) AND 1 AS SHOWN IN &IGURE B AND C !FTER THE FILTERS THE COMPLEX SIGNAL IS DECIMATED BY TO PRODUCE A -(Z OUTPUT SAMPLE RATE 4HE FINAL SPECTRAL CONVOLUTION BY A n -(Z TONE IS ACCOMPLISHED BY NEGATING EVERY OTHER SAMPLE )N &IGURE WE TRANSFORM THE SYSTEM OF &IGURE TO MAKE IT MORE COMPUTA |
Begovich. N. A.: Frequency Scanning, chap. |
To this end, however, it is most important that microwave components employed in the feedthrough nulling as well as in the remainder of the microwave circuitry be as rigid as possible.8 It is customary to use a milled-block form of construction. In the rare cases where a single antenna plus duplexer or a pair of nested antennas has been used in an airborne high-power CW radar, the mechanical design problems have been all but insurmountable. Even in a ground-based radar, fans, drive motors, motor-generator sets, rotary joints, cavitation in the coolant, etc., are very troublesome. |
NORMAL DENSITY IT IS NECESSARY TO ESTIMATE MORE THAN ONE P ARAMETER AND THE ADAP |
1See footnote onp.651. ... SEC. |
Accordingly, a different form of the radar equation must then be employed.) Propagation factors (Fp): Several propagation phenomena, including Faraday polarization rotation, ground-reflection multipath, multiple hop propagation, and ionospheric focusing may need to be included in the equation, depending on the scenario of interest. Faraday rotation refers to the variation of the polarization of the signal incident on the target as a function of time and distance, arising from its propagation through the magnetized ionospheric plasma; linearly polarized trans - mitted signals often arrive in the target zone with a rotated axis of polarization but still essentially linearly polarized. Since many targets have RCS that vary with polarization, an important result is that the most favorable polarization will illu - minate the target recurrently. |
GAIN AUXILIARY ANTENNA !N IMPLEMENTATION OF THE 3," PROCESSOR IS SHOWN IN &IGURE B WHERE THE SQUARE |
IEEE Tra11s., vol. AES-8, pp. 743-750, November, 1972. |
The theoretical accuracy with which distance can be measured depends upon thc band width of the transmitted signal and the ratio of signal energy to noise energy. In addition, measurement accuracy might be limited by such practical restrictions as the accuracy of the frequency-measuring device, the residual path-length error caused by the circuits and trans mission lines, errors caused by multiple reflections and transmitter leakage, and the frequency error due to the turn-around of the frequency modulation. A common form of frequency-measuring device is the cycle counter, which measures the number of cycles or half cycles of the beat during the modulation period. |
108 INI'KODUCTION TO RADAR SYSTEMS Blind speeds. The response of the single-delay-line canceler will be zero whenever the argu- ment ?/; T in the amplitude factor of Eq. (4.6) is 0, rr, 2n, . |
Power is coupled from the end of the central stabilizing cavity by a circular waveguide. The geometry of the inverted coaxial magnetron makes it suitable for operation at the higher frequencies. Figure 6.5 is an example. |
Since vacuum tubes are not appropriate asswitches insuch low- impedance circuits, itisnot possible tofixthe sweep origin bymethods analogous tothat ofFig. 13.46. Ithas been necessary touseeither the method ofaseries dry-disk rectifier switched (ifnecessary) bythescan- ner, ortoapply some method ofwaveform balance. |
Inpeacetime, usually only the surface- search function isofimportance. Because ofthe different beam-shape requirements, separate radar systems areordinarily used forairsearch and forsurface search, Airborne radar equipments employing aPPI areused forpilotage in thevicinity ofshorelines orover land. This pilotage may beofageneral navigational character, asitalways isinpeacetime and usually isinwar; oritmay beasprecise asthelimitations oftheradar will permit, forthe purpose ofblind bombing ofaradar target. |
ATE A GEOPHYSICAL PARAMETER SUCH AS OCEANIC WIND SPEED TO THE OBSERVED CALIBRATED RADAR BACKSCATTER PROPERTIES OF THE ILLUMINATED SURFACE AND SOUNDERS WHICH INCLUDES BOTH ATMOSPHERIC AND SUBSURFACE RADAR SYSTEMS %ACH SECTION INCLUDES AN OVERVIEW OF ALL RELEVANT 3"2S NOTING KEY TURNING POINTS OR WATERSHED INNOVATIONS IN THE THEMES HISTORY 3ELECTED EXAMPLES HAVE BEEN CHOSEN FOR MORE IN |
Note that the clutter-to-noise ratio is a rms power ratio measured at the A/D converter. A peak power ratio would be 3 dB higher. FIGURE 4.15 Dynamic-range example ch04.indd 25 12/20/07 4:52:46 PMDownloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2008 The McGraw-Hill Companies. |
M. I. Skolnik, Introduction to Radar Systems , New York: McGraw-Hill Book Company, 1962, Chap. |
The limiter also protects the receiver from signals from nearby radars that may not be strong enough to fire the T/R tubes but could be large enough to hurt the receiver. A ferritc duplexer (Fig. 4.2/?) uses a ferrite circulator,3 instead of T/R tubes, to send the transmitter power to the antenna and the received signals to the re- ceiver. |
In the auto position, the rings were rotated at a speed of 300 –450 rpm, causing the energy to be transferred in a continuously varying proportion between one horn and the other. This resulted in a beam continuously scanning in azimuth over ±2.5 ° at a rate of between 300 and 450 scans per minute, or between 50 and 75 deg/s. This is shown in figure 4.9. |
In this chapter, the receiver design is considered mainly as a problem of extracting desired signals from noise. Chapter 13 considers the problem of radar design when the desired signals must compete with clutter. The current chapter also includes brief discussions of radar displays and duplexers. |
Thepresence ofmorethanonepossible modeofoperation meansthatthemagnetron canoscillate inany oneofthese'frequencies andcandosoinanunpredictable manner. Thisistheessenceofthe stahility problem. Themagnetron mustbedesigned withbutonemodedominant. |
CONTENT MINES 4YPICAL EXAMPLES OF RADAR IMAGES AT VARIOUS SCALES ARE SHOWN IN &IGURE AND &IGURE '02 HAS BEEN USED FOR SURVEYING MANY DIFFERENT TYPES OF GEOLOGICAL STRATA RANG |
COUPLED AND LOADED |
For the particular set of recorded measurements, it has been shown a substantially enhanced performance of the adaptive filter over the nonadaptive filter . * As mentioned previously, the lower frequencies might be preferred for long-range surveillance because the usual radar equation does not include all the pertinent factors. In the jamming case, one should take account that the jamming antenna on an aircraft has a lower gain at lower frequencies so the jamming power density might be less at the lower frequencies. |
Lematta, “A test of ocean surface cur - rent mapping with over-the-horizon radar,” IEEE Trans. Geosci. and Rem. |
138. Skolnik, M. I., J. |
Except fortheburning-in tendency, thenormal persistence issatisfactory through about the same scan intervals asisthat ofthe P-7screen. 13.3. The Selection ofthe Cathode-ray Tube.—Both electrostatic andmagnetic tubes areavailable invarious sizes and with various screens (Table 131). |
ERROR |
, &ILTERING OF THE %NTIRE 2ADAR 3YSTEM &ILTERING PROVIDES THE PRINCIPAL MEANS BY WHICH THE RADAR DISCRIMINATES BETWEEN TARGET RETURNS AND INTERFERENCE OF MANY TYPES 4HE FILTERING IS PERFORMED BY A VARIETY OF FILTERS THROUGHOUT THE RECEIVER AND . 2!$!2 2%#%)6%23 È°Óx IN THE SUBSEQUENT DIGITAL SIGNAL PROCESSING -OST RADARS TRANSMIT MULTIPLE PULSES AT A TARGET BEFORE THE ANTENNA BEAM IS MOVED TO A DIFFERENT DIRECTION AND THE MULTIPLE RETURNS ARE COMBINED IN SOME FASHION 4HE RETURNS MAY BE COMBINED USING COHERENT INTEGRATION OR VARIOUS DOPPLER PROCESSING TECHNIQUES INCLUDING -4) TO SEPARATE DESIRED TARGETS FROM CLUTTER &ROM THE RADAR SYSTEM STANDPOINT THESE ARE ALL FILTER |
Shown also are the canceler config- urations assumed, with appropriate Z-plane pole-zero diagrams. The Z plane is the comb-filter equivalent of the S plane,16'17 with the left-hand side of the S plane transformed to the inside of the unit circle centered at Z = O. Zero fre- quency is at Z = 1 + y'O. |
The objective of signal processing is to detect and characterize echoes from scatterers of interest, either discrete (aircraft or ships) or extended (the sea surface), and this is customarily achieved by decompos - ing the time series data from the receivers into the natural radar domain dimensions of group range (based on time delay), direction of arrival (beam space), and doppler frequency, hopefully separating the echoes of interest from unwanted clutter and noise. The standard tool for this decomposition is the FFT, at least in operational skywave radars, in part because it is computationally quite feasible to analyze the incoming sig - nal into typically ~102 range bins, 101 – 102 beams, and ~102 doppler cells, in perhaps ~100 seconds, using general purpose computing hardware. Thus, the FFT (or DFT for short transforms) is commonly used for the three dimensions of analysis. |
In partic- ular, this makes conical-scan systems susceptible to AM jamming at the scan frequency (the spin frequency jammer).5 The monopulse system extracts the angular information instantaneously by comparing the difference and sum channel signals. The gain normalization can therefore be made instantaneous (fast or instantaneous AGC), and the external amplitude variations, since they affect sum and difference channels by the same relative amount, are never detected as erroneous guidance signals. The early systems all used conical scan for angle tracking because of its sim- plicity. |
Among the 1792 modules per face, groups of 32 transceiver modules are op- erated as a subarray. In transmit, a high-power array predriver is used to drive 56 subarray driver amplifiers. Each of these power amplifiers provides enough RF drive for all 32 modules in one subarray. |
SCALE MODEL !N ADDITIONAL AD HOC SPECTRAL PARTITION IS INTRODUCED BETWEEN THE LONGEST AND SHORTEST WAVE COMPONENTS OF THE SEA SPECTRUM BUT THIS PRODUCED ONLY MODEST IMPROVEMENT. |
PULSE -4) CANCELER AFTER 4 - (ALL AND 7 7 3HRADER Ú )%%% $" &) &% ' # % $%% ! (! '" &!' ) ) #%#+ &!' )#& ) * ! ! ! ! |
MATCHED SPATIAL CHANNELS ANTENNA AND RECEIVER ARE DRIVEN BY JAMMING CANCELLA |
BAND RADAR SHOWN IN &IGURE USES SIX SIMULTANEOUS FREQUENCY |
Alperin, R. R. Bronski, J. |
,/ |
ING BOTH DOPPLER AND SPATIAL TRANSFORMATIONS PRIOR TO 34!0 PROCESSING 4HE APPROPRIATE ARCHITECTURE SOLUTION DEPENDS UPON THE RADAR DESIGN CONSTRAINTS 4HE NUMBER OF ANTENNA ELEMENTS AND BEAMFORMING REQUIREMENTS ARE KEY DRIVERS IN THE |
Modern mixers typically provide a significant reduction in the effect of STALO amplitude modulation as their conversion gain is relatively insensitive to LO power variation when operated at their specified drive level. For systems requiring high sensitivity, AM noise can become disruptive if unin - tentional conversion of AM to PM noise occurs in the receiver chain. This process can occur via suboptimum component bias techniques where high amplitude signals or noise create a phase shift resulting in another phase noise contribution to the receiver chain. |
Considering the high SNR ratio, the threshold can generally be set as about 0.05 of the energy of the echo signal. At this time, most of the scattering centers on the target can be accurately reconstructed; whereas, with the increase of noise in echo signal, the set threshold value also increases, so as to avoid more false scattering points caused by noise in the generated image. If the sparsity Kis known, the reconstruction results obtained by applying the CS matching pursuit reconstruction algorithm are quite excellent but it is difficult to obtain accurate sparsity in actual engineering. |
vol. AP-8, pp. 629-631. |
Therearethreebasicmethods foremploying semiconductor diodesindigitalphase shifters, depending onthecircuitusedtoobtainanindividual phasebit.Theseare:(I)the switched-line, (2)thehybrid-coupled, and(3)theloaded-line. Theswitched linewasshownin Fig.8.6.Eachphasebitconsists oftwolengthsoflinethatprovide thedifferential phaseshift, andtwosingle-pole, double-throw switches utilizing fourdiodes. Thehybrid-coupled phasebit,asshowninFig.8.7,usesa3-dBhybridjunction with balanced reflecting terminations connected tothecoupled arms.Twoswitches (diodes) control thephasechange.The3-dBhybridhastheproperty thatasignalinputatport1isdivided equallyinpowerbetween ports2and3.Noenergyappearsatport4.Thediodesacttoeither passorreflectthesignals.Whentheimpedance ofthediodesissuchastopassthesignals,. |
12. Coquin, G. A., T. |
7.1 if the phase distribution across the aperture is not constant. Following the first side\obe are a series of minor lobes which decrease in intensity with increasing angular distance from the main lobe. In the vicinity of broadside (in this example 100 to 115°), spillover radiation from the feed causes the sidelobe level to rise. |
Models and Their Uses. Knowledge of the conditions to be expected for a par - ticular radar deployment is vital to radar design, as well as providing a guide to echo interpretation and a means to simulation and performance prediction. This type of information, based on decades of ionospheric observations and theory, is conveniently distilled in models that are widely available and used extensively. |
Remote Sens. 2008 ,56, 1968–1975. 10. |
The improvement factor (l) is equal to the subclutter visibility (SCV) times the clutter visibility factor (Voe), In decibels, /(dB)= SCV(dB) + Voc(dB). When the MTI is limited by noiselike system instabilities, the clutter visibility factor should be chosen as is the signal-to noise ratio of Chap. 2. |
43/20, 18th May 1943 (TNA AIR 65/15) [6] Ward K D, Tough R J A and Watts S 2013 Sea Clutter: Scattering, the K Distribution and Radar Performance 2nd edn (London: Institution of Engineering and Technology) [7] Performance Stability of ASV Mark 6 Equipment on an Operational Squadron, TRE Report T.1894, July 1945 (TNA AVIA 26/896) [8] Pound R V 1948 Microwave Mixers MIT Radiation Laboratory Series vol 16 (New York: McGraw-Hill) [9] Horst M, Dyer F and Tuley M 1978 Radar sea clutter model Int IEEE AP/S URSI Symposium (IEEE Antennas and Propagation)Airborne Maritime Surveillance Radar, Volume 1 7-13. IOP Concise Physics Airborne Maritime Surveillance Radar, Volume 1 British ASV radars in WWII 1939–1945 Simon Watts Chapter 8 Conclusions 8.1 Other ASV radars 8.1.1 USA radars [ 1] The ASV radars described in chapters 1–5were designed in the UK and installed on British aircraft. Coastal Command also flew on long-range American aircraft made available under the Lend –Lease programme. |
P . Wei et al.10, the Boeing Company. Original data courtesy of the Boeing Company, Seattle, Washington .)40 30 20 10 0RCS (dBsm)−10 −20 −30 −40 −50−100−80−60−40−20 0 Azimuth (deg)20 40 60 80 100VV, VH, HH-5, HV-5,8-feet Square Plate 0.79 GHz ch14.indd 9 12/17/07 2:46:49 PMDownloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2008 The McGraw-Hill Companies. |
JAMMING TECHNIQUES AT THE 'ERMAN !!! RADARS IN 7ORLD 7AR )) v SUPPL TO )%%% )NT 2ADAR #ONF 2EC PP n -AY n $ # 3CHLEHER )NTRODUCTION TO %LECTRONIC 7ARFARE .ORWOOD -! !RTECH (OUSE )NC $ # 3CHLEHER %LECTRONIC 7ARFARE IN THE )NFORMATION !GE .ORWOOD -! !RTECH (OUSE )NC " * 3LOCUMB AND 0 $ 7EST h%#- MODELING FOR MULTITARGET TRACKING AND DATA ASSOCIATION v IN -ULTITARGET |
The detail with which path tracing is treated can vary greatly. A geometrical optics code that envolves integration along the ray as de- scribed by Jones and Stephenson51 can provide paths in three dimensions, includ- ing delays and losses for both ordinary and extraordinary rays. When the details of electron distributions are uncertain, such comprehensive calculations are ex- cessive. |
(I) 0. C -30 I ltlls, low rough 0 .: u Arizona mountainous (I) V) VI Defowore Boy V) e -40 - Arizona deserl u N J marshland -50 -60 UHF 1000 L C X 10,000 Frequency (MHz) (al Downtown phoenix x 0-Highest median value x----------------..._ SS WOO x --..__x ·- @ .:9 -10 - Phoeai,, SS > 25,000 I~~:~ 0 b 0 NJ residential (I) o -20 X X X ~ NJ rnrnl ,---::::::::1 i~ g 30 _Arizona hills, low rough )(~------=::::~~x fj Arizona mountainous x~x---- ~ Ar,zonodeserfX~ ~ -40 -Arizona cullivoled x x----x u formfond ------- (" N.J marshland x ------ -50 ·· Delaware Boy x I -GQL-~~~~~~-U-H~F~~~~-1-0~0~0~L~~~~~~~~C::--~~~~X~10,000 Frequency_ (MHz) (bl Fi~ure B.11 Medi:in values of <T0 as a function of frequency. Grazing angle= 8°. |
However, other aspects of performance may suffer and should be examined carefully in the tradeoff process. Another ad- vantage of phase-only monopulse, relative to vector and amplitude-only, is that the need for precise amplitude matching channel to channel is reduced. Phase-only monopulse processing does not utilize the full target angle- of-arrival information available in the two beams. |
STANT |
Although the above are limitations to the phased array in radar, they are probably not sufficiently serious to restrict its greater use. However, the major limiratioa that has limited the widespread use of the conventional phased array in radar is its high cost, which is due in large part to its co~nplexity. The software for the computer system that is needed to utilize tllc inherent flexibility of the array radar also contributes significantly to the system cost and con~plexity. |
58. Hopkin, V. D.: Colour Displays in Air Traffic Control, International Conference on Displays for Man-Machine Systems, Apr. |
In conclusion, the proposed studies represent valid examples of the fertile research ongoing in the field of SAR processing and applications, and demonstrate as SAR imaging still presents large margins for investigations. Funding: This work was partially supported by the Italian Ministry of University and Research (MIUR) in the framework of “CLOSE to the Earth” project (ARS01_00141), PON Ricerca e innovazione 2014–2020. Acknowledgments: The guest editor would like to thank the authors’ contribution to this Special Issue and all reviewers for providing valuable and constructive recommendations. |
The undesired fluctuations that cause difficulty occur at about the same rate as the scan rate. Since target scintillation energy of aircraft is concentrated in the lower frequency range below approximately 100 Hz (particularly the trouble- some propeller modulation), it is desirable to increase the scan rate as high as possible. The maximum practical rate is one-fourth of the pulse repetition fre- quency (PRF) so that four pulses provide a complete scan with one each up, down, right, and left. |
The transmitter power does not appear explicitly. Increasing the transmitter power will indeed increase the target signal, but it will also cause a corresponding increase in clutter. Thus there is no net gain in the delectability of desired targets. |
. -4) 2!$!2 Ó°Èx Ó°£ÓÊ , ,Ê-9-/ |
In contrast, bipo- lar devices are minority carrier devices, and since minority carriers are thermally generated, bipolar power transistors tend to generate localized hot spots and can become thermally unstable. Resistive ballasting techniques used in both the col- lector and the emitter leads of a bipolar transistor reduce the intrinsic device gain and efficiency but offset the thermal-instability problem. In the power FET, how- ever, large active cell areas can be combined without using these ballasting tech- niques and without experiencing the problems of thermal runaway. |
5 of "Radar Handbook," M. I. Skolnik (ed.), McGraw-Hill Book Co., Inc., New York, 1970. |
EFFECTIVENESS CONSIDERATIONS !NGLE OF ARRIVAL IS THE MOST IMPORTANT SORTING PARAMETER AVAILABLE TO THE DEINTERLEAV |
J. Pattern Recognit. Artif. |
31 Antenna scanrate.Theseaclutterbackground doesnotchangesignificantly duringthetime theusualcivil-marine radarantenna (witha20rpmrotation rate)scansbyaparticular clutterpatch.Thatis,theseacanbeconsidered" frozen"duringtheobservation time.Fora medium-resolution X-bandradaratlowgrazingangles,thetimerequired fortheseaclutter echotodecorrelate isabouttoms.16•21Anypulsesreceived fromseaclutterduringthistime willbecorrelated andnoimprovement insignal-to-clutter ratiowillbeobtained byintegra tion.(Thisisunlikereceiver noisesinceintegration ofsignalpulsesandnoisecanprovide significant improvement insignal-to~noise ratio,asdescribed inSec.2.6.)Although theclutter received duringasinglescanpastatargetwillbecorrelated, theseasurfacewillusually chang~ bythetimeofthenextantenna scansothattheclutterwillbedecorrelated fromscantoscan. Thusscan-to-scan integration canusuallyresultinanimprovement oftarget-to-c1utter ratio. Tomakeavailable moreindependent clutterechoes, theantenna rotation ratecanbe increased.21•23If,forexample, theradarantenna hasa 20beamwidth, apulserepetition frequency of3600Hz,anda20rpmrotation rate,therewillbe60pulsesreturned froma targetoneachscanoftheantenna. |
Kingsmill and R. M. Wakimoto, “Kinematic, Dynamic, and Thermodynamic Analysis of a Weakly Sheared Severe Thunderstorm over Northern Alabama ,” Monthly Weather Review, vol. |
26. McGraw-Hill Book Company, New York, 1948. 15. |
CLUTTERv CONTROLS 4HE GAIN CON |
A. F. Barnett: On Some Direct Evidence for Downward Atmospheric Reflcctiori of I:lcctric Rays, I'r.oc.. |
This may involve detecting a coded beacon on the tanker, skin tracking tankers and other aircraft at close range. Station keeping ranges can be between 30 and 1000s of meters. Special short-range radar modes are usually used for this purpose. |
m2 R = range to target, m I-, = orie-way pr opiigatiori loss L, = systelil losses 'I'lte correspondirlg equation for tile bistatic radar is \\lli*rc (;, - 11;\11~11iittirig ;111terlr1;1 g;~iri ill dirt'ction of target (;, = rcccivir~g arltcrlrla gi1i11 ill dircctior~ ol' target rr, = I4sl;\tic cross sectioti. m 2 I), = irarlsrnitter-to-hr gct distallcc, 111 I), = receiver-to-target distance, 111 L,(r) = propagation loss over trarisn~itter-to-target path L,(r) = propagation loss over receiver-to-target path Equations (14.35) and (14.36) represetit but one of the several forms in which the radar equation may be written. They are not meant to be complete descriptions of the performance or radar systems since they do not cxplicitly include many important factors, but they are suitable if or~ly relative comparisons are to be made. |
AGC is necessary to keep the gain of the angle-tracking loops constant for stable automatic angle tracking. Some monopulse systems, such as the two-TRANSMlTTER TR DEVICE RECEIVER FRONT ELEVATIONDIFFERENCE SUM AZIMUTHDIFFERENCE FEEDHORNSSUM CHANNELTR MIXERATR TRANSMITTER AGCRANGETRACKER IFAMPLIFIERAMPLITUDEDETECTORVIDEOAMPLIFIER ELEVATIONDIFFERENCECHANNELMIXERIFAMPLIFERPHASE-SENSITIVEDETECTORELEVATION-ANGLEERROR HYBRIDJUNCTIONDIFFERENCECHANNELAZIMUTHMIXERIFAMPLIFIERPHASE-SENSITIVEDETECTORAZIMUTH-ANGLEERROR LO . channel monopulse, can provide instantaneous AGC or normalizing as described later in this section. |
THE |
IEEE. vol. 65. |
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AND DIFFERENCE |
A 64-element network, for example, requires 192 directional couplers and 160 fixed- phase shifters. The construction of a large Butler network requires a large number of cross-over connections in the transmission lines. These can present practical difficulties in the fabrication of the microwave printed circuits used to make up the device.z6 Many beams also require many parallel receivers, an added complexity. |
§ ©¨¨¶ ¸·· PDI . 05,3% $/00,%2 2!$!2 {°{Ç WHERE N. .E ª « ¬ PDI PDIFOR3WERLING)TARG GETCHI |
Beamwidths of ≤ 1° are commonly used for longer-range radars. Admittedly, this is somewhat arbitrary, but the choice of 1 ° is based upon several decades of experi - ence. A 1 ° beam will provide a cross-range resolution of 1 km at a range of 60 km. |
12] HOWRADAR WORKS 3 the radar picture would have been unaffected while photography or ordinary vision would have been useless. 1.2. How Radar Works.—The coined word rodaris derived from the descriptive phrase “radio detection and ranging. |
Excellent results may be obtained for NS, as small as 2 bits (per I and per Q) by adapting the quantization thresholds to the mean signal level. (Refer to Section 18.4 for more on this topic.) Quantization noise, which is larger for fewer bits, is proportional to signal strength; hence it is a factor in the MNR budget. Exacting applications such as interfer - ometry are better served by more bits per sample, subject to the rate and volume limits of the data handling subsystems. |
SWITCHING TECHNIQUE SUCH AS THE EQUAL |
SPREADING CONSIDERATIONS SINCE DUR ING THE &- PERIODS THE CLUTTER IS SMEARED IN FREQUENCY AND CAN APPEAR IN FREQUENCY REGIONS NORMALLY CLEAR OF CLUTTER ! NO |
The four-thirds earth approximation has several limitations. It is only an average value and should not be used for other than general computational purposes. The correct value ofk depends upon meteorological conditions. |
OUTPUT CURVE )LLUSTRATED IS THE EFFECT OF NONLINEARITY . £È°ÓÓ 2!$!2 (!.$"//+ .OTE THAT ONLY THE RATIO OF TRANSMITTED TO RECEIVED POWER IS REQUIRED SO THE TECH |
This may be identical to the acquisi - tion zone but is there to provide an alarm if any tracked target passes into the zone. In common with other radar trackers, strategies have to be evolved to cope with the target being potentially invisible in some scans. IMO requires that the specified performance is maintained when the target is invisible in up to 50% of scans. |
It is dependent on feed type, say, horn or dipole. This H field is nor- malized such that the total power into a surrounding sphere (the magnitude of the tangent field squared) is equal to 1 W. This may be done by numerical in- tegration using as much symmetry as possible to reduce computation time. |
The dual-mode spiral has been the preferred choice, since a single aperture generates all the direction-finding information (and thus makes full use of the limited available space), requires only two receiver channels, has excellent polarization character- istics, and is frequency-independent.20 The four arms of the spiral are fed by a mode-forming network to form a sum G) and a delta (A) mode (hence the name dual-mode). The directional informa- tion is contained in the relative amplitude and phase of the S and A channels. The A/2 ratio represents the magnitude of the BSE (the angle off axis in a cone of rotation about the boresight), while the relative phase indicates the direction on the cone of rotation. |
LIMITED DETECTION AS APPLIES ESPECIALLY TO AIRCRAFT TARGETS THE ADDITIONAL COM |
Pearson, “Moving target experiment and analysis,” Hughes Aircraft Report No. P76-432, pp. 5–15, 22–35, December 1976, declassified 2/28/94. |
GRAPHIC RADAR ALTIMETER MISSIONS 4/0%80OSEIDON *ASON |
ARE PARALLEL TO LEADING EDGES 8 |
These distributions might not always fit the observed data, but they are fair approximations in many cases and are used nevertheless for convenience. The chi-square distribution is described by two parameters: the average cross section a..,, and the number of degrees of freedom 2m. Analysis39 of measurements on actual aircraft Hying straight, level courses shows that the cross-section fluctuations at a particular aspect are well fitted by the chi-square distribution with the parameter m ranging from 0.9 to approximately 2 and with aav varying approximately 15 dB from minimum to maximum. |
Adaptive array prin- ciples have found a thorough mathematical treatment since the early 1970s.40 The basic result is given by the expression of the optimum set of weights: W = JJiIVr1S* (9.6) where M = E(V514V7) is the Af-dimensional covariance matrix of the overall dis- turbance (noise and jammer) V received by the array and S is the Af-dimensional vector containing the expected signal samples in the array from a target along a certain direction of arrival. The similarity of Eq. (9.6) to Eq. |