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The implementation of the adaptive array concept is more and more related to digital beamforming85–87 and to digital array radar (DAR) technologies.88,89 Jammer Cancellation and Target Signal Enhancement. Adaptive array prin - ciples have found a thorough mathematical treatment since the late 1960s83,84; for a brief history of adaptive arrays, see Reed90; for an overview of least squares adap - tive processing in military applications with celebration of B. Franklin medal to B.

111. F. T.

With a scan capability of ?6O0, a minimum of three planar apzr- tiires, or faces, are required to cover the hemisphere. But when other factors are considered, more than three faces are usually desired. The greater the number of faces, the less will be the loss in gain, beam broadening, VSWR variation, polarization change, and the niirnber of elements per face.

15.11 .—AN/APS-l Olow-altitude PPI. Range mark at 10miles; altitude 1600 ft.; Washington, D.C,at0°, 8to13miles. (a) Photograph ofscope.

LEVEL$"&WILLHAVESIGNIFICANTLYBETTERPERFORMANCETHANSUBARRAY

Consequently, an input pulse shape with very exaggerated slow rise and fall times may be necessary to achieve the desired output-pulse spectral composition.FIGURE 11.16 Power amplifier combining configurations that provide minimum input port reflected power: ( a) quadrature-coupled amplifier pair and ( b) split-T amplifier pair with a 90 ° offset. The amplifier input voltage reflection coefficient is given as Γ and the amplifier voltage gain as A. (Reprinted with permission from E.

(23.36) becomes . A/>r2 var (Pr) - -^- (23.37) 2CT1To This expression is valid for high signal-to-noise cases. Velocity Estimation.

D"WIDTHOFTHERETRO

This blinking has the effect of introducing artificial glint into the radar tracking cir- cuits, which, if introduced at the proper rate (typically 0.1 to 10 Hz), can cause the radar to break angle track. In addition, blinking has the desirable effect of confusing radiation homing missiles which might be directed against the jammer radiations.12 A self-screening jammer (SSJ) is used to protect the carrying vehicle. This sit- uation stresses the capability of an ECM system relating to its power, signal- processing, and ESM capabilities.

Ionospheric outages do not exist in the sense that long-distance illumination is impossible. Path outages are due to defi- ciencies in frequency channel allocations and insufficient radiated power. Addi- tional factors that can affect radar performance are ionization irregularities that degrade path quality and backscatter from spread-in-doppler ionization gradients that can obscure targets.

5.16x9 Handbook / Radar Handbook / Skolnik / 148547-3 / Chapter 5 Multifunctional Radar Systems for Fighter Aircraft David Lynch, Jr.

.KFT -KMOR -KFT 3UPERREFRACTION

Trials of ASV Mk. VII [ 3] also made comparisons with these radars. It is of interest to look at these comparative performance results and assess them in the light of modern radar modelling methods.

TO

WHILE

(7.36) corre­ sponds to a diameter of about 1600 wavelengths for maximum gain. The beam width of such an antenna would be about 0.04° with a gain of about 68 dB. In practice, the construction tolerance of an antenna is often described by the" peak" error, rather than the rms error.

Angle ^ 1 deg.- = NoiseOCTSSN= 1OTIME= 8 GMTLOCATION 38.65 N LAT 76.53 W LON BEARING= 90.00 OEGOCT SSN = 100 TIME = 8 GMTLOCATION 38.65 N LAT 76.53 W LON BEARING= 90.00 OEG FIG. 24.25 Radar performance estimate; October, 0800 UTC. (a) SSN = 10.

The “doorknob” transition ofFig. 11.12bisdesigned tominimize breakdown. Itcan be thought ofasaquarter-wave probe with aspecial form ofstub support forthetipoftheprobe inwhich capacitive and inductive effect have been balanced against each other sothat asasupport itpresents noloading ofthe waveguide.

27, no. 2, pp. 188-190, February, 1954.

Radar Range Equation. In the doppler region where the signal does not fall in clutter, performance is limited only by system noise. The signal-to-noise power ratio in the range-doppler cell at the detector prior to postdetection integration for a target at range R is given by SNR=  R Ro4 (4.15) RP G G kTB LoT R T s n T=  av λ σ π2 31 4 4( )/ (4.16) where Ro = range at which SNR is equal to 1 sT = target radar cross section LT = losses applicable to the target The remaining terms are as defined following Eq.

10.25. The pulse voltage never rises above thecritical value Vc,because, asitreaches Vs,the magnetron draws current and loads thepulser. If oscillation fails tostart promptly after the pulse voltage hasreached Vs, thevoltage continues torise and may exceed Vcbefore current isdrawn.

INCLINATION n ANDALONG

On two occasions contact was established in complete darkness, at distances of 12 and 20 miles, and on one occasion whenvisibility was only 500 yards, at a distance of 12 miles. Attack : when the cloud base is below 1500 ft an approach from any desired direction can be made to a ship which is otherwise invisible from the aircraft.Thus an element of surprise can be obtained by a diving attack through the clouds, emerging at the last stage at very close range. Considerable experience of the use of ASV was developing and the shortcomings of the existing equipment were becoming clear.

This is illustrated in Fig. 19.6«. However, by introducing a frequency offset before the coherent detector,5 the resulting spectrum will be as shown in Fig.

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TIPLEANTENNASWITHOVERLAPPINGNONSQUINTED BEAMSPOINTEDATTHETARGET)NTERPOLATINGTARGETANGLESWITHINTHEBEAMISACCOMPLISHED ASSHOWNIN&IGURE BYCOMPARINGTHEPHASEOFTHESIGNALSFROMTHEANTENNASFORSIMPLICITYASINGLE

Provided the wind speed is greater than about 3λ kt (with l in meters) and the sea is fully developed, the clutter cross section s 0 is about –29 dB and is rela - tively independent of wind speed and frequency. (The definition of s 0 in HF radar is complicated by problems in properly defining antenna gains for ground-wave and sky-wave paths and by propagation effects due to the ionosphere.) The clutter spectrum tends to fill in around and between the lines as the wind picks up. For horizontal polarization (which is possible only for sky-wave paths over which the plane of polarization can be rotated by the Earth’s magnetic field), the cross section is much smaller and shows the characteristic fourth-power decay with a decreasing grazing angle.

(c) Variation of frequency with current for the SFD-377A X-band coaxial magnetron at a frequency of 9.373 GHz, with 0.001 duty cycle, and 1.0 ps pulse width (Courtesy Varian Associates, Inc., Beverly, MA.) RADAR TRANSMITIERS 197 30600.-----r------.--------,r---------,----~ Peakvoltage Efficienc (a)-50 800----------- ------------10---·---I--=----F-----;7'o<C----j40 ;:e !:.... >- ----------1----::::7~-t_---__j30 g <V U ~ ---+---------120 W 400 600 .Average powerinput(Wafts)20025500-- 5100 o~ ~20c400------ ~'SE- O) a300 Q:; ~a100200 -'"a <Vn ------------29 ------------r----f- -------- ----f------ 28 -------------f---t---t--f--- r- oL..--------'-_-l----l_---'-_L..--------'-_-'------"-_-'-----' 245455 56 5_75_8 5_9 Frequency (GHzl N I ::'!:+1 - ---------------------------- 0'c ... c:.

C.; Techniques of Radar reflectivity measurement; Artech House; 1984 ; UB-Ka [ 85A3011] − Ruck, G. et al; Radar Cross Section Handbook (Band 1 -2); Plenum Press NY; 1970 − Ulaby, F. T.

INGOFSEAICE WHICHTHESYSTEMHASBEENDOINGSUCCESSFULLYSINCE  4HE 2USSIAN8

pp. 73-75. January.

Sensors 2019 ,19, 1701 Pulse compression needs to eliminate the quadratic term of frin Equation (10), and a matched filter can be constructed in frequency: Hr(fr)=exp(jπf2 r γ) (11) After multiplication of Equation (9) and Equation (11) to complete pulse compression, the phase after pulse compression is: θ(fr,fa)=−4πRb(fc+fr) c/radicaltp/radicalvertex/radicalvertex/radicalbt1−(cfa)2 4(fc+fr)2v2−2πfaXi v(12) Let kr=4π(fr+fc) c,kx=2πfa v, Formula (12) is rewritten as: θ(kr,kx)=−Rb/radicalBig k2r−k2x−kxXi (13) Since the signal processing of the RMA algorithm is performed in the two-dimensional frequency domain, and Rbrepresents the time domain, the phase compensation cannot handle the change along the range direction. At this time, a reference range is first selected, and the phase at the reference distance is compensated. Generally, the reference range is set at the center of the scenario.

The rms time-delay error for a trapezoidal-shaped pulse of width 2 T1 across the top, fiat portion and with rise and fall times of T2 may be shown from Eqs. ( 11.16) and ( 11.17) to be oTi =(Ti+ JTi T2)112 trapezoidal pulse (11.21) R 6E/N0 When the trapezoidal pulse approaches in shape the rectangular pulse. that is, when T1 ~ T2, Eq.

CIENTALGORITHMICPROCEDURETOEXTRACTTHEWEIGHTS NAMED)NVERSE 12 ISDETAILEDIN "OLLINIETAL /THERPOSSIBILITIESARETOUSEMODERNCOMPUTINGTECHNOLOGIESLIKETHE &0'! 0OWER0# ORHIGH

.

At higher frequencies, the plant attenu - ation prevents a significant surface echo, so the angular variation is more uniform. FIGURE 16. 36 4.5-GHz scattering coefficient versus soil moisture (percent of field capacity) for vegetation-covered soil ( after F .

S. Haykin and A. Steinhardt, Adaptive Radar Detection and Estimation , New York: John Wiley & Sons, Inc., 1992.

Those relative target velocities which result in zero MTI response are called hli~ld SIIL~LY~S and are given by nll nllfp v =-=- " 2T 2 n= l,2, 3, ... where 17, is the nth blind speed. If J.

Section 3verifies the correctness of the proposed method based on ENVISAT-1 ASAR and ERS-2 SAR images. The influence of different radar looks directions, wind directions and wind speeds on SAR eddy imaging are discussed in Section 4. We conclude with a discussion of the applicability of our research for future investigations on shear-wave-generated eddies in Section 5.

This [nay be acconiplislied by providirig tlie PPI-scope operator with a grease pencil to mark tlie target pips or1 the face of the scope. A line joining those pips tliat correspond to the same target prcwidcs ttie target track. Wlieti tlie traffic is so dense that operators cannot maintain pace tvith the irifortnatiori available from the radar, the target trajectory data may be processed autotnatically iri a digital computer.

Xing, M.; Jiang, X.; Wu, R.; Zhou, F.; Bao, Z. Motion Compensation for UAV SAR Based on Raw Radar Data. IEEE T rans.

ch16.indd 58 12/21/07 10:26:10 AMDownloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2008 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Ground Echo.

Although both bands have distinctive advantages for ship application, when only a single radar is employed it is usually at X band for the reasons give11 above." I'hus the fact that sea clutter is less at the lower frequencies is but one of several factors to be collsidered in the selection of the optimum frequency for a particular radar application. Polarization. Figure 13.3 indicates that horizontal polarization results in less sea clutter than vertical, for the sea conditions whicl~ apply to that data.

The latter is the more usual of the two possible coordinate systems since it is easier for the microwave engineer to measure the VSWR and the position of the voltage-standing-wave minimum (or phase) than it is to measure the conductance and susceptance directly. The radial coordinate can also be specified by the reflection coefficient r of the load since the VSWR p and reflection coefficient are related by the equation Irl = (p - l)/(p + 1). The center of the Smith chart (Rieke diagram) corresponds to unity VSWR, or zero reflection coeficient.

The control element ofthe regulator isasolenoid coil and armature. The current through the solenoid coil isproportional tothe voltage to beregulated, andthe pull ofitscore onthearmature isproportionalto the airgap between the two, and tothe coil current. The air gap isadjustable by movement of120 thecore; this constitutes one ofthe ~ adjustments tobemade onthe &:regulator.~115 With the core infixed position ~ and the pile-adjusting screw tight, ~ theoutput voltage ofthegenerator will behigh.

A 24-mm chip would therefore have an expected yield of only 30 percent. 2. Difficulty of impedance matching: Increases in power output are the result of adjacent channels being connected in parallel.

1-lock. W. I,.: Monitoring Bird Movements by Radar, IEEE Sl)c~ctrto~r, vol.

BANDSOLID

D. K. "Radar Systems Analysis," Prentice-Hall, Inc., New Jersey, 1964.

Skolnik, M. I., and D. D.

The reduction in radar signal power when propagating over a distance Rand back (two-way path) may be expressed as exp ( -2et.R), where a. is the (one-way) attenuation coefficient measured in units of (distance) 1. Instead of plotting a., it is more usual to plot the one-way attenuation in decibels per unit distance.

It has the proper phase <Pm + <Pn at each element to steer in the two directions. The mixer would be followed by a power amplifier if a transmitter, or it might be used _to obtain the local Oicillator frequency if a receiver. Only M + N -2 phase shifters are required, but the mixer and power amplifier required at each element adds to the complication.

4. pp. 116 125.

The res~ltant loss with the combining of a large number of devices in some microwave circuits can sometimes negate the advantage achieved by combining. Thus as a direct replacement for conventional microwave tubes, solid-state devices have been limited to low or moderate power applications. A phased-array transmitting-antenna combines in space the power from each of many transmitting sources.

The approxima- tion is reasonable .when (RT + RR)»L or when L»CTU. Other implementations of pulse chasing are possible. In one concept the n- beam receive antenna is retained and two receiver-signal processors (RSPs) are time-multiplexed across the n beams.

sensors Article Extended Multiple Aperture Mapdrift-Based Doppler Parameter Estimation and Compensation for V ery-High-Squint Airborne SAR Imaging Zhichao Zhou1,2, Yinghe Li3, Yan Wang1,2,*, Linghao Li1,2and T ao Zeng1,2 1School of Information and Electronics, Beijing Institute of Technology, Beijing 100081, China; [email protected] (Z.Z.); [email protected] (L.L.); [email protected] (T.Z.) 2Beijing Key Laboratory of Embedded Real-Time Information Processing Technology, Beijing 100081, China 3Beijing Institute of Radio Measurement, Beijing 100081, China; [email protected] *Correspondence: [email protected]; Tel.: +86-10-6891-8550 Received: 31 October 2018; Accepted: 3 January 2019; Published: 8 January 2019/gid00030/gid00035/gid00032/gid00030/gid00038/gid00001/gid00033/gid00042/gid00045 /gid00048/gid00043/gid00031/gid00028/gid00047/gid00032/gid00046 Abstract: Doppler parameter estimation and compensation (DPEC) is an important technique for airborne SAR imaging due to the unpredictable disturbance of real aircraft trajectory. TraditionalDPEC methods can be only applied for broadside, small- or medium-squint geometries, as they at most consider the spatial variance of the second-order Doppler phase. To implement the DPECin very-high-squint geometries, we propose an extended multiple aperture mapdrift (EMAM) method in this paper for better accuracy.

6.14, but itwill beuseful here todescribe afew principal features ofaradar that employs conical scan solely forthepurpose ofheight-finding. This principle was used inthe British CMH, amobile 10-cm equip- ment designed specifically for height-finding. Itused a6-ft dish, a power of500kw, and was capable ofmeasuring heights towithin ~500ft.

Here attention will be confined to echoes from airborne and surface targets. Aircraft and ships have dimensions that put them in the resonant scattering region. The smallest aircraft and cruise missiles will be in the Rayleigh scattering region for the lower half of the HF band.

The radar operator, observ- ing the existence of an error and its direction, could position the antenna to regain a balance between the two beam positions. This provided a manual tracking loop. This lobing technique was extended to continuous rotation of the beam around the target (conical scan) as in Fig.

There have been many methods proposed in the literature for determining the elerrlent spacings (or locations within the aperture) of such arrays. Only two will be mentioned here: dynamic prograrnrning and density tapering. 1I1EFI.ITTRONIrAI.IY STEFRED PHASED ARRAY ANTENNA INRADAR331 calarrayalsoattracts attention whenhemispherical coverage isdesired.

A K$ WHEN $K4HEFORWARD

A radar system that has the ca- pability of changing frequency over a very wide band can, with advantage, adapt its transmission to take into account frequency-dependent multipath characteris- tics, target response, environmental conditions, interference, and jamming. Fur- ther, wideband processing can give fine range resolution. Phased arrays have the potential of operating over very wide bandwidths.

Figure 11b is a result of interpolation of the point (1025 −135, 2050−120) in Figure 11a. It can be seen that the point target in forward-looking beam is well focused. The profiles of range and azimuth-spread function of the target are presented in Figure 11c,d.

d.Estimated number ofaircraft. e.Height. ~.Dhection oftight.

For example, if L = 120 km and hT = 0.3 km, then from Eq. 23.6, the transmitter would only illuminate a target flying directly above the receiver at an altitude ht > 0.14 km. Thus, the target could readily under-fly the illumination, and low-altitude air surveillance capability is lost.

WIDEFIGURE

By "ideal" conditions is meant an antenna with negligible sidelobes and negligible resistive losses, and which looks at a distributed source of brightness teuiperature (the cosmic noise) in the absence of the earth's atmosphere or any other source of noise. For a practical antenna the antenna temperature is defined as the integral of the brightness temperature over all angles, weighted by the antenna pattern. Atmospheric absorption noise.

267 Focused SAR.519 Forward scatter.557 Foxphaseshifter.296-297 Fraunhofer region.anlenna. 229INDEX575 Frequency agility: ECCM.548 forglintreduction, 170-172 andseaecho,485 Frequency diversity, 548 Frequency measurement accuracy, 407-408 Frequency modulated CWradar,81-92 Frequency-scan arrays,298-305 Frequency-scan radar.andpulsecompression. 433 Fresnelregion,antenna, 229 Fresnelzoneplate,523.527 Gain.antenna.

13.2 and 13.12, may be considered real and related to differences in grazing angle rather than in resolution cell size. In fact, distributions closely resembling those in Fig. 13.12 were obtained much earlier from similar measurements with considerably broader pulse widths.35 At Very Low Grazing Angles.

Finally, a pulse transformer matches the PFN to the impedance seen at the magnetron cathode. A pulse of around 10 kV is required to fire the magnetron. In order to get good performance over a wide range of pulse lengths, designs utilize a great deal of empirically derived knowledge, and actual circuits can be surprisingly complex.

24.1 example, 16 simultaneous receiver-processor channels are required for the multiple receive beams. Figure 24.27c gives the cor- responding power-level distributions. These approximately log-normal distribu- tions are typical.

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The spatial scale of the polarization “fringes” in the radar footprint is typically in the range 10–100 km, and the change of frequency needed to rotate the plane of polarization by 90 ° at a given location in the radar footprint (the polarization bandwidth) is of the order of 100 kHz, so differential ch20.indd 6 12/20/07 1:15:29 PMDownloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2008 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. HF Over-the-Horizon Radar.

TIVEMICROWAVEMEASUREMENTSOFAWIDEVARIETYOFSURFACEFEATURES ENABLEDBYTHESEMULTICHANNELCAPABILITIES4HEFOLLOWINGPARAGRAPHSPROVIDEONLYAGLIMPSEINTOTHESETOPICSTHEDISCUSSIONISMEANTTOWHETTHEAPPETITEOFTHEREADERANDTOPROVIDELEADSTOTHEVOLUMINOUSLITERATURE )NTERFEROMETRY )NTERFEROMETRYBYRADAR&IGURE  IMPLIESMEASUREMENTSTHAT AREBASEDONPHASEDIFFERENCESSENSEDTHROUGHTWODIFFERENTOBSERVATIONSOFTHESAMEPHENOMENA n0HASEDIFFERENCESARISEFROMMICROWAVE

2.2). Evidently some sort offanbeam, as narrow aspossible inthehorizontal direction but spread outvertically, is demanded. Tofind theshape which thebeam should have, inavertical plane, theproperties ofthetarget must betaken into account.

One example is ARI 5136 [ 8], installed in Barracuda aircraft, which had only homing antennas. A radar interconnection diagram is shown in figure 2.17. Aerial coupling box type 8 housed the aerial switch unit type 98A, together with spark gaps for receiver protection.

Precision of the geoid measurement was specified as ±10 cm.18 The Seasat-A satellite was launched at 6:12 P.M. PST on June 26, 1978. The orbital altitude was 783 km at apogee and 778 km at perigee.

20 array simulator for, 13.25 to 13.26 bandwidth of, 13. 38 to 13.45 beam switching, 13.8 calibration of active arrays, 13.60 to 13.62 circular polarization, 13.6 constrained feed, 13.46 Counter Battery Radar (COBRA), 13.62 digital beamforming, 13.56 to 13.57 diode phase shifters, 13.51 to 13.52 and ECM, 24.43 to 24.48 element pattern, 13.22 to 13.23 errors in, 13.30 to 13.38 feed networks, 13.46 to 13.50 ferrite phase shifters, 13.52 to 13.53 frequency scan, 13. 7 to 13.8 gain, 13.13 to 13.15 gr ating lobes, 13.10 to 13.12, 13.17 to 13.19 ground-based, 13.63 to 13.65 illumination functions, 13.28 to 13.29 instantaneous bandwidth, 13.42 to 13.45 limited scan, 13.

S.: Paraboloidal Reflector Patterns of Off-axis Feed, IRE Trat~s., vol. AP-8, pp. 368-379, July, 1960.


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- 4HEAMPLITUDEOFGROUNDECHOESRECEIVEDBYRADARSONMOVINGVEHICLESFLUCTUATESWIDELYBECAUSEOFVARIATIONSINPHASESHIFTFORRETURNFROMDIF FERENTPARTSOFTHEILLUMI

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Trotter, “Design considerations for the NOAA airborne meteorological radar and data system,” in 18th Conf. on Radar Meteorol. , AMS, Atlanta, 1978, pp.

L. Moffatt: Natural Resonances of Radar Targets via Prony's Method and Target Discrimination, IEEE Trans., vol. AES-12, pp.

Stevens: A Technique for the Generation of Highly Linear FM Pulse Radar Signals, IEEE Tra~rs., vol. MIL-9, pp. 32-38, January, 1965.

BEAMCLUTTER ISAFUNCTIONNOTONLYOFTHEBASICRADARPARAMETERSSUCHASPOWER ANTENNAGAIN ETC BUTOFRADARALTITUDEABOVETHETERRAINANDTHERADARCROSSSECTION2#3 OFLOW

PULSE&)2FILTERSANDASSUMEAPROCESS

Madsen, E. Rodriguez, and R. Goldstein, “Synthetic aperture radar interferometry,” Proc.

It has 2688 radiating elements with a T/R module per element. Although the active radiating aperture is approximately circular, the corners have been filled in ch13.indd 62 12/17/07 2:41:08 PMDownloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2008 The McGraw-Hill Companies. All rights reserved.

W.: lnterclutter Visibility in MTI Systems, IEEE Eascon Record. 1969. pp.

GTD and PTD are both based on the exact solution of the two-dimensional wedge problem, for which the directions of incidence and scattering are perpendicular to the edge. When extended to the case of oblique incidence, the direction of observation must lie along a generator of the Keller cone depicted in Figure 14.19. If the edge is straight and of finite length, as in the three-dimensional world, Eq.

  
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Walker: Recursive Methods for Computing Detection Probabilities, IEEE Trans., vol. AES-7, pp. 671-676, July, 1971.

The scanning capability can be implemented via use of either a single movable feed or an array with switchable feeds. Self-blockage (reflector blocking itself) is another potential limiting factor in spher - ical reflector systems. However, 360° of azimuth steering can be accomplished via a polarization design scheme similar to the polarization twist subreflector described FIGURE 12.

J. L. Allen et al., “Phased array radar studies,” MIT Lincoln Lab.

This success can beviewed as demonstrating the principle that, when acomplicated task must be carried out quickly and accurately under trying conditions, extreme mechanization iswell worth while, ifitremoves from human operators the necessity foremploying judgment and forperforming complicated operations. Such mechanization substitutes fortheskill ofoperators the design, manufacturing, and maintenance skills that are necessary to 1Sections 7.1, 7.2, 7.4, 7.7, and7.8byL.N.Ridenour, Sec. 7.3byL.J.Haworth, Sec.7.5byB.V.Bowden, andSec.7.6byC.L.Zimmerman.

Another ,t reason for preferring the liigller frcquetlcics in some applications, in spite of the larger clutter, is that greater range-resolution and azimuth-resolution (shorter pulse width and narrower beanlwidths) are easier to obtain than at lower frequencies. The higher resolution usually results iri greater target-to-clutter ratio. Civil marine radars are available at both S band (10 cln wavelength) and X band (3 cm).

The results are almost indistinguishable from those obtained bytheuseoftwo channels. TheLogarithmic Receiver.—A more involved method ofincreasing thedynamic range ofthesystem isbyuseoftheso-called “logarithmic” receiver, whose gain characteristics are such that the response varies approximately asthe logarithm ofthe input signal. One method of attaining such aresponse, which isactually anextension ofthethree-tone method, isillustrated inFig.

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