796:, on which NRL and RCA collaborated. The earliest version, XN-1, utilised a metal plate lens. The second version XN-2 used a conventional 3.65 meter parabolic antenna, and was the version which went to production. These radars played an important part in the Mercury, Gemini, and early Apollo missions, being deployed in Bermuda, Tannarive, and Australia, among other places for that purpose. The IRACQ modification was installed on certain of these installations; certainly the one located at Woomera, Australia was so modified. One of the larger installations first appeared in the 1970s as the
604:). This compensates for temperature changes that alter the size and length of wave-guide, which will cause phase variations that produce incorrect angle error signals for long wave-guide runs. The Cal term is created by injecting a calibration signal into the receive waveguide while the system is not active (sum and delta). The angle error of the calibration signal is used to evaluate angle error during normal operation. Antenna tuning is used to make adjustments that create the desired error signal when the antenna is calibrated on an antenna range.
247:
314:
25:
192:
569:
225:
locations within the beam. Jamming of this sort can be made more effective by timing the signals to be the same as the rotational speed of the feed, but broadcast at a slight delay, which results in a second strong peak within the beam, with nothing to distinguish the two. Jammers of this sort were deployed quite early. The
British used them during
421:
313:
607:
When the waveguide run is short between the antenna and receiver, the calibration signal can be omitted and the calibration term can be set to a fixed value. A fixed value may also be stored for systems with long wave-guide runs to allow degraded operation when RF calibration cannot be performed. The
581:
The angle error is used to make an adjustment to position the target along the centerline of the antenna. On mechanically steered radar, the vertical angle error drives a motor that moves the antenna up or down, and the horizontal angle error drives a motor that steers the antenna left or right. On a
763:
Conical scan and monopulse antennas are susceptible to interference from weather phenomenon and stationary objects. The resulting interference can produce feedback signals that move the antenna beam away from the aircraft. This can produce an unreliable antenna position when the antenna is aimed too
585:
A wheel, mirror and a light can be used to visualize real and imaginary described in this equation. The mirror is placed at a 45 degree angle above the wheel so that you can see the front and top of the wheel at the same time. The light is attached to the wheel so that you can see the wheel when the
322:
Monopulse antennas produce a sum signal and two delta signals. This allows angular measurement to be performed using a single receive pulse. The sum signal usually passes back down the waveguide used to send the transmit pulse. The two delta signals are elevation (up-down) and traverse (left-right).
288:
If the lobes are closely spaced, this signal can produce a high degree of pointing accuracy within the beam, adding to the natural accuracy of the conical scanning system. Whereas classical conical scan systems generate pointing accuracy on the order of 0.1 degree, monopulse radars generally improve
216:
By looking for this maximum and moving the antenna in that direction, a target can be automatically tracked. This is greatly eased by using two antennas, angled slightly to either side of the boresight. Tracking can be accomplished by comparing the signal from the two antennas in simple electronics,
759:
RADAR signal processing uses this technique. This is combined with conical scanning or monopulse to improve track reliability. It is necessary to separate the object signal from the interference to avoid being pulled off the object. This avoids problems where the system is fooled by aircraft flying
402:
The + or − value for each delta signal is created by phase shift of 0 degrees or 180 degrees when compared with the sum signal. A calibration signal is injected into the receive path when the radar is idle, and this establishes a known phase shift between different microwave signal paths (quiescent
384:
performs a mathematical subtraction on the electrical signals arriving from the feedhorns. That subtraction produces the delta signal. A similar feedhorn configuration is used to produce the up/down delta signal (not shown). The waveguide assembly can be used by itself. For a high gain antenna, the
262:
Making such a comparison requires that different parts of the beam be distinguished from each other. Normally this is achieved by splitting the pulse into two parts and polarizing each one separately before sending it to a set of slightly off-axis feed horns. This results in a set of lobes, usually
259:
other, indicating which direction has a stronger return, and thus the general direction of the target relative to the boresight. Since this comparison is carried out during one pulse, which is typically a few microseconds, changes in target position or heading will have no effect on the comparison.
220:
One problem with this approach is that radar signals often change in amplitude for reasons that have nothing to do with beam position. Over the period of a few tenths of seconds, for instance, changes in target heading, rain clouds and other issues can dramatically affect the returned signal. Since
212:
and then rotate the feed horn to make the lobe rotate around the boresight line. A target centered on the boresight is always slightly illuminated by the lobe, and provides a strong return. If the target is to one side, it will be illuminated only when the lobe is pointed in that general direction,
371:
structure positioned to maximize signal at the center of the antenna beam. The delta RF signals are created by pairs of antenna feed-horns located adjacent to the sum feed-horn (sum feed-horn not shown in the figure). The output of each pair of delta feed-horns are added together, and this creates
733:
radar, position and velocity is maintained for multiple aircraft. The last position of the aircraft is coasted using the velocity, and that information is used to direct a beam of energy toward the aircraft. The monopulse angle error information that is received is used to adjust the position and
725:
For a mechanically steered antenna, the horizontal signal and vertical signal are used to create a drive signal that creates torque for two antenna positioning motors. One motor moves the antenna left/right. The other motor drives the antenna up/down. The result is to move the antenna position so
224:
Jamming a conical scanner is also relatively easy. The jammer simply has to send out signals on the radar's frequency with enough strength to make it think that was the strongest return. In this case, a series of random short bursts of the signal will appear to be a series of targets in different
258:
Monopulse radars are similar in general construction to conical scanning systems, but split the beam into parts and then send the two resulting signals out of the antenna in slightly different directions. When the reflected signals are received they are amplified separately and compared to each
296:
Jamming resistance is greatly improved over conical scanning. Filters can be inserted to remove any signal that is either unpolarized, or polarized only in one direction. In order to confuse such a system, the jamming signal would have to duplicate the polarization of the signal as well as the
379:
RF signal arrives at the two feed horns to produce a left/right delta signal. The arriving energy from the RF wavefront is launched into both waveguide feedhorns. The RF signal from both feedhorns travels up the waveguide where the signals from the left and right feedhorn are combined. The
178:. Modern systems determine the direction from the monopulse ratio, which contain both amplitude and phase information. The monopulse method does not require that the measured signals are pulsed. The alternative name "simultaneous lobing" has therefore been suggested, but not popularized.
812:
and research. The cost and complexity of implementing monopulse tracking was reduced and reliability increased when digital signal processing became available after the 1970s. The technology is found in most modern tracking radars and many types of disposable ordnance like missiles.
326:
The sum signal corresponds with the antenna beam along center-line of the antenna. The delta signals are pairs of beams that are adjacent to the center-line of the sum antenna beam. The delta beam measurements produce plus or minus values depending upon the quadrant.
564:{\displaystyle {\text{Error}}={\frac {\frac {({\text{Real Delta}})+i({\text{Imaginary Delta}})}{({\text{Real Sum}})+i({\text{Imaginary Sum}})}}{\frac {({\text{Real Delta Cal}})+i({\text{Imaginary Delta Cal}})}{({\text{Real Sum Cal}})+i({\text{Imaginary Sum Cal}})}}}}
221:
conical scanning systems depend on the signal growing or weakening due only to the position of the target relative to the beam, such changes in reflected signal can cause it to be "confused" about the position of the target within the beam's scanning area.
721:
The horizontal signal and the vertical signal created from antenna RF samples are called angle errors. These angle error signals indicate the angular distance between the center of the antenna beam and the position of the aircraft within the antenna beam.
317:
Radio frequency signals arriving at the surface of the antenna feed-horns are combined electrically to produce delta signals. The assembly that is shown produces a left/right delta signal based on an arriving radio frequency signal that is horizontally
764:
near the ground or too near to heavy weather. Systems with no Pulse
Doppler tracking mode may remain aimed at irrelevant objects like trees or clouds. Constant operator attention is required when there is no Doppler signal processing.
701:
586:
room lights are turned off. You sit directly in front of the wheel while a friend rotates the wheel. The view of the front of the wheel (real) and the top of the wheel (imaginary) tell you the position of the wheel.
263:
two, overlapping on the boresight. These lobes are then rotated as in a normal conical scanner. On reception the signals are separated again, and then one signal is inverted in power and the two are then summed (
406:
The angle error is created from the delta signal by performing a complex ratio. This is done for the left/right delta beams, and this is also done for the up/down delta beams (two ratios). An explanation of how
372:
zero output signal when the incoming RF signal is located at the center of the antenna beam. The signal strength from each delta beam increases as the aircraft drifts further away from the antenna center-line.
213:
resulting in a weaker signal overall (or a flashing one if the rotation is slow enough). This varying signal will reach a maximum when the antenna is rotated so it is aligned in the direction of the target.
780:
experiment. As a result, it was very expensive, labor-intensive due to complexity, and less reliable. It was only used when extreme accuracy was needed that justified the cost. Early uses included the
620:. The angle θ (in either elevation or azimuth) is estimated from the monopulse ratio, which is the ratio of the difference signal over the sum signal. The estimation equation is given by:
582:
missile, the angle error is an input to the guidance system that positions the guidance fins that rotate the body of the missile so that the target is in the centerline of the antenna.
283:
848:
Frid, Henrik; Jonsson, B. L. G (2018). "Determining
Installation Errors for DOA Estimation with Four-Quadrant Monopulse Arrays by using Installed Element Patterns".
714:
Tracking systems produce constant aircraft position information, and the antenna position is part of this information. Antenna error signals are used to create
626:
792:
system which went into service in 1960 on the RAF's
English Electric Lightning interceptor aircraft. An early monopulse radar development, in 1958, was the
388:
For the waveguide image that is shown, the sum signal would be created by a single waveguide feedhorn centered between the two feedhorns that are shown.
578:. The outcome of the calibration process is to rotate the complex antenna angle error vector onto the real axis to reduce signal processing losses.
297:
timing, but since the aircraft receives only one lobe, determining the precise polarization of the signal is difficult. Against monopulse systems,
726:
that the center of the antenna beam remains aimed directly at the aircraft even when the aircraft is moving perpendicular to the antenna beam.
205:
Conical scanning is not considered to be a form of monopulse radar, but the following summary provides background that can aid understanding.
132:
signal to provide accurate directional information. The name refers to its ability to extract range and direction from a single signal pulse.
147:
more difficult. Most radars designed since the 1960s are monopulse systems. The monopulse method is also used in passive systems, such as
924:
809:
285:
in the image). If the target is to one side of the boresight the resulting sum will be positive, if it's on the other, negative.
89:
61:
68:
108:
600:
Dynamic calibration is needed when there are long waveguide runs between the antenna and first down converter (see
42:
75:
741:
46:
195:
Conical scanning and monopulse radars use a beam that is slightly spread out across the antenna's centreline.
57:
266:
148:
616:
The four-quadrant array antenna consists of four sub-arrays. The sub-arrays are separated by a distance
894:
298:
171:
777:
601:
594:
408:
35:
919:
293:
are accurate to 0.006 degrees. This is an accuracy of about 10 m at a distance of 100 km.
788:
launches. The world's first airborne monopulse radar system was the
British Ferranti-designed
784:
missile, which demanded very high accuracy, or for tracking radars used for measuring various
608:
waveguide assembly may need to be tuned using an antenna range to obtain consistent results.
82:
217:
as opposed to having to hunt for a maximum point over the period of the antenna's rotation.
376:
696:{\displaystyle \Delta /\Sigma =-j\tan \left({\frac {\pi d}{\lambda }}\sin \theta \right).}
8:
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862:
805:
175:
156:
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385:
feedhorn assembly is located facing the reflecting surface at or near the focal point.
144:
396:
305:
to simply blind the radar, instead of attempting to produce false localized returns.
209:
391:
The sum and delta radio frequency signals are converted to a lower frequency in the
230:
730:
392:
200:
136:
152:
140:
914:
752:
590:
164:
908:
756:
412:
208:
Conical scan systems send out a signal slightly to one side of the antenna's
735:
251:
226:
160:
772:
Monopulse radar was extremely "high tech" when it was first introduced by
760:
too close to the surface of the earth or aircraft flying through clouds.
744:
provides an explanation of the antenna signals involved in this process.
302:
706:
The derivation of a more general form of this equation is presented in.
246:
793:
781:
290:
191:
24:
801:
715:
381:
368:
850:
Proceeding of the
Atlantic Radio Science Conference (AT-RASC) 2018
899:
797:
789:
785:
170:
Historically, monopulse systems have been classified as either
289:
this by a factor of 10, and advanced tracking radars like the
129:
125:
734:
velocity data for the aircraft. This is a common mode with
755:
can be used to separate different objects based on speed.
139:
radar systems, which can be confused by rapid changes in
308:
411:
are used with RADAR can be found in the description of
375:
For the waveguide image that is shown, a horizontally
270:
629:
424:
269:
611:
718:as part of a RADAR system that can track aircraft.
49:. Unsourced material may be challenged and removed.
843:
841:
695:
563:
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155:. Monopulse radar systems can be constructed with
906:
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399:produces the error signal using these samples.
829:
128:system that uses additional encoding of the
847:
589:Pairs of real and imaginary values form a
810:Tartar Guided Missile Fire Control System
109:Learn how and when to remove this message
245:
190:
135:Monopulse radar avoids problems seen in
830:Barton, David; Sherman, Samuel (2011).
301:has generally resorted to broadcasting
907:
709:
309:Implementation for reflector antennas
278:{\displaystyle \scriptstyle \Sigma }
229:against the German conical-scanning
47:adding citations to reliable sources
18:
832:Monopulse Principles and Techniques
241:
13:
925:Multidimensional signal processing
638:
630:
312:
271:
14:
936:
612:Implementation for array antennas
23:
367:The sum signal is created by a
186:
34:needs additional citations for
868:
856:
823:
742:Amplitude-Comparison Monopulse
554:
546:
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529:
524:
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507:
499:
492:
484:
475:
467:
462:
454:
445:
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395:where sampling takes place. A
236:
1:
816:
181:
7:
883:
254:antenna split in two lobes.
149:electronic support measures
10:
941:
895:Phase-comparison monopulse
808:, and MK-74 radar used on
767:
747:
198:
172:phase-comparison monopulse
778:Naval Research Laboratory
16:Single-pulse radar system
602:Superheterodyne receiver
595:real and imaginary parts
409:real and imaginary parts
358:Quadrant III: −ΔEl −ΔAz
143:. The system also makes
361:Quadrant IV: −ΔEl +ΔAz
347:Quadrant II: +ΔEl −ΔAz
697:
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350:Quadrant I: +ΔEl +ΔAz
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279:
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196:
698:
566:
316:
280:
249:
194:
865:on the Radartutorial
627:
422:
267:
250:Monopulse beam of a
43:improve this article
890:Amplitude monopulse
806:Aegis Combat System
710:Antenna positioning
521:Imaginary Delta Cal
176:amplitude monopulse
863:Monopulse Duplexer
804:radar used on the
693:
561:
320:
275:
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197:
157:reflector antennas
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559:
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551:Imaginary Sum Cal
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443:
428:
365:
364:
119:
118:
111:
93:
58:"Monopulse radar"
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731:track while scan
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574:The result is a
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397:signal processor
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242:Monopulse basics
201:Conical scanning
137:conical scanning
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107:
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100:
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51:
27:
19:
940:
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738:radar systems.
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459:Imaginary Delta
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153:radio astronomy
141:signal strength
122:Monopulse radar
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52:
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774:Robert M. Page
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753:Doppler effect
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591:complex number
572:
571:
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531:
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518:
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512:
509:
504:Real Delta Cal
501:
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231:Würzburg radar
199:Main article:
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165:array antennas
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31:
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920:Radar imaging
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776:in 1943 in a
775:
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757:Pulse Doppler
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593:explained as
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576:signed number
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489:Imaginary Sum
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413:pulse Doppler
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161:lens antennas
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60: –
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54:Find sources:
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32:This article
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21:
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736:phased array
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534:Real Sum Cal
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252:phased array
227:World War II
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187:Conical scan
169:
134:
121:
120:
105:
96:
86:
79:
72:
65:
53:
41:Please help
36:verification
33:
875:Mountaintop
303:white noise
237:Description
909:Categories
817:References
442:Real Delta
333:Quadrants
318:polarized.
182:Background
99:March 2022
69:newspapers
794:AN/FPS-16
782:Nike Ajax
683:θ
680:
672:λ
665:π
654:
645:−
639:Σ
631:Δ
377:polarized
291:AN/FPS-16
272:Σ
210:boresight
884:See also
802:AN/SPY-1
716:feedback
472:Real Sum
393:receiver
382:combiner
369:feedhorn
900:AIRPASS
798:US Navy
790:AIRPASS
768:History
748:Doppler
403:mode).
145:jamming
83:scholar
786:rocket
729:For a
339:Right
85:
78:
71:
64:
56:
915:Radar
427:Error
355:Down
336:Left
130:radio
126:radar
124:is a
90:JSTOR
76:books
151:and
62:news
800:'s
677:sin
651:tan
344:Up
299:ECM
174:or
167:.
163:or
45:by
911::
840:^
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415:.
233:.
159:,
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87:·
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39:.
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