191:) that can be accurately determined by the radar. Conversely, a high PRR/PRF can enhance target discrimination of nearer objects, such as a periscope or fast moving missile. This leads to use of low PRRs for search radar, and very high PRFs for fire control radars. Many dual-purpose and navigation radars—especially naval designs with variable PRRs—allow a skilled operator to adjust PRR to enhance and clarify the radar picture—for example in bad sea states where wave action generates false returns, and in general for less clutter, or perhaps a better return signal off a prominent landscape feature (e.g., a cliff).
166:), which is the elapsed time from the beginning of one pulse to the beginning of the next pulse. The IPP term is normally used when referring to the quantity of PRT periods to be processed digitally. Each PRT having a fixed number of range gates, but not all of them being used. For example, the APY-1 radar used 128 IPP's with a fixed 50 range gates, producing 128
380:
80:
radar's desired range. Longer periods are required for longer range signals, requiring lower PRFs. Conversely, higher PRFs produce shorter maximum ranges, but broadcast more pulses, and thus radio energy, in a given time. This creates stronger reflections that make detection easier. Radar systems must balance these two competing requirements.
541:
905:
For example, if 30 samples are taken during the quiescent phase between transmit pulses using a 30 kHz PRF, then true range can be determined to a maximum of 150 km using 1 microsecond samples (30 x C / 30,000 km/s). Reflectors beyond this range might be detectable, but the true range
79:
After producing a brief pulse of radio signal, the transmitter is turned off in order for the receiver units to detect the reflections of that signal off distant targets. Since the radio signal has to travel out to the target and back again, the required inter-pulse quiet period is a function of the
1042:
Sonar systems operate much like radar, except that the medium is liquid or air, and the frequency of the signal is either audio or ultra-sonic. Like radar, lower frequencies propagate relatively higher energies longer distances with less resolving ability. Higher frequencies, which damp out faster,
122:
Electromagnetic (e.g. radio or light) waves are conceptually pure single frequency phenomena while pulses may be mathematically thought of as composed of a number of pure frequencies that sum and nullify in interactions that create a pulse train of the specific amplitudes, PRRs, base frequencies,
1072:
Light waves can be used as radar frequencies, in which case the system is known as lidar. This is short for "LIght
Detection And Ranging," similar to the original meaning of the initialism "RADAR," which was RAdio Detection And Ranging. Both have since become commonly-used english words, and are
1076:
Laser range or other light signal frequency range finders operate just like radar at much higher frequencies. Non-laser light detection is utilized extensively in automated machine control systems (e.g. electric eyes controlling a garage door, conveyor sorting gates, etc.), and those that use
546:
The maximum range also defines a range ambiguity for all detected targets. Because of the periodic nature of pulsed radar systems, it is impossible for some radar system to determine the difference between targets separated by integer multiples of the maximum range using a single PRF. More
706:
Range and velocity can both be identified using medium PRF, but neither one can be identified directly. Medium PRF is from 3 kHz to 30 kHz, which corresponds with radar range from 5 km to 50 km. This is the ambiguous range, which is much smaller than the maximum range.
329:
with an adjustable PRF to measure rotational velocity. The PRF for the strobe light is adjusted upward from a low value until the rotating object appears to stand still. The PRF of the tachometer would then match the speed of the rotating object.
439:
308:
875:
radar using a PRF of 10 kHz would be 1,500 m/s (3,300 mile/hour) (10,000 x C / (2 x 10^9)). True velocity can be found for objects moving under 45,000 m/s if the band pass filter admits the signal (1,500/0.033).
1050:
in the medium (almost always water), and maximum PRF depends upon the size of the object being examined. For example, the speed of sound in water is 1,497 m/s, and the human body is about 0.5 m thick, so the PRF for
685:
1029:
866:
733:
is required to identify true range and speed. Doppler signals fall between 1.5 kHz, and 15 kHz, which is audible, so audio signals from medium-PRF radar systems can be used for passive target classification.
801:
964:
624:
83:
Using older electronics, PRFs were generally fixed to a specific value, or might be switched among a limited set of possible values. This gives each radar system a characteristic PRF, which can be used in
698:
issues that complicate the receiver. Low PRF radar intended for aircraft and spacecraft detection are heavily degraded by weather phenomenon, which cannot be compensated using moving target indicator.
562:
Systems using PRF below 3 kHz are considered low PRF because direct range can be measured to a distance of at least 50 km. Radar systems using low PRF typically produce unambiguous range.
267:
428:
96:
battery had "locked on", for instance. Modern radar systems are generally able to smoothly change their PRF, pulse width and carrier frequency, making identification much more difficult.
1058:
As another example, ocean depth is approximately 2 km, so sound takes over a second to return from the sea floor. Sonar is a very slow technology with very low PRF for this reason.
92:
in aircraft include a library of common PRFs which can identify not only the type of radar, but in some cases the mode of operation. This allowed pilots to be warned when an
547:
sophisticated radar systems avoid this problem through the use of multiple PRFs either simultaneously on different frequencies or on a single frequency with a changing PRT.
536:{\displaystyle {\text{Max Range}}={\frac {c\tau _{\text{PRT}}}{2}}={\frac {c}{2\,{\text{PRF}}}}\qquad {\begin{cases}\tau _{\text{PRT}}={\frac {1}{\text{PRF}}}\end{cases}}}
229:
433:
For accurate range determination a pulse must be transmitted and reflected before the next pulse is transmitted. This gives rise to the maximum unambiguous range limit:
1034:
It becomes increasingly difficult to take multiple samples between transmit pulses at these pulse frequencies, so range measurements are limited to short distances.
891:
Systems using PRF above 30 kHz function better known as interrupted continuous-wave (ICW) radar because direct velocity can be measured up to 4.5 km/s at
741:
radar system using a PRF of 10 kHz with a duty cycle of 3.3% can identify true range to a distance of 450 km (30 * C / 10,000 km/s). This is the
1080:
Unlike lower radio signal frequencies, light does not bend around the curve of the earth or reflect off the ionosphere like C-band search radar signals, and so
278:
135:(especially United States armed forces terminologies) and equipment specifications such as training and technical manuals for radar and sonar systems.
632:
72:
had a basic carrier frequency of 209 MHz (209 million cycles per second) and a PRF of 300 or 500 pulses per second. A related measure is the
970:
807:
576:
above 75 m/s (170 mile/hour), while detecting true range up to 300 km. This combination is appropriate for civilian aircraft radar and
56:
is turned on and off; the term "frequency" refers to the carrier, while the PRF refers to the number of switches. Both are measured in terms of
1077:
pulse-rate detection and ranging are at heart, the same type of system as a radar—without the bells and whistles of the human interface.
1158:
751:
333:
Other types of measurements involve distance using the delay time for reflected echo pulses from light, microwaves, and sound transmissions.
45:) is the number of pulses of a repeating signal in a specific time unit. The term is used within a number of technical disciplines, notably
912:
690:
Low PRF radar have reduced sensitivity in the presence of low-velocity clutter that interfere with aircraft detection near terrain.
586:
364:
A radar system uses a radio frequency electromagnetic signal reflected from a target to determine information about that target.
573:
1123:
565:
Unambiguous
Doppler processing becomes an increasing challenge due to coherency limitations as PRF falls below 3 kHz.
237:
272:
PRF is usually associated with pulse spacing, which is the distance that the pulse travels before the next pulse occurs.
393:
88:
to identify the type or class of a particular platform such as a ship or aircraft, or in some cases, a particular unit.
73:
708:
551:
387:
A radar system determines range through the time delay between pulse transmission and reception by the relation:
1192:
1052:
691:
170:
filters using an FFT. The different number of range gates on each of the five PRF's all being less than 50.
31:
139:
128:
89:
1187:
730:
719:
500:
1098:
715:
212:
350:
85:
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Pulse-repetition frequency (PRF) is the number of times a pulsed activity occurs every second.
1154:
53:
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124:
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High PRF is limited to systems that require close-in performance, like proximity fuses and
17:
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303:{\displaystyle {\text{Pulse Spacing}}={\frac {\text{Propagation Speed}}{\text{PRF}}}}
371:
operation. This is the rate at which transmitter pulses are sent into air or space.
694:
is generally required for acceptable performance near terrain, but this introduces
326:
65:
1084:
is useful only in line of sight applications like higher frequency radar systems.
131:
and some sciences), and the latter (PRR) more commonly used in military-aerospace
106:
systems also have PRFs, as does any pulsed system. In the case of sonar, the term
383:
A real target in 100 km or a second-sweep echo in a distance of 400 km
132:
69:
1150:
680:{\displaystyle {\text{75 m/s velocity}}={\frac {500\times C}{2\times 10^{9}}}}
322:
93:
726:
return is generally not ambiguous until velocity exceeds the speed of sound.
64:. The PRF is normally much lower than the frequency. For instance, a typical
899:
1024:{\displaystyle {\text{4,500 m/s}}={\frac {30,000\times C}{2\times 10^{9}}}}
861:{\displaystyle {\text{1,500 m/s}}={\frac {10,000\times C}{2\times 10^{9}}}}
177:
technology PRF is important since it determines the maximum target range (
379:
796:{\displaystyle {\text{450 km}}={\frac {C}{0.033\times 2\times 10,000}}}
318:
PRF is crucial to perform measurements for certain physics phenomenon.
127:). The first term (PRF) is more common in device technical literature (
892:
872:
738:
569:
76:, the amount of time the transmitter is turned on during each pulse.
1055:
of the human body should be less than about 2 kHz (1,497/0.5).
959:{\displaystyle {\text{150 km}}={\frac {30\times C}{2\times 30,000}}}
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368:
355:
345:
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46:
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Different PRF allow systems to perform very different functions.
619:{\displaystyle {\text{300 km range}}={\frac {C}{2\times 500}}}
341:
PRF is crucial for systems and devices that measure distance.
745:. Unambiguous velocity is 1,500 m/s (3,300 mile/hour).
554:
is used to identify true range when PRF is above this limit.
30:"Pulses per second" redirects here. Not to be confused with
529:
114:) is more common, although it refers to the same concept.
1145:. Electrical Engineering Handbook. Vol. 20071745.
973:
915:
810:
754:
711:
is used to determine true range in medium PRF radar.
635:
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262:{\displaystyle \mathrm {T} ={\frac {1}{\text{PRF}}}}
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423:{\displaystyle {\text{Range}}={\frac {c\tau }{2}}}
422:
302:
261:
223:
883:issues that require redundant detection schemes.
1043:provide increased resolution of nearby objects.
895:, but range resolution becomes more difficult.
209:PRF is inversely proportional to time period
8:
1073:therefore acronyms rather than initialisms.
572:radar with 500 Hz pulse rate produces
206:used to describe other types of waveforms.
1143:RF and Microwave Applications and Systems
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52:In radar, a radio signal of a particular
231:which is the property of a pulsed wave.
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123:phase characteristics, et cetera (See
27:Number of pulses of a repeating signal
1137:Piper, Samuel; Wiltse, James (2007).
7:
552:range ambiguity resolution process
242:
217:
25:
722:capability in military systems.
184:) and maximum Doppler velocity (
871:The unambiguous velocity of an
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142:of PRF (or PRR) is called the
1:
1124:"Pulse Repetition Frequency"
224:{\displaystyle \mathrm {T} }
1209:
1151:10.1201/9781420006711.ch14
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709:Range ambiguity resolution
39:pulse-repetition frequency
29:
18:Pulse repetition frequency
1046:Signals propagate at the
152:pulse-repetition interval
718:, which is required for
714:Medium PRF is used with
1139:"Continuous Wave Radar"
692:Moving target indicator
90:Radar warning receivers
32:Pulse-per-second signal
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906:cannot be identified.
879:Medium PRF has unique
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129:Electrical Engineering
68:radar like the Type 7
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144:pulse-repetition time
108:pulse-repetition rate
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731:ambiguity resolution
720:look-down/shoot-down
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367:PRF is required for
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1099:Pulse-Doppler radar
729:A technique called
716:Pulse-Doppler radar
202:This is similar to
1021:
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743:instrumented range
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574:ambiguous velocity
533:
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351:Laser range finder
300:
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160:inter-pulse period
86:electronic warfare
1160:978-0-8493-7219-3
1053:ultrasound images
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293:Propagation Speed
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54:carrier frequency
16:(Redirected from
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1126:. Radartutorial.
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125:Fourier Analysis
58:cycle per second
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1188:Radar theory
1164:. Retrieved
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1071:
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1033:
904:
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592:300 km range
567:
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327:strobe light
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118:Introduction
111:
107:
98:
82:
78:
66:World War II
51:
42:
38:
36:
1166:January 29,
337:Measurement
133:terminology
74:pulse width
1182:Categories
1110:References
702:Medium PRF
325:may use a
323:tachometer
195:Definition
140:reciprocal
1006:×
995:×
976:4,500 m/s
942:×
931:×
843:×
832:×
813:1,500 m/s
779:×
773:×
662:×
651:×
608:×
505:τ
459:τ
445:Max Range
412:τ
70:GCI radar
1088:See also
887:High PRF
94:SA-2 SAM
558:Low PRF
314:Physics
173:Within
168:Doppler
1157:
918:150 km
893:L band
873:L-Band
757:450 km
739:L band
570:L-Band
158:), or
1094:Radar
1082:lidar
1068:lidar
1062:Laser
1038:Sonar
770:0.033
399:Range
369:radar
356:Sonar
346:Radar
175:radar
104:lidar
100:Sonar
62:hertz
60:, or
47:radar
1168:2011
1155:ISBN
550:The
138:The
102:and
37:The
1147:doi
992:000
951:000
829:000
788:000
648:500
611:500
522:PRF
509:PRT
488:PRF
463:PRT
296:PRF
255:PRF
189:max
182:max
164:IPP
156:PRI
150:),
148:PRT
112:PRR
43:PRF
1184::
1153:.
1141:.
1010:10
986:30
945:30
928:30
902:.
847:10
823:10
782:10
666:10
580:.
49:.
1170:.
1149::
1014:9
1003:2
998:C
989:,
980:=
948:,
939:2
934:C
922:=
851:9
840:2
835:C
826:,
817:=
785:,
776:2
766:C
761:=
670:9
659:2
654:C
642:=
605:2
601:C
596:=
519:1
514:=
498:{
483:2
479:c
474:=
469:2
455:c
449:=
416:2
409:c
403:=
288:=
252:1
247:=
243:T
218:T
186:V
179:R
162:(
154:(
146:(
110:(
41:(
34:.
20:)
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