Phazotron Sapfir-23 and Sapfir-25 radar

Thread to discuss MiG-23 Avionics

Sapfir-23E Radar

This post is by mrdetonator, at the acig.org forums, hopefully he will be here soon to repost himself.

The Sapfir-23E (izdelie 323E).

The Sapfir-23E radar itself represents a coherent pulse Doppler system and it allows:
-search and track of enemy targets in all-aspect at any weather condition, day/night, natural interference (earth /clouds) and active/passive jamming.
-target recognition in co-op. with the SRZO-2 (friend-foe) interrogator
-single target track, measuring target range, azimuth and angular positions.
-search and track of targets emitting heat, the radar antenna controlled by IRST sensor.
-to form control signals for the SAU-23A autopilot in co-op. with LASUR-M (Vozdukh-1M) and RSBN-6S (ROMB-1K) systems, e.g. giving the "break-away" signal...
-to form control signals for launching guided A-A missiles, provides continuous illumination of the target for the RGS-23 seeker, to form control signals during the gun aiming and ensures launching of unguided missiles in the synchronous/asynchronous mode.
-to indicate RADAR/IRST information on the SEI indicator and one-way command symbols on the symbol indicator mounted on the gun sight ASP-23DE.

The Sapfir-23E uses the mono-pulse technique to track a single target. Such a radar system consists of two parabolic antennas (moving, fixed) and the four-cone T/R element. In this system, each returning radar pulse provides target pointing information by being focused at the antenna onto a group of four-cone T/R elements.
Description of the tracking process: After pushing the „Zachvat“ button, the radar proceeds an additional search in the antenna position where the target has been found. During this additional search the scan zone shrinks to ±8º in azimuth and ±52` in elevation. If the target signal is present, the antenna performs angular tracking of the target and the radar range-finder is switched on. The range-finder searches the target in the 9km range zone. If the target is within the 9km zone, the antenna performs range tracking of the target. The SEI indicator changes its appearance. It is now showing the crosshair and the circle guidance indicator instead of selection lines (range zone). The radar is tracking the target. The tracking principle is based on summing the elevation, azimuth and the reference signal taken from the 4-cone receiver.

The Sapfir-23E radar is linked with following other systems.

-the IRST sensor TP-23-1
-the analogue computer AVM-23
-the indicator SEI
-the optical gun-sight ASP-23DE
-the gun camera PAU-473-2
-the radar emission receiver SPO-10
-the IFF system SRZO-2M
-the transponder SO-69 (SOD-57)
-the short range navigation system RSBN-6S
-the radio-telemetric system ARL-SM
-the autopilot SAU-23A
-the gyro-platform SKV-2N-2
-the radio altimeter RV-4A
-the angle of attack probe DUA-3M
-the angle of slide probe DUS-3-1
-the true air-speed probe DVS-7 (DVS-10)
-the barometric altitude probe DV-30
-the SARH missile with the RGS-23 and the coupling block "RBS"
-the IR guided missile with the TGS-23 and the coupling block "TBS"
-the A2G radio-commanded missile CH-23M with pod "DELTA NG"

Basic data of the Sapfir-23E system.

The S-23E radar contains of 46 parts weighting total 641kg. Main parts:
The two-mirror cassegrain antenna: 78kg
Impulse transmitter: 160kg
KNP transmitter: 160kg (continuous wave illuminator for the R-23R)
AVM-23 analog computer: 10.2kg
Radar max. scan limits in azimuth: ±52º
Radar max. scan limits in elevation: +43º, -38º
Antenna scan coverage in azimuth: ±30º
Antenna scan coverage in elevation: 8.5º to 12º
Scan cycle: 3.5sec
Pulse width: 4 or 1 µsec
PRF: ~1KHz
Peak power of impulse transmitter: 70kW
Power output of KNP transmitter: 270W
Time to ready: 6min
Antenna gyro-stabilization
Pitch 30/-35º
Roll 70/-70º
Radar self check time: max. 100s
Target altitude: 40-25000m
Target speed: up to 2500km/h. 2.35M

Typical range of the Sapfir-23E against fighter/bomber sized target


Detailed description of the Sapfir-23E radar modes.

The radar scan modes BSV, BSV-delta H4, BSV-delta H1, SMV, MV are switched automatically according to aircraft altitude Hs (DV-30 barometric probe) and the antenna position ”Delta H” switch. The scan mode BSV-SC can be selected manually by the pilot with the radar mode switch "BSV SC-R-BSMV switched to the BSV-SC position.
e.g. the aircraft is flying with its nose below the horizon (descending), but the antenna bearing is above the horizon. At altitude of 1500m the BSV mode changes to SMV automatically. If the antenna bearing is below the horizon at the same conditions (descend flight), at altitude of 1500m the BSV-deltaH1 mode switches to the MV automatically and vice-versa.
The BSV-SC mode hasn’t altitude limitations, the delta H switch doesn’t have an effect on it.
When the switch NAVED AVT/RUCHN is set to AVT, the radar mode selection is done automatically by the GCI datalink (ARL-SM). The radar scan patterns under GCI are better optimized due to known PPS/ZPS aspect. The one-way commands from GCI are displayed on special symbol indicator mounted on the ASP-23DE gunsight. Pilot can interrupt the GCI datalink anytime setting the switch to RUCHN.


The S-23E modes operating conditions.

The mode BSV for high/medium altitudes and all-aspect intercepts, to engage targets flying higher than the Mig-23. (Hc>Hs), pulse width ~4 µsec(search), pulse width ~1 µsec(track), PRF 1Khz, Beam width in search 2,5°. Indicated range scale on SEI is 60km(search), indicated range scale on SEI is 30km(track). The maximal target altitude surplus is 6km. (delta H switch).

The mode BSV-delta H4 uses one half of the PRF compared to the BSV mode. The mode BSV-delta H4 for high/medium altitudes, rear-aspect intercepts, to engage targets flying lower than the Mig-23 on the earth background (LD/SD mode) (Hc<Hs). Pulse width ~4 µsec(search), pulse width ~1 µsec(track), Beam width 2,5°(search). The max. altitude deficit of the target is -4km. (delta H switch).

The mode BSV-delta H1 differs to the BSV-deltaH4 by using the pulse width of 1 µsec (search, track). The mode BSV-delta H1 for high/medium altitudes, rear-aspect intercepts, This mode is used to engage targets flying lower than the Mig-23 on the earth background (LD/SD mode) (Hc<Hs). The signal is further processed, filtered out in the “differential clutter filter” (DKP)

The SMV mode for medium/low altitudes and all-aspect intercepts, to engage targets flying higher than the Mig-23. (Hc>Hs). Indicated range scale on SEI is 30km(search, track). The pulse width of ~1 µsec(search, track)

The MV mode is used to engage targets flying lower than the Mig-23 on the earth background. (LD/SD mode) (Hc<Hs). It`s used only for rear-aspect intercepts, pulse width ~1 µsec(search, track), Beam width in search 1,5°. The MV mode uses the „SDC with external coherence“ technique to compare Doppler shifts between the target and earth background. The antenna scan zone is locked in azimuth and elevation.

The BSV-SC mode is for high/medium altitudes and all-aspect intercepts, to engage targets flying higher than the Mig-23. (Hc>Hs) . The radar mode exploits the same form of doppler processing of the received signal as in the MV mode, but on the background of radio-reflective clouds. The antenna scan zone isn`t locked as in the MV mode.

(Hs- altitude of the Mig-23, Hc- target altitude)

The Sapfir-23E controls and others in the cockpit of the Mig-23MF.

The panel "Block34" contains:

The main radar operating switch "BSV-SC-R-BSMV" chooses between two radar main operating modes. The position BSMV switches among BSV, BSV-H4, BSV-H1, SMV and MV. In the BSV-SC position the radar switches between the BSV-SC and MV modes

The SIST switch has 5 operating modes. „R, T-R, T, T-phi0, NAV.
The „R“ mode determines the onboard radar as a main targeting system. Also during ground attack the radar can measure distance to the target.
The „T-R“ mode means cooperation between the radar and the IRST, if the radar is jammed the IRST can pick up the target distance and vice-versa.
The „T“ mode prioritizes the IRST as a main targeting system. Also this mode is used in case of radar damage or hidden approach. The S-23E radar works in so called quasi-scan mode. The radar antenna is slaved to IRST sensor and is providing the data for the launch of R-23T.
In the „T-phi0“ mode the R-23T missile seeker is caged to the axis of the plane.
The „NAV“ mode is for navigation flights under RSBN, or “return to base” command (VOZVRAT). The HUD display is showing “K”(curse), “G”(inclination) symbols, which the pilot has to follow.
The switch IZL-EKV-VYK impulse transmitter (emit/equivalent/off)
The switch NAVED-AVT-RUCHN, the instrument guiding by datalink ARL-SM on/off
The switch MSKC-PPS-ZPS, low-speed target engagements (<500km/h)/front/rear hemisphere. If no jamming occurs, the MSKC switch position allows the radar to detect targets with any closure speeds.

The panel „Block95„ contains the one-way command symbol indicator on the gunsight ASP-23DE

K- ASP-23DE self control indicator
PPS- front hemisphere intercept
AVT-the radar range-finder is automatically controlled by ARL-SM
100,60,30- range to target
F- afterburner ignite
<- target on left
I- target straight
>- target on right
!- target change
A- the „zachvat“ command.
G- the “Gorka” maneuver
PR- the „Pusk razreshen“ command
T- end of interception, return to base,
OT- the „Otvorot“ –„break-away“ command
PD- radar range-finder malfunction
K- ASP self control system


The panel „Block24„

The switch “STROB/VYKL”. In the position “STROB”, target selection impulses (lines) for the RL are generated on the SEI. In the position “VYK”, target selection impulses (lines) for the IRST are generated.
The potentiometer “US T”: amplifies video-signal from the IRST, used when jamming is encountered.
The potentiometer “US ”: amplifies radar signal in the “BSV-delta H, MV” used when jamming is encountered.
The potentiometer switch “delta H”: antenna scan zone presets in elevation(+6km/-4km), The antenna scan zone/radar range-finder is also controlled through the potentiometer located on the „POM“ throttle
The joystick/switch “ZONA R ,STROB T, SBROS” controls radar scan zone in azimuth, controls target selection impulses (lines) for IRST in azimuth and elevation. The SBROS switch position is used to cancel the RL and the IRST lock.
The switch APKH/PPKH serves to switch-on the radar protective circuits against active/passive jamming.


The panel „Block75“

The Switch „VYKL, 3, 1, 2, 4“ is used to select the IR missile (R-13M, R-3S) carried on the pylon which locked-on the target. The pilot has to switch the proper position after the „PR“ command is shown on the SEI and pilot hears the beep tone.


The LITERA S-23 switch with positions 1,2,3,4 is located on the right vertical console. It is dedicated to switch one of four radar pulse repetition frequencies. During a formation flight by using radar modes the pilot has to switch one of the LITERA frequencies to prevent mutual radar interferences. In the MV radar mode the switch is deactivated. The switch also determines the total number of aircrafts operating in the group with radars activated.

The OKHLAZH RLS switch activates liquid cooling of the radar during ground tests. The switch should be OFF in the flight.

Detail description of the lookdown/shootdown capability of the S-23E.

1. When the MV radar mode has been selected, the returned signal is further processed in the Pulse-doppler channel of the Sapfir-23E. At first the signal is led to the linear receiver, where it is amplified and sorted out by the amplitude detector. Then it is routed to the 49 multi-channels Doppler filter (a comb filter), where the selection of moving target takes place.
The doppler shift of the radar is given by:

Fpd= Fd-nxFp =2x(Vr/c)xFo-nxFp

Fpd-doppler shift of pulse radar
Fd-doppler shift cw radar
c- speed of light
Vr-radial velocity component
Fo-source signal frequency of pulses
Fp-pulse repetition frequency
n-integer from 0 to infinite

If the pulse repetition frequency „Fp“and the source signal frequency „Fo“ is constant, the amount of doppler shift depends only by the component of radial velocity. Considering that the radial velocity can change in a wide range, the doppler shift of the clutter (earth background) is taken as a reference (coherent) signal to process the doppler filtering. Therefore the filtering technique itself is called the „СДЦ (селекции движущихся целей с внешней когерентностью)“- The moving target selection with external coherence.

Then the doppler shift of the radar is given by:
Fdp=Fdc-Fdt-nxFp=2xFo/cx(Vrc-Vrt))-nxFp

Fdc- doppler shift of the clutter
Fdt- doppler shift of the target
Vrc- radial velocity of the clutter
Vrt- radial velocity of the target

There are operational limitations such as limitations upon altitude of use or so-called blind-speeds. To operate correctly the SDC with external coherence technique needs to synchronize the target signal with the clutter phase. To simplify this task, the clutter signal received by the radar sidelobes in the second/third scan cycle is used to process the doppler filter.
To deal with the “blind speeds” the radar is changing the pulse repetition frequency during each scan line. More than 90% of “blind speeds” are covered, what ensures sufficient target detection.

2. At higher altitudes the SDC with external coherence technique becomes ineffective, the radar uses the BSV-deltaH1 and the BSV-delta H4 mode. Both the BSV-deltaH modes use a technique called the Single-beam space-time selection. This filtering technique makes use of the difference between the spatial target location and the earth surface segment illuminated, which distances to the radar are the same. By utilizing the antenna high spatial selectivity it is possible to separate the target signal from the clutter. The advantages over the SDC with external coherence technique are no limitations in scanned sector and the target heading. Its disadvantage is the strong relationship between detection range and the target altitude. Lower target altitude means smaller detection range. The detection range equals:

D =k x Hc (km)

D- detection range
k- coefficient given by the antenna directivity pattern, characteristics of the surface background, target RCS and the surplus altitude over the target.
Hc- target altitude.

When illuminating the surface by a high directive antenna, the returned signal from the earth comes a bit later compared to the target signal. Then it is possible to separate the target signal from the clutter by using common methods of processing. The power of the clutter signal depends on the distance to the earth by a given antenna bearing as shown on the picture.

There are three specific regions.

-The first sector is evoked by the antenna sidelobes, which receive signals directly from beneath the plane. It is also here possible to separate the target signal from the clutter, because the target signal coming from the mainlobe uses to be stronger compared to the clutter signal coming from the sidelobes.
-In the second region the ground clutter can be filtered out easily, the power of the target signal greatly exceeds the clutter received by radar mainlobe.
-In the third region the ground clutter exceeds the target signal due to strong ground echoes received by the mainlobe. There is no possibility to detect the target signal.

The radar suffers from the clutter even more by illuminating the surface at very low elevation angles. Using of the high directive antenna will result in intense backscattering, the ground clutter increase in beam width. To filter the ground clutter the BSV- delta H1 mode uses the DKP „the differential clutter filter“ which processes the return signal further. The DKP filter operates only while the target is tracked in the BSV-delta H1 mode.

The S-23E cooling system

The high-power transmitters (klystron tubes) are cooled by “closed cycle” liquid system. The working temperature of the liquid “antifriz 65” is +55°C. The cooling system is engaged immediately after the radar is switched on. The front radar bay is cooled with “ram” air. The flow volume is 650-800kg/h. The air-cooling system maintains operating temperature of 55-60°C inside the radar bay. If the temperature exceeds limit, the cooling slots are closed.

Sapfir-23ML Radar

Again by mrdetonator

The fire control system of the Mig-23ML contains:
-the N003E coherent pulse Doppler multimode radar
-the analogue computer AVM-23
-the IRST TP-26Sh
-the HUD sight ASP-17MLE
-the gun camera PAU-473-5
Other system interconnections are: ARL-SML, SRZO-2M, SPO-10, A-031, SAU-23AM, SKV-2N-2M, DUA-M-1, DVS-7, DV-30, RSBN-6S, SO-69, weapon system with guided/unguided missiles/guns/bombs.

The fire control system/radar system ensures:

1. target acquisition in all-aspect at any weather condition, day/night
2. identification friend or foe
3. tracking of single target in head-on/pursuit, measuring range and angular position
4. all-aspect engagements of air targets at altitudes =>1.5 km with the R-23R and rear-aspect engagement with the R-23T,R-3S,R-13M,R-60. (Hc <>= Hs)
5. rear-aspect engagements of targets flying at low altitudes using the R-23T,R-3S,R-13M,R-60. (Hc > Hs)
6. rear-aspect engagements of small/big targets flying at low altitudes using the R-23R, R-23T,R-3S,R-13M,R-60. (Hc < Hs)
7. rear-aspect engagements of maneuvering targets using asynchronous aiming methods and gun weapons.
8. detection and engagements of low-speed targets
9. giving command signals to fire, end of intercept,......when manual/automatic(ARL-SM) flight controls.
10. giving command signals for ready/launch of R-23R,R-23T,R-3S,R-13M,R-60.
11. providing STT mode for the R-23R.
12. giving the range information to the ASP HUD-sight when gun firing at air targets.
13. giving the range information to the ASP HUD-sight when gun firing at ground targets and bombing.

(Hs- altitude of the Mig-23, Hc- target altitude)

The N-003E contains of 44 parts weighting total 475kg. Main parts:
Antenna : 56kg
Impulse transmitter: 98kg (klystron type tubes)
KNP transmitter: 48.5kg (providing STT for R-23R)
Parametric amplifier: 8kg
AVM-23 analogue computer : 8.2kg


Radar scan limits in azimuth: ±56º
Radar scan limits in elevation: +52º, -42º
Peak power: 40kW

Basic performance data of the N003E:

The radar detects targets at altitudes from 50 to 25000 m flying at speeds from 500 to 2500km/h.

The range in the “BSV” mode:

-search range against Tu-16 is 72km
-track range against Tu-16 is 52km
-search range against Mig-21 is 53km
-track range against Mig-21 is 35km

The range in the “MV” mode:

-search range against Tu-16 is 24km
-track range against Tu-16 is 14km
-search range against Mig-21 is 19km
-track range against Mig-21 is 10,5km

The range in the “BSV-delta H” mode (when Hs=2Hc):

-search range against Tu-16 flying at 2.5-5km is 54km
-track range against Tu-16 flying at 2.5-5km is 39.5km


Control panels in the cockpit:

The panel N003-34 contains.

The weapon system selector switch “SIST” with modes:

-RL (BSV, BSV - Delta H4, BSV - Delta H1, SMV, MV)
-BS (I BS, II BS, III BS)
-T (T I, T II, T III, T – Phi 0-I, T – Phi 0-II)
-NVG

The switch IZL-EKV-VYK, impulse transmitter (emit/equivalent/off)
The switch NAVED-AVT-RUCHN, the GCI datalink ARL-SML on/off
The switch MSKC-PPS-ZPS, low-speed target engagements/front/rear hemisphere
The switch PU-VYK, parametric amplifier ON-OFF

The modes BSV, BSV-delta H4, BSV-delta H1, SMV, MV are switched automatically according to aircraft altitude Hs (DV-30 barometric sensor) and the antenna position ”Delta H” switch. The modes I BS, II BS, III BS must be switched manually. When the switch NAVED AVT/RUCHN is set to AVT, the radar mode selection is done automatically by GCI command link (ARL-SML). The radar scan patterns under GCI are better optimized due to PPS/ZPS aspect. The one-way commands from GCI are displayed on special symbol indicator on the HUD sight. Pilot can interrupt the GCI anytime setting the switch to RUCHN.

The mode BSV for high/medium altitudes, all-aspect intercepts (Hc<>=Hs), pulse width ~4 µsec, PRF 1Khz, switching altitude Hs>4,5km, Beam width in search 2,5°. Scan patters depend on NAVED AVT/RUCH switch position. Beam width in STT 1.7°.

The modes BSV-delta H4, BSV-delta H1 for high/medium altitudes are useful for searching targets on earth background not using the Doppler shifts (MTI). For all-aspect intercepts, switching altitude is 4.5km>Hs>1,5km. It uses half/third PRF compared to BSV mode. The “differential compensator device” (DKP) filters false ground signals out. For greater search range the parametric amplifier can be switched on. The receiver sensitivity gains of 5-10% (dB/mW).

The modes BS (I BS, II BS, III BS) for high/medium altitudes are used for all-aspect intercepts (Hs<>=Hc) in case of false targets (clouds) and for picking up targets on earth background by using reference coherent signal received by radar side-lobes. The “III BS” mode has the largest search range of 65km, the “I BS” the smallest one of 27km. The most used mode is the “II BS” with 45km search range. The "III BS" mode works only as a search mode. The FFT Doppler filtering techniques are used to select moving targets flying on the earth background. The so-called “blind speeds” are overcome by changing PRF pulses during each scan line. More than 90% of “blind speeds” are covered, what ensures good MTI.

The mode SMV for medium/low altitudes, only rear-aspect intercepts (Hs<Hc), The switching altitude is Hs<1.5km, pulse width ~1 µsec, PRF 1Khz. The scan patters depend on NAVED AVT/RUCH switch position.

The mode MV is used to engage targets flying at low altitudes on the earth background. It is only for rear-aspect intercepts (Hs>Hc), The switching altitude Hs<1.5km, switch “Delta H”<0, pulse width ~1 µsec, Beam width in search 2,5°. The MV mode uses the MTI based on Doppler shifts.

The modes TP (T I, T II, T III, T-phi 0-I, T-phi 0-II) are used in case of radar damage, jamming or hidden approach. The device TP-26Sh is used for target searching/tracking. Leading the aircraft into the target area is done via ARL-SML/Voice commands.

The search scan pattern in mode “T I“ is 60º in azimuth and 15º in elevation.
The search scan pattern in mode “T II” is 15º in azimuth and 6º in elevation.
The mode “T III” is automatically switched if the target is acquired in the “T II” mode. The “T III” mode has different parameters (target selection impulses-lines) compared to T II/T I.
If the target is acquired by IRST, the N003E radar switches to quasi-search mode. The radar antenna is slaved to IRST sensor and is providing the data for the launch of R-23T. The HUD brightness (IRST signal) can be set via the “USIL T” switch.

The modes (T-phi 0-I, T-phi 0-II) are used when radar activity isn`t required. The R-23T missile seaker is slaved to the IRST.

The mode NVG is used for navigation flights under RSBN, or “return to base” commands (VOZVRAT). The HUD display is showing “K”(curse), “G”(inclination) symbols which the pilot has to follow.

The ARL-SML symbol indicator shows following commands on the “ASP17MLE”.

one-way command symbols:

PPS – front hemisphere intercept
100,60,30 – range to target
F – afterburner ignite
< - target on left
I – target straight
> - target on right
T – end of interception, return to base
G - the “Gorka” maneuver
! – target change
PD – radar ranger malfunction
K - ASP self control system

The last two symbols are not related to ARL-SML.

The panel S23ML-24

The switch “STROB/VYK”. In the position “STROB”, target selection impulses (lines) for the RL are generated. In the position “VYK”, target selection impulses (lines) for the IRST are generated.
The potentiometer “USIL T”: amplifies video-signal from the IRST,
The potentiometer “USIL R”: amplifies radar signal in the “BSV-delta H, MV” modes when the command “Pomekha” is present.
The switch “delta H”: antenna presets in elevation
The potentiometers/switch “UPR STROBA” controls RL scan zone in azimuth, controls target selection impulses (lines) for IRST. The SBROS switch position is used to cancel the RL and the IRST lock.
The switch APkh/PPkh:

N003E cooling system

The high-power transmitters (klystron tubes) are cooled by “closed cycle” liquid system. The working temperature of the liquid “antifriz 65” is +55°C. The cooling system is engaged immediately after the radar is switched on. The front radar bay is cooled with “ram” air. The flow volume is 650-800kg/h. The air-cooling system maintains operating temperature of 55-60°C inside the radar bay. If the temperature exceeds limit, the cooling slots are closed.


Schematic timeline in rear-aspect engagement under ARL-SML data-link.

1. Switching NAVED-AVT/RUCHN to AVT.
2. ARL-SML indicator shows “100”, HUD display shows search range scale “90”.
3. ARL-SML indicator shows “60”, HUD display shows search range scale “60”, AVM counts target range/closure rate according to ARL-SML information. Target range is on HUD.
4. ARL-SML indicator shows “36”, HUD display shows search range scale “30”, RL is engaged automatically in proper mode.
5. target searching and identification (IFF). 3-4 radar cycles
6. Lock-on 0.2-3.5sec. The AVM receives accurate data from RL.
7. “PODGOT” for missile ready, the radar switches to STT mode. The R-23R missile head seeker is tuned to the target signal.
8. HUD shows “PR”, fire, missile leaves the pylon.

Wow! Sapfir was coherent pulse-Doppler with look-down?!

I had no idea. It makes me wonder what, in the end, MiG-29's N-019 radar is for.

Thanks!

While it had a rudimentary lookdown capability, and used pulse-doppler techniques, it was quite a complex system, built with analogue processing. Detection range in lookdown mode was short, and the pilot had a multiplicity of modes to select to find the target. Some modes worked only in rear aspect engagements, or were search only. "MV" mode for low altitude lookdown locked the antenna in a fixed forward position, so you couldn't slew the radar left or right. A well-trained MiG-23 pilot, working with ground support, could do pretty well especially with an MLD, but the MiG-29;s N019 radar would make it so much easier for a rookie pilot.

Really, that's interesting... also from mrdetonator? Was he a former pilot or engineer?

I generally reserve the term "rudimentary" lookdown for non-coherent radars that base their MTI on envelope-detection interferometry techniques, as described in the Russian text:


...coherent pulse-Doppler is quite a technological leap forward IMHO - i.e. "Sapfir-E" seems to have a lot more in common with N-019 than with original "Sapfir" with which it shares the name, despite the differing user interface layout.

You're maybe familiar with this site? Some intresting extracts, apparently from a Russian air defense engineering textbook, including a general description of both coherent and non-coherent look-down modes:

the doppler shift of the clutter (earth background) is taken as a reference (coherent) signal to process the doppler filtering. Therefore the filtering technique itself is called the SDTs- The moving target selection with external coherence.

Click to expand...

From above. Sounds exactly like the technique described below;

3rd generation (1970 years) compose pulse BRLS, which ensure target detection, that fly against the background of the earth, with the attack by fighter from top to bottom. This problem for the first time was posed in our country, but the necessary scientific technical reserve was absent for its solution. The method of the selection of the moving purposes (SDTs) with the application of a external coherency of the signals reflected from the earth's surface and the moving purpose was selected as the basis of the solution. In the systems with the external coherency reference signal is created due to the reflexions of sounding pulses BRLS from the extensive local objects on the earth's surface. The signals from these objects reflected can n 3.… 80 dB exceed the level of internally-produced noise of receiver and mask useful signal.

To isolate target by the method SDTS is possible, when the signals reflected occupy one permitted pulse capacity and the radial velocity of purpose such, that the corresponding to it Doppler frequency not to the multiple frequency of the repetition of sounding pulses. The signal reflected from the target does not pulsate with the multiplicity of such frequencies and by hardware it is compensated as the coherent signal of a constant amplitude of reflections from the local objects on the earth's surface. The indistinguishability of purpose contribute also the instability of the work of equipment and the external reasons, connected with the fluctuation of amplitude and phase of the signal reflected.

For the realisation of this resolution OF NII RTNII - SCIENTIFIC RESEARCH INSTITUTE radio construction was preset the development BRLS “Sapfir-23” for the aircraft MiG-23 (chief designer Kunyavsky g. M.). After connexion to these work OF NII RTNII - SCIENTIFIC RESEARCH INSTITUTE instrument manufacture and creation in 1969 OF NPO “Phazotron” the chief designer OF BRLS “Sapfir-23” becomes Figurovsky Yu. n.

Fundamental difficulties in the creation of mode SDTS arose during the guaranty of the necessary level of noise of the transmitting device and dynamic range of receiving device. The first led to the appearance of the large number of false target blips, and the second coarsened sensitivity BRLS, that it did not make it possible to isolate the weak signals of the purpose of the against the background powerful signals, reflected from the earth.

Solution of these problems required the concentrations of the efforts of the specialists of many scientific and production organisations. To the development of system “Sapfir-23” is assigned the group of the specialists OF NII RTNII - SCIENTIFIC RESEARCH INSTITUTE instrument manufacture headed by by the deputy design project leader of association Grishin v. k., which together with the specialists OF NII RTNII - SCIENTIFIC RESEARCH INSTITUTE radio construction conducts performance and tests of this system. According to the results of tests is finished a large quantity of units BRLS of the, including transmitting and receiving channels. In 1976 g. the aircraft MiG-23 with the system “Sapfir-23” was accepted for the armament.

BRLS 3rd generation with the mode SDTs are executed on the semiconductors and the micromodules, in practise without the application of electron tubes; in them is realised the illumination of purpose by continuous emission for Doppler radar GSN, ensuring defeat of targets, which fly at the low altitudes (lower than the fighter). Furthermore, they joined through the systems of aircraft with the ground-based guidance systems and ensured capture and target tracking according to the data of ground-based ASU. This - BRLS of the development BY NII RTNII - SCIENTIFIC RESEARCH INSTITUTE of radio construction of the type “Sapfir-23” for the aircraft MiG-23 different modifications and “Sapfir-25” for the aircraft MiG-25

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Source:

• http://www.permag.perm.ru/real_brls.htm

Dilbert said:

Really, that's interesting... also from mrdetonator? Was he a former pilot or engineer?

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As a main source for the description above I used the radar technical manuals, so please make your own decision, and yes if it helps, I`m an engineer.

As I indicated above, I think both sources are saying the same thing.

I'm currently reading through Stimson's Introduction to Airborne Radar (2nd Edition) ebook to see if I can find some relavant information.

Page 204

In still another approach, called noncoherent or clutter-referenced moving target indication, the equivalent of coherence is achieved by detecting the “beat” between the target echoes and the simultaneously-received ground return. But as explained in page
24 in Chapter 2, this technique has serious limitations.

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Sources

• George W Stimson, Introduction to Airborne Radar (2nd Edition), Scitech 1998

Page 280

There are two basic approaches to implementation of MTI systems: (a) coherent MTI and (b) noncoherent MTI. The first provides better performance, but the second is simpler, using clutter to perform the same function as does the reference signal in coherent MTI. This is termed clutter-referenced or externally coherent MTI.

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Page 280-1

Clutter referenced MTI is “a type of noncoherent MTI that uses clutter as a reference.” Usually it is an adaptive MTI in which the average velocity of clutter surrounding the target cell is used to control the center velocity of the rejection notch.

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Page 282

In the conventional noncoherent MTI system, targets in range cells containing no clutter are lost for want of a phase
reference. Various clutter gating procedures are used to enable a normal video channel in such cells, bypassing the canceler to avoid loss of targets. A alternative noncoherent MTI detector uses the hard-limited output of adjacent cells as the reference to a phase detector, such that moving targets are detected in the absence of clutter through the random phase of noise in the reference cells.
Advantages of noncoherent MTI are simplicity and its inherently adaptation to moving clutter. Disadvantages are reduced improvement factor and inability of most types to operate in the absence of clutter.

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Source

• David K. Barton & Sergey A. Leonov, eds, Radar Technology Encyclopedia Artech House, 1998

Hats off to you, overscan!

What you found in Stimson is EXACTLY the problem I was having, and the reason why I was interested if mrdetonator was an engineer, and could maybe comment on this technical question...

It seems that what Russian engineers call "coherent", Western engineers specifically identify as "noncoherent"!! Can it really be true??

I could not have expressed it better myself - hence my surprise and confusion. I've never seen such an astonishing technical translation mix-up.

So, what's going on here? mrdetonator, can you comment? Sapfir-E is really coherent, or noncoherent after all?

As if we poor enthusiasts didn't have enough information/translation problems already, now this! Most upsetting!

Good gravy!

Hats off to you again, overscan... It seems that while writing my last post you went and confirmed everything.

Barton and Leonov must be an American and Russian author, respectively, who had this exact argument while preparing their book, hence the new definition "noncoherent MTI" = "externally coherent MTI". ???

What a mess.

Ok, at least I will personally continue to NOT call Sapfir-E a "coherent pulse-Doppler" radar, to keep from getting confused with N-019 capabilities.

Quite amazing. Fine research, thanks!

It depends from what angle you are approaching this from, after all the radar sapfir-23 acts as coherent pulse doppler, so the Soviets called it a coherent pulse doppler design, but how exactly they achieved that is a different thing.

Dilbert said:

Ok, at least I will personally continue to NOT call Sapfir-E a "coherent pulse-Doppler" radar, to keep from getting confused with N-019 capabilities.

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honestly that`s up to you. Yes, the N-019 differs a hell of a lot from the Sapfir familly radars, the N-019 is a true coherent pulse-Doppler radar. Hmm, I thought you already knew that...

The Sapfir-23 is generally a pulse radar that uses doppler processing of the signal. It uses "a method of moving target selection by external coherence", which is best described as clutter-referenced MTI rather than non-coherent MTI.

A true coherent pulse doppler radar produces identical trains of pulses, allowing you to process doppler information confident in the phase/frequency that the pulse was given by you. A Coherent-On-Recieve radar transmits varying pulses, but stores the information on the pulse so that on receiving the returning pulse it can be compared to the original transmitted pulse.

In contrast Sapfir-23 doesn't store the transmitted pulse information. Instead, it uses the clutter return as a reference signal.

To operate correctly the SDTs with external coherence technique needs to synchronize the target signal with the clutter phase. To simplify this task, the clutter signal received by the radar sidelobes in the second/third scan cycle is used to process the doppler filter.

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I think that the use of sidelobe clutter return means that, at low levels, the problem outlined above in the quotes (targets can only be detected in the presence of clutter) should not be an issue, as the sidelobes should always be generating some ground clutter.

It may be a matter of perspective, and in that case I'm probably biased by the Western definition, but as far as I understood, the whole point of "coherence" is to allow the integration of multiple pulses. This can only be done when the phase between one pulse and the next is an integer number of wavelengths (i.e. the Western definition of "coherence"). Does the Sapfir-E actually perform MPRF or HPRF (Medium- or High-Pulse Repetition Frequency) pulse integration? I don't understand how signals reflected from the ground can be argued to have the property of "coherence," when no such claim is made for the original transmitted pulses from the radar. ???

From my perspective, it seems there was a Soviet theft or convenient re-definition of the words "coherent pulse-Doppler look-down/shoot-down" to describe "whatever radar technology we have right now" in 1970s (perhaps to claim parity with the West in some kind of negotiations?), that required them to invent a new label for what the west calls "coherent pulse-Doppler" when they finally invented that, in the 1980s, with N-019. So, maybe this is where that strange Russian word "quazicontinuous" came from, that didn't appear in any English-language radar texts: Russian definition of "quazicontinuous" equals western definition of "coherent"?

"quazicontinuous" is best understood as "interrupted continuous wave".

I've never quite understood the difference between high prf pulse doppler with fm ranging and frequency modulated interrupted continuous wave. Aren't they basically the same thing?

overscan said:

"quazicontinuous" is best understood as "interrupted continuous wave".

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So is "coherence", by the western definition - in order for the pulse phase to be an integer number of wavelengths apart, it means that the pulses are simply on/off interruptions of a continuous wave. Hence my suspicion that Western "coherence" = Russian "quazicontinuous", rather than Russian "coherence".

I've never quite understood the difference between high prf pulse doppler with fm ranging and frequency modulated interrupted continuous wave. Aren't they basically the same thing?

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I came to the same conclusion.

overscan said:

To operate correctly the SDTs with external coherence technique needs to synchronize the target signal with the clutter phase. To simplify this task, the clutter signal received by the radar sidelobes in the second/third scan cycle is used to process the doppler filter.

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I think that the use of sidelobe clutter return means that, at low levels, the problem outlined above in the quotes (targets can only be detected in the presence of clutter) should not be an issue, as the sidelobes should always be generating some ground clutter.

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Wow, you're on a roll today! When I read that quote, I couldn't understand what it was saying at all. I think you're right.

So I think we've got somewhere.

The Sapfir-23 is a pulse radar, uses doppler processing, and uses an external method of obtaining coherence. Hence, you could, at a stretch, say is is a "coherent pulse doppler" radar without actually lying.

The Sapfir-23 was continuously developed, the later versions used greater numbers of doppler filters for better range accuracy, and introduced additional modes to pick out targets in different situations. Later versions are better in lookdown, but still not comparable to a true pulse-doppler radar.

The N-019 is a pulse-doppler radar with true internal coherence, and hence is an interrupted continuous wave ("quazicontinuous") radar.

Thus Lincoln Laboratory researchers attempted to make signals passing through the MTI canceler coherent by locking a coherent local oscillator (or COHO) to the phase of the return from a single range-gate sample of clutter. The COHO then ran at its own frequency until reset in phase by the clutter sample following the next transmission. This technique did not work well because of the finite width of the main-beam clutter spectrum. The COHO locked onto a spread of Doppler frequencies and produced ugly radial streaks on the PPI. A solution for the streaking problem was found by deriving the COHO phase from the average phase of a large number of clutter range elements. This technique, which became known as Time-Averaged Clutter-Coherent Airborne Radar (TACCAR), was conceived by one of the authors, Melvin Labitt

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A quick search founds dozens of PDFs about "TACCAR". I'm sure they might be illuminating. Its the basis of the original E-2 Hawkeye radar.

Source

• Muehe and Labitt Displaced-Phase-Center Antenna Technique Lincoln Laboratory Journal Volume 12, No. 2, 2000
  found online at http://www.ll.mit.edu/news/journal/pdf/vol12_no2/12_2displaced.pdf

Dilbert said:

From my perspective, it seems there was a Soviet theft or convenient re-definition of the words "coherent pulse-Doppler look-down/shoot-down" to describe "whatever radar technology we have right now" in 1970s (perhaps to claim parity with the West in some kind of negotiations?), that required them to invent a new label for what the west calls "coherent pulse-Doppler" when they finally invented that, in the 1980s, with N-019. So, maybe this is where that strange Russian word "quazicontinuous" came from, that didn't appear in any English-language radar texts: Russian definition of "quazicontinuous" equals western definition of "coherent"?

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I was thought that the "quasicontinuous wave" consists of pulses with high repetition frequency. So, at some aspect you can say the wave appears as a continuous but in real it is not, thus the word "quasi=nearly"continuous or in russian (Квазинепрерывный режим излучения-KNI). The Sapfir radar is thus quasicontinuous wave, a pulse radar with high repetition frequency, which at last enabled them to utilize various doppler filtering techniques.
The meaning of the word "coherence" is the same for both the east(russian) and west world, but in case of the Sapfir radar, the difference is here merely how/where the coherence is achieved.
Then the N-019 is a radar with quasicontinuous coherent wave or "true" coherent pulse doppler or "импульсно-допплеровские РЛС с квазинепрерывным излучением".....etc
Does it make sense to you at all, because sometimes I`m confused by your explanations....

mrdetonator said:

The meaning of the word "coherence" is the same for both the east(russian) and west world, but in case of the Sapfir radar, the difference is here merely how/where the coherence is achieved.

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From Stimson's "Introduction to Airborne Radar":

Coherence

By coherence is meant a consistency, or continuity, in the phase of a signal from one pulse to the next.

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Are you sure that this is the Russian definition of "coherence" also? How can reflections from the earth maintain the same phase from one pulse to the next? I would expect the ground clutter reflections to be filled with phase noise - i.e. to have completely random phase from one pulse to the next.

NOTE: I am not a radar engineer. This is my opinion

Given that the "MV" mode has a fixed, known scan pattern, the average phase of the ground clutter return will vary with the speed of the host aircraft. If you therefore take the average of a number of ground clutter returns over a reasonably short period of time, during which the velocity and altitude of the host aircraft can be regarded as constant, the average phase shift is likewise constant (hence 'time-averaged clutter coherent'). This defines a baseline "ground return" which you can compare to any individual returned pulse. A return from a moving target that is moving significantly differently from the ground will be a "spike" away from this 'average noise'.

Paul

P90

COHERENCE is the concept generally applied to harmonic oscillations:
u(t) = V0 sin(wt + y)
Two or more harmonic oscillations are termed coherent at the interval Tc if the phase shift between them is constant for the whole interval Tc. In radar, coherence is considered in a broader sense, and typically the signals are considered to be coherent if their phase structure is linked and the character of this linkage is known.

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Source:

• David K. Barton & Sergey A. Leonov, eds, Radar Technology Encyclopedia, Artech House, 1998

overscan said:

Given that the "MV" mode has a fixed, known scan pattern, the average phase of the ground clutter return will vary with the speed of the host aircraft.

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I think you might be confusing "phase" with "Doppler".

The Doppler frequency profile of the ground clutter will shift according to the speed of the host aircraft, yes.

"Phase" refers to something else. A 10 GHz radar signal like that of a fighter radar will pass through a full 360 degrees of phase in a space of only 3 centimeters - much, much smaller than the swath of earth being illuminated. The ground clutter signal will be the sum of reflected signals from many different points on the ground, and thus the phase of this combined reflected signal will be something totally random and unrelated to anything. To apply the word "coherent" to this signal makes about as much sense as saying white noise is "coherent" - you can say it, but it's meaningless, because then there doesn't anymore exist any signal in the universe that could be called NOT coherent.

And therein lies my objection. By the western definition, Stimson is able to provide concrete illustrative examples of two signals - one coherent, and one non-coherent, and all is understood by the comparison.

This is impossible for the Russian definition, because it says that all waves are coherent. Without an example of a non-coherent signal to compare against, the word "coherent" becomes devoid of meaning. It's like trying to draw a map of the continents, after you have redefined "land" to also include "water" - or, trying to see stars during the daytime, or a snowman in a blizzard... there's no contrast to separate one from the other.

In radar, coherence is considered in a broader sense, and typically the signals are considered to be coherent if their phase structure is linked and the character of this linkage is known.

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This is not a definition, it is a plea for acceptance, at best... or simply nonsense at worst. ("Character of the linkage of the phase structure" ???)

A plea that I must objectively refuse, until Leonov (or anyone who agrees with him) can give a counter-example: what is a non-coherent signal?

Any example he gives, I will be able to use his own definition against him, to prove that it's coherent, exactly as they have done with ground clutter - one of the noisiest, most random signals that could be imagined!

Of course you are completely innocent in this overscan, and I don't know what to say... As a self-professed electrical engineer, I feel shamed by this turn of events - that someone should open an Artech House textbook and find gibberish inside! Who are you supposed to believe now, an anonymous, faceless forum poster named after a cartoon character, to correct this mess?? It's a travesty. Bankers, lawyers, doctors, politicians, pilots, economists... these people can tell you hand-waving meaningless feel-good nonsense and I don't mind, that's life. But a degreed engineering professor writing a textbook?!? Champion of the one cold, hard, true mathematics that never lies?!? Is nothing sacred?!? I can't express the personal shame and humiliation I feel to be in any way associated with this - after all the times I encourage people to research, to read books, and now this. On behalf of my colleagues - I'm sorry. Really I am. :-[

I realised after reading back what I wrote that I was confusing frequency and phase.

However, how do you account for the Western use of "TACCAR" (Time-Averaged Clutter-Coherent Airborne Radar) to describe a clutter referenced MTI technique used on the E-2? In what way is it coherent?

TACCAR relies on a coherent local oscillator (COHO) as the reference signal. The signal from this oscillator must fully satisfy the western definition of "coherent" - maxima are separated by an integer number of wavelengths, with extremely low phase noise.

Does Sapfir-E have one of these as well? I thought that it was using the ground clutter reflection itself as the reference.

Sapfir-23 (Izdeliye 323)

From Phazotron museum, missiles.ru.

Nope, this is not a 323, this should be a Sapfir-23MLx Radar. The Sapfir-23DIII (item 323) or Sapfir-23E (323E) has the transmitter/receiver centered.
BTW, the yellow wave guide on top is part of the, so called, "compensation channel". Introduced with the RP-22 radar (MiG-21 variants and MiG-23MS) it was one step to reduced the minimal operational altitude from 1500m to 1000m (because of ground clutter). It was also used with the Sapfir-23. Normally extend above the fixed part of the radar antenna, except the Sapfir-23DIII and Sapfir-23E. There it is directed to the moveable part of the antenna. You can see it on the first picture of mrdetonator's description about the Sapfir-23E.
This channel was activated only in "SMV" radar mode (scan lines above horizont Hs < 1.5km).

Yes, you are correct.

Phazotron museum labelling sucks, apparently.

Seems to be a Sapfir-25 display

overscan said:

Yes, you are correct.

Phazotron museum labelling sucks, apparently.

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The picture doesn`t show the Sapfir-23MLx either. According to manuals both radars the 323E and the N-003 share the same design where the trasmitter/receiver waveguide is placed in the middle of the antenna.

Well- the Sapfir-25 definitely has the offset feed;


The antenna of the radar posted above looks just like the Sapfir-25, except smaller.

crossiathh said:

BTW, the yellow wave guide on top is part of the, so called, "compensation channel"... Normally extend above the fixed part of the radar antenna, except the Sapfir-23DIII and Sapfir-23E. There it is directed to the moveable part of the antenna.

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Got some new information. While with the rp-22 and the sapfir-23MLx the "compensation channel" is a receiver the Sapfir-23DIII/E has a transmitter with two emitter directed to the moveable reflector of the antenna.
@mrdetonator: Could you please double-check this.

After browsing through my archive I found a photo clearly showing this type of antenna mounted on czechoslovak Mig-23ML(variant A). Gentlemen, I give up..... :-[ :-[

Don't worry Martin- its enough to drive anyone mad!

I think on this occasion you were mistaken- that or the manual was wrong!

overscan said:

I think on this occasion you were mistaken- that or the manual was wrong!

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the document is not describing the antenna in detail, that`s all.

The Sapfir-23E uses the mono-pulse technique to track a single target.[

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If on picture Sapfir-23 in the description it is written that it has the latent conic scanning

@Vadifon

Could you please provide the picture with higher resolution which would makes it possible to read the descriptions?! Thanks.