FCR AN/APQ-153: Limitations / Capabilities

[NaCH]

Question, is a look down FCR?

 

 

What are the limitation at low level? because flying at low level I was able to pick target at less than 100 feet of ALT with no problems at a distance of more than 10nm.

 

Does the ground clutter affect the look down when flying at High altitude?

 

 

 

Is there any documentation that explain which of these capabilities and limitations are modeled ?

 

 

Thanks.

[NaCH]

Question, is a look down FCR?

 

 

What are the limitation at low level? because flying at low level I was able to pick target at less than 100 feet of ALT with no problems at a distance of more than 10nm.

 

Does the ground clutter affect the look down when flying at High altitude?

 

 

 

Is there any documentation that explain which of these capabilities and limitations are modeled ?

 

 

Thanks.

 

 

Anyone from Belsimtek has info on this?

At this moment the radar is able to see everything even when looking straight at the ground and doing a DG mode is able to pick perfectly the contact.

 

Not being a doppler radar is this and expected behavior ?

At less than 1000 FTs how is able to differentiate a echo from the ground of a valid echo?

[GGTharos]

It is a pulse doppler radar - also IIRC it's the AN/APQ-159, not 153, but I'll check to make sure.

 

Certainly ground clutter should interfere, that's shown in the -34 ... keep in mind that this is WIP, and some caveats may not be modeled.

 

https://en.wikipedia.org/wiki/AN/APQ-159

 

The planar antenna has some serious reduction in sidelobes, which reduces issues like low altitude self-jamming compared to a parabolic dish antenna.

[NaCH]

It is a pulse doppler radar - also IIRC it's the AN/APQ-159, not 153, but I'll check to make sure.

 

Certainly ground clutter should interfere, that's shown in the -34 ... keep in mind that this is WIP, and some caveats may not be modeled.

 

https://en.wikipedia.org/wiki/AN/APQ-159

 

The planar antenna has some serious reduction in sidelobes, which reduces issues like low altitude self-jamming compared to a parabolic dish antenna.

 

Thanks GG, I was not aware that is the 159 the one we have not to mention that is a doppler radar!

 

Thanks and any info will be most welcome.

[GGTharos]

No problem. It might just be a pulse radar, not doppler. Will find more info later. It's still an old radar so you might not be wrong to suspect its look-down performance.

Edited August 24, 2016 by GGTharos

[Ramsay]

What are the limitation at low level? because flying at low level I was able to pick target at less than 100 feet of ALT with no problems at a distance of more than 10nm.

 

Does the ground clutter affect the look down when flying at High altitude?

 

Is there any documentation that explain which of these capabilities and limitations are modeled ?

The radar fitted to the F-5E-3 is the AN/APQ-159 which was an upgrade

 

The APQ-159's primary upgrade was the addition of a new planar phased array antenna, replacing the -153's parabolic dish. This made the antenna smaller front-to-back and allowed it to be pointed to higher angles within the nose. It also greatly reduced the sidelobes, which improved gain and allowed the range to be greatly increased from the -153's roughly 10 nautical miles (19 km) to the -159's 20 nautical miles (37 km).

https://en.wikipedia.org/wiki/AN/APQ-159

 

However there is a NASA test report on the APQ-153 that will hopefully answer some of your questions.

 

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19750008534.pdf

 

The older radar detection range was tested against a co-altitude T-38 in 1974

• 20,000 ft AGL @ 8.7 nm
  
• 12,500 ft AGL @ 6 nm
  
• 2,500 ft AGL @ 2.5 nm
  

Perhaps we can double these for the APQ-159, perhaps not. At least it gives something to work from.

Edited August 25, 2016 by Ramsay

[IvanK]

Its Pulse only

[NaCH]

 

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19750008534.pdf

 

The older radar detection range was tested against a co-altitude T-38 in 1974

• 20,000 ft AGL @ 8.7 nm
  
• 12,500 ft AGL @ 6 nm
  
• 2,500 ft AGL @ 2.5 nm
  

Perhaps we can double these for the APQ-159, perhaps not. At least it gives something to work from.

 

Thanks! yes I'm reading the doc, 2.5 nm for a contact of the size of the F-4 or the F-104

below 2.500 ft.

 

LOW ALTITUDE 2500 FT ALT: 3NM DET, 2NM LOCK-ON

(F4 OR F-104 TARGET) 1000 FT ALT: DOGFIGHT LOCK-ON AT 2700 FT.

 

I think in DCS what we have is not modeled right, I will verify, also being pulse radar if you are nose down against the ground should be possible to acquire a target in DM / DG?

[GGTharos]

Maybe, but it shouldn't be easy in look down. It might depend on the relative distance the target and the ground from the radar.

 

However the new antenna should provide huge low altitude gains.

Edited August 25, 2016 by GGTharos

[Ramsay]

However the new antenna should provide huge low altitude gains.

The prototype flat plate antenna used with frequency agility (that later became the AN/APQ-159) did have 19% better range in the tests but I wouldn't call it huge by today's standards.

• 20,000 ft AGL @ 10.5 nm (+21%)
  
• 12,500 ft AGL @ 9 nm (+50%)
  
• 2,500 ft AGL @ 4.5 nm (+80%)
  

The gains at low/medium altitudes are larger but the distances were already reduced due to ground clutter.

 

The radar spec's AN/APQ-153 -> prototype

• parabola -> flat plate
  
• Gain 28 dB -> 29.5 dB
  
• Sidelobes -19 dB -> -24 dB
  
• Downlobe -28 dB -> -45 dB
  

 

How radar target area affects detection range

 

Typical frontal areas

2 m^2 T-38/F-5 ?

3 m^2 MiG-21

5 m^2 F-16 fighter

10 m^2 F-15/Su-27 fighter

100 m^2 bomber

 

RCS (dB) of the target

X m^2 = log(X) x 10 dB

 

EDIT: Formula is on page 139

http://calhoun.nps.edu/bitstream/handle/10945/37502/Fuhs_Radar_Cross_Section_1982.pdf

 

Known data (Flat plate Antenna)

 

T-38

2 m^2 = 3 dB

Detection range = 10.5 nm @ 20,000 ft

 

Estimated detection ranges @ 20,000 ft

 

MiG-21

3 m^2 = 5 dB

Detection range = (5dB/3dB)^(1/4) x 10.5 nm = 1.14 x 10.5 nm = 12 nm (+14%)

 

F-16

5 m^2 = 7 dB

Detection range = (7dB/3dB)^(1/4) x 10.5 nm = 1.24 x 10.5 nm = 13 nm (+24%)

 

F-15/Su-27

10 m^2 = 10 dB

Detection range = (10dB/3dB)^(1/4) x 10.5 nm = 1.35 x 10.5 = 14 nm (+35%)

 

Bomber

100 m^2 = 20 dB

Detection range = (20dB/3dB)^(1/4) x 10.5 nm = 1.61 x 10.5 = 17 nm (+61%)

 

Edited August 25, 2016 by Ramsay
Fix my maths in the spoiler