Why the pitot tube of some fighters doesn't affect their radar?.

[Vanessa1402]

As far as I know, pitot tube made from metal like steel, it fully reflecting radar wave. So how can some fighters have their pitot tube right in front of their radar without totally ruined their radar performance?

 

[1635yankee]

More than one possibility:

1. It's located to minimize the effect on the radar
2. It's outside of the radar's normal field of view
3. It does have a negative effect, but the radar is so bad, who cares?
4. It's made of fiberglass and is transparent to radar.

 

[Vanessa1402]

More than one possibility:

1. It's located to minimize the effect on the radar
2. It's outside of the radar's normal field of view
3. It does have a negative effect, but the radar is so bad, who cares?
4. It's made of fiberglass and is transparent to radar.

1. it literally right in front of the radar
2. same as above
3. That could be true for Mig-21 but F-16 block 60 and Gripen E both have very good radar
4. Pitot tube must be heated to very high temperature to prevent icing, so it must be made from steel, even on stealth aircraft

 

[overscan (PaulMM)]

Correct design can minimise the effect, though obviously it is easier to not have to. Correct design could include shaping of the rear of the pitot and material treatments, but also suppression techniques in the radar design itself.

Radars have sidelobes, so you often get spurious returns from the sidelobes bouncing off things - that is why radars modern radars use a guard channel to suppress sidelobes.

Radars have a minimum range. With a pulse doppler radar, the bounced signal from a pitot tube would be ignored, as the pulses are encoded and you would know it was far too soon to be expecting a returned signal from a target -in fact you might still be transmitting and not even receiving at that time.

With a very simple pulse radar you typically send a pulse and wait for the time it takes to hit maximum range and return. By ignoring anything for a time period equal to a few dozens of meters distance, you would never see the bounce from the pitot tube.

 

[helmutkohl]

I'm wondering why most AESA equipped jets don't have pitot tubes
but the Gripen E retains it

 

[BLACK_MAMBA]

I'm wondering why most AESA equipped jets don't have pitot tubes
but the Gripen E retains it

Most AESA equipped jets started life without a pitot tube. Gripen didn't and Saab seems happy with measurements taken that way so why change?

 

[Ronny]

More than one possibility:

1. It's located to minimize the effect on the radar
2. It's outside of the radar's normal field of view
3. It does have a negative effect, but the radar is so bad, who cares?
4. It's made of fiberglass and is transparent to radar.

1. it literally right in front of the radar
2. same as above
3. That could be true for Mig-21 but F-16 block 60 and Gripen E both have very good radar
4. Pitot tube must be heated to very high temperature to prevent icing, so it must be made from steel, even on stealth aircraft

Pitot tube does affect the radar, on F-16 block 60, it was removed

 

[Dilandu]

Mainly because it so close, that echo from it came long before echo from any real target, and thus could be ignored easily.

 

[Dilandu]

Essentially (if I recall correctly) it was not a concern for early radars, because radio echo, reflected from Pitot tube - very close to radar itself - came while antenna was still transmitting, not recieving. So antenna just ignored it completely. By the time duplexer switched antenna into receiver mode, the echo from Pitot tube was long gone.

 

[TomcatViP]

Remember that a FBW aircraft like the F-16 will put a higher priority on good airstream sensing than slight degradations of its radar performances.

Then with AESA and narrow Beaming capability, the masked area behind the pitot tube might have become a luxury too great for the price to pay.

 

[siegecrossbow]

I'm wondering why most AESA equipped jets don't have pitot tubes
but the Gripen E retains it

So does F-16V.

 

[Ronny]

I'm wondering why most AESA equipped jets don't have pitot tubes
but the Gripen E retains it

So does F-16V.

F-16V is like a cheap upgrade for legacy F-16, it is not a redesign like F-16 E/F.

 

[helmutkohl]

I'm wondering why most AESA equipped jets don't have pitot tubes
but the Gripen E retains it

Most AESA equipped jets started life without a pitot tube. Gripen didn't and Saab seems happy with measurements taken that way so why change?

actually quite a few AESA jets of today started WITH a pitot tube before removing it in later variants that use AESA

MiG-29 to MiG-35
Flanker to Super Flanker
early F-16 vs F-16E
J-10A/B and J-10C
etc

 

[siegecrossbow]

I'm wondering why most AESA equipped jets don't have pitot tubes
but the Gripen E retains it

Most AESA equipped jets started life without a pitot tube. Gripen didn't and Saab seems happy with measurements taken that way so why change?

actually quite a few AESA jets of today started WITH a pitot tube before removing it in later variants that use AESA

MiG-29 to MiG-35
Flanker to Super Flanker
early F-16 vs F-16E
J-10A/B and J-10C
etc

J-10B production variant doesn't use nose pitot either.

 

[stealthflanker]

From what i understand, the effect of Pitot tube is on the radiation pattern of the antenna. Along with radome it will affect sidelobes and mainlobe of the antenna, in kind of negative way by make them somewhat larger. Such however were not of major importance back then.

But now there is increasing emphasis toward sidelobe controls and stealth. Obstruction and increase in sidelobes caused by pitot tube may no longer be tolerable, thus why it goes away.

 

[Dynoman]

Here is an answer from another blog:

"The F-16 radar is not a CW (constant wave) type of radar (like the old F-4 or FB-111 radar systems), but is a pulsed radar system. Instead of constantly broadcasting, and constantly receiving like a CW system, the APG-66 or APG-68 pulsed radar transmits for a very brief period, and then must stop all transmissions to listen for a radar return (like an echo) off of a target. If the radome has been properly designed and characterized, the pitot tube isn't "seen" as a target in front of the radar antenna. In fact, the radar cannot see targets too close to the nose of the aircraft anyway. Not only must the signal bounce back from a target to be seen, but the entire signal sent out must bounce back completely, from start to finish."

"The transmission pulse is indeed a very short burst (nano seconds), but it travels at the speed of light, (186,000 miles per second), and reflects almost as fast. The first part of the transmission, and actually all parts of the transmission are more than just a blast of raw RF (radio frequency) energy, and contain certain characteristics that the source radar will recognize. What's contained in the radar pulse are not common knowledge, and will stay that way here. But if something is too close to the transmitting antenna, the first part of the signal will reflect back while the radar is still transmitting, and not yet in the receive mode. Therefore, the first part of the radar pulse isn't seen by the receiver, and therefore it is not recognized as a good return from a real target."

"Side note: While this transmitting and receiving of the radar is taking place, an electrical signal is sent to one box on the F-16, called the IBU (Interference Blanking Unit). This IBU acts sort of like a signal traffic cop, to allow certain components to transmit, and others to receive, and some to do neither, for a brief period. This keeps each from interfering with the other system, and possibly "blinding" each other with RF energy. Imagine an ECM (electronic countermeasures) pod transmitting a whole lot of power to try and to jam a radar system, while at the same time other on-board sensors are in the receive mode. The sensors would "see" all this power and be blinded. Damage could be done, and systems could be smoked."

 

[Nik]

IIRC, back when the Rus 'Woodpecker' 'Over the Horizon' radar was spamming Ham frequencies, it was noted that each pulse was coded sufficiently different that multiple distance returns could be distinguished. Didn't have to wait for furthest possible return before transmitting another pulse...

Sorta 'pseudo-random' encoding, as no predictive algorithm could be found by Hams. And, believe me, from what several of my friends said about that [UNPRINTABLE] 'Woodpecker', a lot of work was done by the community to try to crack the sequence...

( If the US or eg GCHQ solved it, that remains their deep, dark, [CLASSIFIED] secret... )

But, 'Woodpecker' pulse timing, the repetition rate, was remarkably stable. So, a fast audio-gate with a phase-locked loop could effectively mute the interference, let Hams use their band again...