IFF antennas location
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Dear all,
I am wondering about the IFF transponder / interrogator antenna location on the jet.
From what I understand, the IFF interrogator always transmits on +/- 60° vertical, the horizontal transmission depending on the request mode (LOS or SCAN mode).
In LOS mode, only 2 of the 4 antennas are used, the ones being the closest to the actual requested direction, correct ?So, to my question as I cannot find the answer from my research :
- Where are the interrogator antennas located ? Is it only the 4 bird slicers on the top of the nose ? How can they interrogate 60° down from that position ?
- Where are the transponder antennas located ?
Thank you Happy flying !
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I just found the answer, after posting the question (and searching for some time…)
The non-ADF F-16 aircraft use the AN/APX-101(V) IFF System, built by Northrop-Grumman (Litton). This system uses the combined UHF/IFF antenna system (upper UHF/IFF is visible atop the forward rudder island, and the lower UHF/IFF antenna is either under the intake on early F-16 blocks, or between the ventrals, near the tailhook on newer aircraft), to receive the interrogation query, and transmit the coded reply accordingly. The IFF LRU also integrates altitude data from the CADC (central air data computer) to send Mode C altitude information.
The ADF F-16 uses the BAE Systems AN/APX-113(V), with an interrogator, transponder, and cryptographic computer module. The antenna arrays (aka the “Bird Slicers) are electronically scanning elements, to determine bearing information of the target aircraft relative to the host.
Edit : so I guess the bird slicers have both roles of emitting the interrogation, and receiving the answer ? I see in the BAE PDF presentation that it has an Azimuth accuracy of +/-2° and a Range accuracy and resolution of <500 feet (152 meters).
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Totally different to my information.
APX-101(V) seems to be just a Transponder that most FMS F-16s had in the 1980s with associated aerials around the jet.
The F-16ADF had an older APX-109 AIFF combined Interrogator / Transponder which is the only system AFAIK that had 4 blades under the inlet as well as on the nose. (they are also raised)
The Later Blocks and MLU appear to have APX-113 AIFF (a modified APX-111)…combined F-16 Interrogator/Transponder this has only 4 bird slicers on the nose and a conformal lower antenna as described……there are other designations for combined F-16 Interrogator/Transponders out there also.
Tracking down the various other IFF aerials for the various models might take some doing let alone defining exactly what does what with public info.
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Totally different to my information.
APX-101(V) seems to be just a Transponder that most FMS F-16s had in the 1980s with associated aerials around the jet.
The F-16ADF had an older APX-109 AIFF combined Interrogator / Transponder which is the only system AFAIK that had 4 blades under the inlet as well as on the nose. (they are also raised)
The Later Blocks and MLU appear to have APX-113 AIFF (a modified APX-111)…combined F-16 Interrogator/Transponder this has only 4 bird slicers on the nose and a conformal lower antenna as described……there are other designations for combined F-16 Interrogator/Transponders out there also.
Tracking down the various other IFF aerials for the various models might take some doing let alone defining exactly what does what with public info.
+1 for the 101 & 113. I didnt know about the 109, good to know.
The transponder function is done with 2 blade antennas that are apparently shared with the UHF radio. They receive incoming interrogations and emit replies.
The interrogation is done with the bird slicers (which emits the interrogation and receives corresponding replies) and the conformal lower antenna (which helps with receiving replies).
BTW, AFAIK, all bird slicers emit when you interrogate. However, each one is phase-shifted a bit to provide electronic steering of the beam in azimuth, similar to an electronically scanned radar antenna.
As for the 60° coverage in elevation, I can only assume that with a bit of diffraction the beam does go lower than the nose.
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Thank you for the details guys ! This makes sense.
So the UHF antennas are responsible for receiving a request and replying to it.
The bird slicers and the conformal antenna are responsible for emitting a request (bird slicers only), and receiving the answer (bird slicers + conformal antenna).
As for the IFF variants, I did not go into those details, but I saw some pictures of bird slicers below the intake, which is an early version of the interrogator it seems.It seemed strange that the bird slicers could interrogate on +/- 60° vertical with their position, but I guess that the nose cone is also pretty permissible when it comes to RF emissions
l3crusader, you will have an MP in a couple of minutes