MrWolf Posted August 5, 2024 Posted August 5, 2024 The antenna used by the IFF system is the forward array (most commonly known as the RADAR antenna). This means that the beam of the fwd array is what dictates what you are iluminating at the moment (RADAR signal, IFF signal or both). What we need to know if how the antenna array is distributed for each signal. An array with 3x3 aprertures could use the middle aperture for the IFF interrogation pulse and reply pulse TX/RX (respectively); the rest of the apertures for the RADAR signal. In that case (with simultaneous operation of RADAR and IFF) the IFF beam would be much more wider than the RADAR beam. A pretty standard microstrip aperture antenna has about ~120° Beamwidth (-3dB) E and H planes. The point is that it all matters on the antenna. The IFF signal it's not sent/received isotropically. So if the bogey aircraft is outside the beam of the IFF antenna then you shouldn't receive a reply. And the IFF antenna it's bound to the RADAR antenna (unless there's another array in the aircraft that I'm unaware). In civilian aviation it's called secondary radar because there's actually a second antenna (besides the one that belongs to the scanning radar, on the image the top one): In an aircraft there's only one main antenna ( not counting the comms, and navigation ones). You can convert one antenna in two either as explained above by subdividing the array or performing some kind of timing between the usage of the main antenna. Even in the civilian case, if the antenna is not moving and it isn't pointing at the aircraft neither the Primary Radar or the Secondary radar will get any return from the aircraft. So in conclusion this issue could be a bug or not. That depends on how the antenna works for the IFF in comparison to when it works as a RADAR. In either case this should be stated in the manual. For example: IFF has an effective beamwidth pointing at the LOS of the antenna dish of 120° (or 180° or 200°), at a given range.
CaptPickguard Posted August 6, 2024 Posted August 6, 2024 @MrWolf The Hornet actually doesn't utilize its radar antenna for IFF interrogation (aside from NCTR prints of course but that's not what we're talking about). It is a separate antenna array mounted on top of the nose (the bird slicers as many call them). You can read up on the APX-111 here: https://www.baesystems.com/en-media/uploadFile/20230124201524/1434555671810.pdf I appreciate the contribution to this thread, but since the CIT is its own thing and not bound to the radar in any way, just like on the F-16 which is behaving correctly in DCS (https://www.baesystems.com/en-media/uploadFile/20210404040301/1434555677018.pdf), it just doesn't hold up. 1
MrWolf Posted August 7, 2024 Posted August 7, 2024 On 8/6/2024 at 10:20 PM, CaptPickguard said: @MrWolf The Hornet actually doesn't utilize its radar antenna for IFF interrogation (aside from NCTR prints of course but that's not what we're talking about). It is a separate antenna array mounted on top of the nose (the bird slicers as many call them). You can read up on the APX-111 here: https://www.baesystems.com/en-media/uploadFile/20230124201524/1434555671810.pdf I appreciate the contribution to this thread, but since the CIT is its own thing and not bound to the radar in any way, just like on the F-16 which is behaving correctly in DCS (https://www.baesystems.com/en-media/uploadFile/20210404040301/1434555677018.pdf), it just doesn't hold up. Alright didn't know the hornet had a separate antenna for the IFF transciever. Then the whole point is clear. The implementation is wrong because it's linked to the radar antenna. All my comments on this thread were because I thought the IFF system used the radar antenna. I don't know why this is not fixed then... 2
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