Need more information about IFF transponder...

Hello,

I want to apply for a job but a prerequisite is to understand how to design an IFF transponder. Does anyone here can tell me where can I find more information about Identification Friend and Foe Transponder. Maybe some books from artech house (or some patent) explain how to design an IFF (at least a book who can give me an intermediate level in such field - the field of "How to design an IFF transponder and grasp a full understanding of what Identification Friend or Foe is ?" -
My background :
2 Bachelor's degree (Mathematics+Electrical engineering)
3 Master's degree (Mathematics(PDE)+physics(HF/Electromagnetism)+EE)
1 PhD --> about IFF transponder

Thanks for your help.

well, there are not many good resources on this kind of tech. however, this is considered the classic reference for this sort of thing:
search amazon for: 0890062927
that is the ISBN for an old book on IFF

here is the quick rundown of how a transponder works (pre year 2000):
the transponder receives an interrogation at 1030mhz that consists of a set of pulses, known as P1, P2, and P3. P1 and P3 (OOK modulated) which tell the transponder what mode it should reply with (1, 2, 3/A, or C). the spacing of the pulses is 3,5,8, and 21 micro seconds for respective modes. the P2 pulse, known as the suppression pulse, is used by the transponder to determine if it is in the main beam of the interrogation antenna or a side lobe. the P2 pulse is (usually) transmitted omnidirectionally. therefore, the relative power of the pulses will tell the transponder what lobe of the interrogating antenna it is looking at. if the power of P2 is greater than that of P1 and P3 then the transponder can assume it received a side-lobe interrogation (since the main lobe of the antenna will is certain to be much stronger than an omni antenna) and therefore not transmit a reply. this cuts down on what is known as FRUIT (friendly replies unsynchronized in time), which allows the interrogator to significantly reduce the amount of noise in the air.

once the transponder gets a non-suppressing interrogation, it will reply to one of the 4 SIF (selective interrogation feature) modes (1,2,3/A or C). modes 1,2, and 3/A are basically just a set of pulses (OOK modulated) at 1090mhz that indicate a code. Mode C is similar but the code represents altitude of the aircraft. civillian aircraft usually only use modes 3/A and C.

that is the basics of IFF, pre year 2000. ohh, and in the IFF real, Mode 3/A is usually just called Mode 3. it is called Mode A by air traffic control.

there is also Mode 4, which I can't tell you much about. you'll have to google that one.

now, in the last few years, Mode S ahas come onto the scene. Mode S is a much more advanced data link. basically, acts similar to the legacy modes but with much more data in both directions of the link. for example, the interrogation can now selectively interrogate aircraft based on their previously provided information (so called "roll calls") or it can do "all calls" which are similar to the SIF in that everyone replies who has not been suppressed. moreover, Mode-S has the ability to "squitter" replies. a squirter is a reply that was not solicited by an interrogation. a transponder can squitter it's GPS location so other aircraft and passive ground stations can track them. this helps with collision avoidance, since individual aircraft can see each other, instead of relying on a ATC tower to tell them who is out there.

I am not sure what resources will be available for Mode-S. you might be best off googling. ohh, yeah, Mode S is DPSK modulated (unlike the SIF OOK modulation).

There is also mode 5, but you'll have to google that.

on a side note, I found your post because I am actually trying to build a Mode S squitter receiver. maybe you can help me with that. I have a BSEE, but my specialty is more FPGAs, microcontrollers, and other embedded stuff. not so much in the RF realm. the ADS-B transmission(s) from a transponder are not encrypted, so any joe shmoe (like me) can track aircraft from our living rooms. one can buy COTS equipment to track them, but I wanted a weekend project. hopefully I can build this thing and get decent range out of it.

anyway, good luck.

Sorry for the delay, I'm always busy and thanks for your answer! Long time ago I was an ASIC/FPGA engineer (Altera), there aren't many jobs in this field in France. If you want to build a Mode S squitter receiver you should ask "satellite" (see thread about DRFM => https://www.edaboard.com/thread20757.html). He seems to be more reliable than me in this field of knowledge. You could certainly find more information in this book
158053743X (latest edition of this book here : Artech House -- High-Tech Books & Software for Engineers and Managers).

Good luck

Look for ICAO Annex 10.It describes all the details and standards concerning Mode A/C, Mode S and ADS-B transponders. If you have difficulty finding the document for free, I think I have some (maybe old) version of it.

Hello
Does anyone can tell me about how is iff antenna pattern in different modes?