1. Aug 22, 2011

### johnsmi

Hi, I havn't posted for quite some time yet I have been reading through from time to time.

I would like to ask about Radars. I wish to be able to look at a radar antena and be able to say as possible. Such as frequency ranges from the antenna size etc...
Does the size of the 'Ball' in which it is in tell me anything?

Thank you,

P.S.
Can a radar detect friendly or foe according to some physical parameters?

2. Aug 22, 2011

### Floid

If you know the size and shape of the antenna you can guess at what frequency ranges the radar might operate. Of course if you knew enough about antennas to do this I doubt you would have asked this question.

Not sure what "ball" you are talking about. I guess you might mean the radome. You can't really tell anything from it.

"Can a radar detect friendly or foe according to some physical parameters?"

Sure, the easiest way is to keep track of the signatures of different objects for that particular object and check received patterns versus those signatures. There are other more advanced methods also.

3. Sep 13, 2011

### Bob_K

Ah yes, and I suspect that if Floid knows about the size of the antenna (expressed in wavelengths of course) he should also tell you that the "fingerprint" of a radar return from an object is quite complex and being able to "recognize" the target from the return (sometimes called non-cooperative target recognition), is more than just a little bit sporty! :-) On the other hand, a long time ago I learned to recognize aircraft, at least by type, fairly accurately using the headphones on a HAWK illumination radar! LOL!

4. Sep 13, 2011

### Integral

Staff Emeritus
All of our military planes are equiped with a IFF transponder. Our Radar systems have a IFF Transmitter/Reciver. When the planes IFF recieves a signal from a IFF transmitter, it sends a coded reply signal. If the radars IFF reciever gets the correct signal back it flags that plane as friendly, if not then it is NOT friendly. (IFF = Identification Friend or Foe.)

5. Sep 13, 2011

### AlephZero

Civilian aircraft have a similar transponder system, so air traffic control radars can indentify individual planes. In that case the ATC tells the flight crew by radio what ID number to use, since the numbers are only 4 digits long and obviously there are more than 9999 planes in the world!

This system also has emergency ID numbers meaning "the plane has been hijacked", etc.

6. Sep 15, 2011

### johnsmi

I would like to be able to look at an antenna and understand for example that if the antenna is a wire antenna then it is meant to be used for... as opposed to ring antennas, dish antennas or horn antennas.
And what can I tell from the location angle and size of the dish?
If the dish is simillar to a net what can I tell from the net resolution?
And why do some radar antennas (Navy normally) have a non circular dish with wires going only in one direction? (I guess it is because the sea is a polarier)
Here are a few examples:

And so on

7. Sep 15, 2011

### Floid

For the first two parabolic antennas:

Wire mesh is used instead of solid material to save weight/cost. As long as the spacing of the wire is less than about 1/10th of the wavelength the antenna is designed to handle then there isn't much difference functionally between the wire mesh design and a solid design.

For the last antenna what you really have is an array of dipole antennas. The most common configuration is a log-periodic antenna where each dipole's size varies so that one antenna array can efficiently handle a range of frequencies. In the picture you included it looks like each dipole is of the same size so not sure what the exact purpose is unless it used for some kind of phase detection (receiving) or increased output stength (transmitting assuming you can get the phases right).