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Utility / Re: Iranian Radar 11 meters 27 Sep 2013
« on: October 02, 2013, 2238 UTC »
No, completely unrelated. The one in Chris’s example is a traditional radar operating in the HF spectrum. A traditional radar transmits some kind of signal (there are many possible radar waveforms and techniques, although this radar, like most, uses only a few) and then listens for that signal to be reflected off a target. The transmitter used can either be co-located with the receiver (called a mono static system, such as a police officer’s radar gun or an NWS weather radar) or the transmitter and receiver can be geographically separated (called a bistatic system, like many HF radars, such as the British Chain Home system, the Russian Woodpecker, or the US AN/FPS-118 in Maine). It then processes and uses the reflected energy to detect whatever target parameters (range, bearing, elevation, altitude, size, speed, etc) it is capable of based on its specific design.
The system defined in that article is a “passive radar”. I have had many discussions of if such a system should be called radar at all, I say it should not (to me a radar has a transmitter, and passive radars do not have a specifically associated transmitter), but I am in a minority, so passive radar it is
A passive radar (not a new idea, been around a long time) works by using someone else’s transmitted signal as the source of energy, it does not have a transmitter of its own. The specific transmitter used will depend on the design of the system, but it can be many things. You could, for example, use the transmitted energy of FM broadcast radio, TV stations, cell phone towers, etc, etc.
So think of a passive radar as a bistatic radar (transmitter and receiver separately located) but the transmitted energy used might be energy of opportunity. So the passive radar might use the broadcasted energy of a TV station as its source. It then looks for reflected energy off of targets. Using a variety of techniques it either measures or calculates angle of arrival (direction) and motion. Using other techniques it might directly measure distance based on reflected energy from more than one transmitter or it might perform target motion analysis to determine position. So on and so forth (a complete description is probably beyond what should be in a thread like this, it can run to pages and pages of potential techniques…and still be incomplete).
Here is a similar application of the passive radar techniques. In this image I am using the transmitted energy of a TV station (Channel 7 out of LA). The ATSC pilot for this channel is a CW signal (and I mean CW as it applies to the rest of the world, not ham radio, CW means continuous wave, an unbroken carrier) transmitted at 174.310 MHz. I can look for the Doppler shift of this energy to detect things in motion. It just so happens that the location of the transmitter is pretty nice for me to get significant reflected energy off of aircraft in the LA basin. So, the “squiggly” lines on this picture are Doppler shifted energy from aircraft in and out of LAX. The ones slanting up to the right (bottom to top, left to right) are aircraft on departure, the ones slanting down to the right (top to bottom left to right) are on approach. The one almost straight up and down was probably something transiting across and above the LAX pattern (but that is just a guess). I am only pulling Doppler data, and that amounts to radial velocity in reference to the transmitter source, but with a bit more effort I could start to pull more information.
So, what are the advantages of a passive radar vs a “normal” radar?
A traditional radar radiates energy to operate, this means any time it is tracking you, you know it is on the air, and probably know if it is or could be tracking you. Think of a radar detector in your car, a similar system can be used to detect any radar, or even one system that can detect all radars. So, a passive radar can be tracking you and you have no idea it is doing so.
The radiated energy of a traditional radar also provides great targeting if you desire to remove that radar from operation. An ARM (Anti Radiation Missile) can literally ride the energy to its source and destroy the transmitter or transmit antenna, if not the entire system. The radiated energy can be used with detection systems and geolocation techniques to provide a point in space for delivery of munitions or sub-munitions…it can tell you were to drop a bomb or put cannon rounds, if you don’t have an ARM handy. A passive radar does not give away its position like that.
Passive radar systems can be smaller, lighter, more mobile / portable, and use less energy. The transmitter of a traditional radar is often a large part of its physical makeup. To handle the transmitted power it generally requires waveguide instead of coax (if higher than VHF), it requires more cooling to disepate the heat load of the transmitter, it requires a circulator or something along those lines to isolate the receive energy and path from the transmitter side, and it requires larger and heavier power supplies / sources since the transmitter almost always uses many times as much (often by orders of magnitude) primary power as the rest of the system does.
And passive radar often can have some counter-stealth applications that a traditional radar might not have. I will not go into them but a Google search (or your favorite search engine) of “bistatic radar and stealth” or “passive radar and stealth” will give some of the basics. Remember what I said above, a passive radar can be thought of as a bistatic radar.
T!
The system defined in that article is a “passive radar”. I have had many discussions of if such a system should be called radar at all, I say it should not (to me a radar has a transmitter, and passive radars do not have a specifically associated transmitter), but I am in a minority, so passive radar it is
A passive radar (not a new idea, been around a long time) works by using someone else’s transmitted signal as the source of energy, it does not have a transmitter of its own. The specific transmitter used will depend on the design of the system, but it can be many things. You could, for example, use the transmitted energy of FM broadcast radio, TV stations, cell phone towers, etc, etc.
So think of a passive radar as a bistatic radar (transmitter and receiver separately located) but the transmitted energy used might be energy of opportunity. So the passive radar might use the broadcasted energy of a TV station as its source. It then looks for reflected energy off of targets. Using a variety of techniques it either measures or calculates angle of arrival (direction) and motion. Using other techniques it might directly measure distance based on reflected energy from more than one transmitter or it might perform target motion analysis to determine position. So on and so forth (a complete description is probably beyond what should be in a thread like this, it can run to pages and pages of potential techniques…and still be incomplete).
Here is a similar application of the passive radar techniques. In this image I am using the transmitted energy of a TV station (Channel 7 out of LA). The ATSC pilot for this channel is a CW signal (and I mean CW as it applies to the rest of the world, not ham radio, CW means continuous wave, an unbroken carrier) transmitted at 174.310 MHz. I can look for the Doppler shift of this energy to detect things in motion. It just so happens that the location of the transmitter is pretty nice for me to get significant reflected energy off of aircraft in the LA basin. So, the “squiggly” lines on this picture are Doppler shifted energy from aircraft in and out of LAX. The ones slanting up to the right (bottom to top, left to right) are aircraft on departure, the ones slanting down to the right (top to bottom left to right) are on approach. The one almost straight up and down was probably something transiting across and above the LAX pattern (but that is just a guess). I am only pulling Doppler data, and that amounts to radial velocity in reference to the transmitter source, but with a bit more effort I could start to pull more information.
So, what are the advantages of a passive radar vs a “normal” radar?
A traditional radar radiates energy to operate, this means any time it is tracking you, you know it is on the air, and probably know if it is or could be tracking you. Think of a radar detector in your car, a similar system can be used to detect any radar, or even one system that can detect all radars. So, a passive radar can be tracking you and you have no idea it is doing so.
The radiated energy of a traditional radar also provides great targeting if you desire to remove that radar from operation. An ARM (Anti Radiation Missile) can literally ride the energy to its source and destroy the transmitter or transmit antenna, if not the entire system. The radiated energy can be used with detection systems and geolocation techniques to provide a point in space for delivery of munitions or sub-munitions…it can tell you were to drop a bomb or put cannon rounds, if you don’t have an ARM handy. A passive radar does not give away its position like that.
Passive radar systems can be smaller, lighter, more mobile / portable, and use less energy. The transmitter of a traditional radar is often a large part of its physical makeup. To handle the transmitted power it generally requires waveguide instead of coax (if higher than VHF), it requires more cooling to disepate the heat load of the transmitter, it requires a circulator or something along those lines to isolate the receive energy and path from the transmitter side, and it requires larger and heavier power supplies / sources since the transmitter almost always uses many times as much (often by orders of magnitude) primary power as the rest of the system does.
And passive radar often can have some counter-stealth applications that a traditional radar might not have. I will not go into them but a Google search (or your favorite search engine) of “bistatic radar and stealth” or “passive radar and stealth” will give some of the basics. Remember what I said above, a passive radar can be thought of as a bistatic radar.
T!
