How does the Low Noise Amplifier (LNA) work?

VanMan

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I understand the basic concept of it (somewhat self explanatory), but how does this process work? Does it simply take a weaker signal and increase its strength while the signal is in route inside the horn enclosure along the way in traveling to being processed, or is the link far more complicated? Does it act as a basic preamp? What are the basic steps in order and how does it interact with other components in the unit? Did the LNA have to do with the decision for the M3 to have X on one horn and K/KA on the other, or is that more the oscillator and 'tube' design to reduce LO noise emitted?
 

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There are people on here that are far more qualified to answer your question than I am, but to give a super-simplified answer, yes, a LNA amplifies the signal. In the M3 platform I think it also serves to isolate the horn from the mixer, reducing LO leakage.

In RD designs that don't use LNAs, the incoming signal hits the mixer directly which mixes the LO signal with the incoming signal. The LO signal in the mixer is what causes leakage that sets off RDDs (and other RDs).
 

Nine_C1

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I understand the basic concept of it (somewhat self explanatory), but how does this process work? Does it simply take a weaker signal and increase its strength while the signal is in route inside the horn enclosure along the way in traveling to being processed, or is the link far more complicated? Does it act as a basic preamp? What are the basic steps in order and how does it interact with other components in the unit? Did the LNA have to do with the decision for the M3 to have X on one horn and K/KA on the other, or is that more the oscillator and 'tube' design to reduce LO noise emitted?

Insidercw3 could write a book on this but I'll give you the layman's version.

Yes, the LNA is simply a pre-amp with a eye towards keeping induced noise by the amp to a minimum. Hence the term Low Noise Amplifier.

LNAs have their pros and cons though. In a wideband application they tend to amplify broadband noise as well........so that is the primary reason for having two horns instead of one in the M3. Having just one LNA to cover all that bandwidth is not possible without sacrificing sensitivty.

Why Bel even uses LNAs is most likely due to the fact they are absolutely necessary to have a stealth superheterodyne detector. They act as a one way switch keeping the LO signals generated inside the detector from riding the microstrip out to the horn.

Also, as another aspect of the stealth design of the M3, the signal path from the horns microstrip connection to the mixers is a VERY long one! Too long for a conventional detector design in that long signal paths are very lossy. Normally you would want the mixer as close to the microstrip connection on the horn as possible. This is where the LNA performs another very important task.......it boosts the signal coming in off the horn for that long ride down to the mixers.
 

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Insidercw3 could write a book on this but I'll give you the layman's version.

Yes, the LNA is simply a pre-amp with a eye towards keeping induced noise by the amp to a minimum. Hence the term Low Noise Amplifier.

LNAs have their pros and cons though. In a wideband application they tend to amplify broadband noise as well........so that is the primary reason for having two horns instead of one in the M3. Having just one LNA to cover all that bandwidth is not possible without sacrificing sensitivty.

Why Bel even uses LNAs is most likely due to the fact they are absolutely necessary to have a stealth superheterodyne detector. They act as a one way switch keeping the LO signals generated inside the detector from riding the microstrip out to the horn.

Also, as another aspect of the stealth design of the M3, the signal path from the horns microstrip connection to the mixers is a VERY long one! Too long for a conventional detector design in that long signal paths are very lossy. Normally you would want the mixer as close to the microstrip connection on the horn as possible. This is where the LNA performs another very important task.......it boosts the signal coming in off the horn for that long ride down to the mixers.

So part of its reason is the elongated throat that the M3 has to prevent LO emissions from leaking out? How does this affect the M3 designs handling multiple signals at once or within a very short period of time?
 

Nine_C1

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So part of its reason is the elongated throat that the M3 has to prevent LO emissions from leaking out? How does this affect the M3 designs handling multiple signals at once or within a very short period of time?

Not at all.

Ummmm, well in a round about way I guess it does.

The Valentine uses an LNA on the X-Band circuit but not on the K/Ka circuit since it checks for mutliple responses when sweeping the K/Ka frequencies..........that is also why it is inherently faster than the M3/M4/S7 when sweeping the entire Ka frequency. It does not have to actually sweep the LO through the entire 2.6 GHZ bandwidth but rather just a portion of it since it can detect 2 or more specific frequencies for any given LO frequency. But that is also one reason why it does not use an LNA on that circuit either........again something to do with broadband noise.

But in any case, the longer signal path itself has no ill effect on response time or it's ability to detect multiple signals.
 

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Question(s): Do LNA's benefit detection of all radar sources overall?

Are they more specific to working better on one band vs another (Ka Vs. K)? Or is it manufacturer specific in how they decide to implement/configure LNA's in their RD's? Do the manufacturers have to decide a trade off of the use of LNA's as to tailoring them to focus more on one band over another?

TIA for any responses
 

Deacon

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Question(s): Do LNA's benefit detection of all radar sources overall?

Are they more specific to working better on one band vs another (Ka Vs. K)? Or is it manufacturer specific in how they decide to implement/configure LNA's in their RD's? Do the manufacturers have to decide a trade off of the use of LNA's as to tailoring them to focus more on one band over another?

TIA for any responses
An amplifier amplifies inputs. That’s all. Like anything else in life, there are variations in specified frequencies a given amplifier works on, and there are different styles and quality levels. You can get a cheap one or an expensive one, or one with a narrow frequency range or a wide frequency range. It’s just an amplifier.
 

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