Yes, I think the AWGN technique gets used a lot, both with real hardware and with simulations (eg Matlab or Octave etc).
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I had a go at measuring the BFR91 preamp section on an old 26.5GHz Agilent PSA analyser today (with my HP 346A noise source) and it did a pretty good job across 2MHz to 20MHz, even with the internal HPAK preamp.? This is the only analyser I know of that has a chance of getting good results across this frequency range when using a 346A noise source with its low ENR of about 5dB. I think this particular analyser has an improved preamp in it compared to earlier models. However, the internal preamp only works up to about 3GHz. It offers a noise floor of about -170dBm/Hz down to a few MHz and I think it degrades to about -168dBm/Hz by about 1MHz. This is much better than any other HPAK analyser model that I know of. The input VSWR is quite good too at these frequencies.
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I haven't used any averaging for either the cal or the measurement and it has given a fairly flat result as expected. I don't actually know what the correct noise figure is for this preamp. The simulation predicted a flat 3.6dB noise figure to below 1MHz but it usually gives a result that is slightly low.
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I had to tweak my original ENR table at 2MHz to get a flat result at 2MHz though. I reduced it by 0.6dB. I also reduced the 3MHz entry by?about 0.3dB. This is in line with my earlier noise floor measurements using the RSA3408A. This gave a very pleasing result!
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However, I'll try and tweak the BFR91 preamp for best VSWR and then revisit this with a bit more time. I'll also use averaging and I'll accurately measure the small signal gain with a 2 port VNA (calibrated with an Ecal module).
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Although this result looks good, I don't think it's worth trying to use it below 2MHz with the 346A noise source as the ENR of this 346A really drops down quite quickly below 2MHz.
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My homebrew noise source using a Noisecom noise diode is probably more suitable for use below 2MHz as the diode is supposed to work down to 200kHz and HPAK suggest that the analyser can be used down to 200kHz in noise figure mode. I'm not convinced of this though. It will also take ages to do the measurement as it dynamically reduces the detection bandwidth for lower frequencies and this really slows it down.
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