100+ GHz Noise Sources
Which is the best factory that build noise source?
Russian or American?
To my knowledge, it is difficult to use avalanche diodes as noise sources above ~90 GHz. The ENR drops fast due to P/N junction reactance.
I have seen ELVA-1 Russian High Power W-band noise source; I think they use one or more special IMPATT diodes to generate a high noise power.
I have seen a paper in which the authors fed a standard avalanche diode with a normal DC Bias for avalanche breakdown, and added a RF injected signal at e.g. 50 GHz. Upon using a high-pass filter at output, they claimed to achieve a higher ENR at 100 GHz.
So far I know there is an UK company still making gas-discharge noise tubes up to 140 GHz. I wonder if there is any other method to generate a reasonable ENR for >90 GHz.
You may have to roll your own.
Have you thought about "upconverting" an existing noise source through a mixer?
You will possibly need to calibrate it NIST has published some work for this area,
http://tf.nist.gov/general/pdf/1801.pdf
Yes, I know several methods how to generate signals or noise at >90 GHz.
The problem is that by using multipliers (US Patent of 1993) or upconverters introduces many uncertainties and the resulting ENR is rarely as good as 13-15 dB used < 90 GHz.
We have used gas-discharge tubes with ENR ~ 15 dB for many years, but they are not too practical now. You need several kV to kick-on the tube, and several Watts to run it.
The people working in THz range use either frequency multipliers or beating two laser signals in a non-linear device. Both have a low efficiency and output power.
---------- Post added at 20:15 ---------- Previous post was at 20:09 ----------
To Lurchman:
I am afraid you have confused two quite different problems: we have discussed noise sources with ENR>13 dB suitable for >90 GHz noise measurement.
The NIST paper of 2002 refers to the correlation measurement of AM and PM noise in oscillators. This is completely different issue.
By the way, I invented the described correlation method in 1966 (M.S.thesis, CVUT, Prage, CZ) two years before Litton patented it in the U.S.
Jiripolivka,
I mentioned upconverting a noise source which can be done by beating an oscilator with your hot/cold nois source.
I further mentioned that there might be a need to calibrate it which is what the NISt paper is partly about (and the reason I remember the 1801 paper is the number is the same as an early CPU = worked on which was the only "space ready" one of it's time).
Now I don't know what method you use for calibrating a noise source when you have to "roll your own" equipment at a frequency above any available test equipment and I actually would be interested to know which method you would prefer.
But one method is using a linear downconverter and true RMS reading meter and direct comparison to a known source if you have one. But if you don't have a known source you have to know what your downconverter behaviour is for a sanity check and you have to be able in turn to measure such things as it's oscillator quality.
At Spacek Labs. we calibrate our noise sources and low-noise receivers up to 110 GHz using a liquid-nitrogen-cooled load. Such device radiates exactly 77 Kelvins as we live at the Pacific shore. I do not think there is a more accurate noise-temperature source.
With Sergio we were discussing the problem that >90 GHz, finding a noise source with ENR>10 dB (comparable to the old gas-discharge tubes) is difficult.
Upconverting lower-frequency noise spectrum is possible as well as frequency multipliers, but the stability of such ENR is a problem as well as achieving ENR >10 dB.
The 2002 IEEE paper by NIST authors refers to a completely different problem, measuring AM and PM noise in oscillators.