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A spectrum analyzer for measuring linearity

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Wuerstchenhund:

--- Quote from: xzswq21 on March 26, 2021, 02:30:25 pm ---I have designed a new sensor in 2018 so I need to have a spectrum analyzer to measure the harmonics and noise of the sensor. Unfortunately I haven't accessed to a Spectrum Analyzer yet!

I apply 10KHz to my sensor and check the output response to measure HD2 (second harmonic distortion), HD3 (third harmonic distortion), THD then I will increase the input frequency upto 100MHz step by step (for example 100KHz, 200KHz, 300KHz,...., 1MHz,...) to plot HD2, HD3, THD over frequency axis, another test is only to plot magnitude of the bode plot of the sensors, this is all of I want :) finally I will publish the results in a journal.

I see most of good spectrum analyzers have Amplitude accuracy better than 1dB and it's very good for me, 90dBc/Hz of phase noise is very good, which spectrum is good for me? Old HP8560a, HP856x, E440x series or etc? Plus I've found HP3588a dynamic signal analyzer as an interesting choice:

https://accusrc.com/uploads/datasheets/4629_3588A.pdf

What do you think about HP3588a for my application?! HP8560 (a or e) or HP3588a?!
--- End quote ---

With that little information it's mostly up to what one can pull out of thin air.

First of all, you need to define what your requirements are. What's the frequency range that this sensor covers? What are the expected RF parameters (and have you confirmed them through simulation)? Because if you don't know how good the sensor is you don't know how good your test equipment must be, and then you're looking at big $$$ test equipment to find that out.

Also, since we're talking about some kind of sensor, have you considered the performance of the stimuli equipment and the impact it will have on your measurements?

Once it's clear what performance you expect from your UUT (and what limits there are because of your stimuli equipment) you can start narrowing down to suitable equipment that is good enough to confirm the UUT's RF performance.

Now, as far as test equipment is concerned, your budget is a very important factor. Because just buying some antique HP SA for a few bucks from ebay will not guarantee that you get the results you need. Test equipment ages, and pretty much everything which carries the HP label is now >23 years old and in many cases will have reached the limits of its service life. So instead of a functional test instrument you can rely on you might well end up with a project on its own (and fixing SAs is difficult if you don't have the equipment for it).

Lastly, since it seems you're mostly interested in THD, a THD analyzer might be a better alternative than a spectrum analyzer.

But first you need to do your homework and specify your requirements.

xzswq21:
I analyzed all the circuits in theory and then simulated and built the sensors. In simulation the SFDR is from 70dBc to 90dBc. the results are very good for my application. For example if the input signal is 0dB the second harmonic distortion is 80dB or 85dB or something similar (it depends on the frequency). One of my sensors covers from 10KHz to 50MHz but another sensor can cover from 10KHz to 100MHz and all the outputs are 50 Ohm, 1Vp-p and the SNR is from 75 to <87 (it depends on the bandwidth). now I want to measure the HD2, HD3, THD, AC response (magnitude of the bode plot) of my sensors.

srb1954:

--- Quote from: xzswq21 on March 26, 2021, 02:30:25 pm ---I analyzed all circuits in theory and then simulated and built the sensors. In simulation the SFDR is from 70dBc to 90dBc. the results are very good for my application. For example if the input signal is 0dB the second harmonic distortion is 80dB or 85dB or something similar (it depends on the frequency). One of my sensors covers from 10KHz to 50MHz but another sensor can cover from 10KHz to 100MHz and all the outputs are 50 Ohm, 1Vp-p and the SNR is from 75 to <87 (it depends on the bandwidth). now I want to measure the HD2, HD3, THD, AC response (magnitude of the bode plot) of my sensors.

I apply 10KHz to my sensor and check the output response to measure HD2 (second harmonic distortion), HD3 (third harmonic distortion), THD then I will increase the input frequency upto 100MHz step by step (for example 100KHz, 200KHz, 300KHz,...., 1MHz,...) to plot HD2, HD3, THD over frequency axis, another test is only to plot magnitude of the bode plot of the sensors, this is all of I want :) finally I will publish the results in a journal.

--- End quote ---
If you are applying an external excitation signal to your sensor you are going to need find a very clean signal source if you are hoping to measure distortion products below -80dBc for 100MHz signals. Ideally, your signal generator should have distortion products at least 10dB below than of the sensor under test for you to be able to have any confidence in the measured distortion figures of your sensor.

You might find the selection of a suitable signal generator a bigger problem than choosing a spectrum analyser.

SilverSolder:

--- Quote from: xzswq21 on March 29, 2021, 07:34:09 am ---I analyzed all circuits in theory and then simulated and built the sensors. In simulation the SFDR is from 70dBc to 90dBc. the results are very good for my application. For example if the input signal is 0dB the second harmonic distortion is 80dB or 85dB or something similar (it depends on the frequency). One of my sensors covers from 10KHz to 50MHz but another sensor can cover from 10KHz to 100MHz and all the outputs are 50 Ohm, 1Vp-p and the SNR is from 75 to <87 (it depends on the bandwidth). now I want to measure the HD2, HD3, THD, AC response (magnitude of the bode plot) of my sensors.

--- End quote ---

In theory, practice doesn't matter.  In practice, it does!

xzswq21:

--- Quote from: SilverSolder on March 29, 2021, 02:26:37 pm ---In theory, practice doesn't matter.  In practice, it does!

--- End quote ---

In practice I need a low distortion Spectrum Analyzer :)

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