Say goodbye to noise floors: how to boost your dynamic range on a VNA Sign up now for the Wave giveaway:
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Today's tip is all about how to increase the dynamic range of a network analyzer. The dynamic range is critical for making VNA measurements and getting your signals above the noise floor of your vector network analyzer.
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When you’re looking at network analyzers, dynamic range is always one of the most prominently featured specifications. But what actually is dynamic range, and what does it do for you?
The textbook definition of dynamic range is “the difference between the network analyzer receiver's maximum input power and the minimum measurable power”.
Okay.
So what does that actually mean? I’ll illustrate dynamic range conceptually, then we’ll see how that ties back to the network analyzer.
I have a message on two pages here, and I want to capture them both in a photo. If I do a fast shutter speed, the camera quickly takes in light then shuts. I’ve captured one page, but not the other. This is like if I’m able to see the high-power portions of a signal, but the low power portions are lost in the noise. I don’t have the dynamic range to see the whole signal.
Now if I make the shutter stay open longer, the camera takes in more light, giving me visibility into the darker, noisy regions. I can now see the full signal!
Looking at the pictures side by side, we can see the second one has better dynamic range because more of the subject is visible, from the bright areas to the darker areas.
Let’s apply this concept to a real network analyzer trace. Here we’re looking at the S21 trace of a bandpass filter. S21 means we’re measuring at port 2 what’s coming from port 1, so this trace shows us which frequencies get through the filter.
You’ll notice in the stopband, where the test signal does not pass through the filter, the trace is noisy. This part of the trace is called the noise floor. You can think of it as the dark part of the photos I took earlier. It’s the power level at which the network analyzer cannot distinguish the test signal from the noise. The noise floor is the lower bound of the dynamic range of this measurement.
In the passband, indicated by marker 1, our power level is -1.26 dB. So the dynamic range of this measurement is the difference between the maximum power and the noise floor, which comes out to 104.36 dB. So when you’re looking at network analyzer specifications, dynamic range tells you the power range over which you can accurately measure.
Just like improving dynamic range on a camera, there’s a few ways you can improve dynamic range on a network analyzer by reducing the noise.
Number one, you can increase the power of your signal. This will boost your signal away from the noise. This is a great method because you do not lose any measurement speed, but you have to be careful to stay within the power limits of your equipment.
If you can’t increase the signal power, the next best thing to try is to reduce the IF bandwidth. This will make your network analyzer process smaller chunks of the measurement. You’ll get a more accurate result, but the measurement will take longer.
Finally, you can use averaging to reduce noise. There’s two types of averaging – point and sweep. Point averaging measures each point a specified number of times and then moves to the next point. Sweep averaging takes a specified number of sweeps and averages the traces. Both give you the average of multiple measurements, which reduces the effects of random noise. The tradeoff of averaging is that it takes longer since you’re taking more measurements.
Thanks for watching and check back on the channel for more tech tips!
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