Narrow vs. Wide IF Bandwidth - How it Impacts Your VNA Measurements + Wave Winners

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Whenever you read about improving measurement accuracy and dynamic range, you’ll see a lot about IF bandwidth. But what exactly is IF bandwidth, and how does it affect your measurements? The textbook definition of IF bandwidth is the span of the center frequency of the intermediate frequency filter. Okay. So what does that actually mean? First, we have to talk about mixers. When you put two signals at different frequencies, f1 and f2, into a mixer, the output will be two more signals: one at a frequency of f1+f2 and one at a frequency of f1-f2. Here’s where it gets interesting. You can use a local oscillator as one of your mixer inputs to tune input frequencies to your desired output frequency. This output frequency is called the intermediate frequency, or IF. Those of you with a radio background are probably saying “this is just your standard superheterodyne receiver”. And you’re right. Network analyzer receivers operate in a very similar way to radio receivers. Modern network analyzers have very wide frequency ranges, like 100 kHz to 53 GHz on our new midrange network analyzers. It’s impossible for the instrument to actually analyze all of those frequencies, so the receivers convert the input, piece by piece, into the instrument’s intermediate frequency using the mixer. So on the block diagram we have a bandpass filter at the output of the mixer. This is our intermediate frequency, or IF, filter. When you change the IF bandwidth of your instrument, you’re changing the bandwidth of this filter. A wider IF bandwidth means bigger portions of your measurement sweep can be converted to the intermediate frequency, meaning your measurement is faster, but there is a tradeoff in accuracy. A narrow IF bandwidth means only small parts of your measurement are converted to the intermediate frequency. Analyzing smaller portions of the signal reduces noise and improves your dynamic range, at the cost of measurement speed. Let’s look at a visual example. When it comes to image processing, IF bandwidth is anal ... https://www.youtube.com/watch?v=fwSlFJPaDBE