How to read a smith chart
Or is the issue just with the way that ADS plots S parameters? Would I expect the same plot on an actual VNA on the Smith chart display.īTW, I'm also including magnitude and phase charts of S11 to show that those reading are behaving as expected.
I figured that with S parameters being complex they would normally be plotted on the smith chart, but what I'm seeing doesn't seem to make sense to me. Or, is the Smith chart not appropriate for plotting S parameters? So what is the meaning of the S11 plot on the smith chart? I would expect it to show 0 at resonance. The Smith chart doesn't seem to show the same thing. The SWR circle contains all the possible combinations of resistance and. Another useful attribute of the Smith Chart is called a constant SWR circle. From here you can read the SWR for this load. Looking at the other graphs of S11 and S21, they seem to makes sense, where at 5GHz S21 goes to 0 dB and S11 goes to very low, meaning %100 of the signal from port 1 goes to port 2 as you would expect. Measure the distance of that line, then draw the same length line along the bot-tom SWR scale. In the Smith chart below, at resonance, 5GHz, it shows S11 as being ( 1 + i0 ). By my understanding at 5GHz, the input to the filer, S11 should be 0, with maybe a phase change, and also the reflection coefficient should be 0. My issue that I'm having is interpreting the Smith chart results. It's a simple band-pass, the resonates at 5GHz. To get the feel of it I used the circuit below as a test, and analyzed it. Just to get some practice I'm using Keysite ADS simulator.
HOW TO READ A SMITH CHART HOW TO
I'm trying to become reacquainted with microwave circuits and how to analyze them, especially with a VNA.