Hello everyone, I'm having difficulty with the line input impedance of a patch antenna signal. It's showing s1,1 impedance of 117 ohms on the smith chart but the correct impedance should be 50 ohms, I am not able to lower the value to 50 ohms.
Meanwhile the return loss result of the antenna seems to look good but at the same time, the smith chart plot does not look so nice. Please see attached.
Could anyone suggest how the s1.1 impedance could be normalize to 50 ohms?
Thank you.
You probably have a 100 ohm input line. CST will reference the impedance to the impedance of the input port, if you use a waveguide port.
Thank you Malcolm White for your valuable input. Your answer will hopefully guide me to address the issue.
You say that the smith chart does not look nice, but this is not a bad smith chart plot. It shows the same as the reflection plot, but with added phase and/or distance data. Multiple loops round the centre usually mean that the reference plane is not where the reflection is coming from (except for multi-element filters). Offset the reflection plane and lots of the loops will unwind. The reference plane is at the port, the reflection is probably from where the feed-line meets the patch.
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