S parameter changes with transmission line length

[mianjuyan]

Hi everyone,

I am doing some simulations with the four patch antenna array. I used lumped port. The port is connected to the probe by transmission line. And the patch is fed by probe. I already did the matching work. However, when the length of the transmission line changes, the results of S parameters also change. Is it normal? Or I make a mistake somewhere? Can someone help me?

 

[G4BCH]

Yes this is normal, the impedance as viewed on a smith chart will rotate round the center following the vswr circle repeating every 0.5 wavelengths.
Adding transmission lines of suitake impedance is commonly used for matching purposes.
Make you transmission line 0.5 wavelengths and the s paramters will return to the orignailly simulated values.
Peter