CST Microwave 2010 warning： degenerated mode at port1 not considered in time domain

Hi guys, i am simulating broad band dual frequency microstrip antenna with fractal geometry using CST MICROWAVE STUDIO(2010), while simulating i am getting one warning that warning is "1 degenerated mode(s) at port1 is/are not considered in time domain calculation! it might be better to increase the number of modes at port1". I am using only one port and one mode. I tried with two modes also, but result is not coming, only straight line is coming. I changed the boundary conditions then also only straight line is coming. can any one help how to sort out this problem?
Thanks.

this would be better accomplish in sonnet

What type of port are you using? Coaxial probe, microstrip line?
I think it is quite likely that there is some mistake in the port geometry, because the dominant mode is not degenerate, neither for coaxial nor microstrip ports.

This is due to small size if port. Better you increase the port size... sure it work fine!

I think you are confused: The error message you describe means that your simulation disregards a few modes which do propagate in your simulated frequency range. So your simulation is not correct this way. Two solutions:
1. Reduce the frequency range
2. Increase the number of modes. Start with 40 e.g. and only calculate modes. Then count how many modes propagate.

Could you please clarify what you mean with "only straight line is coming"

Hi

If you're using waveguide port as excitation try to change port dimensions . Search "waveguide port overview" in help.

Hope that helps

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