Waveports and discontinuities

[hfssnewbie]

Hi,

I am wondering what happens if you place a discontinuity too close to a waveport (say a 50 ohm stripline with a section with a differing trace impedance). This will generate reflections back to the port and I am wondering which reflections would be absorbed (terminated) by the waveport and which would be reflected.

Thanks in advance for your help!

[sjapollo]

If you place a discontinuity too close to a waveport, any reflections (in the form of fundamental and higher order modes) generated from that discontinuity will propagate back to the port. Any fundamental mode energy will be perfectly absorbed in the waveport. Any higher order modes that are not accounted for in the waveport, will be short-circuited, and reflected back into the model.

This is the reason why it is important to include a section of uniform transmission line with every waveport. The higher order modes will decay to a level such that any re-reflections will not affect the dominant mode. This extra length can be de-embedded during the solution.