How to use wave ports within the model in HFSS?

wave ports can be used when you have two different medium on each side of port, when you need internal port inside model lump port is used, which ask for same medium on both side of port.

When I need to place a wave port inside a model I place a thin block of PEC directly behind the port so the excitation from the wave port is directed the desired direction.

Yes, but the PEC block will change the response for your structure because it will couple to things outside of it. You couldn't use something like this for ports inside of a structure that are very close together, like with multiple SMD pads on a circuit board. That would be a disaster.

My response was to a general question about how to use a wave port inside a model. I would not expect it to be useful in all situations and one has been pointed out where it may not be the best choice.

Going further, the impact of the cap could be changed by applying different boundary conditions.

I use wave ports when I am modeling feed structures that resemble coax, various stripline and microstrip constructs or waveguides. I often place ports inside a model, particularly when I want to ease the computational load and am not particularly concerned about the propagation inside the transmission line. The best choice for bond wires and pads on IC's are less clear, at least to me.

Azulykit:
Yes, I think this would probably work well as long as there is only one mode of propagation, evenescent modes die fairly quickly, and you use a BC that matches the mode of propagation at the frequency of interest. A TEM mode should work fine, but TE or other dispersive modes would only work over a fairly narrow band (how wide would depend on your error requirements and the degree to which the waveguide of interest is dispersive).

Also, I think you would still need to have the port well away from other electrically active structures in the analysis space, or undesired coupling from other structures may occur to the BC since this is a non-physical construction.

I think CST Microwave Studio allows you to use internal waveguide ports that include match to as many modes as desired. So they will terminate internal waveguide ports properly as part of the port structure. However, again, if the port is near other parts of a circuit or near areas of significant electrical potential or current, that port could couple, leading again to undesirable model effects for a non-physical arrangement.

According to the manual, wave ports have to be specified to object faces which
are exposed to the background or outer.

Probably you have to use lumped ports if you want to use a port within the 3D model

Hi jimguo,

The manual says that wave ports are usually assigned at the interface to the background, not that they must be assigned in that manner.

I have attached a simple model of an open ended waveguide illustrating this technique. You might want to review this model and my earlier comments as I have shown several of the features I mentioned.