Discussion Forum

Port phase and orientation have basically nothing to do with setting the sign of the direction of the power flow, at least not directly. In most cases, a port is on a computational boundary (and deliberately so). If power is explicitly applied to such a port, it (usually) flows from the port into the computational volume (from outside to inside, so to speak), and that is usually what is desired. If no power is explicitly applied to that kind of port, then typically some power may flow into it from the computational volume (from inside to outside, so to speak), at least if there is some other source of power in the model. I use the RF module all the time, for many kinds of problems, and I pretty-much never attempt to explictly specify any "power flow direction" to my ports. Rather, I power them on or off; the power then flows out of them or into them (if power has a source elsewhere), appropriately. Of course, you may be working on a different class of RF problems than what I normally do. Or perhaps you are embedding your ports in your model, such that they are not on a computational boundary. If so, I suggest you post your .mph file to this forum, ideally along with some note(s) about exactly what port(s) you are trying to specify as having particular power directions, and which way you would like the powers to flow. Now, I can't be sure, but my best guess is that your model (if it is anything like my models) can also be formulated in a manner such that you don't ever need to actually specify any explicit power-flow direction.

p.s. Comsol 4.4 is old. A lot has changed. If you have any reasonable means of doing so, I encourage you to upgrade to a newer version.

Hi, Thank you for your detailed response. I am modelling a corrugated conical horn antenna as part of a interferometer model. Since I am beginner, I am simply following the steps in the existing model from the COMSOL 5.6 library. In this case, when I turn on the power the arrow actually points from the computational volume to outside of the port (oppsite of what is desired i.e. opposite of the arrow shown in page 12 of the attached pdf). I am not sure if the problem can be formulated without specifying a power flow direction. Please take a look at the pdf and let me what you think.

Thanks!

Ah of course, I should have guessed. You do have an interior port. And the Comsol example activates the "slit condition" on the port. That said, I usually don't bother with those or with interior ports at all. You can always put a small rectangle (in this 2D example) (subtracted from the problem space, so as to leave a small unmeshed hole there) where your port is, then your port will become an exterior port (surrounded by PECs, by default) and then you shouldn't need a slit condition there either. On the other hand, in the example you cited, there is a button that says "Toggle Power Flow Direction." So forget my advice and go ahead and click that... unless possibly you don't have that option in your old version 4.4?? In that case, I suggest you try what I described above.