HFSS coaxial excitation outer conductor

coax port hfss

Hello to everybody,
does someone know how to define outer conductor of a coaxcable in HFSS 10?
I simulate patch antenna with coaxial excitation, probe = pec and dielectricum = teflon and it still works, but what about the coax outer conductor in my simulation. It's not necessery to define?
greetings
armant

coaxial port hfss

How far away from the ground plane are you injecting the signal? I usually define my wave port at the point where the coaxial cable meets the antenna. That way I can define my waveport vector as starting at the probe, through the teflon, and then to the groundplane directly.

If you have to propagate through a coax, then why not just define a hollow cylinder of PEC that will act as the outer conductor? Just make sure it is touching your ground plane.

conductor simulation using hfss

Sorry, I was wrong with my description, I meant coax pin = pec and dielectric of coaxcable = teflon. So I have coax cable with coax pin and dielectric (for feeding my patchantenna) but without outer conductor. But maybe the last part of your answer could be the solution?! ("If you have to propagate through a coax, then why not just define a hollow cylinder of PEC that will act as the outer conductor? Just make sure it is touching your ground plane.") I will try this but anyway I have the question, why does my simulation work with coax excitation even without any outer conductor? And will the use of a pec-outer-conductor influence my results in comparison to these without any outer conductor? Thank u very much for your answer.

coaxial exitation hfss

armant said:

why does my simulation work with coax excitation even without any outer conductor? And will the use of a pec-outer-conductor influence my results in comparison to these without any outer conductor?

Click to expand...

If you define your radiation boundary where your coaxial is outside the boundary, you don't need to define the outer conductor. This is because, HFSS covers the whole area with perfect conductor. In that case, the use of pec-outer-conductor does not influence your result.

However, if your coaxial is inside the radiation boundary, the wave propagating in your outer-conductor-less coaxial is not the fundamental mode of coaxial. It is more or less a guided wave over a dielectric. if you take a look at the port mode, you can understand that (No TEM occurs for such waveguide).

regards,
shameemkabir

defination explain what is coax conductor

I tried to do different simulations for coaxial feed.
I assigned Pef e to the outer face of the probe, with pin, without pin, only the face of pin, the results arent very different. Now I get it from the answers, I must assigne Pef e to the outer face of the coaxial part because of the outer metal grid.
And what about the wave port?
just drew the port at the end of the coax material. I difine the port line starting the center and to the end side of the coax. Is there any problem about my design? If you want to, I can send my simulation files.

hfss coax exitation

As shameemkabir was saying, if you have any propagation through the pin-with-teflon that lies inside the PEF, then you have to cover it with PEC.

If the pin-wth-teflon is outside the radiation boundary, then the PEC cover becomes implied.

So if you are placing the boundary at the outer face of the coax, then the length of coax that lies between the boundary and the antenna is not considered shielded. This is why I usually try to place my ports as close to the point where the signal gets injected to the actual antenna as possible.

If you post your file, I'll be glad to take a look at it.

coaxial excitation

Thank u guys,
first I post an image. So if my radiation boundary is including the substrate but not going beneath the substrate, then I don't need any outer conductor for my coaxcable, right? Another short question is, what means PEF? But the main questions are: If I want to extend the coax-pin up to the patch (like it's drawn in the image), an error message "coax-pin and air intersected" appears, Air means my Radiation Boundary. Up to now my my coax-pin ends up at the height where the substrate begins and I have a probe throughout the substrate which follows the coax-pin and ends up at the height of the patch. Is it possible, instead of the last sentence, to extend the Coax-pin up to the patch an then to define the probe not as a cylinder but as a circle at the height of the patch? What means probe? Do I really need it? Would it not be enough to contact the patch with the coax-pin by not using any probe? As u see, I have to concede that I'am a real beginner in HFSS ;-).

cylinder conductor hfss

To explain more exactly: In my simulation up to now the coax-pin is as long as T+height of the groundplane and the probe is as long as h=height of substrate, but I want to extend the coax-pin up to the patch...

hfss coax boundaries

although you are beginner of HFSS, you have very good sense of what you are doing. That's really great.

armant said:

Would it not be enough to contact the patch with the coax-pin by not using any probe?

Click to expand...

yes, you are right. In my view, the easiest way to simulate such kind of patch antenna is to extend the central conductor of coaxial until the patch (don't need any probe). Draw the airbox (radiation boundary) including the coaxial conductor (therefore starts from the other end of the coaxial). Use the waveguide port by drawing circle at the coaxial.

hfss, coaxial ports

armant said:

To explain more exactly: In my simulation up to now the coax-pin is as long as T+height of the groundplane and the probe is as long as h=height of substrate, but I want to extend the coax-pin up to the patch...

Click to expand...

Just use void in substrate at the dimension and location of your probe. it ll work

coax port in hfss

I have a question for armant and all of you. How can we find the T parameter (height of the coaxial)?It changes the resonant frequency, I tried lots of times. Is there any formulas or calculations for T?

have a question for armant and all of you. How can we find the T parameter (height of the coaxial)?It changes the resonant frequency, I tried lots of times. Is there any formulas or calculations for T
you can draw T=2h or T=3h
this is best propose for getting good answer