SOS! Can somebody help?? Simulation on HFSS v9.1

leaky hfss

Hello! I am an HFSS v9.1 user and I face many problems. I have to simulate a leaky-wave antenna which consists of a rectangular waveguide and a stub waveguide wiht a smaller length above it. I have designed the geometry in terms of boxes united together and two tapers that connect the two boxes of different length. I have assigned the perfectH boundary to the surface indicating the apperture of the antenna (the top of the stub-waveguide). I have defined the small surfaces of the rectangular waveguide (the longer box at the bottom) as waveports. I have also designed a virtual box arround the geometry and I have assigned the radiation boundary to the surfaces of the box, to obtain the far field. Although I have worked really hard on it, neither the far field pattern nor the diagrams of the leaky constant and phase constant versus frequency are correct. Can somebody tell me what are the possible mistakes that I have made? I am really desperate and I would appreciate any help! (sorry for the long forum)

pml aperture antenna hfss

Hello !
plz look at PM.

hfss propagation constant wave port

is the sitimulation right,for, example,the input wave mode is the mode
that the leaky waveguide antenna works

virtual object hfss

At first, I want to thank you for your interest. In order that the leaky waveguide antenna works, the rectangular waveguide at the bottom is fed in its dominant mode.

pml with wave ports hfss

How to calculate "leaky constant and phase constant" in HFSS? I don't think this is possible with built-in post-processing tools. What you got is not the pattern for only "leaky wave".

calculation of phase constant from abcd parameter

Hello again. Thank you all for your replies. I post you the antenna structure in order to get a better idea of what it is all about (leaky-wave antenna geometry.rar). The red surfaces is where the aperture is supposed to be (the only reason why I created objects from those faces is to be able to assign color on them). The rest surfaces consist of metal.
I also post you what I have done in order to make it work (antenna leaky-wave.rar, project only-not results). As you see, I have created a virual object (box), after having copied the parts of the antenna body that overlapped with the box and having substracted them out from the box. I had read that the surfaces that would remain inside the box should be assigned with perfE boundary and the aperture with the perfH boundary. In order to assign boundaries to overlapping surfaces I had to create objects from these faces and then an intersection of them (according to the help menu). I was instructed lately that I shouldn't use the PerfH boundary for the aperture and that I should assign the PML boundary instead of the radiation boundary to the outer surfaces of the virtual object. I have tried it and the results were not correct, but this may be due to the fact that I am not familiar with the PML boundary and maybe I have not used them correctly.
Can you indicate any mistakes that I have made? I have noone else to help me here, since none of my collegues know HFSS. I appreciate any help, thank you!

who can help designing simulation

You described how the model is built. Could you tell us the main idea of your custom post-processing code from which the leaky constant and pahse constant are extracted? I haven't opened your attachments, because I am not in office and don't have HFSS handy.

From your desccription, I can see that your virtual box intersects with the antenna body. Consequently, portion of the metal structure penetrates into the PML media. This might not be a good idea, because the PML doesn't work well for evanescent waves and it is difficult to judge what is the spectrum of wave along the PML-cut-by-Antenna boudary. If possible, I would make the virtual box big enough so as to enclose the whole structure, including the waveguide feed. If not, I would plot the magnitude of the field along some surface near the problematic boundary. These fields should be much smaller than those on the opposite side of the virtual box. The latter is suppose to be the intended direction of radiation.

For the waveguide feed, did you pad it with a metal on the back (namely the feeding port is short circuit on the source side)? Did you plot field of the feeding mode, look at its phase constant/characteristic impedance to see if they agree with those of a rectangular waveguide? I am wondering if the fact that the waveguide feed is submerged in PML has an effect on the calculation of the feeding mode.

+ hfss waveguide antenna

Dear Loucy,
I just read your reply. In order to find the leakage and phase constant, I considered the sructure as a transmission line section and I defined the ABCD parameters which are related to the S parameters and the characteristic impedances Zo1, Zo2 (at each waveport) as well as to the propagation constant γ=α+βj. From this point I found the leakage constant α and the phase constant β multiplied by the total length of the structure l.
I had tried to make the virtual box include the whole geometry, but in order that the simulation is performed, the waveport should not be included in a structure. The feeding port is not short circuit on the source side.
I will also plot the field on the surface of the wave port, look the other characteristics on that face and compare them with the ones of a normal rectangular waveguide, as soon as I go home and work on my computer.
Thank you very much for your interest and the advice!!

pml boundary with port hfss

Hmm, I think the modeling of the feed might not be correct. Looks like at a significant portion of the feeding waveguide is enclosed by the PML. The feeding plane is also in the PML. I think a wave port in HFSS can only be applied correctly with a metal backing. An obvious reason is to send in a waveguide mode along only one direction (toward the aperture). It is not possible for the PML on the back to absorb all the energy guided toward it by the waveguide.

What is the reason for your statement that "the waveport should not be included in a structure"? This is simply not true. You can define a waveport inside a computation domain (the virtual box). And I think it is better to do so because any discontinuity close to the radiation boundary would increase the spatial bandwidth the fields on the radiation boundary (not so pure--Idealy, we should have only one local outward propagating plane wave).

Where did you get the design? Any reference discusing why it is a leaky wave antenna?

hfss evanescent

Dear Loucy,
thank you for your reply. I had tried to include a waveport in a structure, but a warning appears:"a port must have a non-existent material on one side". Only a lumped-port can be used in a structure. Do you think it would be appropriate? How can I apply a metal backing on a wave-port?
By the way, the characteristic impedance at the ports is exactly the same as the one of a normal waveguidebut the phase constant has no connection.
Concerning the design, my supervisor gave it to me and it is based on an article of IEEE where it is stated that it is a leaky-wave antenna. I appreciate any help, since I don't expect any help from anybody here.
Thank you in advance.

unassigned geometry in hfss

hello
i find your leaky wave antenna type, i have project about leaky wave antenna but not like yours, my project is a waveguide with a lot strips placed peiodicaly, i have the HFSS(i'm new user of this soft) but i can't resolve the problem can you help me please?.
thunks
Bob