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[SOLVED] Something is wrong with my antenna simulation

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elanus

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Hi guys.

I was trying to simulate a rectangular fractal dielectric antenna in cst microwave studio, and i hit a bummer:

Simulation just keeps going on and on and on, and i don't think it should act like this. I need to get some farfields simulation, but when i select it, it says "result unavailable".

I have to apply a coaxial probe, and i did it, on the right side of the fractal geometry, but i somehow get the feeling i did something wrong. (do i need to place a coaxial probe in the center of the fractal shape ?).

Please help, as i am new to this, and i can't figure it out :(

Thanks.
 

Hi,dude
once check ur design,it may consits some discontinuities.If it is gud then let simulation take for 1 time and wen it is going for 2nd,abort it u can c the results.r u using student version or scholar version ????
 

I tend to think it is scholar version.

I've let it run for a couple of hours, and it keesp "solving". Indeed, the 1D representation modify, but what i need - farfields - are nowhere to be found (still unavailable). It should work. There are no discontinuities in the design, but i think there is something wrong with the coaxial probe. Can you (or anyone) explain to me how it should be placed ? T

Thanks!
 

Have you set your background material to "Normal", cause sometimes the standard setting is PEC.

Have you set a Far-File monitor?

I think even with a wrong feed you should be able to view the farfield plot, however the farfields would than look strange.
 

I did set the background material as normal, and i "extended" the background at a negative height and made it as PEC. so that is correct (i think). I did set a monitor.

I managed to get some farfield simulations, but i don't think they are correct, plus i only seem to get a 2D simulation around the port. The antenna does nothing. That's why I think I placed the feed wrong. But a new question arises: if I placed the feed wrong, supposedly I have to place it in the center of the fractal geometry. Now, does the feed (which is a cylinder) need to pass through the background AND the fractal shape ? or only through the background, and only "meet" the fractal shape ?

Please advise. Thanks !
 

For an antenna simulation the background material have to be normal. PEC background material reflect the waves.

Can you post a picture of your antenna?
 

i must say: green is normal material, grey is PEC, fractal shape also PEC

https://i262.photobucket.com/albums/ii115/elanu/front.png - front
https://i262.photobucket.com/albums/ii115/elanu/back.jpg - back (feed)

Another problem I seem to have is the farfield, which looks like this:
https://i262.photobucket.com/albums/ii115/elanu/field.jpg

I heard the field should look more like a ... tunnel/half a donut ? :)

My S param in dB, looks even worse:
https://i262.photobucket.com/albums/ii115/elanu/params.jpg

it should be around -40 or so ?

I have these design parameters, and i am not sure I entered them properly:
- dielectric permitivity 60, which i entered in the epsilon field when i defined material.
- stationary wave coef <=1.5, which i defined in the mue field (i think this is wrong)
- entry impedance 50 ohms, i defined when i started solver
- i picked a central freq. of 2.5 GHz, thus i set f min 2GHz, and f max 3GHz, but somehow i got the feeling that my bandwidth is wrong, or i didn't set it.

Thanks a lot !
 

Can you check the settings in Solve->Background Material?

- dielectric permitivity 60, which i entered in the epsilon field when i defined material.
- stationary wave coef <=1.5, which i defined in the mue field (i think this is wrong)
Which material are you meaing?

What port are you using? Wavport or Lumpedport?

Am I right with the assumption that your antenna is made of one PEC block?
Are your sure about this?

You should set fmin always to 0.

Your farefiled looks bad, the should be in the region of zero or above, otherwise the structure isn't radiating.
 
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    elanus

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if i go to Solve->Background Material, epsilon and mue are both 1, but this is for the "material", not for PEC. I will set them for the "material" as epsilon 60, and mue-1.2. By "material" i mean the green one. Is that correct ?

what do you mean by "What port are you using? Wavport or Lumpedport?", I'm sorry, but i don't know :( I set the port the center of the coaxial feed, by that i mean the center of the lateral cylinder.

I thought that my structure isn't radiating, but how do I fix it? should i place the feed beneath the structure ?

My antenna is made from one PEC block. Yes, I am sure, i drew it, then i selected material as PEC. Was that wrong ?

Thanks for wasting your time with me. I really appreciate it!
 

You have to set for the Background Material epsilon and mue to 1. This simulates the vacuum in which your antenna radiates.
And under Boundary Conditions select "Open (add space) "

I'm not sure if that PEC block can act as an antenna - but I'm not familiar with fractal antennas so I can't help your here.
For example a patch antenna needs a metallic patch a dielectric spacer and metallic ground plane.

Did you define your port by two points or did you draw a rectangle?
 
Last edited:

One requirement in the design is: fractal rectangular dielectric resonator antenna. I followed a tutorial for a patch antenna, and they set the material as PEC as well. I guess the only difference should be the shape, right ? Thus, where they placed the cylinder, i placed my fractal shape.

What could be the reason why the fractal shape would not radiate ? I have to say that the feed doesn't touch the shape in any way. And i am using a dielectric space as well.

When i defined my port, I picked a face (the PEC core of the port) and i went to Solve->Waveguide Port.

I changed my Port to the whole feed, and I got this farfield:

https://i262.photobucket.com/albums/ii115/elanu/field2.jpg ---- dielectric material epsilon 60 and mue 1.2

The way i changed the port is that now it looks like this:
https://i262.photobucket.com/albums/ii115/elanu/port.jpg

before it didn't touch the PEC of the fractal.

However, i believe that my s param in dB still is wrong, it looks like this:
https://i262.photobucket.com/albums/ii115/elanu/params2.jpg
 

Ah ok, I have misinterpreted your pictures.

The radiation pattern looks better.

From the port picture it looks like that the port is beside your Fractal?
Can you try it with the port inside the fractal?

If this works you have to vary the port position. When the port position changes the impedance changes and so the S11 parameter.
You have to find the port position with an impedance near to 50 Ohm, or other expressed with a good S11 value.
The S11 is good if it is at the desired frequency in the region or below -10dB
 
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    elanus

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Yes, the port is besides the fractal.

So, if I understood you corectly, i have to variate the posistion of the port so that i get my S11 parameter somewhere below -10 dB ?

How do I find the port position near 50 Ohm ? I am asking this because i need to have the impedance around 50 Ohm, so this is very important.

Any idea how can i change the position of the port, without drawing it again ?

Also, if i have to draw it again, does the port need to "pass through" the fractal ? or it must "extend" from the other side until it "meets" the fractal ?

How do i set the band width, so that my frequency (2,5 GHz) is the central frequency ?

Thaks a lot !
 

At a normal patch antenna the S11 parameter is depended of the feed position.
The resonant frequency of a patch antenna is set by its dimensions.

The length of a patch antenna can be calculated with this calculator:
em: talk - Microstrip Patch Antenna Calculator
(They use an edge feed so you can't use the calculated Impedance, however the dimensions for the length are the same)
I think the dimension for your fractal should roughly be the same.

A normal patch antenna with an coaxial feed is build the like the picture under Coaxial Cable or Probe Feed in Antenna-Theory.com - Rectangular Microstrip (Patch) Antenna - Feeding Methods
so I assume the port must be extended from the other side until it meets the fractal.

I don't know how to calculate the best port position but as a starting point it could be on the symmetry axes.

Perhaps you could find in this forum or elsewhere in the net formulas for the calculation of the patch size and feed point, an eventually there are formulas for a fractal.

---------- Post added at 16:59 ---------- Previous post was at 16:56 ----------

For varying the port position you could use parameter when building the port (or transform/move the port with parameter) for example port_x and port_y. With the parameter you could do a parametric sweep or an optimization (if your software can do this)
 
Thank you so very much ! :p

I hope this will be it !

I will post later when i'll be able to make the adjustments.

Again, thank you a lot!
 

wow it took me a while to check back.

It seems i have another problem: i have to raise the frequency at 9,75 GHz, and now i have no idea how to do that. I had to mofify the feed to get 50 Ohms impedance. The problem is that i have a bandwidth of 9.5 - 10 GHz, so that makes my resonant frequency somewhere around 9.75 GHz.

How do i calculate the final resonant frequency ? as i suppose the resonant frequency changes ass i increase the iteration in fractal geometry. Please help
Thanks

---------- Post added at 18:46 ---------- Previous post was at 18:46 ----------

wow it took me a while to check back.

It seems i have another problem: i have to raise the frequency at 9,75 GHz, and now i have no idea how to do that. I had to mofify the feed to get 50 Ohms impedance. The problem is that i have a bandwidth of 9.5 - 10 GHz, so that makes my resonant frequency somewhere around 9.75 GHz.

How do i calculate the final resonant frequency ? as i suppose the resonant frequency changes ass i increase the iteration in fractal geometry. Please help
Thanks
 

A very basic rule:
When you decrease the size of your antenna, the resonant frequency increases and vice versa.

Perhaps you can simple downscale your antenna?
 

i will try that :)

also, can the position of the feed modify the resonant frequency ? i've heard that it can, but not sure :p
 

Hello can u plz send me ur design.....i will c tat nd tell u....:)
 

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