CST MWS boundary conditions problem?

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winsonwhy

Joined: 05 Jun 2009
Posts: 21

16 Jun 2009 15:13 frequency range lower limit cst

Hi everybody,

I'm new to this forum and also new to CST microwave studio. Just finish constructed a structure of an L-probe patch antenna (from IEEE paper) and just run the simulation by transient time solver, the curve of the return loss(S11) against frequency that i get is different from what showing on the IEEE paper, so is it the boundary condition setting will affect the simulation results? And actually what is the function of setting the boundary condition?

During the simulation, a warning message "some PEC material is touching the boundary" was show. After change the boundary condition setting to "open(add space)" then the warning will eliminate when run again the simulation. But the s11 curve still different from the "actual" results.

Anybody can help?
Any comments will be appreciate.

Thanks. Very Happy

ravi8331

Joined: 04 Jul 2008
Posts: 337
Helped: 95
Location: India

17 Jun 2009 4:43 boundary setting for cst simulation

plz upload ur structure with IEEE result...
then i will tell where is problem exist.....................

winsonwhy

Joined: 05 Jun 2009
Posts: 21

17 Jun 2009 17:57 boundary condition cst

Hi ravi,

I have bundle the related information into the .rar file and attached here.
It contain the .cst file and the paper also my simulation results which is a return loss plot.

Thanks in advance.

Sorry, but you need login in to view this attachment

smiling84

Joined: 03 Dec 2008
Posts: 14

24 Jun 2009 13:20 impedance set in cst mws

Hello
When I see your results, i observe that your antenna is de tuned. Have you followed the same boundary conditions which are mentioned in that paper?

winsonwhy

Joined: 05 Jun 2009
Posts: 21

24 Jun 2009 18:23 boundary conditions in cst

Hi,

Can i know what is means by "de tuned"? The paper does not give any setting about the boundary condition. But i think it should be set to open (add space), and set electric (et = 0) for the ground plane boundary.

Thanks.

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ravi8331

Joined: 04 Jul 2008
Posts: 337
Helped: 95
Location: India

25 Jun 2009 4:58 cst mws boundary condition

Hello Dear,
i think this structure is CST 2008 version and i m using 2006 so if u send me structure in 2006 version then i will try to improve ur result...........
thanx

winsonwhy

Joined: 05 Jun 2009
Posts: 21

25 Jun 2009 13:55 Re: CST MWS boundary conditions problem?

Hi,

My model is draw by using CST 2009. Actually after i going through some tuning on the dimension of some critical part for the model, now the results that i obtain is getting improved, and near the "actual" results. Almost ok. Anyway i'll try to get a CST 2006 if possible and post the model later. So is it any difference between the 2009 version and 2006 version, will the two version give different results? Very Happy

Regarding tuning of the model in cst, can i get some hints on using the "optimization" function for the transient time solver? It look like useful when we doing model tuning.

Thanks in advance.

ravi8331

Joined: 04 Jul 2008
Posts: 337
Helped: 95
Location: India

26 Jun 2009 6:11 Re: CST MWS boundary conditions problem?

yaa why not ..optimization tool is very useful when u don't have exact dimesions of ur structure like probe height or microstrip line length like that ..then u can firstly assign a simple unkonown like x or y and provide one value then perform simulation . after getting result then u go to transient solver tab and where go to optimization tab then new window appera where u directly see the parameter which u want to optimize in which term like s parameteer or VSWR or input impedance and then provide the condition upto which it can perform.........
then u get the optimize value of that parameter..........

winsonwhy

Joined: 05 Jun 2009
Posts: 21

27 Jun 2009 6:53 Re: CST MWS boundary conditions problem?

Hi,

Thanks giving the hints for using optimization. Look like useful, l'll try it out.
Hopefully can understand all the parameter and term inside the optimization function.

Winson

winsonwhy

Joined: 05 Jun 2009
Posts: 21

29 Jun 2009 20:21 Re: CST MWS boundary conditions problem?

Hi friends,

If i want to shift the resonance frequency to a lower level, say around 0.8GHz, so what are the critical dimensions of the antenna that i should change or vary?

Thanks

winsonwhy

Joined: 05 Jun 2009
Posts: 21

03 Jul 2009 8:08 Re: CST MWS boundary conditions problem?

Hello,

Just find some method to shift the resonance frequency of the antenna to lower level, it can be done by 2 ways, the first one is by using proper scaling like if you want to shift the resonant frequency from 3GHz to 1GHz then just simply calculated the scaling factor by 3GHz/1GHz = 3, that we have to enlarge the dimension of the antenna to approximately 3 time larger than the original size and we will get the same bandwidth at lower resonant frequency of 1GHz. Although this might not a best method but it is the fastest way to tune the resonant freq to low level but not so accurate from my little experience.

The second method that i found is by using equation from book, that is "speed of light = resonant frequency x lambda", just plug in the value for the C and resonant frequency, then we will able to get the value for lambda and the width of the antenna will be equal to lambda/2, then from here we can get our dimension for the low freq antenna.

Currently, the s11 results that i'm getting now is quite wide in bandwidth (as in high freq model) but still not very good in impedance matching i think, thus make the return loss value still less than 10dB, so might have to spend more time for tuning, hopefully can achieve a return loss of 30dB and over.

I have try to use the "optimization" function located in the transient time solver, but on the whole still not so sure how to use it, anybody can show some detail steps on using that function? say as an example optimize a parameter called "length" and achieve our target results in s11 plot say 30dB.

prafuldeo

Joined: 26 Mar 2008
Posts: 153
Helped: 10
Location: UK

03 Jul 2009 9:39 CST MWS boundary conditions problem?

Hello winsonwhy,
Optimization process is straight forward. I've seen your cst model. say you want to optimize a parameter patch width, so when you define patch give it a variable say 'a'. give the optimizer starting and finishing values of 'a' and it will calculate the optimized parameter.
Can you upload the IEEE paper for this model? I've seen that your model is bit different as you used air all the way, especially for port too. So I want to double check. Also for antenna simulations its good to keep all the boundries as open-add space and set accuracy for atleast -50 dB.
Hope it helps.
Regards
Praful

winsonwhy

Joined: 05 Jun 2009
Posts: 21

03 Jul 2009 20:29 Re: CST MWS boundary conditions problem?

Hi Praful,

Thanks for reply. Very Happy

So after i define the starting and finishing values of 'a', i should set the goal and start the optimizer but i still have some doubts about the goal setting, say if i want to optimize the parameter 'a' for achieve a s11 return loss of at least -30dB in resonant frequency of 0.85GHz, so i have choose type 'Mag. (dB)', operator '>', and target '30' with the frequency range set to 'total' like the screenshot that i attached below so is my setting correct? Or i have miss somethings important?

The model attached above is my earlier work, and at that time i was not so sure how to draw out the brick structure in certain Z value (height) so i just draw out the air and 'thick' patch then let them intersect in order to obtain a 'thin' patch and etc, so you see many of the air structure. Now i was no more using that method. Anyway i have attached also the IEEE paper.

Sorry, but you need login in to view this attachment

prafuldeo

Joined: 26 Mar 2008
Posts: 153
Helped: 10
Location: UK

06 Jul 2009 10:55 CST MWS boundary conditions problem?

Hi winsonwhy,
you can use < -30. If simulation time is resonable say 5-10 mins/simulation you can narrow the upper and lower limits of 'a' by doing 2-3 simulations around both the limits. This will decrease the optimization time significantly.

Regards