problems of impedance in hfss
1 I am currently simulating a multi-band monopole antenna fed with a microstrip-line.In hfss ,i set the impedance of the lumped port placed at one end of the microstrip-line to be 50ohms.From the S11 plot i find two resonances at about 8GHz and 26GHz,but what i really want is a resonance appearing between these two resonances(about 16GHz).My question is if i did not set the lumped port with a right impedance ,some key resonances would disappear ?
2 Then i was suggested to change the impedance of the lumped port at the possible lost resonance point to simulate the S11,but what the impedance of the lumped port should be?Is there any method to obtain it?
3 how can i get the curve depicting impedance of the antenna versus Freq in my case ?then i can get the the impedance of the lumped port .another quetion is what is the difference between the impedance of the lumped port and the impedance of the antenn?
so many questions ! i know.but any help will be appretiated,thank you in advance,sincerely!
Hi,help me ,please.I will appreciate your help and indication.
Best regards!
Hello buddy!
You can construct a model of microstrip line and then make an air box to contain the line, note that, you should assign two wave ports on both sides of the microstrip line, the assign air box radiation boundary, when calculation is finished, you can plot Port(z0), it is the charactoristic impedance of the microstrip line. Just try it!
hope it helpful~!
Edmund
first thank you for your advice!
I have been advised not to set the wave port in the air box ,so here you advise to construct a model of microstrip line and then make an air box to contain the line and assign two wave ports on both sides of the microstrip line,i think the wave port will be in the air box , it would be incompatible!
another problem is as the wave port (rectangle) should be set enough big (often 4w and 5h) to get accurate results ,and at high freqenciy its λ/4 may be smaller than 4w or 5h , then how to solve it? enlarge the air box to more than λ/4 to slow the simulating speed?
the last question: can the wave port set on the sides of the air box?
so many questions ,too.any comment and help will be appreciated,yet.
Best regards!
Hello Sanders,
"I have been advised not to set the wave port in the air box ,so here you advise to construct a model of microstrip line and then make an air box to contain the line and assign two wave ports on both sides of the microstrip line,i think the wave port will be in the air box , it would be incompatible!"
If your waveport is inside the airbox, it is a problem but if the waveport is on the face of the airbox, it is not a problem although HFSS will give you a warning that they lie on each other..
The method suggested was the best to find the impedance of the transmission line. You could also use free software like Txline from AWR (if I'm not wrong) to get a very good approximation without EM simulating a transmission line.
To plot the impedance of the antenna w.r.t frequency, you can write an equation for the impedance as an output variable in your report.
I haven't worked with lumped ports a lot, so my comments about those may not be accurate. But wherever possible, I use waveports. In my opinion, tey give better results and more functionality for post processing too..
Let me know if you have problems after this..
Ananth.
Thank you!
Then how to write an equation to descripe the impedance of the antenna vs frequency,thank you !
another quetion: from which the S11 is obtained? Z:lumpport or the impedance of the antenna ?is there any difference between them?
Best regards!