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That´s because the filter is only transformed in frequency but not scaled in impedance. I didn´t do it because at that point I introduce the impedance inverter to make all the resonators shunt as in the first schematic I shared.
If you are interesting in the theory, I started with the method described in the chapter 8.3 in Microwave Engineering. This is Chebyshev filter of order 3 at fc = 1GHz and the LP prototype I used have the following elements:
g0 = g4 = 1
g1 = g3 = 0.8516
g2 = 1.1032
You can also find the table for frequency transformation in Table 8.6.
Both filter are actually the same in a different stage of the design.
The one in the bottom is the result of transforming the impedance inverters (2-port ABCD) into a pi network. The series element is a stub and the shunt elements are absorbed by the resonators at both sides. That´s why they resonator stubs are different in both circuits.
Anyway, the filter is well designed, I replicated everything in ADS and the results are what I expected, but not in QucsStudio. So, my conclusion is that I´m using the TL wrongly or the ideal model isn´t correct when it´s in series.
If you are interested in the original LC prototype, you can run the attached schematic.
Hi Carsten,
The simulation with series stubs is not accurate, the BW of the filter is too wide. For example, the simulation of both circuits with ADS shows a very similar results, see the figure below.
I can´t say much, but you can execute oct files by opening then and clink the simulation button.
Check the examples if you need some help: Examples – QucsStudio
I don’t know if this solve your problem but I have used the S-parameters files from commercial lumped components. Many companies have them available in their website, like coilcraft or Vishay.
You can use a n-port S-parameter file component in your schematic, load you file and change the symbol to capacitor or inductor.
I removed them already :). They appear from time to time, but in this ocassion the same user posted many times in a short period.
We are working on cleaning all the spam from the forum and we´ll try to delete the new unwanted post as soon they are published.
Every component except for OP1 in your sch has a parameter called “Temp”. You can create a variable to change the operating temperature by tunig, sweep or optimization. I´ve never use it, so I don´t know which is the performance will be affected.
I wouldn´t mind to collaborate.
Which´s the software development stage? Normally in Open Sourse you can get an idea but in the case of QucsStudio is more difficult to know. Please, don´t get me wrong, I like QucsStudio and I try to use it as an alternative to other commercial solutions but I´m willing to see which is the next step.
Hi,
I am an Ph.D. and RF engineer who is trying to move to open/free software for design and simulation. I find QucsStudio very interesting and I see it has potential. I would like to participate in teaching and problem solving to improve the software.
Please, contact me if you are interested.
Hi Carsten,
There is an indirect way to do it with Matlab or octave. You can generate a netlist from your schematic with Simulation\Show Last Netlist or shift+F5, and save the file as a txt document.
Then flowchart would be something like this:
- Load the file in Matlab or Octave
- Run the simulation with a for loop to go through the lookup table
- Modify the lines where the capacitor and resistor are to introduce the values you want in each step of the loop
- Read the ‘dat’ files with the S parameters from simulation
- Process data in a convenient way for you
I’ve done it in the past for other circuits and it works well. Find attached the matlab functions that will help you to run QucsStudio and read the S-parameters. I built them from the information I gathered time ago in this forum so I am not the original author, I just put the information together for my needs.
Remember to share the solution when you implement it 😀
