Hello QUCS developers

My name is Simon Svendsen and I am a antenna designer at Molex. I have been evaluating QUCS for 1 month to see if it could fulfill our needs when designing match circuits for our antenna solutions. The simulation modes I have used the most are S-parameter and AC, with Harmonic Balance used a few times.

Basically QUCS fulfills our needs in up to 90 % of the time and is a very useful tool for our kind of work. However I have experienced a few oddities with QUCS, which I will try to describe below, together with a feature wish list, which hopefully also could be beneficially for people not working with antennas.

Feature wish list:

  1. The possibility to change the working project directory, so that new projects created from QUCS can be saved in other locations that the default one (C:\Documents and Settings\”user name”\.qucs). Right now I have to manually move my projects, in explore, from this location on to a network drive. Since no automatically backup are performed on our c drives, we are not allowed to store work related data here, but have to use specific network drives.
  2. Real time tuning of components values. Similar to the feature in ADS where it is possible to change a component value while simulations are performed automatically.
  3. Install component libraries for vendors. Best solution would be if component libraries made for ADS could also be installed in QUCS. If this is not possible, then it could be useful to be able to define a user library based on s-parameter files of the specific components. Most of this is already possible by using the subcircuit file component, with the schematic file consisting of for example a 2 port s-parameter file component and two ports and where the circuit symbol have been changed to for example a capacitor. However, it is not possible to group these subcircuits in a user defined libraries, which could be very helpful when having defined maybe hundreds of different capacitors and inductors for different vendors this way.
  4. Export full s-parameter sets to touchstone format. When working with for example two antennas sharing the same volume, S11, S22 and S21 are very important for the design and it would be very helpful if full s-parameter sets could be exported, instead of only one curve at the time in CSV format.
  5. Export all values from a Tabular Diagram into a text file. I know that these values probably will be available in the dataset file. However, this is a big file and not always easy to find what you need.
  6. Setting the frequency span of a smith chart plot. It is possible to do this on Cartesian plots (change the limits on the x-axis) but not on smith chart plots, here you are stuck with the full sweep range.
  7. Put on markers on plots by entering the desired frequency or the possibility to change the frequency after a marker has been added to a curve. When working with smith charts it can be difficult to find a specific frequency point on a curve and when you can only set a marker by clicking on the curve, you have to use a lot of tries to get a marker at the desired frequency.
  8. The frequency text in Cartesian plots are always written in Hz and always aligned horizontally. This means that the frequency plot text (when simulating at GHz) will overlap unless a huge span is used in the axis limit definition. This problem could be solved if it was possible to write the frequency text in for example MHz of GHz and align the text vertically.

Assumed Bug list:

  1. Format error when exporting for example a log magnitude plot of S11 to a CSV file. The calculated log magnitude of S11 in dB are plotted correct in the Cartesian plot, however, when exported into a CSV file a format error occurs. Values between 0 and -1 are exported correct, while values lower than -1 is multiplied by 100 so that for example -1.21 dB is exported as -121 dB. The values in the dataset file are correct, so this error seems to be related to the CSV export function.
  2. Having defined my own component libraries by using subcircuits with different schematic files consisting of a 2 port s-parameter file, with circuit symbols drawn as different types of capacitors and inductors, an assumed error occurs in the follow situation. The text in the circuit symbols is defined in the cubcircuit properties as for example; display:yes, Name:GRM15 and Default:0.2 pF. The 2 port s-parameter component in the schematic is pointing to an s-parameter file representing a GRM15 capacitor from Murata with the value of 0.2 pF. When using this schematic in a subcircuit, the defined circuit symbol and text appears as expected. However, if I then later want to change the value of the capacitor to for example 0.3 pF, I reopen the subcircuit component and change the schematic file to the one representing a 0.3 pF capacitor. Now the subcircuit is pointing to a new and correct s-parameter file, the name of the subcircuit is updated to the correct text, but the default value is not changed, which in my case means that the capacitor value displayed on my schematic is still 0.2 pF even though the subcircuit is pointing to the s-parameter file that represents 0.3 pF capacitor. This means that I have to manually change this value in order to have the right value of the capacitor displayed. I would be very helpful is the default values of subcircuit was updated when changing the schematic file in the subcircuit.

This was all from me for now and I hope that you will consider to implement what I have listed above, whenever it fits into your time schedule. If you need a more detailed description of any of the items on my list, please do not hesitate to contact me, I will gladly help you as much as I can.






 


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