Why doesn't "design()" work the same way with all filter types in the RF PCB Toolbox?

I can use the design function with some filter types, such as with filterHairpin, as shown below:

>> f = design(filterHairpin, 915e6, "FBW", 20)
>> show(f)

But when I use it with other filter types, such as with filterInterdigital, I get an error message:

>> f = design(filterInterdigital, 915e6, "FBW", 20)
Incorrect number or types of inputs or outputs for function design. 
>> f = design(filterInterdigital, 915e6)
Incorrect number or types of inputs or outputs for function design. 

I have looked in the documentation for design, as well as in the documentation for the filters, and cannot find what number or types of inputs or outputs I need to get MATLAB to design a filter of these types for a given target frequency.

In fact, the only documentation I can find on the design function is here, and it does not provide any additional ideas about what else I need to provide. In fact, I only know about the "FBW" value because I saw it in some of the examples, but the examples don't use all the filter types. And when I look at the filter documentation, e.g. for filterInterdigital, it would be here, the word "design" doesn't even appear, nor is there any discussion of how to parameterize it for a call to design().

I can type out the function and press TAB to see what options there are:

I've tried permutations of those options, and can't get it to work.

What documentation am I missing, and what does it take to make this work? Is there some additional error logging I can get to find out what the error message is referring to? Are some rfpcbobjects just not designable?

Answer 1

[Altaïr]

Hey @Joshua,

The ‘design’ function supports creating hairpin, coupled line, and stepped impedance low pass filters. Correspondingly, the first argument to the ‘design’ function should be ‘filterHairpin’, ‘filterCoupledLine’ or ‘filterStepImpedanceLowPass’. Here are the documentation links for each type:

• Hairpin: https://www.mathworks.com/help/releases/R2024b/rfpcb/ref/filterhairpin.design.html
• Coupled line: https://www.mathworks.com/help/releases/R2024b/rfpcb/ref/filtercoupledline.design.html
• Stepped impedance low pass: https://www.mathworks.com/help/releases/R2024b/rfpcb/ref/filterstepimpedancelowpass.design.html

When attempting to design other types of filters using the‘design’ function, an error occurred: "Incorrect number or types of inputs or outputs for function design."

Hence, the unsupported ‘filterInterdigital’ type argument should have caused the error. For designing the unsupported filter types, like comb line, interdigital, and open-loop filter, the examples on this page, titled ‘RF PCB Filters and Stubs’ can be referred:

https://www.mathworks.com/help/rfpcb/rf-pcb-filters-and-stubs.html

I believe this will be of use!