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Output impedance of RF filter

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milansedlak

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Hi guys,
does anyone know, how to design filtr with specific output impdeance? I've done some research on internet and there are calculators, tips etc. how to design filtr with 50 ohms of input and output impedance. But I need filter with complex output impedance (viz. attachement).
Could somebody help me?
Thank you.

eda_borad.png
 

You can design this filter for 50 Ohm Source and Load Impedances then you can add an Impedance Matching Circuit to desired side to obtain wanted Impedance value.
 
Good filter design tools like Nuhertz Filter Solutions can design passive filters for complex source and load impedance. As known from dedicated impedance matching networks, there's a relation between impedance ratio and achievable minimal Q.

I presume, the design procedure is also derived in profound filter text books.
 

I see the problem discussed e.g. in Zverev, Handbook of Filter Synthesis in paragraph 10.13 Source and Load Transformations.
 

A complex output impedance will always be frequency dependent?
 

A complex output impedance will always be frequency dependent?
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Yes. You can possibly assume a constant value for small band filters. Said "Source and Load Transformations" paragraph is using RL or RC series circuits instead of absolute impedance values. Nuhertz is expecting an impedance table for the general case.

Please notice that filters are designed for a nominal termination impedance not an output impedance. The passband output impedance is the complex conjugate of the load impedance.
 

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