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Cut-band band filter simulation with CST

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daminomed

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Hi,
I designed a cut-band filter (resonance frequency = 23 GHz), but I didn t obtain the expected results.
So can someone help me to simulate the model in order to verify it.

tnx
 

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BradtheRad

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The L and C values must be selected so they provide a reactive impedance which is not too different from neighboring impedances, at your operating frequency 23 GHz.
 

daminomed

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thank you brad, but can you clarify further more?
 

BradtheRad

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Since you mention resonant frequency, it suggests an LC tank. I assume you have made a bandstop filter by putting the LC tank in series with the input. Is this correct?

An important factor is the input resistance. If it is high, then it becomes a problem to make your filter with sufficient Q.

These simulations show 3 different values for input resistance.



The ratio of L:C is very important. The inductor should be many times the capacitor value. (I chose 1 pF and 48 pH, but perhaps your simulator will let you test wider spreads of the ratio.)

Input amplitude is 5V.

Output resistance is 50 ohms (a typical value).

As you can see, filtering action is not as steep, when input resistance is high.
 

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