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# Coupling Coeficient Extraction

## Coupling Coeficient Extraction

(OP)
Hi,
I'm trying to do an EM simulation (HFSS) to extract the coupling coeficients of coupled resonators used as building block for a filter design using Jia-Sheng Hong & Michael J. Lancaster. This method extract the coupling coeficient from the S21 response using two resonance frequencies. The problem is that there is no place they explain how to place the ports and what termination to use ! What do they mean by loosely coupling of ports with regards to the resonators ? Where to put exactly the ports relative to the resonators ?

### RE: Coupling Coeficient Extraction

I don't know specifics about anything you are talking about. However "loose coupling" is a well known basic concept. Suppose you have an LC resonant tank. The Q will depend on the load.  Suppose that at resonance you have 100 ohms of inductance and 100 ohms of capacitance in shunt. With no loss the Q is infinite. If you put on a shunt 50 ohm load then your Q is shot to hell. So you put on a loose coupling, say 10K ohms of capacitor in series with 100 ohms of capacitor. The signal on the tank has been divided down a lot in the process but the Q is still high. Sometimes the loose coupling is a small piece of wire which can just about "see" the tank circuit (hence a very small value of series capacitance). Sometimes it is a loop of wire a long distance from the tank.

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