how to determine number of poles in filter

Dear all,

I had simulated a microstrip bandpass filter using Ensemble, and three poles were obtained in the passband. So, can anyone tell me the method to determine the number of poles of a bandpass filter? Thx a lot...

Best rgd!

For bandpass filter:

1st order filter = 3 poles
2nd order filter = 5 poles
3rd order filter = 7 poles

See the transfer function denominator. Also Henry Bode made it some neat rules.