MICROWAVE FILTERS PART I:THE EFFECT OF SMALL LOSS IN THE COUPLING IRISES ON THE Q OF A SHUNT-COUPLED CAVITY PART II:NARROW PASS BAND, LOW INSERTION LOSS FILTERS EMPLOYING RESONANT OBSTACLE COUPLING ELEMENTS

摘要

The speculation that losses in the cavity coupling irises are responsible for the observed discrepancies between the theoretical and measured values for the Q of a high Q cavity is investigated quantitatively in Part I. The losses in the coupling irises of a shunt coupled cavity are expressed as resistances in the shunt equivalent circuits of the irises. Microwave network methods are then used to determine the effect of such resistances on the resonant frequency and Q of the cavity. Approximate solutions obtained by S. Edelberg are used to obtain the value of the resistance in certain cases and numerical results for the cavity Q are presented for inductive strip coupling elements. It is shown that the cavity Q is affected significantly by the losses in the coupling elements, and that the resonant frequency is negligibly influenced.