Study of SIR for designing filters with arbitrary resonant positions

Stepped impedance resonators are a structure consisting of several transmission lines with different admittances. They are used for control the spurious response and insertion loss of filters by changing the impedance/admittance ratio of the stepped impedances. The multiple mode resonator, which is implemented in form of stepped impedance resonator, can be used, either to widen pass/stop bands or to separate pass bands and stop bands from each other. In this work, we study a stepped impedance structure consisting of two transmission line segments, which have the general form of arbitrary ratio between the admittances and arbitrary ratio of lengths. We observe the appearance and movement of the resonances and verify them through computer simulation in microstrip technology. Variation of these ratios lead to appearance and moving of resonant positions. This approach was numerically verified by means of computer simulation with a commercial software. The accuracy of the predicted resonant positions is very good, i.e. about 48 MHz at 4.6 GHz and about 76 MHz at 6.8 GHz.