Combined Frequency Tuning of Resonators from TL Segments

The tunability limitations of distributed resonators with variable lumped capacitances C_i and inductances L_j are established. They significantly exceed the similar limitations of distributed resonators with variable C_i or L_j. This suggests the potential for utilizing resonators with combined frequency tuning. Such frequency tuning is provided by a smooth change in C_i and a step change in L_j by switching. It has been proven that the use of step-impedance resonators (SIR) with combined frequency tuning enables a further increase in the tuning range. The intersection effect of neighboring resonant regions is observed in SIR. Experimental data for a second-order microstrip bandpass filter with combined frequency tuning are presented.