Combined Frequency Tuning of Resonators from TL Segments

The tunability limitations of distributed resonators with variable lumped capacitances Ci and inductances Lj are established. They significantly exceed the similar limitations of distributed resonators with variable Ci or Lj. This suggests the potential for utilizing resonators with combined frequency tuning. Such frequency tuning is provided by a smooth change in Ci and a step change in Lj 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.