Tunable end-coupled ferroelectric-gap filters based on barium strontium titanate capacitors

Tunable filters are desirable components for modern RF and microwave communication systems. It is required that the subsystems be easily integrated, reconfigurable, reproducible and small. Microstrip filters are good candidates for meeting these requirements. These can be made tunable by using ferroelectric interdigital capacitors to couple half wavelength resonators and applying an electrostatic field using a DC voltage. Based on work previously undertaken on ferroelectric capacitors end coupled band pass filters have been modelled. It is shown that the effects of varying the ferroelectric gap capacitors within the expected tuning range will be a modification in the centre frequency of a band pass filter of around 20%.