Tunable resonator for microwave oscillators and filters

A microwave filter, comprising:

• a hollow body formed with walls defining a plurality of resonant cavities disposed in mutual succession, said walls including a first wall having first openings formed therein each leading into a respective one of said cavities;
• tuning screws disposed in each of said first openings, said tuning screws each carrying a dielectric support and a dielectric resonator disposed in each of said cavities, said dielectric supports acting as spacers and penetrating in said first openings;
• said hollow body being formed with an input port for a microwave signal to be filtered, said input port being defined by a second opening leading into a first of said cavities, and with an output port for a filtered signal, said output port being defined by a third opening leading from a last of said cavities to an outside of said body;
• said body further including dividing walls separating said cavities, said dividing walls each being formed with fourth openings electromagnetically coupling adjacent cavities;
• and
• toroidal extensions of said first wall surrounding said first openings, each said toroidal extension extending for a given length inside said respective cavity, said toroidal extensions reducing thermal effect on the bandpass central frequency, and increasing mechanical stability.