A ferroelectric band pass tunable monolithic high Tc superconducting filter, having an electric field dependent permittivity, an input, an output, a tunable operating frequency and comprising:
- a first microstrip line disposed on a ferroelectric film, characterized by said permittivity, and being one quarter wave long at an operating frequency of the filter;
- second, third, fourth . . . (n-1)th, nth microstrip lines;
- said second microstrip line disposed on said ferroelectric film, characterized by said permittivity, and being one half wavelength long, at an operating frequency of the filter, and said second microstrip line having a first one quarter wavelength portion being edge coupled to and separate from the first microstrip line and having a remaining second quarter wavelength being coupled to and separate from the following third microstrip line;
- said third, fourth . . . (n-1)th microstrip lines respectively disposed on said ferroelectric film, characterized by said permittivity, each one of said third, fourth . . . (n-1)th microstrip lines respectively being one half wavelength long, at the operating frequency of the filter, having a first one quarter wavelength portion thereof being edge coupled to and separate from previous (n-2)th one of the microstrip lines, and having a remaining second quarter wavelength portion thereof being coupled to and being separate from a succeeding one of the microstrip lines;
- said nth microstrip line disposed on said ferroelectric film, characterized by said permittivity, and being one quarter wave long, at an operating frequency of the filter, said nth microstrip line being coupled to and being separate from the (n-1)th microstrip line;
- an input ferroelectric transformer, having a bias voltage dependent impedance, being quarter wavelength long at an operating frequency of the filter, and comprised of a ferroelectric film which is the same as a ferroelectric film of the filter, said input ferroelectric transformer being connected to and being a part of the first microstrip line for matching an impedance of an input circuit of the filter to a bias voltage dependent impedance of the first microstrip line and providing a good impedance match over the operating bias voltages;
- a first transmission means for coupling energy into the input ferroelectric transformer at the input;
- an output ferroelectric transformer, having a bias voltage dependent impedance, being quarter wavelength long at an operating frequency of the filter, and comprised of a ferroelectric film which is the same as a ferroelectric film of the filter, said output ferroelectric transformer being connected to and being a part of the nth microstrip line of the filter for matching a bias voltage dependent impedance of the nth microstrip line of the filter to an impedance of an output circuit of the filter and providing a good impedance match over the operating bias voltages;
- a second transmission means for coupling energy out of the output ferroelectric transformer at the output;
- all microstrip lines and ferroelectric transformers being operated at the same tunable frequency;
- voltage means for applying a bias voltage to all said microstrip lines;
- said microstrip lines being comprised of a film of a single crystal high Tc superconductor;
- and
- means for operating said band pass tunable filter at a high Tc superconducting temperature slightly above the Curie temperature associated with the ferroelectric film to avoid hysteresis and to provide a maximum change of permittivity for said ferroelectric film of the filter.