Tunable bandpass filter device and method
An embodiment radio frequency MicroElectroMechanical (RF-MEMS) tunable bandpass filter includes one or more tunable resonators, each of which includes an electrically reconfigurable capacitor bank, a tuning screw, and a resonating structure. In an embodiment, the capacitor bank includes fixed value capacitors and switches to vary the capacitance of the resonator. In an embodiment, the capacitor bank includes variable capacitors and direct current (DC) bias circuits to vary the capacitance of the resonator. The filter may be incorporated into a time division duplexing (TDD) base station or other wireless communications device.
1. A tunable bandpass filter, comprising:
a tunable resonator including:
a body having a bottom wall, a top wall and four side walls surrounding a cavity;
a resonating structure in the cavity;
an electrically reconfigurable capacitor bank including a printed circuit board and at least one capacitor mounted on the printed circuit board, wherein the printed circuit board is mounted outside of the cavity on the top wall of the body; and
a tuning screw capacitively coupled to the resonating structure, wherein the tuning screw is threadably mounted to the printed circuit board, disposed through an unthreaded hole in a spacer mounted in the top wall of the body, and electrically coupled to the at least one capacitor on the printed circuit board, and wherein the tuning screw comprises a plate disposed in the cavity perpendicular to a screw axis of the tuning screw;
an input operably coupled to the tunable resonator; and
an output port operably coupled the tunable resonator.
2. The filter of claim 1 , wherein the at least one capacitor is a fixed capacitor operably coupled to a switch.
3. The filter of claim 1 , wherein the at least one capacitor is a variable capacitor operably coupled to a direct current (DC) bias circuit.
4. The filter of claim 1 , wherein the at least one capacitor is a plurality of fixed capacitors and a plurality of respective switches.
5. The filter of claim 1 , wherein the at least one capacitor is a plurality of variable capacitors and a plurality of respective DC bias circuits.
6. The filter of claim 1 , wherein the plate is vertically disposed above an uppermost surface of the resonating structure to define a gap, and wherein the tuning screw is configured to be tuned to increase or decrease the gap.
7. The filter of claim 1 , wherein the tunable resonator is operably coupled to at least one additional tunable resonator.
8. The filter of claim 1 , wherein the tunable resonator is coupled to at least one additional tunable resonator through an iris coupling.
9. A tunable bandpass filter, comprising:
a plurality of tunable resonators, wherein each tunable resonator includes:
a body having a bottom wall, a top wall and four side walls surrounding a cavity;
a resonating structure in the cavity;
an electrically reconfigurable capacitor bank including a printed circuit board and at least one capacitor mounted on the printed circuit board, wherein the printed circuit board is mounted outside of the cavity on the top wall of the body; and
a tuning screw capacitively coupled to the resonating structure, wherein the tuning screw is threadably mounted to the printed circuit board, disposed through an unthreaded hole in a spacer mounted in the top wall of the body, and electrically coupled to the at least one capacitor on the printed circuit board, and wherein the tuning screw comprises a plate disposed in the cavity perpendicular to a screw axis of the tuning screw;
a plurality of coupling structures operably coupling the tunable resonators; and
an input port and an output port operably coupled to one or more of the plurality of the tunable resonators.
10. The filter of claim 9 , wherein the at least one capacitor is a fixed capacitor operably coupled to a switch.
11. The filter of claim 9 , wherein the at least one capacitor is a variable capacitor operably coupled to a direct current (DC) bias circuit.
12. The filter of claim 9 , wherein each plate of the tuning screws is vertically disposed above each of the resonating structures to define a gap, and wherein each of the tuning screws is configured to be threadably driven to increase or decrease the gap.
13. A wireless communications device, comprising:
a duplexer operably coupled to an antenna;
an amplifier operably coupled to the duplexer; and
a tunable bandpass filter operably coupled to the duplexer and to the amplifier, the filter including a tunable resonator comprising:
a body having a bottom wall, a top wall and four side walls surrounding a cavity;
a resonating structure in the cavity;
an electrically reconfigurable capacitor bank including a printed circuit board and at least one capacitor mounted on the printed circuit board, wherein the printed circuit board is mounted outside of the cavity on the top wall of the body; and
a tuning screw capacitively coupled to the resonating structure, wherein the tuning screw is threadably mounted to the printed circuit board, disposed through an unthreaded hole in a spacer mounted in the top wall of the body, and electrically coupled to the at least one capacitor on the printed circuit board, and wherein the tuning screw comprises a plate disposed in the cavity perpendicular to a screw axis of the tuning screw.
14. The wireless communications device of claim 13 , further comprising a mixer and an additional tunable resonator having an additional electrically reconfigurable capacitor bank.
15. The wireless communications device of claim 13 , wherein the at least one capacitor is a fixed capacitor operably coupled to a switch.
16. The wireless communications device of claim 13 , wherein the at least one capacitor is a variable capacitor operably coupled to a direct current (DC) bias circuit.
17. The wireless communications device of claim 13 , wherein the at least one capacitor is a plurality of capacitors.
18. The wireless communications device of claim 13 , wherein the tuning screw is at least one of manually and mechanically rotatable to adjust a capacitance of the filter.
19. A method of fabricating a tunable bandpass filter having a tunable resonator, the method comprising:
forming a resonator structure in a cavity of a body having a bottom wall, a top wall and four side walls surrounding the cavity;
mounting an electrically reconfigurable capacitor bank outside of the cavity on the top wall of the body, the electrically reconfigurable capacitor bank including a printed circuit board and at least one capacitor mounted on the printed circuit board;
threadably mounting a tuning screw to the printed circuit board, wherein the tuning screw is disposed through an unthreaded hole in a spacer mounted in the top wall of the body, wherein the tuning screw is capacitively coupled to the resonator structure, and wherein the tuning screw has a plate perpendicular to a screw axis of the tuning screw and in the cavity;
electrically coupling the tuning screw to the at least one capacitor on the printed circuit board; and
operably coupling an input port and an output port to the tuning resonator.
20. The method of claim 19 , further comprising operably coupling the tunable resonator to an additional tunable resonator.