Electronically tunable combline filters tuned by tunable dielectric capacitors
A voltage-controlled tunable filter includes at least two cavity resonators electrically coupled to each other. A voltage tunable dielectric capacitor is positioned within each of the resonators. Connections are provided for applying a control voltage to the voltage tunable dielectric capacitors. An input is coupled to the one of the resonators, and an output is coupled to the other resonator.
1 . A voltage-controlled tunable filter including:
first and second cavity resonators capable of exchanging a signal between the first and second cavity resonators;
a first voltage tunable dielectric capacitor positioned within the first cavity resonator and capable of receiving a control voltage;
a second voltage tunable dielectric capacitor positioned within the second cavity resonator and capable of receiving a control voltage;
an input coupled to the first cavity resonator; and
an output coupled to the first cavity resonator.
2 . The voltage-controlled tunable filter of claim 1 , wherein each of the first and second voltage tunable dielectric capacitors includes:
a first electrode;
a tunable dielectric film positioned on the first electrode; and
a second electrode positioned on a surface of the tunable dielectric film opposite the first electrode.
3 . The voltage-controlled tunable filter of claim 2 , wherein the tunable dielectric film comprises:
barium strontium titanate or a composite of barium strontium titanate.
4 . The voltage-controlled tunable filter of claim 1 , further comprising:
a plurality of additional coaxial resonators capable of exchanging a signal between the additional resonators; and
a plurality of additional voltage tunable dielectric capacitors, each of the additional voltage tunable dielectric capacitors being positioned within one of the additional resonators.
5 . The voltage-controlled tunable filter of claim 1 , further comprising:
a first rod positioned in the first resonator, wherein the first voltage tunable dielectric capacitor is positioned at one end of the first rod; and
a second rod positioned in the second resonator, wherein the second voltage tunable dielectric capacitor is positioned at one end of the second rod.
6 . The voltage-controlled tunable filter of claim 5 , wherein:
each of the rods in the cavity resonators is serially connected with one of the voltage tunable dielectric capacitors.
7 . The voltage-controlled tunable filter of claim 5 , wherein:
each of the rods in the cavity resonators is grounded.
8 . The voltage-controlled tunable filter of claim 1 , wherein:
the input comprises a first coupling probe; and
the output comprises a second coupling probe.
9 . The voltage-controlled tunable filter of claim 1 , wherein each of the first and second voltage tunable dielectric capacitors includes:
a substrate;
a tunable dielectric film positioned on the substrate; and
first and second electrodes positioned on a surface of the tunable dielectric film opposite the substrate, the first and second electrodes being separated to form a gap.
10 . The voltage-controlled tunable filter of claim 9 , further comprising:
an insulating material for insulating the first and second electrodes and the tunable dielectric film from the first and second cavity resonators.
11 . A method of controlling a tunable filter with a control voltage comprising:
exchanging a signal between a first and a second cavity resonator within said tunable filter;
receiving a control voltage by a a first voltage tunable dielectric capacitor positioned within the first cavity resonator receiving a control voltage by a a second voltage tunable dielectric capacitor positioned within the second cavity resonator
12 . The method of claim 11 , wherein each of the first and second voltage tunable dielectric capacitors includes:
a first electrode;
a tunable dielectric film positioned on the first electrode; and
a second electrode positioned on a surface of the tunable dielectric film opposite the first electrode.
13 . The method of claim 11 , wherein the tunable dielectric film comprises:
barium strontium titanate or a composite of barium strontium titanate.
14 . The method of claim 11 , wherein said voltage-controlled tunable filter further comprises:
a plurality of additional coaxial resonators capable of exchanging a signal between the additional resonators; and
a plurality of additional voltage tunable dielectric capacitors, each of the additional voltage tunable dielectric capacitors being positioned within one of the additional resonators.
15 . The method of claim 11 , wherein said voltage-controlled tunable filter further comprises:
a first rod positioned in the first resonator, wherein the first voltage tunable dielectric capacitor is positioned at one end of the first rod; and
a second rod positioned in the second resonator, wherein the second voltage tunable dielectric capacitor is positioned at one end of the second rod.
16 . The method of claim 11 , wherein each of the first and second voltage tunable dielectric capacitors includes:
a substrate;
a tunable dielectric film positioned on the substrate; and
first and second electrodes positioned on a surface of the tunable dielectric film opposite the substrate, the first and second electrodes being separated to form a gap.
17 . The method of claim 11 , wherein said voltage-controlled tunable filter further comprises:
an insulating material for insulating the first and second electrodes and the tunable dielectric film from the first and second cavity resonators.