Cavity resonator with thermal compensation

A filter for electronic signals, where the filter contains a plurality of coupled resonant cavities and produces a signal transfer characteristic, each resonant cavity comprising:

• a conductive body containing a cavity,
• a conductive plate attached to the body and enclosing the cavity,
• a mechanical tuning mechanism that protrudes into the cavity, a position of the tuning mechanism in the cavity affecting a tuning of a resonant frequency of the cavity resonator,
• a portion of the enclosed cavity being made of a shape memory alloy (SMA) material that has been trained to have a coefficient of thermal expansion that causes dimensional changes of the portion as a temperature of the cavity resonator varies so that the dimensional changes counteract other dimensional changes due to other parts of the enclosed cavity that are made of materials other than SMA material to stabilize the resonant frequency of the resonant cavity as the temperature changes;
• each of the resonant cavities having a stabilized resonant frequency versus temperature characteristic which produces a stabilization of the signal transfer characteristic during the temperature changes, said portion made of the SMA material comprises a resonator rod attached to the body within the enclosed cavity.

A method for stabilizing a resonant frequency of a cavity resonator during temperature changes comprising the steps of:

• making a portion of an enclosed cavity of the cavity resonator of a shape memory alloy (SMA) material;
• training the SMA material to have a predetermined coefficient of thermal expansion (CTE) that causes dimensional changes of the portion as a temperature of the cavity resonator varies so that the dimensional changes counteract other dimensional changes due to other parts of the enclosed cavity that are made of materials other than the SMA material to stabilize the resonant frequency of the cavity resonator as the temperature changes;
• the training including:
• starting with a first length of the SMA material at one end of a temperature range;
• stretching or compressing the first length of the SMA material while at the one end of the temperature range to a second length that equals a length of the SMA material based on the predetermined CTE:
• (a) when not being stretched or compressed and (b) while at the other end of the temperature range;
• maintaining the SMA material at the second length while the SMA material is cycled back and forth between the ends of the temperature range until a strain versus temperature characteristic of the SMA material is stabilized.