Abstract: The thermal expansion of a microwave device such as a microwave resonator is partially or completely compensated by an externally mounted thermal expansion element. The microwave device includes a sidewall and an endwall affixed at its periphery to the sidewall. The thermal expansion compensation element is disposed external to the microwave device, between the endwall of the microwave device and a rigid external support. As the sidewall lengthens with increasing temperature, the thermal expansion compensation element expands to flex the endwall in the opposite direction to the growth in length of the sidewall, so that the central portion of the endwall remains in approximately the same position regardless of the temperature change.