A study on the frequency-temperature coefficient of a microwave cavity in a passive hydrogen maser

A frequency-temperature coefficient (FTC) model for a magnetron cavity used in a passive hydrogen maser is proposed. The influences of the thermal expansion coefficient of the vane, strut and wall of the microwave cavity on the FTC are analysed. The results show that the FTC of the magnetron cavity can be reduced to a few hertz by choosing vanes and struts with proper expansion coefficients. A low-FTC cavity is fabricated according to the model. Experiments show that the FTC is reduced from −30 kHz K−1 to 2.59 kHz K−1 without using a quartz storage bulb.