Cavity Filter Temperature Compensation Method Study

With the development of communication, requires a large amount of reception and transmission channel. These channels occupy the limited frequency band, and with the use of adjacent frequency bands to communicate becomes more commonly. How to make the adjacent bands non-interaction and make good use of them, which requires filters to have high-frequency selectivity and temperature stability in order to satisfy the demands of the communication system. Cavity filters have been widely used in communication system, which with high Q values (approximately a few thousand) , small-band loss, high stop-band suppression, tuning convenient, affordable power advantages. Temperature drift is an important factor that impact frequency stability of the cavity filter.Due to thermal expansion characteristics, the filter characteristics of the filters changes according to temperature. It is particularly evident to narrowband cavity filters. In order to compensate the temperature drift, some add the device to the cavity filters. However, this method is more difficult to use and lack of universality. More current and the most effective method of temperature compensation is based on the appropriate size and flexible use of material temperature coefficient, so that the changes of the materials that impact on the cavity resonance frequency could counteract each other. However, this method did not give accurate relationship between the components of the cavity and the temperature coefficient of them when the temperature drift of the cavity have been compensated.This paper focuses on the temperature compensation of the comb-like cavity filters. At the point of the size and the temperature coefficient of the material, the exact relationship between the components of the cavity and the temperature coefficient of them when the temperature drift of the cavity have been compensated has been established by introduction of components drift impact factor. When the temperature drift of the cavity can not be fully compensated, the concept of a cavity temperature drift factor has been introduced, which reflects the changes of relative frequency drift under the variation of unit temperature. Through further study, the concept of equivalent temperature coefficient of the cavity has been introduced, and the legitimacy of it has been verified. Then the temperature compensation of the dielectric filters and the waveguide filter are studied. Linear model used to analyze waveguide drift, and a meaningful compensation has been achieved. After analysis the filter, we know that if the temperature drift of single chamber has been compensated that the filters could have no temperature drift.