A cavity filter includes a unitarily formed piece, a cap, a cover, and a tuning adjustment screw. The unitarily formed piece includes a bottom plate portion, a resonator tube body portion formed on a center of the bottom plate portion, and a sidewall portion extending from the bottom plate portion surrounding the resonator tube body portion. The resonator tube body portion defines a resonating cavity therein. The cap is attached onto a distal end of the resonator tube body portion. The cap and the resonator tube body portion cooperatively forms a resonator tube. The cover is attached to the sidewall portion, and the cover includes a screw hole. The cover, the sidewall portion, and the bottom plate portion cooperatively forms a chamber. The tuning adjustment screw is extending through the cover, threadedly engaged in the screw hole and aligned with the resonator tube.