Abstract: A tunable RF cavity resonator having reduced generation of passive inter-modulation, the tunable RF cavity resonator including a cavity body, a fixed tuning post at a first end of the cavity body, a dielectric rod in the fixed tuning post interior space with a first spatial gap between the dielectric rod outer surface and the fixed tuning post inner wall, a tuning screw connected to a first end of the dielectric rod, and a tuning element disposed on a second end of the dielectric rod so that the tuning element moves within the interior space of the fixed tuning post while maintaining a second spatial gap between the tuning element outer surface and the fixed tuning post inner wall. Accordingly, the tuning element forms a short section of very low RF impedance transmission line thereby preventing RF signal leakage through the interior space of the fixed tuning post.