Methods and apparatus for reducing leakage of microwaves at a slit valve of a process chamber. A multi-frequency resonant choke around the slit valve prevents microwave energy from a band of frequencies from escaping from the slit valve. The multi-frequency resonant choke may have a sloping bottom surface or a serrated bottom surface to enable multiple frequencies to resonant in the choke, canceling a range of microwave frequencies at gaps formed by a slit valve gate.