Abstract: A duplexer, usable to interlink a receiver unit, transmitter unit, and an antenna unit of a communication system, has a body that includes cavities and interconnecting apertures. The duplexer further includes resonator covers that cover the cavities and apertures from a bottom side of the body and tuning covers that cover the cavities and apertures from a top side of the body. The resonator covers have integral resonator posts that extend into the cavities when the resonator covers are press-fitted into the body. The tuning covers have threaded openings for the insertion of tuning screws into the cavities and for the insertion of coupling screws into the apertures. The cavities and apertures are tuned to reflect or pass signals of selected frequencies by turning the tuning screws and coupling screws.