An RF duplexer waveguide filter module for the transmission and filtering of TX and RX RF signals comprising a substrate with TX and RX filter assemblies mounted thereon. One or both of the TX and RX filter assemblies comprises an RF waveguide filter assembly including a plurality of blocks of dielectric material coupled together in a side-by-side relationship. Each of the blocks of dielectric material defines at least one slit and at least one internal RF signal transmission window. One or both of the end blocks defines a step and a through-hole terminating in an opening in the step. In one embodiment, the RF duplexer waveguide filter module additionally comprises an RF antenna waveguide filter extending between and coupling the TX and RX filter assemblies to an antenna RF signal transmission line.