A duplex filter includes a core of dielectric material with top, bottom, and side surfaces, and first and second spaced-apart sets of through-holes extending therethrough. A wall extends outwardly from the top surface to define a peripheral rim and cavity. A pattern of metallized and unmetallized areas are defined on selected core surfaces including strips of metallization on the top surface that extend onto the wall and the peripheral rim thereof to define respective transmit, receive, and antenna connection posts. In one embodiment, the core is made from two separate blocks which have been coupled together to define an interior metallized layer which separates the first and second sets of through-holes and an exterior wall on the top surface separates the respective transmit and receive conductive patterns thereon.