A diplexer (44) for coupling plural electronic circuits to a common antenna (46), wherein the antenna has at least a portion which is in the shape of a rod. The diplexer includes a set of dielectric sleeves encircling the rod-shaped portion of the antenna. The diplexer is constructed of plural branches (46a, 46b), each of which has a filter for passing signals in a portion of the spectrum different from the portions of the spectra passed by other ones of the branches. Inductors and capacitors employed in respective ones of the branches are formed by electrical elements disposed on surfaces of the sleeves. Such elements include bands of electrically conductive material which serve as plates of capacitors, and elongated conductive strips which serve as inductors. Resistive material may also be placed on surfaces of the sleeves for construction of resistors of the branches in the event that such resistors are required in the electrical filtering. In the case of a portable electronic component, such as a radiotelephone having a housing (50) with an antenna extending therefrom, the construction of the diplexer (44) provides for a compact configuration enabling use of the diplexer (44) without enlargement of the housing (50) and without inconvenience to a user of the radiotelephone.