Abstract: A diplexer for use in communication of telephony and high-speed data transmission, including television, comprises two filters, each of which is constructed with plural stages in the form of a ladder network, one of the filters being a high-pass filter and the other of the filters being a low-pass filter. The filter components, inductors and capacitors, are located on one or opposed sides of a dielectric substrate. The filter components are arranged to minimize interference between signals traveling in the low-pass filter and the high-pass filter. In the case of a parallel branch of the ladder network in each of the filters, wherein the parallel branch comprises a resonant circuit of inductor and capacitor, the branches of the respective filters are located at opposite parts of the array of the filter components.