A broad band diplexer employing suspended strip-line capacitors is disclosed. The diplexer has a low pass filter circuit and a high band pass filter circuit. The high band pass filter circuit has a first set of conductive pathways formed on the first surface of a suspended dielectric substrate, a second conductive pathway formed on the second surface of the substrate such that first and second conductive pathways are capacitively coupled, and plural resonators. The high pass filter circuit provides plural transmission poles within the band of operation exceeding the number of resonators.