Advanced Receive/Transmit Diplexer Design For Emerging mm-Wave Access Radio Applications

The application of asymmetric filter characteristics with transmission zeros (TZs) in advanced diplexer designs is shown to provide low insertion loss while maintaining the high interband isolation for the operation of radio equipment. The transmission zeros of each filter at finite frequencies are realized by dedicated cavity resonances at the single filter input ports (extracted poles) and by triplet sections in the signal paths between the single and common port interfaces. Consequently, the individual TZs of each filter can be controlled independently in an overall compact cavity structure. All cavities are arranged in an H-plane structure. The interfacing of the respective cavities at all ports by E-plane T-junctions facilitates the compactness. The interfaces are realized at one side (below the cavity structure) for easy integration and mounting. The frequency allocations of the different channels can be easily exchanged by mounting the diplexer in a 180-degree position. This is possible due to a point symmetry for the single channel ports with respect to the common port. The validity of the approach has been proven by an advanced diplexer design for a new 39GHz access radio application. The diplexer with 6th order filters - each having an asymmetric response with two TZs - exhibits good coincidence of theoretical and measured results and thus proves the novel design approach