New cascaded trisections with resonant cross-couplings (CTR sections) applied to the design of optimal filters

Previous techniques for direct design of cascaded trisection (CT) filters are extended to give designs having the maximum number of finite frequency transmission zeros without "nested" cross couplings, i.e. low sensitivity is obtained with non-interacting cross couplings. In previous realizations the cross couplings of CT sections have been either capacitive or inductive, whereas the new section has both types of couplings in parallel, giving a resonated CT section having two finite frequency transmission zeros for each set of three nodes. The filters have the potential of providing lower insertion loss and/or smaller size compared with existing techniques.