Direct Synthesis of Parallel-Connected Symmetrical Two-Port Filters

This brief presents a general technique for the synthesis of parallel-connected two-port networks. This is based on the even- and odd-mode admittances of a standard Chebyshev network. The expressions for the even/odd-mode admittance are used to synthesize the low-pass network into branches of subnetworks connected in parallel between the source and the load. These together will have the same characteristics as a ladder network. It is also shown how a filter of a particular order will have the same parallel branch topology regardless of how many transmission zeros are used in the filter's transfer function. This design technique can be beneficial for various implementation techniques such as multilayer substrate and dual-mode resonators. Examples of fourth- and sixth-order degree networks with various numbers of transmission zeros are presented.