A direct synthesis approach is presented to realize in-line topology filters with adjacent frequency-variant couplings implementing a transmission response with the same number of finite transmission zeros as poles. The proposed method starts with an N-order fully canonical filter response definition. A non-resonant node (NRN) is incorporated into the transversal network to make room for an extra coupling, and as a consequence of the extended similarity transformation applied, the NRN is transformed into a resonant node. The result is a network with N poles and N transmission zeros implemented with N+1 resonant nodes and N FVC, being able to describe a fully canonical response with an inline network without cross couplings.
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