Extended lattice filters enabled by four-directional couplers

Novel lattice-filter structures consisting of four-directional couplers are introduced, analyzed, and discussed. Four-directional couplers are discussed, and energy-conservation relations in a field-wave application are derived. A thick linear lattice filter is presented and studied as a simple extension to the traditional lattice. A two-dimensional lattice structure is also introduced and studied. Transfer functions are derived and discussed for several examples.