Three-waveguide couplers for improved sampling and filtering

Coupling between two uncoupled waveguides in proximity can be affected by introducing a third waveguide between them. One advantage of this scheme is that it can eliminate the need for bends. Another advantage is the resulting improvement in the shape of the transfer characteristic. Improved sampling and tunable filter operation of this new structure are also shown. An analysis of a uniform filter structure is presented. The `sidelobe' analysis of Alferness is adapted to the present case and tapers are investigated for further sidelobe suppression.