Enhanced topologies for the design of dual-mode filters using inductive waveguide structures

This paper presents novel topologies for the design and realization of microwave filters combining dual-mode and single-mode cavities in all-inductive waveguide technology. Examples of orders 3-5 with one or two transmission zeros are synthesized and designed, in order to demonstrate the validity of the proposals. All the coupling schemes explored exhibit the zero-shifting property, so the transmission zeros can be easily placed above or below the passband. A four-pole dual-band-pass filter is also designed to show the flexibility offered by the novel structures. A prototype of this dual-band filter has been manufactured and tested in order to provide experimental validation for these new structures. Important aspects of synthesis techniques, required to obtain the associated coupling topologies and to perform the final physical design of the waveguide filters, are also addressed in this paper.