A Novel Hybrid-Mode Technique for Multiband Filter Design

This work reports on the development of a novel technique for producing multi-band resonator and filter structures through the use of hybrid electro-magnetic modes (HEM modes). A new filtering structure is introduced in the form of a U-shaped (folded) resonator, making use of hybrid electro magnetic modes and allowing for the formulation of a highly versatile resonator structure with two poles and two transmission zeros. One of the primary advantages of this U-shaped structure is its ability to create fully controllable transmission zeros throughout the S-parameter response without the need for complex geometries or physical cross-coupling. Examples of the technique are demonstrated and filters with dual-band and triple-band responses are formulated. A prototype of the triple-band filter is fabricated for Y-band (330 GHz to 500 GHz) operation using high-precision milling. The fabricated structure and measured results demonstrate the elegance of the technique for achieving multi-band solutions well into the sub-terahertz range. A comparison to existing multi-band filters is provided, along with a contrasting of size and performance to the classic Chebyshev design methodology.