Novel Negative Coupling Structure for Rectangular Waveguide Cavity Filters

In this paper, we introduce a novel negative coupling structure that is suitable for fabrication using milling and micromachining technologies. The proposed negative coupling structure is designed in three sections: a central bow-shaped iris is sandwiched between two sections that manipulate electro-magnetic fields, causing a 180-degree phase rotation. To validate this concept, we have developed a silicon micromachined fourth-degree quasi-elliptic bandpass filter with a center frequency of 270 GHz and a fractional bandwidth of 2.2%. The measured results of the filter display two transmission zeros in the stopband thus demonstrating the correct performance of the negative coupling structure.