Highly Compact Silicon Micromachined Filter with Axial Ports at Sub-terahertz Band

This paper presents a narrowband silicon-micro machined 4th-order waveguide filter concept at 300 GHz with 2% fractional bandwidth, which is highly compact and has axial port arrangements, so that it can be mounted directly between two standard waveguide flanges without needing any split-block interposers. This filter is composed of four TE101 series resonators arranged in one plane which leads to a very small size in real application direction. Underetching effects on the response of the filter are investigated. Prototype devices are fabricated by deep-silicon etching on silicon-on-insulator wafers with a standard process. The measured passband insertion loss is 1.65 dB. The corresponding extracted unloaded quality factor of the resonators is about 600. The filters demonstrate excellent repeatability of the measured S-parameters on a single chip. The presented filters are extremely compact in terms of size; their footprints have areas of only 2 mm
²
, and the length reaches 0.6 mm in the practical application direction.