Impedance and Admittance Waveguide Inverter Applications: A Practical Sub-Terahertz Region Tolerance Analysis for Large-Scale Production

This work presents an in-depth analysis of the four most basic waveguide inverter types; E-plane irises, E-plane stubs, H-plane irises, and H-plane stubs. A thorough investigation and tolerance analysis of fourth-order filters, which are comprised of each of the inverter types, is undertaken in order to identify and communicate sensitivity, fabrication practicality, and special considerations for the mass production of waveguide filters operating in the sub-terahertz (THz) region, while, in addition, aims to resolve open questions with regards to the direct comparison of performance between each of the filter profiles. A total of forty filters are fabricated and measured for operation at 267.5 GHz with a 5.6% fractional bandwidth. The results are detailed and a yield summary is presented for an 80% bandwidth criteria with return loss operating conditions at 18 and 20 dB. The highest product yield is found to be of the stub filter types, that being 90% each when a 20-dB criteria is applied, while the lowest yield is of the H-plane iris filter type, that being 50% when a 20-dB criteria is applied. The measured results indicate that both of the stub-type filter profiles also result in a lower insertion loss when compared to the iris-type designs. An additional evaluation is provided at the end of this article with the production of another six H-plane iris-type filter prototypes with per-contra cutting planes in order to discuss and contrast the measured results of E- and H-plane cutting profiles and their respective relationship to the milling depth and attainable aspect ratio in sub-THz applications.