Status of the Rigorous Design of Millimeter Wave Low Insertion Loss Fin-Line and Metallic E-Plane Filters

Abstract

The present state of the rigorous field theory design of millimeter wave low insertion loss rectangular waveguide E-plane integrated circuit bandpass filters is reviewed. The theory takes into account the higher order mode interaction between all discontinuities as well as the finite thickness of substrates, fins, and metal inserts. Recent developments in this area include both a generalized design theory and the construction of filters with improved or novel characteristics. The unified algorithm described for the direct combination of multi-port modal scattering matrices requires only one matrix inversion and yields the overall field theory design of complicated filter structures and fiter groups, such as complete millimeter wave multiplexers. High rejection values and expanded second stopband characteristics are achieved by reduced waveguide sidewall dimensions, multiple strips or cavities with decreased cut-off frequency, respectively. Magnetically tunable E-plane integrated circuit filters, where the waveguide sections are symetrically loaded with ferrite slabs, combine the advantages of low-cost photolithographic fabrication techniques with the high power handling capability of ferrite-slab loaded resonators. Computer-optimized design examples are presented for V-band (50–70 GHz) and E-band (60–90 GHz) large-gap finline filters on RT/Duroid or fused silica substrate material, for W-band (75 110 GHz) and D-band (110–170 GHz) E-plane pure metal insert filters, for Ka-band (26–40 GHz) and W-band multiple metal insert filters, for a Ka-band multiple layered dielectric slab filter, for Ku-band (12–18 GHz) and Ka-band magnetically tunable filters, and for an E-band septate E-plane multiplexer. The theory is verified by measurements.

Indexing terms:

• Millimeter wave fillers
• Field theory design
• Metallic E-Plane filter