Cross-connected waveguide lines as standards for millimeter- and submillimeter-wave vector network analyzers

This paper describes some investigations into establishing primary standards of loss for waveguide Vector Network Analyzers (VNAs) operating at millimeter- and submillimeter-wave frequencies. The standards comprise straight sections of waveguide, where the waveguide line is orientated such that the waveguide aperture is at right-angles to the waveguide apertures on the VNA test ports. This ´cross-connected´ waveguide forms a section of waveguide that is effectively below cut-off. The mechanical discontinuity between the cross-connected waveguide and the VNA test ports also generates significant reflection. The combined effect due to these two loss mechanisms - cut-off attenuation and discontinuity reflection loss - can be predicted from electromagnetic theory and so can be used to establish sections of cross-connected waveguide, of various lengths, as primary standards of loss. The paper describes these standards in detail and compares experimental results, obtained using a VNA operating in the 50 GHz to 75 GHz band, with values predicted by electromagnetic modeling software.