Novel integrated coaxial line to cylindrical waveguide directive couplers in pipelines for process monitoring applications

This paper presents a novel coaxial line to circular cylindrical waveguide directive coupler, using a resonant configuration of two integrated coaxial-fed microstrip patches opposite arranged in a measurement pipeline, this configuration a directivity of more than 4 dB at 5.7 GHz can be achieved without disturbing the cross-section of the pipeline. The insertion loss of the proposed coupler is low and hence about -1 dB of the input signal is transmitted into the desired direction of the circular waveguide which is a gain of 2 dB compared to a conventional E-field probe. Similar to commercial available mass flow meters, two of these couplers, at a distance of 0.4 m in the measurement section, form a mass flow sensor (Penirschke et al., 2004).