Slow-wave propagation in a rectangular waveguide

A theoretical and experimental investigation of the conditions required for the support of the dipole mode as a slow wave inside a rectangular channel is presented. From this a number of conclusions can be drawn. First, it can be concluded that the wall structure, both the bare-metal and grid surfaces, presents to the adjoining field anisotropic impedances significantly different from those which might have been expected from planewave considerations. Secondly, the attenuation and phase-change behaviour can vary, according to boundary conditions, over a wide range of slow waves, and possibly extending to fast waves in some cases, with losses in the 3 GHz region that are of the same order as those of an equivalent TEM line. Thirdly, that a sudden transition can be traced from a transverse evanescent E1n field in the waveguide, when it is open-sided, to a dipole configuration freely propagating when closed by a grid structure. And, fourthly, that the wave can be usefully applied not only to lines employed for ordinary transmission, but also, in cases where coupling is required en route, to an adjacent circuit. Alternatively, by suitable design, it can be used for delay lines.