ToIerance Analysis of Cascaded StructureR

sion we have the largest bandwidth when dealing with non unity aspect ratios and low dielectric constant. In contrast, to obtain good wave guiding ability and low radiation from discontinuities a higher dielectric constant is required. If only one of these conditions is critical we can adjust the parameters of the guide to suit that particular requirement and obtain the largest bandwidth. If all the conditions are equafly important we are limited to a small range of dielectric constants, e.g., for the constraints discussed an image line with unit aspect ratio has the maximum bandwidth at Cfl = 2.5 We have used for the upper limit the first higher order mode cutoff frequency. In practice it seems that it is possible to maintain a single mode operation slightly above this frequency since the first higher order mode has extensive external fields at its cutoff frequency and is unlikely to be propagated in any circuit until a frequency is sufficiently high enough to reduce the evanescent fields down to a manageable size, The purpose of this paper has been to give some guidance about the many parameters involved in the bandwidth of image guide in order to help in the design of broad-band circuits.