Vi. Microwave Electronics A. the X-line Slow-wave Structure Fig. Vi-1. X-line Obstacle. Fig. Vi-2. Schematic Drawing of the X-line Showing Geometric Parameters

In Quarterly Progress Report No. 56 (pages 104-107) some preliminary measurements performed on an elementary X-line were presented. Detailed measurements have been made on several variations of this structure to ascertain the factors that determine the edges of the lowest passband. The X-lines that were tested were made from obstacles like that shown in Fig. VI-1, separated by hollow cylindrical spacers. Figure VI-2 is a schematic drawing of an X-line showing the geometric parameters of the structure. The angle a denotes the angular displacement of even-numbered bars with respect to odd-numbered bars. The w-p diagrams of several X-lines that were tested were obtained by short-circuiting a section of the periodic structure having a length NkQ. For each passband of the structure, this short-circuited line has N + 1 resonant frequencies. The line is resonant when the phase shift per period is piT Po = Nk The resonances are identified by moving a metallic needle along the axis of the structure (this perturbs only the Ez-field) and counting the number of nodes in the field pattern.