608,494. Electric resonators. JOHNSON, W. A., RAWLING, A., and CULLEN, A. L. July 10, 1945, No. 17641. [Class 40 (viii)] [Also, in Group XL (c)] A wave-guide has a plate or rib of conductive material projecting into the guide substantially in the plane of the electric field so as to modify the effective length of the guide and thereby shift the phase of wave energy propagated through the guide. In Fig. 1, a conducting plate 1 may be inserted to a variable degree into a rectangular guide carrying a transverse electric wave through a slot 2 formed with quarter-wave chokes 3 to reduce leakage. To minimize sparking, the lower edge of the plate is not permitted to approach closely the lower wall of the guide, and the lower edge of the plate may be rounded or protected by insulating material. The lower corners of the plate 1 may be chamfered or the plate may taper from one end to the other to reduce mismatch. In Fig. 3, the plate 1, which has rounded edges to reduce sparking and increase mechanical strength, can be cyclically inserted and withdrawn from the guide by insulating radius rods 5 on a shaft 6. The guide has a series of antenna slots 4 or the equivalent, the unit being used for producing an oscillating beam of radiant energy. In Fig. 4a, the vanes are in the form of radial ribs d, f on a conducting cylinder e which rotates close to extension walls h, i of a wave-guide a, b, c. Thus, in the position shown, the guide walls are completed by ribs d, e and the circumference of the cylinder between them. When the cylinder is rotated so that one of the ribs projects into the guide, the ribs on either side serve to complete the guide walls. By rotating the cylinder continuously, a repetitive phase shift is introduced. Alternatively, two cylinders may be used on opposite sides of a rectangular guide (Figs. 6a, 6b, not shown). The ribs may be in the form of ridges along a rotor having a starshaped cross-section (Figs. 5a, 5b, not shown). Fig. 7a shows a form in which the rotor runs gradually into a wave-guide from the lower end where the guide is separated from the rotor which, at this point has a circular cross-section, to the upper end where the rotor has a ribbed cross-section, Fig. 7b. Specification 589,603 is referred to. Reference has been directed by the Comptroller to Specification 617,381, [Group XL (c)].