Patent GB-892681-A (GB)
Title: Resonant cavity
IPC: H01J23/207
Filed: 1958-07-28
Abstract: 892,681. Velocity modulated tubes. EITELMcCULLOUGH Inc. July 28, 1958 [Nov. 21, 1957], No. 24208/58. Class 39(1) [Also in Group XL(b)] A klystron has a tuned cavity resonator of rectangular or circular cross-section of which two walls have opposed surfaces, conductive side wall means which forms a substantially enclosed space, a conductive tuning plunger plate substantially parallel to the A.C. magnetic field and transversely between the opposed surfaces and in electrical contact therewith within the enclosed space, the conductive plate being spaced from the side wall means, and means for moving the conductive plate across the A.C. magnetic field and along the opposed surfaces whereby the A.C. electromagnetic field is shaped to determine the effective size of the resonant cavity. The klystron has one, two or more than two, e.g. four cavity resonators and one, two or more than two tuning plungers in each resonator, the tuning plunger(s) serving to shape the magnetic component of the electromagnetic field to produce in effect a resonant cavity of smaller size than the size of the entire resonator, the movement of the tuning plunger(s) producing a change in dimensions of this smaller equivalent cavity to effect tuning. The klystron preferably has resonators, Fig. 12 (not shown) each having two tuning plungers each resonator being made in 2 sections clamped together and each having a cylindrical ceramic window sealed thereacross the outer resonator portion being attached to the tuner resonator portion by spring fingers or the resonators may be wholly integral with the tube envelope. The resonators may have a square or circular crosssection the tuning plungers being concave and having spring fingers as shown at 51, Fig. 3. The tuning arrangement is said to provide a linear relationship between frequency and movement over a wide frequency range. The tuning plungers in each resonator are preferably but not necessarily moved by equal amounts. The coupling loop 46 for feeding or abstracting energy can be rotated by knob 48 to alter the coupling with the resonator field, the loop is preferably capacitively coupled to rather than directly connected to the resonator wall so that it is stated some of the loop inductance is neutralised so decreasing the inductive coupling with the field in the resonator. The frequency variation is larger at the inner portion than at the outer portion of travel of the tuning plunger. The tuning plungers are spaced from end walls 41 by a distance approximately equal to half the plunger width (both dimensions in plane of paper) in Fig. 1. The coupling loop 46 can be replaced by a probe placed as near as possible to the central interaction gap and extending from the upper or lower wall of the resonator or by an iris opening. The resonator wall may be perforated for air circulation for cooling the ceramic window 28. For operation at the upper frequency end of the tuning range the end walls or small portions of the side walls behind the tuning means 29 could be removed (but preferably the walls are retained to prevent power loss) without disturbing the field distribution.