Patent GB-813711-A (GB)
Title: Cavity resonator type electron tube apparatus
IPC: H01J23/207
Filed: 1956-12-31
Abstract: 813,711. Tuning cavity resonators. EITELMcCULLOUGH Inc. Dec. 31, 1956 [Feb. 27, 1956], No. 39627/56. Class 40 (8). [Also in Group XL (a)] In a discharge tube such as a klystron there is at least one composite cavity resonator comprising a vacuum-tight portion and an external portion separated by an insulating (ceramic) cylindrical tube wall section 26, Fig. 4, the external resonator portion being provided with a radially movable tuning door 41 having a contact rim making sliding contact over the entire periphery of the door with the resonator wall along an endless line lying in one plane, and a body portion of the door extending from the contact rim towards the discharge tube envelope and spaced from the resonator wall, the surface 42 of the tuning door facing the discharge tube being concave. The contact is preferably achieved by flexible fingers 46, 461. The external resonator portions may be detachable but preferably are not. The mode used is the TE101 mode. The external " tuning box " is of rectangular section and is made in two halves secured by bolts or, as shown in Fig. 2, by latches 34 and hooks 35. The wide sides 32 have semicircular recesses at their inner ends, semicircular flanges 36 being brazed to the rim of each recess. A semicircular metal strip 37 is attached to each flange 36 by screws 38 and semicircular strips having contact fingers 39 being clamped between 36, 37 so that when the two halves of the tuning box are clamped together fingers 39 are pressed against the rims of the end plates of the cavities. The concave tuning " door " is preferably a casting and has ribs 43 provided with screws 44 for the attachment of cover-plate 45. Two metal strips formed with contact fingers 46, 461 are clamped between 46, 46<SP>1</SP> and a split collar 49 fixed by screws 50 on top of cover-plate 45 extends into a recess into tuner actuating shaft 47 so that the threaded shaft 47 can rotate by actuating knob 56 but cannot move axially. A threaded plate 51 has a boss 53 to limit the axial movement of 47. The concave tuning door increases the tuning range (a) because the resonator volume at the inner end of travel of the plunger is reduced, compared to the volume with a straight plunger and (b) because with the mode used the high-frequency electric field is strongest at the centre and decreases outwardly. Consequently when the " door " is at its innermost position the capacitances across the narrow gaps to the walls 31, 32 are large and the gaps act as short circuits so the inner edge of 42 is both the real and apparent cavity boundary, while at the outermost position the capacitance is low and a substantial portion of the electric field crosses the gap at fingers 46, 46<SP>1</SP> so increasing the apparent volume of the cavity more than the real volume. The central portion of 42 is an arc of a circle concentric with ceramic cylinder 26 in the innermost position of 42, but the end portions of 42 are non-circular to avoid damage to the coupling loops during tuning. The coupling loop 64 is connected to the inner and outer conductors 62, 61 of a coaxial line feeder. The coupling loop can be'rotated to adjust the degree of coupling by rotating outer conductor 61, a collar 65 and screws 66 enabling the loop to be clamped in any adjusted position. If the external resonator parts are permanently secured in place, the plates 32 may be extended outwardly of the tube and long plates 31 brazed to plates 32 to form the "tuning box." The drift tuberesonator assembly is insulated from the collector by ceramic cylinder 16, and the gun terminals are incorporated in glass-metal stem 6. The collector has an exhaust tubulation 22 and a cooling structure (not shown).