Patent GB-898202-A (GB)
Title: Tunable electromagnetic cavity
IPC: H01P7/06
Filed: 1960-06-29
Abstract: 898,202. Tuning cavity resonators. GENERAL DYNAMICS CORPORATION. June 29, 1960 [Dec. 16, 1959], No. 22753/60. Class 40(8). A cavity resonator comprises a mechanism for tuning the cavity continuously through two spaced frequency bands and for automatically shifting the resonant frequency of the cavity from one frequency band to the other. As shown in Fig. 5, two such cavities 27, 28 coupled by a loop 38 are simultaneously tuned through the same ranges by a ganged tuning mechanism. The input and output circuits to the cavities may comprise inductive loops (not shown) and the output circuit may comprise a rectifier mounted on the side of one of the cavities. Each cavity comprises a fixed, hollow inner conductor 45 within which slides a tuning member 54. During tuning through the higher of the two frequency bands, a portion L 4  of the cavity is short circuited by contacts 60a, Fig. 3 mounted upon a spindle 61. A variable portion L, of the end 56 of the tuning member is exposed and effects continuous linear tuning of the cavity. At the lower limit of the higher frequency band, the spindle 61 is automatically rotated through 90 degrees to remove the short circuit whereby the resonant frequency of the cavity is shifted to the upper limit of the lower frequency band. During tuning through this band, an enlarged portion 57 of the tuning member 54 is exposed, this enlargement being necessary to preserve linearity of tuning which would otherwise be destroyed by removal of the short circuit. The tuning member 54 is rigidly attached to a yoke 73 mounted on the end of an externally threaded shank 92 biased to its right-hand position by a spring 97. Axial movement of the shank 92 is controlled by an annular drive member 84 which is threaded upon the shank and also threaded within a fixed mounting ring 26c. The drive ring 84 is connected by pillars 78, 79 to a rotatable plate 77 and slides axially upon the pillars as it rotates with the plate. In order to allow adjustment of the tuning, the ring 84 is provided with an angularly adjustable hub 90 clamped to the ring by a plate 99. Further adjustment may be effected through the screw connection between the post 54 and yoke 73. Angular movement of the spindle 61 to cause band switching is effected by a pawl 101 rigidly clamped to the spindle and adapted to be actuated by the edge of the drive ring 84 when this reaches the appropriate axial position. The ring is formed with steps 111, 112, Fig. 8, which simultaneously actuate the pawls of both resonators against the bias of coil springs 103, 104. In a modification of this construction (Fig. 9, not shown). the drive ring 84 is made in one piece and carries at its left-hand edge an annular cam for actuating the pawls 101. This cam is adjustable both angularly and axially upon the drive ring. The modified arrangement of Fig. 11 uses only one thread 285, the driving ring 284 being rotatable upon a bearing 278 fixed to the shank 276 of the yoke 273. The ring and the yoke move axially in unison. In the modified construction of Fig. 13, he switch-actuating cam 385 is adjustably mounted upon a driving cylinder 398. This assembly is threaded upon a fixed stud 373 and is rotated by studs 378, 379 extending from a yoke 377 on the driving shaft 381. A bearing 391 transmits the thrust of the driving cylinder 398 to the movable tuning elements. In this construction, and in the others if desired, the short-circuiting contacts 60a may be mounted upon a telescopically adjustable sleeve surrounding the end of the spindle 361. In the embodiment shown in Figs. 15, 16 band-shift is effected by changing the capacitance of the cavities 500 (one only shown). Each cavity is tuned through both frequency bands by a threaded plunger 504 which rotates within a fixed bush 505. Within the low-frequency range the cavity is loaded by the capacitance between the end 524 of the plunger and a plate 509 mounted for rotation upon a dielectric shaft 510. Within the high-frequency range the plate 509 occupies the position shown in broken line in Fig. 16 where it is ineffective. In order to compensate for the change in characteristic impedance consequent upon the change in -capacitance, the shaft 510 carries a metallic paddle 513 which rotates with the plate 509 between the two positions shown in Fig. 16. The edge of the plate 509 is guided by a rail 525. Rotation of the shaft 510 is accomplished by means of a lever 516 which rotates with the plunger 504 and engages a slotted pawl 520 on the shaft when the plunger reaches the appropriate axial position. The frequency at which the band-shift takes place may be adjusted by altering the positions of the lever 516 or the pawl 520.