US 3090018 A
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May 14, 1963 Filed Oct. 6, 1959 D W. FOSS REFERENCE CAVITY RESONATOR 2 Sheets-Sheet l INVENTOR.
DAVID W. FOSS ATTORNE Y May 14, 1963 Filed Oct. 6, 1959 D, w. Foss 3,090,018
REFERENCE CAVITY RESONATOR 2 Sheets-Sheet 2 INVENTOR.
DAVID W. FOSS ATTORNEY 3,090,018 REFERENCE CAVITY RESONATOR David W. Foss, Ipswich, Mass, assiguor, by mesne assignments, to Varian Associates, Palo Alto, Calif., a corporation of California Filed Oct. 6, 1959, Ser. No. 844,768 6 Claims. (Ql. 333--83) The present invention relates to electromagnetic waveguide apparatus and more particularly to a novel structure for mounting standard reference cavity resonators in such apparatus.
Reference cavities have achieved rwide usage in the microwave frequency spectrum to maintain a fixed predetermined precise reference frequency which can be maintained under severe and variable environmental conditions. Mobile transmitters or radar beacons may be regulated or activated accurately with such devices. An example of prior art construction is illustrated in US. Patent No. 2,584,717 issued to D. Alpert et al. Such resonators are generally manufactured as integral units with the resonant cavity and mounting structure combined due to the necessity for control of frequency changes with temperature variations as well as accuracy in maintaining the required frequency response.
Often it becomes necessary to employ several resonators having predetermined frequency settings and in such situations disassembling of the system is required in order to install another unit. This results in delays, increased labor costs and lack of use of critical equipment. A need has arisen, therefore, for an extremely precise, rapidly replaceable structure to facilitate change of reference frequencies within a short time and preferably without tools, in all types of waveguide systems with the same qualities of performance under severe environmental conditions as exhibited by integrally combined resonators.
The present invention, therefore, has for its primary object the provision of a novel standard reference cavity resonator having a separate, easily replaceable unit for a microwave frequency waveguide apparatus to thereby alter the frequency standard.
Another object is the provision of a novel reference cavity resonator for use in microwave frequency waveguide apparatus, the frequency thereof being readily altered Without disassembling of the waveguide apparatus.
Further objects, features and advantages will be apparent after consideration of the following detailed specification and appended drawings, in which:
FIG. 1 is an exploded perspective view of an illustrative embodiment;
FIG. 2 is a cross-sectional view along the line 2-2 in FIG. 1;
FIG. 3 is an end view of the replaceable unit after insertion in the mounting block; and
FIG. 4 is an end view similar to FIG. 3 with the replaceable unit rotated 90 to the locked position.
Referring to the drawings, FIG. 1 is illustrative of the preferred method of mounting the embodiment of the invention in waveguide apparatus. A metallic mounting block 1 is secured between hollow pipe waveguide sections 2 and 3 by means of flanges 4 and 5 abutting opposite faces 6 and 7 of block 1 and screw fastening means introduced through flange holes 3. An opening 9 is provided in opposite walls of block 1 mating with the waveguide sections with the dimensions of the openings being approximately equal to the internal dimensions of the adjacent waveguide sections. Adjacent to the opening 9 in the input face 6 of block 1, two slots 10 and 11 are provided parallel to the wide dimensions of the opening. This arrangement provides a choke to suppress transmitted off-resonance power that would otherwise 3,099,018 Patented May. 141, 1963 pass around the reference cavity resonator unit after it is inserted within the block 1 in the manner to be hereinafter described. If desired the choke slots 10 and 11 may be also provided in the output face 7 to handle any matching problems in the overall waveguide apparatus.
The replaceable reference cavity resonator unit 12 will now be described with particular attention being directed to FIG. 2. A main body cylinder 13, generally fabricated from the metal commonly referred to as lnvar having a low coeflicient of expansion, defines a resonant cavity 14 enclosed at opposite ends by cover members 15 and 16. A choke type plunger 17 is secured to cover member 16 by screws 18 and separated from 16 by spacers 44 of a material having a high coefiicient of expansion thereby maintaining the frequency of the cavity resonator during changes in ambient temperature. An external vane type handle 19 is also secured to body cylinder 13 by means of screws 20 to provide for handling of the unit 12 in the removal and insertion thereof within block 1.
A cylinder 21 extends from cover member 15 and houses a fine tuning mechanism for final adjustment of the resonant frequency of the cavity resonator after the tuning plunger 17 has been positioned. Pins 22 protrude on opposite sides of cylinder 21 in a direction perpendicular to the axis of cavity 14. Recessed dielectric covered windows 23 and 24 enclose opposed openings in main body cylinder 13 to provide for transmission of electromagnetic waves into and out of the cavity 14.
Mounting block v1 is provided with a key-way slot 25 in face 26 dimensioned to receive the end of the replaceable resonator 12 having the cylinder 21 and pins 22 disposed thereon. Metallic locking plate members 27 and 28 are disposed on either side of the arcuate portion of key-way 25 and secured to block 1 by means of screws 2?, 30, 35 and 36. The locking plate members are provided with ramp angles 31 and 32 and grooves 33 and 34. Screws 35 and 36 act as stop members. The positioning of the locking plate members will be noted in FIGS. 3 and 4 with the stop members 35 and 36 disposed angularly to all the parallel Walls of block 1.
The installation of the replaceable cavity resonator unit in block 1 will now be described reference being again directed to FIGS. 3 and 4. A cavity resonator unit 12 set to the desired frequency is held by handle 19 in a position with the windows 23 and 24 disposed approximately from the block openings 9. In this position, pins 22 will enter key-way in the manner shown in FIG. 3. Rotation of the unit will then result in pins 21 riding up ramps 31 and 32 and then dropping into grooves 33 and 34 against stop members 35 and 36 as shown in FIG. 4. Within the cylindrical chamber defined by hollow block 1, two rubber 0 rings '37 and 38 are retained *by two split washers of fluorine polymer 39 and 40 set into counter bores in the chamber walls. The ridged portion 45 of the main body cylinder 13 and the cover member 15 will bear against the washers and gradually compress the 0 rings as the replaceable unit 12 is rotated to the locked position. The 0 rings and washers provide not only the compressive force to retain the replaceable unit in the locked position but also assure that the replaceable unit is concentrically disposed within block 1 to prevent any frequency change due to misalignment. The 0 rings also serve to buffer the effects of shock and vibration so that frequency change under such conditions is negligible. In addition, these components are necessary to thermally isolate the Invar cylinder from the block member, commonly fabricated from aluminum. Since the two metallic members would result in cavity distortion; hence a frequency change with a change in temperature. To eliminate the effect of humidity on the resonant frequency the unit 12 is evacuated and filled with 3 a gas at reduced pressure by means of exhaust tubulation 41 recessed within handle 19. Cover member 42 is secured to face 26 by means of screws 43 to enclose the cylinder 21 and locking plate members 27 and 28.
The invention facilitates the use of any number of replaceable units each pre-set to a different resonant frequency. In actual installations, units have been inserted and released as much as one hundred fifty times while their frequencies have remained Within 0.20 megacycles of the original value. Over the temperature range of 75 C., the frequency change of all the units was less than 0.26 megacycles.
While an illustrative embodiment of the invention has been specifically described, many variations or modifications will occur to skilled artisans. It is my intention to cover in the appended claims such variations r modifications as fall within the spirit and scope of the invention.
What is claimed is:
1. Waveguide apparatus comprising a metallic block member adapted for mounting between hollow-pipe waveguide structure, said block member defining openings in opposed walls to permit passage of electromagnetic wave energy, a reference cavity resonator unit removably mounted within said block member along an axis extending perpendicular to the axis of the waveguide structure, said resonator unit being responsive to a fixed predetermined resonant frequency and having a pair of aligned Windows, metallic means disposed on one wall of said resonator unit for locking said resonator unit within said block member with said pair of windows aligned with said openings in said block member, and means disposed at one end of said resonator unit for engaging said locking means to prevent alteration of frequency response due to improper seating of the resonator unit upon insertion within said block member.
2. Waveguide apparatus comprising a metallic block member adapted for mounting between sections of hollow-pipe waveguide, said block member defining openings in opposed walls adjacent to said waveguide sections, said block member further defining a cylindrical opening in one of the remaining walls and a key-way slot in the opposite wall, a reference cavity resonator unit adapted for insertion and removal in said cylindrical opening with an end thereof projecting through said key-way slot, said resonantor unit being responsive to a fixed predetermined resonant frequency and having a pair of aligned windows, metallic locking plate members disposed on opposed sides of said key-way slot, each of said plate members defining an inclined ramp portion and a groove, a cylindrical extension disposed at one end of the resonator unit with metallic pins extending laterally to the axis of the extension, said pins engaging said ramp portions as said resonator unit is rotated within said block member until said grooves are engaged for aligning said pair of windows with said openings in said block member to thereby positively lock the resonator unit in the position to respond to electromagnetic wave energy transmitted through the adjacent waveguide sections.
3. Waveguide apparatus according to claim 2 wherein paired longitudinal slots are provided in at least one wall of the block member parallel to the longest dimension of the openings adjacent to the waveguide sections.
4. Waveguide apparatus comprising a waveguide structure having first pair of two aligned openings disposed in opposite side walls of said waveguide structure, a reference cavity resonator unit having a pair of aligned Windows disposed in opposite side walls with the alignment of said windows disposed transversely to the alignment of said openings, said resonator being removably mounted within said first pair of openings and the ends of said unit protruding through said opening, twist lock means on said resonator unit and said waveguide structure for locking said resonator to said waveguide structure with the alignment of said pair of windows coinciding with said waveguide alignment for preventing alteration of frequency response due to improper sealing and alignment of said unit within said waveguide member.
5. The apparatus of claim 4 wherein said waveguide structure comprises a hollow block member with a second pair of aligned openings disposed in opposite side walls and aligned perpendicular to said first pair of openings, means disposed on said block member for mounting a pair of waveguide sections to communicate with said second pair of aligned openings, and said pair of aligned windows are aligned with said second pair of openings when said unit is locked within said block.
6. The apparatus of claim 4 wherein said twist lock means comprises a cylindrical extension disposed on one end of said unit and protrudes through one of said first pair of openings, metallic pins extend laterally to the axis of extension, a metallic member disposed around said one opening and having incline ramp portions and grooves, and resilient means disposes between said unit and said waveguide structure.
References Cited in the file of this patent UNITED STATES PATENTS 2,451,982 Scott Oct. 19, 1948 2,734,174 HeinS Feb. 7, 1956 2,781,500 Armstrong Feb. 12, 1957 2,783,295 Ewing Feb. 26, 1957 2,791,720 Lesch May 7, 1957 2,817,760 Dobbertin Dec. 24, 1957 2,831,047 Wadey Apr. 15, 1958