Dielectric material coaxial resonator with improved resonance frequency adjusting mechanism
This application is a continuation of now abandoned application Ser. No. 608,082, filed May 8, 1984. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to a coaxial resonator and more particularly, to a dielectric material coaxial resonator employing a dielectric material block, and provided with an improved resonance frequency adjusting mechanism. 
     Commonly, as shown in FIG. 1, a 1/4 wavelength coaxial TEM resonator includes a dielectric material member 3, for example, of a titanium oxide group ceramic dielectric material or the like provided between an inner conductor 1 and an outer conductor 2. More specifically, a material having superior high frequency electrical conductivity and having a favorable adhesion with respect to the dielectric material member 3, for example, silver paste is baked onto the inner wall surface i.e. the peripheral surface of a through-opening 5 formed in the dielectric material member 3 and the outer wall surface of said dielectric material member 3 to form the inner conductor 1 and the outer conductor 2, with said inner and outer conductors 1 and 2 being short-circuited by an electrode or conductive layer 4 formed on one end face of the dielectric material member 3, thus providing a short-circuited end 3a on said one end face and an open end 3b on the other end face of said dielectric material member 3. 
     Conventionally, for a resonance frequency adjusting mechanism of a 1/4 wavelength coaxial TEM resonator of the above described type, there has generally been known an arrangement in which a sleeve 6 formed with an internally threaded portion 6s therein is fitted into the through-opening 5 against the inner conductor 1 at the open end 3b of the dielectric material member 3, and an adjusting screw 7 of a metallic material is threaded into the internally threaded portion 6s so the resonance frequency can be adjusted by turning or vertically moving the adjusting screw 7. 
     However, in the resonance frequency adjusting mechanism for the dielectric material coaxial resonator as described above, since the adjusting screw 7 is threaded into the internally threaded portion 6s at the inner side of the open end 3b of the dielectric material member 3 at which the current is concentrated, there has been a drawback that the path through which the ground current flow is altered, with a consequent instability of the resonance frequency due to side play, etc. before the adjusting screw 7 has been fixed to the internally threaded portion 6s by a bonding material or the like. 
     SUMMARY OF THE INVENTION 
     Accordingly, an essential object of the present invention is to provide a dielectric material coaxial resonator provided with an improved resonance frequency adjusting mechanism which is capable of eliminating deviations of the resonance frequency after adjustment thereof for adjusting said resonance frequency. 
     Another important object of the present invention is to provide a dielectric material coaxial resonator of the above described type, which has a simple construction and functions accurately, and can be readily manufactured on a large scale at low cost. 
     In accomplishing these and other objects, according to one preferred embodiment of the present invention, there is provided a dielectric material coaxial resonator which includes a dielectric material member having a through-opening axially formed therein, an inner conductor formed on the inner wall surface of the through-opening of the dielectric material member and an outer conductor formed on the outer wall surface of the dielectric material member, a conductive layer formed on one end face of the dielectric material member as a short-circuiting end face for conduction between said inner and outer conductors, and a resonance frequency adjusting mechanism which further comprises a resonance frequency adjusting member which alters the resonance frequency of the dielectric material member by being axially moved within said through-opening thereof, spring means which contacts under pressure, the outer peripheral surface of the resonance frequency adjusting member so as to connect said resonance frequency adjusting member with said inner conductor in the vicinity of the open end of the dielectric material member remote from said short-circuited end face thereof, and a displacing mechanism provided at said short-circuited end face of said dielectric material member for displacing said resonance frequency adjusting member through the interior of said through-opening of said dielectric material member. 
     By the arrangement according to the present invention as described above, a dielectric material coaxial resonator with an improved resonance frequency adjusting mechanism has been advantageously provided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and features of the present invention will become apparent from the following description of preferred embodiments thereof given with reference to the accompanying drawings, in which; 
     FIG. 1 is a longitudinal sectional view of a conventional dielectric material coaxial resonator having a known resonance frequency adjusting mechanism (already referred to), 
     FIG. 2 is a longitudinal sectional view of a dielectric material coaxial resonator provided with an improved resonance frequency adjusting mechanism according to one preferred embodiment of the present invention, 
     FIG. 3 is a view similar to FIG. 2, which particularly shows a modification thereof, 
     FIG. 4 is a cross section of a metallic bar employed in the resonance frequency adjusting mechanism of the dielectric material coaxial resonator of FIG. 3, and 
     FIGS. 5 and 6 are longitudinal sectional views of dielectric material coaxial resonators according to further modifications of the present invention in which displacing mechanisms for frequency adjusting bars are provided in the outside casings of the coaxial resonators. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings. 
     Referring now to the drawings, there is shown in FIG. 2 a dielectric material coaxial resonator RA provided with a resonance frequency adjusting mechanism according to one preferred embodiment of the present invention. The coaxial resonator RA includes a dielectric material body 3 having a through-opening or axial bore 5 extending therethrough generally at its central portion, an inner conductor 1 formed on the peripheral surface of the axial bore 5, an outer conductor 2 formed on the outer wall surface of the dielectric material body 3, and an electrode or conductive layer 4 formed on one end face of the body 3 for connection between the inner conductor 1 and the outer conductor 2, and thus, a short-circuited end 3a is provided on said one end, with an open end 3b formed on the other end face of the body 3 in the similar manner as in the known 1/4 wavelength coaxial TEM resonator described earlier with reference to FIG. 1. In the resonator RA of FIG. 2 according to the present invention, the resonance frequency adjusting mechanism further includes a metallic bar 11 constituting a resonance frequency adjusting member arranged to move through the interior of the through-opening 5 in the axial direction of the dielectric material body 3, a pair of opposed plate springs 12 provided within the through-opening 5, with confronting contact portions 12a which are formed on upper portions of the plate springs 12 being held under pressure contact against the outer peripheral surface of the metallic bar 11 as shown, and first member in the form of a sleeve 13 having an internally threaded portion 13s axially formed therein and a movable member 11b threaded therein and on which said bar is mounted ofr displacing the metallic bar 11 within the through-opening 5 of the dielectric material body 3. 
     More specifically, the metallic bar 11 is prepared by cutting a round metallic rod (not shown), for example, of brass or the like into the bar 11 having a length approximately equal to that of the dielectric material body 3, and the moveable member is formed as an external thread 11b on the bar 11 other than at a frequency adjusting portion 11a provided at its one end, while a groove 11c for rotating the moveable member 11b by fitting an edge of a screw driver (not shown), etc. thereinto is formed in the end face at the other end of said moveable member 11b from said bar 11. 
     Each of the plate springs 12 has the contact portion 12a formed adjacent to one end thereof for contact with the frequency adjusting portion 11a of the metallic bar 11, while the other end of the plate spring 12 is bent inwardly at approximately right angles thereto so as to form a retaining portion 12b for the sleeve 13 having the internally threaded portion 13s. 
     The sleeve 13 formed with the internally threaded portion 13s has a flange portion 13a with a diameter larger than that of the through-opening 5 of the dielectric material block 3, and is provided with an annular retaining groove 13b at its neck portion adjacent to the flange portion 13a for receiving the retaining portions 12b of the plate springs 12 therein. For preventing the sleeve 13 itself from undesirable rotation, said sleeve 13 is fixed to the coaxial resonator, for example, by a bonding agent. 
     Within the through-opening 5 of the dielectric material block 3, the pair of plate springs 12 are inserted, with upper ends thereof being engaged with the inner conductor 1 at positions close to the open end 3b of the dielectric material body 3, while the metallic bar 11 is fitted in between the plate springs 12, with the contact portions 12a of the plate springs 12 being held under pressure contact against the outer peripheral surface of the resonance frequency adjusting portion 11a of the metallic bar 11. Moreover, at the other ends of the plate springs 12, the retaining portions 12b of the plate springs 12 are fitted into the retaining groove 13b of the sleeve 13 for the internal thread 13s, with the external thread of moveable member 11b being engaged with said internal thread 13s of the sleeve 13. 
     The internally threaded portion 13s of the sleeve 13 and the externally threaded moveable member 11b constitute a mechanism for displacing the metallic bar 11 as a resonance frequency adjusting member, and by turning the moveable member 11b, with the tip of a screw driver (not shown) being fitted in the groove 11c at the end of the member 11b adjacent the the short-circuited end 3a of the dielectric material body 3, the frequency adjusting portion 11a of the metallic bar 11 selectively moves out of or into the open end 3b of the dielectric material block 3, and thus, the 1/4 wavelength coaxial TEM resonator has its effective length varied, with a consequent variation of the resonance frequency thereof. 
     In the above case, the frequency adjusting portion 11a of the metallic bar 11 is adapted to be connected to the inner conductor 1 at a predetermined position close to the open end 3b of the dielectric material block 3 through the contact portions 12a of the plate springs 12, and even if there is side play or looseness of the metallic bar 11, the frequency adjusting portion 11a of the metallic bar 11 is connected to said inner conductor 1 at the predetermined position as described above through said contact portions 12a, and thus, the undesirable variation of the resonance frequency is almost eliminated. 
     Referring further to FIG. 3, there is shown a modification of the coaxial resonator RA of FIG. 2. In the modified coaxial resonator RB in FIG. 3, the metallic bar 11 , plate springs 12, and the sleeve 13 having the internal thread 13s, described as employed in the arrangement of FIG. 2, are replaced by a moveable member in the form of an adjusting screw 21 provided with an external thread 21a and having a large head portion 21h, and rotatably supported at the short-circuited end 3a in a fixed member 12F having plate springs 12B extending integrally therefrom, while the external thread 21a of the adjusting screw 21 is engaged with an internally threaded opening 22a axially formed in a metallic bar 22 constituting the resonance frequency adjusting member, whereby upon rotation of the head portion 21h of the above adjusting screw 21 , the metallic bar 22 is displaced between the contact portions 12b of the opposed plate springs 12B so as to emerge from or enter the open end face 3b of the dielectric material member 3. 
     In the modification of FIG. 3, for avoiding simultaneous rotation of the metallic bar 22 together with the adjusting screw 21, the metallic bar 22 is provided with two parallel sliding surfaces 22b which are held in sliding contact with contact portions 12b (provided at four positions in this embodiment) of the plate springs 12B as shown in FIG. 4. 
     By the arrangement of FIG. 3 also, generally similar effects as in the embodiment of FIG. 2 may be obtained. 
     In the foregoing embodiment, the metallic bar 11 or 22 may be replaced by a similarly shaped member having a metallic film on the surface for application as a resonance frequency adjusting member. 
     It should be noted here that, in the foregoing embodiment, the displacing mechanism for the adjusting bar 11 or 22 may be modified so that it is outside the casing (partly shown at W in FIG. 5) of a device employing the 1/4 wavelength coaxial TEM resonator so that the metallic bar 11 or 22 is moved as shown, for example, in the further modifications illustrated in FIGS. 5 and 6. 
     In the modified coaxial resonator RC of FIG. 5, the metallic bar 11 described as employed in the resonator RB of FIG. 3 is replaced by a resonance frequency adjusting member in the form of a cylindrical adjusting bar 30 of a magnetizable material held between contact portions 12c of plate springs 12C fixed in the inner conductor 1 for the through-opening 5, while a moveable member in the form of a spindle P for an outer sleeve M coupled with a known micrometer mechanism (not particularly shown) accommodated in said outer sleeve, extends through a housing f containing a coil C connected to a power source V through a switch Sw, and a wall W which is a part of the casing with a distal end Pa of the spindle P contacting a corresponding inner end 30a of the adjusting bar 30. 
     In the above arrangement, the switch Sw is turned on for the adjustment so as to magnetize the spindle P by the coil C, and thus, the adjusting bar 30 attracted to the spindle P by the magnetic force of said spindle is moved as the spindle P is displaced by the micrometer mechanism in the outer sleeve M. It should be noted here that in the above case, the spindle P is subjected to very slow or fine displacement, with the positional relationship between the device employing the 1/4 wavelength coaxial TEM resonator and the sleeve M being maintained constant. Upon completion of the adjustment, the switch Sw is turned off for de-magnetization of the spindle P. The adjusting bar 30 can be fixed only by the spring force of the plate springs 12C, but a resin may be further applied between the adjusting bar 30 and the plate springs 12C and/or between the plate springs 12C and the inner conductor 1. 
     In the further modified coaxial resonator RD of FIG. 6, the metallic bar 11 in the coaxial resonator RB of FIG. 3 is also replaced by an adjusting bar 40 having a projecting end 40a in which a pair of recesses 40r are formed, and held between contact portions 12d of the plate springs 12D in a similar manner as in FIG. 5. The spindle P of the micrometer mechanism in the outer sleeve M of the same construction as that in FIG. 5 has a holder H secured at its end and having a pair of spaced claws Hc which can be engaged with the recesses 40r of the projecting end 40a of the adjusting bar 40. The holder H is provided with a ring r fitted therearound for manual movement in the axial direction to keep the holder H closed when the claws Hc thereof have been received in the recesses 40r. 
     In the arrangement of FIG. 6 also, the adjusting bar 40 may be displaced and fixed for adjustment in a similar manner as in the arrangement of FIG. 5. 
     It should also be noted that the present invention is not limited in its application only to the single cylindrical dielectric material coaxial resonator as described so far, but may be readily applied to arrangements in which two or more dielectric material coaxial resonators are formed in one dielectric material body as disclosed, for example, in Japanese Patent Laid-open Application Tokkaisho No. 58-9401. 
     As is clear from the foregoing description, according to the present invention, since it is arranged so that the resonance frequency adjusting member which is displaced within the dielectric material body for the adjustment of resonance frequency of the dielectric material coaxial resonator is arranged to be connected to the inner conductor in the vicinity of the open end of the resonator by the spring means held under pressure contact with the outer peripheral surface thereof, the resonance frequency adjusting member can be electrically connected to the inner conductor at a predetermined position close to the open end of the inner conductor, and thus, even when a certain amount of side play or looseness is present in the mounting of the resonance frequency adjusting member, there is almost no variation in the resonance frequency. Another advantage of the present invention is such that, as compared with the conventional arrangements in which the resonance frequency is adjusted by scraping off the dielectric material block for alteration of its dimensions, the resonance frequency may be simply adjusted by a screw driver even after assembly of the resonator. 
     Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be noted here that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention, they should be construed as being included therein.