Abstract:
The present invention relates to a dielectric resonator ( 20 ) comprising a dielectric resonator body ( 30, 40, 50, 60, 70, 80 ), where the resonator body includes at least two resonant elements ( 25, 26 ), wherein by altering the shape of the dielectric resonator body the resonance frequency (fr) in the dielectric resonator can be adjusted. The alteration of the shape of the resonant body is performed by rotation of one element in relation to another element in such a way that said elements are in mechanical contact, through connecting means, in at least one location at any time.

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to a device for tuning of a resonator, more specifically to a resonator comprising a resonator body where the shape of the body can be changed and thus change the resonance frequency. 
     DESCRIPTION OF RELATED ART 
     Among high-frequency and microwave resonator structures, so-called dielectric resonators have recently become increasingly interesting as they offer e.g. the following advantages over conventional resonator structures: smaller circuit sizes, higher integration level, higher efficiency and lower cost of manufacture. Any element having a simple geometric shape made of a material having low dielectric losses and a high relative dielectric constant can be used as a high Q dielectric resonator. For reasons of manufacturing technique, the dielectric resonator is usually cylindrical, such as a cylindrical disc. 
     The resonance frequency of the dielectric resonator is primarily determined by the dimensions of the resonator body. Another factor affecting the resonance frequency is the environment of the resonator. The electric or magnetic field of the resonator and, thus, the resonance frequency can be intentionally affected by introducing a metal surface or any other conductive surface in the vicinity of the resonator. To adjust the resonance frequency of the dielectric resonator, a common practice is to adjust the distance between the conductive metal surface and the planar surface of the resonator. The adjusting mechanism may be e.g. an adjustment screw attached to the housing surrounding the resonator. 
     Alternatively, it is also possible to bring another dielectric body to the vicinity of the resonator body instead of a conductive adjustment body. One prior art design of this kind, based on dielectric plate adjustment is shown in FIG.  1 . 
     In this kind of adjusting method, however, it is typical that the resonance frequency varies nonlinearly as a function of the adjusting distance. Due to the non-linearity and the steep slope of adjustment, accurate adjustment of the resonance frequency is difficult and demands great precision, particularly at the extreme ends of the control range. 
     Frequency adjustment is based on a highly accurate mechanical movement, the slope of adjustment also being steep. In principle, the length and thus the accuracy of the adjusting movement may be increased by reducing the size of the metallic or dielectric adjustment plane. 
     Due to the non-linearity of the above mentioned adjusting techniques, however, the achieved advantage is small, since the portion of the adjusting curve which is too steep or too flat either at the beginning or at the end of the adjusting movement can not be used. As a result, adjusting the resonance frequency of a dielectric resonator with these solutions sets very high demands on the frequency adjustment mechanism, which in turn, increases the material and production costs. In addition, as the mechanical movements of the frequency adjustment device must be made very small, adjustment will be slower. 
     In U.S. Pat. No. 5,703,548, by Särkkä, the above problems was solved by introducing a dielectric resonator comprising a plurality of dielectric adjustment planes. This results in improved linearity of frequency adjustment and a longer adjusting distance, which both improve the accuracy of adjustment. 
     In U.S. Pat. No. 4,459,570, by Delaballe et al., a similar problem has been solved by introducing a resonator having a dielectric constant of an adjustment plate with half the value of the dielectric constant of the resonator disc. 
     In U.S. Pat. No. 5,315,274, by Särkkä, where tuning of a resonance frequency is achieved by a dielectric resonator comprising two cylindrical discs positioned on top of each other, which are radially displaceable with respect to each other and thereby varying the shape of the resonator. 
     SUMMARY OF THE INVENTION 
     The basic idea of the invention is to utilise the linear part of the adjustment curve although the curve is steep, thus difficult to adjust and to keep stable. 
     The object of the invention is a dielectric resonator in which the resonance frequency can be adjusted more accurately than previously within the steep slope. 
     In accordance with the invention this object is achieved by an inventive dielectric resonator, comprising a dielectric resonator body, where the resonator body includes at least two resonant elements, wherein by altering the shape of the dielectric resonator body the resonance frequency of said dielectric resonator can be adjusted. The alteration of the shape of the resonant body is performed in such a way that said elements are in mechanical contact, through connecting means, in at least one location at any time. This contact may be established via an interconnecting element. The dielectric resonator body also comprise means for moving at least a first resonant element in relation to at least a second resonant element of the resonant body and thus altering the shape of said body. The movement is be performed by rotation of the first element around an axis. 
     The dielectric resonator body may further comprise connecting means for connecting said first and second element, and the rotation, of said first element, can cause a displacement of said first element, in relation to said second element, in a direction of the rotation axis. 
     The resonator may comprise additional means for adjustment of the displacement by means for mechanical guidance. These means for adjustment may be incorporated in the connecting means by which the resonating elements are in contact with each other in at least one location. 
     The resonating elements may also be circularly cylindrical, where the connecting means are implemented in a circular or part-circular path, having a centre at said rotation axis. 
     A first advantage with the present invention is that a maximal stability in respect of relative displacement and vibrations between the elements is achieved. 
     A second advantage is that a temperature compensating resonator structure easily can be implemented. 
     A third advantage is that a compact resonator structure is obtainable. 
     A fourth advantage is that a high sensitivity can be obtained in respect of resonance frequency versus displacement. 
     A fifth advantage is that this type of dielectric resonator body can operate in a high power environment. 
     In the following, the invention will be disclosed in greater detail by way of example with reference to the attached drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a  shows a cross-sectional side view of a dielectric resonator in accordance with the prior art. 
     FIG. 1 b  shows a graph of resonance frequency versus displacement. 
     FIG. 2 shows an exploded perspective view of a dielectric resonator in accordance with the inventive concept. 
     FIG. 3 a  shows an exploded perspective view of a two-part resonator body comprising two resonant element with a double slope adjustment means in accordance with the inventive concept. 
     FIG. 3 b  shows a side view of the embodiment in FIG. 3 a.    
     FIG. 3 c  shows an exploded perspective view of an alternative two-part resonator body comprising two resonant element with a single slope adjustment means in combination with a tracking means in accordance with the inventive concept. 
     FIG. 3 d  shows a side view of the embodiment in FIG. 3 c.    
     FIG. 4 a  shows an exploded perspective view of a three-part resonator body comprising two resonating elements and a first type of interconnecting element with a double slope adjustment means in accordance with the inventive concept. 
     FIG. 4 b  shows a side view of the embodiment in FIG. 4 a.    
     FIG. 4 c  shows an exploded perspective view of an alternative three-part resonator body comprising two resonating elements and a first type of interconnecting element with a single slope adjustment means in combination with a tracking means in accordance with the inventive concept. 
     FIG. 4 d  shows a side view of the embodiment in FIG. 4 c.    
     FIG. 5 a  shows an exploded perspective view of a three-part resonator body comprising two resonating elements and a second type of interconnecting element with a non-overlapping tracking guide in combination with a tracking means in accordance with the inventive concept. 
     FIG. 5 b  shows a side view of the embodiment in FIG. 5 a.    
     FIG. 5 c  shows an exploded perspective view of a three-part resonator body comprising two resonating elements and a second type of interconnecting element with an overlapping tracking guide in combination with a tracking means in accordance with the inventive concept. 
     FIG. 5 d  shows a side view of the embodiment in FIG. 5 c.   
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     FIG. 1 a  shows a cross-sectional side view of a dielectric disc resonator according to the prior art, as previous mentioned, which comprises inductive coupling loops  1  (input and output), a dielectric resonator disc  2  installed in a metal casing  3 , and supported by a dielectric support  4 , and a frequency controller attached to the metal casing  3 , comprising an adjustment screw  5  and a dielectric adjustment plate  6 . The resonance frequency of the resonator depends on a displacement L in accordance with a graph shown in FIG. 1 b.    
     As appears from FIG. 1 b , the resonance frequency f r  varies as a non-linear function  7  of the displacement L. With an appropriate choice of material and dimensions of the resonator disc  2  and adjustment plate  6  in combination with the size metal casing  3 , a desired, approximately linear, frequency range A-B may be obtained in a high sensitivity area  9 . The resonator frequency f r  is tuneable within this range when adjusting the displacement L. The problem with this construction, when a high sensitivity is desired, is that the linear frequency range usually corresponds to a very small displacement L, which in turn may cause problems with stability and accuracy. 
     In prior art devices, an area with low sensitivity  8  is used, instead of the linear area with high sensitivity  9  that the present invention is aimed for. 
     FIG. 2 shows an exploded perspective view of an inventive dielectric resonator  20 . The resonator comprises a housing, including a bottom wall  22 , a top wall  23  and side walls  24  forming a cavity  21 , a dielectric resonator body, a support  27 , a bushing  28  and an adjustment rod  29 . The dielectric body comprises, in this example, a first movable element  25  and a second element  26 . The resonator  20  also have input and output means (not shown) mounted on said cavity  21 . 
     An aperture  23 ′ is formed in the top wall  23  in which the bushing  28  is located. The bushing  28  is secured to the top wall  23  by fastening means, such as screws, rivets, glue or the like, and the adjustment rod  29  is slidably arranged inside the bushings aperture  28 ′. A first end  29 ′ of the adjustment rod  29  is inserted into a centrally formed attachment  25 ′ on the first element  25 . A second end  29 ″ of the rod  29  is arranged to be on the outside of said cavity  21 . 
     By rotating means, acting on the second end  29 ″ of said rod  29 , the first element  25  is thus turned relative to the cavity  21 . 
     The support  27  is secured to the bottom plate  22  by fastening means, such as screws, rivets, glue or the like, and the second element  26  is in turn attached to the support, which fixates said element  26  relative to the cavity  21 . 
     The first element  25  and the second element  26  are arranged in such a way that their facing surfaces are partly in contact with each other in at least one location, preferably three locations. To ensure a stable contact the adjustment rod  29  is axially biased, spring loaded in some way (not shown in the drawing), to create a compressing force between the elements  25  and  26 . 
     The position of the second element  25  relative the first element  26 , of the resonator body, determines the resonance frequency f r  of the resonator. The frequency is adjusted by rotating the first element  25  in relation to the second element  26  by an adjustment mechanism, based on mechanical guidance, that is built into the resonator body, which is described in more detail below. 
     FIG. 3 a  and  3   b  show an embodiment of a two-part resonator body  30 , comprising a first dielectric resonating element  31  and a second dielectric resonating element  32 . Both elements are circularly cylindrical with an approximately equal outer diameter d 1  where an annular ridge  31 ′,  32 ′ is arranged circularly on the periphery of each elements facing surface  34  and  35 , each ridge having a substantially equal thickness t. A centrally formed attachment  36  is arranged on the first element  31 , where said attachment has a groove  37  for securing a rotating adjustment rod (not shown) as previously described in FIG.  2 . 
     Each ridge  31 ′,  32 ′ is, in this example, divided into three separate contact sectors  38 . Each sector has an essentially identical size and shaping, including a starting point  38 ′, an end point  38 ″ and an axially increasing slope there between. The shape of the resonator body  30  is thus changed by rotating the first element  31  in relation to the second element  32 , causing the height of the resonating body  30  to change and thus the resonance frequency f r . 
     FIG. 3 c  and  3   d  shows an alternative embodiment of a two-part resonator body  40 , similar to the embodiment described in FIG. 3 a  and  3   b , except for the shaping of the first element. This alternative embodiment of a two-part resonator body comprise an alternative first element  41  having an outer diameter d 2 , where said diameter is less than the outer diameter d 1  of the second element minus the double thickness t of the ridge (d 2 &lt;d 1 −2t). A number of pins  42 , corresponding to the number of contact sectors  38  of the ridge  32 ′ on the second element  32 , extends in a radial direction from the periphery of the first element  41 . The best performance is achieved when the pins  42  are evenly angularly separated, in this case with an angular value a equal to 120 degrees provided identical sectors  38  of the ridge  32 ′ on the second element  32 . 
     The displacement of the elements is performed by rotating the first element  41  while each pin  42  is in contact with the surface of each contact sector  38 , biased by spring means, as previously described in FIG.  2 . 
     FIG. 4 a  and  4   b  show an embodiment of a three-part resonator body  50 , comprising a first dielectric resonating element  31 , as previously described in FIG. 3 a , a second dielectric resonating element  52 , and a ridge formed interconnecting element  51 . The first and second elements  31  and  52  are circularly cylindrical and the interconnecting element  51  is tubular, all with approximately the same outer diameter d 1 , where a first annular ridge  31 ′ is arranged circularly on the periphery of the first elements  31  facing surface  34 . A second ridge  51 ′ is arranged on the ridge formed tubular interconnecting element  51 , where the thickness t of said element is equal to the thickness of the first ridge  31 ′. A centrally formed attachment  36  is arranged on the first element  31 , where said attachment has a groove  37  for securing a rotating adjustment rod (not shown) as previously described in FIG.  2 . 
     The interconnecting element  51  is fixed to the second element  52  by at least of one stopper means  53 , in this example three stopper means, arranged on said element  51 , where said stopper means is placed in a corresponding groove  54  on said second element  52 . 
     Each ridge  31 ′,  51 ′ is, in this example, divided into three separate contact sectors as described previously in FIGS. 3 a - 3   b . The shape of the resonator body  50  is thus changed by rotating the first element  31  in relation to the interconnecting element  51 , which is fixed to the second element  52 , causing the height of the resonating body  50  to change and thus the resonance frequency f r . 
     FIG. 4 c  and  4   d  shows an alternative embodiment of a three-part resonator body  60 , similar to the embodiment described in FIG. 4 a  and  4   b , except for the shaping of the interconnecting element. This alternative embodiment of a three-part resonator body comprise an alternative interconnecting element  61  having an outer diameter d 2 , where said diameter is less than the outer diameter d 1  of the first element minus the double thickness t of the ridge (d 2 &lt;d 1 −2t). A number of pins  62 , corresponding to the number of contact sectors of the ridge  31 ′ on the first element  31 , extends in a radial direction from the periphery of the interconnecting element  61 . The best performance is achieved when the pins  62  are evenly angularly separated, in this case with an angular value a equal to 120 degrees provided identical contact sectors of the ridge  31 ′ on the first element  31 , as previously described. 
     Stopper means  63  on the interconnecting element  61  and corresponding grooves  64  on the second element  65  are arranged to secure a radial fixing of the interconnecting element  61  to the second element  65 . 
     The displacement of the elements is performed by rotating the first element  31  while each pin  62  is in contact with the surface of the first ridge  31 ′, biased by spring means, as previously described in FIG.  2 . 
     FIG. 5 a  and  5   b  show an embodiment of a three-part resonator body  70 , comprising a first dielectric resonating element  71 , a second dielectric resonating element  72 , and a slit formed interconnecting element  73 . The first and second elements  71  and  72  are circularly cylindrical with approximately the same outer diameter d 1  and the interconnecting element  73  is tubular with an inner diameter d 3  which is larger than said outer diameter d 1  (d 3 &gt;d 1 ). A centrally formed attachment  36  is arranged on the first element  71 , where said attachment has a groove  37  for securing a rotating adjustment rod (not shown) as previously described in FIG.  2 . 
     The interconnecting element  73  have a number of slits  74  arranged in the tubular wall extending in an axial direction. Each slit is arranged to be an axially incrementing guide for a pin  75 , where said pins extends in a radial direction from the periphery of the first element  71 . The best performance is achieved when the pins  75  are evenly angularly separated, in this case with an angular value a equal to 120 degrees provided identical slits  74  on the interconnecting element  73 . 
     The interconnecting element  73  is attached to the second element  72  by fastening means, such as glue or the like, for fixing the interconnecting element  73  to the second element  72 . 
     The displacement of the elements is performed by rotating the first element  71  while each pin  75  follows each slit  74 . The accuracy of this embodiment can be increased by creating a compressing force utilising spring means, as previously described in FIG.  2 . 
     FIG. 5 c  and  5   d  shows an embodiment of a three-part resonator body  80 , similar to the embodiment in FIGS. 5 a - 5   b , except for the arrangement of the slits  81  in the tubular wall of the interconnecting element  82 . The slits in this example is of an overlapping type in contrast to previous embodiment where the slits are non-overlapping. 
     By introducing overlapping slits the sensitivity of the rotation of the first element  71  may be reduced and a higher accuracy can be obtained. 
     The slope of the ridges and the slits in the previous figures are linear, but the invention should not be limited to this. An increasing slope of any kind may be used provided that the tracking means of the facing surface is conformably adjusted accordingly. 
     An alternative embodiment (not shown) of said slit formed interconnecting element, is a tubular interconnecting element where the slits are replaced by an inner thread. The pins  75  can be arranged in a manner to fit into the thread and the same function as described in FIGS. 5 a - 5   d  can be obtained. 
     Other combinations of the above described means for mechanical guidance may of course be done and should be included in the scope of the invention. 
     The interconnecting elements  51 ,  61 ,  73  and  82 , may be made out of a dielectric material, glass, aluminium oxide and other material. The resonating elements  31 ,  32 ,  41 ,  51 ,  52 ,  65 ,  71  and  72  may be made a dielectric material with arbitrary characteristics. 
     By arranging the resonating elements, with or without an interconnecting element, in the above described embodiments, stable designs are achieved. Furthermore the designs are insensitive to temperature variations due to the spring loaded means forcing the resonating elements to a firm contact. 
     Maximum power handling capacity of is set by maximum allowed energy storage of the resonator, related to break down voltage of air E max , which is approx. E max =3000 V/mm. The maximum energy storage is directly proportional to maximum peak power. The above described embodiments provides a higher sensitivity (Mhz/mm) and are found, in computer simulations, to be able to handle more power.