DIELECTRIC RESONATOR

Abstract: The invention relates to a dielectric resonator comprising a cylindrical dielectric resonator body (35) comprising a concentric cylindrical recess. A resonance frequency controller comprises an adjustment mechanism (31) and a cylindrical dielectric adjustment body (32), which is movable by means of the adjustment mechanism in the axial direction inside the recess (43) of the resonator body for adjusting the resonance frequency. The frequency controller of the invention further comprises a dielectric fine adjustment body (33) attached to the adjustment mechanism (31) and arranged inside the adjustment body (32) so that the projection of the fine adjustment body (33) at the end of the adjustment body (32) within the recess (43) in the resonator body may be adjusted by a movement of the adjustment mechanism. Thus, the frequency controller has two slopes of adjustment, whereby the adjustment is fast owing to the movement of both adjustment bodies (32, 33) and also extremely accurate owing to the fine adjustment function, which is achieved when the smaller adjustment body (33) is moved alone.

Description: Dielectric resonator The invention relates to a dielectric resonator comprising a cylindrical dielectric resonator body com- prising a concentric cylindrical recess, a frequency controller comprising an adjustment screw and a second cylindrical dielectric adjustment body, which is movable by means of the adjustment screw in the axial direction within the recess in the resonator body for adjusting the resonance frequency, and an electrically conductive casing. Recently, so-called dielectric resonators has become more and more interesting in high frequency and microwave range structures, as they provide the follow- ing advantages over conventional resonator structures: smaller circuit sizes, higher degree of integration, improved performance and lower manufacturing costs. Any object which has a simple geometric shape, and the material of which exhibits low dielectric losses and a high relative dielectric constant may function as a dielectric resonator having a high Q value. For reasons related to manufacturing technique, a dielectric resona¬ tor is usually of a cylindrical shape, such as a cylin¬ drical disc. The structure and operation of dielectric res¬ onators are disclosed e.g. in the following articles: [1] "Ceramic Resonators for Highly Stabile Oscillators", Gundolf Kuchler, Siemens Components XXIV (1989) No. 5, p. 180-183. [2] "Microwave Dielectric Resonators", S. Jerry Fiedziu- sz o, Microwave Journal, September 1986, p. 189-189. [3] "Cylindrical Dielectric Resonators and Their Appli¬ cations in TEM Line Microwave Circuits", Marian . Posp- ieszalski, IEEE Transactions on Microwave Theory and Techniques, VOL. MTT-27, NO. 3, March 1979, p. 233-238. The resonance frequency of a dielectric resona¬ tor is primarily determined by the dimensions of the resonator body. Another factor that has an effect on the resonance frequency is the environment of the resonator. By bringing a metallic or some other conductive surface to the vicinity of the resonator, it is possible to intentionally affect the electric or magnetic field of the resonator, and thus the resonance frequency. In a typical method for adjusting the resonance frequency of the resonator, the distance of a conductive metallic surface from the planar surface of the resonator is adjusted. The resonance frequency varies as a non-linear function of the adjustment frequency. Due to this non- linearity and the steep slope of adjustment, accurate adjustment of the resonance frequency is difficult and demands great precision. Furthermore, an unloaded Q value varies as a function of the distance of the cond¬ uctive plane. It is possible to keep the Q value constant and achieve more linear frequency adjustment in a wider range by bringing another dielectric body to the vicin¬ ity of the resonator body instead of a conductive ad¬ justment plane. In this case, too, the adjustment curve is still steep. One prior art dielectric filter design of this kind is shown in Figure 1, in which a resonator comprises inductive coupling loops 5 (input and output) , a dielectric resonator body 3 in a metal casing 4 and supported by a dielectric or isolating leg 6, and com¬ prising a concentric cylindrical recess 7. The resonator further comprises a frequency adjustment mechanism com¬ prising an adjustment screw 1 and a dielectric cylindri¬ cal adjustment body 2, which is movable by means of the adjustment screw 1 in the axial direction inside the recess 7 of the resonator body 3 for adjusting the re- sonance frequency. The resonance frequency of the re- sonator depends on the distance L between the bottom of the recess 7 of the resonator body 3 and the bottom surface of the adjustment body 2 in accordance with a graph in Figure 2. As appears from Figure 2, frequency adjustment is based on a highly accurate mechanical movement, the slope of adjustment k also being steep. When the reson¬ ance frequency becomes higher, e.g. to the range 1500- 2000 MHz or higher, the dimensions of the basic elements of the dielectric filter, such as those of the resonator body 3 or the adjustment mechanism 1, 2 are reduced. As a result, adjusting the resonance frequency of a dielec¬ tric resonator with prior art 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 fre¬ quency adjustment device must be made vary small, adjus¬ tment will be slower. The object of the invention is a dielectric resonator providing a higher adjustment accuracy and speed. This is achieved with a dielectric resonator, which is characterized in accordance with the invention in that the second cylindrical adjustment body compris¬ es a dielectric fine adjustment resonator body, which is connected to the adjustment screw and arranged inside the second resonator, so that a projection of the fine adjustment resonator body at the end of the resonator body within the recess in the first resonator body can be adjusted by a movement of the adjustment screw. The frequency controller of the resonator of the invention consists of a pair of joined dielectric adjustment bodies, which are mechanically engaged with each other so that their movement with respect to each other and the resonator body provides two adjustment phases during one adjusting movement. At the beginning of the adjusting movement, the smaller adjustment body, i.e. the so-called fine adjustment body moves a pre- determined distance with respect to the larger adjust¬ ment body and the resonator body, while the larger ad¬ justment body remains stationary by due to a specific friction surface. Once the smaller adjustment body has moved said distance, the larger adjustment body also starts to move in accordance with the adjusting move¬ ment. Thus, a dielectric resonator is achieved the fre¬ quency controller of which has two slopes of adjustment, whereby the adjustment is fast owing to the movement of both adjustment bodies, and also extremely accurate owing to the fine adjustment function, which is achieved when the smaller adjustment body is moved alone. By means of the invention, the adjustment accuracy may be improved as much as tenfold, so that the demands on the accuracy of the adjustment mechanics do not have to be made stricter when the frequency is increased, or they may be even moderated for the presently used frequen¬ cies. In the following, the invention will be dis¬ closed in greater detail by way of example with refer- ence to the attached drawings, in which Figure 1 shows a cross-sectional side view of a prior art dielectric resonator, Figure 2 shows a graph illustrating the reson¬ ance frequency of the resonator shown in Figure 1 as a function of distance L, Figure 3 shows a cross-sectional side view of a dielectric resonator of the invention, Figure 4 shows a graph illustrating the reson¬ ance frequency of the resonator shown in Figure 3 as a function of distance L, and Figure 4a shows an enlarged detail of the graph in Figure 4. The structure, the operation and the ceramic manufacturing materials of dielectric resonators are disclosed e.g. in the above-mentioned articles [1] , [2] , and [3] , which are incorporated herein by reference. In the following description, only the parts in the struct¬ ure of the dielectric resonator which are essential to the invention will be disclosed. The term dielectric resonator body, as used herein, generally refers to any object which has a suit¬ able geometric shape, and the manufacturing material of which exhibits low dielectric losses and a high relative dielectric constant. For reasons related to manufactur- ing technique, a dielectric resonator is usually of a cylindrical shape, such as a cylindrical disc. The most commonly used material is ceramic material. Figure 3 shows a dielectric resonator of the invention, comprising a dielectric, preferably cylindri- cal resonator body 35 inside a casing 36 made of an electrically conductive material, such as metal, said body being preferably ceramic and installed at a fixed distance from the bottom of the casing 36, on a support¬ ing leg 38 of suitable dielectric or isolating material. The casing 36 is coupled to the ground potential. The electromagnetic fields of a dielectric resonator extend beyond the resonator body, so it may easily be coupled electromagnetically to the rest of the resonator circuit in a variety of ways depending on the application, e.g. with a microstrip conductor in the vicinity of the resonator, a bent coaxial cable, a norm¬ al straight wire, etc. Figure 3 shows by way of example coupling to the resonator by inductive coupling loops 37, which provide the input and the output of the reson- ator. The resonator frequency of a dielectric resona¬ tor is primarily determined by the dimensions of the dielectric resonator body 35. Another factor that has an effect on the resonance frequency is the environment of the dielectric resonator body. By introducing a me¬ tallic or some other conductive surface to the vicinity of the resonator body, it is possible to intentionally affect the electric or magnetic field of the resonator, and thus the resonance frequency. A dielectric adjusting element used in the adjustment of the resonator of the invention consists of a pair of joined dielectric adjus¬ tment bodies 32 and 33, which are mechanically engaged with each other, so that their movement with respect to each other and with respect to the ceramic object pro- vides two adjustment phases during one adjusting move¬ ment. At the beginning of the adjusting movement, the smaller adjustment plane 33, or the so-called fine ad¬ justment body, moves a predetermined distance L2 with respect to the larger adjustment plane 32 and the diel- ectric resonator body 35, while the larger adjustment body 32 remains stationary due to a specific friction surface. Once the smaller adjustment plane has moved said distance L2, the larger adjustment body 33 also starts to move in accordance with the adjusting move- ment. Described in more detail, the resonance fre¬ quency controller comprises a dielectric (preferably ceramic) cylindrical dielectric adjustment body 33, which is movable by means of an adjustment mechanism in the axial direction inside a cylindrical recess 43 situ¬ ated on the top surface of a resonator body 35 for ad¬ justing the resonance frequency. The adjustment mech¬ anism consists of an adjustment screw 31 and a bushing 42, or another suitable adjustment mechanism. The reson- ance frequency controller further comprises a dielectric fine adjustment body 33 connected to the adjustment mechanism 31 and arranged inside adjustment body 33, so that the projection of the fine adjustment body 32 may be adjusted by a movement of the adjustment mechanism 31 at that end of adjustment body 33 which is located inside the recess 43 of the resonator body 35. The con¬ tact surface between the recess 43 of the resonator body 35 and adjustment body 32 is a friction surface 34 which keeps adjustment body 33 stationary inside the resonator body 35 when the fine adjustment body is moved by means of the adjustment mechanism. In the embodiment shown in Figure 3, a cylin¬ drical adjustment body 32 comprises a vertically I- shaped centre hole 41, which extends in the axial dir- ection through adjustment body 32 from the top surface to the bottom surface. The fine adjustment body 33 is vertically I-shaped, and its arm (narrow middle part) is longer than the narrower middle part of the centre hole of adjustment body 32, so that the fine adjustment body 33 in the centre hole 41 is allowed a predetermined axial movement range L2 inside adjustment body 32 before the upper or the lower end claw (broader end part) of the I-shaped fine adjustment body 33 touches the bottom of the upper or the lower end opening (broader opening of the centre hole) of the I-shaped centre hole 41 of adjustment body 32, causing a grip which transfers the movement of the adjustment mechanism 1 via the fine adjustment body 33 so that it also moves adjustment body 32 axially, which compensates the friction of the frict- ion surface 34. The allowed movement range of adjustment body 32 is LI. Thus, a dielectric resonator is achieved the frequency controller of which has two slopes of adjustment, whereby the adjustment is fast when both adjustment bodies 32 and 33 are moved, and slower, but extremely accurate when the smaller fine adjustment body 33 is moved alone. The graph in Figure 4 shows the res¬ onance frequency fo of the resonator of the invention as a function of the movement L of the adjustment plane. In Figure 4, curve A describes the adjustment when both adjustment bodies 32 and 33 are moved, the slope of adjustment kl being e.g. 5.5 MHz/mm. At the circle marked with a broken line, fine adjustment is performed solely with a movement of adjustment body 33, which is achieved by changing the rotating direction of the adju- stment screw 31. An enlargement of a part of curve A corresponding to the fine adjustment situation is shown in Figure 4a, from which appears that slope of adjust¬ ment k2 of fine adjustment is remarkably lower than kl, e.g. 0.54 MHz/mm. The relation k2/k of the slopes of adjustment is directly proportional to the relation of the areas of adjustment bodies 32 and 33. In other words, it is possible to select the appropriate slopes of adjustment by selecting appropriate areas. The figures and the explanation associated therewith are only intended to illustrate the above invention. The resonator of the invention may vary in its details within the scope of the attached claims.

Claims: Claims : 1. A dielectric resonator comprising a cylindrical dielectric resonator body (35) comprising a concentric cylindrical recess (43) , and a frequency controller comprising an adjustment mechanism (31) and a cylindrical dielectric adjustment body (32) , which is movable by means of the adjustment mechanism in the axial direction within the recess (43) in the resonator body for adjusting the resonance fre¬ quency, and an electrically conductive casing (36) , c h a ¬ r a c t e r i z e d in that the cylindric adjustment body (32) comprises a dielectric fine adjustment body (33) connected to the adjustment mechanism (31) and arranged inside adjustment body (32) , so that a projection of the fine adjustment body (33) at the end of the adjustment body within the recess (43) in the resonator body (35) can be adjusted by a movement of the adjustment mechanism. 2. A dielectric resonator as claimed in claim 1, c h a r a c t e r i z e d in that the fine adjustment body (33) and the adjust¬ ment body (32) are provided with grip means, which allow a predetermined axial movement of the fine adjustment body inside the adjustment body before the grip between the fine adjustment body and the adjustment body, for transferring the movement of the adjustment mechanism into an axial movement of the adjustment body. 3. A dielectric resonator as claimed in claim 1 or 2, c h a r a c t e r i z e d in that the cylindri¬ cal adjustment body (32) comprises a vertically I-shaped centre hole (41) and that the fine adjustment body (33) is vertically I-shaped and longer than said centre hole (41) , so that a specific axial movement of the fine adjustment body (33) inside the adjustment body is allowed before one end claw of the I-shaped fine adjust¬ ment body (33) touches the bottom of one end opening of the I-shaped centre hole (41) of the adjustment body causing a grip, which transfers the movement of the adjustment mechanism (31) so that it also causes an axial movement of the adjustment body. 4. A dielectric resonator as claimed in claim 1, 2 or 3, c h a r a c t e r i z e d by means (34) which keep the adjustment body stationary inside the resonator body when the fine adjustment body is moved with the adjustment mechanism. 5. A dielectric resonator as claimed in claim 4, c h a r a c t e r i z e d in that the contact surface between the recess of the resonator body and the adjustment body is a friction surface (34) , which keeps the adjustment body (32) sta¬ tionary inside the resonator body (35) when the fine adjustment body is moved by means of the adjustment mechanism (31) . 6. A ceramic filter as claimed in any one of the preceding claims, c h a r a c t e r i z e d in that during a common movement of the adjustment body (32) and the fine adjustment body (33) , frequency ad- justment has a first slope of adjustment, and that upon the fine adjustment body (33) moving alone, frequency adjustment has a second slope of adjustment which is re¬ markably lower than the first slope of adjustment. 7. A dielectric resonator as claimed in any one of the preceding claims, c h a r a c t e r i z e d in that the adjustment mechanism comprises an adjustment screw which is attached to the casing.

Inventors: SAERKKAE VELI-MATTI, SAERKKAE, VELI-MATTI
Applicants: NOKIA TELECOMMUNICATIONS OY, SAERKKAE VELI MATTI, SAERKKAE, VELI-MATTI
Application year: 1995
Main classification: H01P7
IPC codes: H01P7