AU687258C - Dielectric resonator - Google Patents

Description

Dielectric resonator ^•

The invention relates to a dielectric resonator comprising a dielectric resonator disc, a frequency controller comprising an adjustment mechanism and a dielectric adjustment plane, which is substantially parallel with the resonator disc, and movable by means of the adjustment mechanism in the perpendicular direc¬ tion with respect to the resonator disc for adjusting the resonance frequency, and an electrically conductive casing.

Recently, so-called dielectric resonators have 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- szko, Microwave Journal, September 1986, p. 189-189. [3] "Cylindrical Dielectric Resonators and Their Appli¬ cations in TEM Line Microwave Circuits", Marian W. 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. 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 filter design of this kind, based on dielectric plate adjustment is shown in Figure 1, in which a res¬ onator comprises inductive coupling loops 5 (input and output) , a dielectric resonator disc 3 installed in a metal casing 4, and supported by a dielectric leg 6, and a frequency controller .attached to the metal casing 4, comprising an adjustment screw 1 and a dielectric adju¬ stment plane 2. The resonance frequency of the resonator depends on the adjustment distance L in accordance with a graph shown in Figure 2. As appears from Figure 2 , the resonance fre¬ quency varies as a non-linear function of the adjusting distance. Due to this non-linearity and the steep slope of adjustment, accurate adjustment of the resonance fre¬ quency is difficult and demands great precision, par- ticularly at the extreme ends of the control range. Frequency adjustment is based on a highly accurate mech¬ anical movement, the slope of adjustment k 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 adjust¬ ing 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. When the resonance 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 the dimensions of the resonator body or the adjustment mech- anism are reduced even more. As a result, adjusting the resonance frequency of a dielectric 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 mech- anical movements of the frequency adjustment device must be made vary small, adjustment will be slower.

The object of the invention is a dielectric resonator providing a higher accuracy and linearity of frequency control. This is achieved with a dielectric resonator, which is characterized in accordance with the invention in that the frequency controller comprises a plurality of dielectric adjustment planes, which are substantially installed concentrically and parallel one after another, the mechanical engagement of said planes to each other and to the adjustment mechanism enabling movement of the adjustment plates both with respect to the resonator disc and each other, so that the adjustment plates are arranged in layers on top of each other as the adjusting movement is proceeding.

In the invention, a conventional single di¬ electric adjustment plate has been replaced with several thin dielectric adjustment plates, which can move both with respect to each other and with respect to the res- onator disc, forming layers on top of the resonator disc as the adjustment is proceeding. The advantages of the invention are improved linearity of frequency adjust¬ ment, and a longer adjusting distance, which both improve the accuracy of adjustment. 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 dielectric resonator in accordance with the prior art, Figure 2 shows a graph illustrating the reson¬ ance frequency of the resonator shown in Figure 1 as a function of the adjusting distance L,

Figures 3 and 4 show cross-sectional side views of a dielectric resonator of the invention in two dif- ferent adjusting positions, and

Figure 5 shows a graph illustrating the reson¬ ance frequency of the resonator shown in Figures 3 and 4 as a function of the adjusting distance L.

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 struc¬ ture 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.

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. by means of a microstrip conductor placed in the vicinity of the resonator, an inductive coupling loop, a bent coaxial cable, a straight wire, etc.

The resonator frequency of a dielectric resona¬ tor is primarily determined by the dimensions of the dielectric resonator body. Another factor that has an effect on the resonance frequency is the environment of the resonator. By bringing a metallic or any other con¬ ductive surface, or alternatively another dielectric body, i.e. a so-called adjustment body, 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.

Figures 3 and 4 show a dielectric resonator provided with a layer plate adjuster in accordance with the invention. The resonator comprises a dielectric, preferably a cylindrical resonator disc 33 inside a casing 34 made of electrically conductive material, such as metal, said disc being preferably ceramic and placed at a fixed distance from the bottom of the casing 34, to rest on a supporting leg 36 made of suitable dielec- trie or isolating material. An example of coupling to the resonator by inductive coupling loops 35, which provide the input and the output of the resonator, is shown in Figures 3 and 4.

The layer plate adjuster structure comprises a plurality of dielectric adjusting planes 37, 38, 39, 40 and 41, which are installed substantially concentric¬ ally and parallel one after another, the mechanical engagement of said planes with each other and to the adjustment mechanism enabling movement of the adjustment plates 37-41 both with respect to the resonator disc 33 and with respect to each other, so that the adjustment plates 37-41 are arranged in layers on top of each other as the adjusting movement is proceeding.

In the embodiment described in greater detail in Figures 3 and 4, an adjusting mechanism, such as an adjustment screw 31 has been attached to the top surface of an adjustment plate 37 which is most remote above a resonator disc 33. Each following lower adjustment plate 38-41 is suspended from the bottom surface of a cor- responding previous adjustment plate 37-40 by a spring means 42, which in free suspension keeps the adjustment plates 37-41 apart from each other. Figure 3 shows a situation in which the layer plate adjuster is in its highest extreme position, and the adjustment plates 37- 41 are hanging freely apart both from each other and from the top surface of the resonator disc 33.

The adjusting mechanism 31 is arranged to move the adjustment plates 37-41 in the perpendicular direc¬ tion with respect to the top surface of the resonator disc 33. Thus, in an adjusting movement which is directed downwards, upon the lowest adjustment plate 41 contacting the top surface of the resonator disc 33, the adjustment plates start to move with respect to each other against the force of the spring means 42 between them, as the adjusting movement is proceeding, said adjustment plates forming layers on top of each other on the resonator disc 33, starting from the lowest ad¬ justment plates. Figure 4 shows a situation in which the lowest adjustment plates 41, 40 and 39 are layered on top of the resonator disc 33 forming a substantially integral object with it. In the other extreme position of the adjusting movement, all the adjustment plates 37- 41 are arranged in layers on the resonator disc 33.

In an adjusting movement which is directed upwards, the adjustment mechanism 31 moves the highest adjustment plate 37, whereby the adjustment plates 37- 41, layered on top of each other in an upward direction, start to become detached from each other actuated by the spring means 42, starting from the highest adjustment plates, until the situation shown in Figure 3 is finally reached.

By means of the layer plate structure of the invention, an adjustment curve in accordance with curve A in Figure 5 is achieved as a function of the adjusting distance L=L1-L0. The highest frequency is achieved when L=0, i.e. in the position in accordance with Figure 3. The lowest frequency is achieved when all the adjustment plates 37-41 are arranged in layers on the resonator disc. Between points 50 and 51 of the adjustment curve, the lowest adjustment plate 41 approaches the resonator disc 33 until it contacts it at point 51. Thereafter, upon the adjusting movement proceeding downwards, the same happens again alternately to the following adjust¬ ment plates at points 52, 53, 54 and 55. Thus, a rela- tively linear frequency adjustment and a long adjustment distance are achieved. The linearity may be increased by reducing the size or the thickness of the adjustment plates, and the adjusting distance may be lengthened by increasing the number of the adjustment plates. 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 (3)

Claims:

1. A dielectric resonator comprising a dielec¬ tric resonator disc (33) , a frequency controller comprising an adjustment mechanism (31) and a dielectric adjustment plane (41) , which is substantially parallel with the resonator disc

(33) , and movable by means of the adjustment mechanism in the perpendicular direction with respect to the res- onator disc for adjusting the resonance frequency, and an electrically conductive casing (34) , c h a ¬ r a c t e r i z e d by the frequency controller comprising a plurality of dielectric adjustment planes (37, 38, 39, 40, 41) , which are substantially installed concentrically and parallel one after another, the mechanical engagement (42) of said planes with each other and with the adjust¬ ment mechanism (31) enabling movement of the adjustment plates both with respect to the resonator disc (33) and with respect to each other, so that the adjustment plates are arranged in layers on top of each other as the adjusting movement is proceeding.

2. A resonator as claimed in claim 1, c h a r - a c t e r i z e d in that the adjustment mechanism (31) is engaged with the adjustment plate (37) situated high¬ est above the resonator disc (33) , and that each fol¬ lowing adjustment plate (38-41) is suspended from the bottom surface of the previous adjustment plate by a spring means (42) , which in free suspension keeps the adjustment plates (37-41) apart from each other.

3. A resonator as claimed in claim 2, c h a r - a c t e r i z e d in that the adjustment mechanism (31) is arranged to move the adjustment plates (37-41) in the perpendicular direction with respect to the top surface of the resonator disc (33), so that in an adjusting movement which is directed downwards, upon the lowest adjustment plate (41) contacting the top surface of the resonator disc (33) , the adjustment plates start to move with respect to each other against the force of said spring means (42) , as the adjusting movement is proceed¬ ing, said adjustment plates forming layers on top of each other on the resonator disc (33) , starting from the lowest adjustment plates, and in an adjusting movement which is directed upwards, the adjustment plates layered on top of each other start to become detached from each other actuated by said spring means (42) starting from the highest adjustment plate.