Dielectric Resonator

The present invention generally relates to an electrical resonator and more particularly, to a dielectric resonator employing TM.sub.010 mode or its variation mode for electromagnetic waves.

The construction of the dielectric resonator of this kind in terms of principle has already been known, and there are various problems to be solved for the actual applications, one of which problems is related to a resonant frequency adjusting construction, which are conventionally disclosed, for example, in Japanese Utility Model Laid-Open Publications Jikkaisho No. 59-57005 and No. 59-88908, and so arranged as shown in FIG. 1, that a frequency adjusting member 4 made of a metal or dielectric member is inserted into a space 3 defined between an inner peripheral surface of a metallic case 2 closed at its opposite ends and a columnar inner dielectric member 1 disposed at a central portion within said case 2. The frequency adjusting member 4 made of a metal is not suitable for actual application, since a loss tends to be large. In the case where the frequency adjusting member 4 is of a dielectric material, it is assumed that the resonant frequency is altered through variation of a capacitance value in an equivalent circuit when the resonant frequency of the resonator is to be considered. However, in the known construction as referred to above, since the frequency adjusting member 4 is located at a place where the density of electric lines of force is low, the resonant frequency can not be effectively altered. Moreover, due to the fact that the capacitance considered between the frequency adjusting member 4 and the surface of the metallic case 2 confronting said frequency adjusting member 4 on an extension line thereof, is small as compared with the capacitance of the frequency adjusting member itself, values of such capacitances are not much altered even when the adjusting member 4 is moved to a large extent upon consideration of a combined capacitance, and it has been impossible to effectively alter resonant frequencies by the known constructions.

By way of example, when the resonant frequency was represented by fo and frequency variable range was denoted by .DELTA.f, the only relation obtainable was

If it is intended to obtain the frequency variable range larger than the above, unloaded Q factor (=Qo) is undesirably lowered to a large extent. For example, on the assumption that the range of lowering of the unloaded Q factor (=Qo) is represented by .DELTA.Qo, the resultant relation would undesirably be

This is considered to be attributable to the fact that, owing to the construction, the current is concentrated upon the resonant frequency adjusting mechanism and a loss is produced by a contact resistance thereof.

Accordingly, an essential object of the present invention is to provide an improved dielectric resonator employing TM.sub.010 mode or its variation mode, and provided with a resonant frequency adjusting mechanism large in the resonant frequency variable range, without reduction of unloaded Q factor.

Another important object of the present invention is to provide a dielectric resonator of the above described type which is simple in construction and stable in functioning, 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 resonator employing TM.sub.010 mode or variation mode thereof, and including a cavity resonator and a columnar inner dielectric member accommodated within the cavity resonator, and characterized in that there are provided a region formed at an end face of said inner dielectric member so as not to contact said cavity resonator, and a resonant frequency adjusting member adapted to be movable toward or away from said region, thereby to adjust the resonant frequency through variation of capacitance value in a path passing through said columnar dielectric member, resonant frequency adjusting member, and cavity resonator.

Furthermore, in a modification according to the present invention, said region is further formed with a recess, and the resonant frequency adjusting member is arranged to be movable toward or away from said recess for the adjustment of the resonant frequency.

By the arrangement according to the present invention as described above, an improved dielectric resonator has been advantageously presented through simple construction.

These and other objects and features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiment thereof with reference to the accompanying drawings, in which:

FIG. 1 is a side sectional view of a conventional dielectric resonator;

FIG. 2 is a side sectional view of a dielectric resonator according to one preferred embodiment of the present invention;

FIG. 3 is a fragmentary side sectional view showing on an enlarged scale, an essential portion of the resonator of FIG. 2;

FIG. 4 is a view similar to FIG. 3, which particularly shows a modification thereof;

FIG. 5 is a view similar to FIG. 3, which particularly shows another modification thereof;

FIGS. 6 and 7 are sectional diagrams for explaining functions of the dielectric resonator according to the present invention; and

FIG. 8 is a graphic diagram showing variations of resonant frequencies.

Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throught the accompanying drawings.

Referring now to the drawings, there is shown in FIG. 2 a main portion 10 of a dielectric resonator of the present invention employing TM.sub.010 mode or variation mode thereof, which includes a columnar inner dielectric member 10a, a cylindrical dielectric member 10b made of a material having the same thermal expansion coefficient as that of the inner dielectric member 10a, and concentrically surrounding said inner dielectric member 10a in a spaced relation therefrom, disc-like dielectric members 10c and 10d also made of a material having the same thermal expansion coefficient as that of the cylindrical dielectric member 10b and provided to close opposite open ends of said cylindrical dielectric member 10b, and electrode layer 11b applied onto the inner peripheral surface of the cylindrical dielectric member 10b, and electrode layer 11c provided over the entire outer surface of the disc-like dielectric member 10c, and another electrode layer 11d provided over the entire outer surface of the disc-like dielectric member 10d, with the respective electrode layers 11b, 11c and 11d being adapted to be continuous onto each other to provide a function equivalent to that of the opposite end closed cylindrical metallic case 2 in the known typical resonator of FIG. 1, and with the opposite end faces of the inner dielectric member 10a being held in close contact with the electrode layers 11c and 11d.

It is to be noted here that the electrode layer 11b described as provided over the inner peripheral surface of the cylindrical dielectric member 10b in the above embodiment may be modified to be provided over the outer peripheral surface of said member 10b.

The main portion 10 of the dielectric resonator as described so far is accommodated in a metallic protection casing 12, which includes a cylindrical barrel portion 12b, an upper lid portion 12c, and a lower lid portion 12d, and input and output connectors 13a and 13b mounted on the upper lid portion 12c to extend therethrough and also, through the disc-like dielectric member 10c, with antennas a attached to center conductors of the respective connectors 13a and 13b being located in the space between the inner dielectric member 10a and the cylindrical dielectric member 10b within the main portion 10, while grounding portions of the connectors 13a and 13b are conducted to the electrode layer 11c of the disc-like dielectric member 10c.

In the upper end face of the inner dielectric member 10a, there is formed a recess 14, while a circular bore 15 is formed in the disc-like dielectric member 10c in a position corresponding to the recess 14. A columnar dielectric member 16 having a low dielectric constant is disposed within the recess 14 and the circular bore 15 to constitute a resonant frequency adjusting mechansim together with an electrode layer 17 formed on the side peripheral surface and bottom surface of the dielectric member 16, and an adjusting screw 18 connected at its lower end, to the dielectric member 16 and extending outwardly, at its upper end, from the upper lid portion 12c, with the intermediate threaded portion of the screw 18 being engaged with a corresponding female thread 19 formed in said upper lid portion 12.

Subsequently, functioning of the resonant frequency adjusting mechanism as referred to above will be described with reference to a diagram in FIG. 3 schematically showing the essential portion thereof.

Electric lines of force pass through the inner dielectric member 10a in the axial direction thereof, and therefore, capacitance C1 is present between the electrode layer 17 and the bottom face of the recess 14, while capacitance C2 is also present between the electrode layers 17 and 11c. Accordingly, when the dielectric member 16 is vertically moved in FIG. 3 by turning the adjusting screw 18, the capacitances C1 and C2 are varied. In one example, by mainly varying the capacitance C1, the resonant frequency was varied more largely than in the conventional practice in such a manner as in .DELTA.f/fo.congruent.2%. It is to be noted here that the resonant frequency may be adjusted also by conducting the electrode layers 11c and 17.

Referring further to FIG. 4, there is shown a modification of the resonant frequency adjusting mechanism in FIG. 3.

In the modified resonant frequency adjusting mechanism of FIG. 4, a cylindrical dielectric member 20 having, on its surface, an electrode layer 21 continuous onto the electrode layer 11c of the disc-like dielectric member 10c is further provided on said dielectric member 10c, with the columnar dielectric member 16 connected to the adjusting screw 18 for the vertical adjustment being concentrically disposed in the space or circular bore 15 within the cylindrical dielectric member 20. The portion of the electrode layer 21 provided over the inner peripheral surface of the cylindrical dielectric member 20 is so set that the capitance C2 becomes a predetermined required value. In the arrangement of FIG. 4, the value of capacitance C2 is made larger than that in FIGS. 2 and 3. The air gap between the electrode layer 17 and the bottom face of the recess 14 is represented by g.

Since other constructions and effects of the resonant frequency adjusting mechanism of FIG. 4 are generally similar to those in the mechanism of FIGS. 2 and 3, detailed description thereof is abbreviated here for brevity, with like parts being designated by like reference numerals.

Referring further to FIG. 5, there is shown another modification of the resonant frequency adjusting mechanism in FIG. 3.

In the arrangement of FIG. 5, the recess 14 described as formed in the upper end face of the inner dielectric member 10a in the foregoing embodiments is not provided. The portion of the electrode layer 17 formed on the outer peripheral side face of the dielectric member 16 may be dispensed with. In this case, the capacitance C2 is to be formed between the electrode layer 17 formed on the bottom surface of the dielectric member 16 and the portion of the electrode layer 11c formed around the upper peripheral edge portion of the inner dielectric member 10a. By the construction as described above, in one example, the resonant frequency was varied by about .DELTA.f/fo.congruent.0.5%. It is to be noted here that the resonant frequency may also be adjusted when the electrode layer 17 formed on the outer peripheral side face of the dielectric member 16 is conducted with the electrode layer 11c formed on the side peripheral face of the circular bore 15.

Between the case where the recess 14 is not formed in the upper end face of the inner dielectric member 10a and the case where such recess 14 is formed therein, differences as follows will take place.

In FIG. 6, upon consideration of an imaginary plane A--A immediately below the upper end face of the inner dielectric member 10a, when the capacitance between the imaginary plane A--A and the electrode layer 11c is represented by C5, the capacitance between the imaginary plane A--A and the electrode layer 17 is denoted by C6, and the capacitance between the electrode layers 17 and 11c is represented by C7, it is necessary to compare C5 with C8(1/C8=(1/C6)+(1/C7) ) for studying the influence thereof on the resonant frequency.

Now, upon comparison of the values for C5 and C8, the former is considerably larger than the latter which is rather small, since for the former, the distance is short, while in the latter, the capacitances C6 and C7 are connected in series in addition to the presence of the air gap. Owing to the fact that the resonant frequency is influenced by the combined effect of both capacitances, if both are in the relation as stated earlier, it is difficult to vary the resonant frequency to a large extent by a slight variation in the value for the latter. However, due to the fact that current does not flow through such a portion, there is no reduction in the unloaded factor Q, and moreover, since the adjustment is effected at a position where density of electric lines of force is higher than that in the conventional arrangement, the resonant frequency adjusting range may be advantageously increased.

Subsequently, in FIG. 7, upon consideration of an imaginary plane B--B immediately below the upper end face of the inner dielectric member 10a, when the capacitance between the imaginary plane B--B and the electrode layer 11c is represented by C15, the capacitance between the imaginary plane B--B and the electrode layer 17 is denoted by C16, and the capacitance between the electrode layers 17 and 11c is represented by C17, it is necessary to compare C15 with C18(1/C18=(1/C16)+(1/C17) for studying the influence thereof on the resonant frequency.

Now, upon comparison of the values for C15 and C18, the ratio of both is not so large as in FIG. 6, since for the former, there is a considerable distance in spite of the intervention of the same medium, while for the latter, the distance is considerably short as compared with the former even in the presence of the air gap, and thus, the resonant frequency is effectively altered when the value of the latter is varied. As described above, in the presence of the recess 14, there is such a merit that the resonant frequency variable range is further widened in addition to the advantage available in the absence of the recess 14.

FIG. 8 shows variations of resonant frequencies based on one example of actually measured values in the presence of the recess 14.

It should be noted here that the dielectric member 16 and the electrode layer 17 described as employed for the resonant frequency adjusting mechanism in the foregoing embodiments may be replaced by a metallic rod (not shown) attached to the adjusting screw 18 through insulation.

As is clear from the foregoing description, according to the present invention, it is so arranged that, at part of the region for joining the inner dielectric member with the cavity resonator, the region without joining is provided, and by selectively bringing the frequency adjusting member close to or away from the region, the factor equivalent to capacitance in the equivalent circuit for a dielectric resonator is varied for the adjustment of the resonant frequency. Moreover, according to the present invention, at part of the region for joining the inner dielectric member and the cavity resonator, the region without joining is provided, with the recess being further formed in said region, whereby the resonant frequency is adjusted through variation of the factor equivalent to capacitance in the equivalent circuit for a dielectric resonator by selectively bringing the frequency adjusting member close to or away from said recess.

Therefore, according to the present invention, since the frequency adjusting member is moved in the position where density of electric lines of force is conventionally high, the resonant frequency may be effectively altered. Moreover, owing to the fact that the frequency adjusting mechanism has no portion where current is concentrated, reduction of the unloaded Q factor may be almost negligible. Furthermore, since the actual construction is not specific or complicated, there is an advantage from the viewpoint of cost, while the adjusting operation is simple, without requiring skillfulness therefor.

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.