TM mode dielectric resonator having coupling holes with voids

A double TM mode dielectric resonator has a broadened adjustable range of a coupling coefficient between two resonators. A dielectric pillar has two intersecting dielectric members in a space surrounded by a conductor, for guiding electric fields in an even mode and an odd mode in a resonance condition; a pair of coupling adjusting holes formed at respective intersections of the dielectric members in a direction orthogonal to a plane defined by the dielectric members; and a pair of coupling adjusting dielectric rods disposed respectively in the coupling adjusting holes for movement into and out of the coupling adjusting holes. The resonator may further have a pair of voids, each provided in a respective coupling adjusting hole and extending therefrom in a direction substantially orthogonal to a direction of an electric field passing through the respective coupling adjusting hole in the resonance condition, and also orthogonal to a direction in which the respective coupling adjusting hole extends. Each of the voids blocks a first electric flux at a first portion in the respective coupling adjusting hole into which the respective coupling adjusting dielectric rod is not inserted, and concentrates a second electric flux at a second portion in the respective coupling adjusting hole into which the respective coupling adjusting dielectric rod is inserted, and thereby enhances a difference between the first electric flux density at the first portion, and a second electric flux density at the second portion.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a TM (transverse magnetic) mode dielectric 
resonator in which a dielectric pillar is disposed in a space surrounded 
by a conductor. 
2. Description of the Related Art 
FIG. 14 and FIG. 15 show the structure of a conventional TM mode dielectric 
resonator. In FIG. 14, numeral 1 designates a prismatic dielectric pillar 
in which a frequency adjusting hole 2 is formed in a direction orthogonal 
to the axial direction of the dielectric pillar. Numeral 3 designates a 
cavity which is integrally formed with the dielectric pillar 1. A 
conductor 4 is formed on the top and bottom faces and on the left and 
right side faces of the cavity 3. A hole 11 is formed in the cavity 3 for 
guiding a frequency adjusting dielectric rod for movement into and out of 
the frequency adjusting hole 2 in the dielectric pillar 1. Two opening 
faces of the cavity 3 are covered with metallic panels 5 and 6. 
FIG. 15 is a view showing a central vertical section of the TM mode 
dielectric resonator shown in FIG. 14, including a frequency adjusting 
dielectric rod. In FIG. 15, numeral 7 designates a frequency adjusting 
dielectric rod, numeral 8 designates a screw member for holding the 
frequency adjusting dielectric rod 7 and numeral 9 designates a holding 
member attached to the hole 11 formed in a side wall of the cavity 3. The 
screw member 8 is threaded to engage with the holding member 9. 
FIGS. 16(A) and 16(B) show examples of electric fields created in the 
dielectric pillar of the TM mode dielectric resonator shown in FIG. 14 and 
FIG. 15. As shown in FIG. 16(A), in a region of the frequency adjusting 
hole 2 into which the dielectric rod is not inserted, electric lines of 
force pass almost totally through the dielectric portion of the dielectric 
pillar, detouring the frequency adjusting hole 2. By contrast, as shown in 
FIG. 16(B), in a region of the frequency adjusting hole 2 into which the 
dielectric rod 7 is inserted, the electric lines of force concentrate on 
the dielectric rod 7 in the frequency adjusting hole 2. In this way, an 
effective dielectric constant of the entire dielectric pillar is changed 
by inserting and withdrawing the frequency adjusting dielectric rod, 
whereby the resonance frequency is changed. 
FIG. 17 and FIGS. 18(A) and 18(B) show an example of a TM mode dielectric 
resonator using a double mode, having a composite dielectric column having 
the shape of two intersecting dielectric pillars. As shown in FIG. 17, a 
composite dielectric pillar 1 has a shape of two intersecting dielectric 
pillars in which frequency adjusting holes denoted by 2x and 2y are 
installed. Holes 11x and 11y are provided in a side wall of the cavity 3 
for holding frequency adjusting dielectric rods in the frequency adjusting 
holes 2x and 2y, respectively, so that they can be inserted and withdrawn. 
A hole 12 is also formed in a side wall of the cavity 3, for holding a 
coupling adjusting member which adjusts the coupling coefficient between 
two resonators formed by the two dielectric pillars constituting the 
composite dielectric pillar 1. 
FIGS. 18(A) and 18(B) are a top view and a sectional view of the resonator 
shown in FIG. 17, respectively. In FIGS. 18(A) and 18(B), screw members 8x 
and 8y are threaded to engage with holding members 9x and 9y, 
respectively, and frequency adjusting dielectric rods 7x and 7y, 
respectively attached to end portions of the screw members 8x and 8y, are 
respectively inserted into and withdrawn from the dielectric pillars by 
turning them, thereby adjusting the frequency of the resonator comprising 
the dielectric pillars extending in the horizontal and the vertical 
directions. Further, in FIGS. 18(A) and 18(B), numeral 13 designates a 
dielectric rod for coupling adjustment between the two pillars that is 
threaded to engage with a holding member 14. The coupling coefficient 
between the two resonators comprising the two dielectric pillars is 
adjusted by inserting and withdrawing the coupling adjusting dielectric 
rod into and from one of four corner portions produced by the intersection 
of the two dielectric pillars. 
However, as discussed further below, the available frequency adjusting 
range is narrowed by downsizing a TM mode dielectric resonator having a 
structure in which cylindrical frequency adjusting dielectric rods are 
inserted into and withdrawn from frequency adjusting holes having a 
circular sectional shape, as is illustrated in FIGS. 14, 15, 16(A), 16(B), 
17, 18(A) and 18(B). Further, a coupling adjusting range is narrowed by 
downsizing a TM mode dielectric resonator having a structure in which a 
coupling adjustment is performed by inserting and withdrawing a coupling 
adjusting dielectric rod into and from a space inside a side wall of a 
cavity as is illustrated in FIGS. 17, 18(A) and 18(B). 
That is, the dimensions of the dielectric pillars are determined in 
compliance with a frequency of use, and accordingly, in downsizing the 
overall TM mode dielectric resonator, the outer dimensions of the cavity 
are reduced as a result, whereby a ratio of the volume of the dielectric 
pillars to that of the cavity is increased and a distance between the 
dielectric pillar and the inner wall of the cavity denoted by S in FIG. 
15, is shortened. As a result, the frequency adjusting dielectric rod 7 
has an insufficient movable range (stroke). The stroke of the frequency 
adjusting dielectric rod must be further restricted to prevent 
interference with, for example, an input and output coupling loop, etc., 
due to the narrowing of the spaces between the metallic panels covering 
the opening portions of the cavity and the dielectric pillars, and between 
the inner walls of the cavity and the dielectric pillars. Finally, the 
range over which the frequency is variable is considerably restricted by 
downsizing the TM mode dielectric resonator. Further, with respect to a 
double mode resonator using a composite dielectric pillar, the adjustable 
range of the coupling coefficient is restricted since the coupling 
adjusting dielectric rod has an insufficient movable range. 
To enlarge the frequency adjusting range given the limited movable range of 
the frequency adjusting dielectric rod, a ratio of frequency change 
relative to a moving distance of the frequency adjusting dielectric rod 
must be enhanced. It is effective for that purpose to enhance, for 
example, the dielectric constant of the frequency adjusting dielectric rod 
or to enlarge its sectional area. However, the dielectric constant is 
determined inherently by the materials that are usable for the frequency 
adjusting dielectric rod, and accordingly, the dielectric constant cannot 
considerably be enhanced. Further, spaces between the inner walls of the 
cavity or the metallic panels and the dielectric pillars are limited, and 
therefore, even if the frequency adjusting dielectric rod is enlarged, the 
structure of the holding member and the like for holding the rod also must 
be enlarged. Therefore, there is a limit on how much the frequency 
adjusting dielectric rod can be enlarged. The same limitations are also 
applicable to enlarging the coupling adjusting dielectric rod. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a wide 
frequency adjusting range in a downsized TM mode dielectric resonator by 
enhancing a ratio of frequency change relative to moving distance of a 
frequency adjusting dielectric rod, without substantially enlarging the 
frequency adjusting dielectric rod. 
It is another object of the present invention to provide a TM mode 
dielectric resonator providing a wide adjusting range of a coupling 
coefficient even in a downsized TM mode dielectric resonator by enhancing 
a ratio of coupling coefficient change relative to moving distance of a 
coupling adjusting dielectric rod. 
According to a first aspect of the present invention, in view of the fact 
that the larger a difference between electric flux densities at portions 
in a frequency adjusting hole caused by the presence or absence of a 
frequency adjusting dielectric rod in the frequency adjusting hole, the 
larger a frequency change ratio of the frequency adjusting dielectric rod 
relative to a moving distance, it is desirable to increase the electric 
flux density of the frequency adjusting dielectric rod when it is inserted 
into the frequency adjusting hole. That is, in the first aspect of a TM 
mode dielectric resonator, a difference between the electric flux density 
at a portion in the frequency adjusting hole into which the frequency 
adjusting dielectric rod is not inserted, and the electric flux density at 
a portion thereof into which the frequency adjusting dielectric rod is 
inserted, is enhanced by providing the frequency adjusting hole with a 
void extending in a direction substantially orthogonal to a direction of 
an electric field that exists at resonance and also orthogonal to a 
direction in which the frequency adjusting hole extends. 
According to a second aspect of the TM mode dielectric resonator, the void 
is extended in a direction away from the frequency adjusting hole with a 
width smaller than a width of the frequency adjusting dielectric rod. 
According to a third aspect of the present invention, in a TM mode 
dielectric resonator of a double mode in which a composite dielectric 
pillar having a shape of two intersecting dielectric pillars is disposed 
in a space surrounded by a conductor, coupling adjusting holes are formed 
in a direction orthogonal to a plane made by the two dielectric pillars at 
an intersection of the two dielectric pillars to enhance a change ratio of 
coupling coefficients relative to a moving distance of coupling adjusting 
dielectric rods between two resonators comprising the two dielectric 
pillars, and a structure is provided for holding the coupling adjusting 
dielectric rods in the coupling adjusting holes in an insertable and 
withdrawable fashion. 
According to a fourth aspect of a TM mode dielectric resonator, to enhance 
an amount of change of the coupling coefficient relative to the distance 
the coupling adjusting dielectric rods are moved into and out of the 
coupling adjusting holes, voids extending in a direction substantially 
orthogonal to a direction of an electric field passing through the 
coupling adjusting holes and also orthogonal to a direction in which the 
coupling adjusting holes extend, are provided to the coupling adjusting 
holes. The voids enhance a difference between a first electric density at 
a first portion in the coupling adjusting hole into which the coupling 
adjusting dielectric rod is not inserted and a second electric density of 
a second portion in the coupling adjusting hole into which the coupling 
adjusting dielectric rod is inserted. 
Other objects, features and advantages of the invention will be appreciated 
from the following description of several embodiments thereof, with 
reference to the drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
FIGS. 4(A) and 4(B) show examples of a change of an electric flux density 
in a frequency adjusting hole that can be brought about by inserting and 
withdrawing a frequency adjusting dielectric rod of a TM mode dielectric 
resonator into and out of the frequency adjusting hole in accordance with 
the first and second aspects of the present invention. FIG. 4(B) 
schematically shows a behavior of electric lines of force at a sectional 
portion of the resonator wherein a frequency adjusting dielectric rod 7 is 
inserted into a frequency adjusting hole 2. FIG. 4(A) schematically shows 
a behavior of electric lines of force at a sectional portion of the 
resonator wherein the frequency adjusting dielectric rod 7 is not inserted 
into the frequency adjusting hole 2. 
As shown in FIG. 4(A), the electric lines of force pass around a portion in 
the frequency adjusting hole into which the frequency adjusting dielectric 
rod is not inserted, detouring the frequency adjusting hole 2 and a void 
2'. The void 2' extends in a direction orthogonal to the frequency 
adjusting hole, and the frequency adjusting hole extends in a direction 
orthogonal to a direction of an electric field. By contrast, as shown in 
FIG. 4(B), the electric lines of force which have detoured the frequency 
adjusting hole 2 and the void 2' in FIG. 4(A), now cross the frequency 
adjusting dielectric rod 7 at a portion in the frequency adjusting hole 2 
into which the frequency adjusting dielectric rod 7 is inserted. As a 
result, the dielectric flux density in the frequency adjusting hole 
changes considerably, depending on the presence or absence of the 
frequency adjusting dielectric rod. Thus a ratio of frequency change 
relative to an amount of movement of the frequency adjusting dielectric 
rod is enhanced. 
FIGS. 12(A) and 12(B) show an example of a change of an electric flux 
density in coupling adjusting holes when coupling adjusting dielectric 
rods are inserted and withdrawn in a TM mode dielectric resonator in 
accordance with the third aspect of the present invention. In FIGS. 12(A) 
and 12(B), notations 10a and 10b designate coupling adjusting holes. FIG. 
12(B) schematically shows a behavior of electric lines of force in even 
mode and in odd mode at a sectional portion of the resonator in which 
coupling adjusting dielectric rods 13a and 13b are inserted into the 
coupling adjusting holes 10a and 10b. FIG. 12(A) schematically shows a 
behavior of electric lines of force in even mode and in odd mode at a 
sectional portion of the resonator in which the coupling adjusting 
dielectric rods 13a and 13b are not inserted into the coupling adjusting 
holes 10a and 10b. As explained hereinafter, arrow marks of solid lines 
indicate electric lines of force in even mode and arrow marks of broken 
lines indicate those in odd mode. As shown in FIG. 12(A), the electric 
lines of force in even mode detour the coupling adjusting holes 10a and 
10b at a portion of the resonator in which the coupling adjusting 
dielectric rods are not present, whereas, as shown in FIG. 12(B), the 
electric lines of force in even mode pass through the coupling adjusting 
dielectric rods at a portion of the resonator in which the coupling 
adjusting dielectric rods 13a and 13b are present. The electric lines of 
force in odd mode stay constant irrespective of the presence or absence of 
the coupling adjusting dielectric rods. In this way, a difference between 
an effective dielectric constant in the even mode and that in the odd mode 
is considerably changed by inserting and withdrawing the coupling 
adjusting dielectric rods into and out of the coupling adjusting holes, 
whereby a wide range of coupling adjustment is made possible by a small 
amount of movement of the coupling adjusting dielectric rods. 
FIGS. 13(A) and 13(B) show an example of a change of an electric flux 
density in coupling adjusting holes when coupling adjusting dielectric 
rods are inserted and withdrawn in a TM mode dielectric resonator into and 
from the coupling adjusting holes in accordance with the fourth aspect of 
the present invention. In FIGS. 13(A) and 13(B), notations 10a and 10b 
designate coupling adjusting holes, and voids 10a' and 10b' extending in a 
direction orthogonal to an electric field passing through the coupling 
adjusting holes 10a and 10b and also orthogonal to the coupling adjusting 
holes, extend from the coupling adjusting holes 10a and 10b. FIG. 13(B) 
schematically shows a behavior of electric lines of force in even mode and 
in odd mode at a sectional portion of the resonator in which the coupling 
adjusting dielectric rods 13a and 13b are inserted into the coupling 
adjusting holes 10a and 10b. FIG. 13(A) schematically shows a behavior of 
electric lines of force in even mode and in odd mode at a sectional 
portion of the resonator in which the coupling adjusting dielectric rods 
13a and 13b are not inserted into the coupling adjusting holes 10a and 
10b. As shown in FIG. 13(A), the electric lines of force in even mode 
detour the coupling adjusting holes 10a and 10b and the voids 10a' and 
10b' at the portion in which the coupling adjusting dielectric rods are 
not present, whereas as shown in FIG. 13(B), the electric lines of force 
in even mode pass through the coupling adjusting dielectric rods at the 
portion in which the coupling adjusting dielectric rods 13a and 13b are 
present. In this way, in comparison with the case shown in FIGS. 12(A) and 
12(B), there is a greater difference between a first electric flux density 
in the coupling adjusting holes at the portion in which the coupling 
adjusting dielectric rods 13a and 13b are not present and a second 
electric flux density in the coupling adjusting holes at the portion in 
which the coupling adjusting dielectric rods 13a and 13b are present, due 
to the voids 10a' and 10b' orthogonal to the direction of the electric 
field passing through the coupling adjusting holes 10a and 10b and 
extending orthogonal to a direction in which the coupling adjusting holes 
extend. Thereby, the change ratio of the coupling coefficient relative to 
the amount of inserting and withdrawing the coupling adjusting dielectric 
rod is further enlarged. 
EXAMPLES 
FIG. 1 through FIG. 5 show the structure of a TM mode dielectric resonator 
in accordance with a first embodiment of the present invention and FIG. 6 
shows its frequency characteristics. 
FIG. 1 is a perspective view showing the structure of a TM mode dielectric 
resonator before assembly. In FIG. 1, numeral 1 designates a prismatic 
dielectric pillar in which a frequency adjusting hole 2 is formed in a 
direction orthogonal to the axial direction of the dielectric pillar. 
Numeral 3 designates a cavity which is integrally formed with the 
dielectric pillar 1. A conductor 4 is formed on the top and bottom faces 
and the left and right side faces of the cavity 3. Two opening faces of 
the cavity 3 are covered with metallic panels 5 and 6. A frequency 
adjusting dielectric rod is held in the metallic panel 5 for movement into 
and out of the frequency adjusting hole 2 in the dielectric pillar 1. 
FIG. 2 is a front view viewing from one opening face of the cavity 3 
integrally formed with the dielectric pillar 1 shown in FIG. 1, and FIG. 3 
shows a vertical sectional view cut through the frequency adjusting hole 
in an assembled state of the TM mode dielectric resonator shown in FIG. 1. 
In FIG. 3, numeral 7 designates a frequency adjusting dielectric rod and 
numeral 8 designates a screw member integrated to the frequency adjusting 
dielectric rod 7. A holding member 9 is installed in the metallic panel 5 
and the screw member 8 is threaded to engage with the holding member 9. 
That is, the frequency adjusting dielectric rod 7 is inserted into or 
withdrawn from the frequency adjusting hole 2 by turning the screw member 
8 in the right direction or in the left direction. 
FIGS. 4(A) and 4(B) show examples of a change in an electric flux density 
that is obtained in the frequency adjusting hole by inserting and 
withdrawing the frequency adjusting dielectric rod of the TM mode 
dielectric resonator into and from the frequency adjusting dielectric 
hole. As mentioned above in reference to FIGS. 4(A) and 4(B), FIG. 4(B) 
schematically shows a behavior of electric lines of force at a sectional 
portion of the resonator in which the frequency adjusting dielectric rod 7 
is inserted into the frequency adjusting hole 2, whereas FIG. 4(A) 
schematically shows a behavior of electric lines of force at a sectional 
portion of the resonator in which the frequency adjusting dielectric rod 7 
is not inserted into the frequency adjusting hole 2. As shown in FIG. 
4(A), the electric lines of force detour the frequency adjusting hole 2 
and a void 2' at a portion in the frequency adjusting hole into which the 
frequency adjusting dielectric rod is not inserted, whereas as shown in 
FIG. 4(B), the electric lines of force which have detoured the frequency 
adjusting hole 2 and the void 2' in FIG. 4(A), now cross the frequency 
adjusting dielectric rod 7 at a portion in the frequency adjusting hole 2 
into which the frequency adjusting dielectric rod 7 is inserted. The void 
2' extends from the frequency adjusting hole in a direction orthogonal to 
the frequency adjusting hole and extends in a direction orthogonal to a 
direction of an electric field. As a result, the electric flux density in 
the frequency adjusting hole is considerably changed depending on the 
presence or absence of the frequency adjusting dielectric rod, whereby a 
ratio of frequency change relative to an amount of movement of the 
frequency adjusting dielectric rod is enhanced. 
Next, a specific example will be shown illustrating the effect on the 
improvement of a frequency change ratio by providing a void when the 
dimensions of the void are changed. Firstly, as shown in FIG. 5, a "pair 
of voids have a width of md and mw is the overall length of the frequency 
adjusting hole plus both voids."; The frequency adjusting hole has an 
inner diameter of 6.0 mm and with it a frequency adjusting dielectric rod 
having the diameter of 5.8 mm is used. The specific dielectric constant of 
a dielectric pillar is 37.5 and that of the frequency adjusting dielectric 
rod is 90.0. FIG. 6 shows a simulation result showing the effect on the 
degree of improvement of a frequency change ratio when md and mw are 
changed. .DELTA.fo designates a frequency change ratio when the frequency 
adjusting hole is not provided with a void and is simply a circular hole, 
.DELTA.fm designates a frequency change ratio when a frequency adjusting 
hole having a void shown in FIG. 5 is used, and .DELTA.fm/.DELTA.fo 
designates a magnification of the frequency change ratio. Therefore, the 
larger the value of .DELTA.fm/.DELTA.fo, the larger the improvement of the 
frequency change ratio by providing the void. .DELTA.fo and .DELTA.fm are 
defined by the following equations: 
EQU .DELTA.fo=(fo'-fo)/fo, 
EQU .DELTA.fm=(fm'-fm)/fm 
where fo and fm designate resonance frequencies when the frequency 
adjusting dielectric rod is not inserted and fo' and fm' designate 
resonance frequencies when the frequency adjusting dielectric rod is 
inserted. 
As shown in FIG. 6, the magnification .DELTA.fm/.DELTA.fo of the frequency 
change ratio is increased by an increase in mw when md stays constant, and 
an increase in the magnification is observed with respect to md when 
md=1.0-5.0 mm. 
FIGS. 7(A), 7(B), 7(C) and 7(D) show examples of other shapes of frequency 
adjusting holes and frequency adjusting dielectric rods. In the example of 
FIG. 7(A), the frequency adjusting hole 2 is elliptical and voids 2' 
extend from both sides where the frequency adjusting dielectric rod 7 is 
inserted. In the example of FIG. 7(B), rounded portions are provided at 
roots and edges of the void 2', which prevents cracks from occurring when 
the dielectric pillar is formed, by dispersing stress concentrations that 
are applied at various portions of the frequency adjusting hole. 
Although a frequency adjusting dielectric rod having a circular section is 
used in the above examples, a frequency adjusting dielectric rod having a 
polygonal section may be used and a frequency adjusting hole may have a 
shape in compliance therewith, for example, as shown in FIG. 7(C). 
Further, although in the above examples, voids extend from both sides of 
the position in the frequency adjusting hole where the frequency adjusting 
dielectric rod is inserted, the void may extend only on one side thereof, 
for example, as shown in FIG. 7(D). 
Following is a simulation result of the magnification of the frequency 
change ratio when the dimensions of the frequency adjusting hole are 
changed using the frequency adjusting hole and the frequency adjusting 
dielectric rod shown in FIG. 7(A). 
FIG. 8 shows the dimensions of the frequency adjusting hole and the 
frequency adjusting dielectric rod. The specific dielectric constant of 
the dielectric pillar is 37.5 and that of the frequency adjusting 
dielectric rod is 90.0. R indicates the radius of the arcuate end portion 
in mm. FIG. 9 shows the change of the magnification of the frequency 
change ratio when rw specified in FIG. 8 is changed, where .DELTA.ft 
designates the frequency change ratio and .DELTA.ft/.DELTA.fo designates 
the magnification of the frequency change ratio. Accordingly, the larger 
the value of .DELTA.ft/.DELTA.fo, the more considerable is the effect of 
improvement of the frequency change by providing the void. .DELTA.fo and 
.DELTA.ft are defined by the following equations: 
EQU .DELTA.fo=(fo'-fo)/fo, 
EQU .DELTA.ft=(ft'-ft)/ft 
where fo and ft designate resonance frequencies when the frequency 
adjusting dielectric rod is not inserted and fo' and ft' designate 
resonance frequencies when the resonance frequency adjusting dielectric 
rod is inserted. 
As illustrated in FIG. 9, an inverse effect is indicated in a range of 
rw=6.0-12.0 mm where the magnification .DELTA.ft/.DELTA.fo of the 
frequency change ratio is smaller than 1.0. However, the magnification of 
the frequency change ratio exceeds 1.0, and there is an improvement of the 
frequency change ratio due to the void, in a range wherein rw exceeds 12 
mm. 
Next, FIGS. 10(A) and 10(B) show the structure of a TM mode dielectric 
resonator in accordance with a second embodiment. In the example of FIG. 
3, a holding member 9 is installed in the metallic panel 5, and the screw 
member 8, to which the frequency adjusting dielectric rod 7 is attached, 
is threaded to the holding member. In the second embodiment, the holding 
member is attached to the side of the dielectric pillar. FIGS. 10(A) and 
10(B) are respectively sectional views cut through a center axis of the 
dielectric pillar. FIG. 10(A) shows the resonator before inserting a 
frequency adjusting dielectric rod, a screw member, and holding member. 
FIG. 10(B) shows a holding member 9 attached to the side of the dielectric 
pillar, and a screw member 8, to which a frequency adjusting dielectric 
rod 7 is attached, is threaded to engage with the holding member 9. 
By accommodating the screw member 8 and the holding member 9 as well as the 
frequency adjusting dielectric rod 7 in the resonator, the stroke of the 
frequency adjusting dielectric rod 7 is limited to a range shown by S in 
FIG. 10(B). When a small cavity is used, the stroke S is shortened. 
However, a sufficient frequency adjusting range can be provided since the 
frequency change ratio relative to the moving distance of the frequency 
adjusting dielectric rod is enhanced by the presence of the void. 
Next, FIG. 11 and FIGS. 12(A) and 12(B) show the structure of a TM mode 
dielectric resonator in accordance with a third embodiment. 
FIG. 11 is a partially broken-away perspective view of a TM mode dielectric 
resonator before assembly. A dielectric pillar 1 is a composite dielectric 
pillar having a shape of two intersecting dielectric pillars respectively 
in the horizontal direction and in the vertical direction, as illustrated 
in FIG. 11. A frequency adjusting hole 2x is provided in the resonator for 
the horizontal dielectric pillar and a frequency adjusting hole 2y is 
provided in the resonator for the vertical dielectric pillar. Further, 
coupling adjusting holes 10a and 10b are formed at the intersection of the 
two dielectric pillars. The dielectric pillar 1 is integrally formed with 
the cavity 3 and a conductor 4 is formed on the outer peripheral faces of 
the cavity 3 as in the first embodiment. Further, a single TM mode 
dielectric resonator is constituted by covering two opening faces of the 
cavity 3 with metallic panels 5 and 6. As shown in FIG. 11, holding 
members 9x and 9y are respectively provided in the metallic panel 5, for 
holding screw members 8x and 8y to which frequency adjusting dielectric 
rods (not shown in FIG. 11) are attached. Holding members 14a and 14b are 
respectively provided in the metallic panel 5 for holding screw members 
13a and 13b to which coupling adjusting dielectric rods (not shown in FIG. 
11) are attached. The frequency adjusting dielectric rods are respectively 
coupled with the frequency adjusting holes 2x and 2y. The coupling 
adjusting dielectric rods are respectively coupled with the coupling 
adjusting holes 10a and 10b. 
FIGS. 12(A) and 12(B) are sectional diagrams cut in a direction orthogonal 
to the axes of the coupling adjusting holes, showing an example of a 
change of the dielectric flux densities in the coupling adjusting holes in 
the TM mode dielectric resonator shown in FIG. 11 upon insertion and 
withdrawal of the coupling adjusting dielectric rods. As mentioned above 
in reference to FIGS. 12(A) and 12(B), FIG. 12(B) schematically shows a 
behavior of electric lines of force in even mode and in odd mode at a 
sectional portion of the resonator in which the coupling adjusting 
dielectric rods 13a and 13b are inserted into the coupling adjusting holes 
10a and 10b, whereas FIG. 12(A) schematically shows a behavior of electric 
lines of force in even mode and in odd mode at a sectional portion of the 
resonator in which the coupling adjusting dielectric rods 13a and 13b are 
not inserted into the coupling adjusting holes 10a and 10b. As shown in 
FIG. 12(A), the electric lines of force in even mode (arrow marks drawn 
with bold lines) detour the coupling adjusting holes 10a and 10b at the 
portion wherein the coupling adjusting dielectric rods are not present. As 
shown in FIG. 12(B), the electric lines of force in even mode pass through 
the coupling adjusting dielectric rods at the portion in which the 
coupling adjusting dielectric rods 13a and 13b are present. In this way, a 
difference between an effective dielectric constant with respect to the 
even mode and an effective dielectric constant with respect to the odd 
mode is considerably enhanced by inserting and withdrawing the coupling 
adjusting dielectric rods into and from the coupling adjusting holes, by 
which a wide range of coupling adjustment is obtainable by moving the 
coupling adjusting dielectric rods only a small distance. 
Next, FIGS. 13(A) and 13(B) show the structure of a TM mode dielectric 
resonator in accordance with a fourth embodiment. FIGS. 13(A) and 13(B) 
correspond to FIGS. 12(A) and 12(B) in the third embodiment, and are 
similar thereto except that voids 10a' and 10b' are provided to the 
coupling adjusting holes 10a and 10b. FIGS. 13(A) and 13(B) show examples 
of a change of electric flux densities in the coupling adjusting holes of 
the TM mode dielectric resonator upon insertion and withdrawal of the 
coupling adjusting dielectric rods. As mentioned above in reference to 
FIGS. 13(A) and 13(B), in FIGS. 13(A) and 13(B), the coupling adjusting 
holes 10a and 10b are provided with the voids 10a' and 10b' orthogonal to 
a direction of an electric field passing through the coupling adjusting 
holes 10a and 10b and also orthogonal to a direction in which the coupling 
adjusting holes extend. 
FIG. 13(B) schematically shows a behavior of electric lines of force in 
even mode and in odd mode at a sectional portion of the resonator in which 
the coupling adjusting dielectric rods 13a and 13b are inserted into the 
coupling adjusting holes 10a and 10b. FIG. 13(A) schematically shows a 
behavior of electric lines of force in even mode and in odd mode at a 
sectional portion of the resonator in which the coupling adjusting 
dielectric rods 13a and 13b are not inserted into the coupling adjusting 
holes 10a and 10b. As shown in FIG. 13(A), the electric lines of force in 
even mode (arrow marks having bold lines) detour the coupling adjusting 
holes 10a and 10b and the voids 10a' and 10b' at the portion in which the 
coupling adjusting dielectric rods 13a and 13b are not present. As shown 
in FIG. 13(B), the electric lines of force in even mode pass through the 
coupling adjusting dielectric rods at the portion in which the coupling 
adjusting dielectric rods 13a and 13b are present. The electric lines of 
force in odd mode stay constant irrespective of the presence or absence of 
the coupling adjusting dielectric rods. In this way, the difference 
between the electric flux density in the coupling adjusting holes at the 
portion in which the coupling adjusting dielectric rods 13a and 13b are 
not present, and the electric flux density in the coupling adjusting holes 
at the portion in which the coupling adjusting dielectric rods 13a and 13b 
are present, is considerably enhanced by providing the voids 10a' and 10b' 
orthogonal to the direction of the electric field passing through the 
coupling adjusting holes 10a and 10b and also orthogonal to a direction in 
which the coupling adjusting holes extend. Thereby, the ratio of the 
change of coupling coefficient relative to the distance of insertion and 
withdrawal of the coupling adjusting dielectric rods is enhanced, more 
than that enhancement in the third embodiment. 
According to the TM mode dielectric resonator in accordance with the first 
and the second aspects of the present invention, the electric flux density 
in the frequency adjusting hole is considerably changed depending on the 
presence or absence of the frequency adjusting dielectric rod, and the 
frequency change ratio relative to the amount of movement of the frequency 
adjusting dielectric rods is enhanced. Accordingly, a wide range of 
frequency adjustment can be provided even in a downsized TM mode 
dielectric resonator without especially magnifying the frequency adjusting 
dielectric rod. 
Especially, according to the TM mode dielectric resonator in accordance 
with the second aspect of the present invention, the electric lines of 
force which have detoured the frequency adjusting hole and the void at a 
portion thereof in which the frequency adjusting dielectric rod is not 
inserted into the frequency adjusting hole, now cross the frequency 
adjusting dielectric rod when the frequency adjusting dielectric rod is 
inserted into the frequency adjusting hole. Therefore, the frequency 
change ratio relative to the amount of movement of the frequency adjusting 
dielectric rod can firmly be enhanced. 
According to the TM mode dielectric resonator in accordance with the third 
and the fourth aspect of the present invention, the difference between the 
effective dielectric constant with respect to the even mode and the 
effective dielectric constant with respect to the odd mode is considerably 
changed by inserting and drawing the coupling adjusting dielectric rods 
into and from the coupling adjusting holes, and a wide range of coupling 
adjustment is made possible by a small amount of movement of the coupling 
adjusting dielectric rods. Therefore, a wide range of coupling adjustment 
can be achieved even in a downsized TM mode dielectric resonator. 
Especially, according to the TM dielectric resonator in accordance with the 
fourth aspect of the present invention, a wide range of coupling 
adjustment is made possible by an even smaller amount of movement of the 
coupling adjusting dielectric rods. 
Although embodiments of the invention have been disclosed herein, the 
invention is not limited to those examples, but rather the fair spirit and 
scope of the invention should be considered to include modifications and 
variations thereof that may occur to a person having the ordinary level of 
skill in the art.