Dielectric filter having dielectric resonators disposed within a casing and secured by an intermediate member

Provided is a dielectric filter that can be anchored in a stable manner without causing damage even when there is variation in the size of the parts. With this dielectric filter, one surface of washers has a concave part, which is equipped with an edge part formed at the perimeter of the one surface, a floor surface provided at a lower position than the edge part, and a tapered part formed between the edge part and the floor surface. The washers are arranged on the upper surface of and fastened by means of screws to dielectric bodies with the concave parts facing the dielectric bodies, with sheet metal therebetween.

TECHNICAL FIELD

The present invention relates to a TM mode dielectric filter.

BACKGROUND ART

Base stations and mobile stations in a mobile communication system are each provided with a filter to suppress an unnecessary wave other than a desired wave when transmitting and/or receiving a radio signal. A dielectric filter is often used for this filter.

The filter on the base station is required to reduce passband loss. Reducing passband loss requires a dielectric having a high Q value, but a reduction of passband loss using a general TE mode dielectric filter would result in an increase in size. Thus, a TM mode dielectric filter which has a lower Q value than the TE mode but can be downsized has been attracting attention in recent years (e.g., see the Citation List for PTLs 1 to 5 listed below).

For the TM mode dielectric filter, upper and lower surfaces of the dielectric need to be shielded based on the principles of the TM mode dielectric filter. For this reason, PTL 1, or the like, discloses a technique for fixing the dielectric in place while shielding the upper and lower surfaces of the dielectric.

As shown inFIG. 1, PTL 1 discloses a technique for firmly fixing dielectric resonator 2 to metal case 1 in a longitudinal direction and a vertical direction of the resonator using resonator fixing plate 3 and spacer 6. Connectors 30 are mounted on both ends of the metal case 1. It is thereby possible to provide a TM mode dielectric filter that remains stable under vibration or impact. PTL 1 corresponds to U.S. Pat. No. 6,320,484 to Furuya et al.

CITATION LIST

Patent Literature

Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2011-529666

SUMMARY OF THE INVENTION

Technical Problem

However, the TM mode dielectric filter described in PTL 1 has a fixing structure in which a sheet metal is sandwiched between a cover and a dielectric, and the dielectric resonator is fixed in place by the sizes of components such as the cover, dielectric, sheet metal. For this reason, if there is a variation in the sizes of the components, the fixing may become unstable or an excessive pressure may be applied to the dielectric, causing damage or the like to the dielectric.

An object of the present invention is to provide a dielectric filter stably fixed without damage even when there is a variation in the size of the components.

Solution to the Problem

A dielectric filter according to an aspect of the present invention includes at least one resonator using a TM mode, in which the resonator includes at least the following elements (1) to (4):

(1) a three-dimensionally shaped dielectric that includes a first surface and a second surface opposite to the first surface;

(2) a case that includes a first inner surface and a second inner surface facing the first inner surface and that accommodates the dielectric so that the first surface faces the first inner surface while the second surface faces the second inner surface;

(3) an intermediate member that is disposed between the first inner surface and the first surface and that is movable at least in a direction from the first inner surface toward the second inner surface; and

(4) a pressing member that is capable of pressing the intermediate member in a direction from the first inner surface toward the second inner surface.

Advantageous Effects of the Invention

According to an aspect of the present invention, it is possible to provide a dielectric filter stably fixed without damage even when there is a variation in size of components.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, each embodiment of the present invention will be described in detail with reference to the accompanying drawings. Throughout the embodiments, the same components are assigned the same reference numerals and the overlapping description thereof will be omitted, however.

Embodiment

FIG. 2is a top view illustrating overall TM mode dielectric filter (hereinafter simply referred to as “dielectric filter”)100according to an embodiment of the present invention,FIG. 3is a cross-sectional view of overall dielectric filter100inFIG. 2andFIG. 4is an enlarged view of the region enclosed by the ellipse inFIG. 3. However,FIG. 2shows the dielectric filter without a cover11.FIG. 3andFIG. 4show a situation in which screw111is inserted into cover11.

Dielectric filter100is provided with at least one resonator using a TM mode. For example, dielectric filter100shown inFIG. 2is provided with ten resonators. Each resonator is provided with at least case101, dielectric102, washer104(FIGS. 3 and 4) serving as an intermediate member, screw111(FIGS. 3 and 4) serving as a pressing member and frequency adjusting screw105(FIG. 3).

More specifically, case101is formed of side and bottom surfaces and provided with case10whose one side (top surface inFIG. 3) is open and cover11that covers the open surface of case10.

InFIG. 3andFIG. 4, case101(FIG. 3) includes regulation section101cthat regulates the movement of washer104along direction d2(FIG. 3) which is parallel to inner surface101a. For example, regulation section101cis a recessed portion provided in inner surface101aof cover11having a size corresponding to an outer shape of washer104.

Washer104is disposed between inner surface101aof case101and surface102aof dielectric102and is movable at least in direction d1from inner surface101atoward inner surface102b.

Screw111can press washer104in direction d1from inner surface101atoward inner surface101b. For example, when screw hole110is provided in inner surface101aof case101and a female thread is formed in screw hole110in a direction from inner surface101atoward inner surface101b, screw111is a male screw that is inserted into the above female thread.

Frequency adjusting screw105adjusts a resonance frequency. More specifically, as shown inFIG. 3, screw hole109is provided at a position facing surface102bof dielectric102at the bottom of case10, and frequency adjusting screw105is inserted into screw hole109and thereby protrudes in direction d3from inner surface101btoward inner surface101aof case11. The resonance frequency is adjusted by changing the length of frequency adjusting screw105protruding from inner surface101btoward inner surface101aof case11.

As shown inFIG. 2, in dielectric filter100, a plurality of columnar dielectrics102are arranged vertically at predetermined positions at appropriate intervals inside case101. As shown inFIG. 4, the open surface of case101(FIG. 3) is covered with sheet metal103. That is, sheet metal103is disposed along inner surface101ainside case101and between washer104and surface102aof dielectric102. Furthermore, as shown inFIG. 2, in dielectric filter100provided with at least two resonators arranged in parallel, sheet metals103(FIGS. 3 and 4) for the at least two resonators are integrated into one piece. Sheet metal103serves as the ground for each dielectric102and contributes to ground reinforcement.

As shown inFIG. 4, washer104is disposed above surface102aof dielectric102with sheet metal103interposed in between. For example, as shown inFIG. 4, washer104has a planar shape including a facing surface (surface104a) facing surface102aof dielectric102and surface104bopposite to surface104a(FIG. 5AandFIG. 5B). Furthermore, washer104has a recessed portion in the facing surface (surface104a).

For example, as shown inFIG. 4,FIG. 5AandFIG. 5B, washer104(FIGS. 4 and 5A) has a recessed portion having a size corresponding to the outer shape of surface102aof dielectric102in surface104aand the recessed portion is disposed so as to be fitted to surface102aof dielectric102. More specifically, as shown inFIG. 5A, the recessed portion of surface104aincludes bottom surface107provided at a position recessed by a predetermined thickness from the circumference of surface104ain the direction of surface104b, and tapered portion108which is formed in a tapered shape between the circumference of surface104aand bottom surface107. Surface104aof washer104has edge portion106around the circumference of the recessed portion of surface104a. That is, inFIG. 5A, washer104is provided with bottom surface107provided at a position one step recessed (corresponding to a predetermined thickness) from edge portion106, and tapered portion108which is formed in a tapered shape between edge portion106and bottom surface107. Washer104shown inFIG. 5AandFIG. 5Bserves as a position regulating member with respect to the d2(FIGS. 3 and 4) direction of dielectric102.

As described above with respect toFIG. 2, cover11that covers sheet metal103and washer104is placed over the open surface of case10. Cover11is provided with screw hole110at a position facing washer104, and screw111is screwed into screw hole110.

In dielectric filter100having such a configuration, when screw111, inserted into screw hole110, is turned clockwise by a predetermined amount, the distal end of screw111comes into contact with surface104bof washer104. When screw111is turned further, screw111presses washer104in a direction from inner surface101atoward inner surface101bof case101. Dielectric102can be fixed with the pressure with which screw111presses washer104. By so doing, even when there is a variation in size of components of each resonator, it is possible to add a pressure on the same (constant) level to dielectrics102of all resonators of dielectric filter100equally by appropriately performing torque management (that is, adjustment of the amount of rotation of screw111) using screw111provided for each resonator for dielectrics102of all the resonators in dielectric filter100. It is also possible to prevent more than necessary pressure from being imposed on each dielectric102and prevent damage to dielectric102.

Therefore, according to the present embodiment, even when there is a variation in the size of the components, it is possible to realize a dielectric filter stably fixed without damage.

Dielectric filter100is provided with screw111which is inserted into screw hole110provided in inner surface101aof case101, and screw105which is inserted into screw hole109provided in inner surface101bof case101. That is, in dielectric filter100, it is possible to appropriately fix each dielectric102using screw111provided separately from frequency adjusting screw105.

InFIG. 4, edge portion106(FIG. 5A) of washer104presses sheet metal103, which applies a pressure to dielectric102and causes tapered portion108to come into line-contact with the circumference of surface102aof dielectric102, making it possible to reduce contact variations and stably fix dielectric102. When screw111is inserted, performing torque management can prevent more than necessary pressure from being applied to dielectric102and prevent damage to dielectric102.

Thus, dielectric filter100according to the present embodiment includes, on one side of washer104, recessed portion105provided with edge portion106formed around the circumference of the one side, bottom surface107(FIG. 5A) provided at a position one step recessed from edge portion106, and tapered portion108formed in a tapered shape between edge portion106and bottom surface107, wherein washer104is disposed so that recessed portion105is positioned opposite to surface102aof dielectric102with sheet metal103interposed in between, and washer104is screwed by screw111.

In this way, edge portion106of washer104presses sheet metal103, tapered portion108(FIG. 5A) comes into line-contact with the circumference of surface102aof dielectric102, a pressure is applied to dielectric102, and dielectric102can be stably fixed. Moreover, threaded engagement of screw111under torque management can prevent more than necessary pressure from being applied to dielectric102to prevent damage to dielectric102. As a result, even when there is a variation in size of components, it is possible to stably fix dielectric102without damage.

Note that sheet metal103is not essential in stably fixing dielectric102.

Other Embodiments

The configuration shown inFIG. 4has been described in the present embodiment, but the present invention is not limited to this. Hereinafter, configurations1to4other than the configuration described above will be described usingFIG. 6toFIG. 9.

FIG. 6is a cross-sectional view illustrating configuration1, which is another configuration of the dielectric filter according to the embodiment of the present invention. Sheet metal201is provided with recessed portion202having a size corresponding to the outer shape of surface102aof dielectric102at a position overlapping with surface102aof dielectric102. When sheet metal201is attached to case101and fixed to case101(not shown herein), recessed portion202provided in sheet metal201is fitted to surface102aof dielectric102, which causes sheet metal201provided with recessed portion202to serve as a position regulating member in the d2direction of dielectric102. Washer203(flat washer) is disposed on surface102aof dielectric102with sheet metal201interposed in between.

FIG. 7is a cross-sectional view illustrating configuration2, which is another configuration of the dielectric filter according to the embodiment of the present invention. The length of dielectric301used here is greater than the height of the side wall of case10(not shown herein) so that, when screw111is inserted, a pressure is applied from dielectric301.

FIG. 8is a cross-sectional view illustrating configuration3, which is another configuration of the dielectric filter according to the embodiment of the present invention. No edge portion is provided in recessed portion402of washer401and tapered portion403is formed on bottom surface107from the circumference of washer401. Washer401having such a shape is disposed on surface102a(not shown herein) of dielectric102with sheet metal401interposed in between, screw111, inserted into screw hole110, is turned by a predetermined amount to press washer401, tapered portion403of washer401thereby penetrates sheet metal103causing tapered portion403to come into line-contact with the circumference of surface102aof dielectric102.

FIG. 9is a cross-sectional view illustrating configuration4, which is another configuration of the dielectric filter according to the embodiment of the present invention. Washer501has a planar shape including surface501afacing surface102a(not shown herein) of dielectric102and surface501bopposite to surface501a. Surface501aof washer501is provided with recessed portion503including edge portion502that contacts (overlaps with) the circumference of dielectric102(surface102a) via sheet metal103and bottom surface503provided at a position recessed by a predetermined thickness from edge portion502(circumference of surface501a) in the direction of surface501b. In the resonator, a current flows over the side face of dielectric102, so that, when current loss is taken into consideration, the angle formed by the side face of dielectric102and surface501aof washer501is preferably a right angle. In other words, since no current flows through the inside of dielectric102, recessed portion503may be formed in the portion of dielectric102other than the circumference of dielectric102, without surface501of washer501being brought into contact via sheet metal103.

A case has been described in the above embodiment where the hollow part penetrates the portion between surface102aand surface102bof dielectric102inFIG. 3, but the present invention is not limited to this configuration. For example, dielectric102may also have a recessed portion open toward inner surface101bof case10(not shown). In this case, frequency screw105is inserted into screw hole109and thereby protrudes from inner surface101bof case10toward the recessed portion of dielectric102.

A case has been described in the above embodiment where a screw is used as the pressing member. However, the pressing member is not limited to a screw, and any member may be used as long as the member can press the intermediate member in a direction from inner surface101aof case101toward inner surface101b. For example, a spring may be used as the pressing member instead of a screw.

The disclosure of Japanese Patent Application No. 2012-179284, filed on Aug. 13, 2012, including the specification, drawings and abstract is incorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

The dielectric filter according to the present invention is applicable to a base station apparatus and the like in a mobile communication system, for example.

REFERENCE SIGNS LIST