Abstract:
A (TM01) dielectric resonator has a metal housing, a dielectric insert, and a resilient element located between one end of the dielectric insert and the housing. The resilient element ensures physical contact between the housing and both ends of the dielectric insert over the entire operating temperature range of the resonator, thereby compensating for differences in the coefficients of thermal expansion of the materials used for the metal housing and the dielectric insert. In one embodiment, the dielectric insert is housed within a cylindrical tube between a top cover and a bottom end cap, the resilient element is an electrically non-conductive (silicone rubber) gasket, and the resonator has a thin, electrically conductive (aluminum) plate located (i) between the dielectric insert and the gasket and (ii) between the end cap and the tube to ensure a contiguous electrically conductive path from one end of the dielectric insert to the other.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to electronics and, more specifically but not exclusively, to dielectric resonators, such as TM01 dielectric resonators, used in RF filters. 
         [0003]    2. Description of the Related Art 
         [0004]    This section introduces aspects that may help facilitate a better understanding of the invention. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is prior art or what is not prior art. 
         [0005]    A dielectric resonator (DR) filter is a type of radio frequency (RF) filter that has a dielectric resonator that resonates at an RF or ultra RF frequency. Dielectric resonators can be categorized into TM (transverse magnetic), TEM (transverse electro magnetic), and TE (transverse electric) mode resonators depending on their structure, which determines their resonant mode. 
         [0006]      FIG. 1  shows a cross-sectional side view of a conventional TM-mode dielectric resonator  100 . Resonator  100  includes an electrically conductive (e.g., metal such as aluminum) housing consisting of a cylindrical container  102  and a circular cover  104 , configured with two electrical connectors  106 , where cover  104  is held in place on the top of container  102  by a number of screws  108 . Positioned within resonator  100  is a hollow, cylindrical dielectric insert  110 , which is centered within resonator  100  using a cylindrical guide pin  112  located at the bottom of container  102 . Tuning screw  114  is used to tune the resonant frequency of resonator  100 . Note that the outer diameter of dielectric insert  110  is smaller than the inner diameter of cylindrical container  102 , such that resonator  100  has a cylindrical, annular gap  116  between insert  110  and container  102 . 
         [0007]    In order to operate with a sufficiently high Q factor in the desired TM resonant mode (e.g., the first resonant mode TM01), with a reduced resonator height to achieve low-profile filter packages, dielectric insert  110  should be in physical contact with both cover  104  and the bottom of container  102 , such that a contiguous, electrically conductive path is provided from the bottom of the dielectric insert to the top of the dielectric insert via container  102  and cover  104 . It is also desirable for resonator  100  to operate in the desired TM resonant mode over a wide range of operating temperatures (e.g., from −40 C to +85 C). Unfortunately, the materials typically used for the metal housing (e.g., aluminum) and the dielectric insert (e.g., conventional ceramic materials with dielectric constants varying from about 20 to about 80 such as barium titanate, BaLnTi oxide, BaZnToTi oxide, and BaTi oxide) have coefficients of thermal expansion that sufficiently differ from one another such that physical contact cannot easily be maintained over the entire operating temperature range. 
         [0008]    In particular, for a typical design of resonator  100  in which the coefficient of thermal expansion of the metal housing is greater than that of the dielectric insert, a configuration of elements that provides good physical contact at a relatively low temperature may result in an air gap between the dielectric insert and the metal cover at a relatively high temperature, which air gap will prevent resonator  100  from operating properly in its desired resonant frequency, since the metal housing expands with rising temperature faster than the dielectric insert. On the other hand, a configuration of elements that provides good physical contact at a relatively high temperature may result in the dielectric insert breaking (e.g., cracking) at a relatively low temperature, due to the increased compressive forces applied by the metal housing at low temperatures, since the metal housing shrinks with falling temperature faster than the dielectric insert. 
       SUMMARY 
       [0009]    Problems in the prior art are addressed in accordance with the principles of the present invention by including a resilient element to the resonator design to compensate for differences in the coefficients of thermal expansion between the metal housing and the dielectric insert by accommodating for different rates of change in the physical dimensions of certain elements over the operating temperature range. 
         [0010]    In one embodiment, the present invention is a dielectric resonator comprising (i) an electrically conductive housing having a top and a bottom, (ii) a dielectric insert located within the housing, such that an annular gap exists between the dielectric insert and the housing, and (iii) a resilient element located between the dielectric insert and either the top or bottom of the housing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Other aspects, features, and advantages of the present invention will become more fully apparent from the following detailed description, the appended claims, and the accompanying drawings in which like reference numerals identify similar or identical elements. 
           [0012]      FIG. 1  shows a cross-sectional side view of a conventional TM-mode dielectric resonator; 
           [0013]      FIG. 2  shows a cross-sectional side view of a TM-mode dielectric resonator, according to one embodiment; 
           [0014]      FIG. 3  shows a cross-sectional side view of a TM-mode dielectric resonator, according to another embodiment; and 
           [0015]      FIG. 4  shows a magnified view of the bottom portion of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]      FIG. 2  shows a cross-sectional side view of a TM-mode dielectric resonator  200  according to one embodiment. Resonator  200  is substantially identical to resonator  100  of  FIG. 1  with analogous corresponding elements, i.e. the Resonator comprises an electrically conductive (e.g., metal such as aluminum) housing consisting of a cylindrical container  202  and a circular cover  204 , configured with two electrical connectors  106 , where cover is held in place on the top of container by a number of screws  108 . Positioned within resonator is a hollow, cylindrical dielectric insert  210 , which is centered within resonator using a cylindrical guide pin  112  located at the bottom of container. Tuning screw  114  is provided to tune the resonant frequency of resonator  200 ; the outer diameter of dielectric insert  210  is smaller than the inner diameter of cylindrical container  202 , such that resonator  200  has a cylindrical, annular gap between insert  210  and container  202 , except that resonator  200  has an electrically conductive (e.g., metallic) spring washer  218  positioned between the bottom of metallic container  202  and the lower end of dielectric insert  210 . Spring washer  218  is designed (or selected) and resonator  200  is configured such that good physical contact is maintained (i) between metal cover  204  and the upper end of dielectric insert  210 , (ii) between the lower end of dielectric insert  210  and spring washer  218 , and (iii) between spring washer  218  and the bottom of container  202  over the entire operating temperature range of resonator  200 . 
         [0017]    In particular, at the low end of the operating temperature range, at which the height of container  202  is at its smallest value, spring washer  218  will be in its highest compression state for resonator  200 . At the high end of the operating temperature range, at which the height of container  202  is at its largest value, spring washer  218  will be in its lowest compression state for resonator  200 . Note that, spring washer  218  is specifically designed (or selected) such that, in it highest compression state, spring washer  218  will not apply compressive forces sufficient to break dielectric insert  210 , while, in its lowest (albeit preferably non-zero) compression state, spring washer  218  will still ensure good physical contact throughout resonator  200 . 
         [0018]    In this case, a contiguous, electrically conductive path is provided from the lower end of dielectric insert  210  to the upper end of dielectric insert  210  via spring washer  218 , container  202 , and cover  204 . 
         [0019]    In an another not disclosed embodiment, the resonator  200  has an electrically conductive spring positioned between the bottom of metallic container  202  and the lower end of dielectric insert  210 . 
         [0020]      FIG. 3  shows a cross-sectional side view of a TM-mode dielectric resonator  300  according to another embodiment.  FIG. 4  shows a magnified view of the bottom portion of  FIG. 3 . Resonator  300  is substantially identical to resonator  100  of  FIG. 1  with analogous corresponding elements, except for the following. 
         [0021]    Instead of having a container formed from a single piece of metal, as in container  102  of  FIG. 1 , the container of resonator  300  is formed from (i) a hollow, cylindrical, electrically conductive (e.g., aluminum or other metal) tube  320  having a tapped bottom opening and (ii) a threaded, circular, electrically conductive (e.g., aluminum or other metal) end cap  322  that screws into the tapped bottom opening of tube  320 . Positioned between the lower end of dielectric insert  310  and end cap  322  is a resilient, annular gasket  324 . 
         [0022]    If gasket  324  is made of an electrically conductive material (e.g., ultra-flexible Cu/Be), a contiguous, electrically conductive path is provided from the lower end of dielectric insert  310  to the upper end of dielectric insert  310  via gasket  324 , end cap  322 , tube  320 , and cover  304 . 
         [0023]    If gasket  324  is made of a electrically non-conductive material (e.g., silicone rubber), then resonator  300  includes a thin, annular, electrically conductive (e.g., metal) plate (e.g., aluminum foil)  326  that extends from (i) functioning as a physical interface between the lower end of dielectric insert  310  and the top side of gasket  324  at the inner radial dimension of the plate to (ii) functioning as a physical interface between tube  320  and end cap  322  at the outer radial dimension of the plate. In this way, a contiguous, electrically conductive path is provided from the lower end of dielectric insert  310  to the upper end of dielectric insert  310  via plate  326 , tube  320 , and cover  304 . Note that, even if gasket  324  is itself electrically conductive, resonator  300  can still include plate  326  in its design. 
         [0024]    In either case, gasket  324  is designed (or selected) and resonator  300  is configured such that: 
         [0025]    At the low end of the operating temperature range, at which the height of tube  320  is at its smallest value, gasket  324  will be in its highest compression state for resonator  300 ; and 
         [0026]    At the high end of the operating temperature range, at which the height of tube  320  is at its largest value, gasket  324  will be in its lowest (albeit preferably non-zero) compression state for resonator  300 . 
         [0027]    Note that, gasket  324  is specifically designed (or selected) such that, in it highest compression state, gasket  324  will not apply compressive forces sufficient to break dielectric insert  310 , while, in its lowest compression state, gasket  324  will still ensure good physical contact throughout resonator  300 . Note further that, as represented in  FIGS. 3 and 4 , throughout the operating temperature range, the thickness of gasket  324  is greater than (or at least equal to) the depth of annular recess  328  in end cap  322  in which gasket  324  resides, such that gasket  324  will always extend above (or at least never fall below) the upper surface of end cap  322 . 
         [0028]    In one possible implementation, resonator  300  is assembled by: 
         [0029]    Placing gasket  324  within recess  328  in end cap  322 ; 
         [0030]    Placing plate  326  over the gasket/end cap assembly; 
         [0031]    Screwing the plate/gasket/end cap assembly into the bottom of tube  320 ; 
         [0032]    Inserting dielectric insert  310  into the end cap/tube container assembly; and 
         [0033]    Mounting cover  304  onto the top of the insert/container assembly. 
         [0034]    Note that mounting cover  304  onto the top of the insert/container assembly at an intermediate temperature within the operating temperature range (e.g., 25 C room temperature) results in gasket  324  being compressed to an intermediate compression state for resonator  300  relative to the highest and lowest compression states associated with the lowest and highest temperatures, respectively, in the resonator&#39;s operating range. 
         [0035]    Although embodiments have been described in the context of dielectric resonators in which a resilient element (e.g., spring washer  218  of  FIG. 2  or gasket  324  of  FIG. 3 ) is located between the lower end of the dielectric insert and the bottom of the container, in alternative embodiments, a resilient element is located between the upper end of the dielectric insert and the top cover, either instead of or in addition to the resilient element located at the bottom of the resonator. When the dielectric resonator has two resilient elements, one at its top and the other at its bottom, those resilient elements may be the same (e.g., two metallic spring washers or two silicone rubber gaskets) or different (e.g., one metallic spring washer and one silicone rubber gasket). 
         [0036]    Although the container of resonator  300  of  FIGS. 3 and 4  is formed from two elements (i.e., tube  320  and end cap  322 ), in alternative embodiments, the container is made from a single piece of material, as in resonators  100  and  200  of  FIGS. 1 and 2 . In this case, when the gasket is made from an electrically non-conductive material, some appropriate means is provided to ensure the electrical connection between the thin plate and the container, such as by purposely shaping the thin plate in an appropriate manner. 
         [0037]    Unless explicitly stated otherwise, each numerical value and range should be interpreted as being approximate as if the word “about” or “approximately” preceded the value of the value or range. 
         [0038]    It will be further understood that various changes in the details, materials, and arrangements of the parts which have been described and illustrated in order to explain the nature of this invention may be made by those skilled in the art without departing from the scope of the invention as expressed in the following claims. 
         [0039]    The use of figure numbers and/or figure reference labels in the claims is intended to identify one or more possible embodiments of the claimed subject matter in order to facilitate the interpretation of the claims. Such use is not to be construed as necessarily limiting the scope of those claims to the embodiments shown in the corresponding figures. 
         [0040]    Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments. The same applies to the term “implementation.” 
         [0041]    The embodiments covered by the claims in this application are limited to embodiments that (1) are enabled by this specification and (2) correspond to statutory subject matter. Non-enabled embodiments and embodiments that correspond to non-statutory subject matter are explicitly disclaimed even if they fall within the scope of the claims.