Abstract:
A dielectric filter includes at least two dielectric resonators, a housing, and a support rod supporting the dielectric resonators and attached to the housing. The support rod may include a first end and a second end attached to the housing. A method of manufacturing a dielectric filter includes fixing dielectric resonators to a support rod and attaching each end of the support rod to a housing.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This patent application claims priority to U.S. patent application Ser. No. 60/575,836 filed on Jun. 2, 2004. 
     
    
     FIELD OF INVENTION  
       [0002]     This invention is related to telecommunications filter technology, and more particularly, to dielectric resonator filters.  
       BACKGROUND  
       [0003]     High Q dielectric (HQD) band pass filters need extremely low in-band insertion loss, steep skirt slope and high out-of-band rejection. HQD band reject filters must have high in-band rejection, steep skirt slope and low out-of-band insertion loss.  
         [0004]      FIG. 1  shows a conventional HQD filter  1 . In the conventional filter, four dielectric “pucks”  2  are each fastened to separate support rods  3  either by epoxy or by using fastening screws and each support rod is attached to a housing  4 . Installing an individual support rod  3  for each resonator puck  2  is a complex and/or time consuming assembly procedure. In addition, since only one end of each support rod  3  is secured to the housing, such a cantilevered structure is subject to vibration or shock damage thereby causing filter failure or performance degradation. Thus, a need exists for an improved HQD resonator filter. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]      FIGS. 1   a  and  1   b  respectively show a top view and a longitudinal cross sectional view of the prior art conventional HQD filter.  
         [0006]      FIGS. 2   a ,  2   b  and  2   c , respectively show a top view, a longitudinal cross sectional view, and a transverse cross sectional view of the HQD filter of the present invention.  
         [0007]      FIG. 3  shows a longitudinal cross sectional view of a four pole HQD filter embodying the present invention.  
         [0008]      FIGS. 4 and 5  show top views of eight pole HQD filters embodying the present invention.  
         [0009]      FIG. 6  shows a housing for an eight pole HQD filter embodying the present invention.  
         [0010]      FIG. 7  shows a lid attached to the housing of  FIG. 6 .  
         [0011]      FIG. 8  shows a housing for the eight pole HQD filter of  FIG. 4 . 
     
    
     SUMMARY  
       [0012]     The present invention uses a single support rod to support all pucks or a series of support rods that each supports more than one puck. Each end of the support rod is mounted to the housing to firmly secure the pucks. This provides excellent shock and vibration durability and improved filter performance. Filter tuning is achieved by inserting set screws with a high dielectric constant inside the support rod or by the use of other types of tuning assemblies that are used with conventional HQD filters. The filter is tuned to optimal performance by gradual adjustment of the set screws.  
         [0013]     In one general aspect, a dielectric filter includes at least two dielectric resonators, a housing, and a support rod supporting the dielectric resonators by attachment to the housing. Embodiments may include one or more of the following features. For example, the support rod may include a first end and a second end attached to the housing. As another example, the housing may be made of metal or of a dielectric with metal plating.  
         [0014]     The dielectric filter may include a tuning apparatus attached to the housing that tunes the resonator frequency along with input and output connectors attached to the housing.  
         [0015]     Each dielectric resonator can be a dielectric puck that may have a threaded center hole. The dielectric resonators may be made of ceramic materials that have a dielectric constant greater than 20, a loss tangent less than 0.0005, and a thermal expansion coefficient in the range of −5 ppm/c to +5 ppm/c. The dielectric resonators may be operated in single mode TEH, single mode T, dual mode, or triple mode.  
         [0016]     The support rod may be made of a dielectric material and may have a threaded outer surface that is inserted through a center hole of each of the dielectric resonators. Dielectric nuts may be threaded onto the threaded outer surface thereby fixing the position of the dielectric resonators on the support rod. The support rod may also be a dielectric tube with a threaded outer surface in which case the dielectric resonators are threaded onto the threaded outer surface to fix the dielectric resonators to the support rod. The dielectric tube may also have a threaded central bore with tuning screws inserted into the threaded central bore to fine tune the dielectric resonators.  
         [0017]     In another general aspect, a dielectric filter includes a plurality of dielectric resonators and a plurality of dielectric rods, with each of the dielectric rods supporting more than one of the dielectric resonators. Embodiments may include one or more of the above or following features. For example, each dielectric rod may have a threaded outer surface, and dielectric nuts may be used to fix the dielectric resonators to the dielectric rods. The dielectric rods and the dielectric nuts may have a dielectric constant ranging from 1.5 to 6, a loss tangent ranging from 0.005 to 0.00005, and a thermal expansion coefficient ranging from −10 ppm/c to +10 ppm/c.  
         [0018]     The dielectric filter may include a housing and both ends of the dielectric rods may be fixed to the housing. Tuning assemblies may be attached to the housing or to a housing cover with a tuning assembly proximate to each of the dielectric resonators. Each tuning assembly may include a tuning screw made of metal, lock nuts made of metal, and a tuning plate or disc that is made of a ceramic material and that has a circular shape.  
         [0019]     In another embodiment, a series of dividing walls define separate compartments within the housing thereby partially isolating a dielectric resonator in each of the separate compartments. A cross coupling apparatus may also be used to couple pairs of partially isolated dielectric resonators. The cross coupling apparatus may include a coaxial transmission line having rods extending from an inner conductor, a plate attached to the inner conductor of the coaxial transmission line, and a ring attached to the inner conductor of the coaxial transmission line and to an outer connector of the coaxial transmission line.  
         [0020]     In another general aspect, a diplexer includes a housing, a receive bandpass filter that includes twelve ceramic dielectric resonators mounted to receive channel support rods, and a transmit bandpass filter that includes six metal dielectric resonators on a transmit channel support rod. Each end of the receive channel support rods and the transmit channel support rod is attached to the housing. Embodiments may include one or more of the above features.  
         [0021]     In a further general aspect, a method of manufacturing a dielectric filter includes fixing dielectric resonators to a support rod and attaching each end of the support rod to a housing.  
       DETAILED DESCRIPTION  
       [0022]     The present invention uses multiple dielectric resonators on a common support rod with each end of the support rod mounted to a housing.  FIGS. 2   a ,  2   b , and  2   c  show an embodiment of the HQD band-pass filter  9  of the present invention. Referring to  FIG. 2   a , a radio frequency (RF) input connector  10  and an RF output connector  11  are attached to the outside of the housing  15 . The housing  15  is a rectangular box with an open top and can be made of metal, such as, for example, aluminum with silver plating.  
         [0023]     A support rod  12  is positioned in the housing  15  with each end of the support rod  12  attached to the housing  15 . The support rod  12  may be attached to the housing  15  by spot welds, an adhesive, hardware, or a combination thereof. The support rod  12  has a threaded outer surface and is made of teflon or other similar material.  
         [0024]     Dielectric resonator pucks  13   a ,  13   b ,  13   c , and  13   d  are secured to the support rod  12  by inserting the support rod  12  through the center hole of each puck  13   a - 13   d . Locking nuts  14   a ,  14   b ,  14   c , and  14   d  are threaded onto the support rod  12  and are positioned on either side of each puck  13   a - 13   d  to fix the pucks  13   a - 13   d  at intervals along the length of the support rod  12 . The locking nuts  14   a - 14   d  are typically made of plastic or any other non-metallic material. In other embodiments, the pucks are adhered to the support rod by an adhesive or the pucks have threaded center holes to secure each puck to the support rod  12 . The pucks  13   a - 13   d  are made of ceramic or any other suitable material, such as, for example, metal. In one embodiment, the ceramic material has a dielectric constant greater than 20, a loss tangent less than 0.0005, and a thermal expansion coefficient in the range of −5 ppm/c to +5 ppm/c.  
         [0025]      FIG. 2   a  shows the housing  15  divided into compartments  16   a ,  16   b ,  16   c , and  16   d  by a large dividing wall  17  and two small dividing walls  18  in order to reduce the coupling between the pucks  13   a - 13   d .  FIGS. 2   b  and  2   c  shows the housing without compartments.  
         [0026]      FIG. 3  shows another embodiment of the present invention. The support rod  22  has a threaded central bore with dielectric set screws  24   a ,  24   b ,  24   c , and  24   d  threaded into the central bore. Each set screw  24   a - 24   d  is positioned proximate to each puck  23   a - 23   d . Movement of the dielectric set screws  24   a - 24   d  adjusts the frequency of each of the respective resonator pucks  23   a - 23   d . Additional tuning screws (not shown) may be located between the resonator pucks  23   a - 23   d  to adjust the coupling between adjacent resonator pucks  23   a - 23   d.    
         [0027]     In another embodiment, frequency tuning assemblies  26   a ,  26   b ,  26   c , and  26   d  are installed on the housing (or on the lid) to fine-tune the frequency of the resonator pucks  23   a - 23   d . Tuning assemblies  26   a - 26   d  include small tuning discs  25   a ,  25   b ,  25   c , and  25   d  positioned at the ends of threaded shafts  27   a ,  27   b ,  27   c , and  27   d . Nuts  28   a ,  28   b ,  28   c ,  28   d  secure the positions of the shafts  27   a - 27   d , which are rotated to move the tuning discs  25   a - 25   d  closer or further from the resonator pucks  23   a - 23   d.    
         [0028]      FIG. 4  is a top view of an eight pole HQD band pass filter. The input connector  30  and the output connector  31  are attached to the same end of the housing  29 . Two support rods  33  and  34  each support four resonator pucks  32   e - 32   h  and  32   a - 32   d , respectively. The rods  33 ,  34  are positioned in parallel and a dividing wall  36  isolates the support rods  33 ,  34 . An aperture or iris  35  in the dividing wall  36  allows coupling between the two pucks  32   d  and  32   h  that are proximate to the iris  35 .  
         [0029]     The transmission path travels from left to right through the filter from the input connector and across the resonator pucks  32   e - 32   h , respectively. The transmission path is then directed down through the aperture  35  from resonator puck  32   h  to resonator puck  32   d . At that point, the transmission path changes direction and travels from right to left from resonator puck  32   d  and though resonator pucks  32   c - 32   a , respectively, exiting at the output connector  31 .  
         [0030]     The size of the iris or aperture  35  may be varied depending on the desired frequency and bandwidth. In addition, the dimensions of separating walls  37  between adjacent pucks may also be changed to accommodate various frequencies and bandwidths.  
         [0031]     Similar to  FIG. 4 ,  FIG. 8  illustrates a housing  81  of an eight pole HQD filter configured to accommodate two parallel support rods (not shown). A main dividing wall  82  bisects the housing  81  and a series of lower walls  83   a - 83   f  further divide the housing into eight compartments  84   a - 84   h . Each lower wall  83   a - 83   f  includes a notched area or iris  85   a - 85   h . The support rods attach to each end of the housing and extend through the irises  85   a - 85   c  and  85   d - 85   f . An opening  86  at one end of the dividing wall  82  allows coupling to occur between pucks adjacent to the opening  86  in compartments  84   d  and  84   e.    
         [0032]     A channel  87  in the dividing wall  82  may be used for a cross coupling apparatus  88  that couples pucks in compartments  84   c  and  84   e . The cross coupling apparatus  88  may include a coaxial transmission line  89  having an extended inner conductor  90 . A plate may be attached to the inner conductor of the coaxial transmission line  89 , and a ring attached to the inner conductor  90  of the coaxial transmission line  89  and to an outer connector of the coaxial transmission line  89  (not shown).  
         [0033]      FIG. 5  is a top view of another embodiment of an eight pole HQD band pass filter with input and output connectors  50  and  51  on opposing ends of the housing  58 . Four resonator pucks  52   e ,  52   f ,  52   g , and  52   h  and  52   a ,  52   b ,  52   c , and  52   d  are each positioned on parallel support rods  53  and  54 , respectively. Three T-shaped dividing walls  56  and a set of smaller separating walls  57  partially isolate the resonator pucks  52   a - 52   e . A series of openings  55   a ,  55   b ,  55   c , and  55   d  between the walls  56 ,  57  provide a circuitous coupling path between adjacent pucks  52   e  and  52   a ,  52   b  and  52   f ,  52   g  and  52   c , and  52   d  and  52   h , respectively. Thus, the transmission path between the input connector  50  and the output connectors  51  goes from  52   e  to  52   a  to  52   b  to  52   f  to  52   g  to  52   c  to  52   d  to  52   h.    
         [0034]      FIG. 6  refers to a housing  61  for another eight pole HQD band pass filter that employs a row of 8 pucks on a single rod (not shown). The housing  61  is divided into a series of compartments  62   a ,  62   b ,  62   c ,  62   d ,  62   e ,  62   f ,  62   g , and  62   h  by a series of inner walls  63   a ,  63   b ,  63   c ,  63   d ,  63   e ,  63   f , and  63   g  each having an iris  64   a ,  64   b ,  64   c ,  64   d ,  64   e ,  64   f , and  64   g . The support rod is positioned in a channel  65  in each end wall  66  of the housing and it passes through the irises  64   a - 64   g  between the compartments.  
         [0035]      FIG. 7  shows the housing of  FIG. 6  with the cover or lid  71  attached. The lid  71  has a series of tuning assemblies  72   a - 72   h  (similar to that described above with respect to  FIG. 3 ) that tune each of the resonator pucks in compartments  62   a - 62   h , respectively (as shown in  FIG. 6 ). In addition, bandwidth tuning assemblies  73   a - 73   g  (as shown in  FIG. 7 ) are positioned proximate to each iris  64   a - 64   g , respectively, to fine tune the bandwidth of the filter. The configuration of the bandwidth tuning assembly is similar to that mentioned above with respect to the frequency tuning assemblies of  FIG. 3 .  
         [0036]     The number of dielectric resonators used in the present invention is not limited. The dielectric resonators may operate in various modes, such as, for example, single mode TEH, single mode T, dual mode, or triple mode. Also, the fine tuning method and mechanical approach shown in  FIG. 3  can be varied and/or can apply to all designs.  
         [0037]     Various changes may be made in the above apparatus without departing from the scope of the invention herein involved. All matter contained in the above description or shown in the accompanying drawing should be interpreted in an illustrative and not in a limiting sense. For example, advantageous results still could be achieved if components in the disclosed systems were combined in a different manner and/or replaced or supplemented by other components. Accordingly, other implementations are within the scope of the following claims.