Patent Publication Number: US-2004041667-A1

Title: Multi-polar cascade quadruplet band pass filter based on dielectric dual mode resonators

Description:
[0001] The present invention relates to a multi-polar bandpass filter based on a group of dielectric dual mode resonators which are arranged in a metal housing and coupled to one another.  
       [0002] From the prior art, dielectric dual mode resonators are known which can e.g. be used in communication satellites for channel separation. It is difficult to couple dual mode resonators without greatly affecting the quality. An axial arrangement of cylindrical dielectric dual mode resonators is known in which individual resonator chambers are coupled by cruciform diaphragms. In this case, relatively elevated high-frequency currents flow in the area of the diaphragms which greatly affect the attainable filtering qualities (U.S. Pat. No. 4,489,293). In an earlier patent application, we merely used a four-polar bandpass filter formed by coupling two dual mode resonators (DE 19824997, pending).  
       [0003] Thus, the object of the present invention is to create a design for a multi-polar bandpass filter with which it is possible to couple as many dual mode resonator pairs (quadruplets) as desired while at the same time maintaining high filtering quality.  
       [0004] According to the invention, the object is solved thereby that metal walls in the metal housing produce the coupling between the dual mode resonators in such a way that, on the one hand, a positive forward coupling takes place between respectively adjacent resonator pairs and, on the other hand, a positive and a negative coupling takes place within each pair of resonators.  
       [0005] With a cascade quadruplet filter of this type, pairs of finite zero lines of transmission can be obtained which are arranged largely symmetrically about the centre of the bandpass.  
       [0006] Further advantages of the present invention can be found in the features of the subclaims 2 to 9.  
     
    
    
     [0007] Embodiments of the present invention are described in greater detail in the following with reference to the drawings, showing:  
     [0008]FIG. 1 a typical characteristic curve of a twelve-polar, cascade quadruplet filter;  
     [0009]FIG. 2 a schematic top view onto an eight-polar filter having four dielectric dual mode resonators;  
     [0010]FIG. 3 a schematic top view onto a twelve-polar cascade quadruplet filter having six dielectric dual mode resonators;  
     [0011]FIG. 4 a schematic top view onto a sixteen-polar cascade quadruplet filter having eight dielectric dual mode resonators. 
    
    
     [0012]FIG. 2 shows a schematic top view onto an eight-polar cascade quadruplet filter or multi-polar bandpass filter according to the present invention. Metal walls  2  are arranged in a metal housing  1 . The metal walls  2  divide the chamber surrounded by the metal housing into more or less defined areas. A dielectric dual mode resonator  3  is placed in each of these areas. On the whole, therefore, there are four dual mode resonators  3  in the metal housing  1  in the present embodiment. The metal housing  1  also has a base plate  1 . 1 , each dual mode resonator  3  being kept at a distance from it by a spacer  4 . The metal walls  2  form coupling gaps  2 . 1  and  2 . 2  between the individual dual mode resonators  3 . The dual mode resonators  3  are arranged behind one another or beside one another in a predetermined sequence or cascade. Two dual mode resonators  3  each that follow one another in the cascade form a quadruplet. In FIG. 2, the dual mode resonators  3  with the mode numbers  1  to  4  (M 1 , M 2 , M 3 , M 4 ) form a first quadruplet and the dual mode resonators with the mode numbers  5  to  8  (M 5 , M 6 , M 7 , M 8 ) form a further, second quadruplet.  
     [0013] The first dual mode resonator  3  in each of a predetermined series or cascade of dual mode resonators, i.e. the dual mode resonator with the mode number  1  (M 1 ), is coupled to this mode M 1  with an input antenna  5   a . The respectively last dual mode resonator  3  in the cascade, i.e. the dual mode resonator with the mode number  8  (M 8 ) is coupled to this mode M 8  with an output antenna  5   b . Each dual mode resonator  3  comprises a dual mode coupler  6  and a dual mode tuner  7 . The dual mode coupler  6  and the dual mode tuner  7  are inserted from the base plate  1 . 1  side.  
     [0014] Control elements  8 , with the aid of which the coupling power can be set between the resonators  3 , are arranged in the coupling gaps  2 . 1 . The metal walls  2  serve to limit the couplings between the resonators  3 . In this way, the metal walls  2  between two dual mode resonators  3  of a quadruplet following one another in the predetermined series or cascade form two coupling gaps  2 . 1 . The metal walls between two dual mode resonators  3  of different quadruplets following one another in the predetermined series form a single coupling gap  2 . 2 .  
     [0015] Two embodiments are shown in FIG. 3 and in FIG. 4 which have the same coupling principle of the embodiment described in FIG. 2: they only differ therein that six dual mode resonators  3  are coupled to one another in FIG. 3 and even eight dual mode resonators  3  in FIG. 4. The connection of the output antenna  5   b  is made at the last mode  12  M 12  in the embodiment shown in FIG. 3 and at the last mode  16  M 16  in the embodiment shown in FIG. 4.  
     [0016] A typical characteristic curve for a twelve-polar cascade quadruplet filter is shown in FIG. 1, said filter being formed from three cascade quadruplets. Three finite zero lines of transmission each are present on both sides of the bandpass.