Patent Publication Number: US-7724106-B2

Title: Coaxial connecting part

Description:
The invention relates to a coaxial connecting element for connecting a coaxial jack to a circuit carrier. 
     In measuring devices used in high-frequency technology, the coaxial jack used as the measurement port, which is installed in the front panel of the measuring device and is accessible from the outside, is generally connected via a portion of coaxial line to the printed conductor of the actual measuring-device circuit formed on a planar circuit carrier (substrate), and the inner conductor of this portion of coaxial line is attached to the printed conductor of the circuit carrier, for example, by soldering. Forces acting on the outer conductor of the coaxial jack are absorbed in the housing, because the coaxial jack and the housing are connected to one another via a screw connection. By contrast, the connection between the inner conductor and the printed conductor of the substrate is mechanically very sensitive. Even extremely small axial or radial forces in the inner conductor can damage the circuit carrier and/or its printed conductors. Such axial and/or radial forces are generated primarily by the user when screwing and unscrewing the plug of the measurement cable to and from the coaxial jack of the measuring device, because even with very careful processing of the jacks, the inner conductor is moved in an axial and radial manner when screwing and unscrewing the plug, and these small movements of the inner conductor are then sufficient to damage the circuit carrier as mentioned above. 
     The object of the invention is therefore to provide a coaxial connecting element, which prevents such damage to the circuit carrier by the inner conductor. 
     This object is solved on the basis of a coaxial connecting element according to the preamble of the independent claim by its characterising features. Advantageous further developments are specified in the dependent claims. 
     As a result of the bellows interconnected in the inner conductor, any axial and/or radial forces occurring in the inner conductor are absorbed and therefore kept away from the sensitive connecting position between the inner conductor and the printed conductor of the planar circuit carrier. The connecting element according to the invention, which is preferably integrated directly in the coaxial jack with the bellows incorporated in the inner conductor, is therefore particularly suitable for high-frequency electronic measuring devices, wherein measuring cables are frequently screwed and unscrewed to and from the externally-accessible coaxial measurement ports, generally mounted on the front panel, and wherein the inner conductor is therefore exposed to strong axial and radial forces especially in cases of rough handling. In spite of the bellows, the connecting element according to the invention can be manufactured with extremely low reflection. 
     The inner conductor according to the invention, which is resilient in the axial and radial directions, is in fact particularly advantageous in measuring devices with coaxial jacks accessible from the outside, but can also be used successfully with all coaxial systems such as jacks, plugs, probe tips or similar, of which the inner conductors are exposed during operation to axial and radial forces, and which are connected at the other end to a sensitive substrate circuit. 
    
    
     
       The invention is explained in greater detail below on the basis of an exemplary implementation with reference to schematic drawings. The drawings are as follows: 
         FIG. 1  shows in a partial perspective view the connection between a coaxial jack of a measuring device with a circuit carrier (substrate) installed in the interior of the measuring device; and 
         FIG. 2  shows details of the coaxial connecting element used in this context in an enlarged view. 
     
    
    
     A coaxial jack  2 , which is used as a measurement port and of which the inner conductor  3  is connected in the interior of the housing to the circuit of the measuring device formed on a planar circuit carrier  4 , is mounted in the front panel  1  of a high-frequency measuring device, which is illustrated in  FIG. 1  only in a fragmentary manner. The end  5  of the inner conductor inside the device is connected to the printed conductors of the circuit carrier  4 , for example, by soldering. The inner conductor  3  of the jack  2  is held in the outer-conductor sleeves  6 ,  8  via a support disk  7  made of an isolating material. 
     Another outer-conductor sleeve  8 , which accommodates an inner conductor  9 , which connects the inner conductor  3  of the jack to the connecting end  5  on the circuit carrier  4 , is inserted in the outer-conductor sleeve  6  of the jack  2 . 
     The details of this coaxial connecting element are shown in an enlarged scale in  FIG. 2 . The inner conductor  9  is held in a concentric manner between the two supports  7  and  10  integrated in the outer-conductor sleeve and screwed with the inner conductors  3 ,  5  into the corresponding supports  7 ,  10 . It is divided in the middle, and a resilient bellows  11  is inserted between its two halves  14  and  15 . The inner-conductor halves  14  and  15  each provide end-face boreholes  12 , into which pin-like projections  13  projecting axially from the bellows  11  are inserted. The bellows  11  is held between the inner conductor halves  14  and  15  in this manner. 
     The bellows  11 , which is hollow inside, preferably consists of a thin foil-like nickel material, which is gold plated on the outside. In order to manufacture this resilient, thin-walled bellows, a blank of aluminium is first manufactured with the required contour, to the outside of which a thin nickel coating is then applied in a galvanic manner. This is finally gold plated. 
     The inner aluminium blank is then etched away to provide an extremely thin-walled bellows with a corrugated outer coating made of gold-plated nickel. The axially-projecting pin-like holding portions  13  of the bellows  11  are also manufactured in the same manner as hollow pins. 
     The contour of the bellows  11  is preferably selected in such a manner that the specified standard characteristic impedance of, for example, 50 ohms is provided even at the position of the bellows within the coaxial outer-conductor sleeve  8 . This can be calculated and implemented using a 3-D simulator for high-frequency electromagnetic problems. 
     The resilient bellows can be deformed in a resilient manner in the axial direction as well as to a limited extent in the radial direction, and in this manner, forces, which act on the inner conductor  3  during the screwing and unscrewing of the measurement cable to and from the jack  2  by the user, can be absorbed. The bellows prevents such forces from being transferred from the inner conductor  3  of the jack to the inner-conductor end  5  at the connecting position with the substrate  4 . 
     The invention is not restricted to the exemplary implementation presented. The elements described can be combined with one another as required.