Radio frequency coaxial switch
FIELD OF THE INVENTION 
     The present invention relates to a radio-frequency, especially high-frequency coaxial switch. 
     BACKGROUND OF THE INVENTION 
     The U.S. Pat. No. 4,206,332 describes a radio-frequency coaxial switch which includes at least one movable contact piece and a stationary contact arrangement having a contact element supported at one extremity of a compression spring. The other extremity of the spring is connected to an inner conductor of the associated coaxial connection. The contact element, prestressed by the compression spring in the direction of the movable contact piece, consists of a sleeve which surrounds the inner conductor and the compression spring and is resiliently supported on the front face of the movable contact piece or stud. 
     The German Pat. No. 341,723 describes a conventional rotary switch in which the stationary contact element is constituted by contact drums upon which compression springs act. The contact drums cooperate with the contact pieces which are arranged in a locked fashion on a switch rotor. 
     The use of contact drums in radio-frequency switches is known from the U.S. Pat. No. 3,394,324. In this prior art, the contact drums are not provided as a contact element arranged at one extremity of a stationary contact piece but instead constitute the movable part. 
     The U.S. Pat. No. 2,951,925 describes a radio-frequency coaxial switch which utilizes a contact element in the form of a leaf spring which extends the inner conductor of an associated coaxial connector and is prestressed in direction toward the movable part. 
     The German published specification No. 1 938 77 illustrates a radio-frequency switch which includes a switch rotor used as a movable contact piece which is contacted on both sides thereof. 
     From the U.S. Pat. No. 1,740,640 a knife switch with contact rolls is known which in order to obtain a contact engages in corresponding recesses of the contact blade. 
     OBJECT OF THE INVENTION 
     It is the primary object of the invention to provide an improved radio-frequency coaxial switch which requires a relatively low switching force especially for separating the contacts even if a substantial contact force is necessitated for obtaining low transfer resistances. 
     SUMMARY OF THE INVENTION 
     This object is realized according to the invention by using a leaf spring which supports at one end portion a contact roll and prestresses the contact roll in direction towards a movable contact piece. 
     Such a radio frequency coaxial switch has only a few and shaped parts which are uncomplicated and which can easily be correctly dimensioned to guarantee a rolling friction between the stationary part and the movable contact piece. Through the use of such a leaf spring, the required force to drive the movable part and to provide a sufficient contact is considerably reduced, thus leading to an increased durability of the switch. 
     The contact roll can easily be supported on the spring by providing the end portion of the latter with a semi-circular shape. It is preferable, however, to clamp the contact roll between two washers and to deform the still projecting section of the leaf spring so as to simply prevent an axial displacement of the contact roll. 
     According to a further feature of the invention, a stop member is provided in the vicinity of the end portion of the leaf spring to limit the deflection during assembly of the coaxial switch thereof. 
     The leaf spring may be provided in various embodiments. Thus it is possible to use a slotted leaf spring which carries at the end portion of each shank a contact roll or the use of a two-legged leaf spring whose shanks are dihedral about 90% with respect to each other. 
     A flat construction of the switch is obtained when the contact roll moves along a plane surface of the contact piece or along a ring segment shaped circumference of the contact piece. In the latter case the roll smoothly rolls up and down with respect to the movable contact piece. Both these constructions allow a contact of both sides of the movable piece by a contact roll. 
     A further feature of the invention resides in the fact that the movable contact piece which is either rotatable or linearly movable is at a higher level relative to the stationary contact roll so that the housing of the switch can provide a shielding between the stationary contact piece and the movable contact piece. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The above and other features of the present invention will now be described in detail with reference to the accompanying drawings in which: 
     FIG. 1 is a first embodiment of a coaxial switch according to the invention; 
     FIG. 2a is a sectional view taken along lines A--A in FIG. 2b; 
     FIG. 2b is a sectional view of the contact roll taken in direction of arrow X according to FIG. 2a; 
     FIGS. 3 and 3a illustrate a second embodiment of the coaxial switch; 
     FIGS. 4 and 4a illustrate a third embodiment of the coaxial switch; 
     FIGS. 5 and 5a illustrate a fourth embodiment of the coaxial switch; 
     FIGS. 6 and 6a illustrate a fifth embodiment of the coaxial switch; 
     FIGS. 7 and 7a illustrate a sixth embodiment of the coaxial switch; 
     FIG. 7b is a view taken in direction of arrow Y according to FIG. 7a. 
    
    
     SPECIFIC DESCRIPTION 
     Referring first to FIG. 1, I have shown a coaxial switch including a casing 1 which serves as an outer conductor, and at one lateral face is provided with a coaxial connection 2. The housing 1 accommodates a switch chamber 5 in which one end of an inner conductor 3 projects. The inner conductor 3 is traversing the connection 2 and is kept in position by an insulating disk 4 disposed in a respective recess 4a of the connector 2 and a recess 4b of the casing 1. 
     The extremity of the inner conductor 3 projecting into the switch chamber 5 supports one end of a leaf spring 6 by means of a fastening element 20. The other end of the leaf spring 6 carries a contact roll 7. The leaf spring 6 and the contact roll 7 constitute a stationary contact stud which cooperates with a movable contact stud 8. In order to provide an exact switch position, the contact stud 8 is provided with a recess (not shown) in which the contact roll 7 is supported under prestress provided by the leaf spring 6. The contact stud 8 is driven by a switch rotor 10 which is arranged on a shaft 9. To limit the deflection of the leaf spring 6 during assembly of the coaxial switch a stop member 11 is located at the inner wall of the switch chamber 5 and projects transversely to the elongation of the spring 6. The use of the stop member 11 facilitates the assembly of the coaxial switch, especially of the switch rotor 10 and the movable contact stud 8 without having any interference from the spring 6, even in case the latter is provided with a substantial prestress. The stop member 11 is made of a sufficiently low-loss plastic material and fixed by any suitable means, e.g., caulking, wedging, rolling, etc. 
     The end of the leaf spring carrying the contact roll 7 is of semi-circular shape (FIG. 2b) and is provided with short transverse slots 6&#39; opposing each other. The fixation of the contact roll 7 on the leaf spring 6, is obtained by placing the roll 7 on the spring 6 between two cylindrical washers 12a, 12b in such a manner that the portion of the spring 6 provided with the slots 6&#39; projects beyond the foremost washer 12b. The spring is then bent outwardly along the slots 6&#39; to provide outwardly extending lugs 6a, 6b. Consequently, lugs 6a, 6b as well as the force exerted by the forward portion of the spring 6 on the roll 7 prevent an axial movement of the roll 7. 
     For improving the contact between the stationary portion and the contact stud 8, a slotted leaf spring 13 is provided which is fixed in like manner to the inner conductor 3 and whose end of each shank carries a contact roll 7a, 7b (FIG. 3a). The rolls 7a, 7b are fixed to the shanks in the same manner as described with respect to the contact roll 7, and thus are rotatably connected but prevented from any axial movement. 
     In the embodiments according to FIGS. 1 and 3, the spring is screwed on the inner conductor 3. It is, however, possible to provide the spring in one piece with the conductor 3 as illustrated, for example, in FIG. 4, in which a leaf spring 3a is integrally connected to the conductor 3. 
     In FIGS. 5a and 5b a contact piece 8a is illustrated which is shaped in the form of a blade and cooperates with a leaf spring 14 provided with two shanks 14a, 14b. Shanks 14a, 14b are elastically prestressed against each other and each supports respective contact rolls 7a, 7b at its extremity which is remote to the inner conductor 3. 
     A further embodiment is shown in FIGS. 6a, 6b, in which the stationary contact piece includes a two-legged leaf spring 15 whose shanks are arranged dihedrally about an angle of 90% with respect to each other. The connection between the spring 15 and the conductor 3 is achieved with a screw 20. 
     In the embodiments according to FIGS. 5 and 6, it can be seen that the contact rolls 7a, 7b are in contact with a respective side of the movable piece 8. Advantageously, the surface of each side of the contact piece 8 is provided in a plane manner to support the contact rolls 7a, 7b when the contact piece 8 is rotated or moved in a linear direction so that both embodiments a relatively flat construction is obtained. 
     The embodiment shown in FIGS. 7, 7a, 7b is especially advantageous with respect to a disengagement of the stationary contact arrangement from the movable contact piece 8 when contact is opened. The stationary contact arrangement corresponds to the one as shown and described in reference to FIG. 4. In contrast thereto, however, a movable contact stud 8b is provided which at its conducting end is angled towards the contact roll 7 in an L-shaped manner. The housing 1 accommodates a switch chamber 5a which is adpated to the shape of the contact piece 8b and thus is also of L-shape so that the movable contact piece 8b is arranged at a higher level with respect to the plane of the conductor 3, spring 3a and roll 7. Consequently, the housing 1 which constitutes the outer conductor provides a shielding between the stationary and movable contact piece with the contacts are open. In this embodiment, a stop member 11 corresponding to the one described in connection with the coaxial switch of FIG. 1 is provided at a suitable location at the inner wall of the switch chamber 5a to limit the deflection of the leaf spring 3a during assembly of the coaxial switch. 
     As can be seen from FIG. 7b, the movable piece 8b has a ring segment-shaped circumference so that the movement of the roll 7 along the circumference is facilitated.