Field of the invention

The invention relates to a coaxial test connector for easy and quick connection to a test object. It further relates to a self-aligning coaxial connector, i.e. a connector, which automatically aligns to a mating connector during the coupling operation.

Description of the related art For testing electronic devices test adapters are often used. These test adapters connect with devices to be tested to external test equipment. When testing RF devices like amplifiers, filters or others, these often have to be connected by RF connectors, which in most cases are coaxial connectors. These have comparatively tight mechanical tolerances and require a precise connection. When the connectors are attached manually to the device to be tested, the test adapter's connectors have flexible cables and are manually attached to the device to be tested. If an automatic connection between a device to be tested and a test adapter is desired, mechanical tolerances may cause severe problems. Basically, a test adapter may be built with close mechanical tolerances, but the devices to be tested are often manufactured in larger quantities and often have wider mechanical tolerances. This may lead to a misalignment of the connectors which may further lead to a damage of the connectors or to incorrect test results. Generally it would be preferred, if the connectors of the measuring adaptor and the mating connectors of the device to be tested are exactly aligned in all planes and directions. US 6,344,736 Bl discloses a self-aligning connector. The connector body is held over an outer radial flange, provided at its outer surface, between an inner radial flange provided at the inner surface of the connector housing and a washer pressed by an axial spring, so that it can align to a mating connector being insert- ed into the centering collar fixed to the connector body at least axially and in the transverse plane.

To provide a low passive intermodulation (PIM) connection, comparatively high contact forces are applied to normal coaxial RF connectors. In normal use, such forces are applied by the connector's locking nut which is tightened with a pre- determined and comparatively high torque. In a test setup, locking the connectors is too time consuming. Simply pressing the connectors together would require a pressure device generating high pressure in axial direction of the connector. This is hardly feasible specifically in devices with a large number of connectors. US 4,374,606 discloses a coaxial connector with a plurality of contacts for radially contacting an outer conductor. The contacts are held by a sleeve in axial direction. The sleeve engages slidably in an outer conductor.

US 4,106,839 discloses a shielded multipole connector having a contact spring which connects the shields of mating connectors.

Summary of the invention

The problem to be solved by the invention is to provide a coaxial RF connector interface providing high return loss in a broad frequency range and a low passive intermodulation which can be connected and disconnected by applying compar- atively low forces. Preferably, the connection should be maintained without applying significant forces in an axial direction of the connector. Furthermore, the connector should have a long lifetime with a large number of mating cycles as are required for test equipment.

Solutions of the problem are described in the independent claims. The dependent claims relate to further improvements of the invention. According to a preferred embodiment, a test connector is provided for connecting to a compatible coaxial connector, which may be connected to or be part of a device to be tested. The test connector provides at least an inner conductor and an outer conductor, most preferably, both conductors have a circular cross section and/or a cylindrical shape and which may be inserted into the test connector in an inward direction. The outer conductor has a circular shape for at least partially enclosing the outer conductor of the compatible coaxial connector in a radial direction. It further provides a groove for holding an approximately circular spring which is provided for radially contacting the outer conductor of the compatible coaxial connector and asserting an approximately radial contact force to said outer conductor.

Preferably, the contact spring is a finger gasket. Preferably, the contact spring has a plurality of individual contact fingers with a preferably small gap between the individual contact fingers. The contact fingers may have additional contact elements or contact points at their outer sides to improve contacting of the compatible coaxial connector. It is preferred, that the width of all or at least of most of the gaps is less than the width of the fingers, preferably equal or less than half and most preferably less than 1/3 than the width of the fingers. It is further preferred, if the width of all or at least of most of the fingers finger is less than 1mm and preferably less or equal than 0.5mm. Furthermore, the individual contact fingers preferably are part of a common base and therefore are held together by the common base. It is preferred, if the base is held by the test connector and the contact fingers are pressed radially against the outer conductor of the compatible coaxial connector. Preferably, the contact fingers extend by a bow from the base.

Preferably, at least one of the contact fingers comprises a first contact section for contacting the compatible coaxial connector in a radial direction. It further comprises a second contact section to contact a sidewall of the groove formed in the outer conductor. Most preferably, the second contact section is in capacitive contact with the sidewall of the groove, although a galvanic contact may also be useful, preferably at lower frequencies. Most preferably, the sidewall of the groove is oriented in outward direction (opposing the inward direction), there- fore facing in a direction towards the compatible connector. By the contact to the sidewall, an area forming a current loop by the current flowing from the outer conductor of the compatible connector is marked to the test connector is reduced, which further in-creases bandwidth of the connector.

Figure 10 shows an embodiment without the capacitive contact by the second contact section 223 to the sidewall 58 resulting in large current loop area 241

In a further preferred embodiment, the outer conductor of the test connector may comprise a spring holder being part of or forming the groove, which holds the contact spring. Preferably, the contact spring is soldered and/or welded to the spring holder. Most preferably, it is soldered and/or welded by its base to the spring holder. Solder may be applied radially outside of the base of the contact spring to the spring holder. For best intermodulation characteristics, there is only one metallurgical connection (the solder connection) between the contact spring and the spring holder. To provide a capacitive contact and to prevent any galvanic contact in an axial direction, an insulating disk may be provided between the bow of the contact spring and the spring holder. The insulating disk may comprise a suitable insulating material which may be ceramics or a plastic material which may be PTFE or Polyimide. Furthermore, it is preferred, if the insulating disc has a high dielectric constant to provide a high coupling capacity between the spring and the spring holder. It is preferred, if the spring holder has a thread interfacing with a thread at the outer conductor of the test connector. This allows the spring holder to be screwed, preferably in an axial direction of the con- nector, on the outer conductor.

In an alternate embodiment, the spring holder may be pressed, soldered or welded to the outer conductor of the test connector.

In a further embodiment, the spring holder may be a part of the outer conductor of the test connector providing a circular gap or groove for holding the contact spring. In this case, the contact spring must have a shape and a size such that when the compatible coaxial connector is inserted into the test connector, the axial force between the contact spring and the outer conductor of the test connector is sufficiently large to deform the contact spring, such that it further asserts a significant force to the outer conductor of the test connector to ensure proper contacting. This may be achieved by arc shaped fingers.

The embodiments shown herein have the advantage, that the contact spring can easily be mounted into the test connector. It is not necessary to solder or weld the contact spring into the test connector. The contact spring can withstand a large number of mating cycles without suffering from material fatigue or poor contacts.

Preferably, the base has a larger radius than the contact fingers with respect to the center axis. Therefore, preferably, the base is essentially radially enclosing the contact fingers. This results in a very compact size and short current paths between the outer conductors of the compatible coaxial connector and the test connector which furthermore results in a good impedance matching in a broad frequency range and therefore in a high return loss. It is further preferred, if the number of contact fingers is higher than 10, preferably higher than 20 and most preferably higher than 40 to achieve a low impedance broadband contact.

It is further preferred, if the outer conductor of the test connector has at least one contact section for providing a mechanical contact to, and therefore a mechanical alignment with the compatible coaxial connector. It is further preferred, if the spring holder provides at least such a contact section. Preferably, there is at least one radial contact section for providing a radial alignment of the compatible coaxial connector and the test connector. It is further preferred, if there is at least one axially oriented contact section for providing an axial alignment between the compatible coaxial connector and the test connector.

In a further embodiment, the test connector provides a connector guide for guiding the compatible coaxial connector towards the test connector when inserting the compatible coaxial connector into the test connector. It is further preferred, if the connector guide has a cone-shaped entrance side for simplifying inserting and alignment of the compatible coaxial connector.

Independently of the previously described embodiments, the center conductor may either be of a male or a female type.

It is preferred, if the contact spring comprises at least one of the following mate- rials: copper-beryllium, brass, steel.

It is further preferred, if the compatible coaxial connector is a 7/16 DIN connector, as specified in the German standard DIN 47223. Description of Drawings

In the following the invention will be described by way of example, without limitation of the general inventive concept, on examples of embodiment with reference to the drawings. Figure 1 shows a preferred embodiment of a test connector assembly.

Figure 2 shows a preferred embodiment of a test connector assembly with attached compatible coaxial connector.

Figure 3 shows a detail of the test connector.

Figure 4 shows a sectional view of a test connector with a mated compatible co- axial connector.

Figure 5 shows a side view of a section of a contact spring.

Figure 6 shows a top view of the contact spring.

Figure 7 shows a modified contact spring.

Figure 8 shows the contact spring in a mated state of the connectors in detail. Figure 9 is a simplified version of figure 8. Figure 10 shows details of the contact area. Figure 11 shows details of a modified contact area.

In Figure 1, a preferred embodiment of a test connector assembly is shown. A test connector 30 is connected to an internal connector 20 by means of a connecting line 25, having a center axis 29, and which is held by a mounting suspension 10, which may allow tilting of the connecting line and which further may allow a displacement in the direction of the center axis 29. There may furthermore a force be asserted into the direction of the test connector to simplify contacting of a compatible coaxial connector 100 as will be shown in the next figure. Preferably, the test connector 30 comprises an inner conductor 40 and an outer conductor 50. It is further preferred, if the test connector 30 comprises a connector guide 60 for guiding a compatible coaxial connector 100 when mating the connectors.

In Figure 2, a preferred embodiment of a test connector assembly is shown with a compatible coaxial connector 100 attached in an inward direction (from the bottom of the page to the top of the page or the left side of the drawing to the right side). The compatible coaxial connector 100 may either be connected to a cable or to a housing of a device to be tested. The compatible coaxial connector 100 preferably comprises an inner conductor 110 and an outer conductor 120. It is further preferred, if the compatible coaxial connector 100 has an outer hous- ing 130, which further preferably has an outer thread. The outer housing preferably encloses the outer conductor.

In Figure 3, a detail of the test connector 30 is shown in a sectional view. Aligned with the center axis 29, an inner conductor 40 is arranged. In this embodiment, the inner conductor 40 is of a male type, but it may also be of a female type. The specific type of the inner conductor is independent of the contacting of the outer conductor, as will be shown later. The inner conductor 40 may be held by a holding disk 41 which may be of a plastic or ceramic material. It centers the inner conductor 40 within the outer conductor 50. Furthermore, it is preferred, if the center conductor 40 has a slot 42 or a hex drive or any similar means for simplify- ing assembly of the center conductor to the test connector. The outer conductor 50 comprises a contact spring 55 for radially contacting the outer conductor of a compatible coaxial connector 100. The contact spring as shown in this preferred embodiment comprises a base 222 holding a plurality of contact fingers 56 with gaps 57 in-between the individual contact fingers. The contact fingers may have additional contact elements or contact points at their outer sides to improve contacting of the compatible coaxial connector 100. Preferably, there is a spring holder 51 which forms a groove, preferably together with the inner side 32, to hold the contact spring 55 at its position at the outer conductor 50. The contact spring 55 is preferably soldered and/or welded to the spring holder 51. The spring holder 51 may either be pressed, welded, soldered or attached by means of the thread 33 to the base 31 of the center conductor.

In an alternate embodiment, the spring holder 51 may be one part with the out- er conductor base 31. In this case, it forms a groove 45 for holding the contact spring 55. It is further preferred, if the outer conductor 50 has at least one mechanical contacting surface. Most preferably, there is at least one axially oriented mechanical contact section 53. There may be a further mechanical contact section 54 which is oriented radially. In Figure 4, a sectional view of a test connector 30 with a mated compatible coaxial connector 100 is shown. The center conductor 110 of the compatible coaxial connector 100 preferably has a center conductor contact element 111 which may be a cylindrical sleeve having slots to provide spring-elastic properties at its end and for contacting the center conductor 40 at a contact section 43 by its inner contact section 113. The center conductor 110 may enclose an inner space 112 which may be hollow.

The compatible coaxial connector's outer conductor 120 preferably has a hollow end section 121 which is contacted in a radial direction by the contact spring 55 in a contact area 122. Mechanical alignment of the compatible coaxial connector 100 to the test connector 30 is done by mechanical contact sections at the outer conductor of the test connector and of the compatible coaxial connector 100. For radial align- ment, an outer section 123 of the outer conductor of the compatible coaxial connector 100 may contact a radial mechanical contact section 54 of the outer conductor of the test connector. Axial alignment may be done by an axial contact section 133 of the compatible coaxial connector 100 contacting the axially me- chanical contact section 53 of the outer conductor of the test connector. Preferably, the axial contact section 133 is part of the housing 130. There may be a chamfer 134 at the edge of the axial contact section 133. Such independent radial and axial alignments ensure proper and reproducible alignment of the connectors. To simplify mating of the connectors, the outer side of the outer con- ductor 50 may have a chamfer 52. To provide an early alignment during mating of the connectors, a connector guide 60 at the test connector 30 preferably has a cone 61 with an interface section 65 to interface and/or guide the housing 130 and/or an outer thread 131 at the housing.

In Figure 5, a side view of a section of a preferred embodiment of a contact spring 55 is shown. The contact spring has a base 222 and a plurality of contact fingers 56, 221 extending thereof. Preferably, the contact fingers are arc-shaped and provide a first contact section 221 close to the end of the arc and a second contact section 223 between the base and the first contact section. The arc shape of the contact fingers allows smooth insertion and removal of a compati- ble coaxial connector 100 into and out of the test connector, as shown in Figure 4. Each of a plurality of the contact fingers acts as an individual spring element and provides a force to the outer conductor of the compatible coaxial connector 100, thus providing an electrical contact. Preferably, the arc has an opening averted to the compatible coaxial connector 100. In Figure 6, a top view of the contact spring 55 is shown in a straight, extended state. The base 222 holds a plurality of contact fingers 56 extending therefrom with gaps 57 in between. The base preferably has no gaps or slits. Preferably, the contact spring comprises at least one of the following materials: copper- beryllium, brass, steel.

In Figure 7, a modified contact spring 55 is shown in a straight, extended state. Here, the base 222 is sectioned, which increases flexibility and bendability of the spring.

In Figure 8, the contact spring 55 is shown in detail in a mated state of the connectors. As previously mentioned, the contact spring 55 is enclosed between the spring holder 51 and the base 31 of the outer conductor, forming a groove for the contact spring. The contact spring 55 is soldered and/or welded with its base 222 to the spring holder 51. Here, solder 59 is shown radially outside of the base 222 of the contact spring 55. For best intermodulation characteristics, there is only one metallurgical connection (the solder connection) between the contact spring 55 and the spring holder 51. To prevent any galvanic contact and to provide a capacitive contact in an axial direction, an insulating disk 230 may be pro- vided between the second contact section 223 of the contact spring and the sidewall 58 of the spring holder 51. If a galvanic contact is desired, this disc may be omitted. The first contact sections 221 are in contact with the outer conductor 120 of the compatible coaxial connector 100 and generate a highly conductive electrical path thereto. Due to the design of the contact spring 55, high con- tact forces can be generated towards the outer conductor base 31 of the test connector and towards the outer conductor 120 of the compatible coaxial connector 100, resulting in low passive intermodulation. Preferably, the base 222 of the contact spring 55 is at a larger radius than the contact fingers 221, 223. Therefore, the contact fingers are oriented inwards from the base. Figure 9 is a simplified version of figure 7, where some edge lines have been removed to clarify the individual components. Figure 10 is based on figure 9 and shows a further enlarged detail of the contact area. Here, the area 240 forming a current loop by the current flowing from the outer conductor 120 of the compatible connector is marked. It forms a parallel resonance circuit with the capacitance between the surfaces 54 and 123 togeth- er with the inductance of the current loop, limiting the bandwidth of the connectors. Due to the capacitive contact by the second contact section 223 to the sidewall 58, the area of this loop can be decreased significantly, which further increases bandwidth of the connector.

Figure 11 shows an embodiment without the capacitive contact by the second contact section 223 to the sidewall 58 resulting in large current loop area 241. A connector with such contacts has significantly less bandwidth than a connector according to figure 10.

List of reference numerals

10 mounting suspension

20 internal connector

25 connecting line

29 center axis

30 test connector

31 outer conductor base

32 inner side

33 thread

40 inner conductor

41 holding disk

42 slot

43 conductor contact section

45 groove

50 outer conductor

51 spring holder

52 chamfer

53 axial mechanical contact section

54 radial mechanical contact section

55 contact spring

56 contact fingers

57 ap

58 sidewall

59 solder

60 connector guide

61 cone

65 interface section

100 compatible coaxial connector

110 inner conductor center conductor contact element inner space

contact section

outer conductor of compatible connector cylindrical contact section

contact area

outer section

housing

outer thread

axial contact section

chamfer

first contact section

base

second contact section

insulating disk

small area of current loop

large area of current loop