Transition between a central contact of a coaxial component and a transmission line, in particular a radio-frequency transmission line

Abstract

An improved transition between a central contact of a coaxial component and a transmission line, such as a radio-frequency transmission line, is provided. The transition may be between a central contact of a coaxial component and a transmission line of a circuit such as a radio-frequency circuit. The central contact has a cylindrical front portion and, extending its front portion, a rear portion that makes contact with the transmission line and that is fastened thereto by a solder joint. The rear portion has at least one gap, defining a volume forming a reserve for the solder of the solder joint.

Claims

1. A transition between a central contact of a coaxial component and a transmission line of a circuit, the central contact comprising: a cylindrical front portion and, extending its front portion, a rear portion that makes contact with the transmission line and that is fastened thereto by a solder joint, the rear portion having at least one gap, defining a volume forming a reserve for the solder of the solder joint, configured to absorb excess solder.

2. The transition as claimed in claim 1, wherein the rear portion incorporating the gap is flat, and bounded by two plane faces.

3. The transition as claimed in claim 2, wherein the rear portion is a right parallelepiped or a shape of trapezoidal cross section.

4. The transition as claimed in claim 2, wherein the height between the two plane faces is between 0.1 and 0.3 mm.

5. The transition as claimed in claim 1, wherein the gap is open height wise.

6. The transition as claimed in claim 5, wherein the gap further opens onto at least one free end of the rear portion of the central contact.

7. The transition as claimed in claim 5, wherein the open gap is at least partially cylindrical or parallelepipedal in shape.

8. The transition as claimed in claim 1, wherein cylindrical front portion of the central contact is away from the circuit.

9. The transition as claimed in claim 8, wherein the distance between the cylindrical portion of the central contact and the facing edge of the circuit is between 0.1 and 0.8 mm.

10. The transition as claimed in claim 1, wherein the circuit is a suspended-microstrip and has a dielectric substrate a major face of which has the transmission line, which takes the form of a microstrip, and conductive ground lines intended to be soldered to a part of the coaxial component, so as to suspend the circuit in a ground conductor formed by said part.

11. The transition as claimed in claim 1, wherein the circuit is of coplanar type and has a dielectric substrate, a major face of which has the transmission line, which takes the form of a strip, inserted into a coplanar ground plane at a distance from the strip.

12. The transition as claimed in claim 1, wherein said transition is configured to operate from DC to 100 GHz, DC being the acronym of direct current.

13. A passive or active electronic device comprising: at least one transition as claimed in claim 1.

14. The passive electronic device as claimed in claim 13, forming a coaxial component selected from an attenuator, a divider, a combiner, a coupler, and a load.

15. The electronic device as claimed in claim 14 comprising: a cartridge that forms part of the coaxial component and that is bounded by a sidewall comprising at least one electrically conductive region within which the circuit is fastened, at least one of the conductive ground lines being connected to said electrically conductive region by at least one electrical connection ensured by a solder joint, said sidewall being passed through by a through-hole that extends right through the thickness of said sidewall and that provides direct access to the electrical connection allowing inspection of said electrical connection therein.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Other advantages and features of the invention will become more clearly apparent on reading the detailed description of examples of implementation of the invention, given by way of non-limiting illustration with reference to the following figures.

[0055] FIG. 1 shows a partial longitudinal cross-sectional view in perspective of one portion of a coaxial load with a transition between a central contact and an RF transmission line, according to the prior art.

[0056] FIG. 1A is a partial longitudinal cross-sectional view of FIG. 1.

[0057] FIGS. 2, 2A and 2B are perspective, longitudinal cross-sectional and rear views of a transition according to the prior art with a first solder joint.

[0058] FIGS. 3, 3A and 3B are perspective, longitudinal cross-sectional and rear views of a transition according to the prior art with a second solder joint different from the first solder joint, resulting from imperfect control of the solder joint.

[0059] FIGS. 4A and 4B are partial longitudinal cross-sectional views of a portion of a coaxial attenuator with a transition between a central contact and an RF transmission line, according to the prior art, showing two different configurations of the relative position between the components, resulting from imperfect control of the position of the rear portion of the central contact in the circuit.

[0060] FIG. 5 is a partial perspective view of one portion of a coaxial attenuator with two transitions between a central contact and RF transmission line, according to the invention.

[0061] FIG. 5A is a detail of FIG. 5.

[0062] FIG. 6 is analogous to FIG. 5 but in addition shows, seen in longitudinal cross section, the cartridge and spacers arranged coaxially around the transitions according to the invention.

[0063] FIG. 7 is a longitudinal cross-sectional view of a coaxial attenuator in its entirety with two transitions as shown in FIGS. 5 and 6.

[0064] FIGS. 8A and 8B are partial perspective views of a transition according to the invention.

[0065] FIG. 9 is a partial perspective view illustrating the contact edge between the rear portion of a central contact devoid of gap and a transmission line for production of a soldered transition.

[0066] FIG. 10 is a partial perspective view illustrating the contact edge between the flat rear portion of a central contact with an open gap and a transmission line for production of a soldered transition according to the invention.

[0067] FIG. 11 illustrates a partial longitudinal cross-sectional view of one portion of a coaxial attenuator with a transition according to the invention, showing a configuration of the relative position between the components.

[0068] FIG. 12 illustrates, in curve form, a simulation of a standing wave ratio (SWR) as a function of frequency, such as obtained with a transition according to the prior art and according to the invention.

[0069] FIGS. 13, 14 and 15 illustrate, in partial perspective, a transition according to the invention with various variants of embodiment of the open gap in the rear portion of a central contact.

[0070] FIG. 16 is a transverse cross-sectional view of a coplanar line according to a first variant of the circuit according to the invention.

[0071] FIG. 17 is a transverse cross-sectional view of a suspended microstrip line, according to a second variant of the circuit according to the invention.

[0072] FIG. 18 illustrates in perspective one advantageous variant of embodiment of a cartridge of a coaxial attenuator with at least one transition according to the invention.

DETAILED DESCRIPTION

[0073] Throughout the present patent application, the terms front and rear are to be understood with respect to a coaxial component employing at least one transition between a central contact and a transmission line of a circuit according to the invention. Thus, the front portion of a central contact is the portion intended to be coupled with another central contact.

[0074] For the sake of clarity, the same reference number has been used for the same element of a transition according to the prior art and of a transition according to the invention.

[0075] FIGS. 1 to 4B have already been described in detail in the preamble. They will therefore not be commented on below.

[0076] FIGS. 5 and 5A show one portion of a coaxial RF attenuator with two transitions according to the invention.

[0077] Each transition 1 between a central contact 2 taking the form of a cylindrical pin in its front portion and a suspended microstrip line 30 of an RF circuit 3 comprises a solder joint B.

[0078] More precisely, according to the invention, the central contact 2 comprises a flat rear portion 21, which takes the form of a right parallelepiped, and which is soldered by means of the solder joint B to the line 30, which takes the form of a suspended microstrip. The edges of the flat portion 21 may be cylindrical.

[0079] The flat portion 21 is positioned directly on the RF line, in order to make the electrical contact, and connection of the contact to the line 30 is completed by the solder joint B.

[0080] The circuit 3 is of suspended micro-strip type: it thus comprises a dielectric substrate 32 one major face of which bears both the transmission line 30 and two conductive ground lines 31 that extend, peripherally, each along one longitudinal edge of the substrate 32.

[0081] The method for producing a transition 1 according to the invention consists in the following steps: [0082] i/ depositing some solder B on the transmission line 30 at the edge of the circuit 3, [0083] ii/ placing the central contact 2 with its flat rear portion 21 on the solder B at the edge of the circuit 3, [0084] iii/ baking in an oven to produce the solder joint and thus form the transition 1.

[0085] Next, as shown in FIG. 6, these components connected by the transition 1 thus formed are secured to a component, called the cartridge 4, for example by means of another solder joint to the conductive lines 31 on the periphery of the dielectric carrier 32 of the circuit 3. These ground lines 31 are intended to be soldered to a cartridge 4 of the coaxial attenuator, so as to suspend the circuit 3 in a ground conductor formed by the cartridge 4.

[0086] The attenuator moreover comprises another central contact taking the form of a male socket 5 at its free end, in which the pin 2 of one of the two central contacts 2 is connected, and a spacer 6 around at least one segment of the central contact 2 and of the socket 5.

[0087] The pin 2 of the other of the two central contacts is connected to a female socket 50 at its free end, a spacer 6 also surrounding at least one segment of the pin 2 and of the socket 50.

[0088] Such as illustrated in FIG. 7, the coaxial attenuator 10 further comprises two insulators 11. One of the insulators 11 is interposed between the pin 5 and a ground body 12 that is aligned with a first metal fastening body 13. The other of the insulators 11 is interposed between the socket 50 and a second metal fastening body 14.

[0089] Preferably, the rear portion 21 of the central contact 2 has an open gap 22 that passes right through this rear portion 21.

[0090] In the example illustrated in FIGS. 8A and 8B, this open gap 22 further opens onto the free end of the rear portion 21 and takes the form of a right parallelepipedal groove.

[0091] FIGS. 8A and 8B illustrate one of the advantages of a transition 1 according to the invention.

[0092] As may be seen, the fact of having a flat shape 21 limits the rise of the solder joint B along the height of this rear portion 21 of the central contact. The existence of a sharp edge at the intersection 210 of the upper flat face and of the free edge stops propagation of the solder over the height of the rear portion of the central contact. Indeed, the solder joint B will generally be limited to the height H of the flat, which is preferably about 0.1 to 0.3 mm, and more preferably about 0.13 to 0.18 mm. Variations in the height of the solder joint B are limited. Thus, better control of the shape of the meniscus of the solder joint B is obtained than in the case of a hemicylindrical rear portion with a flat 20 as shown in FIGS. 2 to 3B. This reduces variations in RF performance from one transition 1 to another. In other words, by virtue of the flat portion 21 of the central contact 2, reproducibility is obtained in RF performance from one coaxial attenuator 10 to another when they are produced using the same method.

[0093] The open gap 22 further makes it possible to provide a volume that serves as a reserve RB for the solder. This reserve may therefore be filled to a greater or lesser extent when the central contact 2 is placed on the solder. The level to which this reserve is filled has no effect on the RF performance of the coaxial attenuator 10. Indeed, this reserve RB, by absorbing excess solder B to a greater or lesser extent, makes it possible to greatly limit the impact of the amount of solder on the performance of the attenuator 10.

[0094] Moreover, the flat portion 21 makes it possible to obtain a good mechanical strength. The value of this strength is proportional to the length of the peripheral edges A of contact between this portion 21 and the transmission line 30, as shown in FIG. 9.

[0095] As shown in FIG. 10, the open groove 22 allows the length of contact A to be increased and therefore the mechanical strength of the central contact 2 to the circuit 3 to be increased.

[0096] Another advantage obtained by a transition 1 according to the invention is illustrated in FIG. 11. The flat portion 21 of the central contact 2 extends beyond the circuit 3, this making it possible to guarantee separation, or in other words an offset D, of the cylindrical portion 23 from the central contact 2 of the circuit 3. The offset is induced by a position of the central contact 2 relative to the edge of the circuit 3, the distance D of which may vary. Preferably, the offset between the circuit edge and the cylindrical contact portion 23 is between 0.1 and 0.8 mm, and preferably between 0.35 and 0.45 mm.

[0097] This offset thus makes it possible to make the transition 1 less sensitive to defects in the position both of the central contact 2 relative to the edge of the circuit 3 and of the sub-assembly consisting of the circuit 3 and of the central contact 2 secured by the transition 1 relative to the cartridge 4 of the attenuator 10. It also makes it possible to dispense with levels of finishing of the edges of the circuit 3.

[0098] The variation in electrical impedance in the zone Z at the free edge of the circuit 3 is therefore not influenced by the relative position of the central contact with respect to the edge of the circuit 3, as symbolized by the encircled region in FIG. 11. This makes it possible to decrease the influence of the position of the central contact 2 on the RF performance of the attenuator 10.

[0099] The inventors have simulated the standing wave ratio (SWR) as a function of frequency, for a coaxial attenuator 10 incorporating two transitions 1 according to the invention, in comparison with a coaxial attenuator incorporating two transitions according to the prior art. The result of this simulation is shown in FIG. 12.

[0100] FIG. 12 shows two curves C1 and C2. Curve C1 shows the standing wave ratio for a coaxial attenuator comprising two transitions according to the prior art, namely, for example, with a central contact with a semi-cylindrical flat-comprising rear portion. Curve C2 shows the standing wave ratio for a coaxial attenuator comprising two transitions according to the invention. Curve C2 shows an improvement in the RF performance of the attenuator, over the frequency range DC-70 GHz, since, for a given frequency, the standing wave ratio of C2 is lower than the standing wave ratio of C1 and approaches the value 1.

[0101] Various variants of the form of the open gap have been illustrated in FIGS. 13 to 15, which show respectively: [0102] the free end 24 of a T-shaped rear portion 21 defining two open grooves on either side, each of substantially parallelepipedal shape, [0103] an open groove 25 taking the form of a hollow cylinder within the rear portion 21, [0104] an open groove 26 taking the form of a hollow cylinder opening onto the transmission line 30 via an extension of right-parallelepipedal shape.

[0105] The coaxial attenuator 10 such as described above employs a circuit 3 of suspended-microstrip type.

[0106] Other circuit variants may be employed within the scope of the invention.

[0107] FIG. 16 shows a circuit 3 of coplanar type in which a transition 1 according to the invention may be produced. This circuit 3 thus comprises a dielectric substrate 32 a major face of which comprises the transmission line 30, which takes the form of a strip, inserted into a coplanar ground plane 34 at a distance S from the strip. The other major face opposite that of the transmission line 30 comprises a ground plane 33.

[0108] FIG. 17 shows a circuit 3 of suspended-microstrip type in which a transition 1 according to the invention may be produced. Specifically, the circuit 3 comprises a dielectric substrate 32 a major face of which comprises the transmission line 30, which takes the form of a strip, and which is inserted between two ground planes 33, 35.

[0109] FIG. 18 shows one advantageous variant of embodiment of a cartridge 4 that incorporates at least one transition 1 according to the invention within it. Here, at least one side wall 40 comprises a through-hole 41 that extends right through the thickness of the side wall 40 and that provides direct access to an electrical connection produced by soldering between one of the ground lines 31 of the circuit 3 of the transition and an electrically conductive region 42 of the side wall. This direct access thus makes it possible to make or inspect said electrical connection.

[0110] Other variants and improvements may be provided without however departing from the scope of the invention.

[0111] Although, in the illustrated examples, the rear portion 21 of the central contact 2 is a right parallelepiped, other shapes with parallel plane faces, one of which makes contact with the transmission line, may be envisioned.

[0112] Open gaps of shapes other than those illustrated may be envisioned.