Patent Application
20180115105
The present invention relates to a transmission line, in particular of the rigid type and for a radiofrequency power application, according to the preamble of claim 1.
It is known in the art that a transmission line, in particular of the rigid type and for radiofrequency power applications, is so designed as to comprise a first conductor (also known as “outer conductor”) having a tubular shape, a second conductor (also known as “inner conductor”) concentrically and coaxially positioned inside said first conductor, and a dielectric positioned between the first conductor (outer conductor) and the second conductor (inner conductor).
In particular, the dielectric positioned between the first conductor and the second conductor may consist of air or gas.
In such a case, preference is given to air, e.g., as used in television broadcasting applications, for the purpose of allowing for fast on-site assembly of the rigid transmission line without requiring subsequent filling of the system with a specific gas.
In order to obtain a desired length of said transmission line, it is known in the art to couple together a plurality of sections of a rigid transmission line by means of a junction comprising a connector associated with at least one end of the transmission line.
In particular, the junction connector is so designed as to comprise a body adapted to be coupled to a terminal tract of the outer conductor, and comprises at least one connection element adapted to be inserted, at least partially, into a seat formed in one end of the inner conductor; in its turn, the connection element comprises a substantially tubular portion from which a plurality of elastic tabs extend.
In accordance with one implementation, the junction connector is so designed as to comprise a casing typically having a cylindrical (sleeve-like) shape, in particular said casing having an inside diameter that makes the ends thereof suitable for being coupled to one end of the outer conductor. In such an implementation, said casing is typically made of metallic materials.
Furthermore, the connector casing is associated with a body (also referred to as “spacer” or “rigid centralizer”) having a substantially discoid (flange-like) shape, which allows the connection element to be positioned coaxially within the casing and the inner connection element to be insulated from said casing. Said body or spacer is preferably made of non-conductive material, in particular plastic material (e.g., polytetrafluoroethylene, also known as “PTFE”, i.e., a polymer of tetrafluoroethylene commercially known as TEFLON® or ALGOFLON® or HOSTAFLON® or FLUON®).
According to another possible implementation, the junction connector may be so designed as to comprise only the substantially discoid (flange-like) body suitable for being coupled to a terminal tract of the outer conductor. From each one of the flat faces of the discoid body of the connector, intended to be coupled to a section of the rigid line, a distinct connection element extends which is adapted to be coupled to the corresponding end of the inner conductor of the rigid line, said connection element comprising a substantially tubular portion associated with a plurality of elastic tabs. In this case as well, the discoid connector allows the connection element to be positioned coaxially within the connector, and the inner conductor to be insulated from the outer conductor. In addition, the discoid body is preferably made of plastic material, e.g., polytetrafluoroethylene (also known as “PTFE”, i.e., a polymer of tetrafluoroethylene commercially known as TEFLON® or ALGOFLON® or HOSTAFLON® or FLUON®), and the two outer conductors of two transmission lines are coupled by contact to the discoid element or body.
It is therefore clear that the connectors known in the art, in addition to allowing the inner conductors of different sections to be joined together, also allow the inner conductor to be coaxially positioned inside said outer conductor and to be insulated from the outer conductor.
In particular, the connection element and the inner conductor are coupled to each other by inserting the connection element into the end of the inner conductor, this insertion being typically achieved through a substantially linear movement; during this movement, the elastic tabs of the connection element are forced to bend (so as to facilitate the insertion of said connection element into the end of the inner conductor) and then flex towards the inner surface of said inner conductor, thus establishing an optimal connection between the two components.
It is therefore apparent that said connection element is so designed as to ensure both elasticity, due to the non-continuous profile obtained by means of the plurality of elastic tabs, and adequate tightness, due to the fact that the diameter of the connection element is slightly smaller than that of the inner conductor.
According to the principles of physics on which signal or energy transmission over rigid lines is based, for each frequency to be used there is a maximum limit to the diameter of the conductors that can be used for making a transmission line. According to a known law of physics, in fact, as the frequency of a signal grows, its wavelength decreases. It is necessary that the wavelength value does not become too small in comparison with the difference in the radii of the two (inner and outer) conductors.
When a signal having a voltage V and a frequency f is applied to one end of the inner conductor, a current I is made to flow along said inner conductor. Said current I is surrounded by a magnetic field B which, as it reaches the outer conductor, induces therein an induced current opposite to the cause that generated it. If the difference between the diameters of the inner conductor and outer conductor is small, the current induced in the outer conductor will be offset by 180° relative to the current flowing along the inner conductor. Equal and opposite currents cancel each other out and produce no radiation. The above does not occur when such high frequencies are reached that reduce the ratio between the wavelength of the applied signal and the difference between the radii of the two conductors. In fact, some time must pass before the field B generated by the current in the central conductor arrives at the outer conductor and induces current therein. When such time becomes significant compared with the period of the applied signal, then the current induced in the outer conductor will no longer be offset by 180° relative to the current in the inner conductor, so that it will not be able to compensate for the effects thereof. Therefore, the wave will travel transversally as opposed to longitudinally, and different modes of propagation may be triggered. In a transmission line this will result, in practice, in strong attenuation of the transmitted signal.
As frequency grows, therefore, precise conductor sizes have been established which must not be exceeded.
It emerges from the above description that, in the solutions known in the art, for any given frequency there is a precise upper limit to the sizes of the inner and outer conductors. As a consequence, a limit also applies to the size of the connection element to be inserted into one end of said inner conductor. However, as said size becomes smaller, also the maximum power that can be carried through the junction decreases, due to problems of localized overheating caused by, among other things, the so-called “Joule effect”. Therefore, the design of the solutions currently known in the art necessarily implies a limitation of the transmissible power as a function of the frequency, which in turn limits the maximum size of the conductors. Said limitation of the transmissible power is not due to the fact that the ordinary sections of the transmission line cannot carry the power being considered, but to the necessity for preventing any potential junction overheating; exceeding this upper limit will lead to destruction of the junction itself or of an adjacent tract of the rigid transmission line.
In this frame, it is the main object of the present invention to provide a transmission line, in particular of the rigid type and for a radiofrequency power application, which is so designed as to allow overcoming the drawbacks of prior-art transmission lines.
In particular, it is one object of the present invention to provide a transmission line, in particular of the rigid type and for a radiofrequency power application, which is so designed as to increase the transmissible power while preventing the junction of said transmission line from suffering from potential overheating.
It is another object of the present invention to provide a transmission line, in particular of the rigid type and for a radiofrequency power application, which is so designed as to include a connection element that can ensure both elasticity and adequate tightness.
It is a further object of the present invention to provide a transmission line, in particular of the rigid type and for a radiofrequency power application, which is so conceived as to be able to effectively dissipate the generated heat, in particular the heat generated at a junction of said transmission line following an increase in transmitted power in excess of the maximum value considered to be admissible for transmission lines made in accordance with the prior art.
Said objects are achieved by the present invention through a transmission line, in particular of the rigid type and for a radiofrequency power application, incorporating the features set out in the appended claims, which are an integral part of the present description.
Further objects, features and advantages of the present invention will become apparent from the following detailed description and from the annexed drawings, which are supplied by way of non-limiting explanatory example, wherein:
The annexed
The transmission line 1 comprises, as is known in the art, a first conductor 10 (which can be defined as “outer conductor”) having a tubular shape, a second conductor 20 (which can be defined as “inner conductor”), concentrically and coaxially positioned inside said first conductor 10, and a dielectric 30 positioned between the first conductor 10 and the second conductor 20.
As is known, the first conductor 10 and the second conductor 20 are made of a material (e.g., copper or aluminium) having a very low resistivity value, whereas said dielectric 30 preferably consists of air; this provision allows for fast assembly of the rigid transmission line 1 in the place where the system is located, without incurring the typical risks deriving from the use of a dielectric consisting of gas.
It should be noted that in
The transmission line 1 further comprises a connector (designated as a whole by reference numeral 40 in the annexed drawings) equipped with a body 40A adapted to be coupled to a terminal tract 11 of the first conductor 10.
In the embodiment shown in the annexed drawings, the body 40A has a substantially discoid shape suitable for being coupled to a terminal tract 11 of the first conductor 10. In particular, as can be observed in
Preferably, the body 40A of the connector 40 is made of non-conductive material, in particular plastic material (e.g., polytetrafluoroethylene, also known as “PTFE”).
The connector 40 comprises at least one first connection element (designated as a whole by reference numeral 41 in the annexed drawings) adapted to be inserted, at least partially, into a seat 21A formed in one end 21 of the second conductor 20, said at least one first connection element 41 comprising a substantially tubular first portion 41A from which a plurality of first elastic tabs 41B extend.
The first tabs 41B allow to confer an adequate elasticity to the first connection element 41, since they allow said connection element 41 to be realized with a non-continuous profile.
In a preferred embodiment, the portion 41A and/or each first tab 41B of the first connection element 41 have straight tracts joined by one or more curved tracts, so as to have one or more narrower sections adapted to facilitate the insertion of the first connection element 41 into said seat 21A formed in one end 21 of the second conductor 20.
It must be pointed out that the second conductor 20 may consist of either a tubular element or a solid bar. In the former case (i.e., when the second conductor 20 consists of a tubular element), the seat 21A substantially corresponds to the final tract of the tubular element; in the latter case (i.e., when the second conductor 20 consists of a solid bar), the seat 21A is formed or milled in the end 21 of the second conductor 20.
Preferably, the connector 40 comprises a pair of first connection elements 41 extending in opposite directions from the body 40A of the connector 40 (in particular, said pair of first connection elements 41 extend in opposite directions from each one of the substantially flat faces of the body 40A having a substantially discoid shape, as shown in the annexed drawings), so that each one of the first connection elements 41 can fit into respective seats 21A formed in the ends 21 of two different second conductors 20 belonging to two different sections of a transmission line 1; it should be noted that said pair of first connection elements 41 may also be made as one piece, particularly by making a single tubular portion 41A from which the first tabs 41B extend in opposite directions.
In accordance with another embodiment (not shown in the annexed drawings), the connector 40 can be realized to include a casing (not shown in the annexed drawings) having a substantially cylindrical (sleeve-like) shape, in particular made of metallic material, wherein said casing encloses the body 40A (which can also be defined as spacer or rigid centralizer, since it performs such functions), which allows at least one first connection element 41 to be coaxially positioned and insulated inside the substantially cylindrical body and said at least one first connection element 41. It should be noted that also in this embodiment the body 40A is made of non-conductive material, in particular plastic material (e.g., polytetrafluoroethylene, also known as “PTFE”).
In this embodiment as well, the connector 40 comprises at least one first connection element 41 adapted to be inserted, at least partially, into the seat 21A formed in the end 21 of the second conductor 20, in particular said at least one first connection element 41 comprising a substantially tubular first portion 41A from which a plurality of first elastic tabs 41B extend.
Furthermore, in this embodiment the substantially cylindrical casing of the connector 40 is at least partially slipped over the outside of the terminal tract 11 of the tubular first conductor 10, the dimensions of said casing being slightly greater than the outer dimensions of the terminal tract 11 of said tubular first conductor 10.
In accordance with the present invention, the second conductor 20 comprises a second connection element 22 at least partially positioned in said seat 21A, said second connection element 22 being adapted to be coupled to the first connection element 41 by inserting it into a cavity 41C of said first connection element 41; in particular, the shape of said cavity 41C is substantially tubular.
Preferably, the second connection element 22 has a shape substantially corresponding to that of the first connection element 41 and smaller dimensions than said first connection element 41, so that it can be inserted into the cavity 41C (which is substantially tubular in shape) of the first connection element 41 with optimal contact between the two components.
In particular, the second connection element 22 comprises a substantially tubular tract 22A from which a plurality of second tabs 22B extend.
The second tabs 22B confer adequate elasticity on the second connection element 22, since they allow said second connection element 22 to be realized with a non-continuous profile.
Furthermore, also the tract 22 and/or each second tab 22B has/have straight tracts joined by one or more curved tracts, so that said second connection element 22A comprises one or more narrower sections that facilitate the insertion of the second connection element 22 (in particular, the second tabs 22B and the tract 22A) into said cavity 41C of the first connection element 41.
It should be noted that, in
Furthermore, as previously specified, the second conductor 20 may consist of either a tubular element or a solid bar. In the former case (second conductor 20 consisting of a tubular element), the second connection element 22 may consist of a separate element that can be at least partially inserted into the seat 21A of the second conductor 20, wherein said seat 21A substantially corresponds to the final tract of the tubular element. In the latter case (second conductor 20 consisting of a solid bar), the seat 21A and the second connection element 22 may be made either as described above or by appropriately machining the end 21 of the second conductor 20; in substance, when the second conductor 20 is a solid bar, the seat 21A and the second connection element 22 may also be substantially formed in the end 21 of the second conductor 20.
The special provision of the second connection element 22 according to the present invention allows realizing a transmission line 1, in particular of the rigid type and for a radiofrequency power application, in such a way as to allow overcoming the drawbacks of prior-art transmission lines.
In particular, the second connection element 22 allows realizing the transmission line 1 in such a way as to make it possible to increase the transmissible power as a function of frequency, and hence of the maximum sizes of the conductors, while at the same time preventing the junction of said transmission line from suffering from potential overheating, since said second connection element 22 ensures effective dissipation of the heat generated in the transmission line 1 following an increase in transmissible power, the dimensions being equal, in particular of the heat generated at a junction of said transmission line 1.
This is made possible by the fact that the provision of the second connection element 22 allows for a significant increase in the contact surface between the first connection element 41 and the second conductor 20; in fact, due to the provision of the second connection element 22, the first connection element 41 is in contact with the inner walls of the seat 21A and also with the outer walls of said second connection element 22 (in particular, with the outer walls of the second tabs 22B).
It is therefore clear that the provision of the second connection element 22 according to the present invention allows decreasing the size of the second conductor 20 and of the first connection element 41 (which must be inserted into the seat 21A) in order to increase the frequency and transmissible power, while at the same time avoiding the junction overheating problems that are known to be suffered by the prior art.
It follows that the provisions of the present invention turn out particularly useful and valuable for transmission lines 1 intended for high-power applications, e.g., in the radio-television broadcasting field.
In a preferred embodiment, the second connection element 22 comprises a thrust element (not shown in the annexed drawings, since said thrust element is preferably positioned within the space defined by the second tabs 22B of the second connection element 22) adapted to expand as the first connection element 41 and the second conductor 20 are coupled together; as a consequence, said thrust element allows exerting more pressure from within the second connection element 22, which will then press against the first connection element 41, which in turn will exert more pressure on the inner walls of the seat 21A.
For example, said thrust element may consist of an element having a substantially truncated-cone shape, which, in an idle condition, is partially inserted in the second connection element 22 with its major base facing towards the first connection element 41. When the second conductor 20 is abutted on and pressed against the first connection element 41 in order to effect the installation, the major base of the truncated cone abuts on the inside of the first connection element 41; as the pressure necessary for causing the second conductor 20 (inner conductor) to come in abutment is exerted, the truncated cone will translate in the second connection element 22, thereby exerting pressure from within and improving the contact between the second tabs 22B of the second connection element 22 and the first connection element 41.
In accordance with said first variant, the second conductor 20 has a variable profile along its longitudinal development, so as to constitute an impedance transformer.
In particular, said variable profile is obtained by means of a second conductor 20 comprising at least two portions (in
In accordance with this second variant, the transmission line 1 comprises at least one tract of a second dielectric 31 made of a different material than the dielectric 30 positioned between the first conductor 10 and the second conductor, in particular said second dielectric 31 being of the solid type and/or being made of a material having a higher thermal exchange coefficient than the dielectric 30 (which typically consists of air).
In such an embodiment, the tract of the second conductor 20 that is surrounded by the solid second dielectric 31 (said tract being, in the representation of
In a preferred embodiment, said solid second dielectric 31 is made of aluminium nitride (AlN); it is however clear that the material of said solid dielectric 31 may be different as well.
Furthermore, in the variant embodiment shown in
The features of the present invention, as well as the advantages thereof, are apparent from the above description.
The particular provision of the second connection element 22 according to the present invention allows realizing a transmission line 1, in particular of the rigid type and for a radiofrequency power application, in such a way as to allow overcoming the drawbacks of prior-art transmission lines.
The second connection element 22 allows realizing the transmission line 1 in such way as to make it possible to increase the transmissible power as a function of frequency, and hence of the maximum size usable for the second conductor 20 (inner conductor) and for the first conductor 10 (outer conductor), while at the same time preventing the junction of said transmission line from suffering from potential overheating, since said second connection element 22 ensures effective dissipation of the heat generated in the transmission line 1 following an increase in transmissible power as a function of frequency, in particular of the heat generated at a junction of said transmission line 1.
In fact, the provision of the second connection element 22 allows for a significant increase in the contact surface between the first connection element 41 and the second conductor 20, since the first connection element 41 remains in contact with the inner walls of the seat 21A and also with the outer walls of said second connection element 22 (in particular, with the outer walls of the second tabs 22B).
It is therefore clear that the provision of the second connection element 22 according to the present invention allows decreasing the cross-section of the considered transmission line 1, with the maximum transmissible power being equal, in that it is possible to reduce the sizes of the second conductor 20 and of the first connection element 41 (which must be inserted into the seat 21A), thus also reducing, according to the known laws of physics, the size of the first conductor 10 (outer conductor). Moreover, the dimensions being equal, the maximum transmissible power can be increased while avoiding the junction overheating problems suffered by the prior art.
The realization of the transmission line 1 including a tract of solid dielectric 31 made of a material having a higher thermal exchange coefficient than that of the dielectric 30 consisting of air significantly contributes to reducing the above-mentioned overheating problems, thereby also contributing to reducing the sizes of the second conductor 20 and of the first connection element 41, which reduced sizes allow for an increase in frequency and transmissible power.
In addition, the fact that the second conductor 20 is realized with a variable profile along its longitudinal development allows realizing an impedance transformer useful for allowing the insertion of a solid dielectric having a relative dielectric constant greater than 1 while still using a diameter of the second conductor 20 (inner conductor) that ensures adequate thermal exchange, adequate mechanical strength and a favourable behaviour towards the flowing currents. Said solid dielectric can remove a considerable amount of heat from the second conductor 20 and transfer said removed heat to the first conductor 10, which, unlike the second conductor 20, can be easily cooled by means of passive and/or active systems; all this contributes to increasing the power transmissible over the transmission line 1.
It is therefore clear that the provisions of the present invention turn out to be particularly useful and valuable for transmission lines 1 intended for high-power and high-frequency applications.
The transmission line described herein by way of example may be subject to many possible variations without departing from the novelty spirit of the inventive idea; it is also clear that in the practical implementation of the invention the illustrated details may have different shapes or be replaced with other technically equivalent elements.
It can therefore be easily understood that the present invention is not limited to the above-described transmission line, but may be subject to many modifications, improvements or replacements of equivalent parts and elements without departing from the inventive idea, as clearly specified in the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102016000107038 | Oct 2016 | IT | national |
