This application claims the benefit of Italian Patent Application No. 102020000005983 filed on Mar. 20, 2020, which application is hereby incorporated herein by reference.
The present disclosure relates to the field of coaxial cables. In particular, the present disclosure relates to radiating coaxial cables and to processes for manufacturing a radiating coaxial cable.
As known, a radiating coaxial cable (also known as “leaky coaxial cable”) is a coaxial cable configured to emit and receive radio waves at a specific radiofrequency or in a specific radiofrequency range, so as to function as an extended antenna. Radiating coaxial cables are typically used to provide uniform radiofrequency coverage (for example, mobile coverage) to extended and/or narrow indoor environments, such as tunnels (metro, railway and road tunnels), buildings (e.g. office corridors, shopping centers or parking garages), mines or ships.
Known coaxial cables comprise an inner conductor surrounded by an insulating layer, a tubular conductive shield (a.k.a. “outer conductor”) and a jacket, which is typically the outermost cable layer. In radiating coaxial cables, a plurality of apertures (like slots or holes) is punched/milled through in the shield to allow the radio waves to leak into and out of the cable along its length.
The power radiated by a radiating coaxial cable has an angular dependence, namely a radiation pattern. The radiation pattern may be represented graphically as a plot of the radiated power as received by a test receiver, placed at a predefined distance from the cable (e.g. 4 meters), as a function of the receiver angular position. The radiation pattern typically shows one or more radiated power maxima called “lobes” separated by “nulls” at which the radiated power is substantially lower, even zero.
The shape of the radiation pattern (in particular, the number of lobes and their angular position) depends on the arrangement of the radiating apertures in the cable shield. For example, a single straight line of radiating apertures may be provided in the cable shield, so that the coaxial cable (a.k.a. “RFX cable”) has a single radiating side. In this case, the radiation pattern exhibits a single, large lobe centered at the angular position of the radiating apertures. As another example, two diametrically opposed straight lines of radiating apertures may be provided in the cable shield, so that the coaxial cable (a.k.a. “RF2X” cable”) has two opposite radiating sides. In this case, the radiation pattern exhibits two substantially diametrically opposed lobes.
U.S. Pat. No. 5,276,413 describes a radiating cable whose shield has a number of openings increasing along the cable. The increase in the number of openings along the cable nearly balances any decrease in the radiated power caused by attenuation of the cable. The radiated power then remains approximately constant along the cable.
In one embodiment a radiating coaxial cable comprises an inner conductor, an insulating layer surrounding and directly contacting the inner conductor, a continuous conductive shield surrounding said insulating layer and comprising a plurality of radiating apertures, and a jacket surrounding the conductive shield. At least one geometric property of the radiating apertures varies along a longitudinal direction of the cable and the cable has a radiation pattern with a shape longitudinally varying in a predefined way.
In one embodiment, a process for manufacturing a radiating coaxial cable includes surrounding an inner conductor with an insulating layer, the insulating layer directly contacting the inner conductor, providing a continuous conductive shield in the form of an electrically conductive metal foil comprising, from end to end, a plurality of radiating apertures, the metal foil longitudinally wrapping the insulating layer, and surrounding the conductive shield with a jacket. At least one geometric property of the plurality of radiating apertures varyies along the longitudinal direction of the cable and the cable having a radiation pattern with a shape longitudinally varying in a predefined way.
In one embodiment, a method for providing a varying radiofrequency coverage includes transmitting a radiofrequency signal by using a single radiating coaxial cable that comprises an inner conductor, an insulating layer, a continuous conductive shield, and a jacket. The insulating layer surrounds and directly contacts the inner conductor, the continuous conductive shield surrounds the insulating layer and comprises a plurality of radiating apertures, and the jacket surrounds the conductive shield. At least one geometric property of the plurality of radiating apertures varies along a longitudinal direction of the cable and the cable has, from end to end, a radiation pattern with a shape longitudinally varying in a predefined way.
The present disclosure will become fully clear after reading the following detailed description, given by way of example and not of limitation, with reference to the attached drawings wherein:
The Applicant has noticed that, while the cable of U.S. Pat. No. 5,276,413 aims at providing a radiofrequency coverage as uniform as possible, in some contexts a non-uniform radiofrequency coverage could be instead desirable.
For example, within a building (e.g. with offices and/or manufacturing facilities), the rooms to be covered may vary in size and arrangement. For examples, in some areas of the building all the rooms may be arranged on a single side of a corridor, while in other areas of the building (or even other parts of the same corridor) the rooms could be arranged on both sides. Large rooms such as auditorium, canteen or meeting rooms require a wider coverage. Besides, other areas of the building could require no coverage at all, e.g. areas that shall be radiation-free for safety reasons (for instance some rooms in a hospital) or passages where no coverage is needed. Some areas could be covered by a reduced field strength.
In principle, a non-uniform radiofrequency coverage could be provided by installing in the various building areas (e.g. along the corridors of the building) lengths of radiating coaxial cables of different types, such as RFX and RF2X. For instance, a length of RFX cable could be installed where the rooms to be covered are arranged on a single side of the corridor, a length of RF2X cable could be installed where the rooms are arranged on both sides of the corridor, while a length of RFX cable with higher radiated power (for example, with larger radiating apertures) could be installed where larger rooms such as auditorium or canteen are located. The various lengths of cables of different types should be reciprocally joined, so as to form a single coverage system which may be fed by a radiofrequency source at one its ends.
The Applicant has noticed that using lengths of radiating coaxial cables of different types makes the installation procedure complex and costly. Joining the various cable lengths of different types is a complex and long operation, which moreover induces additional loss (namely, the insertion loss of the cable joints) in the overall coverage system. Some cable types moreover are not mutually compatible, so they cannot be joined. In this case, they must be fed separately by respective radio frequency sources, thereby further increasing the cost of the coverage system.
The Applicant has then faced the difficulty of providing a radiating coaxial cable which allows reducing duration, complexity and cost of installation in contexts wherein a non-uniform radiofrequency coverage is required, such as for example a building wherein rooms to be covered vary in size and arrangement.
According to embodiments of the present disclosure, a radiating coaxial cable comprises a conductive shield that comprises, from end to end, a plurality of radiating apertures, wherein at least one geometric property of the radiating apertures is varied along the longitudinal direction of the cable so as to longitudinally vary the shape of the radiation pattern of the cable in a predefined way.
The expression “geometric property of the radiating apertures” comprises either a geometric property of the single radiating aperture, in particular shape, size, orientation or angular position, or a geometric property collectively describing the arrangement of radiating apertures in a set on the cable shield, in particular their reciprocal radial and/or longitudinal position, the number of lines according to which they are arranged and the shape of such line(s) (straight, wavy, helical and so on).
By “varying the shape of the radiation pattern of the cable” it is meant varying the number of lobes and/or the angular position(s) of the lobe(s) and/or the angular width of the lobe(s) and/or the amplitude of the lobe(s).
The radiating coaxial cable according to embodiments of the present disclosure allows providing a non-uniform radiofrequency coverage by installing a single cable. In the above exemplary scenario of a building with different areas having different coverage requirements, the geometric properties of the radiating apertures may be varied along the cable, so as to longitudinally vary the shape of the radiation pattern to meet the coverage requirements of the various areas crossed by the cable.
For example, in a first section of the cable shield the radiating apertures may be arranged in a single longitudinal straight line, resulting in a radiation pattern with a single lobe providing radiofrequency coverage in an area with e.g. rooms arranged on a single side of the corridor; the first section may be followed by a second section where the radiating apertures are arranged in two diametrically opposed longitudinal straight lines, resulting in a radiation pattern with two lobes providing radiofrequency coverage in an area with e.g. rooms arranged on both sides of the corridor; and so on.
Use of a single cable makes the installation procedure quicker and simpler, thereby allowing saving installation costs. Moreover, since no joints between different lengths of cable are required, the loss of the overall line is decreased.
Therefore, according to a first aspect, the present disclosure provides for a radiating coaxial cable comprising: an inner conductor; an insulating layer surrounding and directly contacting the inner conductor; a continuous conductive shield surrounding the insulating layer and comprising a plurality of radiating apertures; and a jacket surrounding the conductive shield, wherein at least one geometric property of the plurality of radiating apertures comprised in the continuous conductive shield varies along the longitudinal direction of the cable and the cable has a radiation pattern with a shape longitudinally varying in a predefined way.
According to an embodiment, the cable comprises at least two contiguous sections having different arrangements of the radiating apertures and radiation patterns with different shapes.
According to an embodiment, the arrangement of the radiating apertures in each one of the at least two contiguous sections comprises a single alignment, a double alignment or a multiple alignment of radiating apertures.
The transition between the arrangements of radiating apertures in two contiguous sections may be single-step or gradual.
According to an embodiment, the cable comprises at least one section wherein the at least one geometric property of the radiating apertures is varied in a non-monotonic way.
According to an embodiment, the cable also comprises at least one section with no radiating apertures.
According to a second aspect, the present disclosure relates to a process for manufacturing a radiating coaxial cable, said process comprising: providing an inner conductor; providing an insulating layer surrounding and directly contacting the inner conductor; providing a continuous conductive shield in form of an electrically conductive metal foil comprising, from end to end, a plurality of radiating apertures, the metal foil longitudinally wrapping the insulating layer; and providing a jacket surrounding the conductive shield, wherein at least one geometric property of the plurality of radiating apertures comprised in the continuous conductive shield is varied along the longitudinal direction of the cable and the cable has a radiation pattern with a shape longitudinally varying in a predefined way.
According to a third aspect, the present disclosure relates to a method for providing a varying radiofrequency coverage comprising transmitting a radiofrequency signal by using a single radiating coaxial cable comprising: an inner conductor; an insulating layer surrounding and directly contacting the inner conductor; a continuous conductive shield surrounding the insulating layer and comprising a plurality of radiating apertures; and a jacket surrounding the conductive shield, wherein at least one geometric property of the plurality of radiating apertures comprised in the continuous conductive shield varies along the longitudinal direction of the cable and the cable has a radiation pattern with a shape longitudinally varying in a predefined way.
The frequency of the radiofrequency signal transmitted by the cable of the present disclosure can vary from 20 kHz to 10 GHz, for example from 5 MHz to 4 GHz.
For the purpose of the present description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term “about”. Also, all ranges include any combination of the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.
The present disclosure, in at least one of the aforementioned aspects, can be implemented according to one or more of the following embodiments, optionally combined together.
For the purpose of the present description and of the appended claims, the words “a” or “an” should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise. This is done merely for convenience and to give a general sense of the disclosure.
The reference numbers used in all the Figures shall be the same for equivalent cables and cable portions.
The cable 10 comprises an inner conductor 2 surrounded by an insulating layer 3, a tubular conductive shield 4 and a jacket 5. The jacket 5 may be the outermost layer of the cable 10. The cable 10 may also comprise other layers (e.g. a fire barrier or wrapping tape interposed between conductive shield 4 and jacket 5 and/or interposed between insulating layer 3 and conductive shield 4), which are not shown in the Figures and will not be described herein below.
The inner conductor 2 may be single core or multicore, hollow or solid. In case of hollow conductor/s, it/they can be in form of a corrugated welded tube. The inner conductor 2 is made of an electrically conductive metal such as copper, aluminum or composite thereof. The inner conductor 2 can have an outer diameter comprised between 1 mm and 25 mm.
The insulating layer 3 can be made of polyethylene, optionally foamed, or other suitable electrically insulating material. The insulating layer 3 can have an outer diameter comprised between 5 mm and 55 mm and a thickness comprised between 1 mm and 20 mm.
The tubular conductive shield 4 is made of an electrically conductive metal such as copper, aluminum or composite thereof. The shield 4 may be either a smooth or corrugated metal layer. The shield metal layer may be in form of a metal foil longitudinally wrapped around the insulating layer 3 and either welded or with glued lapping rims. The conductive shield 4 can have an outer diameter comprised between 5 mm and 60 mm and a thickness comprised between 0.03 mm and 4 mm (including corrugations, if present).
The jacket 5 is made of a polymeric material, such as polyethylene. Optionally, the jacket 5 may have flame retardant properties. For example, the jacket 5 may be made of a halogen free flame retardant polymeric material, either thermoplastic or crosslinked.
The conductive shield 4 is provided with a plurality of radiating apertures (not shown in
The conductive shield 4 may be obtained by a single smooth metal foil, which is longitudinally wrapped (and optionally overlapped) about the insulating layer 3. The radiating apertures may be punched (or milled) through the smooth metal foil before it is wrapped about the insulating layer 3.
In an embodiment, at least one geometric property of the radiating apertures is varied along the longitudinal direction of the cable 10, so as to longitudinally vary the shape of the radiation pattern of the cable 10 in a predefined way. In particular, one or more of the following geometric properties may be varied: a geometric property of the single radiating aperture, including its shape, size, orientation or angular position; and/or a geometric property collectively describing the arrangement in a set of radiating apertures on the conductive shield 4, in particular their reciprocal radial and/or longitudinal position, the number of alignments according to which they are arranged and the shape of such alignment(s) (straight, wavy, helical and so on).
As it will be described in detail herein below, indeed, such geometrical properties of the radiating apertures determine the shape of the radiation pattern of the cable 10.
As depicted in
As depicted in
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As depicted in
The arrangements of
In the conductive shield 4 of the cable 10, for example, the variation of the geometric properties of the radiating apertures in the longitudinal direction of the cable 10 may be implemented as a transition from one of the arrangements A1-A6 shown in
Several transitions may be provided along a single cable 10, so that its conductive shield 4 is virtually divided into a number of contiguous sections (e.g. sections 4A, 4B, 4C in
The transition between the arrangements of two consecutive sections 4A-4B or 4B-4C may be either single-step or gradual.
For example, transition between the arrangement A1 (single straight line of radiating apertures) to the arrangement A2 (two diametrically opposed straight lines of radiating apertures) or vice versa may be single-step. As another example, transition from the arrangement A2 (two diametrically opposed straight lines of radiating apertures with the same shape and size) to the arrangement of A3 (two diametrically opposed straight lines of radiating apertures with the same shape but different sizes) may be implemented by gradually increasing the size of the radiating apertures in the first line 41 from their smaller size in the arrangement A2 to their larger size in the arrangement of A3.
If all the geometric properties of the radiating apertures are kept constant in the longitudinal direction of the cable 10, the radiated power slightly decreases along the cable 10, due to attenuation of the cable 10. Instead, by varying a geometric property of the radiating apertures (such as their size or their reciprocal distance) along the longitudinal direction of the cable 10, the radiation pattern still exhibits a single lobe, but its amplitude—namely, the radiated power—may be varied longitudinally in a purported way.
In the arrangement A1′ shown in
The resulting variation of the radiation pattern, in particular of the radiated power, in the longitudinal direction of the cable 10 is depicted in
Similar non-monotonic variations of a geometric property of the radiating apertures may be applied also to other arrangements of radiating apertures, for example any of the arrangements A2-A6 shown in
Hence, by suitably varying at least one of the geometrical properties of the radiating apertures in the longitudinal direction of the cable 10, the shape of the radiation pattern of the cable 10 may be longitudinally varied from end to end according to the radiofrequency coverage needs. This way, the cable 10 may be used to provide a non-uniform radiofrequency coverage, e.g. in contexts (e.g. a building) wherein different areas have different coverage requirements are present.
The first building B1 is a single floor building and has a first area AR1 with rooms arranged on both sides of a corridor, a second area AR2 with rooms arranged on a single side of the corridor and a third area AR3 with rooms on one side of the corridor and a larger room (e.g. a canteen) of the other side of the corridor. A fourth area AR4 corresponds to a cable passage between the two buildings. The second building B2 is instead a double floor building with a single area AR5 with rooms arranged on both sides of the corridor.
In order to provide a radiofrequency coverage to buildings B1 and B2, a single radiating coaxial cable according to the present disclosure may be used, whose conductive shield has a section with radiating aperture arrangement designed for each area. In particular, the conductive shield of the cable may have a first section S1 for the area AR1, whose radiating apertures are arranged according to the arrangement A2 shown in
The first section S1 may be followed by a second section S2 for installation in area AR2, whose radiating apertures are arranged according to the arrangement A1 shown in
The second section S2 may be followed by a third section S3 for installation in the area AR3, whose radiating apertures are arranged according to the arrangement A3 shown in
The third section S3 may be followed by a fourth section S4 with no radiating apertures, for installation in the cable passage of area AR4.
The fourth section S4 may be then followed by a fifth section S5 for installation in the area AR5, whose radiating apertures are arranged according to the arrangement A6 shown in
Use of a single cable 10 to provide radiofrequency coverage to the various areas of the buildings B1, B2 makes the installation procedure quicker and simpler, thereby allowing saving installation costs. Moreover, since no joints between different lengths of cable are required, the loss of the overall line is decreased.
Number | Date | Country | Kind |
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102020000005983 | Mar 2020 | IT | national |