The invention concerns the feeding of HF telecommunication antennas and in particular a feed bushing device for antennas.
Telecommunication systems usually include transmitters/receivers that have to be connected to antennas to radiate and/or to receive an electromagnetic signal.
The RF connection between the transmitter/receiver and the antenna is made by an RF feed line that may be either of balanced type (for example in the most general case a coaxial cable) or of balanced type (most often a balanced two-wire line).
Balanced two-wire lines have the advantage over unbalanced coaxial lines of having lower transmission losses per unit length and high characteristic impedances. Balanced two-wire lines have known and proven characteristics and properties in a gas, solid or hybrid medium the radio-frequency characteristics of which are very similar to those of air (relative dielectric and magnetic permitivity very close to 1), but nevertheless significantly modified by the presence of an environment near the line having a dielectric permitivity different from that of air, notably when that environment is moist or of a metallic nature.
In some configurations for feeding an HF antenna by a transmitter/receiver relatively far from the antenna the balanced two-wire line must be away from the ground to prevent modifications of its radio-frequency characteristics, which would lead to high losses through mismatching of the antenna with the transmitter or coupling with the ground.
In the
This type of overhead solution represented in
To alleviate the drawbacks of the prior art balanced two-wire antenna feeds, the invention proposes an HF feed bushing device designed to connect an HF transmitter/receiver to an antenna via an external medium by means of a balanced two-wire line, the balanced two-wire line being at least partially encapsulated in a central part of a closed conduit including a wall isolating the balanced two-wire line from the external medium, the wall separating the external medium from an internal medium in the closed conduit having dielectric and magnetic permittivity close to that of air.
The balanced two-wire line is held in the central part of the conduit by insulative material spreaders disposed along the two-wire line, the distance of the two-wire line away from the wall of the conduit and the shape of the spreaders being determined on the basis of parameters such as the maximum voltage and current that the two-wire line can withstand, the maximum allowed variation of the characteristic impedance of said two-wire line, the mechanical stresses induced by the required curvature.
In one embodiment the closed conduit has two ends and at each of the ends an insulative material cap for closing the conduit to isolate the internal medium from the external medium.
In another embodiment the conduit is a flexible and watertight material pipe of circular section to provide flexibility and isolation between the external medium and the internal medium.
In another embodiment the spreaders are held in position in the flexible pipe by flexible insulative material separators around the balanced two-wire line, a separator being disposed between two consecutive spreaders to absorb the stresses on the spreaders on curvature of the pipe.
In another embodiment the pipe includes a metal reinforcing armature in its wall.
In another embodiment the metal reinforcing armature is a metal wire wound helically along the wall of the pipe to preserve the flexibility properties of the bushing.
In another embodiment the wall of the pipe is metallized in order to prevent any external radio-frequency influence on the two-wire line.
The invention will be better understood with the aid of an embodiment of an antenna feed through-lead device of the invention described with reference to the appended drawings, in which:
a is a partial view of the feed bushing device of the invention,
b is a plan view of the feed bushing device from
a shows one of the ends of the feed bushing device from
b is a plan view of the end of the feed bushing device from
a is a partial view of the feed bushing device of the invention and
a is a partial view in longitudinal section between two planes P1, P2 of a feed bushing device of the invention. In this embodiment, the bushing device includes a pipe 40 of circular section about an axis of revolution XX′ (in a straight portion of the pipe) and a balanced two-wire line 42 (as represented in
The flexible material pipe 40 includes a separating wall 44 between a medium 46 external to the pipe and an interior medium 48 the dielectric and magnetic permitivity of which are close to that of air. This interior medium 48 is constituted for the most part of air in the present example but it may equally be constituted of any gas or solid or mixture thereof offering a dielectric and magnetic permitivity very close to that of air.
The two-wire line 42 is held in the central part of the pipe by insulative material spreaders 50 in the form of circular rings normal to the axis of the pipe, regularly distributed over all of the length of the pipe. The spreaders ensure a constant distance along the pipe between the two-wire line and the wall 44 of the pipe.
The physical dimensions of the spreaders (among others, the thickness of the spreaders) are chosen to comply with, on the one hand, mechanical constraints, by virtue of a choice between a maximum thickness to withstand the stresses of bending the feed bushing and a minimum thickness for the retention of the two-wire line at the center of the pipe and, on the other hand, the radio-frequency characteristics by virtue of a choice of a maximum thickness and a distribution of the spreaders along the pipe so as not to modify the properties of the two-wire line too significantly.
The shape of the spreaders is also defined on the basis of parameters such as the maximum voltage and current that the two-wire line can withstand, the breakdown voltage between the two-wire line and the wall of the pipe if it is of metal, or the nature of the exterior environment, the maximum allowed variation of the characteristic impedance of said two-wire line, the mechanical stresses induced by the required radius of curvature.
The spreaders 50 are held in place inside the pipe 40 by insulative material separators 54 around the two-wire line 42.
The separators 54 absorb the stresses of movement of the spreaders 50 when the pipe 40 is strongly curved. The separators 54 represented in
The wall 44 of the pipe 40 may be metallized in order to guarantee any influence on the two-wire line 42 of an external medium of a metallic or moist kind and to isolate the line at radio frequencies.
The watertightness of the feed bushing device is completed by closure of the pipe 40 at each of its two ends by an insulative closure cap, for example, in composite material of epoxy type that ensures good resistance to mechanical and environment stresses.
a shows one of the ends of the feed bushing device from
The closure cap 60 closes the ends of the pipe 40 in watertight fashion to ensure total separation of the interior medium 46 of the feed bushing device relative to the exterior medium 48. To this end, the cap is for example stuck to the end of the pipe and to the two-wire line where it passes through the opening 64 in the cap.
b is a plan view of the end of the feed bushing device from
In the usual conditions of use of the feed bushing device of the invention, for example in the case of use of the feed bushing device along a wall or simply on the ground, the crushing force exerted on the pipe remains low. In other cases of use, for example, if the feed bushing device must be buried or resist reduced pressure stresses caused by altitude, the pipe must have an increased resistance to crushing.
In this variant from
The feed bushing device from
The feed to the antenna 28 from the transmitter/receiver 22 includes a feed bushing device 70 of the invention having a part 72 buried in the ground 30 and two ends 74, 76 emerging from the ground 30. One of the ends of the two-wire line leaving the bushing device 70 is connected to a two-wire input 80 of the antenna 28 and the other end to a two-wire port 82 of the transmitter/receiver 22. In contrast to the prior art embodiment from
In this embodiment shown in
The feed bushing device of the invention has the following advantages:
Number | Date | Country | Kind |
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0906180 | Dec 2009 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2010/069956 | 12/16/2010 | WO | 00 | 11/2/2012 |