Horn antenna

• US 6,859,187 B2
• Filed: 03/17/2003
• Issued: 02/22/2005
• Est. Priority Date: 03/18/2002
• Status: Expired due to Term

• Current Assignee: Rosemount Tank Radar AB (Emerson Electric Company)
• Original Assignee: Saab Rosemount Tank Radar AB (Emerson Electric Company)
• Inventors: Ohlsson, Magnus
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): Dinh, Trinh Vo
• Application Number:
  US10/388,763
• Publication Number:
  US 20030179148A1
• Time in Patent Office: 708 Days
• Field of Search: H01/Q01.3/00, 343/772, 343/786, 343/787, 343/784, 343/785, 333/21.A
• US Class Current: 343/772
• CPC Class Codes: G01F 23/284 Electromagnetic waves
• CPC Class Codes: H01Q 1/225 used in level-measurement devices, e.g. for level gauge measurement
• CPC Class Codes: H01Q 13/02 Waveguide horns
• CPC Class Codes: H01Q 19/08 for modifying the radiation pattern of a radiating horn in which it is located corrugated horns H01Q13/0208; producing a circular polarisation H01Q13/0241
• CPC Class Codes: H01Q 19/09 wherein the primary active element is coated with or embedded in a dielectric or magnetic material protective material H01Q1/40, varying the electric or magnetic characteristics of refracting or diffracting devices H01Q3/44

Abstract

The present invention relate to a horn antenna at a radar level gauge for determination of a level of a surface of a medium stored in a tank and a method of making a horn antenna which is mechanically constituted such that the horn antenna will withstand the environment of the tank interior. The antenna comprises a first conductive housing (7) having a wave guide port (8), which is connectable to a wave guide, a first aperture (10), which is separated from the wave guide port (8) and a fist divergent section between the wave guide port (8) and the first aperture (10). A dielectric body (11) is arranged inside and essentially filling the first conductive housing (7), which body (11) displays a free end (12) in the area of the first aperture (10). The horn antenna is characterized in that around the first aperture (10) is arranged a locking device (13), which is arranged to fix the dielectric body (11) in the first housing (7) and that in the area of the locking device (13) is arranged at least one flexible sealing element (16) between the dielectric body (11) and the first cover (7).

Claims

1. A horn antenna intended for transmission and reception of microwaves when gauging a level of a surface of a medium stored in a tank by means of a microwave unit arranged at the roof of the tank, where the antenna comprises:

a first conductive housing (7) having a wave guide port (8), which is connectable to a wave guide,

a first aperture (10), which is separated from the wave guide port (8) and

a first divergent section between the wave guide port (8) and the first aperture (10);

a dielectric body (11) is, for maintaining a mechanically pressure resistant antenna design, arranged inside and essentially filling the first conductive housing (7), which body (11) displays a free end (12) in the area of the first aperture (10),

characterized in that

around the first aperture (10) is arranged a locking device (13),

the locking device (13) is arranged to fix the dielectric body (11) in the first housing (7), and

in the area of the locking device (13) is, for efficiently separating atmospheres inside and outside the tank, arranged at least one flexible pressure sealing element (16) between the dielectric body (11) and the first housing (7).

2. The horn antenna of claim 1, characterized in that, the sealing element (16) is arranged to absorb pressure between the dielectric body (11) and the first housing (7), such that it is arranged to be pressurized in case of displacement of the dielectric body (11) relative to the first housing (7) caused by a pressure inside the tank.

3. The horn antenna of claim 1, characterized in that, in the area of the wave guide port (8) there is arranged at least one additional sealing element (17) between the dielectric body (11) and the first housing (7).

4. The horn antenna of claim 1, characterized in that, at least one of the sealing elements (16, 17) includes at least one O-ring.

5. The horn antenna of claim 1, characterized in that, the free end (12) of the dielectric body is shaped as a lens for correction of a possible phase error of the microwaves, for obtaining an essentially plane wave front.

6. The horn antenna of claim 1, characterized in that, the dielectric body (11) is composed of two different materials having a surface interface to one another.

7. The horn antenna of claim 6, characterized in that, an outermost layer of the free end of the dielectric body is made from a fluoroplastic material while the remainder of the dielectric body (11) is made from a plastic material having better thermal properties, such as a PPS-plastic.

8. The horn antenna of claim 7, characterized in that, a thickness of the fluoroplastic material corresponds to a quarter of the wavelength for which the antenna is intended.

9. The horn antenna of claim 1, characterized in that, around the first aperture (10) there is arranged a second conductive housing (18, 20), which extends the first housing (7) towards a second aperture (19).

10. The horn antenna of claim 9, characterized in that, the second conductive housing (18) includes a second divergent portion between the first aperture (10) and the second aperture (19).

11. The horn antenna of claim 9, characterized in that, the second conductive housing (20) includes a portion having an essentially constant cross-section between the first aperture (10) and the second aperture (19).

12. Method for making a horn antenna intended for transmission and reception of microwaves when gauging a level of a surface of a medium stored in a tank by means of a microwave unit arranged at the roof of the tank, which method comprises:

making a first divergent conductive housing (7) having a wave guide port (8), which is connectable to a wave guide, a first aperture (10) which is separated from the wave guide port (8) and a divergent section between the wave guide port a (8) and the first aperture (10);

for maintaining a mechanically pressure resistant antenna design, fixing a dielectric body (11) inside and essentially filling the first housing (7) such that a free end (12) of the dielectric body (11) appears in the area of the 30 first aperture (10),

arranging a locking device (13) around the first aperture (10), whereby the dielectric body (11) is fixed in the first cover (7) and arranging, in the area of the locking device (13), a flexible pressure sealing (16) between the dielectric body (11) and the first housing (7), for efficiently separating atmospheres inside and outside the tank.

13. The method of claim 12, further comprising:

arranging, in the area of the wave guide port (8), an additional sealing element (17) between the dielectric body (11) and the first housing (7).

14. The method of claim 12, further comprising:

using as sealing element (16, 17) at least one O-ring.

15. The method of claim 12, further comprising:

shaping the free end (12) of the dielectric body as a lens for correction of a possible phase error of the microwaves for achieving an essentially plane wave front.

16. The method of claim 12, further comprising:

making the dielectric body (11) from two materials where an outermost layer of the free end of the dielectric body is made from a fluoroplastic material, while the remainder of the dielectric body (11) is made from a plastic material having better thermal properties, such as a PPS-plastic.

17. The method of claim 16, further comprising:

giving the fluoroplastic material layer a thickness corresponding to a quarter of the wavelength the antenna is intended for.

18. The method of claim 12, further comprising:

arranging around the first aperture (10) a second conductive housing (18, 20), which extends the first housing (7) towards a second aperture (19).

19. The method of claim 18, further comprising:

affixing a second conductive housing (18), which includes a second divergent section between the first aperture (10) and the second aperture (19).

20. The method of claim 18, further comprising:

affixing a second conductive housing (20), which includes a section having an essentially constant cross-section between the first aperture (10) and the second aperture (19).