Radar level gauge system with reduced antenna reflection

• US 8,970,424 B2
• Filed: 10/24/2012
• Issued: 03/03/2015
• Est. Priority Date: 10/24/2012
• Status: Active Grant

• Current Assignee: Rosemount Tank Radar AB (Emerson Electric Company)
• Original Assignee: Rosemount Tank Radar AB (Emerson Electric Company)
• Inventors: Edvardsson, Olov
• Primary Examiner(s): GREGORY, BERNARR E
• Application Number:
  US13/659,021
• Publication Number:
  US 20140111371A1
• Time in Patent Office: 860 Days
• Field of Search: 342/118, 342/124, 342/175, 342/188, 342361-366, 342/82, 342/89, 342/159, 343772-786, 343/700.R, 343/756, 732/90.R, 732/90.V, 324/600, 324/629, 324/637, 324/638
• US Class Current: 342/124
• CPC Class Codes: G01F 23/284 Electromagnetic waves
• CPC Class Codes: G01S 13/88 Radar or analogous systems specially adapted for specific applications electromagnetic prospecting or detecting of objects, e.g. near-field detection, G01V3/00
• CPC Class Codes: G01S 7/026 involving the transmission of elliptically or circularly polarised waves
• CPC Class Codes: G01S 7/038 Feedthrough nulling circuits
• 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

Abstract

A radar level gauge system for determining a filling level in a tank. The radar level gauge system comprises a transceiver, a horn antenna having a first opening connected to the transceiver and a second opening facing a surface of the product in the tank, and processing circuitry connected to the transceiver for determining the filling level based on an electromagnetic surface reflection signal. The horn antenna is configured in such a way that an electrical distance from the first opening to the second opening, along a path defined by an intersection between a wall of the horn antenna and a half-plane starting from and extending in parallel with a cone axis of the horn antenna, is different for different orientations of the half-plane with respect to the cone axis. Hereby, disturbance from an antenna reflection signal can be reduced, which provides for improved measurement of high filling levels.

Claims

1. A radar level gauge system for determining a filling level of a product in a tank, said radar level gauge system comprising:

a transceiver configured to generate and transmit electromagnetic signals having a first polarization and to receive electromagnetic signals having a second polarization different from the first polarization;

a horn antenna for directing an electromagnetic transmit signal transmitted by said transceiver towards said surface of the product, and for returning back to said transceiver an electromagnetic surface reflection signal resulting from reflection of said electromagnetic transmit signal at said surface; and

processing circuitry connected to said transceiver for determining said filling level based on said electromagnetic surface reflection signal,

wherein said horn antenna comprises;

a first opening coupled to said transceiver;

a second opening, larger than said first opening, directed towards said surface of said product in the tank; and

a conductive horn antenna wall connecting said first opening and said second opening to form a horn structure having a central longitudinal axis,

wherein said conductive horn antenna wall exhibits;

a first electrical distance from said first opening to said second opening, along a first path defined by an intersection between said conductive horn antenna wall and a half-plane extending from said central longitudinal axis at a first rotational orientation in respect of said central longitudinal axis; and

a second electrical distance from said first opening to said second opening, along a second path defined by an intersection between said conductive horn antenna wall and a half-plane extending from said central longitudinal axis at a second rotational orientation in respect of said central longitudinal axis, said second electrical distance being different from said first electrical distance, and

wherein a difference between said first electrical distance and said second electrical distance is such that an antenna reflection signal resulting from reflection of said electromagnetic transmit signal by said horn antenna has a polarization being different from said second polarization.

2. The radar level gauge system according to claim 1, wherein said difference between said first electrical distance and said second electrical distance is such that said antenna reflection signal has said first polarization.

3. The radar level gauge system according to claim 1, wherein said first polarization and said second polarization are orthogonal polarizations.

4. The radar level gauge system according to claim 3, wherein said first polarization is a first circular polarization and said second polarization is a second circular polarization.

5. The radar level gauge system according to claim 1, wherein said conductive horn antenna wall further exhibits:

said first electrical distance from said first opening to said second opening, along a third path defined by an intersection between said conductive horn antenna wall and a half-plane extending from said central longitudinal axis, said third path being located opposite said first path with respect to said central longitudinal axis; and

said second electrical distance from said first opening to said second opening, along a fourth path defined by an intersection between said conductive horn antenna wall and a half-plane extending from said central longitudinal axis, said fourth path being located opposite said second path with respect to said central longitudinal axis.

6. The radar level gauge system according to claim 1, wherein said electrical distance as a function of said rotational orientation of said half-plane with respect to said central longitudinal axis exhibits:

a first maximum and a second maximum located opposite each other with respect to said central longitudinal axis; and

a first minimum and a second minimum located opposite each other with respect to said central longitudinal axis.

7. The radar level gauge system according to claim 6, wherein said first minimum is located half-way between said first maximum and said second maximum.

8. The radar level gauge system according to claim 6, wherein:

the electrical distance for said first maximum is substantially the same as the electrical distance for said second maximum;

the electrical distance for said first minimum is substantially the same as the electrical distance for said second minimum; and

a difference in electrical distance for said first maximum and said first minimum is a quarter of a wavelength of said electromagnetic transmit signal.

9. The radar level gauge system according to claim 1, wherein said conductive horn antenna wall exhibits a first physical distance from said first opening to said second opening along said first path and a second physical distance from said first opening to said second opening along said second path, said second physical distance being different from said first physical distance.

10. The radar level gauge system according to claim 1, wherein said horn antenna comprises at least one aperture in said conductive horn antenna wall between said first opening and said second opening.

11. The radar level gauge system according to claim 10, wherein said at least one aperture is elongated in a direction perpendicular to said central longitudinal axis.

12. The radar level gauge system according to claim 10, wherein a length extension of said at least one aperture is approximately one half of a wavelength of said electromagnetic transmit signal.

13. The radar level gauge system according to claim 10, wherein said horn antenna comprises a first aperture in said conductive horn antenna wall between said first opening and said second opening arranged at a first angular position in relation to said central longitudinal axis, and a second aperture in said conductive horn antenna wall between said first opening and said second opening arranged at a second angular position in relation to said central longitudinal axis opening, spaced apart from said first angular position by approximately 180°

.

14. A method of determining a filling level of a product in a tank, comprising the steps of:

transmitting an electromagnetic transmit signal having a first polarization;

propagating, using a horn antenna, said electromagnetic transmit signal towards said surface of the product;

reflecting, by said horn antenna, an antenna reflection signal substantially only having said first polarization;

receiving an electromagnetic surface reflection signal resulting from reflection of said electromagnetic transmit signal at said surface of the product, said electromagnetic reflection signal having a second polarization different from said first polarization; and

determining said filling level based on said electromagnetic surface reflection signal.

15. The method according to claim 14, wherein said first and second polarizations are circular polarizations.