Field strength measuring instrument for the simultaneous detection of E and H fields

• US 5,231,346 A
• Filed: 02/12/1992
• Issued: 07/27/1993
• Est. Priority Date: 02/25/1991
• Status: Expired due to Fees

• Current Assignee: ASEA Brown Boveri SA de CV (ABB Limited)
• Original Assignee: ASEA Brown Boveri SA de CV (ABB Limited)
• Inventors: Gassmann, Felix
• Primary Examiner(s): Snow, Walter E.
• Application Number:
  US07/833,793
• Time in Patent Office: 531 Days
• Field of Search: 324/95, 324/72, 324/72.5, 324/158 P, 324/258, 343/739, 343/741, 343/846, 455/67
• US Class Current: 324/95
• CPC Class Codes: G01R 29/0878 Sensors; antennas; probes; detectors wave guide measuring sections G01R1/24

Abstract

A field strength measuring instrument for simultaneously measuring E and H fields is described. A loop antenna is formed by a half-loop (1) which is terminated by a metal surface (2). Due to the mirror effect of the metal surface (2), this arrangement, in field theory, is equivalent to a loop antenna which is divided into a first and a second half-loop (1, 5) by two load resistors (4a, 4b) arranged at opposite ends of the loop antenna. A circuit (8) for determining the field strengths of the E and H fields by means of the voltages (V₁, V₂) measured across the load resistors (4a, 4b) is arranged in a part-space shielded from the first half-loop (1) by the metal surface (2).

Claims

1. A field strength measuring instrument comprising:

an element having a conductive metal surface and defining a radiation measuring part-space exposed to E and H fields to be measured and a shielded part-space shielded by said metal surface from the field to be measured;

a half-loop antenna disposed in said radiation measuring part-space and having opposed ends which are terminated via respective load resistors connected to said metal surface, said half-loop antenna in combination with said load resistors and said shielded surface producing a mirror image of said half-loop antenna to realize a closed loop antenna suitable for simultaneous detection of E and H fields existing in said radiation measuring part-space; and

a circuit disposed in said shield part-space for determining the field strengths of the E and H fields by means of voltages induced by the E and H fields across the load resistors.

2. The field strength measuring instrument as claimed in claim 1, wherein the half-loop antenna is led through the metal surface at ends and is connected to the metal surface via the load resistors arranged in the shield part-space.

3. The field strength measuring instrument as claimed in claim 1, wherein the metal surface forms a curved surface closed in itself, which encloses the shielded part-space on all sides.

4. The field strength measuring instrument as claimed in claim 2 wherein the half-loop antenna essentially forms a part-section of a circle or of a regulator polygon.

5. The field strength measuring instrument as claimed in claim 1, wherein the two load resistors are essentially of the same size and have resistances of between 50 and 1000 ohms.

6. The field strength measuring instrument as claimed in claim 1, wherein a first-order low-pass filter with an input impedance (R₁) which is large compared with the load resistance and a C section divided into a plurality of parallel part-capacitors is connected in parallel to each load resistor for picking-off the respective voltages present across the load resistors.

7. The field strength measuring instrument as claimed in claim 1 wherein the metal surface is constructed as a spherical surface and three identical half-loop antenna which are orthogonally aligned in pairs, are arranged on the spherical surface so that E and H field can be vectorially determined at the same time.

8. The field strength measuring instrument as claimed in claim 7, wherein the half-loop antenna each enclose area which is not larger than half the effective cross section of the area of the sphere, and wherein the diameter of the sphere is smaller than half, especially less than or equal to one tenth, of the smallest wavelength of the E or H field to be measured.

9. The field strength measuring instrument claimed in claim 1, wherein the half-loop antenna is wire-shaped and has a diameter of more than 0.1 mm, particularly of at least 1 mm.

10. The field measuring instrument as claimed in claim 1 wherein the half-loop antenna is a conductor track applied to an insulating circuit board.

11. The field strength measuring instrument as claimed in claim 1 wherein the half-loop antenna essentially forms on of a square.

12. The field strength measuring instrument as claimed in claim 5, wherein the two load resistors have resistances between 100 and 300 ohms.