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Ground Plane Termination Methods

IP.com Disclosure Number: IPCOM000102590D
Original Publication Date: 1990-Dec-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 2 page(s) / 71K

Publishing Venue

IBM

Related People

McCarthy, WF: AUTHOR [+3]

Abstract

Disclosed are two ground plane termination methods which improve the accuracy of electromagnetic radiation measurements by reducing reflections of electromagnetic waves from the edge of ground planes.

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Ground Plane Termination Methods

       Disclosed are two ground plane termination methods which
improve the accuracy of electromagnetic radiation measurements by
reducing reflections of electromagnetic waves from the edge of ground
planes.

      Radiated emissions from electronic products are measured over
metal ground planes to determine compliance with regulatory
requirements, such as the FCC Rules.  As illustrated in Fig. 1, the
product (or source) 1 and a receiving antenna 2 are placed on the
ground plane 3.  The receiving antenna is placed at a specified
distance from the product (usually 3, 10 or 30 meters).

      Theoretically, accurate measurements of the fields radiated by
the product would be obtained by using an ideal ground plane, defined
as a perfectly conducting plane of infinite extent.  Reflections from
the edges of finite size ground planes add to or subtract from the
direct wave and cause the electromagnetic fields to differ from those
that would exist on an ideal ground plane, resulting in errors in
field strength measurements, especially for vertically polarized
fields.

      A method to reduce edge reflections on a conventional ground
plane made of solid metal or wire mesh is to place lossy
ferromagnetic sheets 4 on top of the ground plane along the edges, as
shown in Fig. 1.  The lossy ferromagnetic sheets are a compound of
rubber loaded with ferromagnetic or ferrite material.  They absorb
and dissipate the surface currents in...