Electrical transmission or interconnection systems – Residual or remanent magnetism control
Reexamination Certificate
1999-02-23
2001-07-17
Paladini, Albert W. (Department: 2836)
Electrical transmission or interconnection systems
Residual or remanent magnetism control
C327S593000, C333S012000
Reexamination Certificate
active
06262495
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The field of the endeavor of the invention relates to ground planes for antennas and in particular to a method of reducing surface currents induced by the antenna on the ground plane.
2. Description of the Prior Art
A ground plane is a common feature of most radio frequency and microwave antennas. It is comprised of a conductive surface lying below the antenna and often performs a useful function by directing most of the radiation into one hemisphere in which the antenna is located. Frequently, the ground plane is present by necessity rather than by intent as in the case of a metal-skinned aircraft. For many types of antennas, the ground plane degrades antenna performance and/or dictates the antenna design itself. The most obvious constraint is that the tangent electric field on the conductive surface must be zero, so that electromagnetic waves experience a 180° phase shift on reflection. This often imposes a minimum height of about a quarter wavelength on the antenna. Furthermore, RF surface currents can propagate freely along the metal surface of the ground plane. These surface currents result in lost power due to radiation from edges or other discontinuities, and interference between nearby antennas on the aircraft. In phased arrays, surface currents are particularly problematic, contributing to coupling between antenna elements and causing blind angles.
What is needed is some type of method or design which provides a metallic surface which forbids RF current propagation and reflects electromagnetic waves with zero phase shift.
What is further needed is some type of method or apparatus whereby surface currents on ground planes associated with antennas can be suppressed to provide more efficient antennas, reduce coupling between elements in a phased array, and reduce interference between nearby antennas on aircraft.
Further, what is needed is a reflector which lacks edge currents that radiate power into the back hemisphere of the antenna.
What is needed is also ground plane in which a non-shifted phase of the reflected waves enable smaller antennas to be realized, since the radiating elements can be located very near the surface of the ground plane without being shorted out by it.
BRIEF SUMMARY OF THE INVENTION
The invention is an apparatus for reducing electromagnetically induced surface currents in a ground plane comprising a plurality of elements. Each element is a resonant circuit. Each of the elements is interconnected with each other to form an array. Each resonant circuit has an exposed surface. The corresponding plurality of exposed surfaces of the plurality of elements define the ground plane.
Each of the elements electrically functions as an LC resonant circuit. Each of the elements has a subplurality of adjacent elements and is capacitively coupled to each of the adjacent elements. Each of the plurality of elements is inductively coupled together in common.
In the illustrated embodiment, the array of elements comprises a corresponding plurality of separate conductive patches forming a surface. A common conductive back plane is separated by a predetermined distance from the surface of the patches. The plurality of patches form a common surface. Each of the plurality of patches is coupled by a conductive line to the separated back plane. The apparatus further comprises a dielectric material disposed between the back plane and the surface defined by the plurality of elements.
In the illustrated embodiment, the dielectric material is a dielectric sheet. The plurality of patches are conductive patches formed on a first surface of the dielectric sheet and the back plane is a continuous conductive surface disposed on an opposing surface of the dielectric sheet. The lines connecting the patches to the back plane are metalizations formed in vias defined through the dielectric sheet. The patches are hexagonal metalizations defined on the first surface of the dielectric sheet.
The plurality of resonant elements are parameterized to substantially block surface current propagation in the apparatus within a predetermined frequency band gap. In particular, the plurality of elements are parameterized to reflect electromagnetic radiation from the apparatus with a zero phase shift at a frequency within a frequency band gap.
The apparatus further comprises an antenna disposed above or inside the surface of resonant elements. In particular the antenna is comprised of a radiative element disposed parallel to the surface of the resonant elements, which act as a ground plane for the antenna.
In one embodiment the antenna is a wire antenna. In another embodiment the antenna is a patch antenna. The patch antenna may be substituted in position for one or more of the resonant elements and is disposed in the surface of the resonant elements.
In another embodiment the plurality of elements comprise at least a first and second set of elements. The first set of elements are disposed in a first defined plane which comprises the ground plane. The second set of elements is disposed in a second defined plane. The second defined plane is disposed above and spaced apart from the first ground plane. The arrays formed by the first and second sets of elements each form an overlapping mosaic, wherein each element of the second set overlaps and is spaced apart from at least one of the elements in the first set of elements. In other words the basic ground plane array has superimposed over it patches which are also connected to the back plane, but which form a second plane of metallic patches over the first plane of metallic patches.
In still another embodiment, the first and second set of elements each comprise in turn one or more corresponding subsets of elements. Each subset of the first set of elements are stacked over each other and each subset of the second set of elements are stacked over each other. The subset of the first set of elements are spaced apart from and adjacent to at least one subset of the second elements, so that two or more layers of alternating overlapping arrays of the first and second set of elements is provided. In other words, the double layered ground plane discussed above can be replicated an arbitrary number of times by vertically disposing alternating layers of the overlapping patches to form tiers of patches. The planes of patches can be added singly to comprise an odd number of planes or pairwise to provide an even number of planes.
A dielectric material can be disposed between each plane of patches and may either be the same type of dielectric material between each layer or the material may be selectively chosen to provide a graded plurality of layers of different types of dielectric materials.
The invention is also defined as a method of reducing surface currents in a conductive surface comprising the steps of providing the surface with a two dimensional array of a plurality of resonant elements. Each resonant element is coupled with each other and parameterized by geometry and materials to collectively exhibit a frequency band gap in which surface propagation is substantially reduced. Electromagnetic energy is radiated from a source disposed above the surface of resonant elements at a frequency within the frequency band gap so that electromagnetic radiation reflected from the surface has a zero phase shift at a frequency within the frequency band gap.
The surface which is provided is a plurality of conductive elements forming a periodic or nearly periodic array. Each element of the array has a subplurality of adjacent elements to which it is capacitively coupled. Each of the plurality of elements is inductively coupled in common with each other. In particular, the resonant array of elements which is provided is a plurality of conductive patches defining the periodic or nearly periodic array on a first surface and a continuous conductive second surface separated by a predetermined distance from the first surface. Each of the conductive patches of the first surface is inductively coupled to the continuous conductive se
Sievenpiper Dan
Yablonovitch Eli
Dawes, Esq. Daniel L.
Myers Dawes & Andras LLP
Paladini Albert W.
The Regents of the University of California
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