Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
1998-05-08
2001-01-30
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C455S269000, C455S703000
Reexamination Certificate
active
06181279
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to patch antennas, and more particularly to a patch antenna having a relatively small ground plate using peripheral parasitic stubs.
BACKGROUND OF THE INVENTION
Patch antennas for transreceiving radio-frequency signals are well known. Such patch antennas generally comprise a patch antenna element which is suitable for receiving and/or transmitting at a desired frequency range or bandwidth. These patch antennas may be linearly or circularly polarized, for example.
A conventional patch antenna is provided with a ground plate or ground plane which is parallel to the antenna and spaced apart therefrom. Thus, the ground plate has a patch side and a non-patch side. Patch antennas such as these are characterized their bore sight directionality (perpendicular to the plane of the patch antenna and in a direction pointed away from the patch side of the ground plate). The ground plate tends to shield or mitigate external signals emanating from non-bore sight directions. Similarly, the ground plate acts to control the direction of outgoing signals when the antenna is used to transmit signals.
Besides defining the directionality of the antenna, the characteristics of the ground plate impacts the antenna performance. It is understood that such a transmitting/receiving patch antenna results in electromagnetic fields emanating between the patch antenna and the ground plate and that the patch antenna and its ground plate have an inductive relationship. The nature of these electromagnetic fields impacts the antenna performance. As such, changing the size of the ground plate affects the antenna gain and pattern or shape. To a certain extent, the larger the ground plate, the greater the antenna gain and the more defined the antenna pattern. In a conventional configuration, the ground plate is larger than the patch antenna. Take for example a patch antenna which is rectangular and defines a length and a width. Typically, the associated ground plate requires a length and a width of approximately three times or greater than that of the patch antenna for optimum or increased antenna performance in terms of gain and pattern shape. Thus, the ground plate would have a surface area of at least nine times greater than the patch antenna.
Based on the foregoing, it is clear that the sizing requirements of such a patch antenna/ground plate arrangement is dominated by the size of the ground plate. In addition, it is understood that the sizing requirements of an antenna assembly directly impacts the overall weight of the assembly. The size and weight of an antenna assembly may impact the range of application of the device. Thus, under certain circumstances it is highly desirable to reduce the size and weight of the antenna assembly without sacrificing antenna performance. It is therefore evident that there exists a need in the art for a patch antenna assembly having a patch antenna with a relatively small ground plate thereby reducing the overall size and weight of antenna assembly.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a patch antenna assembly having a generally planar patch antenna, defined by a first peripheral boundary, and a generally planar parasitic ground plate, disposed to spaced parallel relation to the patch antenna. The assembly further includes at least one conductive parasitic shielding element for segregating electromagnetic fields between the patch antenna and the ground plate. The shielding element is disposed in electrical communication with the ground plate and extends from the ground plate and substantially about the first peripheral boundary of the patch antenna. Preferably, the patch antenna and the ground plate are formed on a common dielectric substrate. The patch antenna, ground plate and shielding element are preferably formed of a similar metallic material.
In the preferred embodiment of the present invention, the antenna is sized and configured for a particular electromagnetic wavelength. The antenna and the ground plate are spaced approximately one twenty-fifth wavelength apart. Preferably, the dielectric material the antenna and the ground plate has a dielectric constant of four. In addition, the shielding element takes the form of a plurality of elongated cylindrical vias. Each of the vias extends from the ground plate towards the patch antenna and the vias collectively surround the patch antenna. The vias are spaced approximately one twenty-fifth of the predetermined wavelength apart or less. In such a configuration, it is preferable that the diameter of the vias are approximately one-two-hundredth of the predetermined wavelength.
The patch antenna may have a variety of polarizations and geometries. The antenna assembly may be further provided with other generally planar layers which may include circuity associated with generating and processing signal transmitted and received from the patch antenna. Thus, it is contemplated that the patch antenna and ground plate formed on the dielectric substrate may be combined with other substrate layers to conveniently form a board stack-up. In addition, the present invention further includes a patch antenna array which is provided with a plurality of patch antenna assemblies as described above.
In another embodiment of the present invention there is provided a method of making a patch antenna assembly. The method begins with the initial step of providing a generally planar dielectric substrate having first and second sides. A conductive material is affixed to the first and second sides of the dielectric substrate. Affixing the conductive material may be accomplished by using a metal plating process. A portion of the conductive material is removed from the first side to form a patch antenna from the remaining conductive material which. The patch antenna defines a first peripheral boundary. Additionally, a portion of the conductive material is removed from the first side of the dielectric substrate to form a plurality of discs having a first diameter from the remaining conductive material. The discs are formed about the first peripheral boundary of the patch antenna to collectively surround the antenna. The discs are formed to have a first diameter. The removal of the conductive material may be facilitated by an etching process. A plurality of holes are drilled through the center of the discs and through the underlying dielectric substrate. The holes are drilled to have a second diameter which is less than the first diameter of the discs. The holes are filled with a conductive material to electrically connect the discs to the conductive material on the second side of the dielectric substrate. A metal plating process may be used to fill the holes.
Based on the foregoing, the present invention mitigates the inefficiencies and limitations associated with prior art patch antenna assemblies. Advantageously, the present invention facilitates use of a reduced sized ground plate in comparison to a ground plate used in a conventional antenna arrangement for comparable antenna performance. Because the overall size of a patch antenna assembly is limited by the size of the associated ground plate, present invention facilitates an overall reduction in the size of the antenna assembly. Such reductions have a corresponding reduction in weight of the antenna assembly. It is contemplated that these reductions in size and weight of the antenna assembly facilitate expanded usage and range of application in circumstances where the size and/or weight constraints are important. In addition, the antenna assembly of the present invention may incorporate antennas having a variety of the polarizations (circular, linear, etc.). As such, the antenna assembly further facilitates a wide range of application.
With respect to ease of manufacture, the antenna assembly of the present invention does not require any special or extraordinary tooling requirements. Conventional methods of manufacture may be used, such as metal plating and drilling processes. In addition,
Anderson Terry J.
Clinger James
Hoch, Jr. Karl J.
Northrop Grumman Corporation
Wong Don
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