Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
1999-05-06
2001-04-03
Le, Hoanganh (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S846000
Reexamination Certificate
active
06211824
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
This application relates to the field of patch antennas and more particularly to the field of directional patch antennas using multiple patch radiating elements to control the direction of a beam of radio frequency energy (RF) over a large scan volume.
2. Description of Related Art
Many applications, such as scanning Radar and communication with satellites in a low orbit, require that the orientation of an RF beam emitted in three-dimensional space be adjusted rapidly with respect to a stationary reference axis without physically moving the antenna. This can be implemented using a stationary array of antenna elements which are coupled to an RF signal source and can be individually controlled. The spatial orientation of the RF beam can be changed by adjusting the relative phase of the RF signal supplied to the antenna elements. An antenna of this type is generally referred to as an “electronically scanned array”, a “phased array” or a “patch” antenna and is described, for example, in the commonly assigned U.S. Pat. No. 5,400,040 “Microstrip Patch Antenna” to J. P. Lane et al., which is incorporated herein by reference.
The array antenna can either be assembled from individual antenna elements, or radiators, that are mounted on a passive support structure to form an array. The radiators represent individual waveguide cavities that terminate in a waveguide aperture; the waveguide apertures are typically co-planar with a ground plane. This approach minimizes the number of elements required for a desired array aperture and scan volume and maximizes scan volume coverage. On the other hand, the radiating aperture does not utilize the entire surface area of a “unit cell” since the area on the support structure located between the waveguide apertures is taken up by the ground plane, limiting the bandwidth of the device. Such antennas are also expensive to manufacture since each antenna element has to be inserted separately in the support structure.
Other known patch antennas are configured as a stacked patch, with each antenna element including a feed patch coupled to an RF signal source and a coupled patch separated from the feed patch by a dielectric layer, as illustrated in FIG.
1
. Patch antennas of this type can be produced inexpensively by conventional integrated circuit manufacturing techniques, e.g., photolithography, on a continuous dielectric substrate. They have excellent frequency bandwidth since the radiating aperture is essentially the entire unit cell. Scan volume performance, however, is impaired due to the excitation of electromagnetic surface waves in the dielectric substrate. Surface wave excitation is especially severe when the dielectric constant of the substrate material is high, e.g., with advanced ceramic materials such as Low-Temperature Co-fired Ceramics (LTCC). It is therefore desirable to improve the antenna performance by eliminating or at least reducing the excitation of surface waves within the dielectric substrate.
SUMMARY OF THE INVENTION
In one aspect of the invention, a patch radiator antenna includes a dielectric substrate having a first and second surface and a plurality of spaced apart first patch radiator elements arranged upon the first surface of the dielectric substrate. Each of the first patch radiator elements defines a patch area and can be electrically coupled to an RF signal source or an RF receiver. Areas with different dielectric constants are defined in the dielectric substrate, wherein a region in the dielectric substrate that substantially overlaps with a patch area has a first dielectric constant and another region in the dielectric substrate that does not overlap with a patch area has a second dielectric constant. This arrangement prevents propagation of surface wave energy in the dielectric substrate between the first patch radiator elements.
According to another aspect of the invention, a patch radiator antenna includes a ground plane element and a first dielectric planar member placed on a major surface of the ground plane element. A plurality of first patch radiator elements is arranged on a surface of the first dielectric member remote from the ground plane element. A second dielectric planar member is placed on first patch radiator elements, and a plurality of second patch radiator elements arranged on a surface of the second dielectric member remote from the first patch radiator elements, with each second patch radiator element associated with a corresponding first patch radiator element. The first dielectric planar member includes areas having a first dielectric constant being separated from areas having a second dielectric constant that is different from the first dielectric constant to effectively prevent surface wave energy from propagating in the first dielectric planar member between the first patch elements.
The integrated patch antenna of the invention provides both a large scan volume and a large bandwidth even with substrate materials having a high dielectric constant. Surface waves which would otherwise limit the bandwidth, are essentially eliminated.
Embodiments of the invention may include one or more of the following features.
At least a portion of the first region may overlap with the patch area. The regions with the first dielectric constant may be the substrate and/or may be made of a metal. The second region may include a plurality of spaced apart openings arranged in the dielectric substrate substantially in a region that overlaps the outer perimeter of the patch area. The openings may extend either partially or completely from one of the first and second surface of the dielectric substrate to the opposite surface of the dielectric substrate and may have the form of, for example, holes and/or slots. The inside surface of the openings may be metallized and/or the openings may be filled with a metal or another material having a dielectric constant with a value that is different from that of the material surrounding the opening. The first patch radiator elements may be placed on a separate support sheet.
The patch radiator elements may have a substantially circular or a polygonal, e.g., rectangular shape. The lateral spacing between adjacent patch radiator elements may be approximately one half of the radiated free space wavelength. The value of the dielectric constant of the dielectric substrate may be selected to lie between approximately 1.5 and 8; the dielectric substrate may be made of a Low-Temperature Co-fired Ceramics (LTCC) with a dielectric constant of between 5 and 7. The value of the dielectric constant of the second dielectric sheet may be selected to lie between approximately 1.0 and 2.5.
The first patch radiator element may be coupled to an RF signal source via a one or more coupling location to effect the polarization of the emitted RF beam. The first patch radiator element may also be coupled to the RF signal source via a waveguide.
Further features and advantages of the present invention will be apparent from the following description of preferred embodiments and from the claims. In the drawings, elements having identical features or performing identical functions are given the same reference numerals.
REFERENCES:
patent: 5227749 (1993-07-01), Raguenet et al.
patent: 5400040 (1995-03-01), Lane et al.
patent: 5434581 (1995-07-01), Raguenet et al.
patent: 5539420 (1996-07-01), Dusseux et al.
patent: 5745079 (1998-04-01), Wang et al.
patent: 5841401 (1998-11-01), Bodley et al.
patent: 5880694 (1999-03-01), Wang et al.
Holden Richard H.
Ledonne Gennaro
Preiss Joseph A.
Foley Hoag & Eliot LLP
Le Hoang-anh
Raytheon Company
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