Abstract:
An antenna architecture containing a broadband resonant cap positioned over a radiating patch is disclosed. The resonant cap consists of a rectangular resonant patch at the center with parasitic patches in close proximity of the four edges of the resonant patch. The parasitic patches may be coplanar with the resonant patch or may be mounted at an angle with respect to the vertical axis of the resonant patch. The resonant cap reduces the HPBW of the emitted radiation and improves emission directivity.

Description:
RELATED APPLICATION INFORMATION 
     The present application claims priority under 35 USC section 119(e) to U.S. provisional patent application Ser. No. 61/133,147 filed Jun. 25, 2008, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to radio communication antenna systems for wireless networks. More particularly, the invention is directed to high-gain radiating patch antennas and antenna arrays. 
     2. Description of the Prior Art and Related Background Information 
     Modern wireless antenna systems generally include a plurality of radiating elements that may be arranged over a ground plane defining a radiated (and received) signal beamwidth and azimuth angle. Antenna beamwidth has been conventionally defined by Half Power Beam Width (“HPBW”) of the azimuth or elevation beam relative to a bore sight of such antenna element. 
     Real world applications often call for an antenna radiating element with frequency bandwidth, pattern beamwidth and polarization requirements that may not be possible for conventional antenna radiating element designs to achieve due to overall mechanical constraints. 
     Accordingly, a need exists for an improved antenna element architecture which allows optimization of antenna array requirements, such as HPBW, antenna gain, side lobe suppression, FIB ratio, etc., without introducing undesirable tradeoffs, while taking into account cost and complexity of such antenna structure. 
     SUMMARY OF THE INVENTION 
     In a first aspect, the present invention provides an antenna radiating structure comprising a generally planar radiating element, a ground plane configured below the generally planar radiating element, and a resonant cap. The resonant cap is configured above and spaced apart from the generally planar radiating element in a radiating direction. The resonant cap comprises a dielectric sheet, a conductive resonant patch configured on the dielectric sheet, and a plurality of conductive parasitic patches configured on the same or a different dielectric sheet. The plurality of parasitic patches are spaced from the resonant patch. 
     In an embodiment, the width and the length of the resonant patch are approximately one half of the wavelength of the radiation. The resonant patch is spaced approximately one half of the wavelength of the radiation above the ground plane. In an embodiment, the resonant patch is generally coplanar with the plurality of parasitic patches. In an embodiment, the plurality of parasitic patches are configured at an angle with respect to the plane of the resonant patch. The plane of the parasitic patches is preferably positioned at an angle with respect to the vertical axis of the resonant patch in the range of approximately 20 degrees to approximately 35 degrees. The plurality of parasitic patches may comprise a set of inner parasitic patches and a set of outer parasitic patches, wherein the inner parasitic patches are positioned adjacent to the edges of the resonant patch, and the outer parasitic patches are positioned adjacent to the outer edges of the inner parasitic patches. For example, the plurality of parasitic patches may comprise four inner parasitic patches and four outer parasitic patches. The length and width of the outer parasitic patches are preferably less than the length and width of the inner parasitic patches. 
     In another aspect, the present invention provides an antenna radiating structure comprising a first generally planar radiating element. The antenna radiating structure further comprises a ground plane configured below the first generally planar radiating element and a resonant cap configured above and spaced apart from the ground plane in a radiating direction. The resonant cap comprises a dielectric sheet, a rectangular resonant patch of conductive material configured on the dielectric sheet, and a plurality of parasitic patches of conductive material configured adjacent to the edges of the resonant patch. 
     In a preferred embodiment, the parasitic patch is adjacent to each edge of the resonant patch. The parasitic patches are preferably rectangular. In an embodiment, the resonant patch is generally coplanar with the plurality of parasitic patches. In a preferred embodiment, the dielectric sheet is configured to position the plurality of parasitic patches at an angle with respect to the vertical axis of the resonant patch. The plurality of parasitic patches are preferably positioned at an angle with respect to the vertical axis of the resonant patch in the range of approximately 20 degrees to approximately 35 degrees. The dielectric sheet is constructed from a material having a dielectric constant E r  in a range of approximately 5.0 to approximately 10. The dielectric sheet is alternatively constructed from a material having a dielectric constant E r  preferably in the range of approximately 4.6 and approximately 6. The plurality of parasitic patches preferably further comprises four outer parasitic patches positioned adjacent to the four outer edges of the inner parasitic patches. The length and width of the outer parasitic patches are preferably less than the length and width of the inner parasitic patches. and a second generally planar radiating element configured above and spaced apart from the first generally planar radiating element in a radiating direction. The antenna radiating structure may further comprise a second generally planar radiating element configured generally coplanar with the first generally planar radiating element and which has an aperture for radiative coupling thereto. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a top view of a high-gain patch antenna in an embodiment of the invention. 
         FIG. 1B  is a cross section along the datum line depicted in  FIG. 1A  and presents a side view of a high-gain patch antenna in an embodiment of the invention. 
         FIG. 2  depicts a high-gain patch antenna with coplanar resonant patch and parasitic patches in an embodiment of the invention. 
         FIG. 3  depicts a high-gain patch antenna with the parasitic patches tilted at an angle with respect to the vertical axis of the resonant patch. 
         FIG. 4  is a representation of the simulated antenna radiation patterns for a resonant cap with coplanar resonant patch and parasitic patches employing an aperture-coupled patch. 
         FIG. 5  is a representation of the simulated antenna radiation patterns for a resonant cap with tilted parasitic patches employing an aperture-coupled patch. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     It is an object of the present invention to enhance the directivity of a standard radiating patch antenna through the use of a broadband resonant cap above a radiating patch and a ground plane. In an embodiment of the present invention, the resonant cap comprises a dielectric sheet, a resonant patch formed on the dielectric sheet, and a plurality of parasitic patches surrounding the resonant patch. The parasitic patches may be coplanar or tilted at an angle with respect to the plane of the resonant patch. The gaps and lengths of the parasitic patches are preferably selected to allow appropriate amplitude weighting for sidelobe suppression. 
     In an embodiment of the invention, a resonant cap is positioned over a generally planar radiating element and a ground plane. The generally planar radiating element is disposed on a dielectric substrate, and the metallic ground plane is disposed on a ground plane dielectric substrate. The resonant cap, the generally planar radiating element, and the ground plane are mechanically coupled through the use of multiple spacers. Radio frequency (RF) energy from feed lines is coupled to the generally planar radiating element. 
     In another embodiment of the invention, a resonant cap is positioned over aperture-coupled antenna elements including a secondary radiating patch, a radiating patch, and a ground plane. Teachings related to the aperture-coupled antenna elements previously disclosed in patent entitled “Dual Polarization Antenna Element with Dielectric Bandwidth Compensation and Improved Cross-Coupling,” filed Aug. 5, 2008, application Ser. No. 12/221,634 (Foo) may be employed herein and the disclosure of such patent is incorporated herein by reference. Also, plural patch antennas in accordance with the invention may be configured in an array on a common ground plane, such as disclosed in application Ser. No. 12/221,634, and such an improved array is disclosed herein by reference. 
     Reference will now be made to the accompanying drawings, which assist in illustrating the various pertinent features of the present invention. 
       FIGS. 1A and 1B  illustrate an antenna architecture employing a resonant cap  101  employing a single radiating patch and ground plane.  FIG. 1A  presents a top view of resonant cap  101  over ground plane  110 .  FIG. 1B  is a cross section along the datum line of  FIG. 1A  and illustrates resonant cap  101 , radiating patch  160 , and ground plane  110  in an embodiment of the invention. 
     The radiating patch  160  may be a conventional generally planar radiating element and is disposed on dielectric substrate  161 . The metallic ground plane  110  is also conventional and is disposed on a ground plane dielectric substrate  111 . The resonant cap, the generally planar radiating element, and the ground plane are mechanically coupled with spacers  115   a - 115   d  which provides the desired spacing. Radiating patch  160  is positioned above ground plane  110  at a distance in the range of approximately 10% to approximately 20% of the emission radiation wavelength. Radio frequency (RF) energy from feed lines (not shown) is coupled to radiating patch  160  in a conventional manner. 
     The resonant cap  101  may comprise a dielectric sheet  120  with the resonant patch  130 , the inner parasitic patches  141 - 144 , and the outer parasitic patches  151 - 154  on the surface of the dielectric sheet  120 . Resonant patch  130  is positioned above the radiating patch  160  in a radiating direction spaced approximately one half of the emission wavelength above the ground plane. The length and width of resonant patch  130  are both approximately one half of the emission wavelength. The resonant patch  130 , the inner parasitic patches  141 - 144 , and the outer parasitic patches  151 - 154  may be constructed from metals such as copper, aluminum, or brass for example. 
     The dielectric sheet  120  may be fabricated out of low-loss dielectric materials with a dielectric constant E r  above 5.0 and preferably between the range of approximately 5.0 and 10. In one or more embodiments of the invention, fibre glass materials with dielectric constants E r  in the range of approximately 4.6 and 6.0 may be employed. Also, plastic materials may be employed. The dielectric sheet  120  may be used for low cost manufacturing of the resonant cap  101 . In one or more embodiments of the invention, the thickness of the dielectric materials is minimized for reducing costs and lessening the impact of the dielectric sheet  101  on the radiation patterns. The thickness of the dielectric sheet may be in the range of approximately 0.25 millimeters to approximately 0.5 millimeters. 
     As depicted in  FIG. 1B , the resonant cap  101  may comprise parasitic patches  141 - 144  and  151 - 154  that, in the view of  FIG. 1B , are tilted with their plane at an angle α with respect to the vertical axis of the resonant patch  130  (i.e., the direction normal to the plane of the resonant patch  130 ). In an embodiment of the invention, tilt angle α typically may be in the range of approximately 20 degrees to approximately 35 degrees. The parasitic patches may be positioned at an angle with respect to the vertical axis of the resonant patch to control sidelobe emission. In an embodiment of the invention, resonant patch  130  may be coplanar with respect to the parasitic patches  141 - 144  and  151 - 154 , i.e., α is approximately 90 degrees. Perspective views illustrating coplanar and tilted resonant caps  101  respectively are shown in  FIGS. 2 and 3  in an alternate embodiment differing only in the radiating patch structure, which embodiments are discussed below. 
     The dimensions and positions of the inner parasitic patches  141 - 144  and the outer parasitic patches  151 - 154  determine the effective weight functions of the antenna aperture, and may be positioned to control radiating patterns, sidelobe levels, and frequency bandwidth. In the illustrative non-limiting implementations shown, the inner parasitic patches  141 - 144  are positioned adjacent to the edges of the resonant patch  130 , and the outer parasitic patches  151 - 154  are positioned adjacent to the outer edges of the inner parasitic patches  141 - 144 . However, it shall be understood that an alternate number, shape, or placement of the parasitic patches and/or type of radiating elements can be used as well. 
     In an embodiment, the dimensions of the outer parasitic patches  151 - 154  may be less than the corresponding dimensions of the inner parasitic patches  141 - 144 . The dimensions and the positioning of the inner parasitic patches  141 - 144  and the outer parasitic patches  151 - 154  may be selected iteratively to achieve the desired antenna patterns. The antenna radiating structure may be adapted for operation within known bands, for example the UMTS band (1900-2200 MHz). The angle α and resonant cap  101  top and bottom height above the ground plane at the parasitic patch edges may be chosen to be approximately one half of the wavelength of the emitted radiation across the bandwidth in broad bandwidth applications. 
     As depicted in  FIGS. 2 and 3 , resonant cap  101  may be positioned over alternate antenna radiating elements including a secondary radiating patch  170 , a radiating patch  160 , and a ground plane  110 . Resonant cap  101  is positioned above the secondary radiating patch  170  in a radiating direction spaced approximately one half of the wavelength above the ground plane. The radiating patch  160  may be a generally planar radiating element. The secondary radiating patch  170  may be a second generally planar radiating element configured above and spaced apart from the first generally planar radiating element in a radiating direction and may be configured generally coplanar. The secondary radiating patch  170  may have an aperture for radiative coupling to the radiating patch  160 . Ground plane  110  is positioned below the radiating patch  160 . Resonant patch  130  is positioned above the secondary radiating patch  170  in a radiating direction spaced approximately one half of the wavelength above the ground plane. The resonant cap and the aperture-coupled antenna elements are mechanically coupled to the ground plane with spacers  115   a - 115   d  as in the embodiment of  FIG. 1A  (not shown in  FIGS. 2 and 3 ). 
     Detailed discussion relating to the antenna elements including the secondary radiating patch  170 , the radiating patch  160 , and the ground plane  110  may be found in application Ser. No. 12/221,634 (Foo) which has been incorporated herein by reference. 
     As depicted in  FIG. 2 , resonant patch  130  may be coplanar with respect to the parasitic patches  141 - 144  and  151 - 154 . The radiation patterns are presented in  FIG. 4  for the high-gain resonant cap with coplanar resonant patch and parasitic patches in one or more embodiments of the invention. As depicted in  FIG. 4 , the resonant cap reduces the HPBW significantly and improves directivity by over 5 db. 
     As depicted in  FIG. 3 , the resonant cap  101  may alternatively comprise parasitic patches  141 - 144  and  151 - 154  that are tilted with respect to the vertical axis of the resonant patch  130  to control sidelobe emission. In one or more embodiments of the invention, the tilt angle α may be typically in the range of approximately 20 degrees to approximately 35 degrees.  FIG. 5  is a representation of the typical antenna radiation patterns for the high-gain resonant cap with the resonant patch and tilted parasitic patches in one or more embodiments of the invention. The resonant cap reduces the HPBW significantly and improves directivity. 
     The present invention has been described primarily for enhancing the directivity of a standard radiating patch through the use of a broadband resonant cap above a radiating patch and a ground plane. In this regard, the foregoing description of an antenna element based on the resonant cap is presented for purposes of illustration and description. Furthermore, the description is not intended to limit the invention to the form disclosed herein. Accordingly, variants and modifications consistent with the following teachings, skill, and knowledge of the relevant art, are within the scope of the present invention. The embodiments described herein are further intended to explain modes known for practicing the invention disclosed herewith and to enable others skilled in the art to utilize the invention in equivalent, or alternative embodiments and with various modifications considered necessary by the particular application(s) or use(s) of the present invention.