Patent Publication Number: US-6664926-B1

Title: Compact planar antenna

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a compact planar antenna for wireless communication devices such as cellular telephones, PCMCIA cards, etc. More particularly, the compact planar antenna of this invention enables the antenna to be used in pairs or in linear array situations. 
     2. Description of the Related Art 
     A number of small patch or planar antennas have been previously provided which were generally useful for their limited intended purposes. In U.S. Pat. No. 6,157,344 (the &#39;344 patent), a patent owned by the assignee of the instant invention, a small indoor/outdoor, shock tolerant, flat panel, transmit/receive antenna is described. U.S. Pat. No. 6,249,254 (the &#39;254 patent), a patent owned by the assignee of the instant invention, describes the method of making the invention of the &#39;344 patent. The disclosure of the &#39;344 and &#39;254 patents are included herein by reference thereto. In the antenna of the &#39;344 patent, the radiating element thereof is triangular-shaped, or pseudo triangular-shaped, and which has two equal length sides that join to form an apex and having a base that is equal or unequal in length to the sides, thus placing the apex coincident with the antenna long axis. Although the antenna of the &#39;344 patent performs very well, it has been found that the antenna thereof is too large for some applications. The need thereof exists for a compact planar antenna which is smaller than the antenna of the &#39;344 patent but which has the proper gain, pattern, and bandwidth performance 
     SUMMARY OF THE INVENTION 
     A planar antenna is described which comprises a substrate fabricated from a commercial PCB laminate or other materials, and an antenna element formed on one side thereof which is formed in the shape of a right triangle or related shape. In some embodiments, a ground plane is provided on one or both sides of the substrate. In some embodiments, a pair of the antenna elements may be used. In other embodiments, a plurality of the antenna elements may be arranged in an array to increase the performance of the antenna. 
     It is therefore a principal object of the invention to provide a compact planar antenna which is small enough to be used in most applications. 
     Yet another object of the invention is to provide a compact planar antenna which is small enough to be used in most applications without sacrificing gain, pattern and bandwidth performance. 
     A further object of the invention is to provide a compact planar antenna which includes an antenna element in the form of a right triangle or related shape. 
     Yet another object of the invention is to provide a compact planar antenna which may be used in groups of two or more antennas in close proximity to one another. 
     Still another object of the invention is to provide a compact planar antenna including antenna elements which may be used in an array arrangement. 
     Yet another object of the invention is to provide a compact planar antenna which is less expensive to manufacture than certain other planar antennas. 
     These and other objects will be apparent to those skilled in the art. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of the planar antenna of this invention positioned on a substrate which also has a ground plane mounted on the same side of the substrate; 
     FIG. 2 is a plan view of the other side of the substrate of FIG. 1 which illustrates a ground plane provided thereon; 
     FIG. 3 is a plan view illustrating an array of the planar antenna elements provided on a substrate; and 
     FIG. 4 is a plan view illustrating a pair of the antenna elements mounted on a substrate. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     FIG. 1 is a top view, i.e., a view from the radiating element side, of an antenna  10  in accordance with this invention wherein a final protective non-conductive plastic coating has not been applied to the antenna, and wherein the centrally located long-axis of antenna  10  is shown by arrow  12 . FIG. 2 is a bottom view, i.e., a view from the ground plane element side, of an antenna  10 . The numeral  14  refers to a through hole which extends through the ground plane  16 , substrate  18 , and the antenna element  20  to facilitate the connection of a feed cable to the antenna. 
     Without limitation thereto, in a preferred embodiment of the invention, antenna  10  is formed from a relatively thin commercial PCB laminate substrate such as glass epoxy. The top and bottom flat surfaces  22  and  24  of substrate  18  carry a thin layer, coating, or film of a metal such as copper. Copper-clad substrate  18  is processed, for example, by using well-known masking and etching techniques, to provide (1) a first metal pattern on the FIG. 1 side of the substrate  18 , this first metal pattern comprising a right-triangle-shaped metal radiating element  20  whose base  26  is positioned coincident with, or closely adjacent to, a first side edge or edge surface  28  of said substrate  18 , and to provide a metal feed line  30  which extends from the apex  32  of the triangle, and to provide (2) a second metal pattern on the FIG. 2 side of the substrate  18 , the second pattern comprising a metal ground plate element  16  having a first edge  32  that is positioned coincident with, or closely adjacent to, the second side edge or edge surface  34 , and having a second edge  36  that dimensionally overlaps a portion of feed line  30 , but does not overlap radiating element  20 . 
     In the preferred embodiment of the invention, but without limitation thereto, substrate  18  is a rectangle, radiating element  20  is formed as a right triangle having sides  38  and  40  extending from the side  26  to the apex  32 . 
     The manner of electrically connecting the antenna&#39;s radiating element  20  and ground plane element  16  take a number of forms within the spirit and scope of this invention. For example, if feed line  30  were extended to the second side  34 , then one conductor of an edge connector could be connected to feed line  30 , while the second conductor of the edge connector could be connected to ground plane element  16 . In the embodiment shown in the drawings, the through hole  14  permits a co-axial cable to be operatively connected to the ground plane element  16  and the antenna element  20 . 
     In an embodiment of the invention, a second ground plane element  42  may be formed on the radiating element side of the antenna  10 , as seen in FIG. 1, with the ground plane element  42  having a cut-out portion  44  which leaves room for the feed line  30  without affecting the characteristics of feed line  30 , as illustrated in FIG.  1 . In a related embodiment, the second ground plane element may be terminated at a location intermediate between the second edge  34  and feed line  30 , and in this embodiment the cut-out portion  44  is not present. In some related embodiments, the second ground plane element  42  may be connected to the first ground plane element  16  including, without limitation, by means of holes in the substrate  18  which are plated through with metal using common circuit board processing techniques. 
     In some embodiments, the planar antenna elements  26  may be combined, as illustrated in FIG. 3, to form an array to increase the performance of the antenna. FIG. 3 illustrates an integrated feed network  46  formed on the substrate  18 . The advantage of the present invention in the array embodiment of FIG. 3 over the antenna of the &#39;344 patent is the narrower spacing that may be achieved between the feed network  46  and the antenna elements  20 , owing to the more compact shape of the antenna elements  20  in the present invention when arranged such that the edge of the antenna element which is generally parallel to the long axis is nearest the feed network, as illustrated in FIG.  3 . 
     In certain applications, it may be required to use two or more antennas independent of one another in a confined space. In FIG. 4, a solution to the same is illustrated. In FIG. 4, a pair of the antenna elements  20  are utilized where the feed  48  is at an angle to the element as compared to being parallel to the long axis of the antenna element  20  shown in FIGS. 1 and 3. 
     In some embodiments which utilize one or more antennas operating independently in a confined spaced, the antennas may utilize a ground plane element of complex shape which may be common between the multiple elements, such as may be created by an extension of a PCMCIA card, the ground plane element being formed by an extension of the ground layers of the PCMCIA card. In these embodiments, the ground plane layer may be an intermediate layer in a multiple-layer PCB construction as is common in the manufacture of PCMCIA cards and other devices. All of these embodiments, which utilize as the antenna element the element depicted in FIGS. 1,  2 ,  3  and  4 , are within the spirit of the present invention. 
     The planar antenna of this invention is ideally suited in wireless applications where small antennas are required for minimal visual impact (stealth) and in telematics applications where small planar antennas are useful to allow the device to be hidden within a vehicle. In addition, the antenna is useful in portable wireless devices including PCMCIA cards wherein the size of the card is predetermined thereby limiting the space which is available for antennas. Due to the small size of the antenna of this invention, it is useful in linear array antennas since it minimizes the resulting size of the array. 
     The antenna of this invention is approximately one-half the size of the Microsphere™ antenna described in U.S. Pat. No. 6,157,344 with similar gain, pattern and bandwidth performance. The antenna of this invention is ideally, suited for all the uses (applications) set forth in the &#39;344 patent. 
     Thus it can be seen that the invention accomplishes at least all of its stated objectives.