Abstract:
An antenna system comprising a ground plane structure on a substrate, an antenna space on the substrate adjacent to the ground plane structure, the antenna space including an ungrounded antenna therein with an associated first resonant length, an extension of the ground plane projecting into the antenna space, the ground plane extension defining a second resonant length that includes at least part of its own length and at least part of a length of the ground plane structure.

Description:
TECHNICAL FIELD 
   This description relates, in general, to antenna systems and methods, and more specifically, to antenna systems and methods that utilize ground plane resonance. 
   BACKGROUND OF THE INVENTION 
   Many antenna systems inside modern wireless devices include one or more antenna elements and a ground plane. Often, a ground plane is a portion of conductive material that is large in surface area when compared to the antenna elements. Further, the ground plane is generally connected to various electronic components through their ground connections. An example ground plane use is to complete a monopole antenna, which is fed against the ground plane and acts like a half-wavelength dipole antenna. 
   Some prior art systems, such as that shown in PCT Publication No. W02003077360, have one or more parasitic elements extending from the ground plane. Those parasitic elements couple with one or more antenna elements so that each parasitic adds its own narrow frequency band when excited. That the parasitic elements are configured to extend from the ground plane is merely a way to ground the parasitics, and the resonant lengths of such parasitics do not include any part of the ground plane. Another prior art use for extensions from ground planes is to provide baluns for differential antenna elements. 
   While some amount of coupling between antenna elements and the ground plane in a device results in ground plane radiation, no design currently uses the ground plane as a radiating structure in its own right. In fact, ground plane resonance is usually a phenomenon to be minimized. Thus, when engineers design antenna systems for use in devices, they focus on the volume that is reserved for the antenna elements. Therefore, it is generally true that in a given PCB-mounted antenna system, less than half of the volume in the design is utilized for signal radiation. 
   BRIEF SUMMARY OF THE INVENTION 
   Various embodiments of the present invention are directed to antenna systems and methods for use thereof, wherein the antenna systems include one or more ground plane extensions. In one example, an antenna system is disposed on a substrate, such as a PCB, and a ground plane includes a conductive layer that covers most of the surface area of one side. Part of the surface area of the substrate is reserved for an ungrounded antenna that is also disposed on the substrate. The ground plane has a portion that extends into the antenna space. The extension is designed such that at least a portion of its length and at least a portion of the length of the ground plane together form a resonant length that corresponds to a communication band. When in operation, the structure formed from the ground plane and its extension electromagnetically couple with the ungrounded antenna element and transmits data in the communication band. Accordingly, in this example, the ground plane and its extension are used as a radiating structure to add performance in one or more communication bands in addition to communication bands offered by the antenna element. 
   In a specific example, the antenna element is an ungrounded, monopole-type antenna that is set to one side of the antenna space. The ground plane extension protrudes onto the opposite side of the antenna space. The distance between the antenna element and the ground plane extension is small enough such that capacitive feeding occurs but large enough such that the presence of the ground pane does not narrow the bandwidth of the antenna element to an undesirable degree. 
   In an example method, a signal is provided to an ungrounded antenna element. Coupling between the ungrounded antenna element and a structure that includes a ground plane and a ground plane extension causes the structure to resonate, thereby transmitting data in an established communication band. 
   The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an illustration of an exemplary system adapted according to one embodiment of the invention; 
       FIG. 2  is an illustration of the exemplary system of  FIG. 1  from a different view; 
       FIG. 3  is an illustration of an exemplary technique for connecting a ground plane extension to a ground plane according to one embodiment of the invention; 
       FIG. 4  is an illustration of an exemplary system according to one embodiment of the invention with example resonant lengths marked; 
       FIG. 5  is an illustration of an exemplary system adapted according to one embodiment of the invention; 
       FIGS. 6A and 6B  are illustrations of exemplary shapes for ground plane extensions according to various embodiments of the invention; 
       FIGS. 7A-D  are illustrations of exemplary shapes for antenna elements according to various embodiments of the invention; 
       FIG. 8  is an illustration of an exemplary three-dimensional geometry according to one embodiment of the invention; 
       FIG. 9  is an illustration of a raised geometry according to one embodiment of the invention; and 
       FIG. 10  is an illustration of an exemplary method adapted according to one embodiment of the invention for operating an antenna system. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is an illustration of exemplary system  100  adapted according to one embodiment of the invention. System  100  is an antenna system for multi-band and/or broadband communications. System  100  includes ground plane  101  disposed upon substrate  102 . Antenna space  103 , in this example, is a portion of the substrate that is reserved for antenna element  104 , and is, in effect, defined by the shape of ground plane  101 . 
   Antenna element  104  is disposed in antenna space  103 . Since antenna  104  is adjacent to, rather than above, ground plane  101  and also does not have a conductive connection to ground plane  101 , it is an ungrounded antenna element. Specifically, antenna element  104  is shown in this example as a monopole antenna element. 
   Projection  105  is an extension of ground plane  101  that is disposed in antenna space  103 . Ground plane extension  105  can be part of the same conductive layer that forms ground plane  101  or can be independently formed or disposed on substrate  102 . The dimensions of ground plane extension  105  and ground plane  101  together form a resonant length that can be used to transmit data signals. Specifically, when ground plane  101  and ground plane extension  105  are placed within the near field of antenna element  104 , antenna element  104  can be operated as a capacitive feed that causes resonance along the resonant length described above. In other words, ground plane extension  105  is designed to adapt a length of a portion of ground plane  101  to conform to a resonant length that corresponds to an established communication band. In this way, the resonance of ground plane  101  can be optimized to provide additional performance to antenna system  100 . 
     FIG. 2  is an illustration of system  100  from a different view.  FIG. 2  shows that substrate  102  is three-dimensional and can be made up of layers. In fact, the view shown in  FIG. 2  is somewhat simplified, as various embodiments may use substrate  102  to host a variety of electronic components (not shown), and the items shown on the surface of substrate  102  are not limited to the top layer as some embodiments may include those items in intermediate layers. An example of a suitable type of substrate is a Printed Circuit Board (PCB), where antenna element  104 , ground plane  101 , and ground plane extension  105  are formed thereon as metallic layers. 
   Substrate  102  is not limited to a single piece of substrate in various embodiments. In fact, substrate  102  can be made of two or more substrate portions, for example, with ground plane  101  disposed on one portion and antenna area  103  disposed on another portion and ground plane extension  105  connected to ground plane  101  through, for example, a soldered connection. 
     FIG. 3  is an illustration of an exemplary technique for connecting ground plane extension  105  to ground plane  101 . While it is possible to form ground plane  101  and extension  105  to be continuous, it is also possible to form such features to be separated by a gap. When ground plane  101  and extension  105  are separated by a gap, various techniques exist to make a connection therebetween. As shown in  FIG. 3 , ground plane extension  105  can be connected to ground plane  101  through lumped element  301  (e.g., a capacitor or inductive/capacitive element). Lumped element  301  provides additional matching and can tune the resonant frequency. Other techniques include, but are not limited to a trace, a soldered wire, and the like. 
     FIG. 4  is an illustration of system  100  with example resonant lengths marked. In this particular example, antenna element  104  is “L” shaped, with the horizontal part of a first resonant length that corresponds to a first frequency band, f 1 , and the vertical part of a second resonant length that corresponds to a second frequency band, f 2 . The perpendicular shape of antenna element  104  minimizes coupling between the f 1  and f 2  bands. 
   In this example, the proximity of the tip of the horizontal portion of antenna element  104  to extension  105  determines, at least in part, the amount of electromagnetic coupling that occurs between element  104  and the resonant structure formed by ground plane  101  and extension  105 . Generally, the greater the distance, the less the coupling, and as coupling between a ground and an antenna increases, the bandwidth of antenna  104  is narrowed. Thus, while it is desirable to minimize coupling to some extent, some amount of coupling is desirable for the capacitive feeding to occur. Similarly, the horizontal orientation of this portion of antenna element  104  reduces coupling since it is substantially orthogonal to the resonant length corresponding the f 3  band. 
   As shown, the length along the outside of the structure formed by ground plane  101  and extension  105  provides a third resonant length that corresponds to a frequency band f 3  that is lower than either f 1  or f 2 . In this example, the width at the top of extension  105  affects the resonant length such that a wider top portion lowers frequency band f 3 . The width at the bottom of extension  105 , like the length of the horizontal portion of element  104 , affects coupling between antenna element  104  and extension  105 . 
     FIG. 5  is an illustration of exemplary system  500  adapted according to one embodiment of the invention. System  500  includes dimensions for some features to aid in understanding the operation of a specific embodiment. The dimensions are approximately drawn to scale so that the width at the top and the bottom of the ground plane extension can be inferred within a reasonable degree of certainty. Also included in  FIG. 5  is frequency response graph  501  showing performance of system  500  in the RF spectrum starting below 3 GHz and extending above 6 GHz, which corresponds to a significant portion of the Ultra Wide Band (UWB) spectrum in some regions. As in nearly all antennas, the frequency response is dependent upon the resonant lengths of the various elements, and response graph  501  shows that the dimensions of an antenna adapted according to one or more embodiments of the invention can be designed to provide communication in a wide frequency band by overlapping f 1 , f 2 , and f 3  bands. In other embodiments, system  500  can be designed with other dimensions to provide communication in two or more distinct bands. 
   The dimensions in  FIG. 5  are for example only, and while system  500  is shown with specific dimensions and shapes, various embodiments of the invention are not limited thereto. In fact, a wide variety of shapes and configurations are possible.  FIGS. 6A and 6B  are illustrations of exemplary shapes for ground plane extensions  601  and  602 . For instance, ground plane extension  601  is similar to extension  105  ( FIG. 1 ), but its inside surface is curved to reduce coupling and amount of material. Extension  602  is “7” shaped and further reduces coupling and materials. 
     FIGS. 7A-D  are illustrations of exemplary shapes for antenna elements  701 - 704 . As shown the widths and lengths of the portions of elements  701 - 704  can vary greatly. Generally, as the length of a portion increases, so does its resonant length. Further, as the width increases, so does capacitive loading in general. Capacitive loading usually affects the electric field distribution of the antenna, making the antenna&#39;s electrical length longer for the overall physical dimensions, thereby lowering the resonant frequency(s) of the antenna. Still further, three-dimensional geometries can be adopted in some embodiments. For instance, while the previous examples have shown planar geometries for the antenna element and ground plane extension, it is possible to include bends in one or both to, for example, conform to volume constraints.  FIG. 8  is an illustration of exemplary three-dimensional geometry wherein portions of both antenna element  801  and ground plane extension  802  are bent so that one or more portions are not coplanar with the substrate.  FIG. 9  is an illustration of a raised geometry wherein both ground plane extension  901  and antenna element  902  are raised above the substrate. In addition to the geometries mentioned above, other characteristics, such as antenna position and signal feed placement can also be modified in some embodiments. 
     FIG. 10  is an illustration of exemplary method  1000  adapted according to one embodiment of the invention for operating an antenna system. Method  1000  may be performed, for example, by a cellular telephone, Personal Digital Assistant (PDA), laptop computer, or other kind of communication device. In step  1001 , a data signal is provided to an ungrounded antenna element. The data signal may contain, for example, digital or analog information modulated using one or more carrier waves in the RF spectrum. In one example, the ungrounded antenna is disposed on a PCB substrate, and the signal is provided to the ungrounded antenna element through a signal feed from a RF module that encodes and modulates the data. The RF module may or may not also be mounted on the same substrate. 
   In step  1002 , a second element electromagnetically coupled to the ungrounded antenna element is resonated, thereby transmitting data in an established communication band, wherein a resonant length of the second element includes at least portions of a ground plane and a projecting member of the ground plane. In other words, coupling with the ungrounded antenna element causes the structure formed by a ground plane and its extension to resonate at its native frequency, thereby transmitting the data. In this example, the data signal of step  1001  includes data at a frequency that corresponds to the native frequency of the structure formed by the ground plane and its extension. 
   In this way, the ground plane of the antenna system is optimized to resonate at a frequency that corresponds to an established communication band, thereby adding at least one frequency band to the antenna system. This can be utilized to create a system that provides performance over a plurality of bands. A particular example is the UWB spectrum that includes bands from 3.1 GHz to 10.6 GHz in the United States (and other bands in various countries). UWB performance can be facilitated, at least in part, by some embodiments of the invention which provide broadband communications from both an ungrounded antenna element and from the ground plane so that operation over a wider spectrum is achieved. 
   Other applications of various embodiments include providing antenna systems for wireless networking, e.g., for IEEE 802.11, or for advanced cellular handsets that use, e.g., various Global Systems for Mobile Communications (GSM) bands. In fact, because of the increased spectrum provided by optimizing the ground plane resonance with a ground plane extension, various embodiments can find use in a variety of high data rate communications applications now known or later developed. 
   Additional advantages of some embodiments include relatively cost-efficient production, especially in PCB designs, since the ground plane extension can be created with few extra steps (if any). In some embodiments, manufacturing a ground plane extension requires only etching a ground plane shape that includes a projection. Some embodiments are manufactured using other steps such as, for example, mounting a lumped element or soldering a connection between the ground plane and its extension. 
   Other advantages of some embodiments include increasing the number and/or size of radiating structures in an antenna system while incurring minimal increases in design volume. For instance, in some designs that include both a ground plane and a reserved antenna space, the extension can be disposed on the antenna space, thereby requiring a negligible difference in volume over that of a similar design without an ground plane extension. 
   A further advantage of some embodiments is apparent when compared to prior art antenna systems that use ground plane extensions as parasitic elements. In those prior art embodiments, a parasitic element extends from a ground plane and provides an extra resonance to the antenna system. The resonant length is due to the length of the parasitic only, such that the added resonance is the parasitic element&#39;s own resonance and tends to be quite narrow. However, various embodiments of the invention use a ground plane extension to create a resonant length that includes at least a portion of the length of the extension and a portion of the length of the ground plane, thereby using the ground plane plus its extension as a radiating structure. Typically, the result is that the added band is lower in frequency and much wider than a band added by a parasitic extension. 
   Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.