Abstract:
A solar panel may be modified to function both as a solar panel and as a patch antenna. The use of combination solar cell and patch antenna allows for a greater amount of the upper surface of a device to be covered with solar panels, and may reduce the size and cost of the device. The ground layer of a printed circuit board in the device may be used as the ground plane of the patch antenna, further reducing the size and cost of the device.

Description:
RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of U.S. Provisional Application Ser. No. 60/841,434, filed Aug. 31, 2006, which is expressly incorporated herein by reference in its entirety. 
     
     BACKGROUND OF THE INVENTION 
       [0002]    1. The Field of the Invention 
         [0003]    The present invention relates to an improved antenna. More specifically, the present invention relates to an improved patch antenna which is integrated with a solar cell so as to provide both a solar cell and a patch antenna in a smaller space than would be occupied by both components separately. 
         [0004]    2. State of the Art 
         [0005]    An increasingly large number of electronic devices are now portable. Many advances allow for portable devices, including smaller and lighter electronics, electronics which use less power, improved batteries and power supplies, etc. These technological advances allow many types of electronic devices to operate without requiring wired connection to communications networks or power grids. 
         [0006]    By way of example, monitoring and control devices are able to monitor desired conditions, such as shipping conditions for a sensitive or valuable object, control the shipping conditions, transmit data regarding the shipment to a remotely located control facility, and can even track the location of the shipment using GPS (Global Positioning Satellite) technology. It is often advantageous that such a device be capable of operating without an outside source of power and capable of communicating with outside facilities and devices. 
         [0007]    It is desirable that such a device may operate without connection to an outside power source for extended periods of time. A solar cell is desirable for facilitating operation without an outside source of power. Batteries are often utilized, but the batteries capable of operating the device for extended periods of time (such as weeks or months) are typically much too large to be conveniently included in the device. Thus, solar panels are often used to power devices. Solar panels are often used in combination with batteries to provide energy to the device and to charge the batteries during the day and thereby extend the time period for which the device may operate. If the solar panel is large enough, the device may operate indefinitely. It is thus often desirable to have a solar panel which is large enough to meet the energy requirements of the device. 
         [0008]    Solar panels have a relatively low power output, which often means using as large of a solar panel as is possible to provide as much energy as possible. Solar panels provide the most energy when the panel faces upwardly and has a clear view of the entire sky, allowing light to be collected during as long of a time period as is possible. Thus, it is often desirable to cover most, if not all, of the upper surface of a device with a solar panel to provide as much power as is possible from the solar panel. 
         [0009]    It is also desirable to track the location of the device, and to communicate wirelessly with the device, such as through satellites. For example, GPS receivers allow for determination of the location of the device and thus allow for improved tracking and monitoring of the device. GPS systems require an antenna to communicate with the GPS satellites. A commonly used type of antenna is a patch antenna. A patch antenna is a flat rectangular antenna including an upper layer and a lower layer. Patch antennas for a GPS typically operate at a frequency of about 1.5 GHz. For best performance, the patch antenna should have a clear view of entire sky. 
         [0010]    For many devices, it is desirable to have both a solar panel and a patch antenna. The patch antenna may not be simply placed underneath a solar panel since the solar panel is made of conductive materials and shields radio frequencies. Thus, the solar panel and patch antenna compete for space on the top surface of the device. Inclusion of a patch antenna typically means the solar panel must be reduced in size, or the device must be made larger. Both of these alternatives are often undesirable as they would either reduce the available power or increase the bulk and cost of the device. 
         [0011]    There is thus a need for a patch antenna which overcomes the limitations of available antennas. Specifically, there is a need for a patch antenna which may be used in combination with a solar panel while allowing the solar panel to cover the entire usable top surface of a device so as to maximize the power available from the solar panel. 
       SUMMARY OF THE INVENTION 
       [0012]    It is an object of the present invention to provide an improved patch antenna. 
         [0013]    According to one aspect of the invention, a combination solar panel and patch antenna is provided. The combined solar panel and patch antenna may utilize the lower layers of a solar panel to form the upper layer of a patch antenna. Such a combination allows for a solar panel which is as large as possible, and which does not interfere with operation of the patch antenna. 
         [0014]    According to another aspect of the invention, the ground layer of a printed circuit board placed under the solar panel may form the ground plane of the patch antenna. Such a configuration eliminates the need for a separate ground layer for the patch antenna. 
         [0015]    These and other aspects of the present invention are realized in a combined solar panel and patch antenna as shown and described in the following figures and related description. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    Various embodiments of the present invention are shown and described in reference to the numbered drawings wherein: 
           [0017]      FIG. 1  shows a top view of a patch antenna of the prior art; 
           [0018]      FIG. 2  shows a side view of a portion of a patch antenna of the prior art; 
           [0019]      FIG. 3  shows a side view of a portion of a patch antenna of the prior art; 
           [0020]      FIG. 4  shows a side view of a solar panel of the prior art; 
           [0021]      FIG. 5  shows a bottom view of a solar panel; 
           [0022]      FIG. 6  shows a bottom view of a solar panel used in accordance with the present invention; 
           [0023]      FIG. 7  shows a side view of a portion of a patch antenna of the present invention; 
           [0024]      FIG. 8  shows a top view of a portion of a patch antenna of the present invention; and 
           [0025]      FIG. 9  shows a side view of a patch antenna of the present invention. 
       
    
    
       [0026]    It will be appreciated that the drawings are illustrative and not limiting of the scope of the invention which is defined by the appended claims. The various embodiments shown accomplish various aspects and objects of the invention. It is appreciated that not all aspects of the invention may be clearly shown in a single figure. Thus, multiple figures may be used to illustrate the various aspects of a single embodiment of the invention. 
       DETAILED DESCRIPTION 
       [0027]    The invention and accompanying drawings will now be discussed in reference to the numerals provided therein so as to enable one skilled in the art to practice the present invention. The drawings and descriptions are exemplary of various aspects of the invention and are not intended to narrow the scope of the appended claims. 
         [0028]    Turning now to  FIG. 1 , a top view of a patch antenna  10  of the prior art is shown. A patch antenna  10  includes conductive active element  14  which is rectangular in shape. The active element  14  is spaced above and parallel to another rectangular conductive ground plane  18 . Standoffs  22  are often used to separate the active element  14  and the ground plane  18 , using the air between the active element and the ground plane as the dielectric. Alternatively, another dielectric material may be used between the active element  14  and the ground plane  18 . A signal line is attached to the signal feed point  26  and a ground line is attached to the ground plane  18 , and a signal is developed between the signal line and the ground line. 
         [0029]    The dimensions of the active element  14  and ground plane  18 , the spacing and dielectric material, if any other than air is used, between the active element and ground plane, location of the feed point  26 , feed line impedence, etc. all determine the operating parameters of the antenna  10 . It is desirable to receive signals from all directions above the patch antenna  10 . Design of ordinary patch antennas is understood in the art. For a GPS receiver operating at about 1.5 GHz, a ground plane  18  measuring 124 mm wide by 133 mm long and an active element  14  measuring 83.5 mm wide by 92.4 mm long which has a feed point located 23.5 mm in from the width edge and 29.8 mm in from the length edge, and attached to the ground plane at the corners by standoffs  22  located 7 mm in from the edges with a spacing of 5 mm between the active element and ground plane may optimum dimensions. Different frequencies, different dielectric materials, etc. will typically change the dimensions and design parameters. 
         [0030]    An air dielectric typically results in the broadest overhead reception, but also results in the largest antenna. Thus, the antenna providing the best reception to a GPS receiver is also the largest antenna, resulting in the greatest reduction of the amount of space remaining for a solar panel. The reduction in size of the solar panel reduces the power output of the panel, requiring the device to carry additional batteries or reducing the time frame during which the device may function without connection to a power source. 
         [0031]    Turning now to  FIG. 2 , a side view of a portion of the prior art patch antenna of  FIG. 1  is shown. It can more clearly be seen how the standoff  22  is used to create a space between the active element  14  and the ground plane  18 . For the dimensions discussed above, the spacing is typically about 5 mm. The standoff  22  should electrically isolate the active element  14  from the ground plane  18 . As such, a small nylon bolt may be used for the standoff, with plastic washers or spacers  34  used to maintain the desired spacing. Many other materials are suitable for use as standoffs. 
         [0032]    Turning now to  FIG. 3 , a side view of the feed point  26  of the prior art patch antenna of  FIG. 1  is shown. The feed point  26  on the active element  14  is soldered to a wire  38 , typically the center conductor of a shielded antenna wire. The wire  38  often passes through a hole  42  in the ground plane  18 . The ground shield  46  of the antenna wire is connected to the ground plane  18 . 
         [0033]    Turning now to  FIG. 4 , a side view of a solar panel  50  of the prior art is shown. The solar panel includes a conductive lower layer  54  which forms the positive terminal, a p-type semiconductor layer  58 , a junction  62 , an n-type semiconductor layer  66 , and a transparent conductive layer  70  forming the negative terminal. Often, solar panels include several discrete sections of solar cells connected in series to thereby increase the voltage of the solar panel. 
         [0034]    Turning now to  FIG. 5 , a bottom view of a solar panel is shown. According to the present invention, the conductive lower layer  54  of the solar panel may be used as the active element of a patch antenna. The lower layer  54  is shown as including multiple sections  78   a - 78   e.  The individual sections  78   a - 78   e  result from having five separate sections of solar cells connected in series to form the solar panel. 
         [0035]    The lower layer  54  may be used to directly form an active element of a patch antenna if the conductivity of the lower layer is sufficiently good at the desired operating frequency and if the insulating barrier between any series connected plates has sufficient capacitance. If needed, a thin copper sheet or other conductive sheet may be attached to or placed directly underneath the solar panel. Such a conductive sheet may be used to improve the effectiveness of the antenna. 
         [0036]    Turning now to  FIG. 6 , a bottom view of a solar panel used as an active element is shown. It will be appreciated that the lower layer  54  of the solar panel is often not the optimum size for a patch antenna. Several solutions to this problems may be used. A custom solar panel which is the desired active element size may be used. Alternatively, a ferrite bar  86  may be clamped or glued to the back of the solar panel to reduce the size of the portion of the solar panel lower layer  54  which will effectively receive the RF signals. It is understood that the ferrite bar shown here may be used with any of the embodiments of the present invention. Additionally, the available size of solar panel may be used, allowing the lower layer  54  to function as the active element by optimizing the remaining design parameters to the size of the lower layer used as the active element. Such may include changing the real and imaginary feed point impedence, location of the feed point, spacing to the ground plane, dielectric material, etc. 
         [0037]    Antenna modeling programs, such as NEC2 (distributed at http://www.nec2.org), may be used to calculate what the feed line impedance should be for a given active element dimension, feed point location, and ground plane spacing. 
         [0038]    Turning now to  FIG. 7 , a side view of a portion of a patch antenna of the present invention is shown. In a typical patch antenna, the feed line is soldered to the active element in the desired location. In using a solar panel  50  for the active element  14 , soldering may not always work as an attachment method. Many solar panels  50  use thin lower layers  54  which are covered by thin insulating layers. It can be difficult to remove the insulating layer and solder or otherwise connect the feed line to the lower layer  54  without damaging the lower layer. 
         [0039]    The feed line can be capacitively connected to the lower layer  54  by placing a small capacitive plate  94  adjacent the lower layer  54 . The capacitive plate  94  need not be soldered or directly connected to the conductive lower layer  54 , as the insulating layer on the lower layer  54  is typically thin enough that the signals are effectively transferred to the capacitive plate  94 . The capacitive plate  94  is typically attached to a spring arm  98 , spring, or other means which presses the capacitive plate against the lower layer  54 , and which is then connected to the signal wire. 
         [0040]    Turning now to  FIG. 8 , a top view of a portion of the ground plane and the capacitive plate of  FIG. 7  is shown. The capacitive plate  94  is shown as round, but other shapes may work equally well. The spring arm  98  is typically made relatively short so as to provide good contact between the lower layer  54  and the capacitive plate  94 . As such, the spring arm  98  often passes through a hole  102  in the ground plane  18 , and is insulated sufficiently to be electrically isolated from the ground plane. 
         [0041]    Alternative arrangements exist which are equally effective in connecting a signal wire to the lower layer  54 . The signal wire may be soldered to the lower layer  54  if the lower layer permits soldering thereto. Alternatively, a small spring or post may be placed below the feed point such that the spring or post is placed in electrical communication with the lower layer  54 . A spring or post with a capacitive plate  98  may be used, or the spring or post may directly contact the lower layer and not need a capacitive plate. 
         [0042]    Turning now to  FIG. 9 , a side view of a patch antenna of the present invention is shown. The patch antenna includes the various aspects and details shown in  FIGS. 5-8 , and shows additional details of a completed antenna. As discussed, the lower layer  54  of a solar panel  50  is used to form the active element  14  of the patch antenna. A thin metal sheet or foil  106  may be used if necessary to improve the RF conductivity or the coupling of separate plates of the lower layer  54 . The active element  14  is parallel to the ground plane  18 . 
         [0043]    The feed point  26  of the antenna is connected to the signal wire  38 . The signal wire may be connected to the active element  14  via a capacitive plate  94  and spring arm  98  as has been discussed. Such a connection allows for easy removal of the solar panel  50  if necessary, as the capacitive plate  94  need not be soldered to the active element  14 . Other connection members may be used, such as a soldered wire, spring or post, or a spring or post with a capacitive plate. The signal wire  38  or spring arm  98  may pass through a hole  102  in the ground plane  18 . 
         [0044]    If desired, a ferrite bar  86  may be used to limit the size of the active element  14 . Alternatively, the remaining parameters of the patch antenna such as the feed point location may be adjusted to compensate for the size of the active element  14 . 
         [0045]    The ground shield  46  of the signal wire is connected to the ground plane  18 . The ground layer of a printed circuit board  106  may be used to form the ground plane  18 . Such is advantageous as it eliminates the need for a separate ground plane, saving cost and allowing the device to be more compact. It is desirable that the ground layer of the circuit board  106  be relatively continuous. It is believed that if the ground layer has too many holes or gaps that signal quality may begin to diminish. If the ground layer of a circuit board  106  is used as the ground plane  18 , it is desirable (but not required) that circuit board is placed so that the electronic components  1   10 , such as resistors and capacitors, are not placed between the active element  14  and the ground plane  18 . A number of electronic components  110  between the active element  14  and the ground plane  18  may interfere with signal quality, or may alter the dielectric constant of the material between the ground plane and active element. 
         [0046]    Analysis has shown that the majority of the high frequency currents from the patch antenna flow on the surface of the active element  14  which faces the ground plane  18  and vice versa. Thus, the operation of the patch antenna should have little effect on the DC current and operation of the solar panel  50  and the operation of the circuit board  106 . If the circuit board  106  contains sensitive devices which may be affected by the high frequency signals from the patch antenna, filters may be used to isolate these devices. Alternatively, a ground plane  18  separate from the circuit board  106  may be used. 
         [0047]    There is thus disclosed an improved combined solar panel and patch antenna. It will be appreciated that numerous changes may be made to the present invention without departing from the scope of the claims.