Abstract:
An antenna grounding connection system is provided for wireless communication devices with two or more ground plane sections. A distance is maintained between an antenna feed and an electrical connection between the two ground plane sections. The distance is determined by the wavelength of the wireless communication signal. The distance should be at least one fifteenth of the wavelength of the wireless communication signal. In the case of a rectangular ground plane section, an antenna feed can be placed near one edge of the first ground plane section, and the electrical connection can be placed near an opposite edge of the first ground plane section.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to wireless communication and more particularly to systems and methods for antennas with multiple ground plane sections. 
     2. Background 
     Consumers are increasingly demanding smaller and smaller feature rich wireless communication devices, such as, for example, cellular telephones (hereinafter “cell phones”). One way to achieve a smaller cell phone with more functions and features is to produce a cell phone with two configurable housing portions. One such configuration is a flip phone. A flip phone opens up like a clam shell. Other such configurations are sliding phones and swivel phones. In a sliding phone, one portion of the cell phone housing slides relative to the other portion. In a swivel phone, one portion of the cell phone swivels open, relative to the other portion. A sliding phone is shown with respect to U.S. patent application Ser. No. 10/931,712, filed on Sep. 1, 2004, attorney docket number UTL 00372, the whole of which is hereby incorporated herein by reference. 
     Typically one configuration of the two housing portions is smaller than the other configuration. Typically, the smaller configuration is called the closed configuration and the larger configuration is called the open configuration. The cell phone user can keep the cell phone in the closed configuration when carrying the cell phone, or for storage. Then the cell phone can be put in the open configuration to be used. Some phones can be used in both configurations. 
     In some configurable cell phones, both housing portions have a ground plane. Ground planes effect the performance of any nearby (proximate) antenna. Specifically, an antenna might perform optimally with the cell phone in one configuration, but sub-optimally with the cell phone in the other configuration. The sub-optimal performance could be due to the positional change of one of the ground planes relative to the antenna. Especially, an antenna that depends heavily on the ground plane, such as a patch antenna or a planar inverted F antenna (PIFA), may perform poorly when a grounded metal is near the antenna in some configurations. 
     SUMMARY OF THE INVENTION 
     In order to overcome the problems associated with conventional approaches for providing compact antennas for wireless communication devices with two or more ground plane sections, a distance is maintained between the antenna feed and an electrical connection between the two ground plane sections. The distance is determined by the wavelength of the wireless communication signal. The distance should be at least one fifteenth of the wavelength of the wireless communication signal. 
     In the case of a rectangular ground plane section, an antenna feed can be placed near one edge of the first ground plane section, and the electrical connection can be placed near an opposite edge of the first ground plane section. 
     The antenna radiation efficiency is the efficiency of the antenna alone, that is, without considering the matching circuitry. In other words, radiation efficiency can be considered as the efficiency of the antenna when the antenna is assumed to have perfect match at all frequencies. Radiation efficiency improves dramatically as a result of moving the ground plane connection away from the antenna feed port. 
     Other aspects, advantages, and novel features of the invention will become apparent from the following Detailed Description of Preferred Embodiments, when considered in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the present inventions taught herein are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings, in which: 
         FIGS. 1–3  illustrate perspective views of antenna ground plane systems. 
         FIG. 4  illustrates a side view of an antenna ground plane system, in a first configuration. 
         FIG. 5  illustrates a side view of the antenna ground plane system shown with respect to  FIG. 4 , in a second configuration. 
         FIG. 6  is a graph showing measured radiation efficiency plotted against frequency for an antenna ground plane system with the electrical connection near the antenna feed port. 
         FIG. 7  is a graph showing measured radiation efficiency plotted against frequency for an antenna ground plane system with the electrical connection farther from the antenna feed port. 
         FIG. 8  is a graph showing measured radiation efficiency plotted against frequency for an antenna ground plane system with the electrical connection near the antenna feed port. 
         FIG. 9  is a graph showing measured radiation efficiency plotted against frequency for an antenna ground plane system with the electrical connection farther from the antenna feed port. 
         FIG. 10  is a graph showing simulated radiation efficiency plotted against frequency for an antenna ground plane system both with the electrical connection near the antenna feed port and with the electrical connection farther from the antenna feed port. 
         FIG. 11  is a graph showing simulated radiation efficiency plotted against frequency for an antenna ground plane system both with the electrical connection near the antenna feed port and with the electrical connection farther from the antenna feed port. 
         FIG. 12  illustrates a perspective view of a sliding antenna ground plane system, disassembled to show the various parts. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a perspective view of antenna ground plane system  100  for transmitting wireless communication signals over the air. System  100  includes a first ground plane section  102  and a second ground plane section  104 . The ground plane sections  102  and  104  are configurable, as will be described more fully below with respect to  FIGS. 4 and 5 . The ground plane sections  102  and  104  overlap partially, as can be seen with respect to  FIG. 1 . 
     Electrical connection  106  connects ground plane sections  102  and  104 . Antenna  108  is affixed to ground plane section  102 . Antenna feed port  110  is located distance  115  away from connection  106 . Distance  115  is empirically determined to be at least one fifteenth of the wavelength of the wireless communication signals that are transmitted over the air by system  100 . Alternately stated, the distance  115  should be at least one fifteenth of the wavelength corresponding to the first resonance of the antenna. For example, in the case of a quarter wavelength antenna, distance  115  is at least 1/15 times 4=0.267, times the electrical length of antenna  108 . 
     For example, the wireless communication signals may be U.S. cellular communications the U.S. cellular band between 824 MHz and 894 MHz. In that case, distance  115  is at least 2.35 cm. Advantageously, placing connection  106  at least distance  115  away from port  110  provides for greatly increased radiation efficiency for antenna  108 . Actual increased radiation efficiency measurements will be described later with respect to  FIGS. 6–9 . Increased radiation efficiency simulations will be described later with respect to  FIGS. 10–11 . 
     Feed port  110  may include a single connection to antenna  108 , such as in the case of a patch antenna. In that case, feed port  110  is not directly connected to ground plane section  102 . Ground plane section  102  is connected to first printed circuit board (PCB)  120 . Ground plane section  102  is shown external to PCB  120 , for illustrative purposes. Ground plane section may be internal to PCB  120 . For example, ground plane section  102  may be formed in one or more layers of PCB  120 . Further, ground plane section  102  may be formed by other means such as flex, metal cans and plated on a housing or structural portion. 
     Transceiver  125  is also connected to PCB  120 . Transceiver  125  is connected to feed port  110 . Wireless communication signals are generated by transceiver  125 , and passed through feed port  110  to antenna  108 . Antenna  108 , in conjunction with first and second ground plane sections  102  and  104 , radiates the wireless communication signals over the air. Ground plane section  104  is shown attached externally to second PCB  104 . Similar to ground plane section  102 , ground plane section  104  may be internal to PCB  105 . Alternatively, ground plane section  104  may be a small piece of metal such as, for example, an LCD back side or shield or, generally, a piece of metal known in the industry as a can. 
     Feed port  110  may include an antenna ground connection (now shown) as well. For example, the antenna may be a PIFA. A PIFA has a feed port  110  and an antenna ground connection (not shown). The antenna ground connection could be adjacent to feed port  110 . The antenna may be any other convenient type of antenna, such as, for example, a monopole antenna such as a stubby antenna, including a helical stubby antenna. 
     Antenna  108  may have long edge  130  and short edge  135 . In some cases, it is advantageous to position antenna  108  such that long edge  130  of antenna  108  is parallel to ground plane edge  140 . This arrangement produces antenna electrical current in a direction parallel to ground plane edge  140 . Advantageously, spacing ground plane connection  106  far from feed port  110  causes an increase in ground plane currents responsive to the antenna electrical current. The increased ground plane currents is indicative of increased radiation efficiency, which will be discussed more fully below with respect to  FIGS. 6–11 . 
     Radiation efficiency is also improved if ground plane connection  106  is a strong electrical connection, such as a metallic spring or screw. A strong metallic connection will be described more fully with respect to  FIG. 12 . In one embodiment ground plane connection  106  has a direct current (DC) electrical resistance less than one ohm. 
       FIG. 2  illustrates a perspective view of antenna ground plane system  150  for transmitting wireless communication signals over the air. In ground plane system  150 , ground connection  152  is near antenna feed port  154 . This configuration is disadvantageous compared to the arrangement of system  100  shown with respect to  FIG. 1 . System  150  does not radiate as efficiently as system  100 . 
       FIG. 3  illustrates a perspective view of antenna ground plane system  160  for transmitting wireless communication signals over the air. In system  160 , first ground plane section  163  and second ground plane section  166  are in the same geometrical plane, as can be seen in  FIG. 3 . Ground plane section  163  and  166  are connected by ground plane connection  169 . Ground plane section  163  and  166  are positioned apart from each other forming slot  175 . Slot  175  is located proximate to antenna  177  and parallel to a long edge  179  of antenna  177 . Advantageously, slot  175  serves to decrease the amount of ground plane near antenna  177 , increasing the radiation due to the fringing fields. 
       FIG. 4  illustrates a side view of ground plane system  100 , shown with respect to  FIG. 1 . Referring to  FIG. 4 , ground plane section  104  is connected to ground plane connection  106 . Ground plane connection  106  is connected to ground plane section  102 . Ground plane section  102  is proximate to feed port  110 , as described above with reference to  FIG. 1 . Referring again to  FIG. 4 , feed port  110  is connected to antenna  108 . 
       FIG. 4  is shown for comparison to  FIG. 5 .  FIG. 5  has all the same components as  FIG. 4 , but in  FIG. 5 , ground plane section  104  is in a lowered position, so that more of ground plane section  104  overlaps with ground plane section  102 . The configuration shown in  FIG. 4  can be called an open or “slide up” position. The configuration shown in  FIG. 5  can be called a closed or “slide down” position. As stated above with respect to  FIG. 1 , ground plane section  104  may interfere with antenna  108  radiation. Putting connection  106  in the position shown with respect to  FIG. 1  helps reduce the negative effects of ground plane  104  interfering with the radiation of antenna  108  when in the “slide up” position. In closed position, it can be advantageous to also have a connection at the bottom between the two boards. 
       FIGS. 6–9  are graphs of actual measured radiation efficiencies of an antenna with two different ground connection configurations.  FIGS. 6 and 7  show radiation efficiency in the U.S. cellular band.  FIG. 7  shows radiation efficiency with ground connection  106  far away from feed  110 , as shown with respect to  FIG. 1 .  FIG. 6  shows radiation efficiency with ground connection  152  closer to feed  154 , as shown with respect to  FIG. 2 . The measurements shown in  FIG. 6  were taken with a flex ribbon connector for ground connection  152 . The measurements shown in  FIG. 7  were taken with a solder connection for ground connection  106 . Thus, the measurements shown in  FIG. 7  were taken with improved ground connection placement relative to the feed and with a stronger electrical connection for the ground connection, as compared to the measurements shown in  FIG. 6 . 
     As can be seen by contrasting  FIGS. 6 and 7 , the improved electrical connection placement and electrical strength resulted in a relative efficiency improvement of about 50%, that is, from about 40% to about 60%, or 3 dB over some of the U.S. cellular band. At the lower edge of the band, at 824 MHz, the relative efficiency improvement is about 30%, from about 15% efficiency to about 20% efficiency. 
     The antenna tested for the measurements shown in  FIGS. 6–9  was a dual band PIFA. Its primary radiating mode is in the U.S. cellular band. Its secondary radiating mode is in the U.S. personal communication service (PCS) band between 1910 MHz and 1990 MHz.  FIGS. 8 and 9  show radiation efficiency for the same antenna in the U.S. PCS band.  FIG. 9  shows radiation efficiency with ground connection  106  far away from feed  110 , as shown with respect to  FIG. 1 .  FIG. 8  shows radiation efficiency with ground connection  152  closer to feed  154 , as shown with respect to  FIG. 2 . The measurements shown in  FIG. 8  were taken with a flex ribbon connector for ground connection  152 . The measurements shown in  FIG. 9  were taken with a solder connection for ground connection  106 . Thus, the measurements shown in  FIG. 9  were taken with improved ground connection placement relative to the feed and with a stronger electrical connection for the ground connection, as compared to the measurements shown in  FIG. 8 . 
       FIG. 10  shows a graph of simulations of radiation efficiency over a range of frequencies, including the U.S. cellular band. The antenna simulated for the simulations shown with respect to  FIG. 10  was a capacitively loaded PIFA. The simulations were made using the commercially available software, IE3D, by Zeland Software, Inc. The software uses the method of moment technique and is widely used for the simulation of planar antennas. Solid line  185  shows simulated radiation efficiency of a PIFA on a ground plane similar to that shown with respect to  FIG. 3 , having ground connection  169  and slot  175 . Dashed line  190  shows simulated radiation efficiency with a solid ground plane, as if ground plane sections  163  and  166  were extended, removing slot  175 , shown with respect to  FIG. 3 . 
       FIG. 11  shows a graph of simulations of radiation efficiency over a range of frequencies, including the U.S. cellular band and the U.S. PCS band. The antenna used for the simulations shown with respect to  FIG. 11  was also a capacitively loaded PIFA. The simulations were made using the commercially available software, IE3D, by Zeland Software, Inc. Dashed line  195  shows simulated radiation efficiency of a PIFA on a ground plane similar to that shown with respect to  FIG. 3 , having ground connection  169  and slot  175 . Solid line  200  shows simulated radiation efficiency with a ground plane connection  169  near antenna feed  172  and slot  175  farther from feed  172 , as if ground plane connection  169  was moved to the edge  182  of ground plane section  163  that is adjacent to feed  172 , shown with respect to  FIG. 3 . As can be seen by contrasting dashed line  195  and solid line  200 , the radiation efficiency is much better in the U.S. cellular and PCS bands with the connection  169  far from feed  172 . 
       FIG. 12  illustrates a perspective view of a sliding antenna ground plane system, disassembled to show the various parts. First PCB  205  contains first ground plane section (not shown) in one or more layers of first PCB  205 . First ground plane section is electrically connected to spring tab  210  through first screw  215  and rail  235 . Other screws  220 ,  225  and  230  are also shown. Screw  215  fastens spring clip  210  to rail  235 . Rail  235  is fastened to PCB  205  by a fifth screw (not shown) clamping rail  235  and PCB  205  between first front housing portion  240  and second front housing portion  245 . Rail  235  makes contact with a trace (not shown) on PCB  205 . 
     Spring tab  210  makes contact with a second trace (not shown) on the back of second PCB  250 . Second PCB  250  contains second ground plane section (not shown) in one or more layers of second PCB  250 . Second PCB  250  is clamped between first rear housing portion  255  and second rear housing portion  250  by four more screws (not shown). Advantageously, rail  235 , screw  215  and spring tab  210  form a strong electrical connection (at RF and DC) between first ground plane section and second ground plane section. The electrical connection formed between first and second ground plane sections has a DC resistance less than one ohm. The configuration described with reference to  FIG. 12  also allows for first and second ground plane sections to slide in position relative to one another. 
     Antenna  270  is a PIFA, having a feed connection  275  and a ground connector  280 . Feed connection  275  connects to antenna feed port (not shown) which is printed on second PCB  250 . Antenna ground connector  280  connects to antenna ground connection (not shown) which is printed on second PCB  250 . 
     Further, while embodiments and implementations of the invention have been shown and described, it should be apparent that many more embodiments and implementations are within the scope of the invention. Accordingly, the invention is not to be restricted, except in light of the claims and their equivalents.