Abstract:
The present invention relates to antennas for radio signal frequencies, an electromagnetic shield and a mechanical package for electronic components. The antenna uses a three-dimensional conductive structure to enclose the components that are used for the transmission and reception of wireless devices. This conductive structure preferably encloses electronic components. The structure can be divided into two or more sections such that each section is enclosed providing shielding from external electromagnetic fields. Each conductive section is connected to the antenna port or ports of the device it contains. The conductive mechanical package is preferably sized to resonant at the desired frequency of operation. If the electromagnetic fields to be radiated are within and outside the package, the internal bulkheads can be used to control the desired resonant modes. Photonic band gap structures can be also used to connect the pole elements.

Description:
BACKGROUND 
     The present invention relates to antennas for radio signal frequencies, an electromagnetic shield, and a mechanical package for electronic components. 
     One of the fast growing segments of the computer industry today is wireless networks. Wireless networks avoid the cost of the wiring infrastructure, and permit computing mobility. Some of the more common wireless networks are based on the 802.11 standard, Bluetooth, cellular networks, i-mode, and WAP. Cell phones are in use nearly everywhere. Some standards such as 802.11, also known as wireless Ethernet or Wi-Fi, are also ubiquitous and can be found in many companies, offices, airports, and even coffee shops. With Wi-Fi you only need to be in range of a peer or a base station which connects the wireless network to a wired one. Thus, a person can carry Wi-Fi enabled personal digital assistant (PDA) or a notebook computer about without giving up his or her network connection. Bluetooth is another known wireless standard designed for interconnection of computing devices such as computer peripherals. 
     No matter what wireless standard is used, there is a fundamental need to increase antenna performance. Wireless devices emphasize compactness, however, which impacts performance. For example, if an embedded antenna is placed on a printed circuit board in close proximity to the ground plane or adjacent metal objects, the antenna performance will be degraded. The ground plane will reduce the antenna&#39;s radiation resistance, which lowers the antenna efficiency and adversely affects the antenna gain pattern. In addition, a completely shielded mechanical package will prevent the antenna from propagating the radio through the shield. Yet, the transceiver must be shielded from stray electromagnetic fields. The shield for the transceiver will also function as a ground plane in close proximity with the antenna. Again, this degrades the antenna performance. Further, the antenna performance generally increases with the length of the radiating elements of the antenna, but this means the printed circuit board will need to increase in size, which conflicts with the small size requirements of mobile devices. 
       FIG. 1A  illustrates how an embedded antenna  14  might be configured for a cell phone to try to address these problems. As shown, the printed circuit board  20  supports a set of electronic components such as the electronic component  22 . A mechanical package  10  encloses the printed circuit board  20 .  FIG. 1A  cuts away a portion of the mechanical package  10  to show the inside of the cell phone. The antenna  14  is adjacent to an area (indicated by dotted lines  12 ) where the ground plane is removed in the printed circuit board  20 . This removal avoids a ground plane in close proximity to the antenna  14 , which would interfere with the antenna pattern. The mechanical package  10  must be also non-conductive to avoid shielding the antenna  14 . Because the mechanical package  10  is non-conductive, a radiation shield  18  must enclose the RF transceiver chips  16 ,  17 , which are sensitive to stray electromagnetic radiation.  FIG. 1A  also cuts away the radiation shield  18  to show the RF transceiver chips  16 ,  17 . The antenna  14  must not be too close to electronic components on the printed circuit board  20  or to the radiation shield  18  to avoid affects on the antenna pattern. As a result of these constraints, the manufacturer will need to increase the size of the printed circuit board  20  and the mechanical package  10 . 
       FIG. 1B  illustrates how a protruding antenna  15  might be configured for a cell phone in another attempt to address these problems. The printed circuit board  20  again supports electronic components such as the electronic component  22 . A mechanical package  24  encloses the printed circuit board  20 , but is cut-away in  FIG. 1B  to show the inner arrangement. The antenna  15  is placed outside the mechanical package  24  so there is no longer the need to remove the ground plane of the printed circuit board  20  as indicated by the absence of dotted lines. The mechanical package  24  also can be conductive because it will no longer shield the antenna  15 . Further, if the mechanical package  24  is non-conductive, a radiation shield  18  must enclose the RF transceiver chips  16 ,  17 , which are sensitive to stray electromagnetic fields.  FIG. 1A  cuts away part of the radiation shield  18  to reveal the RF transceiver chips  16 ,  17 . However, these advantages are dampened because the protruding antenna  15  must now be small enough to avoid user discomfort, and more rugged since it is outside the protection of the mechanical package  24 . This raises the cost of the antenna  15  and limits suitable size and shapes of the antenna. 
     It would be desirable if an antenna could propagate electromagnetic radiation at frequencies of interest, shield against any stray electromagnetic radiation, save printed circuit space, reduce ground plane interference, and provide a rugged low cost mechanical package for the wireless device itself. 
     SUMMARY OF THE INVENTION 
     This invention uses a three-dimensional conductive structure to enclose the components that are used for the transmission and reception of wireless devices. This conductive structure preferably forms a mechanical package with the electronic components inside it. In one embodiment, the structure is divided into two or more sections by conductive bulkheads such that each section is completely enclosed providing shielding from external electromagnetic fields. Each conductive section is connected to the antenna port or ports of the device it contains. The conductive mechanical package is preferably sized to resonant at the desired frequency of operation The electromagnetic fields to be radiated can exist on the inside and outside, or just on the surface of the package. If the electromagnetic fields to be radiated are within and outside the package, internal bulkheads can be used to control the desired resonant modes. In another feature, photonic band gap ground plane printed circuit boards can be used to connect separated sections of the conductive structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  illustrates an antenna embedded in a mechanical package. 
         FIG. 1B  illustrates an external antenna protruding beyond the mechanical package. 
         FIG. 2  illustrates an embodiment of the antenna that also functions as a mechanical package and an electromagnetic shield. 
         FIG. 3A  is an elevation view of the antenna illustrated in  FIG. 2  showing an embodiment for wiring the components between the printed circuit boards. 
         FIG. 3B  is an end view of one pole element of the antenna shown in FIG.  3 A. 
         FIG. 4A  is an embodiment of an antenna with a photonic band gap structure. 
         FIG. 4B  magnifies part of the photonic band gap structure shown in FIG.  4 A. 
         FIG. 5  illustrates an embodiment of a dumbbell shaped antenna with cylindrical pole elements connected by an interconnect structure, which encloses a printed circuit board. 
         FIG. 6  illustrates an embodiment of a dumbbell shaped antenna with thin radiating disk pole elements connected by an interconnect structure, which encloses a printed circuit board. 
         FIG. 7  illustrates an antenna return loss that might be expected from the embodiment of the antenna shown in FIG.  2 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description includes the best mode of carrying out the invention. The detailed description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the claims. Each part, even if structurally identical to other parts, is assigned its own part number to help distinguish where the part appears in the drawings. 
       FIG. 2  shows an embodiment of an antenna  25  functioning as a mechanical package and an electromagnetic shield for the associated electronics. As shown  FIG. 2 , the antenna  25  is no longer mounted on a printed circuit board  30  or printed circuit board  38  as shown in FIG.  1 A. This expands available space on the printed circuit boards  30 ,  38  for added circuitry and electronic components such as the electronic components  28 ,  34 . The antenna  25  also no longer protrudes beyond the mechanical package, because the package is the antenna  25 . This reduces manufacturing costs by eliminating the cost of a separate conventional antenna and permits using conductive materials for the mechanical package shown here as combination of the pole element  26 , the pole element  36 , and the pole interconnect  32  without degrading the performance of antenna  25  by acting as a ground plane in close proximity. Because the antenna  25  is also the mechanical package, the invention permits an increase in the size of the radiating pole elements  26 ,  36 , without extending the structure of the antenna  25  beyond the shape of the mechanical package. This has advantages for wireless applications such as cell phones. The antenna  25  also fully encloses the printed circuit boards  30  and  38 , which permits the antenna  25  to act as an electromagnetic shield against stray electromagnetic radiation which can cause interference. 
     It can be understood by review of the specification that the antennas  25  can be made from a variety of materials including metals such as copper, aluminum, steel, or brass. In addition, the antenna  25  might be made from a metallized plastic, a conductive plastic, a conductive ceramic, a conductive composite, or any other suitable conductive materials useful for antennas, packaging and electromagnetic shielding of electronic components. 
     If the antenna  25  is made of a metal, the sides of the pole elements  26 ,  36 , can be sealed by metal fasteners, brazing, welding, soldering, etc. The material and techniques used will be guided by manufacturing requirements. For example, the thickness of the walls of the antenna  25  will be a function of the material, the characteristics of the antenna, the amount of electromagnetic shielding required, and the cost of the material. If the antenna material is a relative good conductor, for example, such as copper, the walls can be relatively thin. Conversely, if the material is a relatively poor conductor, such as steel, the walls will be necessarily thicker to achieve an adequate electromagnetic shield. 
       FIG. 2  depicts the pole elements  26  and  36  as hollow cubes, but they could be other closed surface figures. For example, the pole elements  26  and  36  might be a rectangular prism, a square pyramid, a cylinder, a right circular cone or a sphere, etc. However, whatever shape is selected, it is preferred that the pole elements  26  and  36  of the antenna  25  enclose the printed circuit boards  30  and  38  to shield against stray electromagnetic radiation reaching the electronic components. Further, as shown in  FIG. 2 , the length of the antenna  25  is preferably ≦λ/2, where λ is the wavelength of the radiation propagated by the antenna  25 . 
       FIG. 3A  is an elevation view of the antenna illustrated in  FIG. 2  showing an embodiment for wiring the components between the printed circuit boards. As shown, the interconnect  32  mechanically joins the pole element  26  to the pole element  36 . A solder joint  50  attaches one end of the interconnect  32  to the pole element  36 , while an insulator  46  spaces and holds the other end of the interconnect  32  in the hole in the pole element  26 . As an alternative, see  FIG. 2  where the end of interconnect  32  is substantially flush with the pole element  26 . The pole element  26  encloses the printed circuit board  30 , while the pole element  36  encloses a printed circuit board  38 . The interconnect  32  also protects and shields a set of wires represented by a data line  40  and a power line  42 . One end of the data line  40  electrically connects, e.g., by soldering it, to a pad  63  on the printed circuit board  30 . The other end of the data line  40  electrically connects to a pad  55  on the printed circuit board  38 . One end of the power line  42  electrically connects to a pad  62  on the printed circuit board  30 . The other end of the power line  42  electrically connects to a pad  57  on the printed circuit board  38 . The antenna  25  includes a low-side pole wire  65 , which is soldered to the interconnect  32  and to a low-side pad  61 . The antenna also includes a high-side pole wire  60 , which is soldered to the pole element  26  and to the high-side pad  59 . Upon review of the specification, it would be understood that different wiring configurations are possible. For example, there can be a different number of wires running inside the interconnect  32 , and the polarities could be reversed, and/or different techniques can be used to connect the wiring. 
       FIG. 3B  is an end view showing the insulator  46  spacing the interconnect  32  from touching the pole element  26  of the antenna shown in FIG.  3 A. 
       FIG. 4A  is an embodiment of an antenna with a photonic band gap structure  66 . The photonic band gap structure  66  rejects unwanted frequencies by acting as an electromagnetic shield as will be explained. The antenna is made as described in connection with  FIGS. 2 and 3A , but removes the opposite adjacent sides of the pole elements there to form the pole elements  70  and  72 . The pole elements  70  and  72  and the photonic band gap  66  enclose a single printed circuit board  71 , which in turn supports electronic components such as the electronic components  67  and  69 . In an alternative embodiment, the photonic band gap  66  can be replaced with an insulator, and the pole elements closed, that is, have six sides not five, and the interconnect  32  reintroduced as shown in FIGS.  2  and  3 A- 3 B. As discussed earlier, the length of the antenna is again preferably ≦λ/2, where λ is the wavelength of the radiation propagated by the antenna. 
       FIG. 4B  enlarges part (dotted lines  74 ) of the photonic band gap structure shown in FIG.  4 A. The photonic band gap  66  includes a periodic lattice structure of photonic band gap cells  76  and photonic band gap cell interconnects  78 . To the unwanted frequencies, the photonic band gap  66  conducts so that the pole element  70 , the pole element  72 , and the photonic band gap  66  together act as an electromagnetic shield. To the frequencies of electromagnetic wave that are to be transmitted and received by the antenna, the photonic band gap  66  functions as an insulator so that the antenna has functionally speaking no conducting structure between the pole elements  70  and  72 . 
     Sievenpiper et al., “High-Impedance Electromagnetic Surfaces with a Forbidden Frequency Band” (IEEE Trans. on Microwave Theory and Techniques, Vol. 47, No. 11, Nov. 1999) describe suitable photonic band gap structures that could be used, which article is incorporated herein by reference. This embodiment is particularly useful when a given application requires that the circuitry reside on a single printed circuit board  71  rather than on a set of physically separate printed circuit boards  30  and  38  as shown in FIG.  2 . 
       FIG. 5  is an embodiment of a dumbbell shaped antenna with hollow radiating cylindrical pole elements connected by an interconnect structure, which encloses a printed circuit board. The first pole element  83  includes a top face  82 , a side wall  80 , and a bottom face  96 . The second pole element  89  includes a top face  88 , a side wall  90 , and a bottom face  92 . The interconnect  94  mechanically joins the pole element  83  to the pole element  89 . The interconnect  94  also encloses a printed circuit board  84 , which supports electronic components such as an electronic component  86 . The antenna of  FIG. 5  is constructed similar to the antenna described in  FIG. 2 , but places the printed circuit board  84  in the interconnect  94 , which eliminates the need for the interconnect wiring shown in FIG.  3 A. Instead, the wiring preferably resides on or in the printed circuit board  84 . At the same time, this antenna still needs connection to the high-side and low-side transceiver outputs as discussed in connection with FIG.  3 A. The materials, the geometric shapes of the pole elements, and the manufacturing techniques would be as described in the specification accompanying FIG.  2 . Further, as shown in  FIG. 5 , the length of the antenna is preferably ≦λ/2, where λ is the wavelength of the radiation propagated by the antenna. 
       FIG. 6  illustrates an embodiment of a dumbbell shaped antenna with thin radiating disks connected by an interconnect structure, which encloses a printed circuit board. The antenna of  FIG. 6  is constructed similar to the antenna described in  FIG. 5 , but employs thin radiating disks for the pole elements, which can reduce the horizontal footprint of the antenna in certain applications. The antenna includes a radiating disk shaped pole element  100  and a radiating disk shaped pole element  106 . The interconnect structure  104  connects radiating disk shaped pole elements  100 ,  106 , and encloses printed circuit board  102  supporting components such as electronic component  108 . Again, the length of the antenna is preferably ≦λ/2, where λ is the wavelength of the radiation propagated by the antenna. 
       FIG. 7  illustrates the antenna return loss expected from an embodiment of the antenna as shown in FIG.  4 A. The dimensions of the antenna should be about 5 cm by 5 cm by 8 mm. In this antenna embodiment, an insulator replaces the photonic bandgap structure  66  shown in FIG.  4 B. Antenna return loss is the ratio of the signal power provided to the antenna to the signal power reflected by the antenna. The best possible return loss ratio is 1:1 which means no signal power is reflected by the antenna. The data shown should be obtainable using a Hewlett Packard 8753D Network Analyzer. The antenna should be at least three feet away from all objects that could affect the return loss, when the measurements are taken. The return loss curve as shown in  FIG. 7  is that expected of a typical resonant antenna, in this case the lowest return loss should be in the order of −41 dB (the return loss ratio in decibels expected as indicated by the HP 8753D analyzer).