Patent Publication Number: US-7595757-B2

Title: Electrical connection elements provided in the AMC structure of an antenna arrangement

Description:
TECHNICAL FIELD OF THE INVENTION 
   The present invention relates to antennas and, more particularly, to an antenna arrangement for portable communication devices, as well as a portable communication device including an antenna arrangement. 
   DESCRIPTION OF RELATED ART 
   There is a trend within the field of portable communicating devices, and especially within the field of cellular phones to have the main communication antenna built-in in the phone. Such phones are also becoming increasing compact, with a need for optimal use of space available in the phone. Accordingly, a need exists to make antennas smaller and reduce the antenna volume as much as possible. However, when this is done, the performance of the antenna is typically degraded. 
   Recently, research has been conducted in the field of artificial magnetic conductor (AMC) materials for use in antennas. An AMC material is a metallic electromagnetic structure that has a high surface impedance. It is implemented through the use of two- or three-dimensional lattice structures of metal or dielectric objects. Such objects may be formed as plates connected to a solid ground layer using conducting vias. The AMC structure does not support propagating surface waves for certain frequency bands. This type of structure is, for instance, described by Sievenpiper et al. in “High-Impedance Electromagnetic Surfaces with a Forbidden Frequency Band,” in IEEE Transactions on Microwave Theory and Techniques, Vol. 47, No. 11, November 1999. 
   These types of surfaces are referred to as electromagnetic band gap (EBG) surfaces and photonic band gap (PBG) surfaces. 
   The evolution of such surfaces allows a considerable reduction of the profile of an antenna. Investigations in this regard have, for instance, been made by Alexandros P. Feresidis et al. in “Artificial Magnetic Conductor Surfaces and Their Application to Low-Profile High-Gain Planar Antennas,” in IEEE Transactions on Antennas and Propagation, Vol. 53, No. 1, January 2005. 
   How to design a material with regard to a frequency band is described by George Gousettis et al. in “Tailoring the AMC and EBG Characteristics of Periodic Metallic Arrays Printed on Grounded Dielectric Substrate,” in IEEE Transactions on Antennas and Propagation, Vol. 54, No. 1, January 2006. 
   However, most of the literature is directed to large antennas, in terms of wavelengths, for example, scaled for use in cellular base stations, and not for use in portable communication devices and cellular phones in which small terminal antennas are utilized and the performance challenges associated with these types of devices. 
   The use of such a material in a cordless phone has been described by Romulo F. Jimenez Broas et al. in “A High-impedance Ground Plane Applied to a Cellphone Handset Geometry,” in IEEE Transactions on Microwave Theory and Techniques, Vol. 49, No. 7, July 2001. In a handset described therein, a part of the ordinary circuit board is provided with an AMC structure, and the document thus suggests placing an antenna side-by-side with other components of such a cordless handset. This type of implementation of these surfaces does not, however, resolve the issues with high current distributions on the printed circuit board itself. 
   Accordingly, a need exists for advantageous uses of an AMC material relative to a portable communication device to, among other things, reduce the size, provide superior broadband properties, as well as for influencing the directivity. 
   SUMMARY OF THE INVENTION 
   Implementations of the present invention are generally directed to providing an improved AMC material relative to a portable communication device and antennas in such a portable communication device. 
   According to a first aspect of the present invention, an antenna arrangement is arranged for provision in a portable communication device and including: 
   a radiating antenna element, and 
   a grounding layer comprising an AMC material structure facing the radiating antenna element, which AMC material structure includes at least one layer of patches and a smooth conducting layer, the AMC material structure further including electrical connection elements that selectively interconnect patches in a layer with other elements of the AMC structure. 
   A second aspect of the present invention is directed to an antenna arrangement including the features of the first aspect, in which at least some of the patches in the layer are connected to the smooth conducting layer using conducting vias. 
   A third aspect of the present invention is directed to an antenna arrangement including the features of the second aspect, including at least one further layer of patches. 
   A fourth aspect of the present invention is directed to an antenna arrangement including the features of the third aspect, in which patches in at least one further layer are floating electrically. 
   A fifth aspect of the present invention is directed to an antenna arrangement including the features of the second aspect, in which elements for at least one layer of patches are provided in vias between the patches of a layer and the smooth conducting layer. 
   A sixth aspect of the present invention is directed towards an antenna arrangement including the features of the first aspect, in which elements for at least one layer of patches are provided in the layer and selectively interconnect patches in this layer. 
   A seventh aspect of the present invention is directed towards an antenna arrangement including the features of the first aspect, in which the elements are passive elements in the form of filters that connect the patches with other elements based on frequency. 
   An eighth aspect of the present invention is directed towards an antenna arrangement including the features of the first aspect, in which the elements are active elements in the form of switches. 
   A ninth aspect of the present invention is directed towards an antenna arrangement including the features of the eighth aspect in which the switches can be operated from fully closed to fully open positions and occupy partially open positions in-between. 
   A tenth aspect of the present invention is directed towards an antenna arrangement including the features of the eighth aspect, in which the switches can be controlled through application of electrical signals. 
   An eleventh aspect of the present invention is directed towards an antenna arrangement including the features of the eighth aspect in which the switches can be controlled through application of optical signals. 
   According to a twelfth aspect of the present invention, a portable communication device is provided comprising: a radiating antenna element, and a grounding layer comprising an AMC material structure facing the radiating antenna element, which AMC material structure includes at least one layer of patches and a smooth conducting layer, the AMC material structure further comprising electrical connection elements that selectively interconnect patches in a layer with other elements of the AMC structure. 
   A thirteenth aspect of the present invention is directed towards a portable communication device including the features of the twelfth aspect, in which at least some of the patches in the layer are connected to the smooth conducting layer using conducting vias. 
   A fourteenth aspect of the present invention is directed towards a portable communication device including the features of the thirteenth aspect, further comprising at least one further layer of patches. 
   A fifteenth aspect of the present invention is directed towards a portable communication device including the features of the fourteenth aspect, in which patches in at least one further layer are floating electrically. 
   A sixteenth aspect of the present invention is directed towards a portable communication device including the features of the thirteenth aspect, in which elements for at least one layer of patches are provided in vias between the patches of the layer and the smooth conducting layer. 
   A seventeenth aspect of the present invention is directed towards a portable communication device including the features of the twelfth aspect, in which elements for at least one layer of patches are provided in the layer and selectively interconnect patches in this layer. 
   An eighteenth aspect of the present invention is directed towards a portable communication device including the features of the twelfth aspect, in which the elements are passive elements in the form of filters that connect the patches with other elements based on frequency. 
   A nineteenth aspect of the present invention is directed towards a portable communication device including the features of the twelfth aspect, in which the elements are active elements in the form of switches. 
   A twentieth aspect of the present invention is directed towards a portable communication device including the features of the nineteenth aspect, in which the switches can be operated from fully closed to fully open positions and occupy partially open positions in-between. 
   A twenty-first aspect of the present invention is directed towards a portable communication device including the features of the nineteenth aspect, in which the switches can be controlled through application of electrical signals. 
   A twenty-second aspect of the present invention is directed towards a portable communication device including the features of the nineteenth aspect, in which the switches can be controlled through application of optical signals. 
   A twenty-third aspect of the present invention is directed towards a portable communication device including the features of the twelfth aspect, in which it is a cellular phone. 
   The invention has a number of advantages. The profile of the antenna arrangement can be made very low that allows the provision of slimmer portable communication devices. The invention furthermore allows the coverage of a broader frequency band and/or provision of directivity and thus the power of the portable communication device is used in a more efficient way. 
   It should be emphasized that the terms “comprises/comprising” and/or “includes/including,” when used herein, generally denote the presence of stated features, integers, steps or components, but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described in more detail relative to the enclosed drawings, in which: 
       FIG. 1  shows a top view of one exemplary lattice structure for an AMC material in which systems and methods described herein may be implemented; 
       FIGS. 2A  and B schematically show side views of the structure of the AMC material for one exemplary structure provided with electrical connection elements according to the principles of the present invention; 
       FIG. 3  shows another AMC structure in which electrical connection elements may be provided; 
       FIG. 4  shows a front view of a portable communication device in which systems and methods described herein may be implemented; 
       FIG. 5  schematically shows a top view of an antenna over an AMC material structure together with a circuit board; and 
       FIGS. 6A  and B schematically shows various electrical configurations in which systems and methods described herein may be implemented. 
   

   DETAILED DESCRIPTION OF EMBODIMENTS 
     FIG. 1  schematically shows a top view of an artificial magnetic conductor (AMC) material structure, according to one implementation. An AMC material structure  10  may include a substrate  14  of dielectric material, for example, and a number of patches  12  of electrically conducting material organized in a symmetrical structure that may include a lattice structure. In  FIG. 1 , each patch  12  is shown as being quadratic. This is just one example of such a patch shape. The patches may have any suitable shape, for instance, in the form of concentric rings or have pentagonal, hexagonal, octagonal, or other regular or irregular shape. It should be appreciated that the lattice structure can be varied in many ways. The patches may have different sizes and shapes between layers or within each layer, for example, to allow wideband or multi-band characteristics. Some, all, or none of patches  12  of the layer may connect to an underlying smooth conducting layer using, for example, a vertical conducting via(s). 
     FIG. 2A  shows AMC material structure  10  that may include a single layer of patches  12 , which may be suitable for use relative to antennas operating at a high frequency band. This structure is also shown to more clearly show the relationship between elements of the present invention. Patches  12  may be provided substantially normally on an exposed surface of substrate  14 , through which vias  16  may extend from patches  12  to a conducting layer  18  that may be substantially planar. When AMC material structure  10  is used as ground for an antenna, conducting layer  18  may connect to ground. AMC material structure  10  may not support propagating surface waves in the frequency band for which it is designed, since AMC material structure  10  may possess a high surface impedance in the subject band. These types of surfaces may be referred to as electromagnetic band gap (EBG) surfaces or photonic band gap (PGB) surfaces. The system of patches and vias, which together may generate the band gaps for surface waves at the designed frequencies, may also generate an effective capacitance and inductance. This capacitance and inductance may help to reduce the design frequency of the combined system of antenna and AMC surface relative to the antenna and patch sizes. The profile of antennas may be thereby be reduced. 
   AMC material structure  10  may include a number of electrical connection elements or switches  20 . In one embodiment of the present invention, electrical connection elements  20  may be disposed in a same layer in which patches  12  are disposed. At least some of electrical connection elements  20  may selectively interconnect ones of patches  12  to other ones of patches  12 , for example, in a same layer. In one embodiment of the present invention, ones of electrical connection elements  20  function as a switch which selectively connects ones of patches  12  to other ones of patches  12 . As previously mentioned, some, all, or none of patches  12  of a layer may be connected to conducting layer  18  using vias  16 . Ones of patches  12  that are not connected to conducting layer  18  may “float,” in an electrical sense. Each of patches  12  in a layer need not be interconnected with ones of electrical connection elements  20 . 
     FIG. 2B  shows AMC material structure  10  according to another embodiment of the present invention, in which electrical connection elements  20  are not provided between patches  12  in a same layer, but in an area with vias  16  that may connect to patches  12 . Ones of electrical connection elements  20  may selectively interconnect ones of patches  12  to conducting layer  18 . It should be appreciated that all, some, or none of patches  12  may be associated with ones of electrical connection elements  20  provided in an area of ones of vias  16 . 
   The present technology of mobile phones or handsets has reached a certain standard of dimensions of such devices and they continue to be produced increasingly smaller. For such dimensions, it becomes evident that AMC material structure  10  of  FIGS. 2A and 2B  is suited for high frequencies, and operatively in the order of several GHz. To enable use of AMC material structure  10  at lower frequencies, for instance, GSM frequencies at around 800 MHz, AMC material structure  10  can be varied. 
     FIG. 3  shows an implementation in which AMC material structure  10  may be varied for obtaining the above-mentioned properties in lower bands.  FIG. 3  shows AMC material structure  10  including three layers of patches  12 ,  22 ,  24 . Patches  12 ,  22 ,  24  may be provided vertically arranged relative to each other, the lattice structure of intermediate layers having been shifted relative to each other so that ones of patches  12 ,  22 ,  24  of one layer may be provided in gaps between ones of patches  12 ,  22 ,  24  of an adjacent layer. It should be appreciated that ones of patches  12 ,  22 ,  24  of adjacent layers may overlap each other. 
   As can be seen in  FIG. 3 , AMC material structure  10  may include patches  22  in a bottom layer of substrate  14  having a certain lattice structure may connect to conducting layer  18  using vias  26 , and an intermediate layer of patches  12  with a substantially same lattice structure but shifted in a horizontal direction. Patches  12  of the intermediate layer may connect to conducting layer  18  using vias  16 . AMC material structure  10  may include a top layer of patches  24  with a substantially same lattice structure and having patches  24  that may align with patches  22  of the bottom layer. 
   In the arrangement described, vias  26  associated with the bottom layer of patches  22  may traverse through substrate  14  from ones of patches  22  to ones of patches  24  of the top layer. Substrate  14  may provided between the top layer of patches  24  and conducting layer  18  and surround the bottom and intermediate layers of patches  22  and  12 . Using this arrangement, where it is possible to add N layers of patches (e.g., patches  12 ,  22 ,  24 ) over each other, and varying the sizes and shapes of the patches e.g., patches  12 ,  22 ,  24 ), it is possible to obtain a lower frequency band where AMC material structure  10  may be used. It is also possible to vary the lattice structure and distances between patches in the lattice structure. It is also possible to have some or all patches  12 ,  22 ,  24  of a layer “floating” and not connected to conducting layer  18 . 
   It should be noted that patches  22  and  24  need not be aligned, and a single dielectric material need not be used throughout substrate  14 . That is, substrate  14  may include strata of two or more types of material. In some embodiments, AMC material structure  10  of  FIG. 3  may include a first dielectric material between conducting layer  18  and the bottom layer of patches  22 , a second dielectric material between the bottom layer of patches  22  and the intermediate layer of patches  12 , and a third dielectric material between the top layer of patches  24 , and the intermediate layer of patches  12 . The above-described alignment using a single material used in substrate  14  may reduce the complexity in manufacturing AMC material structure  10 . 
   In other embodiments, patches  12 ,  22 ,  24  within the same layer of patches  12 ,  22 ,  24  may have shapes that differ, and/or patches  12 ,  22 ,  24  in different layers may have shapes that differ. In other embodiments, ones of patches  12 ,  22 ,  24  may be parasitic and disposed in one or more of the layers of patches  12 ,  22 ,  24 , i.e., unconnected to conducting layer  18   
   The above-described principles of providing electrical connection elements  20  described relative to  FIGS. 2A and 2   b  may be applied to methods and systems described herein to AMC material structure  10  shown in  FIG. 3 , i.e., being disposed in a layer of patches  12 ,  22 ,  24  and interconnecting patches  12 ,  22 ,  24  therein, or be provided in vias  16 ,  26 . 
   Implementations of AMC material structure  10  may allow the profile of an antenna to be lowered, which is of interest with regard to portable communication devices, particularly, cellular phones, where constant efforts are being made to reduce the size of the phone together with an effort to provide increased functionality of a phone or mobile terminal. 
     FIG. 4  shows a top view of a portable communication device  28  in the form a cellular phone. Different functional units of portable communication device  28  may be disposed inside a casing or housing  29 , which, on a front side, may be provided with openings through which a display  30  and a keypad  32  may be provided. The front side of casing  29  may be bounded by a left long side, a right long side, a top short side, and a bottom short side, which sides may be provided at essentially right angles to the front side. Opposite of the front side, a back side (not shown) may be provided, which may be bounded by the left long side, the right long side, the top short side, and the bottom short side. In this manner, casing  29  may form a box-like structure, within which the different components and units of phone  28  may be disposed. An antenna arrangement according to the principles of the present invention may be implemented within casing  29  and near the back side of phone  28 . 
     FIG. 5  schematically shows a top view of a circuit board  34  that may include a section of AMC material structure  10  having electrical connection elements  20  arranged substantially as described above. Over AMC material structure  10 , a radiating antenna element  36  may be disposed. AMC material structure  10  may face radiating antenna element  36 . A small gap may be disposed between AMC material structure  10  and radiating antenna element  36 . Radiating antenna element  36  and AMC material structure  10  together may form an antenna arrangement according to implementations of the present invention. 
   Circuit board  34  may be provided to allow for attachment to a number of components. It may also include a ground plane providing a ground potential. Conducting layer  18  of AMC material structure  10  may, according to implementations of the present invention, connect to a ground potential, which may be provided by such a ground plane. Radiating antenna element  36  may be provided in the form of pieces of sheet metal provided on a substrate. Radiating antenna element  36  may be provided through etching or other suitable placing of conductive plates and strips on a substrate, which substrate may include a dielectric material. The substrate may be provided on top of AMC material structure  10 . Conducting layer  18  of AMC material structure  10  may be grounded. AMC material structure  10  may form a grounding layer of the antenna arrangement. 
   The use of AMC materials has other advantages, for example, allowing the antenna to be placed closer to the circuit board than other structures, thus allowing the provision of slimmer phones. 
   As mentioned above, electrical connection elements  20  in AMC material structure  10  may include switches. The switches may be MEMS switches, transistors, or other switch types. 
     FIG. 6A  shows an exemplary arrangement in which electrical control lines may be provided for switches  20  that are located in the same layer as patches  12 .  FIG. 6A  shows a plan view of a layer of patches  12  arranged in a matrix of rows and columns, for example, two rows and three columns are shown. A grid of control lines  27  may be provided in the layer in which patches  12  are provided. A first vertical line may control switches  20  between patches  12  in a first column and a second column, and a second vertical line may control switches  20  between patches in the second and a third column, while a horizontal line may control switches  20  between patches  12  in a first and a second row. So arranged, it is possible to provide for control of all or some switches  20  provided in a layer. In other embodiments, the substantially same type of structure may be provided for switches  20  located in vias  16 , such that the electrical control lines are provided in a layer where the switches  20  are provided instead of the patches  12 . 
     FIG. 6B  shows a side view of another embodiment of a control structure for switches  20  in a layer.  FIG. 6B  only shows two patches  12  interconnected by switch  20 . The principles shown in  FIG. 6B  may be applied to one or more layers of patches  12  of an AMC control structure. Here, electrical control line  27  for switch  20  may be arranged in a layer underneath the layer including patches  12  and switches  20 . 
   Switches  20  in  FIGS. 6A and 68  may be electrically controlled, i.e., controlled by electrical signals. However, it will be appreciated that they may alternatively be optically controlled, i.e. controlled by optical signals. Other control techniques may be used. 
   According to one embodiment of the present invention, switches  20  may be either operated to a fully open or a fully closed position, which means that in some AMC material structures  10  described, switches  20  may connect/disconnect adjacent patches  12 ,  22 ,  24  to/from each other. In some AMC material structures  10  described, switches  20  may connect/disconnect patches  12 ,  22 ,  24  to conducting layer  18 , for example, patches  12 ,  22 ,  24  may either be grounded or “floating.” It should be appreciated that switches  20  may be controlled independently from each other. That is, ones of switches  20  may be open, while other ones of switches  20  may be closed. With this type of switching, it is possible to change the frequency of the antenna arrangement, i.e., the combination of radiating antenna element and AMC material structure  10 , to cover various frequency bands. This therefore allows the antenna arrangement to cover a wider frequency band and therefore the wideband properties of the antenna arrangement are enhanced. 
   In other embodiments of the present invention, switches  20  may be operated from fully closed to fully open positions and occupy partially open positions therebetween. Switches  20  can thus occupy several positions between the fully open and fully closed positions. This technique may be used, according to implementations of the present invention, in addition to providing superior broadband performance, to provide directivity of the antenna. Through suitable operation of switches  20 , it is thus possible to direct the antenna arrangement in a direction of superior reception. Since an antenna arrangement performs optimally according to these measures, a lower output power can be used, which thus saves power. Since a phone is battery-powered, this is an advantage. 
   Electrical connection elements  20  may be active components, i.e. their performance may be externally controlled apart from the antenna arrangement. Some implementations may use electrical connection elements  20  that are passive. According to one embodiment of the present invention, electrical connection elements  20  do not accomplish switching, but rather filtering. So configured, electrical connection elements  20  may provide selective connection of a patch  12 ,  22 ,  24  with another element, for example, another patch  12 ,  22 ,  24  in the same layer, or conducting layer  18 , based on frequency, for example. The filtering may be any type of filtering, for instance, band-pass filtering, low-pass, or high-pass filtering. This also allows the provision of superior broadband properties with a simpler antenna arrangement structure that does not require external control of electrical connection elements  20 . 
   Through providing electrical connection elements  20  in the above-described techniques in AMC material structure  10 , the associated band gap may be shifted and/or tuned, thereby allowing the provision of superior broadband performance, as well as allows the provision of directivity. 
   Systems and methods of antenna arrangements described herein may be provided for a wireless communication frequency range, such as different GSM and UMTS communication bands, television and radio transmission, such as FM and UHF bands, or Bluetooth™ or WLAN, as well as other wireless communication standards. 
   The present invention may be varied in many ways apart from what has been described above. It is possible to combine the above-described embodiments, for example, in that one section of AMC material structure  10  may have electrical connection elements  20  in layers of patches  12 ,  22 ,  24 , while another section of AMC material structure  10  may have electrical connection elements  20  in vias  16 ,  26 . Thus, the present invention is only to be limited by the following claims.