Abstract:
A differential antenna structure configured to connect to an electronic circuit having differential inputs and output. The antenna structure includes differential feeding points which are connected to the electronic circuit differential inputs/outputs through capacitors thus eliminating the need for baluns. The antenna structure is also configured to connect to multiple differential inputs/outputs thus eliminating the need for a separate antenna for each differential input/output included on an electronic circuit chip set. The antenna structure can include feeding arms which act as differential feeding points. The antenna can also include tongues for adjusting the capacitive part of the antenna to allow for 1 to n frequencies. The antenna can comprise multiple antenna elements in various arrangements and configurations.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application relates to co-pending application Ser. No. 09/892,928, filed on Jun. 26, 2001, entitled “Multi Frequency Magnetic Dipole Antenna Structure and Methods Reusing the Volume of an Antenna” by L. Desclos et al., owned by the assignee of this application and incorporated herein by reference. 
   This application relates to co-pending application Ser. No. 10/076,922, entitled “Multi Frequency Magnetic Dipole Antenna Structures with a New E-Field Distribution for Very Low-Profile Antenna Applications” by G. Poilasne et at., owned by the assignee of this application and incorporated herein by reference. 
   This application relates to co-pending application Ser. No. 10/160,811, entitled “Multi-Band, Low-Profile, Capacitively Loaded Antennas with Integrated Filters” by J. Shamblin et al., owned by the assignee of this application and incorporated herein by reference. 
   BACKGROUND INFORMATION 
   1. Field of the Invention 
   The present invention relates generally to the field of wireless communications, and particularly to the design of antennas with differential inputs and outputs. 
   2. Background 
   Certain wireless communications applications, such as those using Bluetooth and other ISM (Industrial Scientific and Medical) bands, use chipsets with differential inputs and outputs. Typically, antennas are only single-ended with a ground reference. When used together, the aforementioned antennas and chipsets are not fully compatible because the chipsets include a balanced line (one that has two conductors with equal currents in opposite directions) and the antennas an unbalanced line (one that has just one conductor and a ground). 
   To get around this incompatibility, baluns are often included in the design. A balun is a device that joins a balanced line to an unbalanced line. A balun is essentially a type of transformer that is used to convert an unbalanced signal to a balanced one or vice versa. Baluns isolate a transmission line and provide a balanced output. 
   In the case of multi-band applications, classical solutions are problematic because they require that multiple antennas be dedicated to meet the requirements of the targeted application. Especially in the case of mobile communications devices, where space is at a premium, this can be a serious hurdle to implementation. It can also be costly, because the construction of a balun is expensive, and can cost well more than the antenna itself—and at least several times the cost of capacitors. 
   The subject of this invention is an antenna with differential inputs and outputs that can be compatible with chipsets used in applications such as Bluetooth and ISM. Advantages of such a solution include efficiency, which is achieved by extraction of more gain from the chipset. 
   SUMMARY OF THE INVENTION 
   The present invention allows for multiple antenna elements in myriad physical configurations to cover one to n number of frequencies or bands of frequencies. At the same time, this invention allows for a differential input/output that can be connected to a differential amplifier. 
   Antenna elements according to the present invention can include both inductive and capacitive parts. Each element can provide a single frequency or band of frequency. The physical design of each element can vary, but generally allows for multiple frequencies by reusing the same design of a single element in multiple. 
   In one embodiment, a single element has two top plates and a bottom plate. In another embodiment a single element has one unshaped top plate and one bottom plate. In these embodiments, the elements can produce a specific frequency or band of frequency based on their relative size and shape. Different physical configurations can also be considered to adapt the antenna and its elements to the physical environment specific to a particular application. The plates are generally connected to ground and two independent plates can be connected to feeding points. 
   Once metal pieces have been cut and folded into a desired antenna element form for the purpose of matching a frequency or frequency band, they can then be arranged to target multiple bands. In one embodiment, the elements can be placed one next to the other. In another embodiment, the elements can be stacked, one on top of another. In yet another embodiment, the elements can be inserted one inside the other. Once the multiple elements have been arranged to both meet the frequency and space requirements of the specific application, a multi-frequency, multi-band, capacitively loaded magnetic dipole is produced. 
   In the proposed solution, a single antenna can cover several frequency bands, as well as a chipset differential configuration. These designs will reduce the overall cost of the system as well as save space and improve efficiency. 
   This summary does not purport to define the invention. The invention is defined by the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  is a circuit diagram that represents a classical interface between a radio frequency input and an antenna. 
       FIG. 1B  is a circuit diagram that represents a classical interface between a radio frequency output and an antenna. 
       FIG. 2A  is a circuit diagram that represents an interface between a radio frequency input and an antenna, in accordance with the present invention. 
       FIG. 2B  is a circuit diagram that represents an interface between a radio frequency output and an antenna, in accordance with the present invention. 
       FIG. 3A  is a circuit diagram that represents a classical interface between a radio frequency subsystem and an antenna. 
       FIG. 3B  is a circuit diagram that represents an interface between a radio frequency subsystem and an antenna, in accordance with the present invention. 
       FIG. 4A  is a three dimensional view of one embodiment of an antenna element, in accordance with the present invention. 
       FIG. 4B  is a top-view of one embodiment of the antenna element of  FIG. 4A . 
       FIG. 5A  is a three dimensional view of another embodiment of an antenna element, in accordance with the present invention. 
       FIG. 5B  is a side-view of the antenna element of  FIG. 5A . 
       FIG. 5C  is a top-view of the antenna element of  FIG. 5A . 
       FIG. 6A  is a three-dimensional view of one embodiment of an antenna, in accordance with the present invention. 
       FIG. 6B  is a three-dimensional view of another embodiment of an antenna, in accordance with the present invention. 
       FIG. 6C  is a three-dimensional view of another embodiment of an antenna, in accordance with the present invention. 
       FIG. 6D  is a three-dimensional view of another embodiment of an antenna, in accordance with the present invention. 
       FIG. 6E  is a three-dimensional view of another embodiment of an antenna, in accordance with the present invention. 
       FIG. 7  is a top-view of one of the antenna elements shown in  FIG. 6E . 
       FIG. 8  is a three-dimensional view of another embodiment of an antenna, in accordance with the present invention. 
       FIG. 9  is a three-dimensional view of another embodiment of an antenna, in accordance with the present invention. 
       FIG. 10  is a three-dimensional view of an another embodiment of an antenna, in accordance with the present invention. 
       FIG. 11  is a three-dimensional view of an another embodiment of an antenna, in accordance with the present invention. 
       FIG. 12  is a top view of various possible antenna elements for use in accordance with the present invention. 
       FIG. 13  is a three dimensional view of another embodiment of an antenna, in accordance with the present invention. 
       FIG. 14A  is a top-view of an alternative embodiment of the antenna of  FIG. 13 , in accordance with the present invention. 
       FIG. 14B  is a top-view of an alternative embodiment of the antenna of  FIG. 13 , in accordance with the present invention. 
       FIG. 15A  is a top view of another embodiment of an antenna, in accordance with the present invention. 
       FIG. 15B  is a top view of another embodiment of an antenna, in accordance with the present invention. 
       FIG. 15C  is a top view an alternative embodiment of the antenna of  FIG. 15B , in accordance with the present invention. 
       FIG. 15D  is a top view of an alternative embodiment of the antenna of  FIG. 15C , in accordance with the present invention 
       FIG. 16  is a three dimensional view of another embodiment of an antenna, in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In the following description, for purposes of explanation and not limitation, specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known methods and devices are omitted so as to not obscure the description of the present invention with unnecessary detail. 
     FIG. 1A  is a circuit diagram that represents a classical interface between a radio frequency input and an antenna. This diagram illustrates a typical differential circuit where the antenna input  10  is connected to a circuit  12  through a balun  14 . The balun  14  provides the unbalanced to balanced conversion and breaks the antenna input  10  into differential inputs  16  and  18 , which are directly connected to the differential circuit  12 . The circuit  12  shown in this figure is a Gilbert Cell cross-coupled differential amplifier circuit, which is one example of a circuit included in a chipset. 
   Similarly,  FIG. 1B  is a circuit diagram that represents a classical interface between a radio frequency output and an antenna. This diagram illustrates a typical differential circuit where the differential circuit outputs  20  and  22  are integrated through a balun  24  into an antenna output  26 . The circuit  28  shown in this figure is also a Gilbert Cell cross-coupled differential amplifier circuit. 
   As described above, the baluns  14 ,  24  are necessary in order to convert the antenna input  10  into differential inputs  16  and  18  and the differential outputs  20  and  22  into an antenna output  26  Thus, through baluns  14  and  24 , the differential amplifier circuits  12  and  18  can be connected to signal-ended antennas (not shown in  FIG. 1A  or  1 B). 
     FIG. 2A  is a circuit diagram that represents an interface between a radio frequency input and an antenna, in accordance with the present invention. In this embodiment, inputs  30  and  32  are connected to a differential amplifier circuit  34  through capacitors  36  and  38 , respectively. The antenna (not shown in  FIG. 2   a ) will have to then present a shift in phase to compensate for the shift of the input of the transistors  40  and  42  of the differential amplifier circuit  34 . The antenna, discussed in detail below, is configured with differential outputs for connecting to the inputs  30  and  32  of the differential amplifier circuit  34 . The shift in phase can be compensated for by adjusting various dimensions of the antenna, such as plate length and gap or by loading, as disclosed in the related applications referenced above and incorporated herein by reference. The circuit  34  shown in this diagram is also a Gilbert Cell cross-coupled differential amplifier circuit. 
     FIG. 2B  is a circuit diagram that represents an interface between a radio frequency output and an antenna, in accordance with the present invention. In this embodiment differential outputs  44  and  46  are connected to an antenna (not shown in  FIG. 2B ) through capacitors  48  and  50 , respectively. The capacitors  48  and  50  provide isolation between the antenna and chip set and also acts to cut the DC path. Typical capacitor values can be 1 pF for high frequency outputs in the 900 MHz range and 10 pF for low frequency inputs. Obviously, the exact specifications of the capacitors will depend on the particular application. The antenna will have to then present a shift in phase to compensate for the shift of the output of transistors  54  and  56 . The circuit  58  shown in this diagram is also a Gilbert Cell cross-coupled differential amplifier circuit. 
     FIG. 3A  is a circuit diagram of a classical interface between a radio frequency subsystem and an antenna. In this case, there are two frequency bands each produced by a separate radio frequency subsystem  60  and  62 . Each subsystem  60  and  62  requires two baluns  64 ,  66  and  68 ,  70  and two antennas  72 ,  74  and  76 ,  78 , respectively. However, there can be n number of frequency bands with 2n number of baluns and antennas. 
     FIG. 3B  is a circuit diagram of an interface between a radio frequency subsystem and an antenna, in accordance with the present invention. In this embodiment, there are again two frequency bands each produced by a separate radio frequency subsystem  71  and  73 . Each subsystem  71  and  73  connects to a single antenna  75  through four sets of capacitors  77 ,  79 ,  81  and  83 . As described in more detail below, in this embodiment, one antenna  75  can serve n number of radio frequency subsystems each producing a separate frequency band 
     FIG. 4A  illustrates a three dimensional view of one embodiment of an antenna element, in accordance with the present invention. The antenna element  86  comprises two top plates  88 ,  90  and a bottom plate  92 . The top plates generate the capacitive part  94  of the antenna element  86  while the loop between the top plates  88 ,  90  and the bottom plate  92  comprises the inductive part  96 . Power is supplied to the antenna element  86  through the feeding line  98 .  FIG. 4B  illustrates a top-view of the antenna element  86  of  FIG. 4A . As can be seen, a horizontal electric field  100  is produced between the top plates  88  and  90 . 
     FIG. 5A  illustrates a three dimensional view of another embodiment of an antenna element, in accordance with the present invention. In this embodiment, the two top plates  102 ,  104  of the antenna element  106  are arranged in a U-shape. The top plates  102 ,  104  produce the capacitive part  108  of the antenna element  106  and are attached to a grounding plane  110 , which acts as the bottom plate, by a grounding point  112 . 
     FIG. 5B  illustrates a side-view of the antenna element  106  of  FIG. 5A . As can be seen, the loop between the two top plates  102 ,  104  and the grounding plane  110  forms the inductive part  114  of the antenna element  106 . This view also illustrates that the antenna element  106  is attached to the grounding plane  110  by grounding point  112 .  FIG. 5C  illustrates a top-view of the antenna element  106 . This view shows that the antenna element  106  sits atop the grounding plane  110 . 
     FIG. 6A  illustrates a three-dimensional view of one embodiment of an antenna, in accordance with the present invention. The antenna  116  comprises two antenna elements  118 ,  120 , each comprising a ground plane  122 ,  124  and two top plates  126 ,  128  and  130 ,  132 , respectively. This configuration provides for a balanced antenna  116  that can address differential input or output. Antennas in this physical configuration can be fed with or without ground separation. There are two feeding points  134  and  136  which can be used to connect the antenna  116  to a set of differential inputs or outputs. In order to operate at a single frequency or frequency band, preferably, the antenna elements  118  and  120  are of substantially the same size and configuration. 
     FIG. 6B  illustrates a three-dimensional view of another embodiment of an antenna, in accordance with the present invention. In this embodiment, the antenna  138  comprises a single ground plane  140  supporting two separate antenna elements  142 ,  144  each including two top plates  146 ,  148  and  150 ,  152 , respectively. There are two feeding points  154 ,  156  for this antenna  138 , one each for an output and an input. This embodiment provides a balanced antenna  138  that can address one differential input or output. Antennas in this physical configuration can be fed with or without ground separation. 
     FIG. 6C  illustrates a three-dimensional view of another embodiment of an antenna, in accordance with the present invention. In this embodiment, the antenna  158  comprises four separate antenna elements  160 ,  162 ,  164 ,  166  that are fed with separation of the ground planes  168 ,  170 ,  172 ,  174 , to provide for a balanced antenna that can address differential inputs or outputs. Again each antenna element  160 ,  162 ,  164 ,  166  comprises two top plates  176 ,  178 , and  180 ,  182  and  184 ,  186 , and  188 ,  190 , respectively. There are four feeding points  192 ,  194 ,  196  and  198 , where feeds  192  and  194  are utilized for input and feeds  196  and  198  are utilized for output. Antennas in this physical configuration can be fed with or without ground separation. This model can be modified to meet the requirements of the specific application. 
     FIG. 6D  illustrates a three-dimensional view of another embodiment of an antenna, in accordance with the present invention. In this embodiment, two separate antenna elements  202 ,  204  are fed with separation of the ground planes  206 ,  208  to provide for a balanced antenna  200  that can address differential inputs or outputs. Four feeding points  210 ,  212 ,  214 ,  216  can be used for input and output, where  214  and  216  are “arms” that protrude from one  218 ,  222  of the two top plates  218 ,  220  and  222 ,  224  of each antenna element  202 ,  204 . This physical model can be modified and the frequency tuned to meet the requirements of different applications. 
   For example, as shown in  FIG. 6E , arms  214  and  216  can be configured to protrude inward, as opposed to the outward protrusion shown in  FIG. 6D .  FIG. 7  illustrates a top-view of one antenna element  202  of the antenna  200  of  FIG. 6E . Through modification of the physical characteristics of the feed-point “arm”  216 , for example, dimensions  226 ,  227 , and  228 , one can tune the frequency of the antenna  200  to meet the requirements of different applications. However, in this embodiment, the transmitter (not shown) should be turned off when the receiver (not shown) is working and vice versa. 
     FIG. 8  illustrates a three-dimensional view of another embodiment of an antenna, in accordance with the present invention. In this embodiment, the antenna  230  comprises two separate antenna elements  232 ,  234  that are fed atop a single ground plane  236 . The antenna  230  includes two feeding points  238 ,  240 , one for input  238  and one for output  240 , and two grounding points  242 ,  244 . 
     FIG. 9  illustrates a three-dimensional view of another embodiment of an antenna, in accordance with the present invention. This embodiment is similar to the one shown in  FIG. 8 , but includes two additional “arm” feeding points  246  and  248 . Thus, this embodiment includes four feeding points: the two feed-point “arms”  246  and  248 , which can be used for output, and feed points  238 ,  240  which can be used for input. 
     FIG. 10  illustrates a three-dimensional view of another embodiment of an antenna, in accordance with the present invention. This embodiment is similar to one shown in  FIG. 9 , with the addition of tongues  250 ,  252  between the top plates  254 ,  256 , and  258 ,  260 , of each antenna element  232 ,  234 , respectively. The tongues  250 ,  252  enable adjustments in the capacitance of the antenna  230  to allow for one to n frequencies. In this scenario, there will be a set of dual-frequency outputs or inputs that will generate the differential behavior.  FIG. 11  illustrates a three-dimensional view of another embodiment of an antenna, in accordance with the present invention. This embodiment expands upon the one shown in  FIG. 10 . In this embodiment additional feeding arms  262 ,  264 ,  266 , and  268  are added. The additional feeding arms expand the number of inputs and outputs available for multifrequency elements. 
     FIG. 12  illustrates a matrix of potential combinations and arrangements of antennas elements, in accordance with the present invention. By combining or arranging the antenna elements from any row or column in the matrix, one enables one to n frequencies as multi-mode differential antennas. 
     FIG. 13  illustrates a three dimensional view of another embodiment of an antenna, in accordance with the present invention. In this embodiment, the antenna  270  comprises two separate antenna elements  272  and  274  atop a ground plane  276 . There are two feeding points  278 ,  280  that can be used for input and output and there are also two grounding points  282 ,  284 .  FIG. 14A  illustrates a top-view of an alternative embodiment of the antenna of  FIG. 13 . In this embodiment, the feed points  278 ,  280  and grounding points  282 ,  284  are positioned opposite each other on the two antenna elements  272 ,  274 . Similarly,  FIG. 14B  is an alternative embodiment of the antenna  270  of  FIG. 13 . In this embodiment, the feeding points  278 ,  280  and grounding points  282 ,  284  are in the same position as in  FIG. 13 , but the lengths of the top plates  284 ,  286  and  288 ,  290  of antenna elements  272  and  274  are different. 
     FIG. 15A  illustrates a top view of another embodiment of an antenna, in accordance with the present invention. The antenna  292  of this embodiment comprises two antenna elements  294 ,  296 . Each element has a feeding point  298 ,  300  and the two elements  294 ,  296  share a grounding point  302 .  FIG. 15B  illustrates another of the various possible embodiments of an antenna, in accordance with the present invention. The antenna  304  comprises two connected antenna elements  306  and  308 . This embodiment includes four feeding points  310 ,  312 ,  314 , and  316 , and two grounding points  318 ,  320 . In this example, the feeding points  310 ,  312  can be inputs and feeding points  314 ,  316  can be outputs. 
     FIG. 15C  illustrates an alternative embodiment of the antenna  304  shown in  FIG. 15B . This embodiment includes eight feeding points  310 ,  312 ,  314 ,  316 ,  322 ,  324 ,  326 ,  328  and four grounding points  318 ,  320 ,  330 , and  332 . In this example, the feeding points  310  and  312  represent the output group for a first frequency, while feeding points  314  and  316  represent the input group for that same frequency, while feeding points  326  and  328  can represent the input group for that same frequency.  FIG. 15D  illustrates an alternative embodiment of the antenna  304  shown in  FIG. 15C  with the addition of tongues  334  and  336 . The tongues  334  and  336  enable one to n frequencies. 
     FIG. 16  illustrates a three dimensional view of another embodiment of an antenna, in accordance with the present invention. In this embodiment, the antenna  338  comprises four antenna elements  340 ,  342 ,  344 , and  346  that sit atop a single ground plane  348 . The two larger elements  340  and  342  each include a feeding point  348  and  350 , respectively that can be used for input and output. Each element also includes a grounding point  352 ,  354 . The two smaller elements  344  and  346  are stacked inside the two larger elements  340  and  342 . Each of the smaller elements  344  and  346  also includes a feeding point  356 ,  358 , which can be used for input and output, and a grounding point  360 ,  362 , respectively. 
   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.