Abstract:
An antenna having a driven element coupled to multiple additional elements to resonate at multiple frequencies. A magnetic dipole mode is generated by coupling a driven element to a second element, and additional resonances are generated by coupling additional elements to either or both of the driven or second element. One or multiple active components can be coupled to one or more of the coupled elements to provide dynamic tuning of the coupled or driven elements.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to the field of wireless communication. In particular, the present invention relates to antennas and methods of improving frequency response and selection for use in wireless communications. 
       BACKGROUND OF THE INVENTION 
       [0002]    Commonly owned U.S. Pat. Nos. 6,677,915 filed Feb. 12, 2001, titled “SHIELDED SPIRAL SHEET ANTENNA STRUCTURE AND METHOD”; 6,906,667 filed Feb. 14, 2002, titled “MULTIFREQUENCY MAGNETIC DIPOLE ANTENNA STRUCTURES FOR VERY LOW PROFILE ANTENNA APPLICATIONS”; 6,900,773 filed Nov. 18, 2002, titled “ACTIVE CONFIGUREABLE CAPACITIVELY LOADED MAGNETIC DIPOLE”; and 6,919,857 filed Jan. 27, 2003, titled “DIFFERENTIAL MODE CAPACITIVELY LOADED MAGNETIC DIPOLE ANTENNA”; describe an Isolated Magnetic Dipole (IMD) antenna formed by coupling one element to another in a manner that forms a capacitively loaded inductive loop, setting up a magnetic dipole mode, the entire contents of which are hereby incorporated by reference. This magnetic dipole mode provides a single resonance and forms an antenna that is efficient and well isolated from the surrounding structure. This is, in effect, a self resonant structure that is de-coupled from the local environment. 
         [0003]    The overall structure of the IMD antenna can be considered as a capacitively loaded inductive loop. The capacitance is formed by the coupling between the two parallel conductors with the inductive loop formed by connecting the second element to ground. The length of the overlap region between the two conductors along with the separation between conductors is used to adjust the resonant frequency of the antenna. A wider bandwidth can be obtained by increasing the separation between the conductors, with an increase in overlap region used to compensate for the frequency shift that results from the increased separation. 
         [0004]    An advantage of this type of antenna structure is the method in which the antenna is fed or excited. The impedance matching section is almost independent from the resonant portion of the antenna. This leaves great flexibility for reduced space integration. The antenna size reduction is obtained in this case by the capacitive loading that is equivalent to using a low loss, high dielectric constant material. At resonance a cylindrical current going back and forth around the loop is formed. This generates a magnetic field along the axis of the loop which is the main mechanism of radiation. The electrical field remains highly confined between the two elements. This reduces the interaction with surrounding metallic objects and is essential in obtaining high isolation. 
         [0005]    The IMD technology is relatively new, and there is a need for improvements over currently available antenna assemblies. For example, because cell phones and other portable communications devices are moving in the direction of providing collateral services, such as GPS, video streaming, radio, and various other applications, the demand for multi-frequency and multi-band antennas is at a steady increase. Other market driven constraints on antenna design include power efficiency, low loss, reduced size and low cost. Therefore, there is a need in the art for antennas which exceed the current market driven requirements and provide multiple resonant frequencies and multiple bandwidths. Additionally, there is a need for improved antennas which are capable of being tuned over a multitude of frequencies. Furthermore, there is a need for improved antennas which are capable of dynamic tuning over a multitude of frequencies in real time. 
       SUMMARY OF THE INVENTION 
       [0006]    This invention solves these and other problems in the art, and provides solutions which include forming additional capacitively loaded inductive loops by adding additional elements that couple to one of the two elements that form the basic IMD antenna. Other solutions provided by the invention include active tuning of multiple coupling regions, switching over a multitude of frequencies, and dynamic tuning of resonant frequencies. 
         [0007]    In one embodiment, an antenna is formed by coupling a first element to a second element, and then adding a third element which is coupled to the second element. The first element is driven by a transceiver, with both the second and third elements connected to ground. The additional resonance that is generated is a product of two coupling regions on the composite antenna structure. 
         [0008]    In another embodiment, an antenna is formed having a first element driven by a transceiver, and two or more grounded elements coupled to the first element. The space between each of the two or more grounded elements and the first element defines a coupling region, wherein the coupling region forms a single resonant frequency from the combined structure. The resonant frequency is adjusted by the amount of overlap of the two elements. The separation between the two elements determines the bandwidth of the resonance. 
         [0009]    In another embodiment, an antenna is formed having a first element driven by a transceiver, a second element connected to ground wherein the second element overlaps with the first element to form a capacitive coupling region, and a third element. The third element can be either driven or grounded and overlaps with at least one of the first element and the second element. Each overlapping region between the first, second and third elements creates a capacitive coupling region forming a resonant frequency, wherein the resonant frequency is adjusted by the amount of overlap and the bandwidth is determined by the separation distance between the overlapping elements. In this embodiment, an overlapping region can be formed between the driven element and a grounded element, or alternatively the overlapping region can be formed between two grounded elements. 
         [0010]    In another embodiment, the grounded elements are parallel to the driven element. Alternatively, the grounded elements can be orthogonal with respect to the driven element. One or more elements can comprise an active tuning component. The active tuning component can be configured within or near a ground plane. Alternatively, one or more active components can be configured on an antenna element. One or more antenna elements can be bent. One or more antenna elements can be linear, or planar. One or more antenna elements can be fixedly disposed above a ground plane. Alternatively, one or more antenna elements can be configured within a ground plane. 
         [0011]    In another embodiment, an antenna is provided having a high band radiating element and a low band radiating element. A switched network can be integrated with at least one of the high band or low band radiating elements. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  illustrates an exemplary isolated magnetic dipole (IMD) antenna comprised of a first element attached to a transmitter and coupled to a second element which is connected to ground. 
           [0013]      FIG. 2  shows a plot of return loss as a function of frequency for the IMD antenna in  FIG. 1 . A single resonance is present. 
           [0014]      FIG. 3  illustrates an isolated magnetic dipole (IMD) antenna comprised of a first element attached to a transmitter and coupled to a second element which is connected to ground along with a third element which is coupled to the second element. 
           [0015]      FIG. 4  shows the return loss as a function of frequency for the antenna shown in  FIG. 3 . A second resonance is present which is formed by the addition of the third element. 
           [0016]      FIG. 5  illustrates an IMD antenna with two additional elements, a third and fourth, each coupled to the second element of the IMD antenna. 
           [0017]      FIG. 6  illustrates an isolated magnetic dipole (IMD) antenna comprised of an element attached to a transmitter and coupled to a second element which is connected to ground along with a third element which is coupled to the first element. 
           [0018]      FIG. 7  illustrates an IMD antenna with two additional elements, a third and fourth, each coupled to the first element of the IMD antenna. 
           [0019]      FIG. 8  illustrates an isolated magnetic dipole (IMD) antenna comprised of a first element attached to a transmitter and coupled to a second element which is connected to ground along with a third element which is coupled to the second element. A component is connected between the third element and ground. 
           [0020]      FIG. 9  illustrates an isolated magnetic dipole (IMD) antenna comprised of a first element attached to a transmitter and coupled to a second element which is connected to ground along with a third element which is coupled to the first element. A component is connected between the third element and ground. 
           [0021]      FIG. 10  illustrates an IMD antenna with two additional elements, a third and fourth, each coupled to the second element of the IMD antenna. A component is connected between the third element and ground, with another component connected between the second element and ground. 
           [0022]      FIG. 11  illustrates an IMD antenna with an additional element coupled to the second element of the IMD antenna. The additional element is configured in a 3-dimensional shape and is not restricted to a plane containing the first two elements. 
           [0023]      FIG. 12  illustrates an IMD antenna with two additional elements, a third and fourth, with the third element coupled to the second element and the fourth element coupled to the first element. Both the third and fourth elements are bent in 3 dimensional shapes and are not restricted to a plane containing the first two elements. A component is connected between the fourth element and ground. 
           [0024]      FIG. 13  illustrates an IMD antenna with two additional elements, a third and fourth, with a component connecting two portions of the third element. 
           [0025]      FIG. 14  illustrates an IMD antenna with two additional elements, a third and fourth, with a component connecting the third and fourth elements. 
           [0026]      FIG. 15  illustrates an IMD antenna with two additional elements, a third and fourth, with all four elements positioned in the plane of the ground plane. 
           [0027]      FIG. 16  illustrates an antenna configuration where a switch network is integrated into the low band radiating element to provide a tunable antenna. The switch network can be implemented in a MEMS process, integrated circuit, or discrete components. 
           [0028]      FIG. 17  illustrates an antenna configuration where a switch network is integrated into the high band radiating element to provide a tunable antenna. The switch network can be implemented in a MEMS process, integrated circuit, or discrete components. 
           [0029]      FIG. 18  illustrates an antenna configuration where switch networks are integrated into the low band and high band radiating elements to provide a tunable antenna. The switch networks can be implemented in a MEMS process, integrated circuit, or discrete components. 
           [0030]      FIG. 19  illustrates an antenna implementation of the concept described in  FIG. 3 . A driven element is coupled to two additional elements, resulting in a low band and high band resonance. 
           [0031]      FIG. 20  shows the return loss of the antenna configuration shown in  FIG. 19 . The two traces refer to two capacitor values for component loadings of the second element. The capacitor is not shown in  FIG. 19 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]    In the following description, for purposes of explanation and not limitation, details and descriptions are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments that depart from these details and descriptions. 
         [0033]    Embodiments of the present invention provide an active tuned loop-coupled antenna capable of optimizing an antenna over incremental bandwidths and capable of tuning over a large total bandwidth. The active loop element is capable of serving as the radiating element or an additional radiating element may also be coupled to this active loop. In various embodiments, multiple active tuned loops can be coupled together in order to extend the total bandwidth of the antenna. Such active components may be incorporated into the antenna structure to provide further extensions of the bandwidth along with increased optimization of antenna performance over the frequency range of the antenna. 
         [0034]    In a primary embodiment, the invention includes a first element and a second element positioned above a ground plane. The first and second element can be wire, or preferably a planar element. The first element is connected to a transceiver. The second element is connected to ground and at least partially overlaps with the first element to form a first coupling region. The coupling region is defined by the amount of overlap between the first and second elements, and the distance between the first and second elements. The coupling region can include a capacitive coupling between two antenna elements. By adjusting the amount of overlap and the distance between the elements, one can adjust the frequency and bandwidth of the antenna. A third element connected to ground is further positioned near at least one of the first element and the second element. The third element can form a second coupling region when placed near one of the first element or the second element, thus creating a second resonant frequency for which the antenna is operational. Optionally, the third element can be placed within the vicinity of the first and second elements, thereby further generating a third coupling region. Any number of subsequent elements can be positioned near an antenna element to create a coupling region. 
         [0035]    In a preferred embodiment, each of the antenna elements are planar elements and are substantially parallel to the ground plane. In certain embodiments, the antenna elements are not parallel with the ground plane. Other embodiments are described below in more detail. 
         [0036]      FIG. 1  illustrates a driven element  1 , and a capacitively coupled element  2  that is grounded forming an inductive loop. The coupling region  3  between elements  1  and  2  forms a single resonant frequency from the combined structure. The resonant frequency is adjusted by the amount of overlap of the two elements. The separation between the two elements determines the bandwidth of the resonance. 
         [0037]      FIG. 2  illustrates a plot of frequency vs. return loss showing the effect of coupling a driven element and one capacitively coupled element that is grounded. A single resonant frequency is shown. 
         [0038]      FIG. 3  illustrates a driven element  20 , and two capacitively coupled elements  21  and  22  that are grounded forming inductive loops. The coupling  23  between elements  20  and  21 , and the coupling  24  between  21  and  22  produces two resonant frequencies each determined by the amount of overlap and separation between the two elements. The separation between the elements determines the bandwidth for each resonance. 
         [0039]      FIG. 4  illustrates a plot of frequency vs. return loss showing the effect of coupling a driven element and two capacitively coupled elements. Two resonate frequencies are shown. 
         [0040]      FIG. 5  illustrates a driven element  30 , and three capacitively coupled elements  31 ,  32  and  33  that are grounded forming inductive loops. The coupling  34  between elements  30  and  32 , the coupling  35  between  31  and  32  and coupling  36  between  32  and  33  produces three resonant frequencies each determined by the amount of overlap and separation between the three elements. The separation between the elements determines the bandwidth for each resonance. 
         [0041]      FIG. 6  illustrates a driven element  40 , and two capacitively coupled elements  41  and  42  that are grounded forming inductive loops. The positioning of the elements creates an overlapping between the elements that forms three couplings  43 ,  44  and  45 . The separation between the elements determines the bandwidth for each resonance. 
         [0042]      FIG. 7  illustrates a driven element  50 , and four capacitively coupled elements  51 ,  52 ,  53  and  54  that are grounded forming inductive loops. The positioning of the elements creates an overlapping between the elements that forms four couplings  55 ,  56 ,  57  and  58 . The separation between the elements determines the bandwidth for each resonance. 
         [0043]      FIG. 8  illustrates a driven element  60  with one capacitively coupled element  61  that is connected to ground forming an inductive loop and a coupling region  65 . The frequency response generated by this coupling region  65  will be dependent upon the amount of overlap and separation distance of the elements  60  and  61 . A second coupled element  62  is connected to ground via a component  63 . If this component is passive (inductor, capacitor, resistor) it will create a fixed frequency response from the coupling region  64 . If the component is tunable (tunable capacitor, varactor diode, etc.) then the frequency response can be dynamically tuned (in real time). 
         [0044]      FIG. 9  illustrates a driven element  70  with one capacitively coupled element  72  that is connected to ground forming an inductive loop and a coupling region  75 . The frequency of this coupling region  75  will be dependent upon the amount of overlap and separation distance of the elements  70  and  72 . The driven element  70  is also coupled to a second element  71  that is connected to ground via a component  73 . If this component is passive (inductor, capacitor, resistor) it will create a fixed frequency response from the coupling region  76 . If the component is tunable (tunable capacitor, varactor diode, etc.) then the frequency response can be dynamically tuned (in real time). Element  71  is also coupled to element  72  and will have a fixed or dynamically tuned frequency response, dependent on the type and value of component  73 . 
         [0045]      FIG. 10  illustrates a driven element  80  coupled to a second element  81  that is connected to ground via a component  86 . If this component is passive (inductor, capacitor, resistor) it will create a fixed frequency response from the coupling region  76 . If the component is tunable (tunable capacitor, varactor diode, etc.) then the frequency response can be dynamically tuned (in real time). Element  81  forms a coupling  87  with element  84  that is connected to ground. The frequency of this coupling region  87  will be dependent upon the amount of overlap and separation distance of the elements  81 ,  84  and the driven element  80 . Another coupling region  89  is formed by elements  81  and  82 . Both elements are connected to ground by components  85  and  86 . 
         [0046]      FIG. 11  illustrates a driven element  90  with one capacitively coupled element  91  that is connected to ground forming an inductive loop and a coupling region  93 . An additional coupling is formed between capacitively coupled elements  91  and  92 . The frequency of this coupling region  94  will be dependent upon the amount of overlap and separation distance of the elements  91  and  92  and driven element  90 . 
         [0047]      FIG. 12  illustrates a driven element  100  with a capacitively coupled element  102  that is connected to ground forming an inductive loop and coupling region  106 . Element  102  is capacitively coupled to element  103  that is connected to ground forming an inductive loop and coupling region  105 . Element  103  is bent in a 3 dimensional shape and is not restricted to a plane containing the other elements. The driven element  100  is also coupled to a second element  101  that is connected to ground via a component  104  forming a coupling region  107  with driven element  100 . If the component  104  is tunable (tunable capacitor, varactor diode, etc.) then the frequency response can be dynamically tuned (in real time). Element  101  is bent in a 3 dimensional shape and is not restricted to a plane containing the other elements. 
         [0048]      FIG. 13  illustrates a driven element  200  in-line with element  201  that is connected to ground. The driven element  200  is coupled to a second element  202  that is connected to ground via a component  204  forming a coupling region  207  with driven element  200 . If the component  204  is tunable (tunable capacitor, varactor diode, etc.) then the frequency response can be dynamically tuned (in real time). Element  202  also forms a coupling  209  with element  203  that is grounded via a component  205 . In addition element  203  has a component  206  that connects the two parts of element  203  further extending frequency tuning and response. 
         [0049]      FIG. 14  illustrates a driven element  300  in-line with element  301  that is connected to ground. The driven element  300  is coupled to a second element  302  that is connected to ground via a component  304  forming a coupling region  309  with driven element  300 . If the component  304  is tunable (tunable capacitor, varactor diode, etc.) then the frequency response can be dynamically tuned (in real time). Element  302  also forms a coupling  308  with element  301  that is connected to ground forming an inductive loop. A further coupling is formed between element  302  and element. A component  306  is connected to elements  302  and  303 , providing additional tuning of the frequency response. 
         [0050]      FIG. 15   FIG. 12  illustrates a driven element  400  with capacitively coupled elements  401 ,  402  and  403  that are connected to the edge of a ground plane producing three couplings  404 ,  405  and  406  respectively. 
         [0051]      FIG. 16  illustrates an antenna configuration where a switch network  500  is integrated into the low band radiating element  501  to provide a tunable antenna. The switch network can be implemented in a MEMS process, integrated circuit, or discrete components. 
         [0052]      FIG. 17  illustrates an antenna configuration where a switch network is integrated into the high band  600  radiating element to provide a tunable antenna. The switch network  601  can be implemented in a MEMS process, integrated circuit, or discrete components. 
         [0053]      FIG. 18  illustrates an antenna configuration where switch networks are integrated into the low band  700  and high band  702  radiating elements to provide a tunable antenna. The switch networks  701  and  703  can be implemented in a MEMS process, integrated circuit, or discrete components. 
         [0054]      FIG. 19  illustrates antenna implementation of the concept described in  FIG. 3 . A driven element  720  is coupled to two additional elements,  721  and  722 , resulting in a low band and high band resonance. 
         [0055]      FIG. 20  illustrates a plot of frequency vs. return loss for the antenna described in  FIG. 19 . The two traces refer to two capacitor values for a component loading element  721 .