Abstract:
An antenna for use in mobile electronic devices at more than one frequency. A circuit board contains a first antenna element at a first layer and a second antenna element at a second layer. The antenna elements have a common feed connection and ground connection. The antenna elements are arranged substantially parallel to each other on their respective layers in the circuit board. The first antenna element has a length that differs from that of the second antenna element to provide each with a different resonant frequency.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates an internal dual band antenna for a hand portable radio device. Preferred embodiments of the invention are particularly suited for operation at frequencies allocated for Wireless Local Area Network (WLAN) communication. 
       BACKGROUND INFORMATION 
       [0002]    There is a desire for hand portable devices with the ability to communicate, such as mobile radiotelephones, to become increasingly smaller and more compact. Due to such requirements, there is a need to provide compact solutions within the hand portable device. For example, integrated circuits (IC&#39;s) are becoming more densely packed as they include a plurality of circuits and components. 
         [0003]    Additionally, mobile telephones may operate via a plurality of different wireless protocols, for example the global system for mobile communication (GSM), wireless Local Area Network (WLAN), and Global Positioning System (GPS). Each protocol includes associated circuitry contained within the radio handset, and each protocol is able to receive and transmit electromagnetic energy by way of an antenna. 
         [0004]    Wireless Local Area Network is a type of local-area network that uses high-frequency radio waves rather than wires to communicate between nodes. WLANs enable mobile users to connect to a local-area network (LAN) through a wireless (radio) connection. The IEEE 802.11 standard specifies the technologies for wireless LANs. At present, there are a number of variants of WLAN which fall under the 802.11 standards. For example, the 802.11b standard outlines use at approximately 2.4 GHz and with a data rate of 11 Mbits/s, and the 802.11a standard outlines use at approximately 5.8 GHz and with a data rate of up to 54 Mbits/s. Dependent upon the territory, these allocations/standards may differ slightly. 
         [0005]    In older style radio telephones, antennas were traditionally mounted on the external cover of a radio telephone, for example a whip or stub antenna. More recently, radiotelephones have utilized internal antennas so as to provide a more aesthetically pleasing product that may be easily stored in a user&#39;s pocket. However, as the number of wireless protocols that a radiotelephone must support increases, so must the number of antennas. 
         [0006]    An internal antenna such as a planar inverted F antenna (PIFA) can resonate at more than one frequency, the resonant frequencies, for example, corresponding to an electrical length of one quarter wavelength and at three quarters of a wavelength. While the aforementioned antenna provides a space efficient means of providing an antenna resonant at two frequency bands, it is appreciated by those skilled in the art that the ratio between the two frequency bands will be of the order of 3:1. This type of antenna is not therefore suited to covering two resonant frequencies with a ratio of approximately 2:1. 
         [0007]    Also, each resonant frequency of the PIFA has an associated impedance which will be different, possibly of the order of 4:1. It would be preferable that at each resonant frequency the match presented by the antenna to the associated circuitry was 50 ohms. 
         [0008]    Furthermore, in order to operate over as wide a frequency bandwidth as possible, PIFA&#39;s need to be located at a certain distance above a ground plane; generally the greater the separation distance between the PIFA and the ground plane, the larger the antenna bandwidth. Therefore, a disadvantage of using PIFA&#39;s inside a radio telephone is that they are generally not constructed as a part of the printed circuit board to which electronic circuitry may be mounted as the separation distance between the radiation element and the ground plane would be very small. Typically, these antennas are mounted to a radiotelephone housing or to an internal mount within the handset so as to provide a separation distance and therefore an antenna with sufficient operational bandwidth. 
         [0009]    There is therefore a requirement to provide a space efficient antenna structure that can operate in a plurality of wireless protocols yet provide easily alterable matching characteristics. 
         [0010]    It is therefore an aim of embodiments of this invention to provide an antenna structure that is space efficient, can operate at a plurality of frequencies and can be easily matched to coupled radio circuitry. 
       SUMMARY OF THE INVENTION 
       [0011]    According to a first aspect of the invention, there is a dual band antenna comprising a circuit board having a plurality of layers, a first antenna element formed on a first layer and having a ground connection, a second antenna element formed on a second layer and having a ground connection, and a common feed circuit connected to the first and second antenna element, wherein the first and second elements are positioned adjacent to an edge of the circuit board. 
         [0012]    According to a second aspect of the invention, there is a portable radio device comprising a circuit board for mounting components and having a plurality of layers, a first antenna element formed on a first layer of the circuit board and having a ground connection, a second antenna element formed on a second layer of the circuit board and having a ground connection, and a common feed circuit connected to the first and second antenna element, wherein the first and second elements are positioned adjacent to an edge of the circuit board. 
         [0013]    These and other objects, advantages, and features of the invention, together with the organization and manner of operation thereof, will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, wherein like elements have like numerals throughout the several drawings described below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a perspective view illustrating one of the antenna elements constructed as part of a circuit board according to the principles of the present invention; 
           [0015]      FIG. 2  is a side view showing an embodiment of the present invention illustrating the overlap between the first and second element; 
           [0016]      FIG. 3  illustrates a perspective view of a circuit board having the longer of the two traces and the feed connection; 
           [0017]      FIG. 4  is a illustration of the opposite side of the circuit board shown in  FIG. 3 , showing the shorter of the two traces; 
           [0018]      FIG. 5  is a perspective view illustrating both traces of the antenna of one embodiment of present invention and including a signal feed connection and ground connection; 
           [0019]      FIGS. 6(   a ) and ( b ) illustrates one of the antenna elements constructed as part of a circuit board according to the principles of the present invention; 
           [0020]      FIG. 7  is a perspective view of a mobile telephone that can be used in the implementation of the present invention; 
           [0021]      FIG. 8  is a schematic representation of the telephone circuitry of the mobile telephone of  FIG. 7 ; 
           [0022]      FIG. 9  is a perspective view illustrating three traces of the antenna of one embodiment of the present invention, two fed via a signal feed connection, and a third parasitic trace; 
           [0023]      FIG. 10  is a perspective view illustrating three traces of the antenna of one embodiment of the present invention, two fed via a signal feed connection, and a third parasitic trace, with the parasitic trace positioned on the same face of a printed circuit board as the first trace; 
           [0024]      FIG. 11  is a perspective view illustrating three traces of the antenna of one embodiment of the present invention, two fed via a signal feed connection, and a third parasitic trace; 
           [0025]      FIG. 12  is a perspective view illustrating three traces of the antenna of one embodiment of the present invention, two fed via a signal feed connection, and a third parasitic trace which is positioned on a different face of the printed circuit board than the first and second traces; and 
           [0026]      FIG. 13  illustrates a integrated circuit including a first antenna element and a second antenna element in accordance with the principles of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    In one embodiment the antenna of the present invention are mounted on a printed circuit board (PCB)  10 . A PCB  10  is illustrated in  FIG. 1 . The PCB is rectangular and comprises a front face  15  and two parallel edges  17 ,  19 . The PCB  10  may comprise a plurality of solder pads for connecting electronic components during manufacture of a portable electronic device. For clarity, the solder pads and any associated circuitry are not shown, but nonetheless would be understood by those skilled in the art. The PCB is dimensioned so as to be assembled within a portable electronic device, hence the geometry of the PCB is not essential to the present invention. In one embodiment, the PCB may be a board without components placed on it. In an exemplary embodiment, the PCB is a substrate material having a connection to another board or element. Therefore, one skilled in the art will appreciate that the antenna according to the present invention may be mounted or constructed to various PCB&#39;s without departing from the scope of the invention. 
         [0028]    According to a first embodiment an antenna  20  is constructed as part of the etching process on the front face  15  of the PCB  10 . The antenna  20  is planar and realized using strip line. An advantage of this embodiment is that the antenna  20  is produced at reduced cost when compared to the cost of manufacturing the PCB  10 . The antenna is located towards one of the parallel edges, i.e. towards and edge of the PCB  10 . 
         [0029]    The antenna  20  is commonly referred to as an inverted F antenna (IFA); it comprises a radiation element or trace  22  running parallel with the edge  17 . The radiation element  22  has an open circuit end  24  and a short circuit end  26 . Defining the short circuit end  26  is a ground point  28 . The ground point  28  creates a DC path to the ground of the portable electronic device; the electrical length of the radiation element is defined by the distance between the ground point  28  and the open circuit end  24 . Adjacent to the ground point  28  is a feed point  30  that is coupled to radio circuitry contained within the portable electronic device. 
         [0030]      FIG. 2  illustrates a side view of the PCB  10  looking towards the edge  17 . The PCB  10  further comprises a rear face  50  which is parallel to the front face  15  and is separated by a dielectric material  80 . Located on the rear face  50  of the PCB  10  there is a second antenna  60 . In one embodiment, the second antenna  60  is of similar construction to the antenna  20 . The second antenna  60  has a radiation element  66 ,a ground point  62  and a feed point  64 . As with the antenna  20  the second antenna  60  may be an IFA. In accordance with the principles of the present invention, a plurality of antenna may be provided. 
         [0031]    In one embodiment the antenna elements  20 ,  60  are adjacent to the edge  17  of the PCB  10 . In an exemplary embodiment at least one of the antenna elements  20 ,  60  are positioned adjoining the edge  17 . In another exemplary embodiment, at least one of the antenna elements  20 ,  60  are spaced some distance from and not in contact with the edge  17 . In an exemplary embodiment, at least one of the antenna elements  20 ,  60  are positioned with additional material, such as circuit board material, between the antenna elements  20 ,  60  and the edge  17 . 
         [0032]      FIGS. 3 and 4  illustrate the position of the antenna  20  components of one embodiment of the present invention.  FIG. 4  illustrates a shorter (relative to the first radiation element) second radiation element  66  including the signal feed connection  30  in communication with the first radiation element. 
         [0033]    In one embodiment as shown in  FIG. 5 , the ground connection  29  and the signal feed connection  31  connects the first radiation element  22  on the first face  15  of the PCB  10  to the second radiation element  66  on the rear face  50  of the PCB  10 . 
         [0034]    In one embodiment, the antenna includes more than two radiation elements. In one exemplary embodiment as shown in  FIG. 9 , the antenna includes a trace  36  which is not fed via the feed point  30 , i.e. it is a parasitic trace. As shown in  FIGS. 9-11 , the parasitic trace  36  positioned on the first face  15  of the PCB  10  apart from the first trace  22  and is connected to the ground connection  29 . In an alternative embodiment shown in  FIG. 12 , the parasitic trace  36  may be positioned above the first element  22 , off the first face  15  and the second face  50 . 
         [0035]    In one exemplary embodiment, the first radiation element  22  and the second radiation element  66  are disposed on the PCB such that at least part of the elements  22 ,  66  would intersect with a plane orthogonal to the plane of the front and rear face. Preferably, the radiation elements  22 ,  66  would totally overlap as shown in  FIG. 2 , as this would provide a most space efficient solution. 
         [0036]    In an exemplary embodiment, the ground points of the radiation elements  22 ,  66  are coupled to one another either directly as shown in  FIG. 2 , or via a ground plane (not shown) which may exist on an internal or external layer of the PCB  10 . In one embodiment, the feed points  30 ,  64  are connected to one another and then fed to associated radio circuitry. 
         [0037]    In an alternative arrangement, the feed points  30 ,  64  may not be connected to one another and may be connected to circuitry associated with each frequency of operation. In this embodiment, the circuitry associated with the first and second resonant frequency are operable simultaneously. 
         [0038]      FIG. 2  illustrates the first antenna element  22  having a first associated length and the second antenna element  66  having a second associated length; the first and second length being different. The first and second length are dimensioned accordingly so that they resonate at the frequencies of interest. For example, the first radiation element  22  may be dimensioned to resonate at about 2.4 GHz, and the second radiation element  66  may be dimensioned smaller so as to resonate at about 5.8 GHz.  FIGS. 6(   a ) (showing a first side of the PCB) and  6 ( b ) (showing the second side of the PCB) illustrate an exemplary embodiment of the present invention wherein the PCB  10  includes a notched area  68  corresponding to the radiation elements  22 ,  66 . 
         [0039]      FIGS. 7 and 8  show one representative mobile telephone  112  within which the present invention may be implemented. It should be understood, however, that the present invention is not intended to be limited to one particular type of mobile telephone  112  or other electronic device.  FIG. 7  depicts a mobile telephone having digital camera functionality in accordance with the principles of the present invention. The mobile telephone  112  of  FIG. 7  includes a housing  130 , a display  132  in the form of a liquid crystal display (LCD), a keypad  134 , a microphone  136 , an ear-piece  138 , a battery  140 , an infrared port  142 , a smart card  146 , in the form of a universal integrated circuit card (UICC) according to one embodiment of the invention, a card reader  148 , radio interface circuitry  152 , codec circuitry  154 , a controller  156  and a memory  158 . The mobile telephone  112  also includes a dual band antenna  144  in accordance with the principles of the present invention. Individual circuits and elements are all of a type well known in the art, for example in the Nokia range of mobile telephones. Other types of electronic devices within which the present invention may be incorporated can include, but are not limited to, personal digital assistants (PDAs), integrated messaging devices (IMDs), desktop computers, and notebook computers.  FIG. 8  illustrates a schematic of the components of the mobile phone  112  of  FIG. 7 . 
         [0040]    While the invention as been primary described in the context of a PCB, in an exemplary embodiment illustrated in  FIG. 13 , the antenna elements  22 ,  66  of the present invention are positioned on an integrated circuit  70 . In one embodiment, the antenna elements  22 ,  66  are integrated into the body of the integrated circuit  70 . The integrated circuit  70  itself may be mounted on a PCB  10 . 
         [0041]    The foregoing description of embodiments of the present invention have been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the present invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the present invention. The embodiments were chosen and described in order to explain the principles of the present invention and its practical application to enable one skilled in the art to utilize the present invention in various embodiments, and with various modifications, as are suited to the particular use contemplated.