Abstract:
An antenna for a wireless communication may include a ground plane provided on a carrying structure, a feed element, and a radiating element coupled to the feed element, the radiating element being substantially parallel to and vertically displaced from the ground plane by the feed element and a shortening element. The antenna may also include a parasitic element provided directly on the carrying structure as part of the carrying structure ground layer.

Description:
TECHNICAL FIELD 
     The present invention generally relates to antennas and, more particularly, to a semi-planar inverted F-antenna (PIFA) including a parasitic element. 
     BACKGROUND OF THE INVENTION 
     Wireless communication equipment, such as cellular and other wireless telephones, wireless network (WiLAN) components, GPS receivers, mobile radios, pagers, etc., use multi-band antennas to transmit and receive wireless signals in multiple wireless communication frequency bands. Consequently, one of the critical components of wireless devices is the antenna which should meet the demands of high performance in terms of high signal transmission strength, good reception of weak signals, increased (or narrowed, if required) bandwidth, and small dimensions. 
     In mobile telecommunication, electromagnetic waves in the microwave region are used to transfer information. An essential part of telecommunication devices is thus the antenna, which enables the reception and the transmission of electromagnetic waves. 
     Cellular systems may operate in two different frequency bands called GSM (global system for mobile) and DCS (digital communication system). In Europe, the frequency bands for GSM 900, which are located at 880 MHz to 960 MHz, and GSM 1800 (DCS), located at 1710 MHz to 1880 MHz, are used. Additionally, there is the GSM 850 frequency band from 824 MHz to 894 MHz and the GSM 1900 (PCS) frequency band from 1850 MHz to 1990 MHz widely used in the United States. 
     Planar inverted F-antennas (PIFAs) have many advantages. They are easily fabricated, have a simple design, and cost little to manufacture. Currently, the PIFA is widely used in small communication devices, such as cellular phones. This is due to the PIFA&#39;s compact size that makes it easy to integrate into a device&#39;s housing, thereby providing a protected antenna. The PIFA also provides an additional advantage over, for example, the popular whip antennas with respect to radiation exposure. A whip antenna has an omnidirectional radiation field, whereas the PIFA has a relatively limited radiation field towards the user. 
     The PIFA is generally a λ/4 resonant structure and is implemented by short-circuiting the radiating element to the ground plane using a conductive wall, plate or post. Thus, the conventional PIFA structure consists of a conductive radiator or radiating element disposed parallel to a ground plane and is insulated from the ground plane by a dielectric material, typically air. This radiating element connects to two pins, typically disposed toward one end of the element, giving the appearance of an inverted letter “F” from the side view. The first pin electrically connects the radiating element to the ground plane, and the second pin provides the antenna feed. The frequency bandwidth, gain, and resonant frequency of the PIFA depend on the height, width, and depth of the conductive radiator element, and the distance between the first pin connected to the radiating element and ground, and the second pin connected to the antenna feed. 
       FIG. 2  illustrates a conventional PIFA  200  design. The conventional PIFA  200  includes a conductive plate which forms a radiating element  209  of the antenna. Radiating element  209  is disposed about parallel to a ground plane  210  formed on a substrate  211 . This parallel orientation between radiating element  209  and ground plane  210  provides optimal performance, but other orientations are possible. 
     Radiating element  209  electrically connects to ground plane  210  via a tuning or shortening element  212 , most often disposed at one side of radiating element  209  and a feed element  213 . Feed element  213  is somewhat electrically insulated from ground plane  210 . When electric current is fed to radiating element  209  mounted above ground plane  210  through feed element  213 , radiating element  209  and ground plane  210  become excited and act as a radiating device. 
     The operating frequency or the resonance frequency of PIFA  200  can be modified either by adjusting the dimensions and shape of radiating element  209  or by moving the location of feed element  213  with respect to tuning element  212 . The resonance frequency can also be finely adjusted by changing the height and/or width of tuning element  212 . Thus, in the conventional PIFA, the operating frequency or resonance is fixed by the size, shape, or placement of feed element  213 , tuning element  212 , or radiating elements  209 , respectively. To change the bandwidth of PIFA  200 , the height must be increased which will lead to an undesirable increase in the overall antenna size. With a trend towards smaller terminals, i.e., thinner and shorter mobile terminals, with very limited space available for the antenna element (GSM/WCDMA), the bandwidth of the High Band, DCS, PCS, and UMTS (1710 MHz-&gt;2170 MHz) at −6 dB S 11  is becoming more difficult to achieve. 
     PIFAs with parasitic elements are being used currently to enhance the High Band bandwidth, but usually use a flex film on the antenna carrier with an additional connection (c-clip or Pogo Pin) on the PCB. 
     SUMMARY OF THE INVENTION 
     One object of the present invention is to employ a microstrip parasitic element (MPE) as a part of the ground layer of the carrying structure, e.g., printed circuit board (PCB) in such a way that the matching and bandwidth of the antenna are improved and increased. 
     Embodiments of the invention use an antenna arrangement including: a ground plane, a feed element, and a radiating element coupled to the feed element, the radiating element being substantially parallel to and vertically displaced from the ground plane arranged on a first surface of a carrying structure by the feed element and a shortening element. The antenna further includes a parasitic element provided directly on the carrying structure as part of the carrying structure ground layer. The parasitic element me be a microstrip that is arranged at a ground clearance area. The parasitic element may extend over an edge of said carrying structure. The parasitic element may also extend to a second surface of said carrying structure. The carrying structure may be a PCB. 
     The invention also relates to a wireless communication device having an antenna that includes: a ground plane provided on a carrying structure, a feed element, and a radiating element coupled to the feed element, the radiating element being substantially parallel to and vertically displaced from the ground plane by the feed element and a shortening element. The antenna further includes a parasitic element provided directly on the carrying structure as part of the carrying structure ground layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate a number of embodiments of the invention and, together with the description, explain the invention. In the drawings: 
         FIG. 1  illustrates a block diagram of a wireless communication device according to the present invention; 
         FIG. 2  illustrates a conventional PIFA design according to prior art; 
         FIG. 3  illustrates a semi-PIFA according to the invention; 
         FIG. 4  illustrates a block diagram of a wireless communication device according to the invention; and 
         FIG. 5  illustrates a cross section through a part of a PCB. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The antenna designs described in the following description are “planar” antennae. A “planar” antenna has an extended shape that lies generally along a plane, i.e., the antenna may have three dimensions but one of the dimensions may be an order of a magnitude less than the other two dimensions. 
       FIG. 1  illustrates a block diagram of an exemplary wireless communication device  10 . Wireless communication device  10  may include a housing  11 , a controller  101 , a memory  102 , a user interface  103 , a transceiver  104 , a key input unit  105 , a display unit  106 , and a multiband antenna  100 . Transceiver  104  may interface wireless communication device  10  with a wireless network using antenna  100 . It is appreciated that transceiver  104  may transmit or receive signals according to one or more of any known wireless communication standards known to the person skilled in the art. Controller  101  may control the operation of wireless communication device  10  responsive to programs stored in memory  102  and instructions provided by the user via interface  103 . 
     Antenna designs according to the present invention, with a microstrip parasitic element as part of the ground plane on the PCB, may improve and increase the matching and bandwidth. 
       FIG. 3  illustrates an antenna, for example, a semi-PIFA according to the present invention. A PIFA  300  may include a ground plane  310  formed on a substrate  311 . In this embodiment, ground plane  310  may be illustrated as being embedded directly on substrate  311  (e.g., a PCB), which also may carry other electrical components (not shown) of the device. This configuration may provide the advantage that the antenna can be mounted relatively close to the PCB, thus saving volume in the wireless device. 
     PIFA  300  may include a radiating element  309  that may include a low frequency radiating element and a high frequency radiating element respectively. Radiating element  309  may include any known configuration or pattern and vary in size to optimize the bandwidth, operating frequency, radiation patterns, and the like. Radiating element  309  may electrically connect to ground plane  310 , for example, via a tuning or shortening element  312 . Feed element  313  may connect to a signal source from a radio or other RF (radio frequency) transmitter, receiver, or transceiver (not shown) to radiating element  309 . Feed  313  may be at least partially electrically insulated from ground plane  310 , to prevent grounding therefrom. 
     To enhance the matching and bandwidth of the high-band, a parasitic element  315  may be arranged extending from ground plane  310 , preferably on the antenna ground clearance area  316 . Parasitic element  315  may have any regular or irregular shape, such as rectangular, circular, meander, etc. 
     If the size (e.g., length and width) of parasitic element  315  is not sufficient (e.g. &lt;10 mm antenna ground clearance), it is also possible to continue with the microstrip to the other side of the PCB or any suitable direction. This is illustrated in  FIG. 5 , where  315 ′ and  315 ″ denote extension of the parasitic element over the edge of the PCB  311  and the other side of it, respectively. Parasitic element  315 ′″ may also extend through a via. 
     The parasitic element according to the invention, which may be a narrowband, wide-beam antenna, may be fabricated by etching the antenna element pattern in metal trace bonded to an insulating dielectric substrate with a continuous metal layer bonded to the substrate which forms a ground plane. Possible microstrip antenna radiator shapes include square, rectangular, circular, and elliptical, but any continuous shape is possible. For example, the microstrip antenna may be a rectangular patch. The rectangular patch antenna may be approximately a one-half wavelength long section of rectangular microstrip transmission line. When air is the antenna substrate, the length of the rectangular microstrip antenna may be approximately one-half of a free-space wavelength. As the antenna is loaded with a dielectric as its substrate, the length of the antenna decreases as the relative dielectric constant of the substrate increases. 
       FIG. 4  is a block diagram illustrating a structure of a mobile communication terminal  40  in accordance with an embodiment of the present invention. Referring to  FIG. 4 , mobile communication terminal  40  may include a memory  402 , a key input unit  405 , a display unit  406 , a transceiver  404 , a PIFA  400 , including a parasitic element  407 , and a controller  401 . Controller  401  may process voice signals and/or data according to the protocol for a phone call, data communication, or wireless Internet access, and may control the respective components of the mobile communication terminal. Furthermore, controller  401  may receive key input from key input unit  405 , and control display unit  406  to generate and provide image information in response to the key input. Controller  401  may receive current location information from the user or BS. Through the received location information, controller  401  may identify a frequency band mapped to the current location from a region frequency memory  408  included in memory  402 . 
     It should be noted that the word “comprising” does not exclude the presence of other elements or steps than those listed and the words “a” or “an” preceding an element do not exclude the presence of a plurality of such elements. It should further be noted that any reference signs do not limit the scope of the claims, that the invention may be implemented at least in part by means of both hardware and software, and that several “means”, “units” or “devices” may be represented by the same item of hardware. 
     The above mentioned and described embodiments are only given as examples and should not be limiting to the present invention. Other solutions, uses, objectives, and functions within the scope of the invention as claimed in the below described patent claims should be apparent for the person skilled in the art.