Patent Publication Number: US-7911392-B2

Title: Multiple frequency band antenna assembly for handheld communication devices

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     BACKGROUND 
     The present invention relates generally to antennas, and more specifically to multiple-band antennas that are particularly suited for use in wireless mobile communication devices, such as personal digital assistants, cellular telephones, and wireless two-way email communication devices. 
     Different types of wireless mobile communication devices, such as personal digital assistants, cellular telephones, and wireless two-way email communication apparatus are available. Many of these devices are intended to be easily carried on the person of a user, often fitting in a shirt or coat pocket. 
     The antenna configuration of a mobile communication device can significantly affect the overall size or footprint of the device. For example, cellular telephones typically have antenna structures that support communication in multiple operating frequency bands. Various types of antennas for mobile devices are used, such as helical, “inverted F”, folded dipole, and retractable antenna structures, for example. Helical and retractable antennas are typically installed outside a mobile device, and inverted F antennas are usually located inside of a case or housing of a device. Generally, internal antennas are often used instead of external antennas for mobile communication devices for mechanical and ergonomic reasons. Internal antennas are protected by the case or housing of the mobile device and therefore tend to be more durable than external antennas. External antennas also may physically interfere with the surroundings of a mobile device and make a mobile device difficult to use, particularly in limited-space environments. 
     In some types of mobile communication devices, however, known internal structures and design techniques provide relatively poor communication signal radiation and reception, at least in certain operating positions. One of the biggest challenges for mobile device design is to ensure that the antenna operates effectively for various applications, which determines antenna position related to human support frame. Typical operating positions of a mobile device include, for example, a data input position, in which the mobile device is held in one or both hands, such as when a user is entering a telephone number or email message; a voice communication position, in which the mobile device may be held next to a user&#39;s head and a speaker and microphone are used to carry on a conversation; and a “set down” position, in which the mobile device is not in use by the user and is set down on a surface, placed in a holder, or held in or on some other storage apparatus. In these positions, parts of a user&#39;s support frame and other ambient objects can block the antenna and degrade its performance. Known internal antennas, that are embedded in the device housing, tend to perform relatively poorly, particularly when a mobile device is in a voice communication position. Although the mobile device is not actively being employed by the user when in the set down position, the antenna should still be functional at least receive communication signals. 
     The desire to maintain the configuration of the mobile communication device to a size that conveniently fits into a hand of the user, presents a challenge to antenna design. This creates a tradeoff between the antenna performance, which dictates a relatively larger size, and the available space for the antenna within the device. 
     The antenna size versus performance design issue becomes an even bigger challenge when the handheld communication device, which already must operate in multiple frequency bands, is required to accommodate the additional 700 MHz band. A conventional antenna for operation in that frequency range would entail a physical length of about a quarter of a wavelength, which at 700 MHz is approximately 10.7 cm. To accommodate an antenna with such size inside the handheld device is neither feasible nor practical. Moreover, having a single internal antenna that operates in the existing frequency bands, such as GSM/800/900/1800/1900 and UMTS 2100 in addition to the 700 MHz band, presents a design challenge. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic block diagram of a mobile wireless communication device; 
         FIG. 2  is a schematic block diagram of the circuitry for the mobile wireless communication device; 
         FIG. 3  is a perspective view from above a dielectric substrate on which an antenna assembly of the communication device is mounted; 
         FIG. 4  is a perspective view from below the dielectric substrate; 
         FIG. 5  is an enlarged perspective view from a first angle, showing three surfaces of a support frame on which the antenna is formed; 
         FIG. 6  is an enlarged perspective view from a second first angle showing the details of three surfaces of the support frame; and 
         FIG. 7  is an enlarged perspective view from beneath the dielectric substrate and showing three surfaces of the support frame; and 
         FIG. 8  is a perspective view of an embodiment of the antenna mounted on a support frame that is separate from the dielectric substrate. 
     
    
    
     DETAILED DESCRIPTION 
     An antenna assembly for a mobile wireless communication device has conductive elements on selected surfaces of a support frame, that can be a rectangular polyhedron. The support frame has a first surface, a second surface, a third surface, and a fourth surface all extending between a fifth surface and a sixth surface. 
     An F-shaped conductive member is located on the first surface and comprises a conductive stripe from which a first arm and a second arm project in a spaced-apart, parallel manner. The first arm is connected to a conductive loop on the fifth surface and the second arm is connected to a first conductive strip also on the fifth surface. The first conductive strip also is connected to a U-shaped conductive member that is located on the third surface. 
     A rectangular conductive patch is provided on the second surface and is connected to the conductive stripe of the F-shaped conductive member. A conductive remote strip, located on the second surface, is connected to the conductive loop. An L-shaped patch is on the sixth surface and is connected to the conductive remote strip. A second conductive strip, provided on the sixth surface, is connected to the U-shaped conductive member. 
     In one embodiment, the support frame is contiguous with a first major surface of a sheet of dielectric material that has an opposing second major surface with a conductive layer applied thereto that provides a ground plane. In this embodiment a portion of the second major surface, on which the conductive layer is not applied, forms the sixth surface of the support frame. 
     The present antenna assembly is specially adapted for use in mobile wireless communication devices, such as personal digital assistants, cellular telephones, and wireless two-way email communication devices, and for brevity those mobile wireless communication devices are referred to herein as mobile devices and individually as a mobile device. Furthermore, the present antenna assembly will be described in the specific context of a cellular telephone. 
     Referring initially to  FIGS. 1 and 2 , a mobile device  20 , such as a mobile cellular device, illustratively includes a housing  21  that may be a static housing, for example, as opposed to a flip or sliding housing which are used in many cellular telephones. Nevertheless, those and other housing configurations also may be used. A battery  23  is carried within the housing  21  for supplying power to the internal components. 
     The housing  21  contains a main dielectric substrate  22 , such as a printed circuit board (PCB) substrate, for example, on which is mounted the primary circuitry  24  for mobile device  20 . That primary circuitry  24 , as shown in greater detail in  FIG. 2 , typically includes a microprocessor  25 , memory that includes a random access memory (RAM)  26  and a flash memory  27  which provides non-volatile storage. A serial port  28  constitutes a mechanism by which external devices, such as a personal computer, can be connected to the mobile wireless communication device  20 . A display  29  and a keyboard  30  provide a user interface for controlling the mobile wireless communication device  20 . 
     An audio input device, such as a microphone  31 , and an audio output device, such as a speaker  33 , function as an audio interface to the user and are connected to the primary circuitry  24 . 
     Communication functions are performed through a radio frequency circuit  34  which includes a wireless signal receiver  36  and a wireless signal transmitter  38  that are connected to a multiple-element antenna assembly  40 . The antenna assembly  40  can be carried within the lower portion of the housing  21 . The antenna assembly will be described in greater detail subsequently herein. 
     The radio frequency circuit  34  also includes a digital signal processor (DSP)  42  and local oscillators (LOs)  44 . The specific design and implementation of the radio frequency circuit  34  is dependent upon the communication network in which the mobile device  20  is intended to operate. For example a device destined for use in North America may be designed to operate within the Mobitex™ mobile communication system or DataTAC™ mobile communication system, whereas a device intended for use in Europe may incorporate a General Packet Radio Service (GPRS) radio frequency circuit. 
     When required network registration or activation procedures have been completed, the mobile communication device  20  sends and receives signals over the communication network  46 . Signals received by the multiple-element antenna from the communication network  46  are input to the receiver  36 , which performs signal amplification, frequency down conversion, filtering, channel selection, and analog-to-digital conversion. Analog-to-digital conversion of the received signal allows the DSP  42  to perform more complex communication functions, such as demodulation and decoding. In a similar manner, signals to be transmitted are processed by the DSP  42  and sent to the transmitter  38  for digital-to-analog conversion, frequency up-conversion, filtering, amplification and transmission over the communication network  46  via the multiple-element antenna. 
     The mobile device  20  also may comprise one or auxiliary input/output devices  48 , such as, for example, a WLAN (e.g., Bluetooth®, IEEE. 802.11) antenna and circuits for WLAN communication capabilities, and/or a satellite positioning system (e.g., GPS, Galileo, etc.) receiver and antenna to provide position location capabilities, as will be appreciated by those skilled in the art. Other examples of auxiliary I/O devices  48  include a second audio output transducer (e.g., a speaker for speakerphone operation), and a camera lens for providing digital camera capabilities, an electrical device connector (e.g., USB, headphone, secure digital (SD) or memory card, etc.). 
     Structures for the antenna assembly  40  described herein are sized and shaped to tune the antenna for operation in multiple frequency bands. In an embodiment described in detail below, the multiple-band antenna includes structures that are primarily associated with different operating frequency bands thereby enabling the multiple-band antenna to function as the antenna in a multi-band mobile device. For example, a multiple-band antenna assembly  40  is adapted for operation at the Global System for Mobile communications (GSM) 900 MHz frequency band and the Digital Cellular System (DCS) frequency band. Those skilled in the art will appreciate that the GSM-900 band includes a 880-915 MHz transmit sub-band and a 925-960 MHz receive sub-band. The DCS frequency band similarly includes a transmit sub-band in the 1710-1785 MHz range and a receive sub-band in the 1805-1880 MHz range. The antenna assembly  40  also functions in the Universal Mobile Telecommunications System (UMTS) 2100 MHz bands and in the 700 MHz frequency band. It will also be appreciated by those skilled in the art that these frequency bands are for illustrative purposes only and the basic concepts of the present antenna assembly can be applied to operate in other pairs of frequency bands. 
     With reference to  FIGS. 3 and 4 , the electrically non-conductive substrate  22  on which the electronic circuits for the mobile device are formed comprises a flat sheet of dielectric material of a type conventionally used for printed circuit boards. Alternatively, the substrate  22  may be contoured to fit the interior shape of the mobile device housing  21 . The dielectric substrate  22  has a first major surface  50  with one or more layers of patterns of conductive material, such as copper, to which circuit components are connected by soldering, for example. The antenna assembly  40  can be mounted at one corner of the dielectric substrate  22  projecting away from the first major surface  50 . An opposite second major surface  51  of the substrate  22  has a layer  52  of conductive material, such as copper, applied thereto. The conductive layer  52  extends over the majority of the second major surface  51 , except for a portion adjacent the antenna assembly  40 . The conductive layer  52  forms a ground plane for the mobile device  20 . 
     The multi-frequency antenna assembly  40  comprises specific electrically conductive patterns on surfaces of a rectangular polyhedron which forms the support frame  54  of the antenna assembly. In one version, the support frame  54  is constructed of a dielectric material, such as FR-4 laminate which is a continuous glass-woven fabric impregnated with an epoxy resin binder. The rectangular polyhedron support frame  54  may be 30 mm by 15 mm by 9 mm high. In one embodiment, the antenna support frame  54  is hollow being fabricated of five panels of dielectric material that are 1.5 mm thick and secured together at their edges and to the first major surface  50  of the dielectric substrate using appropriate means, such as an adhesive. Alternatively, a solid support frame for the antenna assembly can be utilized. Regardless of the specific construction, the antenna support frame  54  is considered as having six surfaces, including a portion of the second major surface  51  of the dielectric substrate  22  which is directly beneath the remainder of the support frame  54  as seen in  FIG. 4  and demarked by dashed line  55 . As a further alternative, the support frame  54  can be formed by six panels secured together to form a separate rectangular polyhedron that is spaced from the dielectric substrate  22 , as seen in  FIG. 8 . 
     Referring to  FIGS. 5 ,  6  and  7 , the rectangular polyhedron support frame  54  has a first surface  61 , a second surface  62 , a third surface  63  and a fourth surface  64  forming four sides of the support frame. A fifth surface  65  forms the top surface and a sixth surface  66 , comprising a portion of the second major surface  51  of the dielectric substrate  22 , forms a bottom of the antenna support frame. The first, second, third and fourth surfaces  61 - 64  extend between the fifth and sixth surfaces  65  and  66 . The antenna support frame  54  is located at one corner of the dielectric substrate  22  with the second and third surfaces  62  and  63  of the support frame flush with and incorporating a portion of two edges of that substrate. The first surface and fourth surfaces  61  and  64  abut and project away from portions of the first major surface  50  of the dielectric substrate  22 . 
     The antenna assembly  40  comprises electrically conductive material applied to different surfaces of the support frame  54  in selected patterns to form segments of the antenna assembly  40 . There is no conductive pattern on the fourth surface of the support frame  54 . As shown in  FIG. 5 , an F-shaped member  70  is formed on the first surface  61  and has a first conductive stripe  71  extending from an edge at which the first surface meets the second surface along the portion of the first surface that is immediately adjacent to the dielectric substrate  22 . Electrical connection to the antenna assembly  40  is made at a conductive area  74  on the first major surface  50  of the dielectric substrate  22  and connected to a middle section of the first conductive stripe  71 . The antenna assembly  40  is excited by a signal applied from the transmitter  38  between the ground plane conductive layer  52  and the conductive area  74 . The F-shaped member  70  further comprises first and second spaced-apart, parallel arms  72  and  73  attached to the first conductive stripe  71  and projecting upward therefrom and away from dielectric substrate  22 . The first and second arms  72  and  73  extend to the edge  67  of the first surface  61  that abuts the fifth surface  65 . The first arm  72  is spaced from the edge  68  at which the first surface  61  adjoins the second surface  62 . The second arm  73  and the first conductive stripe  71  are spaced from the edge  69  at which the first surface  61  abuts the fourth surface  64 . 
     The first arm  72  of the F-shaped member  70  is connected, at the edge  67  between the first and fifth surfaces  61  and  65 , to a corner of a conductive loop  76  on the fifth surface  65 . The conductive loop  76  extends to an opposite edge  75  where the fifth surface  65  abuts the third surface  63 , and extends along another edge  77  in common with the fifth and second surfaces  65  and  62 . The conductive loop  76  is rectangular, however other loop shapes can be employed. The conductive loop  76  extends across approximately two-thirds of the area of the fifth surface  65 . A first straight conductive strip  78  also is located on the fifth surface  65  extending between the edge  67  shared with the first surface  61  to the opposite edge  75  shared with the third surface  63 . The first conductive strip  78  has one end that is connected at edge  67  to the second arm  73  of the F-shaped member  70 . 
     The opposite end of the first conductive strip  78  extends around edge  75  onto the third surface  63  where, as seen in  FIG. 6 , it is connected to one end of a U-shaped member  80 . Specifically the first conductive strip  78  connects to a first end of a first leg  81  of the U-shaped member  80 , which first leg is parallel to and spaced from a second leg  82  that extends along the bottom edge  85  of the third surface  63  that abuts the first major surface  50  of the dielectric substrate  22 . A cross leg  83  connects a second end of the first leg  81  to an adjacent end of the second leg  82 . The cross leg  83  is slightly spaced from the edge  87  at which the third surface  63  abuts the second surface  62 . The U-shaped member  80  is oriented as though it is lying on its side against the bottom edge  85  of the third surface  63  that is contiguous with the dielectric substrate  22 . 
     With particular reference to  FIGS. 6 and 7 , a first patch  86  is located on the second surface  62  of the support frame  54  and has a rectangular shape abutting the edges  68  and  77  where the second surface interfaces with the first and fifth surfaces  61  and  65 , respectively. The first patch  86  is connected to the end of the first conductive stripe  71  of the F-shaped member  70  on the first surface  61 . A conductive remote strip  84  also is located on the second surface  62  and extends between the edges  77  and  85  which the second surface respectively shares with the fifth and sixth surfaces  65  and  66 . The conductive remote strip  84  is parallel to and spaced from the edge  87  at which the second surface  62  abuts the third surface  63 . One end of the conductive remote strip is connected to the loop  76  on the fifth surface  65 . 
     With particular reference to  FIG. 7 , the other end of the conductive remote strip  84  is connected to an L-shaped patch  88  on the sixth surface  66  of the antenna support frame  54 . That interconnection is at one end of a leg of the L-shaped patch  88  with another leg near the center of the support frame  54  projecting parallel to the edge  85  between the second and sixth surfaces  62  and  66 . A straight second conductive strip  89  also is located on the sixth surface  66  on the remote side of the L-shaped patch  88  from the second surface  62  and parallel to the second surface  62 . The second conductive strip  89  is connected to the free end of the second leg  82  of the U-shaped member  80  on the third surface  63 . The L-shaped patch  88  and the second conductive strip  89  on the sixth surface of the antenna support frame  54  are spaced from the ground plane conductive layer  52 . The rectangular first patch  86  and the L-shaped patch  88  provide impedance matching of the antenna assembly  40  with the impedance of a radio frequency circuit  34 . Specifically the first patch  86  provides impedance matching at the lower frequency bands, while the L-shaped patch  88  performs impedance matching at the higher frequencies. 
     The conductive components on the antenna support frame  54  can be formed by applying a layer of conductive material, such as copper, to the entirety of the respective surface of the support frame  54  and then using a photolithographic process to etch away the conductive material from areas of that surface where a conductive part is not desired. 
     The various electrically conductive antenna components combine to form elements of the antenna assembly  40 . A first antenna element comprises the first arm  72  of the F-shaped member  70 , the conductive loop  76 , and the conductive remote strip  84 . The first antenna element resonates in the 800 MHz and 900 MHz frequency bands. A second antenna element comprises the second arm  73 , the first conductive strip  78 , the U-shaped conductive member  80 , and the second conductive strip  89 . A second antenna element is longer that the first antenna element and resonates in the 700 MHz frequency band. The wrapping of the first and second antenna elements in close proximity to each other widens the bandwidth of the antenna assembly. Sections of the two antenna element resonate at higher frequencies in the 1800 MHz, 1900 MHz and 2100 MHz frequency bands. 
       FIG. 8  illustrates a second antenna assembly  90  that is formed on a second support frame  92  of dielectric material. The second support frame  92  is a six-sided rectangular polyhedron that is the same as the first support frame  54  described previously, except that the second support frame  92  is separate from the dielectric substrate  94  on which the components of the mobile device are mounted. The second antenna assembly  90  comprises the same configuration of conductive patterns on each of its surfaces as on the surfaces of the first support frame  54 , however the sixth surface is not also a surface of the dielectric substrate  94 . 
     The foregoing description was primarily directed to a certain embodiments of the antenna. Although some attention was given to various alternatives, it is anticipated that one skilled in the art will likely realize additional alternatives that are now apparent from the disclosure of these embodiments. Accordingly, the scope of the coverage should be determined from the following claims and not limited by the above disclosure.