Patent Publication Number: US-2004046697-A1

Title: Dual band antenna

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to an antenna, and in particular to an antenna which is capable of operating in two distinct frequency bands.  
       [0003] 2. Description of the Prior Art  
       [0004] There is a growing need for dual-frequency antennas for use in wireless communication devices to adapt the devices for dual-frequency operation. In particular, enabling a device to communicate both in the 2.45 GHz (IEEE 802.11b) and in the 5.25 GHz (IEEE 802.11a) frequency bands is desirable. Several conventional dual-frequency planar antennas are disclosed in U.S. Pat. No. 6,002,367 and in a paper titled “Wide-Band E-Shaped Patch Antennas for Wireless Communications” by Fan Yang, Xue-Xia Zhang and Yahya Rahmat-Samii, IEEE Transactions on Antennas and Propagation, Volume 49, Number 7, July 2001, pp. 1094-1100. However, these antennas have high profiles, so occupy a relatively large space in an electrical device.  
       [0005] Hence, an improved antenna is desired to overcome the above-mentioned shortcomings of existing antennas.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006] A main object of the present invention is to provide a dual band antenna having a low profile.  
       [0007] A dual band, antenna in accordance with the present invention for an electronic device comprises an insulative substrate, a planar conductive element disposed on the insulative substrate, and a feeder cable electrically connecting to the conductive element. The conductive element comprises a first radiating portion, a second radiating portion, and a ground portion. The first and the second radiating portions, and the ground portion are all disposed in the same plane, thereby occupying a relatively small space in an electrical device.  
       [0008] Other objects, advantages and novel features of the invention will become more apparent from the following detailed description of a preferred embodiment when taken in conjunction with the accompanying drawings. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0009]FIG. 1 is a top view of a first embodiment of a dual band antenna in accordance with the present invention, attached to a ground element of an electrical device;  
     [0010]FIG. 2 is a top view of the dual band antenna of FIG. 1, shown in isolation;  
     [0011]FIG. 3 is a test chart recording for the dual band antenna of FIG. 1, showing Voltage Standing Wave Ratio (VSWR) as a function of frequency;  
     [0012]FIG. 4 is a horizontally polarized principle plane radiation pattern (where the principle plane is an X-Y plane) of the dual band antenna of FIG. 1 operating at a frequency of 2.5 GHz;  
     [0013]FIG. 5 is a vertically polarized principle plane radiation pattern (where the principle plane is an X-Y plane) of the dual band antenna of FIG. 1 operating at a frequency of 2.5 GHz;  
     [0014]FIG. 6 is a horizontally polarized principle plane radiation pattern (where the principle plane is an X-Y plane) of the dual band antenna of FIG. 1 operating at a frequency of 5.35 GHz;  
     [0015]FIG. 7 is a vertically polarized principle plane radiation pattern (where the principle plane is an X-Y plane) of the dual band antenna of FIG. 1 operating at a frequency of 5.35 GHz;  
     [0016]FIG. 8 is a perspective view of a second embodiment of the present invention; and  
     [0017]FIG. 9 is a test chart recording for the dual band antenna of FIG. 8, showing VSWR as a function of frequency. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0018] Reference will now be made in detail to a preferred embodiment of the present invention.  
     [0019] Referring to FIGS. 1, 2 and  3 , a dual band antenna  1  in accordance with a first embodiment of the present invention comprises a flat and rectangular substrate  10 , a planar conductive element (not labeled) disposed on an upper major surface of the substrate  10 , and a coaxial feeder cable  14 .  
     [0020] The substrate  10  can be formed from a dielectric material such as glass, including fused quartz, or ceramics, such as alumina or beryllia. It can also comprise an ordinary electronic substrate such as a printed circuit board or a flexible printed circuit board.  
     [0021] The conductive element comprises a ground portion  13 , and a first radiating portion  11  and a second radiating portion  12  extending from the ground portion  13 . The first and the second radiating portions  11 ,  12  and the ground portion  13  are all in the same plane and are configured to be strip-shaped. The ground portion  13  is horizontally disposed on the substrate  10 . The first radiating portion  11  is T-shaped and extends from a middle section of a rear edge of the ground portion  13 . The first radiating portion  11  comprises a first radiating segment  110  parallel to the ground portion  13 , and a vertical first connection segment  111 . The first connection segment  111  extends from a middle section of the first radiating segment  110  to the middle section of the ground portion  13 . The second radiating portion  12  has an inverted L-shape and is partially surrounded by the first radiating portion  11 . The second radiating portion  12  comprises a vertical second connection segment  121  parallel to the first connection segment  111  and a horizontal second radiating segment  120  parallel to the ground portion  13  and extending from a rear end of the second connection segment  121 . The second connection segment  121  extends from a side section of the rear edge of the ground portion  13  and is adjacent to the first connection segment  111 .  
     [0022] The coaxial feeder cable  14  has an inner core conductor  140  and an outer shield conductor  141  surrounding the inner core conductor  140 . The inner core conductor  140  is soldered to the first radiating segment  110  of the first radiating portion  11  for transmitting signals between the dual band antenna  1  and a signal unit of an electrical device (not shown). The location of the solder point of the inner core conductor  140  on the first radiating portion  11  is predetermined to achieve a desired matching impedance for both frequency bands. The outer shield conductor  141  is soldered to the ground portion  13  for grounding the dual band antenna  1 .  
     [0023] Referring to FIG. 1, in assembly, the dual band antenna  1  is assembled in an electrical device, such as a laptop computer (not shown), with a front edge of the ground portion  13  soldered to an electrically conductive ground element  15  of the electrical device. The ground portion  13  is substantially in the same plane as the ground element  15 .  
     [0024] In the preferred embodiment, a length of the first radiating segment  110  is 49 mm. A distance between the first radiating segment  110  and the ground portion  13  is 5.4 mm (as shown in FIG. 2). A length of the second radiating segment  120  is 7 mm. A distance between the second radiating segment  120  and the ground portion  13  is 1.8 mm (as shown in FIG. 2). A distance between the first and the second radiating segments  110 ,  120  is 1.8 mm. The dimensions are such that each of the radiating portions  11 ,  12  is configured to resonate within a respective frequency band. For example, the first radiating portion  11  is configured to resonate between 2.38 GHz and 2.67 GHz (i.e. the 2.45 GHz frequency band). The second radiating portion  12  is configured to resonate between 5.02 GHz and 5.40 GHz (i.e., the 5.25 GHz frequency band). The first and second radiating portions  11 ,  12  constitute nearly independent regions having different resonant frequencies. This is an advantage where the dual band antenna must operate in different environments.  
     [0025]FIG. 3 shows a test chart recording of Voltage Standing Wave Ratio (VSWR) of the dual band antenna  1  as a function of frequency. Note that VSWR drops below the desirable maximum value “2” in the 2.45 GHz frequency band and in the 5.25 GHz frequency band, indicating acceptably efficient operation in these two frequency bands.  
     [0026] FIGS.  4 - 7  respectively show horizontally and vertically polarized principle plane radiation patterns of the dual band antenna  1  operating at frequencies of 2.5 GHz and 5.35 GHz (the principle plane is the X-Y plane shown in FIG. 2). Note that each radiation pattern is close to a corresponding optimal radiation pattern.  
     [0027] Referring to FIG. 8, a dual band antenna  2  according to a second embodiment of the present invention comprises a substantially rectangular ground portion  23 . The ground portion  23  of the second embodiment is larger than that of the first embodiment. In this alternative embodiment, other elements of the dual band antenna  2  have constructions similar to those of the first embodiment, so a detailed description thereof is omitted herefrom.  
     [0028]FIG. 9 shows a test chart recording of VSWR of the dual band antenna  2  as a function of frequency. Note that VSWR drops below the desirable maximum value “2” in the 2.45 GHz frequency band (2.35 GHz-2.47 GHz) and in the 5.25 GHz frequency band (5.00 GHz-5.24 GHz), indicating acceptably efficient operation in these two frequency bands.  
     [0029] It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.