Abstract:
The present invention relates to a chip antenna which comprises a substrate, a feeding pad, a feeding conductor, a matching unit, and a meandering conductor. The substrate formed with a dielectric material. By varying the length of the meandering conductor, the central frequency of the chip antenna can be properly obtained and controlled. The matching unit, which is formed by joining a matching conductor with a ground plate, uses the short-circuit function of the matching conductor to obtain the desired bandwidth. In this way, the chip antenna is well suited for applications in wireless communication systems, including personal mobile communication networks and equipment.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to chip antennas, and more particularly, to a broadband chip antenna for use in wireless communication networks and equipment, including short-distance wireless communication and personal mobile communication networks and equipment. 
     2. Description of the Related Art 
     When developing and designing wireless mobile communication devices, due to the constraint on size, monopole antennas  10  with a quarter wavelength, as shown in FIG. 1, are generally incorporated in device as basic units. However, the developing direction is moving slowly toward devices that are lighter, thinner, shorter, and smaller. 
     The concept of using a special winding shape to shorten the length of a wire antenna is first developed in 1984. For instance, a winding antenna of a zigzagging or meandering shape is disclosed by H. Nakano, H. Tagami, A. Yoshizawa, and J. Yamauchi in an article entitled “Shortening Ratios of Modified Dipole Antenna”, which is published in  IEEE Trans. Antennas Propagat ., AP-32, pp. 385-386. In 1996, a winding antenna of a bow-tie shape, which further shortens the antenna length, is disclosed in “IEEE AP-S International Symposium”, pp. 1566-1569 by M. Ali and S. S. Stuchly. 
     FIG. 2 shows a conventional chip antenna  20  of a meandering type (European patent 0 764 999 A1). The chip antenna  20  has a substrate  22  of a dielectric and/or magnetic material. A metal conductor  24  is disposed in or on the outer surface of the substrate as a meandering line, or a zigzagging line (not shown). One end of the metal conductor  24  is used as a feeding point  26 , which is connected to the feeding pad  28 . By utilizing the intrinsic characteristic, length, and number of turns or curves of the metal conductor, the general design principle regarding self-matching functions can be achieved so that the antenna can have proper resonance and radiation. However, one drawback of this type of chip antenna is that it has limited range on reduction of size. 
     As shown in FIG. 3, another type of conventional chip antenna  30  (U.S. Pat. No. 5,764,198) uses a spirally wounding conductor  32  and a capacitor  34  connected in parallel to achieve the matching function for the antenna. Although the chip antenna of this type is of a reduced size, its bandwidth is limited. 
     SUMMARY OF THE INVENTION 
     Due to the difficulty in bandwidth expansion for the above-discussed chip antenna, it is a primary object of the present invention to provide a chip antenna having a substrate, feeding pad, feeding conductor, matching unit, and meandering conductor to effectively expand bandwidth and reduce size. 
     The above and other objects, which will become apparent in reading the specification below, are realized by a chip antenna that has a substrate of a dielectric material and one or more layers, and a feeding pad formed on an outer surface of the substrate for signal injection. In particular, a meandering conductor is disposed on at least one layer of the substrate for use as a radiator unit. A conductor is disposed on a substrate layer for use as a feeding conductor for the antenna, and for propagating signals when connected to a signal source. A matching unit disposed on the layers of substrate includes a matching conductor and a ground in which the matching conductor is shielded by at least one plate of the ground. In particular, portions of the matching conductor are respectively connected to the meandering conductor, ground, and feeding conductor. 
     Other objects and the features will be apparent from the following detailed description of the invention with reference to the appended drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more fully described and better understood from the following description, taken with the appended drawings, in which: 
     FIG. 1 shows a conventional monopole antenna having a quarter wavelength; 
     FIG. 2 is a perspective view of a conventional chip antenna; 
     FIG. 3 is a perspective view of another conventional chip antenna; 
     FIG. 4 shows a chip antenna according to a first embodiment of the present invention; 
     FIG. 5 is a graph illustrating the characteristic of the chip antenna according to the present invention; 
     FIG. 6 shows a chip antenna according to a second embodiment of the present invention; 
     FIG. 7A is an exploded view showing one arrangement for a meandering conductor, feeding conductor, and matching conductor of the present invention; 
     FIG. 7B is an exploded view showing another arrangement for the meandering conductor, feeding conductor and matching conductor of the present invention; 
     FIG. 8 is an exploded perspective view showing a chip antenna according to a third embodiment of the present invention; 
     FIG. 9 is an exterior perspective view showing the chip antenna of FIG. 8; 
     FIG. 10 is an isolated perspective view showing one embodiment for a ground, feeding pad, feeding conductor, and matching conductor of the present invention; 
     FIG. 11A is a partial front perspective view showing one embodiment for a meandering conductor, feeding conductor, and matching conductor of the present invention; 
     FIG. 11B is an isolated front perspective view of the meandering conductor of FIG. 11A; 
     FIG. 12 an exploded view showing layers of the chip antenna of FIG. 8; 
     FIG. 13 is an isolated perspective view showing another embodiment for a ground, feeding pad, feeding conductor, and matching conductor of the present invention; 
     FIG. 14 is yet another embodiment for a ground, feeding pad, feeding conductor, and matching conductor of the present invention; 
     FIG. 15 is still yet another embodiment for a ground, feeding pad, feeding conductor, and matching conductor of the present invention; and 
     FIG. 16 is another exploded view showing layers of the chip antenna of FIG.  15 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 4 is a partially exploded view of a first embodiment in accordance with the present invention. A substrate  41  formed from a dielectric material is consisted of, e.g., ceramics, glass/epoxy, or the like. A meandering metal conductor  42  made from, e.g., gold, silver, silver-palladium, copper or alloys, is meanderingly disposed in the substrate  41 . A first end  421  of the meandering conductor  42  is linked to a first portion of the matching conductor  45 . A second end  422  of the meandering conductor  42  extends longitudinally and meanderingly toward a welding plate  44 . As a result, the overall length of the chip antenna is shortened while the effective resonance length and characteristics are nearly that of a monopole antenna of a quarter wavelength. In addition, one end of the feeding conductor  46  is linked to the feeding pad  43 , and the other end of the feeding conductor  46  is linked to a second portion and the first portion of the matching conductor  45 . 
     Thus, by controlling the length of the meandering conductor  42 , the central frequency of the antenna is affected accordingly. Moreover, the meandering conductor  42  can be wholly or partially placed at the outer surface of the substrate  41 , or the interior thereof (not shown). In order to adjust the dimensions of the antenna, the meandering conductor  42  is meandering or zigzagging in shape, and wounding longitudinally or spirally in three dimensions. 
     When the number of wounding of the meandering conductor  42  increases, the radiation resistance of the antenna decreases and the inductance increases that reduce the overall radiation efficiency and bandwidth of the antenna. Thus, a matching metal conductor is used in the present invention to increase the radiation efficiency and bandwidth. The first embodiment of the present invention is configured to form a strip line structure in which a ground  47  having opposing metal plates shields the matching conductor  45 . Moreover, the ground  47  is linked to the second portion of the matching conductor  45  as to propagate a short-circuit condition. It is also permissible to design or implement a specific length and/or width for the matching conductor as to match the input impedance and acquire the desired bandwidth. 
     FIG. 5 shows the measured result of the antenna&#39;s return loss of the present invention. In particular, the central frequency thereof is set at 2.44 GHz, and the bandwidth (−10 dB) can reach upwards of 220 MHz (about 9.2%). 
     One way to further reduce the size of the chip antenna is shown in FIG. 6, which is directed to a second embodiment of the present invention that adopts a microstrip line structure. The chip antenna in this embodiment is comprised of a substrate  61 , a meandering conductor  62 , a feeding pad  63 , a feeding conductor  66 , and a matching unit. 
     The meandering conductor  62  is disposed in the substrate  61 . One end  621  of the meandering conductor  62  is linked to a first portion of the matching conductor  65 . The other end  622  of the meandering conductor  62  extends longitudinally and meanderingly toward the opposite direction of a welding plate  64 . One end of the feeding conductor  66  is linked to the feeding pad  63 . The other end of the feeding conductor  66  is linked to a first and second portion of the matching conductor  65 . The matching unit of the present embodiment is comprised of a ground  67  and matching conductor  65  which is shielded by the metal plate of the ground  67 . In particular, the ground  67  is linked to the second portion of the matching conductor  65  as to propagate a short-circuited condition. As discussed before, it is permissible to design or implement a specific length and/or width for the matching conductor as to match the input impedance and acquire the desired bandwidth. Moreover, since the physical area in the substrate occupied by the ground  67  is reduced, more space can be allotted to the meandering conductor for use thereof. 
     One way to increase the central frequency of the antenna is to shorten the length of a meandering portion  710  of a meandering conductor  711  as shown in FIG.  7 A. In FIG. 7A, the meandering portion  710  of the meandering conductor  711  is disposed on a planar surface of one of the substrate layers. In particular, a feeding conductor  713 , the matching conductor portions  715 ,  712  and the meandering conductors  711  are all disposed on the same substrate layer. A matching conductor portion  717 , which passes through a plurality of substrate layers, is connected to the ground (not shown) at a surface point  719 . Different sizes and widths of the feeding conductor, matching conductor and meandering conductor can be used. 
     Referring to FIG. 7B, different components or portions relating to the meandering conductor and matching conductor can be spread out over different substrate layers in order to reduce the central frequency of the antenna. More specifically, the main portion  720  of the meandering conductor is disposed on a top layer of the substrate; one end  721  of the meandering conductor is connected to the first portion  722  of a matching conductor, and an end portion  725  of the meandering conductor disposed on a different substrate layer from that of the main portion  720  or feeding portion  723  is disposed on through a linking portion  724  (e.g., extended end portion of the meandering conductor), which also passes through multiple substrate layers. The first portion  722  passes through a plurality of substrate layers and connects to a feeding conduction  723  a portion  729  of a second matching conductor. The portion  729  of a second matching conductor which passes through multiple substrate layers and connects with another portion  726  of the second matching conductor, which is disposed on a substrate layer that is different from the substrate layers of the feeding portion and main portion. The portion  726  is then connected to the ground (not shown) at a surface point  728  through a portion  727 . 
     The meandering conductor of the instant invention controls the central frequency of the antenna and decreases the overall size of the antenna, and the matching unit of the instant invention matches the input impedance of the antenna at the feeding point. Thus, the bandwidth is increased and size is effectively reduced. 
     FIGS. 8-16 illustrate a chip antenna according to a third embodiment of the present invention. In FIG. 8 a ground  832 , which is divided into sections by three plates, is disposed in a substrate  837  formed from a dielectric material is consisted of, e.g., ceramics, glass/epoxy, or the like. A feeding pad  831  is disposed on the surface of the substrate  837  and connected to a feeding conductor  833 . A first matching conductor portion  835 , which is bent and passes through multiple substrate layers, is coupled to a meandering conductor  836 , while a second matching conductor portion  834  is coupled to one of the three plates. 
     The manner in which the feeding pad  831  and ground  832  are disposed on the exterior surface of the substrate is shown in FIG.  9 . 
     In FIG. 10, the three plates of the ground include a top plate  852 , middle plate  854 , and bottom plate  856 . The second matching conductor portion  834  is connected to the bottom plate  856  and disposed underneath the middle plate  854 , while the second matching conductor portion is mainly disposed between the top plate  852  and middle plate  854 . As such, a strip line structure is formed for both the first and second conductor portions  835  and  834  due to the fact that the second conductor portion  834  is sandwiched between the bottom plate  856  and the middle plate  854 , and the main portion of first conductor portion  835  is sandwiched between the top plate  852  and the middle plate  854 . 
     FIGS. 11A and 11B show the three-dimensional aspect of the meandering conductor  836 . In particular, as shown in FIG. 11A, the first and second matching conductor portions are disposed at different levels relative to the vertically disposed feeding pad  831  in order to achieve the effect of impedance exchange. By parallel connecting first and second matching conductor portions  835  and  834 , an input impedance matching circuit is formed and this circuit series connected to the feeding conductor  833  and meandering conductor  836 . FIG. 11B shows the manner in which the meandering conductor  836  is extended relative to x, y and z coordinates. By extending in the x, y and z directions and reaching for at least two or more distinct levels or layers of the substrate, various sections of the meandering conductor can be specifically set in the substrate  837  at different depths and in different directions. Moreover, the desired bandwidth can be obtained through input impedance matching by varying the length and width of the second matching conductor portion  834  and/or first matching conductor portion  835 . 
     In FIG. 12, an exploded view of the substrate is shown to illustrate various locations of, e.g., the top, middle, and bottom plates  852 ,  854  and  856  with respect to different layers of the substrate. 
     When the first matching conductor portion  835  is not sandwiched between plates, but shielded by only one plate (e.g., the middle plate  854 ) as shown in FIG. 13, a microstrip line structure is formed. By contrast, the second matching conductor portion  834  as shown in FIG. 13 forms a strip line structure (see above discussion with respect to FIG.  10 ). Conversely, when the second matching conductor portion  834  is connected to and shielded by only one plate (i.e., the middle plate  854 ) as shown in FIG. 14, then the microstrip line structure is formed as compared to the first conductor portion  835 , which is in the strip line structure since it is shielded by both top plate  852  and the middle plate  854 . 
     One way to simplify the structures as shown in FIGS. 13 and 14 is to only use a microstrip line structure as shown in FIG. 15 so that the second matching conductor portion  834 , which is coupled to a simplified first matching conductor portion  835 ′, is connected to and shielded by the bottom plate  856 . The various locations of, e.g., the simplified second matching conductor portion  835 ′ and bottom plate  856  with respect to different levels or layers of the substrate is shown in FIG.  16 . 
     While the present invention as shown and described above has provided examples for explaining in detail the application of the invention, these examples do not limit the scope of the invention. It is understood by those skilled in the art that various changes or modifications of the invention may be made therein without departing from the spirit and scope of the invention. 
     The terms and expression which have been employed herein are used as terms of description and not of limitation, and there is no intent, in the use of such terms and expressions, of excluding any of the equivalents of the features shown and described or portions thereof but it is recognized that various modifications are possible within the scope of the invention claimed.