Abstract:
The present invention is a low profile, wideband, high gain and high efficiency multi-band antenna with good return loss for wireless applications such as WLAN Access Point, ZigBee or WiMAX module, notebook computer, tablet computer and other mobile and portable devices applications and it can be used with any RF-front end circuitry that is working at 2.4-2.5 GHz, 3.1-3.4 GHz and 4.9-5.9 GHz frequency band. Moreover, the antenna assembly comprises a planar body sealed in a plastic housing with the feed pin and ground pin exposed for soldering onto a printed circuit board and thus it is easy for customers to assemble; they just need to solder the antenna pins on a printed circuit board and it will be operational. The flat structure and the plastic housing make the antenna to be low profile and compact in size so it can be easily fabricated and embedded into a notebook computer and tablet computer.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application claims the benefit of U.S. Provisional Application No. 61/476,710 filed on Apr. 18, 2011, the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to the architecture of a low profile, wideband, high gain and high efficiency multi-band antenna with good return loss for wireless communications and the antenna can be used with any RF-front end circuitry that is working at 2.4-2.5 GHz, 3.1-3.4 GHz and 4.9-5.9 GHz frequency band. 
         [0004]    2. Description of Related Art 
         [0005]    Current wireless communication devices such as notebook computer, tablet computer etc. have an increasing demand for wide bandwidth, high gain multi-band antennas. However, in most cases the multi-band antenna design is difficult since it is hard to get enough bandwidth with good return loss for each frequency band (For example, cellular phone antenna often has a −5 dB return loss at the edges of operating frequency band even if matching circuit is applied). 
         [0006]    Accordingly, there is a need in the art for a high gain wide bandwidth, multi-band antenna with excellent return loss characteristics across typical operating bandwidths. There is also a need in the art for an antenna capable of stable performance under various environmental conditions such that the likelihood of de-tuning resulting from nearby components and other objects placed in close proximity to the antenna is reduced. 
       SUMMARY OF THE INVENTION 
       [0007]    The primary object of the present invention is to provide a high gain, high efficiency, wideband and low profile multi-band antenna with good return loss for wireless applications such as WLAN Access Point, ZigBee or WiMAX module, notebook computer, tablet computer and other mobile and portable devices applications. 
         [0008]    Aside from performance considerations, another object of the present invention is to provide an antenna that is cost effective so that the antenna can be manufactured and sold at a sufficiently low price for market acceptance. 
         [0009]    Another object of the present invention is to provide a low profile antenna that is compact in size especially small in one dimension so it can be easily fabricated and embedded into a notebook computer and tablet computer. 
         [0010]    Yet another object of the present invention is to provide an antenna that is easy for customers to put on a printed circuit board. 
         [0011]    In an exemplary embodiment of the present invention, there is disclosed a low profile, wideband, high gain and high efficiency multi-band antenna with good return loss for wireless communications and it can be used with any RF-front end circuitry that is working at 2.4-2.5 GHz, 3.1-3.4 GHz and 4.9-5.9 GHz frequency band. 
         [0012]    The antenna of the present invention has a planar body which is sealed in a housing and two pins (a feed pin and a ground pin) which are exposed outside the housing. It is easy for customers to assemble; they just need to solder the antenna pins on a printed circuit board and it will be operational. The flat structure and the plastic housing make the antenna to be low profile and compact in size; the total height of the antenna is much smaller than the conventional antennas so it can be easily fabricated and embedded into a notebook computer and tablet computer. Moreover, the antenna&#39;s planar body and two pins are constructed of a single thin sheet of conductive material, preferably a copper sheet so it is cost effective. The housing may be made from PVC plastic and/or RF4. 
         [0013]    The antenna&#39;s planar body has slots specially arranged in such a way that a high frequency current loop can be formed, and the electromagnetic fields are confined in antenna body and the coupling between antenna and surrounding circuit components is significantly reduced, thus high peak gain and high radiation efficiency can be obtained. The distance between the feed pin and the ground pin is optimized to reduce the impedance of the high frequency current loop, thus improving the return loss. 
         [0014]    Moreover the antenna further comprises two parasitic branches, one is attached to the feed pin and another is attached to the ground pin, to increase the bandwidth. By adjusting the dimensions of the parasitic branches, the bandwidth can be increased. 
         [0015]    Antenna return loss is better than −13 dB across the operating frequency band 2400-2490 MHz, better than −10 dB across the operating frequency band 3.1-3.5 GHz, and better than −15 dB across the operating frequency band 4.9-6.5 GHz, and no matching circuit is needed. The peak gain at 2.45 GHz is +4.3 dBi, at 3.25 GHz is +3.1 dBi, and at 5.4 GHz is 5.0 dBi. The radiation efficiency at 2.45 GHz, 3.25 GHz and 5.4 GHz are 97.2%, 98.4% and 96.8% respectively in HFSS simulation. Particularly, this antenna performance is very stable and will not be de-tuned easily by surrounding objects. 
         [0016]    The more important features of the invention have thus been outlined in order that the more detailed description that follows may be better understood and in order that the present contribution to the art may better be appreciated. Additional features of the invention will be described hereinafter and will form the subject matter of the claims that follow. 
         [0017]    Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. 
         [0018]    As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
         [0019]    The foregoing has outlined, rather broadly, the preferred feature of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention and that such other structures do not depart from the spirit and scope of the invention in its broadest form. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    Other aspects, features, and advantages of the present invention will become more fully apparent from the following detailed description, the appended claim, and the accompanying drawings in which similar elements are given similar reference numerals. 
           [0021]      FIG. 1  is a perspective view of an embodiment of an antenna assembly mounted on a printed circuit board. 
           [0022]      FIG. 2  is a perspective view of an embodiment of an antenna assembly showing three dimensions of the antenna assembly. 
           [0023]      FIG. 3  is a side view of the antenna structure of the  FIG. 1 . 
           [0024]      FIG. 4  is a perspective view of the embodiment of the antenna assembly of  FIG. 1  showing details of the antenna dimensions and a high frequency current loop. 
           [0025]      FIG. 5  is a graph showing the simulated return loss of the dual-band antenna of the present invention. 
           [0026]      FIG. 6  is a graph showing the simulated radiation and peak gain at 2.45 GHz. 
           [0027]      FIG. 7  is a graph showing the simulated radiation pattern and peak gain at 3.25 GHz. 
           [0028]      FIG. 8 : a graph showing the simulated radiation and peak gain at 5.4 GHz. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0029]    The present invention provides a small, good performance and low cost antenna design. For wireless communication applications, there are generally three challenging requirement for embedded antenna: small size, good performance and low cost. The good performance means that the antenna should have wide bandwidth, good return loss, high gain and high radiation efficiency. To reach the aforementioned goal, Field-Confined Wideband Antenna Technology principle is used in the antenna design of the present invention (See US patent application Publication No. 20110128199, “Field-Confined Wideband Antenna for Radio Frequency Front End Integrated Circuits”, publication date Jun. 2, 2011, the disclosure of which is incorporated herein by reference). 
         [0030]      FIG. 1  shows a perspective view of an embodiment of the antenna assembly  100  mounted onto an exemplary printed circuit board  200 . It will be appreciated that, while not otherwise depicted, additional components necessary for wireless communications may also be mounted to the printed circuit board  200  and electrically interconnected. The printed circuit board  200  has a planar, quadrilateral configuration having a top surface  201 , a length given by L 1 , a width given by W 1  and a height given by H 1 , as well as a lengthwise axis y, a widthwise axis x, and a vertical axis z. By way of example, the printed circuit board  200  may have dimensions of 80 mm×50 mm×1.6 mm (L 1 ×W 1 ×H 1 ). 
         [0031]    The antenna assembly  100  comprises an antenna  10  which has a planar body  11  sealed in a plastic housing  30  and two “legs” (a feed pin  12  and ground pin  13 ) which are exposed outside. The antenna assembly  100  is mounted onto the printed circuit board with the planar body  11  (inside the plastic housing  30 ) generally parallel to the circuit board  200  by soldering the two legs  12  and  13  onto the printed circuit board  200 . The antenna  10  is connected to RF front-end IC  25  on the printed circuit board  200  either with a 50 ohm micro-strip line  23  or a 50 ohm coaxial cable, and no matching circuit is needed. 
         [0032]    Referring to  FIG. 2  and  FIG. 3  there is disclosed the preferred embodiment of the antenna assembly  100 .  FIG. 2  shows a perspective view of the antenna assembly  100  illustrating the three dimensional structure and  FIG. 3  shows a side view of the antenna assembly  100 . The antenna assembly  100  comprises an antenna  10  sealed in a plastic housing  30 . The antenna  10  may be made of any conductive material, preferably a copper sheet which has a thickness of approximately 0.2 mm. The antenna  10  comprises a planar body  11 , which has a radiating element  18 , and two parallel “legs”, one is a feed pin  12  and the other is a ground pin  13 ; both legs extending from the front of the planar body  11  are in an angularly offset relationship to the planar body  11 . The plastic housing  30  has a rectangular configuration having a top  31 , bottom  32 , two opposed longitudinal sides which are front  33  and back  34 , and two opposed lateral sides  35  and  36 . The length L 2 , width W 2 , and height H 2  of the plastic housing  30  and the dimensions of the antenna planar body  11  and two legs  12  and  13  are selected for the desired operating frequency of the antenna  100 . The antenna bandwidth may be adjusted by changing the dimensions of the antenna planar body  11  and two legs  12  and  13  and the height that the antenna planar body  11  is located on the printed circuit board  200 . 
         [0033]    In the preferred embodiment as shown in  FIGS. 1-3 , the L 2 , W 2  and H 2  are approximately 23 mm, 15.8 mm and 3.2 mm respectively. The antenna&#39;s planar body  11  is located horizontally in the middle of the plastic housing  30  where it is 1.5 mm away from the top  31 , bottom  32  and back  34  of the plastic housing  30 . Both of the feed pin  12  and ground pin  13  extend from the planar body  11  through the front side  33  of the housing and bent down in a curve shape along the front side  31  of the housing. The bottom end of feed pin  21  and bottom end of ground pin  22  (not observable) are flush with the bottom  32  and are about 1.58 mm away from the front  33  of the plastic housing. That means the height of the antenna planar body  11  is approximately 1.5 mm above the printed circuit board  200 . The plastic housing  30  is used to cover and support antenna, and can help to reduce the antenna dimensions. The total height of the antenna assembly  100  is approximately 3.2 mm which is small compared to the conventional antenna assemblies. This flat structure makes the antenna to be a low profile with small dimension in one direction and thus can be easily fabricated and embedded into a notebook computer and tablet computer. The two feed pin  12  and ground pin  13  are designed to be exposed outside the plastic housing  30  so that the antenna can be easily installed on a printed circuit board. The customer only needs to solder the two pins  12  and  13  on the printed circuit board  200  for operation. The feed pins  12  is designed to electrically couple the radiating element  18  to an RF feeding port  24  which receives the RF signal for transmission over a micro-strip line  23 . The ground pin  13  electrically couples the radiating element  18  to the grounding island on the printed circuit board. The antenna  10  of the present invention can be connected to RF front-end IC  25  either with a 50 ohm micro-strip line or a 50 ohm coaxial cable, and no matching circuit is needed. The housing  30  is made from polyvinyl chloride (PVC) plastic in this embodiment, but it may be made from other materials including but not limited to FR4 which is a composite material composed of woven fiberglass cloth with an epoxy resin binder that is flame resistant. 
         [0034]      FIG. 4  shows a top view of an antenna  10  with the planar body  11  and unbent feed pin  12  and GND pin  13  illustrating the details of the antenna element layout. The specific dimensional parameters of the antenna may be adjusted to optimize the antenna performance for a particular application. The overall flat dimension of the antenna is approximately 20×16.8×0.2 mm (L 3 ×W 3 ×H 3 ) before the feed and ground pins  12  and  13  are bent. The antenna&#39;s planar body  11  has a radiating element  18 . The length and width of the feed pin  12  are given by L 4  and W 4 , the length and width of the GND pin  13  are given by L 5  and W 5 . 
         [0035]    As mentioned earlier, Field-Confined Wideband Antenna Technology principle is used in the antenna design (see US patent application Publication No. 20110128199, “Field-Confined Wideband Antenna for Radio Frequency Front End Integrated Circuits”, publication date Jun. 2, 2011, the disclosure of which is incorporated herein by reference). Slots on the antenna are used to confine the electric field so that the antenna has less interaction with other components around it and thus has good isolation from other components near it. The slot length can be selected for a specific application. Depending on the application, the slot direction and location may be selected to optimize performance. The confining slot  14  on the antenna planar body  11  is arranged in such a way that a high frequency current loop  19  can be formed ( FIG. 4 ), and the electromagnetic fields are confined in antenna body and the coupling between antenna and surrounding circuit components is significantly reduced, thus high peak gain and high radiation efficiency can be obtained. 
         [0036]    The high frequency current loop  19  is formed from the feed pin  12  which is fed by an external source via an RF feeding port, to the radiating element  18  on the antenna planar body  11 , around the confining slot  14  and to the ground pin  13 . The feed pin  12  is the origin of the high frequency loop  19  while the ground pin  13  is its terminus. The impedance of the high frequency loop  19 , and hence the return loss, is dependent upon the dimensions between the feed pin  12  and the ground pin  13 . Thus, by adjusting the distance between the feed pin  12  and ground pin  13 , it is possible to change the impedance of the loop and improve the return loss. Furthermore, the length of the high frequency loop  19 , and by definition, the dimensions of the confining slot  14 , correspond to the resonant frequencies of the radiating element  18 . Hence, the multi-band features and the center frequency of the antenna can be obtained by changing the length of the antenna planar body and adjusting the length of the slots. The antenna bandwidth can also be adjusted by changing the height and the width of the antenna planar body. 
         [0037]    To improve the bandwidth of the antenna, the antenna further comprises a first parasitic branch  14  which is attached to the feed pin  12  and a second parasitic branch  15  which is attached to the ground pin  13 ; both of the parasitic branches are attached to antenna body (see  FIG. 4 ). By adjusting the dimensions of the parasitic branches, the bandwidth of the antenna can be increased significantly. Moreover, due to the small coupling between the antenna and the surrounding components, the antenna performance is very stable and will not be de-tuned easily. 
         [0038]    The tri-band antenna of the present invention with operating frequency of 2.4 to 2.485 GHz, 3.1 to 3.5 GHz and 4.9 to 5.9 GHz bands was designed and simulated with HFSS. The dimensions of the antenna of the present invention have been optimized until excellent performance was obtained in simulation. The optimized dimensions of the antenna including dimensions for the radiating elements  18 , the feed and ground pins  12  and  13 , the parasitic branches  15  and  16 , and the slot  14  are illustrated in  FIG. 4 . The overall dimensions of the antenna flat structure  10  are approximately 20 mm×16.8 mm×0.2 mm (L 3 ×W 3 ×H 3 ) before the feed and ground pins  12  and  13  are bent. The overall dimensions of the radiating element  18  are about 15 mm×5 mm×0.2 mm (L 6 ×W 6 ×H 6 ). The optimized length (L 4 ) and width (W 4 ) of the feed pin  12  are approximately 2 mm and 4.48 mm, respectively. The length (L 5 ) and width (W 5 ) of the ground pin  13  are 3 mm and 4.48 mm, respectively. The optimized distance (D 1 ) between the feed pin  12  and ground pin  13  is 2 mm. The overall dimensions are about 9 mm×7.3 mm×0.2 mm (L×W×H) and 8 mm×6.3 mm×0.2 mm (L×W×H) for the first and second parasitic branch respectively. 
         [0039]    With the special architecture shown in above figures, the antenna assembly  100  of the present invention has compact dimensions, ultra-wide bandwidth, excellent return loss, high gain, high efficiency and weak coupling with surrounding circuit components. Thus a superior performance multi-band antenna is obtained. The performance of this tri-band antenna assembly (2.4 to 2.485 GHz, 3.1 to 3.5 GHz and 4.9 to 5.9 GHz operating bands) has been simulated with high frequency structural simulator (HFSS) for operation in 2.45 GHz, 3.25 GHz and 5.4 GHz operating frequencies. The antenna dimensions have been optimized until excellent performance was obtained in simulation. The antenna was built with 0.2 mm copper sheet, and the antenna housing was built with PVC plastic. The simulated return loss is given in  FIG. 5 . Antenna return loss is better than −13 dB across the operating frequency band 2.4-2.49 GHz, better than −10 dB across the 3.1-35 GHz frequency band, and better than −15 dB across the operating frequency band 4.8-6.5 GHz, and no matching circuit is needed. 
         [0040]    The simulated 3D radiation pattern and peak gain at 2.45 GHz is shown in  FIG. 6 . The radiation pattern is Omni-directional in XZ plane, and the peak gain is +4.28 dBi. The simulated radiation efficiency is 97.2% at 2.45 GHz. 
         [0041]    The simulated 3D radiation pattern and peak gain at 3.25 GHz is shown in  FIG. 7 . The radiation pattern is Omni-directional in XZ plane, and the peak gain is +3.1 dBi. The simulated radiation efficiency is 98.4% at 3.25 GHz. 
         [0042]    The simulated 3D radiation pattern and peak gain at 5.4 GHz is shown in  FIG. 8 . The radiation pattern is approximately Omni-directional in YZ plane. The peak gain is +4.98 dBi at 5.4 GHz and the simulated radiation efficiency is 96.8% at 5.4 GHz. 
         [0043]    From above results it is obvious that due to the special structure of the antenna, the current and electromagnetic fields are confined in antenna body, thus the antenna has weak coupling with surrounding circuit components and small loss, and high gain and high efficiency can be obtained. The narrow shape can be easily fabricated and embedded Into a notebook computer and tablet computer. 
         [0044]    Current illustration is one embodiment only. Other embodiment including but not limited to printed circuit board (PCB), metal plated plastic and other sheet metal configuration. 
         [0045]    The invented architecture and principle can be applied to other frequency bands and other applications. 
         [0046]    While there have been shown and described and pointed out the fundamental novel features of the invention as applied to the preferred embodiments, it will be understood that the foregoing is considered as illustrative only of the principles of the invention and not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are entitled.