Patent Publication Number: US-9413069-B2

Title: Compact, multi-port, Wi-Fi dual band MIMO antenna system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation in part (CIP) of U.S. Ser. No. 14/189,984, filed Feb. 25, 2014; 
     which claims benefit of priority with U.S. Provisional Ser. No. 61/768,541, filed Feb. 25, 2013; 
     the contents of each of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This application relates to wireless communications; and more particularly to multi-port, multi-band Wi-Fi antenna systems having high isolation for providing high speed data communication in Wi-Fi applications. 
     2. Description of the Related Art 
     Wi-Fi technology has become ubiquitous in modern society. Multi-input multi-output (MIMO) technology has been shown to improve transfer speed and signal reliability to achieve better quality of services in various communication platforms. The latest generations of Wi-Fi access points demand high efficiency the associated antenna structures and high isolation. 
     Faced with these demands and requirements, antenna designers are being required to provide multi-port antenna designs with high efficiency and good isolation to help achieve the requirements of modern communication devices. The design challenge is to provide and antenna system in a compact size, with equal performance of all four or more antenna elements, the system being low-cost, and still achieving overall system performance requirements. New compact solutions must be envisaged due to the limited area and volume that is available for antennas in these smaller modern devices. 
     SUMMARY OF THE INVENTION 
     In various embodiments, a compact, multi-port, multi-band, Wi-Fi antenna system is configured for high-isolation and improved performance. The antenna includes four monopole type antennas each having at least two resonances including 2.4 GHz and 5 GHz for use in Wi-Fi applications. 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         FIG. 1A  shows a top view of the antenna system in accordance with an embodiment. 
         FIG. 1B  shows a side view of the antenna system of  FIG. 1 . 
         FIG. 2  shows a monopole type antenna radiating element associated with the antenna system of  FIGS. 1 (A-B). 
         FIG. 3  shows a plot of return loss as a function of frequency for the antenna system of  FIGS. 1A-2 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A compact, multi-port, multi-band, Wi-Fi antenna system is configured for high-isolation and improved performance in the dual Wi-Fi band including 2.4 GHz and 5 GHz resonances. The antenna system is capable of reduced size and high isolation for providing faster data transfer speeds and other desirable features. for example, increasing transfer speeds relating to large or high quality media transactions. 
     Current standards such as IEEE 802.11n are published for providing increased data transfer speeds and are adapted for use with Multi-Input Multi-Output (MIMO) antenna architectures. The antenna system described herein is designed to support multiple ports with improved self-isolation. 
     In one embodiment, the antenna system comprises four antenna radiating elements, each of the antenna radiating elements comprises a monopole type radiating element. Each antenna element is designed as small as possible resulting in enhanced isolation performance at each and every port. The isolation value can achieve −12 dB. Antenna ground planes have been separated, further resulting in decreased self-interference between multiple ports. 
     The antenna system can be printed, plated, etched, or otherwise fabricated on a substrate. The substrate may include a flexible substrate for providing a flexible antenna product; however, the substrate may alternatively include a rigid substrate. Where a flexible substrate is used, one or more copper pads can be positioned on the flexible PCB for improving antenna main body strength for reducing the likelihood of tearing or breaking. 
     Each monopole type antenna radiating element is configured to separate to two bands if needed, including coverage of Wi-Fi lower resonance (2.4 GHz) and Wi-Fi higher band resonance (5 GHz), depending on how the MIMO system elects to process the signal stream, as single band input/output or dual-band input/output. 
     Now turning to the drawings,  FIG. 1A  shows a top view of the antenna system in accordance with an embodiment. 
     The antenna comprises a substrate  101  having a planar rectangular shape; for example, the substrate can include dimensions of 80 mm (length)×20 mm (width)×0.1 mm (thickness). On the substrate is printed or otherwise disposed a conductive layer  102 ; the conductive layer may include copper or other metal. In particular, a first antenna radiating element  103   a  is positioned at a first corner of the substrate, a second antenna radiating element  103   b  is positioned at a second corner of the substrate, a third antenna radiating element  103   c  is positioned at a third corner of the substrate, and a fourth antenna radiating element  103   d  is shown being positioned at a fourth corner of the substrate. Each of the first through fourth antenna elements  103 ( a - d ) comprises a first radiating portion configured for high band resonance, and a second radiating portion configured for low band resonance. An antenna feed pad  113 ( a - d ) is coupled to each of the respective antenna radiating elements; the antenna feed pad is disposed on the respective antenna radiating element between the first radiating portion and the second radiating portion thereof. Four ground conductors  104 ( a - d ) are shown each having a length and a width aligned with that of the substrate; wherein each respective ground conductor is positioned adjacent to a respective antenna radiating element with the ground conductor being positioned to a side of the first radiating portion thereof. Thus, the first ground conductor  104   a  is positioned parallel with the second ground conductor  104   b;  and the third ground conductor  104   c  is positioned parallel with the fourth ground conductor  104   d.  Each of the respective ground conductors  104 ( a - d ) comprises a ground solder pad  114 ( a - d ). The feed pad  113   a  and ground pad  114   a  of the first antenna radiating element  113   a  and the first ground conductor  104   a,  respectively, are adapted for attachment with a coaxial cable. In this regard, each antennas, ground conductors, feed and ground pads are configured to be attached with one of four coaxial cables associated with the four antennas. 
     For added rigidity, rows of one or more structural conductors  105 ( a - b );  106 ( a - c ) are provided. In this regard the flexible substrate can be bent about a horizontal bending line between the rows of conductors. Structural solder pads  115 ( a - d ) are disposed on the first and third ground conductors  104   a;    104   c,  respectively, and two of the structural conductors  105 ( a - b ); each of these structural solder pads is configured to receive an amount of solder for securing the cable to prevent breakage. 
     The illustrated antenna system is symmetrical about a longitudinal center of the substrate; with the first and second antenna radiating elements being configured to oppose the third and fourth antenna radiating elements. 
       FIG. 1B  shows a side view of the antenna system of  FIG. 1 . The antenna system is shown including a substrate  101  and a conductive layer  102 . 
       FIG. 2  shows a monopole type antenna radiating element  103  associated with the antenna system of  FIGS. 1 (A-B). The monopole type radiating element comprises a feed pad  113 , a first radiating portion  120  extending from the feed pad to a distal end, the first radiating portion  120  is configured for a high band resonance. A second radiating portion  130  extends from the feed pad  113  and comprises a meander line section  152  disposed parallel with a longitudinal conductor  151 , the meander line section  152  is coupled to the longitudinal conductor  151  by a first coupling conductor  153  extending therebetween, and the longitudinal conductor is coupled to the feed pad  113  by a second coupling conductor  154  extending therebetween. 
       FIG. 3  shows a plot of return loss as a function of frequency for the antenna system of  FIGS. 1A-2 . The plot comprises four respective patterns  301 ;  302 ;  303 ; and  304 ; wherein the first pattern  301  is associated with the first antenna radiating element  103   a  and a first port associated therewith; the second pattern  302  is associated with the second antenna radiating element  103   b  and a second port associated therewith; the third pattern  303  is associated with the third antenna radiating element  103   c  and a third port associated therewith; and the fourth pattern  304  is associated with the fourth antenna radiating element  103   d  and a fourth port associated therewith.