Abstract:
The integrated microwave-millimeter wave antenna system with isolation enhancement mechanism is a planar, compact, multi-band microwave multiple-input-multiple-output (MIMO) antenna system integrated with a millimeter wave antenna array. The microwave MIMO antenna system covers multiple standards between (700-6000) MHz, while the millimeter wave array covers a wider bandwidth of at least 1 GHz with a center frequency ranging from 28-38 GHz. The millimeter wave antenna array is based on slot antenna elements and acts as an isolation enhancement structure to the microwave MIMO antenna system. It acts as a defected ground structure that improves port isolation of the MIMO antenna system. This dual functionality within a small form factor wireless device is highly desirable, as space is very limited. The system is for beyond 4G wireless standards.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to multi-band antennas, and particularly to an integrated microwave-millimeter wave antenna system with isolation enhancement mechanism that provides multiple-input-multiple-output (MIMO) microwave antennas combined with millimeter wave integrated antenna arrays for compact wireless devices and 4G+ and 5G mobile handsets and sub-systems. 
         [0003]    2. Description of the Related Art 
         [0004]    The use of wireless terminals is on the rise worldwide, from cell phones and, tablet PCs to iPADs and personal digital assistants (PDAs), among many other devices that have wireless connectivity capability. This tremendous proliferation of wireless devices with Internet connectivity has posed several demands on higher data throughput to allow users to experience multimedia and video streaming. In the fourth generation (4G) mobile terminals, multiple-input-multiple-output (MIMO) technology was a major enabling technology for such increase in data throughput through the use of multiple antenna elements on the mobile device, as well as at the base-station. The demand for higher data rates will keep increasing, and the fifth generation (5G) of wireless standards will try to provide a 1000 times increase of data throughput compared to the current 4G standard speeds through the utilization of several new enabling technologies. 
         [0005]    Although MIMO antenna systems will be key in 5G standards, as they should be backward compatible with previous ones that can cover wide ranges, short-range communication standards are recently investigating millimeter-wave (mm-wave) bands (30 to 300 GHz, or wavelengths from ten to one millimeter) for ultra-high throughput over short distances to allow for real-time multimedia and video transfers, and to achieve the anticipated increase in the data rates. Such bands include, but are not limited to, 28 GHz and 38 GHz, as recently demonstrated. The integration of MIMO technology at microwave frequencies covering the current 4G standards, along with mm-wave bands, will be required in next generation wireless devices, as they are supposed to support both standards. The mm-wave antenna should be able to provide at least 1 GHz of bandwidth, while the microwave MIMO antenna system can still support the regular wireless bands. This integration process needs careful attention and is of primary importance to wireless device manufacturers. 
         [0006]    Thus, an integrated microwave-millimeter wave antenna system with isolation enhancement mechanism solving the aforementioned problems is desired. 
       SUMMARY OF THE INVENTION 
       [0007]    The integrated microwave-millimeter wave antenna system with isolation enhancement mechanism is a planar, compact, multi-band microwave multiple-input-multiple-output (MIMO) antenna system integrated with a millimeter wave antenna array. The microwave MIMO antenna system covers multiple standards between 700-6000 MHz, while the millimeter wave array covers a wider bandwidth of at least 1 GHz with a center frequency ranging from 28-38 GHz. The millimeter wave antenna array is based on slot antenna elements and acts as an isolation enhancement structure to the microwave MIMO antenna system. The array acts as a defected ground structure that improves port isolation of the MIMO antenna system. This dual functionality within a small form factor wireless device is highly desirable, as space is very limited. The system is for beyond 4G wireless standards. 
         [0008]    These and other features of the present invention will become readily apparent upon further review of the following specification and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1A  is a plan view showing the top surface or layer of the antenna board of an integrated microwave-millimeter wave antenna system with isolation enhancement mechanism according to the present invention, showing the MIMO antenna system for operation in the microwave band. 
           [0010]      FIG. 1B  is a plan view of the metallic middle layer of the antenna board of  FIG. 1 a   , showing the ground plane and the millimeter wave antenna array etched in the ground plane. 
           [0011]      FIG. 1C  is a bottom view of the antenna board of  FIG. 1A , showing the feed elements of the millimeter wave antenna array. 
           [0012]      FIG. 2  is a schematic composite top plan view of the antenna board of  FIGS. 1A-1C , showing the relative positioning of the antenna elements on the three layers of the antenna board. 
           [0013]      FIG. 3A  is a top view in section of an alternative configuration of a MIMO microwave antenna element for the top surface of the antenna board of  FIG. 1A . 
           [0014]      FIG. 3B  is a top view in section of an alternative configuration of a MIMO microwave antenna element for the top surface of the antenna board of  FIG. 1A . 
           [0015]      FIG. 4A  is a detailed schematic diagram of the feed elements of the millimeter wave antenna array shown in  FIG. 1C . 
           [0016]      FIG. 4B  is a detailed schematic diagram of an alternative configuration of the feed elements of the millimeter wave antenna array shown in  FIG. 1C . 
           [0017]      FIG. 5A  is a schematic composite top plan view of the antenna board of an alternative embodiment of an integrated microwave-millimeter wave antenna system with isolation enhancement mechanism according to the present invention. 
           [0018]      FIG. 5B  is a schematic composite top plan view of the antenna board of another alternative embodiment of an integrated microwave-millimeter wave antenna system with isolation enhancement mechanism according to the present invention. 
           [0019]      FIG. 6A  is a schematic composite top plan view of the antenna board of another alternative embodiment of an integrated microwave-millimeter wave antenna system with isolation enhancement mechanism according to the present invention. 
           [0020]      FIG. 6B  is a schematic composite top plan view of the antenna board of another alternative embodiment of an integrated microwave-millimeter wave antenna system with isolation enhancement mechanism according to the present invention. 
       
    
    
       [0021]    Similar reference characters denote corresponding features consistently throughout the attached drawings. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    The integrated microwave-millimeter wave antenna system with isolation enhancement mechanism is a multi-band antenna structure covering several microwave wireless standard bands (this can be tuned according to the coverage area) with sufficient bandwidth. The millimeter wave antenna component includes a planar slot-based antenna array having a feeding structure, and provides operation centered at any frequency between 28-38 GHz with at least 1 GHz of operating bandwidth. The mm-wave array will act as a defected ground structure for the MIMO antenna system, and thus a novel isolation enhancement method, although multi-standard integration is also provided. 
         [0023]      FIGS. 1A, 1B, and 1C  show the three printed circuit board layers of the planar printed multi-band microwave and millimeter-wave integrated antenna system having a total width dimension  111  and length dimension  110 . A top layer  100  of the antenna system&#39;s printed circuit board (PCB) has first and second G-shaped element multi-band MIMO antennas  101  and  105 , respectively, providing operation at microwave frequencies. Antennas  101  and  105  are fed from the edge of the board at terminal feed points  102  and  106 , respectively. Multi-band operation can be achieved using shorting strips or posts  103 ,  104  disposed opposite the end of the antennas where the terminal feed points  102  and  106  are located. A middle metallic layer  107  of the PCB is separated from the top layer  100  by a dielectric substrate and contains the ground plane of the system, as well as a group of slot openings  108  within the ground plane (GND) at a locus where metal of the layer is etched off to form the slots. The group of slots  108  forms a planar array  109 . 
         [0024]    The planar slot array  109  will act as an isolation enhancement structure for the MIMO antenna system at microwave frequencies, as well as a millimeter wave antenna array at millimeter wave frequencies. The bottom layer  115  contains the feed network of the millimeter wave slot antenna array  109  of the second substrate layer. The feed arms  112  form a power divider feed network  130  and are fed via an impedance transformer  113  in operable communication with a connector  114 . 
         [0025]      FIG. 2  shows a composite top view of the complete system, with the two MIMO antenna elements G shaped element multi-band MIMO antennas  101  and  105 , their feed points  102 ,  106 , and shorting strips/posts  103 ,  104  on the top layer. Also, the millimeter wave slot antenna array  109  is shown disposed in the middle layer ground plane, along with the feed arms  112  of the feed network  130  in the bottom layer, and the input feed connector  114  of the millimeter-wave array  109 . 
         [0026]    Alternative configurations of the antenna elements for the multi-band microwave MIMO antenna system are shown in  FIGS. 3A and 3B .  FIG. 3A  is a detailed schematic view in section of the second G-shaped element  105  configured as a shorted loop antenna with a feed connector  106  at the terminus of the G-shaped element  105 . Shorting strip/post  104  is disposed on the G-shaped element  105  proximate the end opposing the terminus end. The shorting post  104  selectively connects the G-shaped element with the ground plane in the middle layer when inserted through the board. An exemplary alternative antenna element (shown in  FIG. 3B ) is a shorted meander line  203 . Other alternatives may be, without limitation, an inverted-F antenna, or any other derivative of the shorted meander line-based antenna  203 . The feed point  205  is shown at a terminus of the meander line  203 , and the shorting strip/port  204  is placed in an optimized location to provide dual band coverage with enough impedance bandwidth (shown at a fourth bend, away from the terminus of the meander line  203 ). The band covered can be varied according to the operator specific frequency bands. Possible covered bands would be the lower 800/900 MHz bands, as well as the upper 1800/2100 MHz bands, or even the WLAN band at 2.45 GHz. 
         [0027]    The millimeter wave antenna array  109  with feed arms  112  is shown schematically in  FIG. 4A . The array  109  has two roles in this integrated design. The first is to act as an isolation enhancement structure for the MIMO antenna system working at microwave frequencies. The second is a stand-alone millimeter wave antenna array for short range communication standards, with a center frequency ranging between 28-38 GHz. A bandwidth of at least 1 GHz should be provided for ultra high-speed communication systems for short range links. Two variations are shown for such an array. The array  109  consists of a planar arrangement of slot antenna elements  108  etched out of the ground plane, a feed network/power divider  130 , an impedance transformer  113 , a feed line  304 , and the input connector  114 . 
         [0028]    This antenna array  109  will provide a radiation pattern beam focused at the normal of the array plane from both of its sides. If a tilted beam pattern is required (for example, to lower field interactions with other radiating elements) a modified design can be considered, as shown in  FIG. 4B , wherein some phase shifting (meandering) lines  307  are introduced in the feed arms  112  to provide a progressive phase variation to tilt the beam. 
         [0029]    A possible response curve for such an array covers the 28 GHz band of the millimeter-wave spectrum, and with a bandwidth of at least 1 GHz dedicated for short range ultra high-speed data connections, and a three-dimensional radiation pattern. 
         [0030]    Other possible arrangements of the present multi-layered, integrated microwave MIMO and millimeter wave antenna system are shown in  FIGS. 5A and 5B . The configuration  410  shown in  FIG. 5A  includes microwave multi-band dual element MIMO antenna elements  400 ,  408 , utilizing a modified-G antenna shape, and the two feeds  102 ,  106 . Included are shorting strips  402  and  406 , which are disposed on respective extension ends of the head portion of the G-shaped elements  400  and  408 . Moreover, a MIMO configuration  410  of the millimeter wave antenna system includes two instances of the array  109 . The first instance of the array  109  is disposed in line between the G-elements  400  and  408 . The second instance of the array  109  is disposed opposite G-element  400  in a configuration having an orientation rotated 90° from the first instance of the array  109 . One of arrays  109  serves as an isolation enhancement structure for the microwave MIMO antenna system  410 , while the other is a radiating element for the millimeter wave antenna. The configuration  423  shown in  FIG. 5B  is another possible dual-band microwave MIMO antenna system having meander line antenna elements  416  and  422  integrated with a millimeter wave array  109  aligned between elements  416  and  422 . Included are shorting strips  417  and  420 , which are disposed on respective lines extending from the fifth and sixth meander-lines, respectively, of the meander line elements  416  and  422 . Shorting strip  417  of element  416  is offset from feed point  415 . Shorting strip  420  of element  422  is axially aligned (along an axis running parallel to the PC board) with feed point  421 . A single feed  114  is in operable communication with the millimeter wave array  109 . 
         [0031]    Other alternative designs based on the integrated structure are shown in  FIGS. 6A and 6B . In  FIG. 6A , the top view of configuration  505  of the multi-layered board design shows a four-element multi-band MIMO antenna system operating at microwave frequencies. Elements  500 ,  506 ,  509 , and  513  are disposed on the four edges of the antenna PC board, with their respective input feed points  501 ,  504 ,  510 ,  512 , and integrated with a pair of millimeter-wave antenna arrays  109 . The configuration  505  with positioning of the antenna arrays  109  serves as a MIMO antenna system at millimeter wave, as well as two isolation enhancement structures at microwave frequencies, disposed between each pair of the lower band MIMO antenna elements ( 500  and  506 ,  513  and  509 ). This configuration will provide enhanced microwave MIMO links, as well as millimeter wave communication links through the millimeter wave-MIMO configuration. The isolation enhancement from the millimeter wave arrays will directly affect the performance of the microwave MIMO systems and enhance their port isolation and correlation coefficient, in addition to their efficiencies. 
         [0032]    Another variation for the present multi-layered PCB integrated system is a dual-element MIMO antenna system at microwave as well as a dual antenna array MIMO system at millimeter waves, as shown in a schematic top view of the system  524  in  FIG. 6B . The dual-element multi-band microwave MIMO antenna system  524  includes two instances of MIMO meander line antenna element  416  aligned in mirror image fashion on opposing sides of the PC board, along with two instances of millimeter wave antenna array system  109 , the first instance of the array  109  being aligned between the mirror-imaged elements  416 , the second instance of the array  109  being disposed at the opposite end of the board from the first instance and having an orientation rotated 90° from the first instance of array  109 . The orientation of these arrays  109  are tilted with respect to one another to provide lower field correlations by making the two field maxima  527 ,  531  point in opposite directions. 
         [0033]    It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.