Abstract:
The multi-band active integrated MIMO antenna is a planar structure that includes active devices such as power amplifiers (PA) for transmit modes, as well as low-noise-amplifiers (LNA) for receive modes or complete transceivers (both PA and LNA for bi-directional operation, i.e. transmit and receive modes simultaneously). The antenna provides active loading to facilitate a diversity advantage expected from 4G and 5G wireless systems. The integrated active amplifier device within the antenna increases system throughput while supporting multi-band operation for multi-wireless standards. Moreover, integration with the radio frequency front end eases matching while providing higher gain.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to multi-band wireless electronics, and particularly to a printed multi-band active integrated MIMO antenna directly connected to active transceivers containing both transmit and receive amplifiers 
     2. Description of the Related Art 
     Multiband antennas are currently widely used in all types of wireless handheld devices, from cell phones, to tablet PCs and laptops. Such antennas can support multiple standards, and are usually compact and conformal to the device shape and size. The use of multiple antennas within the user handheld devices is becoming a necessity in fourth generation (4G) and fifth generation (5G) wireless terminals as they provide much higher data rates that are required for high speed and multimedia data transfers that we all enjoy nowadays. The use of multiple antennas is required within the multiple-input-multiple-output (MIMO) system architecture that utilizes the once very undesirable multipath phenomena in single antenna devices to its advantage in increasing the data throughput. 
     Active integrated antennas (AIA) refer to antennas intimately integrated with active devices including the DC bias network without any isolator or circulator. There is no boundary or separable point between active circuits and the antenna in an AIA and both of them are designed as a whole unit. So, neither the antenna nor the active circuits need to be designed for 50Ω except at the AIA input/output port. AIAs have very desirable features such as, increasing the effective length for short antennas (antenna miniaturization), increasing the bandwidth, decreasing the mutual coupling between adjacent array elements, improving the noise factors, and improving the gain of the antenna. 
     Thus, multi-band active integrated MIMO antennas solving the aforementioned problems are desired. 
     SUMMARY OF THE INVENTION 
     The multi-band active integrated MIMO antenna is a planar structure that includes active devices such as power amplifiers (PA) for transmit modes, as well as low-noise-amplifiers (LNA) for receive modes or complete transceivers (both PA and LNA for bi-directional operation, i.e. transmit and receive modes simultaneously). The antenna provides active loading to facilitate a diversity advantage expected from 4G and 5G wireless systems. The integrated active amplifier device within the antenna increases system throughput while supporting multi-band operation for multi-wireless standards. Moreover, integration with the radio frequency front end eases matching while providing higher gain. Thus the present multi-band active integrated MIMO antenna is a miniaturized active integrated antenna (AIA) providing a basic radiating element for multiband MIMO based handheld devices having simultaneous transmit and receive capabilities. 
     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 
         FIG. 1  is a diagrammatic plan view of an exemplary multi-band active integrated MIMO antenna according to the present invention. 
         FIG. 2  is a diagrammatic plan view of an exemplary multi-band active integrated MIMO antenna showing placement of the bias and matching circuits according to the present invention. 
         FIG. 3  is a top plan view of an exemplary microstrip patch multi-band active integrated MIMO antenna showing the active and passive component configuration according to the present invention. 
         FIG. 4A  is a top plan view of a semi-circular array of the multi-band active integrated MIMO antennas according to the present invention. 
         FIG. 4B  is a bottom plan view showing a ground plane of the semi-circular array of the multi-band active integrated MIMO antennas according to the present invention. 
         FIG. 5  is a diagrammatic top plan view of the semi-circular array showing placement of the active and passive components utilizing a single PA according to the present invention. 
         FIG. 6  is a diagrammatic top plan view of the semi-circular array showing placement of the active and passive components utilizing a single PA and a single LNA configured at opposing ends of the semi-circular array according to the present invention. 
         FIG. 7  is a diagrammatic top plan view of the semi-circular array showing placement of the active and passive components utilizing a single PA and a single LNA configured at the same end of the semi-circular array according to the present invention. 
         FIG. 8  is a top plan view of a two element semi-circular array of the multi-band active integrated MIMO antennas according to the present invention. 
         FIG. 9  is a top plan view of a four element semi-circular array of the multi-band active integrated MIMO antennas according to the present invention. 
         FIG. 10  is a plot showing frequency response of the multi-band active integrated MIMO antenna according to the present invention. 
         FIG. 11A  is a plot showing gain response of the higher band antenna of the multi-band active integrated MIMO antenna according to the present invention. 
         FIG. 11B  is a plot showing gain of the lower band antenna of the multi-band active integrated MIMO antennas according to the present invention. 
     
    
    
     Similar reference characters denote corresponding features consistently throughout the attached drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An exemplary multi-band active integrated (MAI) multiple-input and multiple-output (MIMO) antenna system with active components is shown in  FIG. 1 . In this configuration, two printed based multi-band antennas  11 ,  12 , are directly connected to the active elements  13  that represent active transceivers containing both transmit and receive amplifiers. The biasing component  15  and the matching component  14  for both transceivers are included to provide proper operation at the bands of interest. Each MAI antenna has an output for the receive path  17 , and an output for the transmit path  18 . These two input/output connections are to be connected to other components in the transmit/receive chains of the wireless system. The MIMO configuration is created by using the two antennas  11  and  12 , along with their active elements  13 , simultaneously. The system backplane or mobile terminal substrate dimensions are a predetermined width  10 , and a predetermined length  16 . 
     There are various types of AIA, specifically, oscillator type, PA type, LNA type, mixer type and transceiver types. The PA, LNA and transceiver types are within contemplation of the present invention, although the same concepts can be extended to other types easily with careful design of the active circuits. Additionally, the present invention can be applied to any type of printed antennas. 
     In the embodiment shown in  FIG. 2 , the dual element MAI-MIMO antenna is placed on a mobile terminal substrate having a top face, a bottom face, and dimensioned to a predetermined width  20 , and a predetermined length  21 . A ground plane is disposed on the bottom face of the substrate below the multi-band antenna elements  22  and  23  to create a ground plane layer. The transceivers  24  are placed within the antenna structure for seamless integration and actual loading of the circuits of transceivers  24  by the antennas  22  and  23 . The bias circuits  25  and matching circuits  28  are placed above the ground plane layer. Each antenna has an input  26  and an output  27  that are respectively connected to the transmit and receive parts of the MIMO antenna system. 
     In a more detailed description of the MAI structure,  FIG. 3  shows a complete transmit path connected to a microstrip patch antenna  31 . The complete single element MAI antenna is placed on a substrate  30 , the single input  33  of the system feeds the first matching circuit  34 . The first matching circuit  34  directly connects the transmitter output to the power amplifier  35 . The required biasing of the power amplifier is achieved via a biasing network  32  comprised of a series of capacitors and an RF choke inductor. The output of the power amplifier  35  is fed to a multi-band matching network  36  that tracks and matches the variation of the input impedance of the microstrip antenna at various frequencies. This way, multi band active integrated antenna behavior is achieved with good efficiency and matching conditions. 
     Since a MIMO antenna system requires multiple antenna structures, and since for wireless handheld devices space is limited, especially in cellular phones and pocket sized handheld devices, compact antenna structures are desirable. However, placing antennas close to each other increases coupling, reduces efficiencies, and degrades the MIMO system performance though high channel correlations. That is why the present invention also contemplates providing a new multi-band MIMO antenna structure based on a semi-circular antenna array comprised of first semi-ring antenna element  46  and connected second semi-ring antenna element  48  printed on a top side  400   a  of the substrate, as shown in  FIG. 4A . The ground plane side is shown in  FIG. 4B . As shown in  FIG. 4A , two identical dual semi-ring antennas  46  are disposed within a minimum distance S  40  of each other on a substantially rectangular shaped substrate  400   a  having a predetermined length (L)  41  and a predetermined width (W)  42 , for MIMO operation. The feed point  47  on the outer ring is tuned to provide the necessary input matching at one band while the inner semi-ring  48  is used to tune the other band. A shorting post  49  in radial alignment with the connection of the first semi-ring antenna element to the second semi-ring antenna element and extending from the antenna surface  400   a  to the bottom ground plane  400   b  is used to excite the second band of operation. A defected ground meandering rectangular wave patterned structure  44  is disposed between and connects two unbroken rectangular ground planes  43  and  45  to enhance the isolation between the two adjacent antennas  46 . Feeding the semi-ring multi-band antenna from either edge side will provide the same effect. 
       FIG. 5  shows a configuration of the MAI antenna based on the aforementioned semi-ring antenna. The antenna  51  is placed on a top face of substrate  50 . a ground plane is disposed on a bottom face of substrate  50 . The input  53  of this transmit type configuration connects directly to the input matching network  54  which connects to the power amplifier  55 . The amplifier is biased via a biasing network  52 , and the output of the amplifier feeds a multi-band matching network  56  that directly feeds the antenna  51 . Note that the multi-band feeding network is not matching the antenna to have 50 ohms, but rather is used to deal with any arbitrary complex input impedance of the antenna. 
     To provide embedded isolation between the transmit and receive paths, another configuration, as shown in  FIG. 6 , includes input of the transmit path  67  feeding the power amplifier  68  via input matching network  54 . The output signal from PA  68  passes through the multi-band matching network  69  to the antenna  61 . The received signal comes from the other symmetric portion of the semi-ring antenna  61 , and passes through the multi-band receiving matching network  62 , to a low noise amplifier  63  and then through the output matching network  64  to a receiving node  65 . Both amplifiers are biased via a biasing network  66 , and are placed on the same substrate  60 . 
     In yet another configuration using the semi-ring multi-band antenna  71 , as shown in  FIG. 7 , the input terminal  74  and output terminal  76  are connected to the input and output matching networks  75  and  77 , respectively. The LNA  78  and the PA  73  are biased using biasing network  72 . The amplifiers  78  and  73  are connected to a multi-band network  79  that provides isolation between the two paths and connects to the antenna at one end. A common substrate  70  is used for this microstrip design. 
       FIG. 8  shows an embodiment of the MAI-MIMO antenna system on a wireless handset backplane  82 . The two identical multi-band MIMO antennas  84  and  80  are connected to their respective active circuits  83  and  81  via one of the aforementioned configurations. 
     Another configuration would be to have a 4-element MAI-MIMO antenna system, as shown in  FIG. 9 , where four identical (or dissimilar) multi-band antennas  94 ,  98 ,  95 ,  90 , are connected to their respective active sections  93 ,  97 ,  96 ,  91 , using one of the aforementioned configurations for transmit and receive or transceiver structures, and all share the same substrate  92 . 
     Multi-band operation from a MAI-antenna is shown in the plot of  FIG. 10 . The first band is resonating at 750 MHz (plot line  102 ) with a wide bandwidth, and the other band (plot line  101 ) is resonating at 1.57 GHz with a wide bandwidth. Several variations can be obtained here, and several bands other than those shown can be covered. This exemplary configuration shows the multi-band effectiveness of the multi-band active integrated MIMO antenna. Sample radiation gain patterns at the two center bands of operations are shown in  FIGS. 11A and 11B . The lower band has an omnidirectional gain pattern  110  with a maximum gain  111  of approximately −1 dB (this value can change based on the antenna type used, and is shown here for the semi-ring antenna without active loading). The gain pattern  112  at the higher band shows a maximum gain  113  of 2 dB (this value can also be changed and does not show the effect of the power amplifier in the transmit chain). 
     The present multi-band active integrated MIMO antenna also covers any other multi-band printed antenna variation in a MIMO configuration as well as any kind of active element loading or direct integration between active elements and multi-band antennas with multi-band matching and feeding networks. 
     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.