Patent Publication Number: US-6992638-B2

Title: High gain, steerable multiple beam antenna system

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATION 
     This application is a continuation-in-part application of U.S. patent application Ser. No. 10/673,033, filed Sep. 27, 2003, now abandon, which is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     In wireless communications efficient communications can be greatly facilitated by much improved and novel antenna systems. Thus, there is a long standing need in the wireless communications and antenna art for antennas that can provide high-gain, antennas that provide for multi-beams, and antennas that can provide 360 degree radiation. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present invention is a multi-beam antenna system that can be used in microwave frequency applications between 1 GHz and 100 GHz. The multi-beam antenna system covers four 90° sectors for full 360° coverage. Each 90° sector is covered with at least 1 narrow steerable transmit (TX) and 1 narrow steerable receive (RX) beam. The beams are steered in the azimuth dimension. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present invention may be had by reference to the following detailed description when taken in conjunction with the accompanying drawings wherein: 
         FIG. 1  is a plan view diagram that illustrates a multi-beam antenna system in accordance with the present invention; 
         FIG. 2  is a diagram illustrating in greater detail one way a controller can be used to control the multi-beam antenna system shown in  FIG. 1 ; 
         FIG. 3  is a diagram illustrating in greater detail the components of a single aperture that can be used within the multi-beam antenna system shown in  FIG. 1 ; 
         FIG. 4  is a diagram illustrating in greater detail the components of a beam former that can be used within the multi-beam antenna system shown in  FIG. 1 ; 
         FIG. 5  is a diagram illustrating in greater detail the components of a secondary power combiner/splitter and the radiating elements that can be used within the multi-beam antenna system shown in  FIG. 1 ; 
         FIGS. 6A and 6B  are diagrams that illustrate different feed structures that can be used in the primary power combiner/splitter shown in  FIG. 4  and the secondary power combiners/splitters shown in  FIG. 5 ; 
         FIG. 7  is a diagram that illustrates how the beam former shown in  FIG. 4  can be connected to the centre-series feed secondary power combiner/splitter shown in  FIGS. 5 and 6B ; 
         FIG. 8  is a diagram that illustrates one way to package the multi-beam antenna system shown in  FIG. 1 ; 
         FIGS. 9A and 9B  are diagrams of another embodiment of the multi-beam antenna system shown in  FIG. 1 ; 
         FIG. 10  is a diagram of one of the four radiation element array panels used in the multi-beam antenna system shown in  FIGS. 9A and 9B ; and 
         FIG. 11  is a diagram of a controller implemented within the multi-beam antenna system shown in  FIGS. 9A and 9B . 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     The multi-beam antenna system  100  includes four pairs of independent TX (transmit) and RX (receive) apertures  110  that may be arranged into a square formation as shown in  FIG. 1  (see also  FIGS. 8 and 9 ). Each pair of TX and RX apertures  110  emits a pair of TX and RX radiation beams  112  that cover one 90° wide sector, so that the multi-beam antenna system  100  can cover the full 360° range. 
     The multi-beam antenna system  100  also includes a controller  115  (e.g., embedded controller  115 ) shown in  FIG. 2  that performs all of the tasks related to pointing the radiation beams  112 . The controller  115  performs the following functions:
         Receive and execute antenna commands  202     Control the RF switches  204 .   Adjust the tunable phase shifters  206         

     In particular, the controller  115  receives the antenna commands  202  from a radio&#39;s media access controller (MAC)  208  and executes the commands  202  in order to point any of the eight radiation beams  112  to a specific azimuth setting. The radiation beam  112  pointing functions are carried out through the use of electronic RF switches  204  and phase shifters  206 . The RF switches  204  are used to select a particular aperture  110  or antenna quadrant while the phase shifters  206  on each of the four sides of the multi-beam antenna system  100  are adjusted to achieve incremental steering of the radiation beams  112 . Alternatively, the multi-beam antenna system  100  can be fed by four separate transceiver systems, allowing for four simultaneous RX beams  112  and four simultaneous TX beams  112 . 
     Each TX and RX aperture  100  as shown in  FIG. 3  includes multiple rows and columns of radiating elements  302 . The radiating elements  302  in each column are connected together via microwave transmission lines in a column secondary power splitter  304  (in the RX aperture  100 ) or column secondary power combiner  304  (in the TX aperture  100 ). The secondary power splitter/combiners  304  are connected to a beam former  306  that steers the radiation beam  112  in one dimension, which in the preferred embodiment is the azimuth direction. Above 10 GHz, the transmission lines and/or secondary power combiners/splitters  304  are usually realized in waveguides to minimize loss, but microstrip or stripline transmission lines and power combiner/splitters can be used up to about 30 GHz. Waveguide transmission lines and power combiners/splitters can also be used below 10 GHz, but the structure can become quite bulky. Co-axial transmission lines are also practical below about 3 GHz. With the use of microstrip, striplines or co-axial lines, wide bandwidth corporate feed structures are easily realizable, such a structure is shown in  FIG. 6A . Waveguide corporate feed structures are very bulky, requiring significant amounts of volume. For this reason, series fed waveguide structures are used instead when the operating bandwidth is narrow (less than 5% of the operating frequency), as shown in  FIG. 6B . The series fed waveguide structure is used in the preferred embodiment of the primary power combiner/splitter  308  (see  FIG. 4 ) and the secondary power combiners/splitters  304  (see  FIG. 5 ). 
     As shown in  FIG. 4 , the beam former  306  includes a primary power combiner/splitter  308  (e.g., centre fed waveguide  308 ) which distributes/collects power in a serial manner to/from the row of phase shifters  206 . The phase shifters  206  in turn feed the column secondary power combiners/splitters  304  having the form of secondary waveguides fed at their respective centres, which finally distribute power again in a serial fashion to the radiating elements  302  (e.g., antenna elements  302 ) (see  FIG. 3 ). This waveguide feed arrangement is in particular the most practical for Ku-band and Ka band applications since it is compact. In addition, this waveguide feed arrangement ensures low loss power transmission. 
     The beam former  306  as depicted in  FIG. 4  has a co-axial cable  310  feeding the primary power combiner/splitter  308  (e.g., primary waveguide  308 ) at its centre. The primary waveguide  308  is coupled to a row of phase shifters  206  via broad wall slots  312  that are spaced roughly at half guided-wavelengths along the length of the primary waveguide  308 . The spacing is not important, since the phase shifters  206  can be used to correct any phase differences, therefore it can be adjusted to match the widths of the secondary waveguides  304  (e.g., secondary power combiners/splitters  304 ) (see  FIG. 7 ). The phase shifters  206  shown here are slotline phase shifters  206  where the slot gaps are loaded with a voltage tunable ferroelectric material. In the preferred embodiment, the voltage tunable ferroelectric material is made and sold under the name of Parascan™ material by Paratek Microwave, Inc. A bias voltage applied across the slotline gap is used to control the dielectric constant of the voltage tunable material, and hence the velocity of propagation in the slotline. The phase shifters  206  are designed with enough length to vary at least one wavelength in electrical length over the possible bias voltage range, thereby creating 360° of phase shift. The slotline gap width can be varied along its length, to create a non-uniform loaded slotline. This technique, which is done to allow a low biasing voltage to be used without increasing metallic current losses, is described in greater detail in U.S. patent application Ser. No. 10/199,724 entitled “A Tunable Electromagnetic Transmission Structure for Effecting Coupling of Electromagnetic Signals” that was filed Aug. 19, 2002. The contents of this patent application are hereby incorporated by reference herein. 
     Each phase shifter  206  in the beam former  306  couples to the centre of a secondary waveguide  304  (e.g., secondary power combiner/splitter  304 ) as shown in  FIG. 5 . The secondary waveguide  304  couples to a column of the antenna elements  302  via broad wall slots  314  along its length. The slots  314  are spaced at half a guided wavelength apart, alternating on different sides of the waveguide&#39;s centre line. This ensures that the slots  314  are excited in series and in phase, since the broad wall current distribution flows away from the centre line of the secondary waveguide  304 . The antenna elements  302  shown are stacked rectangular patches. These can be of any other shape (elliptical, polygon) as long as the radiated field exhibits polarization purity and power can be transmitted/received into/from space efficiently. Other types of antenna elements  302  can be used such as Vivaldi elements. Alternatively, the slots  314  themselves can be used as radiating elements  302 .  FIG. 7  is another diagram that illustrates how the beam former  306  can be connected to multiple centre-series feed secondary power combiners/splitters  304 . 
     Referring to  FIG. 8 , there is a diagram that illustrates one way to package the multi-beam antenna system  100  shown in  FIG. 1 . The multi-beam antenna system  100  scans 1-D beam(s)  112  (narrow in azimuth with scanning and narrow in elevation with fixed cosecant squared null fill) anywhere within 360 degrees. The package shown is a truncated pyramid where each face or aperture  110  contains individual transmit and receive arrays. All of the components both RF elements (dividers, combiners, switches, phase shifters, amplifiers . . . ) and control elements (power supply . . . ) are contained within the package. 
     One embodiment of the multi-beam antenna system  100  may have the following capabilities shown in TABLE #1: 
     
       
         
           
               
               
               
             
               
                   
                 TABLE #1 
               
               
                   
                   
               
               
                   
                 Transmit 
                 Receive 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Frequency 
                 14.7–14.9 GHz 
                 15.1–15.3 GHz 
               
               
                 Polarization 
                 RHCP 
                 LHCP 
               
            
           
           
               
               
            
               
                 Beam Steering 
                 360 degree Azimuth (fixed beam in 
               
               
                   
                 Elevation) each single panel providing +/− 
               
               
                   
                 45 degree azimuth scan 
               
               
                 Beamwidth Azimuth 
                 5 degree Az 
               
               
                 half-power 
               
               
                 Beamwidth Elevation 
                 5 degree El--shaped with cosecant squared 
               
               
                 half-power 
                 null fill in the up direction 
               
               
                 Beam scan/switching 
                 &lt;10 ms (based on 20 mrad/sec tracking 
               
               
                 time 
                 requirement) 
               
            
           
           
               
               
               
            
               
                 Maximum incoming 
                 20 W 
                 20 W 
               
               
                 power 
               
               
                 Antenna gain 
                 24 dBi 
                 24 dBi 
               
               
                 Antenna EIRP 
                 37 dBW per beam 
                 — 
               
               
                 Front-to-Back ration 
                 &gt;20 dB 
                 &gt;20 dB 
               
               
                 (F/B) 
               
               
                 Return Loss 
                 &lt;−14 dB 
                 &lt;−14 dB 
               
               
                   
                 (1.5:1 VSWR) 
                 (1.5:1 VSWR) 
               
               
                 Impedance 
                 50 Ω 
                 50 Ω 
               
            
           
           
               
               
            
               
                 Polarity 
                 &gt;20 dB 
               
               
                 discrimination 
               
               
                 Antenna Size 
                 ~36″ × 36″ footprint by ~16″ high 
               
               
                   
               
            
           
         
       
     
     Referring to  FIGS. 9–11 , there are several diagrams illustrating another embodiment of the multi-beam antenna system shown in  FIG. 1 . 
     In this embodiment, an active receive only multi-beam system  100 ′ is described and shown whereby one or more of four array panels  110 ′ is selected by a RF switching system  204 ′. As shown, the array panels  110 ′ are connected via the RF switching system  204 ′ to a 4-port phase shifter matrix  206 ′ which includes 4 beam formers  306 ′. It should be appreciated that there could be M-phase shifter matrices  206 ′ and M-beamformers  306 ′. Each beamformer  306 ′ has 1 output port and N input ports, where N corresponds to the number of columns of antenna elements  302  in the corresponding array panel  110 ′ (see  FIG. 3 ). The M beamformers  306 ′ allow the array panels  110 ′ to simultaneously receive N radiation beams  112 ′ (not shown). This is done by connecting input port n (n=1, 2, . . . , N) of each of the M beamformers  306 ′ to an output of a low noise amplifier (LNA)  902  connected to column power combiner  304 ′ number n (n=1, 2, . . . , N), which feeds column no. n of antenna elements  302 ′ in the corresponding array panel  110 ′. M receivers  904  are connected to the M output ports of the M beamformers  306 ′. It should be appreciated that in another embodiment 4 parallel systems of M receivers  904  and M beamformers  306 ′ can be connected to the 4 array panels  110 ′ eliminating the need for the RF switching system  204 . It should also be appreciated that a multi-beam transmit system can be constructed by reversing the direction of the LNAa  902  and connecting the beamformers  306 ′ to transmitters (not shown) instead of to receivers  904 . In yet another embodiment each side of the square of array panels  110 ′ can be constructed to house  1  TX and  1  RX aperture  110 ′ to form a full multi-beam transceiver system  100  that is capable of handling M simultaneous beams per aperture  110 ′. Thus, the main difference between the embodiment shown in  FIG. 9A  and that shown in  FIG. 1 , is that the number of simultaneous beams per antenna array aperture  110  has been increased from 1 to a multitude of M beams. 
       FIG. 9B  shows a further addition/improvement to the antenna system  100 ′ whereby each antenna array element  302 ′ is dual polarized.  FIG. 9B  shows microstrip feed power combiners/splitters  304 ′ feeding array columns consisting of 2 patch-type elements  302 ′ (only two elements per column are shown for simplicity, but this can be increased/reduced to any arbitrary number). Since each of the dual polarized columns of antenna elements  302 ′ now has two isolated ports representing two orthogonal polarizations, a second P-port phase shifter matrix connected to P receivers/transmitters can be used to feed the additional polarization. Thus, each array aperture is capable of handling M simultaneous beams of one polarization, and P simultaneous beams of the orthogonal polarization.  FIG. 10  shows the position of the LNA&#39;s  902 ′ connected to each column of array elements  1010 . Each LNA  902 ′ is connected via a band pass filter  1005  to the array column  1010  to protect the LNA  902 ′ from out of band high power signals.  FIG. 11  shows how the controller  115  of  FIG. 2  will be connected to the different components of the beamformers  306 ′. Components may include V/H Polar Switches  1105 , Panel Beam  1110 , tunable bandpass filter  1115  and phase shifters.  1120 . 
     The phase shifters  206  in the preferred embodiment may incorporate a voltage tunable ferroelectric material comprising Barium-Strontium Titanate, Ba x Sr 1-x TiO 3  (BSTO), where x can range from zero to one, or BSTO-composite ceramics. Examples of such BSTO composites include, but are not limited to: BSTO—MgO, BSTO—MgAl 2 O 4 , BSTO—CaTiO 3 , BSTO—MgTiO 3 , BSTO—MgSrZrTiO 6 , and combinations thereof. 
     The following is a list of some of the patents which discuss different aspects and capabilities of the voltage tunable ferroelectric material all of which are incorporated herein by reference: U.S. Pat. Nos. 5,312,790; 5,427,988; 5,486,491; 5,635,434; 5,830,591; 5,846,893; 5,766,697; 5,693,429 and 5,635,433. 
     The phase shifters  206  can be configured as anyone of the phase shifters disclosed in U.S. Pat. Nos. 6,377,217; 6,621,377; 6,538,603; and 6,590,468. Or disclosed in U.S. patent application Ser. No. 09/644,019 (Aug. 22, 2000); Ser. No. 09/838,483 (Apr. 19, 2001); Ser. No. 10/097,319 (Mar. 14, 2002); Ser. No. 09/931,503 (Aug. 16, 2001); and Ser. No. 10/226,746 (Aug. 27, 2002). The contents of these patents and patent applications are hereby incorporated by reference herein. 
     The multi-beam antenna system  100  enhances the spatial and frequency agility of communication networks—at the antenna and the receiver system. Further, the multi-beam antenna system  100  can be used in mobile ad-hoc networks. 
     While the present invention has been described in terms of its preferred embodiments, it will be apparent to those skilled in the art that various changes can be made to the disclosed embodiments without departing from the scope of the invention as set forth in the following claims.