Abstract:
A satellite antenna module is disclosed. The satellite antenna module includes at least one antenna element disposed on a ground plane. The ground plane is capacitivly coupled to a vehicle surface. The ground plane is disposed over the vehicle surface at an elevation angle that achieves a higher gain of the at least one antenna element.

Description:
FIELD 
   The invention relates to a satellite antenna system. More particularly, the invention relates to a satellite diversity antenna system. 
   BACKGROUND 
   Automotive vehicles are becoming commonly equipped with antennas that receive and process signals other than traditional AM/FM signals, such as, for example, satellite signals. In particular, antennas relating to satellite digital audio radio services (SDARS), which is broadcast on the 2320-2345 MHz frequency band, is becoming widely available in vehicles as an originally-installed component by an original equipment manufacturer (OEM), or, alternatively, as an after-market component that is installed after the vehicle has been manufactured by the OEM. SDARS offer a digital radio service covering a large geographic area, such as North America. Satellite-based digital audio radio services generally employ either geo-stationary orbit satellites or highly elliptical orbit satellites that receive up-linked programming, which, in turn, is re-broadcast directly to digital radios in vehicles on the ground that subscribe to the service. 
   SDARS antennas, such as, for example, patch antennas, presently track two satellites at a time. Thus, the location of the SDARS patch antennas on a vehicle is critical for obtaining proper reception. As a result, SDARS patch antennas may be mounted on the vehicle exterior, usually on the roof. Some SDARS antennas have been located at locations other than the vehicle roof in a “hidden antenna” application; however, reception performance of the antenna may be compromised if the antenna is moved away from the roof. To achieve higher gains for improving the antenna performance, antennas have been positioned at different locations on the vehicle with the output of each antenna summed in a phase array summation implementation. Another methodology to improve antenna performance includes two or more antennas positioned at different locations on a vehicle in a switched diversity application where signal reception is switched amongst antenna elements if the receiving antenna element loses the signal. 
   Although adequate for most situations, the phase array summation implementation introduces design and installation complexities. Even further, the switched diversity implementation does not achieve a higher gain of the received satellite signal. A need therefore exists for an improved antenna system that provides reception of SDARS signals while achieving higher gains and maintaining vehicle aesthetics. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The inventors have recognized the above-described and other problems associated with an antenna system that receives satellite signals. The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
       FIG. 1A  is a sectional view of an antenna system according to an embodiment; 
       FIG. 1B  is a sectional view of an antenna system according to an embodiment; 
       FIG. 1C  is a sectional view of an antenna system according to an embodiment; 
       FIG. 2A  is a block diagram illustrating the electronics for operating a diversity antenna system of  FIGS. 1A-1C  according to an embodiment; 
       FIG. 2B  is a block diagram illustrating the electronics for operating a diversity antenna system of  FIGS. 1A-1C  according to an embodiment; and 
       FIG. 2C  is a block diagram illustrating the electronics for operating a diversity antenna system of  FIGS. 1A-1C  according to an embodiment. 
   

   DETAILED DESCRIPTION 
   The above-described disadvantages are overcome and a number of advantages are realized by an inventive antenna system, which is shown generally at  10   a - 10   c  in  FIGS. 1A-1C , respectively. As illustrated, each antenna system  10   a - 10   c  comprises an antenna module, which is shown generally at  12   a - 12   c , that includes a first patch antenna  14   a - 14   c , a second patch antenna  16   a - 16   c , a ground plane  18   a - 18   c , and a protective radome  20 . The antenna modules  12   a - 12   c  are placed over an outer surface of a vehicle, such as, for example, a vehicle roof  22   a - 22   c , which may comprise metal. 
   Each first patch antenna  14   a - 14   c  and second patch antenna  16   a - 16   c  are generally well-known structures including an antenna element  11   a ,  11   b  ( FIGS. 2A-2C ) that may receive satellite and terrestrial signals, a low noise amplifier  13   a ,  13   b  ( FIGS. 2A-2C ), and a printed circuit board (not shown) including associated electronics (not shown) that processes the received satellite signals. The frequency of the satellite signals may range, for example, between approximately 2320-2345 MHz (i.e. the SDARS frequency range). 
   The ground plane  18   a - 18   c  may comprise a sheet of conductive, lightweight metal that includes at least two surfaces  26   a - 26   c ,  28   a - 28   c  that are bent, pressed, or otherwise shaped to include a peak  30   a - 30   c , which may be shaped to include a corner as illustrated, or, alternatively, a rounded peak. As illustrated, the first patch antenna  14   a - 14   c  is placed over the first side  26   a - 26   c  and the second patch antenna  16   a - 16   c  is placed over the second side  28   a - 28   c . If desired, the ground plane  18   a ,  18   b  may alternatively include a solid piece of lightweight metal rather than a sheet; however, a solid ground plane  18   a - 18   c  may undesirably increase the cost of the part due to the extra material while also increasing the weight of the antenna system  10   a - 10   c . If the ground plane  18   a ,  18   b  is solid, the ground plane  18   a ,  18   b  would include a third side adjacent the vehicle roof  22   a - 22   c.    
   If the vehicle roof  22   a - 22   c  is metallic, the ground plane  18   a - 18   c  is capacitively coupled to the vehicle roof  22   a - 22   c . As illustrated, the generally triangular, ramp-shape of the ground plane  18   a - 18   c  is selectively shaped or otherwise formed to include any desirable pair of elevation angles with respect to the vehicle roof, which is shown generally at θ 1  and θ 2  ( FIG. 1A ), θ 3  and θ 4  ( FIG. 1B ), and Δ 1  and Δ 2  ( FIG. 1C ). The elevation angles θ 1 -θ 4 , Δ 1 , Δ 2  may range, for example, approximately between 5 0 °-60 0 °. The elevation angle range could be optimized for low or high elevation angles for a particular market within or outside of the elevation range. In an application-specific example, the design of some antennas used in Canada may have low elevation angles, and therefore, the antennas may have to be tuned to a narrow beamwidth. 
   Preferably, to maintain antenna performance, each ground plane  18   a - 18   c  is shaped or otherwise formed to include equivalent pairs of elevation angles θ 1  and θ 2 , θ 3  and θ 4 , Δ 1  and Δ 2 , thereby forming the ground plane  18   a - 18   c  into an isosceles triangle. However, it will be appreciated that the elevation angles θ 1  and θ 2 , θ 3  and θ 4 , Δ 1  and Δ 2 , for each respective ground plane  18   a - 18   c  may be shaped to include non-similar angles such that the triangular shape of each ground plane  18   a - 18   c  is a non-isosceles triangle. 
   The elevation angles θ 1  and θ 2 , θ 3  and θ 4 , shown in  FIGS. 1A and 1B , respectively, are fixed with respect to the vehicle roof  22   a ,  22   b . As shown in  FIG. 1A , the vehicle roof  22   a  is substantially flat with respect to the ground that the vehicle travels on. As shown in  FIG. 1B , the vehicle roof  22   b  includes a contour with respect to the ground that the vehicle travels on, and, as a result, the elevation angles, θ 3  and θ 4 , of the patch antennas  14   b ,  16 , b  with respect to sky are effected by a pitch angle, φ. The pitch angle, φ, may alternatively result from the title angle of a roof-rack or sunroof that may carry the antenna module  12   b . Accordingly, in comparison to a substantially flat vehicle roof  22   a  with respect to ground, the pitch angle, φ, related to the second antenna module  12   b  effectively decreases the elevation angle, θ 3 , with respect to sky to (θ 3 −φ) while the elevation angle, θ 4 , with respect to sky is increased to (θ 4 +φ); however, if desired, the elevation angles, θ 3  and θ 4 , may be shaped as described above with angles that forms a non-isosceles triangle such that when the pitch angle, φ, is considered, the patch antennas  14   b ,  16   b  may be elevated with respect to sky at the same angles. 
   Referring to  FIG. 1C , another embodiment shows an adjustable ground plane  18   c . The adjustable ground plane  18   c  includes a first hinge point  24  proximate the vehicle roof  22   c  and a second hinge point substantially located at the peak  30   c . As illustrated, the second side  28   c  rests against a retainer or tab  32  proximate the vehicle roof  22   c . To adjust the elevation angles Δ 1  and Δ 2 , the second side  28   c  may be adjusted to rest against a second tab  34 ,  36  proximate the vehicle roof  22   c . Accordingly, the elevation angles Δ 1  and Δ 2  are not fixed (as compared to the elevation angles θ 1  and θ 2 , θ 3  and θ 4 , shown in  FIGS. 1A and 1B ), but rather, may be adjusted in the field of operation of the vehicle if the elevation angles Δ 1 , Δ 2  are not optimized to a maximum gain for the received satellite signal. 
   In design, the elevation angles, θ 1 -θ 4 , are optimized to achieve a desirable gain value for any desirable satellite elevation (i.e. a low or high latitude location). If an adjustable ground plane  18   c  is provided, a skilled technician may adjust the ground plane  18   c , or, alternatively, instructions may be provided in a user-manual so that the user may adjust the ground plane  18   c . Regardless of the fixed or adjustable nature of the ground plane  18   a - 18   c , the desirable gain value for a vehicle receiving satellite signals that is located, for example, in Boca Raton, Fla., is substantially different from a gain value for a vehicle receiving satellite signals in geographically different location, such as, for example, in Bangor, Me. Accordingly, the antenna modules  12   a - 12   c  may be designed to include any desirable fixed or adjustable elevation angles to meet any satellite service provider specification or optimal service performance in the field. 
   Each patch antenna  14   a - 14   c ,  16   a - 16   c  is also tuned to a narrow beamwidth instead of an omni-directional pattern. The average and minimum gain values increase by more than 2.0 dB over an omni-directional pattern placed at a conventionally-inclined patch antenna elevation angles of zero degrees. Beside the pitch angle, φ, of the roof  22   b , the elevation angle, θ 1  and θ 2 , θ 3  and θ 4 , Δ 1  and Δ 2 , of each patch antenna  14   a - 14   c ,  16   a - 16   c  may be varied as described above in view of the effects of cross-coupling from one patch antenna element to another. The patch antenna orientation (i.e., the antenna elements+ground) within each module  12   a - 12   c  may vary from 0° to 360°. Even further, separation of each patch antenna element  14   a - 14   c ,  16   a - 16   c  may range from ½ to 1/16 wavelength in order to minimize the effects of cross coupling/loading from each other. 
   Referring to  FIGS. 2A-2C , each patch antennas  14   a - 14   c ,  16   a - 16   c  may include well-known diversity electronics  50  on the circuit board of the patch antenna  14   a - 14   c  ( FIG. 2A ) or patch antenna  16   a - 16   c  ( FIG. 2B ). Alternatively, the patch antennas  14   a - 14   c ,  16   a - 16   c  may be connected by two cables to a receiver  75  including the diversity electronics  50  ( FIG. 2C ). As shown in  FIGS. 2A and 2B , if the diversity electronics  50  is incorporated within one of the patch antenna elements  14   a - 14   c  or  16   a - 16   c , a cable may extend from one patch antenna element to another for connection at a pin diode switch element  52 . The output of the patch antenna including the diversity electronics is then output at reference numeral  66 . 
   As is known in the art, a diversity application includes one or more antennas elements to improve antenna performance. If a first antenna in a diversity application loses reception of an expected signal, the diversity application will poll the other antenna(s) in the application for expected signal reception so that the diversity system will switch to a different antenna that is receiving the expected signal while the reception of the expected signal by the first antenna is temporarily unavailable. The well-known diversity switching circuitry  50  includes the pin diode switch  52 , a filter  54 , a low noise amplifier (LNA)  56 , a buffer  58 , an amplifier  60 , a rectifier  62 , and a comparator  64 . The LNA  56  and buffer  58  share an output node to a radio-frequency cable  66  and the output of the comparator is fed-back to the pin diode switch  52 , which is shown generally at  68 . 
   The antenna systems  10   a - 10   c  described above essentially utilizes two independent patch antennas  14   a - 14   c ,  16   a - 16   c  that are elevated to any desirable fixed or adjustable elevation angle, θ 1  and θ 2 , θ 3  and θ 4 , Δ 1  and Δ 2 , in a single antenna module  12   a - 12   c . Additionally, one of the patch antennas  14   a - 14   c ,  16   a - 16   c  may include the diversity switching electronics  50  to further reduce wiring and other design complexities. 
   The antenna systems  10   a - 10   c  described above may receive satellite audio signals; however, it will be appreciated that the antenna systems  10   a - 10   c  may receive other satellite signals, such as, for example, satellite video signals. In order to integrate satellite video capability, the use of special hierarchal modulation techniques of the signal may be implemented to receive the satellite video signals. In addition to the functional features described above, the antenna systems  10   a - 10   c  maintain a visually pleasing roof-mount “hidden antenna” design where the antenna elements and electronics are concealed under the protective radome  20 . Even further, it will be appreciated that the antenna systems  10   a - 10   c  are not limited to patch antennas  14   a - 14   c ,  16   a - 16   c . Any desirable antenna element that receives terrestrial and satellite signals may be used in the antenna systems  10   a - 10   c , including, for example, helix or monopole antennas. 
   While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit.