Patent Publication Number: US-2009231186-A1

Title: Compact electronically-steerable mobile satellite antenna system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application 61/026,497, filed Feb. 6, 2008, whose disclosure is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to satellite communication systems, and particularly to antennas for mobile satellite terminals. 
     BACKGROUND OF THE INVENTION 
     Satellite communication systems are used for providing various types of communication services, such as television or other video services, voice communication services, data communication services such as Internet access, and many others. For example, Direct Broadcast Satellite (DBS) systems transmit digitally-compressed television and audio signals to subscriber terminals. 
     Various methods and systems are known in the art for providing satellite communication services to mobile terminals. For example, Raysat, Inc. (Vienna, Va.) offers a family of mobile satellite terminals called SpeedRay™. KVH Industries, Inc. (Middletown, R.I.) offers a line of mobile satellite terminals called TrackVision®. 
     U.S. Pat. No. 6,999,036, whose disclosure is incorporated herein by reference, describes an antenna system that includes a plurality of antenna arrangements. The antenna arrangements form a spatial phased array able to track a satellite in an elevation plane by mechanically rotating the arrangements. A combining/splitting circuit provides phasing and signal delay in order to maintain preconfigured radiating parameters. The arrangements can be mounted on a rotating platform to provide azimuth tracking. The system provides dynamic tracking of satellite signals and can be used for satellite communications on moving vehicles. Yet another mobile satellite antenna system is described in U.S. Patent Application Publication 2008/0129624, whose disclosure is incorporated herein by reference. 
     SUMMARY OF THE INVENTION 
     An embodiment of the present invention provides a satellite antenna terminal, including: 
     a circuit board having first and second opposite surfaces; 
     a plurality of antenna elements, which are disposed on the first surface of the circuit board and are operative to receive Radio Frequency (RF) signals from a satellite; and 
     one or more signal processing devices, which are disposed on the second surface of the circuit board and are coupled to process the RF signals received by the antenna elements. 
     In some embodiments, the signal processing devices include Monolithic Microwave Integrated Circuits (MMICs). In an embodiment, each of the signal processing devices is coupled to accept one or more of the received RF signals at an input frequency, and to produce an output RF signal at an output frequency that is equal to the input frequency. In another embodiment, each of the signal processing devices is arranged to process four of the received RF signals. 
     In a disclosed embodiment, the antenna elements include dual-port antenna elements, each operative to receive and output two RF signal components having mutually-orthogonal polarizations. In another embodiment, the antenna elements include first and second sets of the antenna elements, which are operative to receive and output respective first and second RF signal components having first and second mutually-orthogonal polarizations. 
     In some embodiments, the signal processing devices are coupled to modify relative amplitudes and phases of the RF signals received by the antenna elements, and to combine the RF signals having the modified relative amplitudes and phases to produce a combined output signal. In an embodiment, the signal processing devices are coupled to modify a radiation pattern formed by the antenna elements. The signal processing devices may be coupled to electronically steer an antenna beam formed by the antenna elements. Additionally or alternatively, the signal processing devices may be coupled to modify a polarization inclination angle of the radiation pattern. In an embodiment, the signal processing devices are configurable to switch between receiving circularly-polarized RF signals and linearly-polarized RF signals. 
     In a disclosed embodiment, the terminal further includes Low-Noise Amplifiers (LNAs), which are disposed on the second surface and are operative to amplify the RF signals received by the antenna elements and to provide the amplified RF signals to the signal processing devices, and the signal processing devices include biasing circuits for biasing the LNAs. In another embodiment, the terminal includes a metallic chassis on which the circuit board is mounted, and the chassis includes multiple protrusions that extend toward the circuit board and come to thermally-conductive contact with the signal processing devices. 
     In yet another embodiment, the circuit board includes a multi-layer Printed Circuit Board (PCB). In still another embodiment, the terminal includes at least one additional component, which is disposed on the second surface and is selected from a group of components consisting of a Central Processing Unit (CPU), a Low-Noise Amplifier (LNA), a down-converter, a power supply, a Global Positioning System (GPS) receiver and a gyro sensor. In another embodiment, a total height of the terminal, in a dimension perpendicular to a plane of the circuit board, does not exceed 3 cm. 
     There is additionally provided, in accordance with an embodiment of the present invention, a method for producing a satellite antenna terminal, the method including: 
     disposing a plurality of antenna elements for receiving Radio Frequency (RF) signals from a satellite on a first surface of a circuit board; and 
     disposing one or more signal processing devices for processing the RF signals received by the antenna elements on a second surface of the circuit board, which is opposite the first surface. 
     The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         FIG. 1  is an exploded view of a mobile satellite antenna system, in accordance with an embodiment of the present invention; 
         FIG. 2  is a vertical cross section of a mobile satellite antenna system, in accordance with an embodiment of the present invention; 
         FIG. 3  is a block diagram that schematically illustrates a mobile satellite antenna system, in accordance with an embodiment of the present invention; 
         FIG. 4  is an illustrative vertical cross section of a mobile satellite antenna system, in accordance with an embodiment of the present invention; and 
         FIG. 5  is a vertical cross section of an antenna assembly in a mobile satellite antenna system, in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Overview 
     Embodiments of the present invention provide improved phased array antenna systems for receiving communication signals from satellites. The disclosed antenna systems are particularly suitable for mobile satellite terminals installed in vehicles. 
     In some embodiments, an antenna system comprises a plurality of antenna elements, which receive Radio Frequency (RF) signals from a satellite. The RF signals received by the antenna elements are processed by one or more signal processing devices. The signal processing devices typically adjust the relative phases and amplitudes of the received RF signals, so as to steer the antenna beam toward the satellite. Additionally, the signal processing devices can also control the polarization inclination of the antenna to match the polarization of the satellite signal. 
     In the disclosed antenna systems, the antenna elements are disposed on one surface of a circuit board, and the signal processing devices are disposed on the opposite surface of the board. This mechanical configuration reduces the overall height of the antenna system (the dimension perpendicular to the circuit board). The reduced height simplifies the installation of the antenna system in a vehicle, and may enable higher flexibility in choosing the installation location. Moreover, disposing the antenna elements and signal processing devices on opposite surfaces of the same circuit board typically reduces the number of circuit boards, and the number of interconnections between circuit boards. A simpler mechanical structure having fewer boards and interconnections typically means lower signal losses, higher reliability and lower cost. 
     System Description 
       FIG. 1  is an exploded view of a mobile satellite antenna system  20 , in accordance with an embodiment of the present invention. System  20  comprises an electronically-steerable phased array antenna for tracking and receiving communication signals from satellites. The system is designed for installation in vehicles, and is able to steer the radiation pattern of the phased array antenna toward the satellite while compensating for vehicle motion. 
     System  20  has a flat and compact mechanical profile that is particularly suitable for mounting in vehicles, such as cars, buses, Recreational Vehicles (RVs), trains, boats or airplanes. In the present example, system  20  receives satellite signals in the KU band, e.g., in the range 12.2-12.7 GHz, although any other suitable frequency bands, such as the KA band, can also be used. 
     System  20  comprises an antenna assembly  22 . Assembly  22  comprises a circuit board  24 , which has two opposite surfaces. Multiple antenna elements  28  are disposed on one surface of the circuit board. One or more signal processing devices (not shown in this figure) are disposed on the opposite surface of the circuit board. The antenna elements receive signals from a satellite, and the signal processing elements process the received signals using methods that are addressed below. Cross sections showing the antenna elements and signal processing devices on the opposite surfaces of the circuit board are shown in  FIGS. 2 ,  4  and  5 . The example antenna system of  FIG. 1  comprises ninety-four printed patch elements that are arranged in a hexagonal grid. In alternative embodiments, however, the antenna system may comprise any other number or type of antenna elements in any desired geometrical arrangement. 
     In addition to the antenna elements and the signal processing devices, assembly  22  further comprises gyro sensors  32  for sensing the movements of system  20 , and a GPS receiver  36  for measuring the geographical coordinates of system  20 . The information provided by the gyro sensors and GPS receiver are used for steering the radiation pattern of the phased array antenna toward the satellite. A coaxial connector  40  is used for outputting the received signal produced by the signal processing devices out of system  20 , as well as for supplying electrical power and control commands to system  20 . 
     Assembly  22  is mounted on a metallic, mechanical chassis  44 . The chassis comprises multiple protrusions  48 , which absorb heat that is produced by the signal processing devices and dissipate it to the chassis. When system  20  is packaged, protrusions  48  come to mechanical contact with the signal processing devices on the bottom surface of circuit board  24 . This feature is shown in detail in  FIG. 2  below. A sealing ring  52  seals the gap between circuit board  24  and chassis  44 . A sheet  56  of radiation absorbing material is placed on the bottom of chassis  44  in order to prevent RF radiation from being reflected from the chassis toward assembly  22 . 
     Assembly  22  is covered by a metallic cover  60 , which also comprises heat sink fins for additional heat dissipation. Cover  60  has an opening above the antenna elements. A radome  64  is placed over the opening, and a sealing ring  68  seals the contact between the radome and the opening in cover  60 . 
     In the present example, the horizontal aperture of the phased array antenna has a typical diameter in the range of 20-40 cm, and in some implementations less than 20 cm. The height dimension of antenna system  20  (the dimension perpendicular to the plane of circuit board  24 ) is typically in the range of 2.5-3 cm. In alternative embodiments, however, any other suitable dimensions can be used. 
       FIG. 2  shows a partial vertical cross section of system  20 , in accordance with an embodiment of the present invention. The figure shows the different structural elements of system  20  that were shown in FIG.  1  above. In particular,  FIG. 2  shows one of antenna elements  28  disposed on one surface of circuit board  24 , and an Analog Signal Processing (ASP) device  72  disposed on the opposite surface of the circuit board. The ASP device is in contact with one of protrusions  48 , in this example by means of thermo-conductive grease or a thermo-conductive pad fitted between the ASP device and protrusion  48 . 
     The mechanical configuration shown in  FIGS. 1 and 2  is an exemplary configuration, which is shown purely for the sake of conceptual clarity. In alternative embodiments, system  20  may have any other suitable mechanical configuration, in which the antenna elements and the signal processing devices are disposed on opposite surfaces of a circuit board. Alternative configurations are shown in U.S. Provisional Patent Application 61/026,497, cited above. 
       FIG. 3  is a block diagram that schematically illustrates mobile satellite antenna system  20 , in accordance with an embodiment of the present invention.  FIG. 3  shows the different electronic components comprised in assembly  22  and their interconnections. In the example of  FIG. 3 , each antenna element  28  comprises a dual-port element, which comprises two outputs that produce two mutually-orthogonal signal components received by the antenna element. The outputs of the different antenna elements are amplified by Low-Noise Amplifiers (LNAs)  76 . The outputs of the LNAs are processed by Analog Signal Processing (ASP) devices  72 , which apply signal processing operations such as phase shifting, variable attenuation and summation to the signals received by the antenna elements. 
     In some embodiments, LNAs  76  are internal to the ASP devices. In some embodiments, ASP devices  72  comprise biasing circuitry for biasing LNAs  76 . Typically, the ASP devices do not perform frequency conversion operations. In other words, each ASP device receives as input one or more RF signals and produces an output signal having the same frequency as the input signals. 
     In a typical implementation, each ASP device  72  comprises a Monolithic Microwave Integrated Circuit (MMIC) that processes four signals received by two dual-port antenna elements. The MMICs may be fabricated on any suitable semiconductor substrate, such as Gallium-Arsenide (GaAs) or Silicon-Germanium (SiGe). The MMICs may be packaged in Multi-Chip-Modules (MCMs), which also comprise control and/or biasing circuits. ASP devices of this sort are described, for example, in U.S. patent application Ser. No. 12/354,024, entitled “Analog Signal Processing Device for Phased Array Antennas,” filed Jan. 15, 2009, which is assigned to the assignee of the present patent application and whose disclosure is incorporated herein by reference. In alternative embodiments, system  20  may process the signals received by the antenna elements using any other suitable kind of analog signal processing devices. Each such device may apply any suitable signal processing operation and may be assigned to process any suitable number of signals. 
     ASPs  72  comprise components such as configurable phase shifters and gain stages (e.g. attenuators), using which the relative phases and amplitudes of the different signals received by antenna elements  28  can be adjusted. By performing these phase and amplitude adjustments, system  20  can steer its radiation pattern (and in particular its antenna beam or main lobe) electronically in any desired direction, in order to point toward the satellite. 
     Moreover, since elements  28  comprise dual-port elements that receive signal components having mutually-orthogonal polarizations, appropriate phase and amplitude adjustments enable system  20  to receive satellite signals having any desired polarization, such as vertical polarization, horizontal polarization, linear polarization that is tilted at any desired angle, Right-Hand Circular Polarization (RHCP) or Left-Hand Circular Polarization (LHCP). In alternative embodiments, elements  28  may comprise single-port antenna elements. In these cases, some of the elements are oriented on board  24  so to receive a given polarization, and other elements are oriented so as to receive the orthogonal polarization. In other words, ASP devices  72  may obtain the mutually-orthogonal signal components either from dual-port antenna elements or from single-port antenna elements. 
     The outputs of ASP devices  72  are combined by combining circuits  80  and  88 , and may be amplified by LNAs  84 . The combined output of the different ASP devices is provided at the output of combining circuit  88 . When the appropriate phase shifts and attenuations are applied in ASP devices  72 , the radiation pattern formed by elements  28  is pointed toward the satellite, and the signal at the output of combining circuit  88  represents the signal transmitted from the satellite with a high Signal-to-Noise Ratio (SNR). 
     The signal produced by combining circuit  88  is down-converted to a lower frequency (to L-band in the present example) by a Low-Noise down-converter Block (LNB)  92 . The down-converted signal is output on connector  40  (see  FIG. 1 ) via a power injector  96 . The signal is provided for further processing by a Set-Top Box (STB—not shown in the figures), which is typically mounted inside the vehicle. 
     System  20  further comprises a control modem  100 , which receives from the STB control commands for controlling the different elements of system  20 . In some embodiments, the commands are produced by a modem in the STB and are sent over the same cable used for providing the down-converted signal to the STB. In addition, the same cable can also be used for supplying electrical power from the STB to system  20 . Power injector  96  receives the different signals (down-converted signal to the STB, control commands from the STB and electrical power from the STB) separates them and forwards each signal to its proper destination. Typically, the STB comprises a similar power injector at the other end of the cable. 
     System  20  comprises a Power Supply (PSU)  104 , which receives the electrical power from the STB and produces the appropriate voltages for powering the different elements of system  20 . A Central Processing Unit (CPU)  108  manages and controls the different system elements, at least partially in response to commands received by modem  100  and to information produced by gyro sensors  32  and GPS receiver  36 . 
     In the present example, the different components of system  20  are mounted on a single circuit board. Alternatively, however, the components can be divided among any suitable number of circuit boards or modules. An example configuration, in which the components are divided between two printed circuit boards, is described in U.S. Provisional Patent Application 61/026,497, cited above. 
       FIG. 4  is an illustrative vertical cross section of system  20 , in accordance with an embodiment of the present invention.  FIG. 4  shows circuit board  24  with multiple antenna elements  28  disposed on one of its surfaces. ASP devices  72 , as well as LNAs  76 , GPS receiver  36 , gyro sensors  32 , LNB  92 , PSU  104 , control modem  100 , CPU  108  and output connector  40 , are mounted on the opposite surface of board  24 . 
       FIG. 5  is a vertical cross section of antenna assembly  22  in system  20 , in accordance with an embodiment of the present invention. In this embodiment, circuit board  24  comprises a multi-layer Printed circuit Board (PCB), which comprises multiple conducting layers  116  that are separated by dielectric layers  120 . One of antenna elements  28 , in this example a printed patch element, is shown on the top surface of the PCB. Conducting layers  116  in this configuration comprise (progressing down from element  28 ) a ground layer, an interconnection layer comprising microstrip lines, another ground layer and an additional interconnection layer. As noted above, conductive layers  116  are separated by dielectric layers  120 . 
     Interconnections between the different conducting layers of the multi-layer PCB (e.g., interconnections between antenna elements  28  and LNAs  76 ) may be implemented using any suitable technique, such as using plated via holes (not shown) that traverse the PCB. 
     Electronic components  124  are disposed on the bottom surface of board  24  (the surface opposite to the surface on which the antenna elements are disposed). Components  124  may comprise, for example, gyro sensors  32 , GPS receiver  36 , ASP devices  72 , LNAs  76 , LNB  92 , control modem  100 , PSU  104  and/or CPU  108 . 
     It will be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and sub-combinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.