Patent Publication Number: US-6664933-B2

Title: Multi-feed reflector antenna

Description:
CROSS REFERENCE OF RELATED APPLICATION 
     This application claims priority to provisional U.S. Application Ser. No. 60/195,247, filed Apr. 7, 2000 and a continuation of pending application Ser. No. 09/827,370, filed Apr. 6, 2001 herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to the field of satellite communications. More particularly, the present invention relates to a multi-feed antenna suitable for satellite communications. 
     Geostationary direct broadcast systems (DBS) are geostationary satellite systems that are direct competitors to terrestrially-based cable television systems. Such DBS systems have the advantage of allowing a terrestrially-based receiver to receive a plurality of television channels from virtually any location on Earth, while a cable television subscriber must be connected to a cable television system to receive television signals. Terrestrial-based cable television systems have the advantage over DBS systems of allowing a subscriber to have a high-bandwidth Internet connection through the cable television system, while such a connection is unavailable through a DBS system. Currently, digital links to the Internet are available through the fixed satellite system (FSS), another system of geostationary satellites. 
     U.S. Pat. No. 5,859,620 to Skinner et al. relates to a multiband feedhorn satellite receiving antenna that receives signals from more than 30 satellites that are longitudinally spaced in geosynchronous orbits above the equator of the Earth. According to Skinner et al., a satellite receiving antenna includes a torodial reflector having a circular cross-section in a horizontal (longitudinal or azimuthal) plane and a parabolic cross-section in an elevational plane. The size of the Skinner et al. reflector requires a plurality of braces for support and is far too large for use in a residential environment. 
     U.S. Pat. No. 5,805,116 to Morley discloses to an ultra-small aperture antenna for a satellite communications terminal having a dish reflector and separate transmit and receive feedhorns. According to Morley, a receive feedhorn is spatially offset from a transmit feedhorn. Both feedhorns are disposed within a focal point zone such that the receive feedhorn is positioned at an ideal focal point of the dish reflector. The transmit feedhorn is positioned to have an aperture offset from the ideal focal point, but is still within the focal point zone of the dish reflector. The receive feedhorn is disposed at the ideal focal point for maximizing gain of received signals. A disadvantage with the Morley antenna is that the transmitter requires a relatively greater power output for compensating for the mispointing of the transmitted signal. 
     Consequently, what is needed is a small single antenna that is suitable for residential use, can simultaneously communicate with a geostationary FSS satellite and with a plurality of geostationary DBS satellites, and minimizes the amount of transmitters output power for transmitting to the FSS satellite. 
     SUMMARY OF THE INVENTION 
     The present invention provides a small single antenna that is suitable for residential use, can simultaneously communicate with a geostationary FSS satellite and with a plurality of geostationary DBS satellites, and minimizes the amount of transmitter output power for transmitting to the FSS satellite. 
     The advantages of the present invention are provided by an antenna that includes a reflector having a first axis, a second axis, a focal zone that is about parallel to the first axis, and a focal point located within the focal zone. According to the invention, a transmit feed is located at or about at the focal point, and at least one receive feed is located at about the focal zone. Preferably, the reflector is an elliptically-shaped offset-type parabolic reflector, and the transmit feed is part of a bidirectional feed that includes an integral receive feed. The bidirectional feed transmits and receives an RF signal carrying digital information signals to and from a first satellite, such as an FSS satellite, and each respective receive feed receives a signal from satellite, such as a DBS satellite. 
     In a preferred embodiment, the present invention provides an antenna that includes an elliptically-shaped offset-type parabolic reflector having a first axis, a second axis, a focal direction, a focal zone that is about parallel to the first axis, and a focal point located within the focal zone. Accordingly, a transmit feed is located within the focal zone, and at least one receive feed located at about the focal zone. A support arm extends from the bottom of the reflector in the focal direction of the reflector and supports the transmit feed at the focal point and each receive feed within the focal zone. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The present invention is illustrated by way of example and not limitation in the accompanying figures in which like reference numerals indicate similar elements and in which: 
     FIG. 1A shows a front view of a first configuration of an antenna according to the present invention; 
     FIG. 1B shows a front view of an alternative configuration of an antenna according to the present invention; 
     FIG. 2 shows a combination side/cross-sectional view of the first configuration of an antenna according to the present invention; 
     FIG. 3 shows a combination top/cross-sectional view of the first configuration of an antenna according to the present invention; 
     FIG. 4 shows a side perspective view of a preferred embodiment of an antenna according to the present invention; 
     FIG. 5 shows a front perspective view of a preferred embodiment of an antenna according to the present invention; 
     FIG. 6 shows a rear perspective view of a preferred embodiment of an antenna according to the present invention; and 
     FIG. 7 shows another front perspective view of a preferred embodiment of an antenna according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a front view of a first configuration of an antenna  100  according to the present invention. FIG. 2 shows a combination side/cross-sectional view of antenna  100 . FIG. 3 shows a combination top/cross-sectional view of antenna  100 . 
     As shown by FIGS. 1-3, antenna  100  includes a reflector  101  having a horizontal major axis  102  and a vertical minor axis  103 . Preferably, reflector  101  is elliptically-shaped parabolic antenna so that a plurality of geostationary satellites are within the field of view of antenna  100 . Also, reflector  101  is preferably an offset-type parabolic reflector for minimizing the field of view of reflector  101  that is blocked by feed and feed-support structures. The physical dimensions of reflector  101  are preferably 36.2 inches along major axis  102 , and 26 inches along minor axis  103 . The projected dimensions of antenna  100  are preferably 36.2 inches along major axis  102  and 24.6 inches along minor axis  103 . The physical dimensions are the actual dimensions of the reflector  101 , while the projected dimensions are the functional dimensions of the antenna, that is, the dimensions that a satellite “sees”. The projected dimensions are a function of the shape and topography of the antenna. 
     Antenna  100  has a focal zone  104  (FIGS. 2 and 3) that parallel to horizontal major axis  102 . When antenna  100  is oriented to communicate with the plurality of geostationary satellites, focal zone  104  is about parallel to the geostationary orbits (GSO) of the satellites, that is, focal zone  104  is about GSO parallel. Antenna  100  also has a focal point  105  that is defined by the shape of reflector  101 . 
     A support arm  106  extends from the bottom of reflector  101 . A feed-support member  107  extends from the end of support arm  106  substantially parallel to major axis  102 . A transmit/receive feed  108  is mounted on feed support member  107  and is positioned at or about at focal point  105 . Preferably, transmit/receive feed  108  is an integral bidirectional feed that transmits and receives an RF signal carrying digital information signals, such as used by computers for communicating between computers in a well-known manner. At least one additional receive feed  109  is positioned within focal zone  104 . While the FIGS. 1-3 show two receive feeds,  109   a  and  109   b , any number of additional receive feeds can be positioned within focal zone  104 . Preferably, each receive feed  109  receives direct broadcast (DBS) television signals. 
     FIG. 1B shows a front view of an alternative configuration of an antenna  100   a  according to the present invention. For this configuration, transmit/receive feed  108  can be used as a transmit/receive (Tx/Rx) feed and a receive-only (Rx) feed at the same time. Transmit/receive feed  108   a  is positioned at or about at focal point  105  together with receive feed  108   b . Together transmit/receive feed  108   a  and receive feed  108   b  operate as a bidirectional feed that transmits and receives an RF signal carrying digital information signals, such as used by computers for communicating between computers in a well-known manner. 
     In operation, antenna  100  is oriented so that signals transmitted to and received from an FSS satellite are respectively transmitted and received from focal point  105 , while signals received from each DBS satellite are respectively received at points within focal zone  104 . More specifically, antenna  100  is oriented so that an FSS geostationary satellite  110 , such as a Gstar 4 satellite, is focussed at focal point  105 . Transmit/receive feed  108  is positioned on feed-support member  107  at or about at focal point  105  so that a signal transmitted to FSS geostationary satellite  110  is about optimized with respect to the pointing direction to the FSS satellite. Signals that are to be transmitted to FSS satellite  110  are generated by a computer system  111 , such as a personal computer (PC), and converted in a well-known manner to an RF signal having an appropriate frequency for transmission to FSS satellite  110 . Signals received from FSS satellite  110  are detected in a well-known manner and supplied to computer system  111 . 
     Each additional receive feed  109  is positioned within focal zone  104  at a point that is about optimum for receiving a signal from a corresponding geostationary DBS (direct broadcast service) satellite  112  based on the pointing direction of antenna  100 . Exemplary DBS satellites include the Echostar I and II system satellites and the Echostar IV system satellites. Signals received by additional receive feeds  109  are directed to a television  113  through, for example, a dish network multi-satellite switch  114  and a dish network integrated receiver/descrambler (IRD)  115 . 
     FIGS. 4-7 show different views of a preferred embodiment of an antenna  400  according to the present invention. Antenna  400  includes an elliptically-shaped parabolic reflector  401 . A support arm  406  extends from the bottom of reflector  401 . A feed support member  407  extends from the end of support arm  406  substantially parallel to the major axis of reflector  401 . A transmit/receive feed  408  is mounted on feed support member  407  and is positioned at or about at the focal point of reflector  401 , as described above in connection with FIGS. 1-3. Transmit/receive feed  408  is an integral bidirectional feed that transmits and receives an RF signal carrying digital information signals. An additional receive feed  409  is positioned within the focal zone of reflector  401 , as also described above. Both feeds  408  and  409  are mounted on support member  407  using an adjustment bracket  410  for optimizing each feed along a vertical direction. 
     In operation, antenna  400  is oriented so that signals transmitted to and received from an FSS satellite are respectively transmitted and received by transmit/receive feed  408 , while signals received from a DBS satellite are respectively received by receive feeds  409   a  and  409   b.    
     While the present invention has been described in connection with the illustrated embodiments, it will be appreciated and understood that modifications may be made without departing from the true spirit and scope of the invention.