Patent Publication Number: US-10770791-B2

Title: Systems and methods for reducing signal radiation in an unwanted direction

Description:
FIELD 
     The present invention relates generally to radio frequency communication hardware. More particularly, the present invention relates to systems and methods for reducing signal radiation in an unwanted direction while simultaneously preserving signal radiation outside of the unwanted direction. 
     BACKGROUND 
     Technical advantages and regulatory compliance rules make it desirable to limit the amount of signal radiation that extends in a particular direction from an antenna system. For example, in some scenarios, the signal radiation in a particular direction must be controlled to meet regulatory requirements or to mitigate interference with other systems. Indeed, the Federal Communications Commission (FCC) limits the effective isotropic radiated power (EIRP) radiated in a conical region of +/−60° around the zenith (i.e. a skyward direction) to 21 dbm for a WiFi antenna operating in the 5 GHz U-NII 1 band, meaning that, for a radio with a maximum output power of 0.5 W (27 dBm), the maximum antenna gain in the skyward direction is less than −6 dBi. However, antenna gain outside of such the skyward direction, that is, in a primary region of interest, must be maintained with a specific gain requirement for a good RF communication signal. Indeed, the WiFi antenna operating in the 5 GHz band may have a peak gain requirement of 6 dBi for a good communication link. Accordingly, there are conflicting requirements, and such conflicting requirements are poorly addressed by known systems and methods. For example, known systems and methods to limit the amount of signal radiation in a particular direction include reducing the antenna system&#39;s overall gain, modifying the antenna system&#39;s radiation pattern, and modifying the antenna system&#39;s antenna beam width. However, each of these systems and methods includes disadvantages. 
     For example, systems and methods that reduce the overall gain of the antenna system detune the antenna system, add an attenuator, or reduce output power of a power amplifier. However, such adjustments lower the signal strength from the antenna system in all directions rather than in just an unwanted direction and, in addition to reducing the signal strength of a signal transmitted by the antenna system, may even reduce the signal strength of a signal the antenna system can receive. Furthermore, systems and methods that modify the antenna system&#39;s radiation pattern do so by adding a mechanical or electrical beam tilt to shift a main lobe of radiation away from the unwanted direction where low levels of signal radiation are desired. However, when the antenna system includes the mechanical down tilt, the antenna system must be mounted on a fixed or adjustable platform that is tilted so that a main antenna beam points away from the unwanted direction, thereby adding large and potentially complex mechanical structures to implement, which are dependent on an operator for correct installation. When the antenna system includes the electrical down tilt, a progressive phase shift is implemented to individual antenna elements of an antenna array, shifting a main lobe of radiation away from the unwanted direction, but limiting range because, at larger phase shifts, side lobes start to emerge and increase the signal radiation emitted in the unwanted direction. Further still, systems and methods that modify the antenna system&#39;s beam width do so by adding additional antenna elements to the antenna system, such as reflectors or directors, or increase a number of the antenna elements in the antenna array. However, these additional elements require additional volume and may increase peak gain, thereby exceeding FCC limits. 
     In view of the above, there is a continuing, ongoing need for systems and methods that can reduce radiation in an unwanted direction while simultaneously preserving signal radiation outside of the unwanted direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an antenna system in accordance with disclosed embodiments; 
         FIG. 2  is a block diagram of an antenna system and an antenna feed network in accordance with disclosed embodiments; 
         FIG. 3  is a graph of a primary radiation pattern in the elevation plane for an antenna system in accordance with disclosed embodiments; 
         FIG. 4  is a graph of a secondary radiation pattern in the elevation plane for an antenna system in accordance with disclosed embodiments; and 
         FIG. 5  is a graph of a primary radiation pattern and a total combined radiation pattern in the elevation plane for an antenna system in accordance with disclosed embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     While this invention is susceptible of an embodiment in many different forms, there are shown in the drawings and will be described herein in detail specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention. It is not intended to limit the invention to the specific illustrated embodiments. 
     Embodiments disclosed herein can include an antenna system that can reduce signal radiation in an unwanted direction, for example, a skyward direction, while simultaneously preserving signal radiation outside of the unwanted direction. The antenna system can include a signal input source, a main antenna electrically coupled to the signal input source, and a secondary antenna electrically coupled to the signal input source. In some embodiments, the main antenna can include an array of antennas, in some embodiments, the main antenna can have various geometries, including a dipole, a monopole, and a helix, among others, and in some embodiments, the main antenna can be dual polarized. In some embodiments, the secondary antenna can include a small (volume and footprint) patch antenna relative to the main antenna, in some embodiments, the secondary antenna can be the same type as the main antenna, in some embodiments, the secondary antenna can have a smaller frequency bandwidth than the main antenna, and in some embodiments, the secondary antenna can have a single polarization or be dual polarized. 
     The main antenna can transmit a primary signal producing a primary radiation pattern in response to energy from the signal input source, and the secondary antenna can transmit a secondary signal producing a secondary radiation pattern in response to the energy from the signal source. The secondary signal can be amplitude modified and phase shifted to position the secondary radiation pattern to cancel out or reduce a portion of the primary radiation pattern extending in the unwanted direction while substantially preserving portions of the primary radiation pattern extending outside of the unwanted direction. For example, a first maximum point (peak gain) of the primary radiation pattern that extends in the unwanted direction can be identified, and a physical position of and electrical input into the secondary antenna can be adjusted so that a second maximum point (peak gain) of the secondary radiation pattern extends in the unwanted direction at an angle that aligns with the first maximum point of the primary radiation pattern. That is, an amplitude (gain) and phase shift of the secondary signal can cancel out or reduce the peak gain of the primary radiation pattern in the unwanted direction, but can simultaneously preserve portions of the primary radiation pattern outside of the unwanted direction. 
     In some embodiments, a ground plane can be coupled to both the main antenna and the secondary antenna, and the ground plan can be continuous or discontinuous between the main antenna and the secondary antenna. In some embodiments, the ground plane may include various reflectors, such as corner reflectors, and the reflectors may be associated with one or both of the main antenna and the secondary antenna for use in positioning the primary radiation pattern and the secondary radiation pattern. In some embodiments, the ground plane can include a reflector portion separating the main antenna and the secondary antenna to assist in positioning the secondary radiation pattern. 
       FIG. 1  is a perspective view of an antenna system  20  in accordance with disclosed embodiments. As seen in  FIG. 1 , the antenna system  20  can include a first main antenna  22 , a second main antenna  24 , and a secondary antenna  26  coupled to, for example, a continuous ground plane  28 . The continuous ground plane  28  may include a reflector portion  30  separating the first main antenna  22  and the second main antenna  24  from the secondary antenna  26 . 
       FIG. 2  is a block diagram of the antenna system  20  and an antenna feed network  32  in accordance with disclosed embodiments. As seen in  FIG. 2 , the antenna system  20  can be fed by an electrical signal input source  34 , for example, a radio, in combination with a power divider or coupler  36 , a main phase shifter  38 , and a secondary phase shifter  40 . In operation, the power divider or coupler  36  can split electrical energy transmitted by the electrical signal input source  34  into a main branch serving the first main antenna  22  and the second main antenna  24  and a secondary branch serving the secondary antenna  26 . In some embodiments, the power divider or coupler  36  can divide the electrical energy transmitted by the electrical signal input source  34  unequally between the main branch and the secondary branch such that a secondary signal feeding the secondary antenna  26  has a lower amplitude and gain than a primary signal feeding the first main antenna  22  and the second main antenna  24 . The main branch can further split the primary signal between the first main antenna  22  and the second main antenna  24 , and the portion of the primary signal directed towards the second main antenna  24  can be fed through the primary phase shifter  38  to induce portions of a main lobe of a primary radiation pattern formed collectively by the first main antenna  22  and the second main antenna  24  to tilt away from an unwanted direction. The secondary signal directed towards the secondary antenna  26  can be fed through the secondary phase shifter  40  to cancel out or reduce a portion of the primary radiation pattern extending in the unwanted direction while substantially preserving portions of the primary radiation pattern outside of the unwanted direction. 
     Although the antenna system  20  and the feed network  32  shown in  FIG. 1  and  FIG. 2  are shown with the first main antenna  22 , the second main antenna  24 , the power divider or coupler  36 , and the main phase shifter  38 , embodiments disclosed herein are not so limited. For example, in some embodiments, the antenna system  20  can include the first main antenna  22  without the second main antenna  22 . Accordingly, the feed network  32  need not include the power divider or coupler  36  and the main phase shifter  38 . Furthermore, in some embodiments, the antenna system  20  can include a plurality of main antennas in addition to the first main antenna  22  and the second main antenna  24 . Accordingly, the feed network  32  can include additional branches for the power divider or coupler  36  and a plurality of phase shifters in addition to the phase shifter  38 . 
       FIG. 3  is a graph  42  of the primary radiation pattern  43  in the elevation plane for the antenna system  20  in accordance with disclosed embodiments. For example, the primary radiation pattern  43  can be produced by the first main antenna  22  and the second main antenna  24  being fed with the primary signal. The primary radiation pattern  43  may include a main lobe  44  tilted away from the unwanted direction, for example, a skyward direction, and a secondary lobe  45  radiating power in the unwanted direction. In the graph  42  shown in  FIG. 2 , the zenith is at an angle of 90°, and the skyward direction is from 30° to 150°. 
     A maximum point (peak value)  46  of the secondary lobe  45  in the unwanted direction can be identified and used to position and otherwise tune a secondary radiation pattern produced by the secondary antenna  26  fed with the secondary signal. For example,  FIG. 4  is a graph  48  of the secondary radiation pattern  50  in the elevation plane for the antenna system  20  and includes a maximum point (peak value)  52  that is phase shifted and aligned with the maximum point  46  to reduce or cancel out a portion of the primary radiation pattern in the unwanted direction, including the peak value  46  thereof. In some embodiments, an amplitude (gain) of the secondary signal producing the secondary radiation pattern  50  may be identified based on a ratio of a first gain of the primary radiation pattern  43  in the unwanted direction to a second gain of the secondary radiation pattern  50  in the unwanted direction. In some embodiments, an amount of a phase shift of the secondary signal can be equal to a phase difference between the first gain of the primary radiation pattern  43  in the unwanted direction and the second gain of the secondary radiation pattern  50  in the unwanted direction. 
       FIG. 5  is a graph  54  of the primary radiation pattern  43  and a total combined radiation pattern  56  in the elevation plane for the antenna system  20  in accordance with disclosed embodiments. As seen in  FIG. 5 , by combining the secondary radiation pattern  50  with the primary radiation pattern  43 , the maximum point  46  of the primary radiation pattern  43  can be reduced in the unwanted direction to the maximum point  58  of the total combined radiation pattern  56  in the unwanted direction while the total combined radiation pattern  56  outside of the unwanted direction can be substantially equal to the primary radiation pattern  43  outside of the unwanted direction, meaning that the primary radiation pattern  43  outside of the unwanted direction can be substantially unchanged by combining the secondary radiation pattern  50  with the primary radiation pattern  43 . Although, as seen with point  60 , the total combined radiation pattern  56  may increase relative to the primary radiation pattern  43  at some points, systems and methods disclosed herein still reduce the maximum point  46  of the primary radiation pattern  43  in the unwanted direction to provide for improved functionality and compliance with regulatory requirements. 
     Systems and methods disclosed herein have been described in connection with the antenna system reducing signal radiation in an unwanted direction to comply with regulatory requirements while simultaneously preserving signal radiation produced outside of the unwanted direction. However, it is to be understood that applications of systems and methods disclosed herein are not so limited. Instead, systems and methods disclosed herein can be used to reduce signal radiation in any direction and for any reason as would be known and desired by one of ordinary skill in the art. For example, systems and methods disclosed herein can be used to mitigate interference with other devices, such as adjacent access points or base stations, by reducing signal radiation in a direction towards such devices while simultaneously preserving signal radiation produced outside of such a direction. 
     Although a few embodiments have been described in detail above, other modifications are possible. For example, other components may be added to or removed from the described systems, and other embodiments may be within the scope of the invention. 
     From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific system, method, or application described herein is intended or should be inferred. It is, of course, intended to cover all such modifications as fall within the spirit and scope of the invention.