Abstract:
A directional antenna formed by associating a stationary generally omni-directional antenna element with an RF reflector formed from, for example, a folded, parabolic or elliptical RF reflecting surface. Rotating the RF reflector about the stationary antenna element creates a directional characteristic in the resulting antenna over, for example, a 360 degree range of azimuth. Rotation of the RF reflector may be remotely driven by a motor coupled, for example, to a gear connected to the RF reflector. The direct connection of the antenna element and the enclosed lightweight rotating assembly provide a reliable, easy to install and cost effective antenna.

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The invention relates to antennas. More specifically, the invention relates to a highly directional rotatable antenna module suitable for use, for example, with consumer multi-channel multi-point distribution systems (MMDS). 
     2. Description of Related Art 
     MMDS are useful for communications and or entertainment. A consumer may have several MMDS sources from which to choose from and each of the different MMDS sources may not always be available/in service. To select between sources and or obtain the best possible signal strength, a user may be required to access, reposition and or redirect an antenna. 
     Rotatable antennas, for example TV antennas equipped with rotators, have previously used motors to allow a user to remotely point the antenna to a desired azimuth direction where the strongest signal for a desired channel/frequency is available. However, because the antenna feed is rigidly coupled to the antenna, rotation is limited to a 360 degree (or less) span with a stop and associated sensors for disabling the motor when the stop is reached from either direction. Where a rotator with a stop is used, to move between one side of the stop and the other, the antenna must be reversed across its full sweep causing a period of interrupted reception. Rotatable antennas with a full sweep, for example surveillance radar antennas, require use of a rotary joint or similar rotatable feed coupling on the antenna feed connection, which increases costs and introduces an opportunity for signal losses. 
     Competition within the antenna industry has created a need for antennas that are configurable for remote redirection having minimized materials and manufacturing costs. 
     Therefore, it is an object of the invention to provide an antenna, which overcomes deficiencies in the prior art. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
         FIG. 1  shows a partial cut-away isometric view of a first embodiment of the invention. 
         FIG. 2  shows a top section view of the first embodiment of the invention. 
         FIG. 3   a  shows a first side (front) view of an antenna element of the first embodiment of the invention. 
         FIG. 3   b  shows a second side (back) view of an antenna element of the first embodiment of the invention. 
         FIG. 3   c  shows a first side (front) view of an antenna element of the first embodiment of the invention, with hidden lines to show the alignment of transmission lines and ground traces located on either side of the antenna element. 
         FIG. 3   d  is a close up view of a section of the antenna element of the first embodiment of the invention, identifying dimensions and interspacing of the conductive layers which form the antenna element. 
         FIG. 4  shows azimuth angle test performance data of the first embodiment of the invention. 
         FIG. 5  shows elevation angle test performance data of the first embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIGS. 1 and 2 , an antenna  1  may be optimized for use with MMDS signals. A Radio frequency (RF) transmissive radome  10  encloses a fixed omni-directional antenna element  20 . An RF reflector  30  formed from an RF reflective material, for example metal or metal coated material, is arranged proximate the omni-directional antenna element  20  to receive and or transmit RF from/into a desired direction. The RF reflector  30  may be mounted on a rotatable gear  40  driven by a motor  50 , for example a stepper motor. Alternatively, the motor  50  may be configured for direct drive, coupled to the RF reflector  30  at the axis of rotation and located at the end opposite from the antenna element  20  feed connection. 
     An angle of the RF reflector  30  may be adjusted larger or smaller to configure the azimuth directional characteristic of the antenna  1 . Alternatively, the RF reflector  30  may be formed with a shape configured for a desired azimuth pattern, for example, a parabolic or elliptical curve. In these configurations, the antenna element  20  may be generally positioned at a focus point of the elliptical or parabolic curve. Elevational coverage of the antenna may be adjusted by adding RF absorbing elements  60  and or additional reflectors at either end of the RF reflector  30 . 
     Because the RF reflector  30  rotates enclosed within the radome  10 , the reflector  30  and associated structure need not be reinforced to resist wind loading and therefore may be formed of relatively lightweight materials. The rotatable gear  40  may be keyed to rotate about a low friction bearing surface with a locating shoulder, for example a plastic bearing ring  45 . A center pin may be located at the top of the radome  10  to operate as a guide for the rotation of the RF reflector  30 , allowing further reduction in the structural requirements of the RF reflector  30 . As the rotating assembly is lightweight, a relatively inexpensive low torque motor  50  may be used. 
     A first embodiment of the omni-directional antenna element  20  is formed from conductive layers or trace(s)  70  on a printed circuit board (PCB)  80 . As shown in  FIGS. 3   a–d , the conductive layers form a series of microstrip transmission line  87  sections along the length of the PCB  80 . As shown in  FIG. 3   c , at each transition between sections, the transmission line  87  sections become the ground plane  85  trace of the adjacent section on the other side/alternate layer of the PCB  80  and vice versa. In the first embodiment, these overlaying sections are separated by 10 small radiating gaps “G” that serve as omni-directional radiating gap elements, forming a linear antenna array as will be appreciated by those familiar with the microstrip antenna arts. Alternatively, any number of transmission line sections and radiating gap elements could be used. The spacing “d” between gap “G” centers in  FIG. 3   d  may be uniform along the array, and may be selected to be half a guide wavelength for the microstrip line at or near the desired center frequency of operation. Alternatively, other spacings may be used, including non-uniform spacing between radiating gap(s) “G”. The radiating gap “G” and ground plane  85  widths “W” shown in  FIG. 3   d  are adjusted to control the electrical parameters of the radiating gap “G”, namely, the load admittance presented to the microstrip transmission line  87 , as well as the radiation pattern. Similarly, the gap “G” and ground plane  87  widths “W” may be varied or uniform along the array. 
     In the first embodiment, the array is terminated in a short circuit  88  located a distance “T” approximately one-quarter guide wavelength of the microstrip line away from the center of the last radiating gap “G”, forming a standing-wave array. Those skilled in the art will appreciate that the line could also be terminated in a matched load, or some similar impedance. As indicated in  FIGS. 3   a  and  3   b , in the first embodiment the microstrip transmission line  87  and microstrip ground  85  traces at the connector end are electrically coupled, for example by soldering, to the inner conductor  95  and outer conductor  97 , respectively, of a feed connection  90 . 
     Antenna element  20  embodiments using trace(s)  70  on PCB  80  allow a plurality of different configurations, each tuned to a desired frequency or frequency band, to be quickly and cost effectively produced for use with the same surrounding components. Further, antenna tuning circuitry, for example capacitors, inductors and or resistors may be economically added to the PCB  80  for antenna impedance and or q-factor tuning. 
     In alternative embodiments the generally omni-directional antenna element  20  may be configured, for example, as a single dipole, linear array of dipole or dipole pair elements. The antenna element  20  need not be formed using a PCB  80 ; a stamped metal element, coil or other form of antenna structure may be applied as desired. 
     Because the omni-directional antenna element  20  is fixed in place, a low signal loss and inexpensive direct feed connection  90 , for example, a standardized coaxial connector may be used. In alternative embodiments, the antenna element  20  may be coupled to diplexer, transceiver and or receiver circuits contained in the antenna  1  assembly. 
     As shown in  FIGS. 4 and 5  the antenna  1  may be configured to have directional azimuth coverage ( FIG. 4 ) in any desired direction by actuating the motor  50  to rotate the gear  40  and associated RF reflector  30  about the antenna element  20 . Elevational coverage ( FIG. 5 ), adjustable for example via the selected antenna element  20 , reflector  30  and or RF absorbing elements  60 , is fixed throughout the azimuth range. 
     The radome  10  may be configured to provide an environmental seal for the internal components and or a minimized wind load. Also, the radome  10  operates to conceal mechanical operation and or fragile components of the antenna  1 , making it suitable for use/installation by untrained consumers. 
     Integrated with a receiver and or transceiver system, the motor  50  may be automatically or manually controlled to seek a specific signal and or the signal providing the strongest signal strength, which once detected may be focused in upon by selective positioning of the RF reflector  30 . Because the control of the motor  50  may be via remote electrical control, the antenna  1  may be located in a remote location providing the best reception characteristics, for example at a high point on a structure or within attic space. 
     
       
         
               
             
               
               
             
           
               
                   
               
               
                 Table of Parts 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 10 
                 radome 
               
               
                 20 
                 antenna element 
               
               
                 30 
                 RF reflector 
               
               
                 40 
                 gear 
               
               
                 45 
                 bearing ring 
               
               
                 50 
                 motor 
               
               
                 60 
                 RF absorbing element 
               
               
                 70 
                 trace 
               
               
                 80 
                 PCB 
               
               
                 85 
                 ground plane 
               
               
                 87 
                 microstrip transmission line 
               
               
                 88 
                 short circuit 
               
               
                 90 
                 feed connection 
               
               
                 95 
                 inner conductor 
               
               
                 97 
                 outer conductor 
               
               
                   
               
             
          
         
       
     
     Where in the foregoing description reference has been made to ratios, integers or components having known equivalents then such equivalents are herein incorporated as if individually set forth. 
     While the present invention has been illustrated by the description of the embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departure from the spirit or scope of applicant&#39;s general inventive concept. Further, it is to be appreciated that improvements and/or modifications may be made thereto without departing from the scope or spirit of the present invention as defined by the following claims.