Patent Publication Number: US-2016233577-A1

Title: HF Antenna for Rotor Wing Aerial Vehicles

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without payment of any royalties thereon or therefor. 
    
    
     BACKGROUND 
     Typically high frequency (HF) communication on rotary wing aerial vehicles is accomplished via a towel bar type antenna. The towel bar is mounted on the fuselage of the rotary wing aerial vehicle. While effective at higher frequencies, towel bar antennas do not operate efficiently in the 2-4 MHz range where impedance matching and radiation pattern issues result in significant wasted energy and poor communication quality. Additionally towel bar antennas sometimes lose their ability to transmit in certain directions. 
     In general, one of the most important characteristics of an antenna is its transmit/receive polarization. There are two basic types of linear polarization formats, vertical and horizontal. A vertically polarized antenna transmits/receives vertically polarized signals, but cannot transmit/receive horizontally polarized signals. Similarly, a horizontally polarized antenna can only transmit/receive horizontally polarized signals. 
     Circular polarization is a combination of vertical and horizontal polarizations. Circular polarization of an electromagnetic wave is, but without limitation, a polarization where the tip of the electric field vector, at a fixed point in space, describes a circle as time progresses. A circularly polarized antenna has the ability to transmit/receive vertical signals, horizontal signals or a simultaneous combination thereof. This provides circularly polarized antennas the versatility to transmit/receive all types of polarizations, without being blind to any type of signal polarization. 
     Due to the motion and maneuvering of a helicopter (rotor wing aerial vehicle), a radio frequency (RF) signal can change polarization continuously from vertical to horizontal and vice versa. This causes intermittent loss of communications. Therefore, circular polarization must be utilized on a rotor wing aerial vehicle. 
     SUMMARY 
     The present invention is directed to a HF antenna for rotor wing aerial vehicles the needs enumerated above and below. 
     The present invention is directed to a HF antenna for rotor wing aerial vehicles which includes a plurality of circularly configured arcs, where each arc has a first end and a second end, the first end is attached to one of the blades, the second end is attached to another blade that is adjacent to the blade attached to the first end, such that each blade of the vehicle is attached to one first end of one of the arcs and one second end of another arc. 
     It is a feature of the invention to provide a HF antenna for rotor wing aerial vehicles that significantly improves performance in the 2-4 MHz range compared to traditionally employed towel bar antennas and works for all modes of HF propagation. 
     It is a feature of the invention to provide a HF antenna for rotor wing aerial vehicles that can be used on every type of rotor wing aerial vehicle (manned or unmanned) and is a circularly polarized antenna. 
     It is a feature of the present invention to provide a HF antenna for rotor wing aerial vehicles that offers significant radiation efficiency improvement, improved radiation resistance and reactance, and increased antenna gain. 
    
    
     
       DRAWINGS 
       These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims, and accompanying drawings wherein 
         FIG. 1  is a perspective view of a rotor wing aerial vehicle with an HF antenna attached; and, 
         FIG. 2  is a top perspective view of the blades with the HF antenna. 
     
    
    
     DESCRIPTION 
     The preferred embodiments of the present invention are illustrated by way of example below and in  FIGS. 1 and 2 . The HF antenna for a rotor wing aerial vehicle  10  is for an aerial vehicle  20  with a plurality of blades  50 . As shown in  FIGS. 1 and 2 , the HF antenna for a rotor wing aerial vehicle  10  includes a plurality of circularly configured arcs  100 , each arc having a first end  105  and a second end  110 , the first end  105  attached to one of the blades  50 , the second end  110  attached to another blade  50  that is adjacent to the blade attached to the first end  105 , such that each blade of the vehicle is attached to one first end  105  of one of the arcs  100  and one second end  110  of another arc  100 . 
     In the description of the present invention, the invention will be discussed in a military aircraft environment; however, this invention can be utilized for any type of application that requires a HF antenna for a rotor wing aerial vehicle. 
     In the preferred embodiment of the HF antenna for a rotor wing aerial vehicle  10 , the number of circularly configured arcs  100  is equal to the number of blades  50 . Each arc  100  is attached to two adjacent blades  50  forming a blade-arc-blade sectorial loop. Optimally, as shown in  FIGS. 1 and 2 , each arc end is attached on opposite sides of each blade  50 . 
     Each arc  100  is a conducting arc and may be a wire. The preferred embodiment of each circularly configured arc  100  is manufactured from highly conductive lightweight material such as, but without limitation, aluminum. Each arc  100  may also be a hollow tube. As shown in  FIG. 1 , the rotor wing aerial vehicle  20  has a main rotor  55  with a main rotor axis  56 . Each arc  100  is mounted in a plane that the main rotor is in and the antenna  10  is centered on the main rotor axis  56 . Additionally, the antenna  10  has a diameter. The diameter of the antenna  10  is any straight line segment that passes through the center of the circle created by all the blade-arc-blade sectorial loops and whose endpoints lie on the circle. The diameter (shown as d in  FIG. 2 ) of the antenna  10 , centered about the main rotor axis  56 , is optimally 160 inches or greater. Additionally, the antenna  10  has a circular polarization. 
     An antenna requires radio frequency (RF) energy to be provided to it from a signal power source. Such RF signal is usually provided through a cable that connects the power source to the antenna. The point where the cable connects to the antenna and provides RF power is known as the antenna feed point. Each arc  100  includes a feed point  115 . A feed point can be described, but without limitation, as a point on the arc  100  where the arc  100  is energized from a power supply. The HF antenna  10  may include a HF signal power source (not shown) such that the HF signal source power is equally split and supplied to each feed point  115  of each arc  110 . The phase of the signal should be increased by a constant value related to the total number of blades  50  from one arch to the next. The increment in phase from arc to arc must be equal to 360/N, where N is the number of blades. 
     Although the present invention has been described in considerable detail with reference to certain preferred embodiments thereof, other embodiments are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiment(s) contained herein.