Abstract:
A low drag TCAS antenna includes a plurality of broadband antenna elements in a housing having at least three fins. L band radios in the aircraft may utilize the broadband antenna elements, thereby reducing power consumption, cost and aerodynamic inefficiency due to a plurality of antennas protruding from the aircraft.

Description:
FIELD OF THE INVENTION 
     The present invention is directed generally toward traffic collision avoidance system (TCAS) antennas, and more particularly toward TCAS antennas configured for broadband operation. 
     BACKGROUND OF THE INVENTION 
     A traffic collision avoidance system (TCAS) is an aircraft collision avoidance system designed to reduce the incidence of mid-air collisions between aircraft. TCAS monitors the airspace around an aircraft for other aircraft equipped with a corresponding active transponder, independent of air traffic control, and warns pilots of the presence of other transponder-equipped aircraft which may present a threat of mid-air collision. 
     The antennas used by TCAS may include a directional antenna mounted on the top of the aircraft and a directional or omnidirectional antenna on the bottom of the aircraft. This antenna may enable a transponder to receive interrogations at 1030 MHz and reply to the received interrogations at 1090 MHz. 
     Because TCAS antennas are attached to the exterior surface of an aircraft, drag created by the antenna is a serious concern. TCAS antennas must, therefore, be as streamlined and low-profile as possible. Traditional TCAS antennas employ a low-profile radome configuration. The radome configuration offers a low-profile but generally operates over a very narrow band of approximately 1030 MHz to 1090 MHz; adequate for TCAS only. 
     In addition to TCAS, aircraft generally include other L-band radios. Because TCAS antennas generally operate in a very narrow band, such antennas are not suitable for use by other L band radios operating outside that narrow band. Aircraft must therefore incorporate additional antennas. Additional antennas and associated cables may cause additional drag, consume power, add weight and add cost. 
     Consequently, it would be advantageous if an apparatus existed that is suitable for use as a low-drag TCAS antenna, and for integrating various L-band radios in an aircraft. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a novel apparatus for use as a low-drag TCAS antenna, and for integrating various L-band antennas in an aircraft. 
     One embodiment of the present invention is a TCAS antenna having four directional antenna arrays in a tri-fin antenna housing. Directional antenna arrays are less expensive to manufacture than traditional folded monopole antenna for a TCAS application. In addition, the tri-fin antenna housing provides low drag characteristics. 
     In another embodiment of the present invention, four directional antenna arrays provide a broadband capability. The four directional antenna arrays may be effective in a frequency range of at least 800 MHz to 1500 MHz. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention claimed. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention and together with the general description, serve to explain the principles. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The numerous objects and advantages of the present invention may be better understood by those skilled in the art by reference to the accompanying figures in which: 
         FIG. 1  shows a perspective view of an antenna housing according to the present invention; 
         FIG. 2  shows a perspective view of directional antenna array elements according to the present invention; 
         FIG. 3  shows a perspective view of directional antenna array elements as in  FIG. 2 , inside an antenna housing as in  FIG. 1 ; and 
         FIG. 4  shows a block diagram of computer system incorporating four directional TCAS antennas; 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to the subject matter disclosed, which is illustrated in the accompanying drawings. The scope of the invention is limited only by the claims; numerous alternatives, modifications and equivalents are encompassed. For the purpose of clarity, technical material that is known in the technical fields related to the embodiments has not been described in detail to avoid unnecessarily obscuring the description. 
     Referring to  FIG. 1 , an antenna housing is shown. The antenna housing may include a base  100 . The base  100  may be configured to occupy the same area on the surface of an aircraft (“footprint”) as prior art TCAS antennas. The antenna housing may also include three fins  102 ,  104 ,  106 . The fins  102 ,  104 ,  106  may extend perpendicularly from the base  100 , and be substantially parallel to each other. The fins  102 ,  104 ,  106  may be oriented in the direction of travel of an aircraft to provide the minimum possible drag. Each of the fins  102 ,  104 ,  106  may be configured to cover and protect one or more antenna arrays. The fins  102 ,  104 ,  106  may be positioned such that a first lateral fin  102  and a second lateral fin  104  are substantially equidistant from a central fin  106 , and a line defined by a center point of the first lateral fine  102  and a center point of the second lateral fin  104  substantially intersects a center point of the central fin  106 . Each of the fins  102 ,  104 ,  106  may extend no more than two inches (approximately five centimeters) from the base  100 . 
     Referring to  FIG. 2 , an antenna having four antenna arrays  202 ,  204 ,  206 ,  208  is shown. Each of the antenna elements  202 ,  204 ,  206 ,  208  may protrude perpendicularly from a base  100 . The antenna elements  202 ,  204 ,  206 ,  208  may be organized as an array antenna for use in a TCAS system such that signals from a transponder may be effectively determined by a processing device connected to the directional antenna. The point at which each antenna element  202 ,  204 ,  206 ,  208  protrudes from the base  100  may be substantially equidistant from a point on the base  100  defined by the intersection of a line defined by the point of protrusion of a first lateral element  202  and a second lateral element  204 , and a line defined by the point of protrusion of a first center element  206  and a second center element  208 . For a directional TCAS antenna, the effective distance of antenna elements from the center point may be approximately one quarter of the operative wavelength, or approximately eight centimeters. 
     Each of the antenna elements  202 ,  204 ,  206 ,  208  may comprise a broadband monopole (blade) antenna. Each antenna element  202 ,  204 ,  206 ,  208  may be configure to operate in a range of at least 800 MHz to 1500 MHz. 
     Referring to  FIG. 3 , a directional array antenna having four elements in an antenna housing is shown. The antenna may comprise four antenna elements  202 ,  204 ,  206 ,  208  protruding from a base  100  as in  FIG. 2 , with each of the four antenna elements  202 ,  204 ,  206 ,  208  covered by a fin  102 ,  104 ,  106  as depicted in  FIG. 1 . A first lateral antenna element  202  may be contained within a first lateral fin  102 ; a second lateral antenna element  204  may be contained within a second lateral fin  104 ; and a first center antenna element  206  and a second center antenna element  208  may be contained within a center fin  106 . The antenna depicted in  FIG. 3  may substitute for a prior art directional TCAS antenna where each antenna element  202 ,  204 ,  206 ,  208  may substitute for a non-broadband antenna element in the prior art TCAS antenna. In addition, an antenna according to the present invention may provide broadband capabilities that a prior art TCAS antenna cannot provide. Furthermore, a TCAS antenna utilizing antenna elements  202 ,  204 ,  206 ,  208  configured as blade antennas may experience improved performance characteristics both in terms of TCAS functionality and in terms of aerodynamic efficiency. 
     Referring to  FIG. 4 , a computer system incorporating four directional TCAS antenna elements  402 ,  404 ,  406 ,  408  configured as a TCAS top antenna, and four TCAS antenna elements  412 ,  414 ,  416 ,  418  configured as a TCAS bottom antenna is shown. The computer system may comprise a processor  401  connected to memory  410  and to a radio  400 . The radio  400  may be a TCAS radio. The radio  400  may be connected to four TCAS elements  402 ,  404 ,  406 ,  408  configured as a TCAS top directional antenna. At least one of the four TCAS elements  402 ,  404 ,  406 ,  408  may be further configured as a broadband antenna such as a blade antenna. Furthermore, the radio  400  may be connected to at least one TCAS omnidirectional antenna  412  configured as a TCAS bottom antenna. Alternatively, the radio  400  may be connected to four TCAS elements  412 ,  414 ,  416 ,  418  configured as a TCAS directional bottom antenna. At least one of the four TCAS elements  412 ,  414 ,  416 ,  418  may be further configured as a broadband antenna such as a blade antenna. It may be appreciated by those skilled in the art that in certain configurations, one or more of the antenna elements  414 ,  416 ,  418  comprising a TCAS bottom antenna may be optional. Specifically, where the TCAS bottom antenna is configured as an omnidirectional antenna, a single antenna element  412  may be sufficient as a TCAS bottom antenna. 
     The processor  401  may comprise a software defined radio configured to transmit and receive signals in the L band through one or more of the four TCAS elements  402 ,  404 ,  406 ,  408  comprising a TCAS top directional antenna, or one or more of the TCAS elements  412 ,  414 ,  416 ,  418  comprising a TCAS bottom antenna. In one embodiment, the software defined radio and TCAS elements  402 ,  404 ,  406 ,  408 ,  412 ,  414 ,  416 ,  418  are configured to operate in a frequency range greater than 1090 MHz; in another embodiment, the software defined radio and TCAS elements  402 ,  404 ,  406 ,  408 ,  412 ,  414 ,  416 ,  418  are configured to operate in a frequency range less than 1030 MHz. 
     It is believed that the present invention and many of its attendant advantages will be understood by the foregoing description, and it will be apparent that various changes may be made in the form, construction, and arrangement of the components thereof without departing from the scope and spirit of the invention or without sacrificing all of its material advantages. The form herein before described being merely an explanatory embodiment thereof, it is the intention of the following claims to encompass and include such changes.