Abstract:
A low-profile, electronically scanned antenna that can scan a hemisphere is comprised of three, phased array radiators. Each radiator face has an azimuth and elevation scan angle equal to 120 degrees. The three radiator faces are arranged in a truncated 3 sided pyramid such that they prove continuous hemispherical coverage. The three radiators are mounted to cooled panels of a truncated pyramid-shaped frame such that the radiators enable a full hemisphere to be scanned by radar.

Description:
STATEMENT OF GOVERNMENT RIGHTS 
       [0001]    The Government of the United States of America has rights in this invention pursuant to Contract No. F19620-00-C-0002 awarded by the United States Air Force. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates generally to radar and communications antennas and more particularly to a phased array antenna for use with aircraft. 
       BACKGROUND 
       [0003]    There is growing commercial as well as military need for wideband radar and communications on aircraft, ships and ground-based craft. In many of these applications, low-height antennae are needed that can provide spherical or hemispherical coverage. 
         [0004]    Low-cost electronically scanned antennas exist but these prior art antennas are planar and have scan angles limited to approximately ±60 degrees. At 60 degrees, the performance of these antennas is very poor. 
         [0005]    As is known, antennas used on aircraft, ships and vehicles require radomes to protect radiating elements from wind and water. Radomes strong enough to withstand weather and bird strikes typically have thick walls, which reduce their RF transmissivity and hence their electrical performance but increasing their cost and weight. A simple and inexpensive antenna that provided hemispherical or spherical coverage without requiring a lossy and expensive radome, and which could be on aircraft, ships and terrestrial vehicles would be an improvement over the prior art. 
       SUMMARY 
       [0006]    There is provided an antenna for mounting on the exterior surface of an aircraft, ship or other vehicle, which is comprised of three phased array radiators. The arrays are mounted to a frame such that the radiators and the frame are in the shape of a truncated pyramid. 
         [0007]    Each radiator has a center axis that is normal to the radiator. Each radiator has a radar scan angle substantially equal to ±60 degrees relative to the center axis. The radiators are mounted to a frame such that the angle between adjacent center axes forms an angle of 120 degrees. 
         [0008]    Since each radiator has a scan angle substantially equal to ±60 degrees relative to each radiator&#39;s center axis, and since the radiators are positioned on the circumference of a geometric circle, three of the radiators can sweep an azimuth angle of 360 degrees and an elevation angle of ±60 degrees =120 degrees. A full hemisphere can be swept by the three antennas. 
         [0009]    Because of their truncated pyramid shape, their mounting arrange provides a robust, wind-resistant structure with flush mounted radomes protecting each of the three radiating surfaces. A hemispherical radome is not needed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a top view of an electronically scanned hemispheric antenna; 
           [0011]      FIG. 2  is a side view of the antenna shown in  FIG. 1 ; 
           [0012]      FIG. 3  is a cross-sectional view of one of the panels or sides of the antenna shown in  FIG. 1  and  FIG. 2 ; 
           [0013]      FIG. 4  illustrates an application for the antenna, namely its attachment and use with an airplane; and 
           [0014]      FIG. 5  shows an exploded view of the antenna depicted in each of  FIGS. 1-4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0015]      FIG. 1  shows a top view of an electronically scanned hemispheric antenna  10  and  FIG. 2  shows a side view of the antenna  10 . As can be seen in  FIGS. 1 and 2 , the antenna  10  is comprised of an airfoil or fairing  11  in the shape of a truncated pyramid in that it has three inclined sides  2 ,  4  and  6  joined to each other but also joined to a flat top  15 . The three sides  2 ,  4  and  6  also rest on a flat surface  28 , such as a surface of an airplane, helicopter or terrestrial vehicle. 
         [0016]    The three inclined sides  2 ,  4  and  6  of the fairing  11  accommodate three, inclined phased array radiators  12 ,  14  and  16 . Each of the radiators  12 ,  14  and  16  is substantially planar and has a geometric center axis that is normal or substantially normal to a geometric plane in which the corresponding radiator lies. The axes of the radiators  12 ,  14  and  16  are identified in the figures by reference numerals  18 ,  20  and  22  respectively. Since each center axis  18 ,  20  and  22  is normal to its corresponding radiator ( 12 ,  14  and  16  respectively), each center axis forms a geometric angle with adjacent axes such that the projected angle, on plane  28 , between any two adjacent axes is one-hundred twenty degrees (120 degrees). 
         [0017]    The three radiators  12 ,  14  and  16  and the sides  2 ,  4  and  6  they are attached to, abut each other such that they enclose a substantially triangular-shaped area, readily seen in  FIG. 1 . As is well-known, the sum of the interior angles of a triangle equals 180 degrees. Therefore, the sum of the angles formed between the radiators  12 ,  14  and  16  is equal to 180 degrees. 
         [0018]      FIG. 3  depicts the cross section of one of the phased array radiators  14  as it lies in one of the sides  4 . (The cross sections of the other phased array radiators are identical to the cross section depicted in  FIG. 2 .) As can be see in  FIG. 3 , the phased array radiators are inclined relative to the antenna&#39;s flat top  15  and relative to the surface  28  by an elevation angle  29 . Since the flat top  15  and the surface  28  are depicted in  FIG. 3  as being parallel to each other, the angle between the axes  18 ,  20  or  22  and the top surface  15  or the “bottom” surface  28  is the same. 
         [0019]    Each radiator  12 ,  14  and  16  is a phased array radiator, the operation of which is well-known to those of ordinary skill in radar. Each radiator  12 ,  14  and  16  has a radar azimuth and elevation scan angle that is substantially equal to ±60 degrees relative to each radiator&#39;s center axis  18 ,  20  and  22  such that each radiator  12 ,  14  and  16  is capable of scanning an azimuth and elevation angle of up to one hundred twenty degrees (120 degrees). 
         [0020]    Since there are three phased array radiators  12 ,  14  and  16  that each sweep a different 120 degree azimuth angle, and since each radiator  12 ,  14  and  16  can sweep an elevation angle of ±60 degrees from its respective center axis  18 ,  20 ,  22 , the three phased array radiators  12 ,  14  and  16  enable the antenna to electronically scan a full, or substantially full, hemisphere. 
         [0021]    Referring to  FIG. 1  and  FIG. 5 , the radiators  12 ,  14  and  16  are mounted to a pyramidal-shaped frame  31  (shown in  FIG. 5  but not in  FIG. 1 ) such that the lower apexes of each of the radiators  12 ,  14  and  16  lie on the circumference of a geometric circle that is centered about the geometric triangle enclosed by the sides  2 ,  4  and  6  and/or the radiators  12 ,  14  and  16 . For purposes of this disclosure, the radiators are therefore considered to lie “on” the circumference of a circle, however, only the apexes or corners of the radiator&#39;s are actually on a geometric circle. 
         [0022]    Referring now to  FIG. 4  there is shown an airplane  40  with one of the antennas  10  shown as being mounted on top of the fuselage of the airplane  40 . A second antenna  10  mounted on the underside or bottom of the fuselage (not shown) can provide the ability to scan a second hemisphere, except for the small space between the antenna on top of the fuselage and the antenna on the bottom of the fuselage. 
         [0023]    While the embodiment shown in  FIG. 4  depicts the antenna  10  mounted on the fuselage, alternate embodiments of the invention disclosed and claimed herein include mounting one or more of the antennas on an upper and/or lower wing surface by which a full hemispherically-shaped volume could be scanned by the arrays  12 ,  14  and  16  in the respective antennas. After viewing  FIG. 4 , those of ordinary skill in the art will recognize that one or more of the antennas  10  could also be mounted on a helicopter, ship or a terrestrial vehicle to provide a hemispheric radar or communications antenna to helicopters, ships or terrestrial vehicles. 
         [0024]    Referring now to  FIG. 5  there is shown an exploded view of the antenna  10 . The planar arrays  12 ,  14  and  16 , which can also be considered as electromagnetic signal radiating elements, are mounted to a frame  31  in the shape of a truncated pyramid in that the frame  31  has three planar sides  30 ,  32 , and  34  that are inclined relative to flat, top and bottom surfaces. 
         [0025]    Each of the sides  30 ,  32  and  34  can include an integrated cooling channel or panel  42  to cool the arrays  12 ,  14  and  16  if the power level emitted from the arrays  12 ,  14  and  16  is so great that it heats or overheats the frame  31 , the fairing material or the material from which the arrays are constructed. In one embodiment, a cooling fluid (not shown) circulates through the channels  42  to remove heat from the planar arrays  12 ,  14  and  16  that are mounted against the sides  30 ,  32  and  34  to be in thermal contact with the sides. Heat from the arrays  12 ,  14  and  16  travels from the arrays into the planar sides and then into the coolant by conduction, such that the coolant ultimately absorbs thermal energy emitted from the radiating elements  12 ,  14  and  16 . 
         [0026]    The coolant circulated through the channels  42  could include any appropriate refrigerant gas or liquid. In an alternate embodiment, a ventilated or unventilated heat sink is used with one or more such heat sinks being in thermal communication with its corresponding radiator element  12 ,  14  and  16 . 
         [0027]    Not shown in the figures are substantially planar radar-transmissive radomes that cover or “extend over” the radiating surfaces  12 ,  14  and  16 . Radar-transmissive radomes and the materials they are usually constructed from are well known to those of ordinary skill in the art. Radomes extending over the arrays are useful to protect the radiators  12 ,  14  and  16  from damage that can be caused by impacts with precipitate, animals as well as damage that can be caused by impacts with small objects. The radomes used in one embodiment were substantially flush with the surface of the fairing that covers the radiator elements  12 ,  14  and  16 . 
         [0028]    Those of ordinary skill in the art will appreciate the cost effectiveness of using multiple phased array elements  12 ,  14  and  16  that are capable of beam steering or directing a radar or communications beam up to 120 degrees. Those of ordinary skill in the art will also recognize the value of not using a rotating radome as the prior art teaches but instead using a low-cost and low-profile, fixed, i.e., non-rotating radome with emitted signals being electronically steered. The truncated pyramidal-shaped antenna  10  depicted in the drawings provides superior beam scan angles in a low-profile antenna that is more rugged than prior art rotating radomes and less expensive to manufacture. 
         [0029]    It should be borne in mind that the description above is purposes of illustration only and not for purposes of limitation. The true scope of the invention is defined by the appurtenant claims.