LIST OF FIGURES


   Figure                                                  Page

     1.  Physical parameters of zigzag cells  . . . . . . . 4
     
     2.  k-diagram for a periodic show-wave structure . . . 6
     
     3.  Uniform zigzag model . . . . . . . . . . . . . . . 8
     
     4.  Uniform helical zigzag model . . . . . . . . . . . 8
     
     5.  Azimuthal radiation patterns of UZZ-1  . . . . . . 9
     
     6.  Azimuthal radiation patterns of UHZZ-1 . . . . . .10
     
     7.  Azimuthal radiation patterns of UHZZ-2 . . . . . .11
     
     8.  k-diagram of the zigzag structures . . . . . . . .12
     
     9.  Impedance locus of UZZ-1  . . . . . . . . . . . . 14
     
    10.  Impedance locus of UHZZ-1 . . . . . . . . . . . . 15
    
    11.  Parameters of a log-periodic helical zigzag . . . 18

12.  A photograph of a log-periodic zigzag antenna   
            over the ground plane . . . . . . . . . . . . .19
            
    13.  H-plane radiation patterns of LPHZZ-1  . . . . . .21
    
    14.  H-plane radiation patterns of LPHZZ-2  . . . . . .22
    
    15.  H-plane radiation patterns of LPHZZ-3  . . . . . .23
    
    16.  Input impedance referred to 50 ohms of LPHZZ-1 . .24
    
    17.  Input impedance referred to 50 ohms of LPHZZ-2 . .25
    
    18.  Far-field radiation patterns of LPHZZ-3A . . . . .28
    
    19.  Far-field radiation patterns of LPHZZ-3B . . . . .29
    
    20.  Far-field radiation patterns of LPHZZ-3C . . . . .30
    
    21.  Far-field radiation patterns of LPHZZ-3D . . . . .31
    
     
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