Körner 15.12

Peter Körner in Lund, Sweden, designed this Yagi array. It has a boom length of 3.73 m (147″), 15 elements, five reflectors, a horizontal folded dipole, and uses a halfwave coaxial balun.

Unlike log-Yagis, the 15.12 has no phasing lines that can induce current in the boom and degrade the pattern.

This overhead view shows the horizontal folded dipole. It is unusually long and the two conductor currents differ, as does their coupling to the first director. Because of these factors, conductor spacing strongly affects antenna performance and can be optimized. It provides only a weak degree of freedom for a vertical folded dipole.

This shows how the 15 mm × 5 mm folded dipole conductors join at the ends. The element mount on the right is a repurposed support for 10 mm hydraulic fluid lines.

Modeling Results

I modeled the antenna with the AO 9.57 Antenna Optimizer program using 28 analysis segments per conductor halfwave. Forward gain includes mismatch and conductor losses. F/R is the ratio of forward power to that of the worst backlobe in the rear half-plane.

Frequency  Impedance    SWR   Mismatch  Conductor   Forward    F/R 
   MHz        ohms             Loss dB   Loss dB   Gain dBd     dB 
    88     342 + j33    1.18     0.03      0.01      7.81     32.08
    89     354 + j20    1.19     0.03      0.01      7.94     33.86
    90     361 + j4     1.20     0.04      0.01      8.07     34.47
    91     363 - j9     1.21     0.04      0.01      8.21     34.45
    92     361 - j21    1.22     0.04      0.01      8.35     34.46
    93     355 - j30    1.21     0.04      0.01      8.51     34.52
    94     346 - j36    1.20     0.04      0.01      8.66     34.31
    95     337 - j39    1.18     0.03      0.01      8.82     34.23
    96     328 - j39    1.17     0.03      0.01      8.98     34.31
    97     319 - j39    1.15     0.02      0.01      9.13     34.61
    98     309 - j36    1.13     0.02      0.01      9.28     34.47
    99     297 - j31    1.11     0.01      0.02      9.41     34.30
   100     285 - j23    1.10     0.01      0.02      9.52     34.13
   101     272 - j9     1.11     0.01      0.02      9.59     34.10
   102     263 + j13    1.15     0.02      0.03      9.61     34.19
   103     267 + j37    1.19     0.03      0.03      9.57     34.44
   104     286 + j55    1.22     0.04      0.04      9.45     34.65
   105     318 + j46    1.17     0.03      0.05      9.24     34.04
   106     318 - j1     1.06     0.00      0.06      8.91     33.36
   107     265 - j31    1.18     0.03      0.08      8.43     32.29
   108     203 - j41    1.53     0.19      0.13      7.78     30.80

Ground Effects

This shows how ground proximity affects F/R at 1° elevation angle for various antenna heights.

Antenna File

Körner 15.12
Free Space Symmetric
98 MHz
18 6061-T6 wires, meters
r0 = 1.015		; reflector half-lengths
r1 = 1.006
r2 = .985
x0 = 0			; reflector positions
x1 = 0
x2 = .11
z1 = .326		; reflector heights
z2 = .73
de = .805		; driven element half-length
de1 = .431		; driven element positions
de2 = .546
d1 = .657		; director half-lengths
d2 = .659
d3 = .65
d4 = .617
d5 = .615
d6 = .608
d7 = .635
d8 = .624
d9 = .565
p1 = .654		; director positions
p2 = .827
p3 = 1.086
p4 = 1.41
p5 = 1.629
p6 = 1.888
p7 = 2.376
p8 = 2.98
p9 = 3.73
1   x2  -r2 -z2    x2  r2 -z2   .01		; reflectors
1   x1  -r1 -z1    x1  r1 -z1   .01
1   x0  -r0   0    x0  r0   0   .01
1   x1  -r1  z1    x1  r1  z1   .01
1   x2  -r2  z2    x2  r2  z2   .01
1  de1  -de   0   de1  de   0   .01148		; driven element
1  de2  -de   0   de2  de   0   .01148
1  de1  -de   0   de2 -de   0   .015
1  de1   de   0   de2  de   0   .015
1   p1  -d1   0    p1  d1   0   .01		; directors
1   p2  -d2   0    p2  d2   0   .01
1   p3  -d3   0    p3  d3   0   .01
1   p4  -d4   0    p4  d4   0   .01
1   p5  -d5   0    p5  d5   0   .01
1   p6  -d6   0    p6  d6   0   .01
1   p7  -d7   0    p7  d7   0   .01
1   p8  -d8   0    p8  d8   0   .01
1   p9  -d9   0    p9  d9   0   .01
1 source
Wire 7, center

The 11.48 mm diameters are cylindrical equivalents of the 15 mm × 5 mm rectangular folded dipole conductors. The 15 mm conductors are short tubes that connect the folded dipole ends.

Sensitivity Analysis

The following table shows the largest performance degradation over 88, 93, 98, 103, and 108 MHz in dB when altering a symbol value by Tol.

Symbol      Tol   Gain    F/R
    r0   0.0005   0.00   0.03
    r1   0.0005   0.00   0.03
    r2   0.0005   0.00   0.02
    x0   0.0010   0.00   0.01
    x1   0.0010   0.00   0.01
    x2   0.0010   0.00   0.04
    z1   0.0010   0.00   0.00
    z2   0.0010   0.00   0.05
    de   0.0005   0.00   0.02
   de1   0.0010   0.00   0.05
   de2   0.0010   0.02   0.04
    d1   0.0005   0.02   0.03
    d2   0.0005   0.01   0.03
    d3   0.0005   0.01   0.14
    d4   0.0005   0.00   0.07
    d5   0.0005   0.02   0.05
    d6   0.0005   0.00   0.04
    d7   0.0005   0.05   0.14
    d8   0.0005   0.01   0.09
    d9   0.0005   0.00   0.06
    p1   0.0010   0.02   0.11
    p2   0.0010   0.02   0.15
    p3   0.0010   0.01   0.10
    p4   0.0010   0.01   0.01
    p5   0.0010   0.00   0.03
    p6   0.0010   0.00   0.03
    p7   0.0010   0.01   0.08
    p8   0.0010   0.00   0.11
    p9   0.0010   0.00   0.04

Gallery

This is Georgiy Markiev's 15.12 in Petrozavodsk, Russia. It rotates here.

Petr Vozár erected this 15.12 near Javornik, Czechia.

Johan Meezen built this 15.12 in Drieborg, Netherlands. The OIRT Yagi below will degrade its performance.

Gerard Noordhof of Gronigen, Netherlands, assembles a portable 15.12 that will be mounted 9 m above ground. Performance drops greatly when the feedpoint is at the rear driven-element conductor as shown.

Julian Hardstone of Stockport, Greater Manchester, England, plans to use this 15.12 for DXpeditions.


December 13, 201688–108 MHz