High-Performance Yagis for 8892 MHz

It's difficult to make a Yagi work well over the entire 88108 MHz band. Multiple driven elements or multiple reflectors are necessary for really good performance. But if bandwidth is restricted, a simple design with excellent performance is possible. I optimized this ten-element Yagi for 8892 MHz with the AO 9.63 Antenna Optimizer. The boom length is 239″. The red dot marks the 75Ω feedpoint.

Modeling Results

Calculated performance is for 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 
  88.0    56.8 - j1.0   1.32     0.08      0.05      10.34     34.54
  88.5    64.0 + j1.1   1.17     0.03      0.05      10.55     34.85
  89.0    73.1 + j2.0   1.04     0.00      0.06      10.72     35.35
  89.5    82.9 + j1.1   1.11     0.01      0.06      10.83     36.06
  90.0    92.5 - j2.6   1.24     0.05      0.07      10.89     36.47
  90.5    99.8 - j7.9   1.35     0.10      0.09      10.90     35.93
  91.0     105 - j13    1.44     0.14      0.11      10.84     34.97
  91.5     104 - j16    1.45     0.15      0.14      10.76     37.27
  92.0    80.3 + j8.5   1.14     0.02      0.24      10.67     36.82

Construction

Use ⅜″ tubing. Dimensions are valid only for isolated elements (nonconductive boom or insulated mounts). The matching network is the lowpass equivalent of a hairpin match. Split the driven element leaving a gap no larger than ¼″, solder a 27-pF capacitor across the feedpoint, and feed with 75Ω coax. Use a current balun at the feedpoint.

Antenna File

High-Performance Yagi for 88-92 MHz
Free Space
88 88.5 89 89.5 90 90.5 91 91.5 92 MHz
10 6061-T6 wires, inches
x1 = 0					; element positions
x2 = 21.11459
x3 = 24.88291
x4 = 31.17103
x5 = 41.9917
x6 = 72.39083
x7 = 112.0712
x8 = 154.2972
x9 = 198.2206
x10 = 238.5
y1 = 33.80075				; element half-lengths
y2 = 34.85089
y3 = 31.29524
y4 = 30.21306
y5 = 29.70498
y6 = 29.17727
y7 = 28.86884
y8 = 28.35921
y9 = 28.01402
y10 = 25.71585
1  x1  -y1  0   x1  y1  0    0.375
1  x2  -y2  0   x2  y2  0    0.375
1  x3  -y3  0   x3  y3  0    0.375
1  x4  -y4  0   x4  y4  0    0.375
1  x5  -y5  0   x5  y5  0    0.375
1  x6  -y6  0   x6  y6  0    0.375
1  x7  -y7  0   x7  y7  0    0.375
1  x8  -y8  0   x8  y8  0    0.375
1  x9  -y9  0   x9  y9  0    0.375
1 x10 -y10  0  x10 y10  0    0.375
1 source
c = 27.03467				; shunt matching capacitance
Wire 2, center c pF

Sensitivity Analysis

The following table shows the largest performance degradation over the antenna file frequencies in dB when altering a symbol value by Tol.

Symbol      Tol   Gain    F/R
    x1   0.0394   0.00   0.02
    x2   0.0394   0.02   0.32
    x3   0.0394   0.03   0.41
    x4   0.0394   0.01   0.21
    x5   0.0394   0.00   0.15
    x6   0.0394   0.00   0.24
    x7   0.0394   0.00   0.35
    x8   0.0394   0.00   0.32
    x9   0.0394   0.00   0.33
   x10   0.0394   0.00   0.18
    y1   0.0197   0.00   0.09
    y2   0.0197   0.01   0.09
    y3   0.0197   0.04   0.99
    y4   0.0197   0.01   0.33
    y5   0.0197   0.02   0.73
    y6   0.0197   0.01   1.73
    y7   0.0197   0.02   1.72
    y8   0.0197   0.01   1.14
    y9   0.0197   0.01   0.76
   y10   0.0197   0.00   0.34
     c   1.3517   0.02   0.00

Shorter Antenna

This design uses seven elements on a 119″ boom.

Modeling Results

Calculated performance is for 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 
  88.0    42.2 + j0.3   1.78     0.35      0.05      8.18      29.22
  88.5    48.2 + j2.5   1.56     0.21      0.06      8.42      29.96
  89.0    56.4 + j3.7   1.34     0.09      0.07      8.63      30.86
  89.5    65.9 + j3.4   1.15     0.02      0.07      8.76      31.21
  90.0    76.7 + j0.8   1.02     0.00      0.08      8.81      30.18
  90.5    89.1 - j4.4   1.20     0.04      0.10      8.75      29.22
  91.0     103 - j13    1.42     0.13      0.12      8.57      29.23
  91.5     110 - j27    1.62     0.25      0.16      8.28      29.24
  92.0     106 + j6     1.43     0.14      0.28      8.09      29.22

Construction

Use the same construction as for the larger Yagi. The matching capacitance is 36 pF.

Antenna File

Shorter Yagi for 88-92 MHz
Free Space Symmetric
88 88.5 89 89.5 90 90.5 91 91.5 92 MHz
7 6061-T6 wires, inches
x1 = 0
x2 = 7.072542
x3 = 12.136979
x4 = 24.279008
x5 = 51.962416
x6 = 83.73561
x7 = 118.5
y1 = 34.113223
y2 = 33.82153
y3 = 31.187681
y4 = 30.339674
y5 = 29.509943
y6 = 29.103275
y7 = 26.58679
1  x1  -y1  0   x1  y1  0    0.375
1  x2  -y2  0   x2  y2  0    0.375
1  x3  -y3  0   x3  y3  0    0.375
1  x4  -y4  0   x4  y4  0    0.375
1  x5  -y5  0   x5  y5  0    0.375
1  x6  -y6  0   x6  y6  0    0.375
1  x7  -y7  0   x7  y7  0    0.375
1 source
c = 36.79368
Wire 2, center c pF

Sensitivity Analysis

The following table shows the largest performance degradation over the antenna file frequencies in dB when altering a symbol value by Tol.

Symbol      Tol   Gain    F/R
    x1   0.0394   0.00   0.02
    x2   0.0394   0.02   0.17
    x3   0.0394   0.03   0.26
    x4   0.0394   0.01   0.16
    x5   0.0394   0.00   0.16
    x6   0.0394   0.00   0.20
    x7   0.0394   0.00   0.10
    y1   0.0197   0.00   0.10
    y2   0.0197   0.02   0.08
    y3   0.0197   0.09   0.59
    y4   0.0197   0.04   0.75
    y5   0.0197   0.03   1.14
    y6   0.0197   0.02   0.53
    y7   0.0197   0.01   0.16
     c   1.8397   0.05   0.00

Gallery

Joe Hageli built an earlier version of the ten-footer in Spring Grove, Illinois.

Performance Comparison


December 10, 201688108 MHz