brainwagon

I’ve been reading up a bit on antenna design, particularly the design of Yagi style antennas, and decided to give it a whirl. In particular, I decided to try to design a Yagi that actually is supposed to work on 137.62 megahertz, to see what is possible. I actually am not displeased with the paper specs for the resulting four element 137Mhz Yagi. I designed it using the suite of programs written by David Kirkby, G8WRB. Here’s the resulting pattern at the design frequency.

Here is the specification for the resulting design…

NOTES Optimised with the genetic algorithm
FREQUENCY 137.620000
MIN_FREQUENCY 137.000000
MAX_FREQUENCY 138.000000
STEP_FREQUENCY 0.020000
ELEMENTS 4
DRIVEN 1
PARASITIC 3
ANGULAR_STEP   2.000000
#DATA_DRIVEN        x         y       length     diameter voltage(r) voltage(i)
DATA_DRIVEN     0.38625    0.00000    1.02524    0.00475    1.00000    0.00000
#DATA_PARASITIC     x         y       length     diameter
DATA_PARASITIC
                0.00000    0.00000    1.08740    0.00475 reflector
                0.95210    0.00000    0.94818    0.00475 D1
                1.78574    0.00000    0.92937    0.00475 D2

And here is the analysis over the entire 137-138 Mhz band.

# Driven=1 parasitic=3 total-elements=4 design=137.620MHz
# Checked from 137.000MHz to 138.000MHz.
  f(MHz) E(deg) H(deg)  R     jX    VSWR   Gain(dBi)     FB(dB)    SideLobes(dB)
  137.000 58.1  79.6  28.25  -4.35  1.790      9.202     26.440      0.000
  137.020 58.1  79.6  28.24  -4.22  1.789      9.205     26.547      0.000
  137.040 58.1  79.6  28.23  -4.08  1.788      9.209     26.650      0.000
  137.060 58.1  79.5  28.23  -3.95  1.788      9.212     26.750      0.000
  137.080 58.1  79.5  28.22  -3.81  1.787      9.216     26.845      0.000
  137.100 58.1  79.5  28.21  -3.68  1.786      9.219     26.936      0.000
  137.120 58.0  79.4  28.20  -3.55  1.786      9.222     27.023      0.000
  137.140 58.0  79.4  28.20  -3.41  1.785      9.226     27.104      0.000
  137.160 58.0  79.4  28.19  -3.28  1.785      9.229     27.179      0.000
  137.180 58.0  79.3  28.18  -3.14  1.784      9.233     27.250      0.000
  137.200 58.0  79.3  28.17  -3.01  1.784      9.236     27.314      0.000
  137.220 58.0  79.3  28.16  -2.87  1.784      9.240     27.371      0.000
  137.240 58.0  79.2  28.16  -2.73  1.784      9.243     27.423      0.000
  137.260 57.9  79.2  28.15  -2.60  1.783      9.247     27.467      0.000
  137.280 57.9  79.2  28.14  -2.46  1.783      9.250     27.505      0.000
  137.300 57.9  79.1  28.13  -2.33  1.783      9.254     27.535      0.000
  137.320 57.9  79.1  28.12  -2.19  1.783      9.257     27.558      0.000
  137.340 57.9  79.0  28.11  -2.05  1.783      9.261     27.574      0.000
  137.360 57.9  79.0  28.10  -1.92  1.783      9.264     27.582      0.000
  137.380 57.9  79.0  28.09  -1.78  1.783      9.268     27.582      0.000
  137.400 57.8  78.9  28.08  -1.64  1.784      9.271     27.575      0.000
  137.420 57.8  78.9  28.07  -1.51  1.784      9.275     27.561      0.000
  137.440 57.8  78.9  28.06  -1.37  1.784      9.278     27.539      0.000
  137.460 57.8  78.8  28.04  -1.23  1.784      9.282     27.509      0.000
  137.480 57.8  78.8  28.03  -1.10  1.785      9.286     27.473      0.000
  137.500 57.8  78.8  28.02  -0.96  1.785      9.289     27.429      0.000
  137.520 57.8  78.7  28.01  -0.82  1.786      9.293     27.379      0.000
  137.540 57.7  78.7  28.00  -0.68  1.786      9.296     27.322      0.000
  137.560 57.7  78.6  27.98  -0.55  1.787      9.300     27.258      0.000
  137.580 57.7  78.6  27.97  -0.41  1.788      9.304     27.189      0.000
  137.600 57.7  78.6  27.96  -0.27  1.788      9.307     27.114      0.000
  137.620 57.7  78.5  27.95  -0.13  1.789      9.311     27.034      0.000
  137.640 57.7  78.5  27.93   0.01  1.790      9.315     26.948      0.000
  137.660 57.6  78.4  27.92   0.15  1.791      9.318     26.858      0.000
  137.680 57.6  78.4  27.91   0.29  1.792      9.322     26.763      0.000
  137.700 57.6  78.4  27.89   0.43  1.793      9.326     26.664      0.000
  137.720 57.6  78.3  27.88   0.56  1.794      9.330     26.561      0.000
  137.740 57.6  78.3  27.86   0.70  1.795      9.333     26.455      0.000
  137.760 57.6  78.3  27.85   0.84  1.796      9.337     26.345      0.000
  137.780 57.6  78.2  27.84   0.98  1.797      9.341     26.233      0.000
  137.800 57.5  78.2  27.82   1.12  1.799      9.345     26.118      0.000
  137.820 57.5  78.1  27.81   1.26  1.800      9.348     26.000      0.000
  137.840 57.5  78.1  27.79   1.40  1.801      9.352     25.881      0.000
  137.860 57.5  78.1  27.78   1.55  1.803      9.356     25.760      0.000
  137.880 57.5  78.0  27.76   1.69  1.804      9.360     25.637      0.000
  137.900 57.5  78.0  27.74   1.83  1.806      9.364     25.512      0.000
  137.920 57.4  77.9  27.73   1.97  1.807      9.367     25.387      0.000
  137.940 57.4  77.9  27.71   2.11  1.809      9.371     25.260      0.000
  137.960 57.4  77.9  27.70   2.25  1.811      9.375     25.133      0.000
  137.980 57.4  77.8  27.68   2.39  1.812      9.379     25.005      0.000
  138.000 57.4  77.8  27.66   2.54  1.814      9.383     24.876      0.000

This was mostly just an exercise, to understand how the software works. It’s kind of silly to use a linearly polarized antenna for the circularly polarized polar orbiting satellites (3db mismatch), but I’d still be interested in hearing any comments about this design from knowledgeable antenna design people.