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.