# `Yagi-Uda Antenna Design`

 Introduction to the Yagi Antenna Antennas List Antenna Theory

 The design of a Yagi-Uda antenna is actually quite simple. Because Yagi antennas have been extensively analyzed and experimentally tested, the process basically follows this outline: Look up a table of design parameters for Yagi-Uda antennas Build the Yagi (or model it numerically), and tweak it till the performance is acceptable As an example, consider the table published in "Yagi Antenna Design" by P Viezbicke from the National Bureau of Standards, 1968, given in Table I. Note that the "boom" is the long element that the directors, reflectors and feed elements are physically attached to, and dictates the lenght of the antenna. Table I. Optimal Lengths for Yagi-Uda Elements, for Distinct Boom Lengths
 Boom Length of Yagi-Uda Array (in ) d=0.0085SR=0.2
 R 0.482 0.482 0.482 0.482 0.482 0.475 D1 0.442 0.428 0.428 0.432 0.428 0.424 D2 0.424 0.420 0.415 0.42 0.424 D3 0.428 0.420 0.407 0.407 0.420 D4 0.428 0.398 0.398 0.407 D5 0.390 0.394 0.403 D6 0.390 0.39 0.398 D7 0.390 0.386 0.394 D8 0.390 0.386 0.390 D9 0.398 0.386 0.390 D10 0.407 0.386 0.390 D11 0.386 0.390 D12 0.386 0.390 D13 0.386 0.390 D14 0.386 D15 0.386
 Spacing between directors,    (SD/) 0.2 0.2 0.25 0.2 0.2 0.308 Gain (dB) 9.25 11.35 12.35 14.4 15.55 16.35

 There's no real rocket science going on in the above table. I believe the authors of the above document did experimental measurements until they found an optimized set of spacings and published it. The spacing between the directors is uniform and given in the second-to-last row of the table. The diameter of the elements is given by d=0.0085 . The above table gives a good starting point to estimate the required length of the antenna (the boom length), and a set of lengths and spacings that achieves the specified gain. In general, all the spacings, lengths, diamters (including the boom diameter) are design variables and can be continuously optimized to alter performance. There are thousands of tables that further give results, such as how the diamter of the boom affects the results, and the optimal diamters of the elements. As an example of Yagi-antenna radiation patterns, a 6-element Yagi antenna (with axis along the +x-axis) is simulated in FEKO (1 reflector, 1 driven half-wavelength dipole, 4 directors). The resulting antenna has a 12.1 dBi gain, and the plots are given in Figures 1-3. Figure 1. E-plane gain of Yagi antenna. Figure 2. H-Plane gain of Yagi-Uda antenna. Figure 3. 3-D Radiation Pattern of Yagi antenna. The above plots are just an example to give an idea of what the radiation pattern of the Yagi-Uda antenna resembles. The gain can be increased (and the pattern made more directional) by adding more directors or optimizing spacing (or rarely, adding another refelctor). The front-to-back ratio is approximately 19 dB for this antenna, and this can also be optimized if desired. Introduction to Yagi Uda Antennas Antennas (Home) This page on Yagi-Uda (Yagi antennas) design parameters is copyrighted. No portion can be reproduced or copied except by permission of the author. Copyright antenna-theory.com, 2009-2011. Yagi-Uda antennas, yagi antennas.