Yagi-Uda Antenna Design

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 length of the antenna. Table I. Optimal Lengths for Yagi-Uda Elements, for Distinct Boom Lengths

d=0.0085 SR=0.2	Boom Length of Yagi-Uda Array (in )

	0.4	0.8	1.2	2.2	3.2	4.2

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	0.420	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	0.390	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/)	0.20	0.20	0.25	0.20	0.20	0.308
Gain (dB)	9.25	11.35	12.35	14.40	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, diameters (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 diameter of the boom affects the results, and the optimal diameters of the elements. As an example of Yagi-antenna radiation patterns, a 6-element Yagi antenna (with elements spaced along the +x-axis and the individual elements oriented parallel to the z-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 reflector). The front-to-back ratio is approximately 19 dB for this antenna, and this can also be optimized further if desired. Introduction to Yagi Uda Antennas Antennas Types Antennas (Home) This page on Yagi-Uda (Yagi antennas) design parameters is copyrighted, but can be reproduced or copied if the original webpage is cited. Copyright antenna-theory.com, 2009-2022.