There are two options: the first one is director spacing is not equal and with the increase of the serial number of director, the spacing of adjacent director increases; another is that a director is equally spaced. Former program adjustment is more troublesome while the latter solution is simple, therefore generally use the solution of equal space. The lead spacing is usually selected at range of 0.15-0.4 wavelength. When the spacing is large, the main lobe of pattern of yagi wifi antenna is narrower, the frequency response of the input impedance is relatively stable, but the minor lobe is large; when the pitch is small, the minor lobe is lower with better anti-interference performance, but the gain and directivity is worse. Considering the former, the spacing is preferable to 0.3 wavelength; while considering the latter, the spacing preferable to less than 0.2 wavelength. Whatever the situation, the distance between the first director oscillator and active oscillator should be made smaller.
Spacing between the reflectors active and oscillator in Yagi antenna
The distance between the active oscillator and reflector is the wavelength of 0.15-0.23. This spacing affects the field strength ratio and input impedance of Yagi antenna. When the spacing is the wavelength of 0.15-0.17, the input impedance of the antenna (about 15-20 euro) is small; When the pitch is the wavelength of 0.2-0.23, the antenna input impedance (about 50-60 Europe) is large, and it is easy to match with the coaxial cable.
The selection of director length of Yagi antenna
There are two options in the choice of the length of the wave director. One is the length of each director, about to take 0.38-0.44 wavelength. The advantage of this scheme is that the processing and adjustment are more easily, but frequency band is narrow. Another is that the length of the director changes with the serial number.
The choice of the length of the Yagi antenna’s reflector
The length of the reflector is generally selected in the wavelength between 0.5-0.55. Its length is not shorter than the design minimum frequency of 1/2 wavelength. The radius of parasitic element is determined by the requirements of the frequency band of Yagi antenna. Usually the transducer radius is selected in the 1 / (500-80) wavelength.
The structure and size of the active oscillator
Active oscillator can select single half-wave dipole or equivalent oscillator, the general length is 0.475 wavelengths. The thicker the Oscillator is, the shorter the length should be. Gain and the width of the main lobe can be estimated. Gain ≈ 10 * (the antennas length) / wavelength, and the width of the main lobe ≈ 55 * square root (the antenna wavelength / length).
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