Yagi-uda antenna
YAGI-UDA ANTENNA
Dr. Shintaro Uda and Dr. Hidetsugu Yagi of the Tohoku Imperial University invented a directional antenna system consisting of an array of coupled parallel dipoles.
Yagi-uda or simply yagi antennas or yagi’s are the most high gain antennas. It consists of a driven element, a reflector and one or more directors. i.e., yagi uda antenna is an array of a driven element and one or more parasitic elements.
The driven element is a resonant half wave dipole usually of metallic rod. The parasitic elements of continuous metallic rods are arranged parallel to the driven element. They are arranged collinearly and close together with one reflector and one director as shown in figure (a).
Figure (a) Yagi-uda antenna
Figure (b) Radiation pattern of yagi-uda antenna
Yagi-Uda antennas are directional along the axis perpendicular to the dipole in the plane of the elements, from the reflector toward the driven element and the directors as shown in figure(b).
Due to the current flow in the driven element, voltage will be introduced in the parasitic elements. The phase and current flowing due to induced voltage depend on the spacing between the elements and upon the reactance of the elements. The reactance may be varied by dimensioning the length of the parasitic element. The spacing between driven and parasitic elements is of order 0.1λ to 0.15λ.
The parasitic element in front of driven element is known as director and its number may be more than one, whereas the element in the back of it is known as reflector. The reflector is 5% more and the director is 5% less than the driven element. The driven element is λ/2 at resonant frequency. In practice, for 3-element array of yagi-uda antenna, the following formulae give lengths which work satisfactorily.
Reflector length= feet
Driven element length= feet
Director length= feet
The parasitic elements can be clamped on metallic support rod because at the middle of each parasitic element, the voltage is
Dr. Shintaro Uda and Dr. Hidetsugu Yagi of the Tohoku Imperial University invented a directional antenna system consisting of an array of coupled parallel dipoles.
Yagi-uda or simply yagi antennas or yagi’s are the most high gain antennas. It consists of a driven element, a reflector and one or more directors. i.e., yagi uda antenna is an array of a driven element and one or more parasitic elements.
The driven element is a resonant half wave dipole usually of metallic rod. The parasitic elements of continuous metallic rods are arranged parallel to the driven element. They are arranged collinearly and close together with one reflector and one director as shown in figure (a).
Figure (a) Yagi-uda antenna
Figure (b) Radiation pattern of yagi-uda antenna
Yagi-Uda antennas are directional along the axis perpendicular to the dipole in the plane of the elements, from the reflector toward the driven element and the directors as shown in figure(b).
Due to the current flow in the driven element, voltage will be introduced in the parasitic elements. The phase and current flowing due to induced voltage depend on the spacing between the elements and upon the reactance of the elements. The reactance may be varied by dimensioning the length of the parasitic element. The spacing between driven and parasitic elements is of order 0.1λ to 0.15λ.
The parasitic element in front of driven element is known as director and its number may be more than one, whereas the element in the back of it is known as reflector. The reflector is 5% more and the director is 5% less than the driven element. The driven element is λ/2 at resonant frequency. In practice, for 3-element array of yagi-uda antenna, the following formulae give lengths which work satisfactorily.
Reflector length= feet
Driven element length= feet
Director length= feet
The parasitic elements can be clamped on metallic support rod because at the middle of each parasitic element, the voltage is