18-09-2012, 12:08 PM
Yagi-Uda Antenna Theory, Design and Results
[attachment=33933]
Theory
Yagi uda anteena was invented in Japan in 1962.
It was originally invented by Uda but the work was presented in english first time by Yagi,hence named Yagi-Uda antenna
A Yagi-Uda antenna is a linear array of parallel dipoles.
The basic Yagi unit consists of three elements:
1. Driver or driven element
2. Reflector
3. Director
This antenna has relatively high gain but low input impedance narrow bandwidth.
Yagi-Uda Antenna
Develops an endfire radiation pattern.
Optimum spacing for gain of a reflector and driven element is 0.15 to 0.25 wavelengths
Director to director spacings are 0.2 to 0.35 wavelengths apart.
Reflector length is typically 0.05 wavelengths longer or a length 1.05 that of the driven element.
The driven element is calculated at resonance without the presence of parasitic elements. Driven element is a ½ wave dipole.
The directors are usually 10 to 20% shorter than at resonance.
Gain is related to length and number of directors.
Max directivity of a 3 element Yagi is 9 dBi
Addition of directors up to 5 or 6 provides significant increase in gain. Addition of more directors has much less impact on gain.
Adding a director to go from 9 to 10 presents a 0.2 dB gain improvement.
Adding more reflectors has minimal impact on gain however does impact on feedpoint Z and the backlobe.
[attachment=33933]
Theory
Yagi uda anteena was invented in Japan in 1962.
It was originally invented by Uda but the work was presented in english first time by Yagi,hence named Yagi-Uda antenna
A Yagi-Uda antenna is a linear array of parallel dipoles.
The basic Yagi unit consists of three elements:
1. Driver or driven element
2. Reflector
3. Director
This antenna has relatively high gain but low input impedance narrow bandwidth.
Yagi-Uda Antenna
Develops an endfire radiation pattern.
Optimum spacing for gain of a reflector and driven element is 0.15 to 0.25 wavelengths
Director to director spacings are 0.2 to 0.35 wavelengths apart.
Reflector length is typically 0.05 wavelengths longer or a length 1.05 that of the driven element.
The driven element is calculated at resonance without the presence of parasitic elements. Driven element is a ½ wave dipole.
The directors are usually 10 to 20% shorter than at resonance.
Gain is related to length and number of directors.
Max directivity of a 3 element Yagi is 9 dBi
Addition of directors up to 5 or 6 provides significant increase in gain. Addition of more directors has much less impact on gain.
Adding a director to go from 9 to 10 presents a 0.2 dB gain improvement.
Adding more reflectors has minimal impact on gain however does impact on feedpoint Z and the backlobe.