Antenna Loop Feed Array Yagi on 50 MHz band
The Yagi antennas with a frame vibrator, located in the plane of the antenna, are called LFA-Yagi (Loop Feed Array Yagi) and are characterized by a greater operating frequency range than the usual Yagi.
One of the most popular LFA Yagi is Justin Johnson’s (G3KSC) 5-element antenna, on the 6-meter band.
The antenna design, the distances between the elements and the dimensions of the elements are shown below in the table and in the drawing.
The dimensions of the elements, distances to the reflector and the diameters aluminum tubes, which the elements are made according to the table:
The elements are mounted through insulating parts on a beam, with length approx. 4.3 m. Beam designed from a square aluminum profile section 90 × 30 mm .
The vibrator is fed via a 50-ohm coaxial cable through a 1:1 balanced transformer.
Adjustment of the antenna by the minimum SWR in the middle of the band, produced by selecting position of the U-shaped parts of the vibrator, which designed from tubes with a diameter 10 mm.
Changing the position of these parts should be symmetrical. For example: If the right U-part is pull out on 1 cm, then the left one needs to be pulled out on the same amount.
The antenna has the following characteristics:
- Maximum gain 10.41 dB at 50.150 MHz
- Maximum front-to-back ratio 32.79 dB
- Operating frequency range 50.0-50.7 MHz by SWR level = 1.1