Seven element 70 cm Yagi antenna

I found the specifications of the Yagi on the internet (here) and decided to run a NEC-2 analysis on it, here are the results.

Screen Shot 2016-02-23 at 11.24.19
The voltages across the elements in the Yagi, the driven element has the circle in the middle, behind it is the reflector, in front are the directors
Screen Shot 2016-02-23 at 11.22.22
This is what the NEC-2 program needs, element 1 has the excitation turned on, the ground is turned off so all calculations assume free space

 

Screen Shot 2016-02-23 at 11.23.55
For the center of the 70 cm band the impedance is 45 Ohm, it is mostly real and the theoretical standing wave ratio is 1.2 for a 50 Ohm transmission cable.
Screen Shot 2016-02-23 at 11.22.52
This is the same plot but not in three dimensions, note that the Yagi has a dominant front lobe but also a number of side lobes, the front to rear and front to side lobe ratios are pretty impressive. The directionality seems to be better than +/-30 degrees.

The driven element is symmetric and needs to be balanced with a balun transformer when you use a 50 Ohm coaxial cable, there are several solutions for this and a possible design is on this webpage.

Last update: 23-feb-2016

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