> A hurricane blew the reflector element of my 2 element 40 out of exact
> horizontal. I would guess that the reflector is about 20 degrees off of
> horizontal. I have noticed a degradation in my yagi performance.
> Can anyone tell me from experience or modeling what effect 20 degrees
> of rotation of the reflector in a 2 element yagi, or any element for
> that matter has on forward gain and beam performance.
Since none of the experts has responded, I ran a home made model of the
Cushcraft XM402 through AO and rotated the reflector around the boom.
The model was run in free space with no other antennas present (not in
a stack with antennas for other bands).
Here are the results:
Angle Gain F/B
(degrees) (dBi) (dB)
0 5.07 11.04
5 5.05 10.74
10 4.96 10.14
15 4.84 9.15
20 4.66 8.09
30 4.17 6.07
40 3.57 4.20
50 2.92 2.69
60 2.32 1.53
70 1.82 0.67
80 1.51 0.17
90 1.40 0.00
I doubt that you will notice ca. 0.5 dB loss in forward gain but
the 3 dB loss in F/B is significant. The trend shown by this one
set of runs indicates an increasingly rapid loss of performance as
the reflector gets beyond +/- 10 degrees from coplanar with the
I would encourage someone more experienced that I to confirm these
results in their own studies.
... Joe Subich, W8IK/4 ex-AD8I
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