The "Nominal Impedance" of an antenna is a compromise across all operating frequencies.
The "Impedance" Chart depicts frequency dependence of REAL and IMAGINARY components.
To find "best" impedance for an antenna, change (JUST) "Char-Impedance" under the 4nec2
"SETTINGS" tab until you get the "best" SWR curve. [Click on SWR chart to see each change.]
Try 50, 75, 150, 300 & 600-ohms (etc) and "eye-ball" an answer....
Sometimes this is the impedance with smallest-maximum within the operating band,
but can also be a joint compromise with the Raw Gain curve so that the
Net Gain isn't adversely affected--loss due to higher SWR can be tolerated better
on those channels that have higher Raw Gain.....such as Hi-VHF 2-Bay below...
1. Results for the above UHF DB-4 are in the ball-park for typical 4-Bays (NO Reflector):
http://photos.imageevent.com/holl_a... NO Reflectors - UHF Raw_Net Gain and SWR.jpg
2. Your above Hi-VHF 2-Bay with Triple-Element-Triangles has excessive SWR on
higher channels, which probably indicates that you sized it for maximum Raw Gain,
rather than Net Gain. Since it is slightly "too big"....adjust & try again....
3. Here's a Hi-VHF 2-Bay with standard Four-Whisker Elements after I optimized it:
Note typical rising Raw Gain curve and SWR under 3.5 (Reflector will lower it):
4. Six-Whisker Element Bowtie (open at ends) was better than Four-Whiskers:
But I did not compare when used in Multi-Bay Bowties.....
Nor have I (yet) analyzed the above Triple-Element-Triangle Bowtie...