Ch22 9-Element Folded-Dipole (FD) Yagi (518-524 MHz) analyzed using 4nec2 [see *.nec.doc file below]. Dimensions, incl. Loop Width and Height, were determined using nikiml's Python Optimization Scripts. It is Optimized for 8 MHz Bandwidth (to ensure no problems on the band edges...and if ReScaled Upwards) centered on Ch22 [518-524 MHz].
Note that nikiml's EVAL function [for Horizontally Polarized signals, listed in summary below] calculates somewhat higher F/B & F/R Ratios than 4nec2 Chart [for TOTAL Gain = Horizontal + Vertical Gains].
Ch22 9-El FD-Yagi - 300ohm OPTimized: Ch22 Raw Gain = 12.9 to 13.1 dBi, F/B & F/R Ratio Min. = 34.3 dB and SWR (300-ohms) Under 1.5. BTW: Gain for Optimized 75-ohm FD-Yagi was not quite as Good. Also note the F/B Ratio NULL directly to the Rear (which you might have to STEER toward severe Interference). Forward Sidelobes are quite good, being suppressed about 21 dB on 521 MHz. Note that there is a Deep NULL in the Elevation Pattern, which could be used to advantage to suppress Ground Bounce using an Antenna Tilter to aim the Antenna somewhat UPWARDS. BOOM LENGTH = 1042-mm, and is UNCONSTRAINED.
BTW: Gain for 9-El FD-Yagi Optimized for 75-ohm was not quite as Good.
Dimensions incl. Min-Max Search Range (all in cm) from below 4nec2 Text File [Variable SYmbol Statements]:
' Cumulative Element Spacings (cm): [May round all Dimensions to nearest 0.1-cm] SY S1=0 SY D2=10.90266' 3, 20 SY S2=S1+D2 SY D3=3.002401' 3, 20 SY S3=S2+D3 SY D4=8.143348' 3, 20 SY S4=S3+D4 SY D5=14.07628' 3, 20 SY S5=S4+D5 SY D6=12.63379' 3, 20 SY S6=S5+D6 SY D7=19.3514' 3, 20 SY S7=S6+D7 SY D8=19.94919' 3, 20 SY S8=S7+D8 SY D9=16.46316' 3, 20 SY S9=S8+D9 ' ' Element Lengths (cm): SY L1=29.79505' 15, 40 SY L2=30.69886' 15, 40 SY L3=25.98962' 15, 40 SY L4=24.79525' 15, 40 SY L5=23.60214' 15, 40 SY L6=22.73211' 15, 40 SY L7=22.03925' 15, 40 SY L8=23.61077' 15, 40 SY L9=21.62618' 15, 40 ' ' Distance of Yagi above & below Center line (NOT USED IN THIS MODEL): SY Zyag=0 SY Relem=0.3175 SY RACT=Relem' Yagi Active Element Radius (in cm for 1/4-in O.D.)
' Half Width between Long Elements in Folded Dipole: SY FW=1.25 SY FD=FW/2' Distance between Center of Boom and Folded Dipole Element SY Gap=2.5
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