The InnovAntennas FMDX-9 uses one reflector, seven driven elements, and one director on a 4.1 m (161″) boom.
I modeled the antenna with the AO 9.61 Antenna Optimizer program. This image shows the antenna geometry and segmentation detail. Blue dots mark segment boundaries. The red dot is the 75Ω feedpoint. Green dots mark loads for parasitic element mount capacitance.
The lower phasing line extends to support the insulated parasitic elements. I did not model the support truss, which connects to the lower phasing line and is electrically active, as is the mast.
Click pattern to denormalize
Calculated performance is for 28 analysis segments per element halfwave, phasing line segment length equal to the line spacing, and parasitic element mount capacitance of 10 pF. Forward gain includes mismatch and conductor losses. F/R is the ratio of forward power to that of the worst backlobe in the rear half-plane.
Frequency Impedance SWR Mismatch Conductor Forward F/R
MHz ohms Loss dB Loss dB Gain dBd dB
88 62.3-j2.6 1.21 0.04 0.02 7.35 20.25
89 62.3-j4.0 1.21 0.04 0.02 7.46 22.97
90 61.7-j5.3 1.23 0.05 0.02 7.54 25.26
91 60.9-j7.2 1.26 0.06 0.02 7.60 26.53
92 59.0-j9.9 1.33 0.09 0.02 7.60 25.32
93 53.3-j14.0 1.50 0.18 0.03 7.38 20.52
94 35.8-j10.6 2.15 0.62 0.04 5.55 12.34
95 40.6+j18.2 1.99 0.51 0.04 5.44 11.59
96 59.6+j16.1 1.39 0.12 0.02 7.29 17.15
97 64.9+j10.1 1.23 0.05 0.02 7.63 19.23
98 66.7+j5.8 1.15 0.02 0.02 7.74 20.10
99 67.5+j2.8 1.12 0.01 0.02 7.75 20.20
100 68.8+j0.7 1.09 0.01 0.02 7.69 19.49
101 72.8-j1.5 1.04 0.00 0.02 7.51 17.22
102 78.5-j23.2 1.36 0.10 0.04 7.00 11.20
103 49.0-j18.4 1.68 0.29 0.03 7.71 14.57
104 49.7-j10.4 1.56 0.21 0.02 7.75 19.02
105 49.7-j9.7 1.55 0.21 0.02 7.59 20.89
106 45.4-j11.9 1.72 0.31 0.02 7.17 19.21
107 29.8-j6.8 2.54 0.91 0.04 4.76 11.00
108 34.2+j19.7 2.38 0.79 0.04 4.55 10.46
This image shows the antenna current distribution for constant source voltage. Note the unequal current in adjacent phasing line conductors and in dipole halves, and the nonzero current in the phasing line extensions.
The reflector and director mount to the lower phasing line extension with plastic bushings. These curves show the effect of mount capacitance over four orders of magnitude.
InnovAntennas FMDX-9 Free Space 98 MHz 33 6063-T832 wires, meters x1 = 0 ; element positions x2 = .8 x3 = 1.3665 x4 = 1.8875 x5 = 2.367 x6 = 2.808 x7 = 3.2135 x8 = 3.587 x9 = 4.1 y1 = .78 ; element half-lengths y2 = .833 y3 = .765 y4 = .703 y5 = .646 y6 = .593 y7 = .56 y8 = .48 y9 = .51 d = .5" ; element diameter p = 1.56" ; 1.56" round wires spaced 1.02559" yield same line Z s = 1.02559" ; in AO as 3/4" square wires with surfaces 7 mm apart n2 = (x3 - x2) / s ; # segments for phasing lines n3 = (x4 - x3) / s n4 = (x5 - x4) / s n5 = (x6 - x5) / s n6 = (x7 - x6) / s n7 = (x8 - x7) / s 1 x1 -y1 0 x1 0 0 d ; elements 1 x1 0 0 x1 y1 0 d 1 x2 -y2 0 x2 0 0 d 1 x2 0 s x2 y2 s d 1 x3 -y3 s x3 0 s d 1 x3 0 0 x3 y3 0 d 1 x4 -y4 0 x4 0 0 d 1 x4 0 s x4 y4 s d 1 x5 -y5 s x5 0 s d 1 x5 0 0 x5 y5 0 d 1 x6 -y6 0 x6 0 0 d 1 x6 0 s x6 y6 s d 1 x7 -y7 s x7 0 s d 1 x7 0 0 x7 y7 0 d 1 x8 -y8 0 x8 0 0 d 1 x8 0 s x8 y8 s d 1 x9 -y9 0 x9 0 0 d 1 x9 0 0 x9 y9 0 d 1 x1 0 0 x2 0 0 p ; lower phasing line n2 x2 0 0 x3 0 0 p n3 x3 0 0 x4 0 0 p n4 x4 0 0 x5 0 0 p n5 x5 0 0 x6 0 0 p n6 x6 0 0 x7 0 0 p n7 x7 0 0 x8 0 0 p 1 x8 0 0 x9 0 0 p n2 x2 0 s x3 0 s p ; upper phasing line n3 x3 0 s x4 0 s p n4 x4 0 s x5 0 s p n5 x5 0 s x6 0 s p n6 x6 0 s x7 0 s p n7 x7 0 s x8 0 s p 1 x8 0 0 x8 0 s #18 ; feedpoint jumper 1 source Wire 33, center 2 loads Wire 19, end1 10 pF ; capacitance between lower Wire 26, end2 10 pF ; phasing line and parasitics
88–108 MHz