Peter Körner designed this Yagi array with 15 elements on a 3.73-meter (147″) boom. It uses five reflectors, a horizontal folded dipole, and a halfwave coaxial balun.
Unlike other high-performance designs, the 15.11 has no phasing lines that can induce current in the boom and degrade the pattern.
This overhead view shows the horizontal folded dipole and nearby directors. The driven element is long, the two dipole currents are unequal, and their relative magnitude and phase change with frequency. This varies the critical coupling to the closely spaced first director across the FM band, a very neat trick. In this particular design, the feedpoint must be at the forward conductor.
Peter Körner testing a prototype antenna at VHF Teknik AB in Trelleborg, Sweden.
This shows the connections for the feedline and halfwave coaxial balun, which has negligible loss. The folded dipole is temporarily positioned on the boom without its weatherproof enclosure.
This shows how the 15mm × 5mm folded dipole conductors join at the ends. The all-dielectric production element mount on the right differs from the prototype mount that used a metallic clamp.
Sven Jacobson of VHF Teknik AB measured this SWR curve for a production antenna (model FM15.11) with an HP 8714B network analyzer.
I modeled the antenna with the AO-Pro 8.50 Antenna Optimizer program. Below are calculated performance figures for a segmentation density of 28 segments per halfwave. Mismatch loss is due to SWR. Wire loss is due to conductor resistance. Mismatched gain is forward gain including wire and mismatch losses. F/R is the ratio of forward power to that of the worst backlobe in the rear half-plane. The SWR reference impedance is 300Ω.
88.000 MHz: Impedance 306 - j18 ohms
SWR 1.06
Mismatch Loss 0.00 dB
Wire Loss 0.01 dB
Mismatched Gain 7.85 dBd
F/R 29.76 dB
93.000 MHz: Impedance 308 - j30 ohms
SWR 1.11
Mismatch Loss 0.01 dB
Wire Loss 0.01 dB
Mismatched Gain 8.57 dBd
F/R 35.58 dB
98.000 MHz: Impedance 293 - j24 ohms
SWR 1.09
Mismatch Loss 0.01 dB
Wire Loss 0.02 dB
Mismatched Gain 9.34 dBd
F/R 34.15 dB
103.000 MHz: Impedance 271 + j61 ohms
SWR 1.27
Mismatch Loss 0.06 dB
Wire Loss 0.04 dB
Mismatched Gain 9.47 dBd
F/R 32.74 dB
108.000 MHz: Impedance 241 + j47 ohms
SWR 1.32
Mismatch Loss 0.08 dB
Wire Loss 0.19 dB
Mismatched Gain 7.92 dBd
F/R 27.90 dB
Korner 15.11 Yagi Free Space Symmetric 98.000 MHz 18 6061-T6 wires, meters 1 0.11 -1.00 -0.73 0.11 1.00 -0.73 0.01 ; reflectors 1 0.0 -1.04 -0.35 0.0 1.04 -0.35 0.01 1 0.0 -1.04 0.0 0.0 1.04 0.0 0.01 1 0.0 -1.04 0.35 0.0 1.04 0.35 0.01 1 0.11 -1.00 0.73 0.11 1.00 0.73 0.01 1 0.565 -0.82 0.0 0.565 0.82 0.0 0.01148 ; driven element 1 0.595 -0.82 0.0 0.595 0.82 0.0 0.01148 1 0.595 -0.82 0.0 0.565 -0.82 0.0 0.015 1 0.595 0.82 0.0 0.565 0.82 0.0 0.015 1 0.68 -0.663 0.0 0.68 0.663 0.0 0.01 ; directors 1 0.79 -0.669 0.0 0.79 0.669 0.0 0.01 1 1.01 -0.657 0.0 1.01 0.657 0.0 0.01 1 1.3 -0.632 0.0 1.3 0.632 0.0 0.01 1 1.615 -0.637 0.0 1.615 0.637 0.0 0.01 1 2.045 -0.625 0.0 2.045 0.625 0.0 0.01 1 2.475 -0.629 0.0 2.475 0.629 0.0 0.01 1 3.01 -0.629 0.0 3.01 0.629 0.0 0.01 1 3.73 -0.578 0.0 3.73 0.578 0.0 0.01 1 source Wire 7, center
The 11.48mm diameters are cylindrical equivalents of the 15mm × 5mm rectangular folded dipole conductors. The 15mm diameters are for short tubes that connect the folded dipole ends. Peter says to measure the driven element length to the element ends, not to the centerline of the short tubes.
88–108 MHz