Calculated influence of metal mast passing through element plane on super low noise Yagi Antenna PA432-26-7BGP with G/T 9dB
Original question:
What is the real effect of a metal support mast going through the element plane of a 432 MHz long yagi? I am talking about an array of 4 long yagi’s 4-8 m long, horizontally polarized and mounted on the usual H-frame. In real life this means that 2 yagi’s are mounted above each other on a vertical metal support mast, about 50-60 mm in diameter. This mast crosses the horizontal element plane, and is mostly due to the construction not located in the element center. As this mast is half way the boom at several wavelengths distance from the dipole, the influence might be minimal to the antenna pattern, and in fact a lot of people seems to use this configuration on their 70 cm EME station, without reporting any performance issues.
Besides some technical / theoretical discussions, I haven’t seen any reports from people who really did some measurements on this. An computer simulation might be difficult as we have to deal with a, compared to the elements, “thick” element crossing the horizontal plane under a 90 degrees angle, of element center. So, it looks as if it is not a problem but did anyone actually measured or simulated this?
73 Dick, PA4VHF
Dick’s question was clear. He was asking about the effect of 50 mm/ 2 inch aluminium tubes when placed orthogonal to the boom for Horizontally polarized Yagis. This is a typical scenario for most people using a conventional H frame support for 4 horizontally polarized Yagis which is by far the most common configuration.
73 Conrad PA5Y
Answer:
For the calculations we will use latest professional full-3D electromagnetic modelling software. For the simulations we will use super low noise 70cm antenna PA432-26-7BGP with G/T 9dB.
Used mast for simulation was 50 mm/ 2 inch aluminum pipe 450 mm above the elements plane with guy rope support.
First we will simulate whole antenna with boom without influence of the mast.
Gain 19. 6dBi with high suppression of all side lobes
Now we will add 50 mm aluminum pipe passing through element plane 450 mm to see influence of the mast (look above picture).
Gain 19.57 dBi. Small impact on side lobes. Lower gain 0.03 dB.
Conclusion: Influence of the 50 mm/ 2 inch aluminium tube when placed orthogonal to the boom for Horizontally polarized PA432-26-7BGP 70 cm Yagi is NEGLECTABLE.
Goran YU1CF
