Marconi's model now clearly shows why this is a bad idea. The effect is actually much worse then I thought. The 4 element version I experimented with showed approximately 10 degrees of downward tilt. I suspect this has to do with the 2 directors trying their best to refocus that energy back inline with the boom. The free space model shows that simply adding the SPT500 above the beam caused the beam to nose dive its pattern 20 degrees downwards! That would be a very bad thing as far as performance.
So why don't we hear many more people saying how much the performance of the beam was messed up after placing a groundplane with horizontal radials above it? The answer has to do with how the earth will reflect that pattern back upwards in the far field. This is why when you model over real earth, you see distortion in the pattern but the far field TOA remains virtually unchanged.
One might be quick to think if the height above earth is going to correct the angle, then you don't have to be concerned with this interaction. Not so because the near field radiation will still be directed downwards by the radials above the beam and will increase RFI. Even though the primary lobe TOA does not change over earth, the gain at that angle has been reduced by the loss of power that is radiated downwards.
So why don't we hear many more people saying how much the performance of the beam was messed up after placing a groundplane with horizontal radials above it? The answer has to do with how the earth will reflect that pattern back upwards in the far field. This is why when you model over real earth, you see distortion in the pattern but the far field TOA remains virtually unchanged.
One might be quick to think if the height above earth is going to correct the angle, then you don't have to be concerned with this interaction. Not so because the near field radiation will still be directed downwards by the radials above the beam and will increase RFI. Even though the primary lobe TOA does not change over earth, the gain at that angle has been reduced by the loss of power that is radiated downwards.
Last edited: