Vertical Field Strength Calculation for Multi-bay antennas

[johncalvinhall]

I am working with two bay FM (88-108MHz) antenna array (vertically stacked), and am looking for an equation that will take the known values:

1. Vertical Relative Field Strength Pattern of a known "Off the shelf" antenna
2. Distance that seperates the two elements

I am looking to see how to calculate the combined field strength at each angle (Vertical Pattern).

Thanks Ahead of Time,
John Calvin Hall
Twin Falls, Idaho

 

[VEBill]

Depending on the complexity of each of your two bays, it might be within the capabilities of the free version of EZNEC.

http://www.eznec.com

This would give you an "exact" answer.

(There are plenty of freeware versions of NEC around as well, without any limits on number of elements. But EZNEC is quick to learn and easy to use.)

In general, if the two bays occupy the same space (too close together) then they are essentially the same as one antenna. Assuming that they are adequately spaced, then the gain improvement (from having two) will approach +3dB minus the loss of the combiner (perhaps ~1dB). The net gain improvement is likely to be about +2dB or so.