Yagis and phasing harness 1

[robertjo24]

We have a site with a 900 MHz ISM band data radio (902-928 MHz FHSS), connected to a pair of Yagi antennas through a phasing harness. The antennas are stacked vertically as per manufacturer’s instructions to increase directional gain.

What would be the result if one of the Yagi antennas were rotated 180 deg. in azimuth? Would the phasing harness setup then just work like a power divider, splitting the power between each antenna?

 

[VEBill]

Assuming that they're stacked with sufficient spacing and mutual isolation to avoid interaction (as you would anyway), and assuming that each Yagi provides adequate Front/Back ratio (as they probably do), then it should work more-or-less as you'd expect.

Keep in mind that each direction would have only the gain of the single antenna, and (for transmit, for example) would only have one-half the RF transmit power. So you not only don't have the benefit of the two stacked antennas, but you're also sending one-half of the RF in the wrong direction (so to speak).

Your phasing harness presumably has the one-quarter wavelength lengths of (probably) 75-ohm coaxial cables to transform each 50-ohm antenna up to about 100-ohms for paralleling, resulting in a 50-ohm array. For critical applications, there would be better types of power dividers.