Vertical and Horizontal Oriented Difference?

[ateet101]

Hi,

I have the following 2 antennas:
Tunable dipole: tuned to 375MHz for my measuements
Broadband Dipole: 200-500MHz

I put the antennas in an anechoic chamber 3 meters from each other. First, I oriented both dipoles vertically and receiver -35dB in power on the network analyzer at 375MHz. Second, I oriented both dipoles horizontally and received -28dB in power.

Question: Why is there such a big difference of 7dB in power received? Shouldn't the power received be the same because both the antennas are positioned the same relative to each other?

Thanks

 

[betwixt]

The reading should be the same so some other factor is present. My first guess would be the feeder is radiating/receiving, try rotating the feeder cables at both ends at the same time as the antenna and see it that is responsible.

Brian.

 

[vfone]

You cannot do this polarization test if the antenna height of both dipoles is less than 2λ (1.6m in your case).
For vertical polarization might be a challenge to reach this height in a normal chamber.
At these frequencies is better to do the test in open air using wooden antenna supports. And if is nice weather you can have a beer also