Hello,
I just excited a parabola reflector antenna with a linear slant feed horn. So I have the vertical and horizontal planes for different polarizations.
I need to know what the relationship is between the main lobe magnitude value(31.9dBi) in the absolute diagram and the co and cross pole main lobe magnitude(28.8dBi) of the antenna.
if the relationship is not well defined what is the difference between the main lobe magnitude value(31.9dBi) in the absolute diagram and the co and cross pole main lobe magnitude(28.8dBi) of the antenna
The polarization is 45 degrees, so vertical and horizontally polarized antennas will only pick up half the power. That is -3dB, which is the difference between 31.9dB and 28.8dB.
V and H (0 and 90 degrees) are not the co and cross polar signals. -45 degrees would be the cross-polar signal, and 45 degrees the co-polar signal.
Dear Malcom white,
I appreciate your response. I need to correct my understanding based on your explanations.
1) Yes, as I understood the total power is divided between horizontal and vertical polarization powers.
2) Please check my understanding of co-pol and cross-pol measurements
a) If I assume the axis of the reflector is on Z and my horn antenna (as feed) is y-polarized then the Vertical value(y) is co-pol and the Horizontal value(x) is cross-pol. Right?
b) Because the feed is rotated for 45 degree, then the pattern at 45 degrees is co-pol and 90 degrees from this values deviation (135 or -45) is cross-pol. Right?
Thank you.
And remember that 45 degrees changes direction when you turn round to face the other way.
Co-polar can also be right hand circular, or left hand, or some elliptical polarization. Cross-polar is the polarization that doesn't receive it, what ever it is. Read the Ludwig and Poincare definitions of polarization.
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