Hello, In the link bellow they describe the idea behind cosecant square antenna radiation
I have few problems understanding the concept:
1.Why they say that h is constant?
the height of the plane is not constant the plane is descending constantly

https://www.radartutorial.eu/06.antennas/Cosecant Squared Pattern.en.html

 

This is confusing and subtle. The idea is to make an antenna pattern whose gain is csc^2. If you can do this- then the radar return is relatively constant and depends only on the angle- the range doesn't matter and the height doesn't matter. That derivation is manipulating the radar equation to show that. They make this funny pattern by offsetting the feed of the antenna to give it a low radiation angle. Wikipedia has a better explanation but its still somewhat confusing. Its designed to a solve a problem where the relative sensitivity of a radar was very non linear with range and height- This flat pattern makes a lot of this go away. The best way to intuitively understand it is to read some history of the evolution of radar. I hope tis helps a little.