Hello.

Well known, x²= 4py :

http://dy185677.en.ec21.com/C_180_Cm_Satellite_Dish--2988376_3112840.html

has the focus at its axis, and the axis aims direct to the radio sorce, as learned decades ago.

 

But this one has the focus offset from the axis :

http://www.bikudo.com/product_search/details/13760/satellite_dish_antenna.html

Is the radio source not collinear with its axis ?

 

How does the latter aiming works? Is there any ray-tracing graph on the web for an offset focus parabola you can link please ?

 

Never came across that second version in my years of analytical geometry

For both antennas, the focal point is, that, a point. If the radio source drifts position but the antenna does not track, does the focal describe a line ? How to calculate/determine the line ? (path of focal point)

Hi,

 

I never saw any problem with this. You just cut out an 'asymetric' part of parabola shape (like the red part in the picture below).

 

Thanks Danijel !

Understand now; an offset portion of the parabola is still parabolic and will have the focus away from the axis.

Glad to help . You can cut out any part or shape from a parabolic reflector, and the focal point remains intact.