Why is a Sky dish oval?

The larger the dish, the narrower its focal angle.

Since the focal angle is more important in the "horizontal" plane, in order to reject signals from adjacent satellites, it was deemed satisfactory to have a 50cm diameter dish (widthwise) but a 40cm dish (heightwise).

However, to make full use of the total dish area, this shape requires a special design of LNB. Explanation and photos by Satcure here.

But FORGET "oval". It's merely the width factor I'm considering. The point I'm trying to make is that a chopped off 55cm "circular" dish has precisely the same side-rejection as a complete 55cm circular dish.

Obviously it will have less gain than a full size dish and obviously the LNB has to be specially designed to match it (which is what BskyB did).

So, basically, Sky took a circular dish, chopped off top and bottom sectors, rounded the corners to make it look "oval" and they got a dish with the gain of a 45cm but with the side rejection of a 55cm dish - and it was smaller than a full 55cm dish so it looked prettier.

(The fact that the gain is really too low to give a decent "rain margin" for anywhere north of Leeds is incidental!)