This is a topic that I have initiated since 2010,on other forums. A cardioide is the caustic of a circle when a light source is on the circumference of a circle.We can see this on a conical cup partially filled with cofee.When a light is shining from a distance and at a angle equal to the angle of the cone,a cardioide will be visible on the surface of the liquid. A metal ring can also be used to create a cardioide   Following these images, I agreed antenna with patches, having such a geometrical configuration   A simple patch antenna...     and a panel antenna