Hello !
I think he means by Ripples that the far field doesn't have a smoth curve of charactersitic and, due to scatterd surface waves, this far field pattern has a noisy (distorted) pattern.
Thinks of it as an unwanted noise reflected from the antenna as shown at far field pattern image attached.
If you have something else to show me - you're more then welcome.
Itzik !
P.S.
the far field pattern was taken from 3rd edition of Antenna Thoery of Balanis C.
(Last chapter of measurements antenna's paramters)