Current high throughput satellites (HTS) in Ka-band are required to provide multiple spot beam coverage based on frequency and polarization reuse, both in transmission (Tx, 19.2-20.2 GHz) and reception (Rx, 29-30 GHz). A four colour scheme with two frequencies and two polarizations is normally used, in which adjacent spots must be generated in a different frequency and/or polarization. The design of multi-beam antennas for Ka-band HTS systems must cope with some challenging requirements: generation of a large number of beams (normally between 50 and 100), very small separation between adjacent spots (a typical value is 0.56º), low spillover, etc. To xiv