what type of stacked antenna is this.

Hi,

can someone please tell me what kind of stacked antenna is this. My professor has asked me to reproduce it and I have no clue what kind of stack antenna is this. it has a very high bandwidth and high gain. how he couples i have no clue.

Planar-fed folded notch (PFFN) arrays_A novel wideband technology for multi-function active elec.pdf

Regards