Compared　to　small　radiating　elements,　large　elements　can　reduce　the　stages　and　the　losses　of　power　dividers　(PD)　within　the　same　array　aperture,　significantly　enhancing　the　array＇s　radiation　efficiency.　However,　it　faces　the　grating　lobe　challenge　when　they　are　formed　into　an　array.　This　paper　investigates　the　factors　that　affect　the　rectangular　lattice　large　element　array＇s　sidelobe　levels　(SLL).　Results　show　that　the　sidelobes　are　independent　of　element　spacing　but　closely　related　to　aperture　efficiency　(AE)　and　array　scale.　The　element＇s　AE　and　number　in　the　arraying　dimension　are　suggested　to　be　at　least　82%　and　4,　respectively.　The　lens　is　selected　as　the　large　element＇s　architecture　because　its　optimized　feed　and　phase-shifting　surface　make　it　relatively　easy　to　achieve　a　higher　field　uniformity,　that　is,　a　higher　AE.　Methods　for　extracting　the　1-D　aperture　efficiencies　of　a　2-D　region　are　proposed　in　this　paper　to　validate　the　derived　SLL　rules　in　full-wave　simulations,　and　a　simplified　form　is　employed　for　the　rapid　optimization　of　architectural　parameters.　Finally,　a　4　×　4　scale　high　AE　lens　array　is　designed　with　an　element　size　of　6　λ0　×　10　λ0.　The　reached　directivity　at　220　GHz　is　39.7　dBi,　with　aperture　efficiency　almost　above　70%　within　the　170　~　260　GHz　band.　For　the　convenience　of　measurement,　a　prototype　with　a　16-way　power　divider　is　fabricated.　The　measured　peak　realized　gain　is　37　dBi,　with　a　peak　total　efficiency　of　42%　and　a　3-dB　gain　bandwidth　of　20.7%.　　©　1963-2012　IEEE.