Grating-lobe　suppression　in　low-profile　planar　high-gain　antenna　arrays　has　been　always　an　interesting　topic　to　antenna　researchers.　Grating　lobes　would　appear　in　＇visible＇　space　when　the　element　spacing　of　antenna　arrays　is　large　enough.　In　a　uniform　linear　array,　when　the　element　spacing　is　greater　than　the　operating　wavelength,　the　grating　lobe　will　definitely　appear;　when　it　is　greater　than　half　wavelength　and　less　than　a　wavelength,　the　grating　lobe　would　appear　if　the　main　beam　is　scanned　to　a　large　angle.　In　practical　applications,　only　one　main　beam　is　required　to　exist　in　＇visible＇　space;　therefore,　the　array　spacing　is　constrained　by　the　application　requirements.　Nevertheless,　increasing　the　element　spacing　is　an　attractive　method　to　reduce　the　cost　and　manufacturing　difficulty　in　antenna　arrays,　because　it　will　reduce　the　number　of　elements　of　antenna　arrays.　Especially　in　millimeter-wave　antenna　arrays,　additional　challenges　are　introduced,　such　as　the　heat　dissipation　and　the　processing,　tunable,　and　reliability　difficulties.　Increasing　element　spacing　in　antenna　arrays　is　an　effective　solution　to　these　challenges.　©　2024　IEEE.