Beam　synthesizing　antenna　arrays　are　essentially　demanded　for　on-chip　millimeter　wave　and　terahertz　systems.　In　order　to　achieve　a　particular　radiation　beam,　specific　amplitude　and　phase　distributions　are　required　for　all　the　array　elements,　which　is　conventionally　realized　through　a　properly　designed　feeding　network.　In　the　current　work,　a　low-loss　feeding　network　design　approach　based　on　epsilon-near-zero　(ENZ)　medium　was　proposed　for　large-scale　antenna　arrays　with　different　beam　requirements.　Due　to　the　infinite　wavelength　within　the　ENZ　medium,　a　newly-discovered　stair-like　resonant　mode　was　adopted　for　assigning　a　uniform　phase　distribution　to　each　element,　while　the　amplitudes　and　positions　of　these　elements　were　optimized　for　generating　particular　beams.　To　implement　the　design　philosophy　in　a　low-loss　manner,　a　hollow　air-filled　waveguide　near　cutoff　frequency　was　employed　to　emulate　the　ENZ　medium,　and　the　bulk　silicon　microelectromechanical　systems　(MEMS)　micromachining　technology　was　utilized　for　chip-scale　integration.　As　a　specific　example,　a　low-sidelobe　antenna　array　at　60.0　GHz　was　designed,　which　realized　an　impedance　bandwidth　of　2.57%,　a　gain　of　13.6　dBi　and　a　sidelobe　level　as　low　as　-20.0　dB　within　the　size　of　0.5　×　3.4λ02.　This　method　is　also　compatible　with　a　variety　of　applications,　such　as　the　high-directivity　antenna　array,　non-diffractive　Bessel　beam　antenna　array,　and　so　on.　Based　on　this　innovative　concept　of　applying　ENZ　medium　to　the　on-chip　antenna　array,　it　shows　the　advantages　of　simple　structure　and　low　loss　for　on-chip　beam　synthesis　without　complex　lossy　feeding　networks.　©　2023　The　Author(s)