Fig. 1. THz active phased array based on 65 nm-CMOS technology^[26]. (a) Phased array structure based on locally coupled radiators; (b) integrated chip micrograph

Fig. 2. 370‒410 GHz phased array transmitter. (a) System circuit block diagram^[30]; (b) phased array transmitter micrograph^[29]

Fig. 3. 0.53 THz subharmonic phased array based on injection-locked oscillator (ILO) chain^[31]. (a) Block diagram of 0.53-THz phased array; (b) 0.53 THz phased array chip micrograph

Fig. 4. 0.416 THz 2D emission array based on dual-core distributed oscillator^[32]. (a) Dual-core distributed oscillator network structure and robustness analysis; (b) chip microphotograph of coupled dual-core oscillator; (c) micrograph of antenna array

Fig. 5. Scalable wafer-scale phased array at 140 GHz^[33]. (a) Internal composition of TRX and UDC channels; (b) chip layout

Fig. 6. 340-GHz amplifier-frequency-multiplier chain design^[34]. (a) Architecture of amplifier-frequency-multiplier chain; (b) chip photo

Fig. 7. 320-GHz 1×4 fully integrated phased array transmitter^[35]. (a) Schematic diagram of fully integrated phased-array transmitter; (b) micrograph of proposed THz phased array transmitter

Fig. 8. Standing-wave 2D phased array at 318‒370 GHz^[36]. (a) Structure of 2×2 standing-wave phased array with onchip patch antennas; (b) photo of proposed standing-wave 2D phased array

Fig. 9. 0.41-THz coherent harmonic radiation array based on mode-dependent boundaries^[38]. (a) Physical structure of coherent array; (b) CPW coupling; (c) shared slot coupling; (d) electrical field distributions for odd-mode and even-mode; (e) layout of half unit in HFSS software

Fig. 10. 1×4 bidirectional D-band phased-array transceiver in 130-nm BiCMOS technology^[39]. (a) Block diagram of IQ transceiver with direct conversion; (b) micrograph of phased-array transceiver chip

Fig. 11. THz passive phased array based on liquid crystal programmable metasurface^[60]. (a) Unit cell of liquid crystal programmable metasurface; (b) THz programmable metasurface and its controlling circuit; (c) coding sequence of programmable metasurface

Fig. 12. Manipulations of THz beams by transmissive programmable metasurfaces based on liquid crystals^[61]. (a) Fabricated prototype; (b) microscopic image of a group of metasurface unit cells; (c) 3D schematic diagram of metasurface unit; (d) 3D diagram of proposed programmable metasurface with different beam manipulation functions

Fig. 13. Flexible THz beam manipulations based on liquid-crystal integrated programmable metasurfaces^[62]. (a) Schematic of beam steering based on THz programmable metasurface array; (b) schematic of THz metasurface array placed on PCB; (c) schematic of THz far-field measurement setup for metasurface array

Fig. 14. Two-dimensional THz beam manipulations based on liquid-crystal-assisted programmable metasurface^[63]. Structures of designed metasurface elements at (a) 94 GHz and (b) 220 GHz; (c) schematic diagram of 2D THz programmable metasurface

Fig. 15. THz on-chip programmable metasurface based on CMOS technology^[64]. (a) 12×12 metasurface array and metasurface unit; (b) schematic diagram of THz metasurface

Fig. 16. Electronic THz beam forming and 2D steering for high angular-resolution operation^[65]. (a) Diagram of 1-bit phase-shifting operation; (b) diagram of antenna unit; (c) architecture and operation of presented 265 GHz CMOS reflectarray; (d) photos of CMOS chip and array assembly

Fig. 17. Programmable metasurface based on GaN HEMT^[66]. (a) 3D schematic diagrams of element and programmable metasurface; (b) photos of programmable metasurface

Fig. 18. Phase modulation of terahertz programmable metasurface based on free carrier plasma dispersion effect^[67]. (a) Schematic diagram of working principle of unit structure; (b) demonstration of beam deflection function

Fig. 19. THz metasurface based on VO₂^[68]. (a) Schematic diagram of metasurface; (b) schematic diagram of metasurface unit cell; (c) photograph of metasurface sample

Fig. 20. THz metasurface based on GeTe^[69]. (a) Schematic diagram of metasurface; (b) reconfigurable mechanism of metasurface

Fig. 21. Programmable metasurface based on dual layer graphene structure^[70]. (a) Programmable metasurface unit based on dual layer graphene structure; (b) unit equivalent circuit model; (c) schematic diagram of metasurface functions

Fig. 22. Tunable metasurfaces based on nonuniform periodic graphene arrays^[71]. (a) Schematic of metasurface; (b) nonuniform periodic graphene arrays; (c) graphene sheet; (d) schematic of beam scanning, whereθmax is maximum deflection angle

Fig. 23. All-solid-state reflective THz phased array based on graphene metasurface^[72]. (a) Schematic diagram of graphene metasurface unit structure; (b) schematic diagram of wide-angle scanning based on graphene metasurface

Fig. 24. Programmable graphene metasurface for terahertz propagation control based on electromagnetically induced transparency^[73]. (a) Schematic diagram of basic cell; (b) schematic diagram of programmable graphene metasurface

Fig. 25. Terahertz passive phased array based on dual resonance characteristics^[74]. (a) Schematic diagram of antenna array; (b) left view of structural unit; (c) top view of structural unit; (d) equally spaced phase difference encoding; (e) microscope image of processed sample; (f) processed graphene-metal hybrid metasurface

Fig. 26. Passive multifunctional MEMS THz passive phased array^[75]. (a) Model of MEMS-based MIM metadevice in one-port system with incidence and reflection; (b) one-dimensional encoding scheme; (c) two-dimensional encoding scheme

Fig. 27. Electrically programmable THz diatomic passive phased array for chiral optical control^[76]. (a) SEM images of one bimorph microhelix in suspended state (defined as OFF, 3D configuration) and actuated states (ON, 2D planar configuration); (b) scheme of metamaterial array comprising of diatomic metamolecules with microhelices of opposite handedness and two actuation channels (C1 and C2); (c) schematic diagram of electrically programmable chiral platform

Fig. 28. All-optical active THz passive phased array for ultrafast polarization switching and dynamic beam splitting^[77]. (a) Schematic diagram of hybrid metasurface operating as active polarizing beam splitter; (b) schematic illustrations of anisotropic h-SRR with different configurations relative to incident electric field polarization; (c) microscopic image of fabricated hybrid metasurface

Fig. 29. Spatiotemporal dielectric THz passive phased array for unidirectional propagation and reconfigurable steering of terahertz beams^[78]. (a) Schematic diagram of spatiotemporal metasurface; (b) scanning electron microscopy (SEM) image of fabricated samples with Kerker resonators, and schematic illustration of unit cell with optimized geometrical parameters