Terahertz phased array technology, an emerging field within electromagnetic wave applications, operates between microwave and infrared frequencies, offering unique spectral characteristics. Its potential advantages, including large bandwidth, high resolution, high integration, non-destructive capabilities, and strong penetration are increasingly being developed. These features make it highly promising for applications in wireless communication, high-resolution imaging, biological imaging, and security inspection. In terms of architecture, terahertz phased arrays are broadly divided into active and passive types. Active arrays feature transmit/receive components for each array element, enabling independent generation, manipulation, and reception of terahertz waves. This configuration enhances beam control, integration, and reliability, leveraging semiconductor chip processes for high-resolution imaging and high-speed communication. Passive arrays distribute electromagnetic waves to phase-controllable metasurface units via passive networks or aperture-fed systems. They excel in array scalability and power capacity, utilizing materials like liquid crystals, semiconductors, phase-change materials, and graphene for greater flexibility and broad application potential. Research in this field not only advances fundamental science but also supports the development of related industries, paving the way for next-generation communication technologies and imaging devices.

In active phased arrays, researchers have developed novel terahertz transmitters and receivers using advanced chip technologies, efficient semiconductor materials, and microwave integrated circuit techniques, achieving broader phase dynamic range, higher output power, and greater control precision. For instance, a two-dimensional delay-coupled oscillator structure is constructed using a 65 nm CMOS process, leveraging the phenomenon of injection locking [Fig. 1(a)] to create a beam-scanning radiative source operating at 338 GHz with scanning angles of 50° and 45° in two directions and an equivalent omnidirectional radiation power of 17 dBm. A 1×8 phased array, operating within the 370?410 GHz band, is realized using a 45 nm CMOS process, achieving a scanning range of 75° and an in-band peak equivalent omnidirectional radiation power of 8.5 dBm. This design not only reduces power consumption but also demonstrates compatibility with efficient on-chip microstrip antennas, marking a milestone as the first CMOS-based phased array operating at 400 GHz with a wide operational bandwidth. In addition, a compact terahertz amplification and frequency doubling chain at 340 GHz is proposed, enabling 360° phase shift capabilities for phased arrays in the 324?346 GHz range [Fig. 6(a)]. A 1×4 phased array transmitter operating at 320 GHz, designed using a 130 nm SiGe BiCMOS process, achieves an equivalent omnidirectional radiation power of 10.6 dBm and an E-plane beam scanning angle of ±12° [Fig. 7(a)]. Another innovative approach involves a simplified design method for a terahertz coherent harmonic radiation array, employing mode-dependent boundary modeling on half units (Fig. 9). This method leads to the creation of a 0.41 THz radiator with 16 coherent units using 130 nm SiGe BiCMOS technology, delivering an equivalent omnidirectional radiation power of 12.7 dBm, a directivity of 21.6 dBi, and a power consumption of 212 mW at a supply voltage of 1.7 V, thus providing a robust foundation for designing large-scale terahertz coherent arrays. In passive phased arrays, researchers have explored designs based on programmable metasurfaces, enabling dynamic phase and amplitude variations in reflected or transmitted electromagnetic waves for functionalities such as terahertz beam scanning. A liquid crystal-based transmissive programmable metasurface is proposed [Fig. 12(d)], which successfully excites Fano resonance through asymmetric structures, significantly reducing radiation loss, increasing transmission rates, and extending phase tuning ranges to nearly 180°. This innovation introduces a new method for enhancing phase-shifting capabilities while maintaining transmission efficiency. Furthermore, a two-dimensional terahertz beam control method utilizing liquid crystal programmable metasurfaces is developed [Fig. 14(c)], enabling two-dimensional beam scanning with advantages such as a broad frequency range, low cost, and high reliability, demonstrating significant potential in reconfigurable intelligent surfaces and holographic imaging. A 1-bit two-dimensional reflective programmable metasurface array, sized 98×98 and fabricated with a 22 nm CMOS process, experimentally demonstrates terahertz beam control with approximately 1° beamwidth, as well as sidelobe reduction and angular correction [Fig. 16(c)]. Moreover, a programmable metasurface design driven by thin-film transistors (TFTs) achieves phase modulation of up to 270° at 0.4 THz with an average reflection efficiency exceeding 30%. Across frequencies ranging from 0.36 to 0.43 THz, phase modulation exceeding 180° is maintained, achieving a peak gain of 13 dB at far field with a deflection angle of 50° (Fig. 18). A metasurface for terahertz wave detection and modulation, based on VO₂ enables a beam deflection range of 42.8° at 425 GHz and establishes a software-defined sensory response system for intelligent terahertz wave manipulation, enhancing communication security and reducing interference [Fig. 19(a)]. A dual-layer graphene metasurface unit is introduced [Fig. 21(c)], offering greater flexibility compared to single-layer designs, enabling a wide phase response range and high reflection efficiency. Simulations show that a 68×68 programmable metasurface achieves an effective focusing error of only 6%. In addition, a terahertz passive phased array with dual resonance modes, based on graphene-metal hybrid metasurfaces [Fig. 25(a)], achieves beam deflection angles of ±25° at a frequency of 1.03 THz with a reflectivity of 23%. A reflective metasurface driven by microelectromechanical systems (MEMS) enables complete polarization control, dynamic wavefront deflection, and real-time rewritable holographic displays, achieving ±70° beam deflection at 0.8 THz [Fig. 26(b)] and hologram design in two dimensions [Fig. 26(c)]. By integrating spatial and temporal dimensions into metamaterial systems, a time-space medium metasurface is proposed for unidirectional propagation and reconfigurable steering of terahertz beams [Fig. 29(a)]. Advances in perfect and symmetry-preserving Huygens metasurfaces demonstrate significant improvements in transmission efficiency, reaching up to 90%, with unit transmission spectra achieving 360° phase coverage. As research continues, terahertz phased array technology steadily progresses toward higher performance and broader applications.

Active phased arrays demonstrate high control efficiency but face challenges in scaling and power capacity. Conversely, passive phased arrays excel in beam control and scalability while maintaining lower efficiency in control devices. While current terahertz phased arrays are primarily suited for mid-range applications due to their shorter effective range compared to microwave and millimeter-wave bands, ongoing developments suggest significant potential for high-mobility platforms. Terahertz phased arrays are anticipated to become critical modules in high-precision radar and high-throughput communication systems, driving the future application of terahertz technology on dynamic platforms.