Transparent antennas have been continuously developed for integration with solar cells, vehicular communications, and ultra-high-speed communications such as 5G in recent years. A transparent antenna takes advantage of spatial extensibility more so than all other antennas in terms of wide range of usable area. In addition, the production price of transparent antennas is steadily decreasing due to the development of nano-process technology. This paper reviews published studies of transparent antennas classified by various materials in terms of optical transmittance and electrical, sheet resistance. The transparent electrodes for the transparent antenna are logically classified and the transparent antennas are described according to the characteristics of each electrode. Finally, the contributions transparent antennas can make toward next-generation 5G high-speed communication are discussed.

This study presents a novel implementation of vanadium dioxide (VO2) phase change material in an electromagnetic (EM) surface with beam steering capabilities. For the first time, we present the design, fabrication, and measurement of a globally actuated, VO2-based beamforming reflective EM surface. We propose a design featuring complementary unit cells that enable beam steering with a single excitation, marking a pioneering use of low-loss VO2 in creating a complementary EM surface for the mmWave band. The unit cells incorporating VO2 exhibit low-loss characteristics, with −0.92 and −1.9 dB in the hot state and −0.49 and −0.25 dB in the cold state, respectively. We incorporate both positive and negative phase variants alongside two temperature-independent phase unit cells. The complementary design enables us to utilize two beam operating states, effectively exploiting the otherwise unused cold state. We experimentally demonstrated beamforming at ±5° and ±10° from the broadside. In the case of ±10°, the measured gains at 35 GHz in the cold and hot states were 19.4 and 20.3 dB, respectively, which aligned well with the simulated gains of 20.9 and 21.5 dB. Manipulation of the electromagnetic wave direction with a single excitation has the potential for imaging, sensing, and communication applications. The complementary unit cell design methodology can be further adapted for mmWave beamforming, absorbing, and cloaking reconfigurable EM surfaces. Furthermore, the use of VO2 can be extended up to sub-THz frequencies due to the wideband, low-loss characteristics compared with conventional reconfigurable devices, such as PIN diodes or MEMS switches.

The demand for millimeter-wave (mmWave) bands is growing due to the need for high-throughput communications, high-resolution sensing, and data-intensive applications such as massive Internet of Things (IoT), virtual reality, augmented reality, and metaverse platforms. Designing antennas for mmWave bands, unlike traditional microwave bands, requires multidimensional considerations such as antenna design methodologies, appropriate material selection, high-performance packaging technologies, and integration with surrounding circuitry. Antenna-in-package (AiP), which integrates transceiver (TRX) dies and antennas into a standard surface-mount package, effectively leverages advanced antenna engineering and heterogeneous integration processes. Codesigned with silicon integrated circuits (ICs) and built on the same silicon dies, antenna-on-chip (AoC) benefits significantly from frequency increases into the terahertz (THz) range. AoC takes advantage of silicon’s low surface roughness and monolithic integration to effectively incorporate antennas alongside peripheral ICs. Glass technology is emerging as a strong candidate for large-volume high-performance applications due to its low dielectric loss, similar thermal expansion coefficient to silicon, large-area panel/wafer size, and low surface roughness. Glass core AiP, which utilizes the low dielectric loss of glass, and antenna-on-display (AoD), which exploits the optical transparency of glass, are both promising concepts for 5G/6G mmWave applications. In this two-part article, we provide a comprehensive overview of antennas in packaging technologies in the mmWave band. In Part 1, we investigate design methodologies and features from different perspectives: material (organic or inorganic) and application [base station (BS) or user mobile terminal (UMT)]. We also review the historical development of multilayer antenna packaging. We then discuss the packaging integration of antenna arrays and radio-frequency ICs (RFICs), which are silicon-based phased-array systems. In Part 2, we focus on emerging techniques for antenna packaging, such as silicon, glass, and 3D integration

We present a V-band 1×8 on-chip miniaturized cavity coplanar folded slot antenna (CFSA) array with high efficiency and reduced mutual coupling. Substrate-integrated air cavities (SICs) are used to enhance efficiency and gain, diminish element-to-element coupling, and counter parasitic parallel-plate modes to improve CFSA efficiency. We developed CPW corporate feeds using SiO ₂ bridges and rounded bends to demonstrate beamsteering. The E and H-planes of the radiation pattern were measured with a custom robotic setup. The measured CFSA single element −10 dB bandwidth is 55.4–60.3 GH (8.5%) with an efficiency of 93%. The measured broadside array’s bandwidth spans 52–60.2 GHz (14.6%), with a total efficiency of 67% and 11.0 dBi gain. This study marks the first demonstration of beamsteering using on-chip antennas with SICs, steering up to 45°, and corresponding gains of 8.1, 8.9, and 9.2 dBi.

We present a W-band on-chip planar inverted-F antenna (PIFA) featuring high efficiency and wide bandwidth. The proposed on-chip antenna (OCA) incorporates a miniaturized 0.12λ ₀ ² -sized substrate-integrated air cavity (SIC) that creates a high dielectric discontinuity between air and silicon enabling an increase in radiation efficiency by suppressing the parallel plate modes. Forming air cavities in the substrate avoids the need for precise heterogeneous packaging, in contrast with integrating dielectric resonators or superstrate dielectrics with OCAs. To the best of the authors’ knowledge, a through-silicon via (TSV) was incorporated into a commercial silicon-based OCA die for the first time, enhancing the electrical connection to the off-chip ground and mechanical stability. The OCA is fabricated using a 180 nm SiGe BiCMOS process, with CMOS-compatible post-processing for SICs and TSVs. The proposed OCA complies with various design rule check (DRC) guidelines, including minimum trace width sizing and metal density considerations to achieve a high manufacturing yield. The SIC is created by etching the bottom silicon substrate using a deep reactive-ion etching (DRIE) process. We manufacture an Ag TSV by filling the SIC with Ag epoxy to prevent expensive post-processing. Measurements of the radiation patterns of the W-band antenna were performed using a robotic arm. The PIFA achieves a −10-dB bandwidth from 89 to 105 GHz with a fractional bandwidth of 16.3%. It also delivers an 11.4 GHz 1-dB gain bandwidth with a maximum realized gain of 1.6 dBi, corresponding to a peak efficiency of 71.6%. This research leverages commercial SiGe BiCMOS technology to achieve high efficiency and wide bandwidth, with TSVs providing a robust ground plane and potential for use as signal paths in monolithic integrated circuits.