Miao Zhang

This article develops a novel holey electromagnetic bandgap (EBG) structure comprising dumbbell-shaped (DS) holes. They enable the self-assembly of multilayer metallic plates constituting the waveguide and cavity-based components. Compared to conventional circular holey EBG structures, the proposed DS irregular holes feature a compact size, a wide stopband, and insensitivity to misalignment. Moreover, the methodology of connecting multiple holes based on the DS holey EBG structure significantly reduces the number of holes, thereby simplifying their distribution in different layers and enhancing the integration of complex devices. For demonstration, straight rectangular waveguides integrated with DS holey EBG structures are designed in the $W$ -band first. Furthermore, two $W$ -band over-mode cavity-backed $8\times 8$ slot arrays, integrated with and without DS holey EBG structures, are also designed for comparison. The constitutive multilayer metallic plates are fabricated by applying the deep reactive ion etching (DRIE) and physical vapor deposition (PVD) processes. Abroadband measurement bandwidth is obtained. According to measurement, the transmission loss per unit length of the rectangular waveguide is evaluated as low as 0.012dB/mm at 100GHz. The $8\times 8$ slot arrays achieve wideband operation and low sidelobe levels (SLLs). The measured −10-dB impedance-matching bandwidth is 90–109.5GHz (19.5%), while the 3-dB down boresight gain bandwidths are 90–108GHz (18%) with in-band SLLs less than −12.9dB. An improvement of about 2dB has been observed in the antenna gain by comparing the antennas with and without DS holey EBG structures.

A novel low-temperature wafer-level hybrid bonding technique utilizing metal micro-bumps (Cu/SnAg) and non-photosensitive dry films has been developed and investigated. The bonding process is conducted at low temperatures: 160°C for the dry film and within the range of 260°C to 280°C for the micro-bumps. The micro-bumps are fabricated using conventional electroplating, while the patterning of the non-photosensitive dry film is achieved through laser ablation, bypassing the need for traditional lithography. Furthermore, optimizing the thickness of the micro-bumps, the opening dimensions of the dry film, the maximum bonding pressure, and the bonding temperature has enabled the development of a stepped control profile, which allows a seam-free bonding interface between the micro-bumps and the dry films. For demonstration, superior interconnect performance with an average tensile strength of approximately 8.11 MPa is achieved. The non-photosensitive dry film exhibits low transmission loss when applied to glass packaging due to its low dielectric constant and dissipation factor. Consequently, the proposed hybrid bonding technique provides a highly cost-effective and promising approach for future multilayer glass/PI RF 3D integration.

A new type of reconfigurable wideband self-decoupled coupled line antenna pair (CLAP) is proposed for mobile terminals. The CLAP adopts the coupled transmission line with two separated opposite ports and two open ends, which is naturally built-in with the band-isolation characteristic when its electrical length is half a wavelength. Since this coupled line retains the intrinsic self-isolation between two ports even for asymmetric structures, the CLAP doesn't require balanced feeding ports or a symmetric environment. To enhance the working frequency bandwidth, an electromagnetic capacitive (EC) feed structure is proposed with two reconfigurable states covering the N77 (3.3-4.2 GHz) and N79 (4.4-5 GHz) bands, respectively. The measured isolations within two reconfigurable states are higher than 11 dB and 17.5 dB, respectively. The measured total efficiencies of both antennas in two working states are 58%-88% and 61%-88%, respectively. The results demonstrate that the proposed CLAP design concept will provide a simple and wideband self-decoupled antenna for MIMO application.

A low-loss and compact on-chip filter solution for the narrowband specification, especially within the 3% fractional bandwidth (FBW) range, is proposed in this letter. It consists of high-Q dual-mode substrate integrated waveguide (SIW) resonators, which are realized by a wafer-level glass interposer through glass via (TGV) process. The proposed on-chip filter is based on the dual-mode resonator (DMR), namely TE₁₂₀ and TE₂₁₀ modes, and a higher order response can be achieved by cascading DMR via a nonresonating node (NRN). The utilization of DMR can provide a high-Q value and better selectivity due to the transmission zero (TZ) generated by DMR. The measurement results show good filtering performance and good consistency with the simulation results. The measured insertion loss (IL) of the proposed on-chip filter is 2.5 dB at 60 GHz with a narrow FBW of 2%, and the out-of-band suppression is better than 25dB. The filter die area is only $1.71\lambda _{g} \times 0.69\lambda _{g}$ , which shows a great potential application in ultranarrowband millimeter-wave wireless data communication systems.

This paper proposes a dual-linearly-polarized (DLP) center-fed quadrifilar helix antenna (CF-QHA) loaded with reverse helices. It features a small transverse area, hollow-core structure, enhanced bandwidth, high cross-polarization discrimination (XPD), and high gain. The proposed antenna comprises two pairs of diagonal helical arms along ±45° directions. By changing the feeding point to the center of each helical arm, the center feed mechanism is introduced first to improve the impedance matching, compared with the previous end-fed DLP-QHA. Loading reverse helices with the CF-QHA in parallel further enhances the XPD performance. In addition, each pair of diagonal helical arms employs a differential feed to ensure LP radiations and high isolation. For demonstration, a prototype is fabricated and tested. According to the measured results, the 10-dB return loss bandwidths of the proposed ±45° DLP CF-QHA respectively range over $2.13-2.68$ GHz (22.87%) and $2.1-2.69$ GHz (24.63%), where XPDs higher than 21 dB and isolation better than 24 dB are achieved. The DLP CF-QHA is expected to provide the industry with more design options in base station applications.

This paper presents a novel dual-linearly-polarized quadrifilar helix antenna (DLP-QHA) with high cross-polarization discrimination (XPD) and high isolation. The antenna comprises four helical arms, each consisting of a pair of counter-wound half-turn helices. Two opposite arms are excited with differential feeding, resulting in linearly polarized radiation along the 45– directions. The quadrifilar geometry combined with differential excitation significantly enhances both XPD and isolation performance. To further improve impedance matching, a branch structure is introduced to produce dual-resonant characteristics. Additionally, a defected ground structure (DGS) is employed to enhance the front-to-back ratio (FBR), without compromising the radiation performance in other directions. The theoretical mechanisms responsible for linear polarization, high XPD, and self-decoupling are rigorously analyzed and discussed. A prototype operating at the 3.55-GHz band is designed and fabricated to validate the proposed design. The antenna achieves a compact size with a diameter and height of only 0.28 λ0 and 0.25 λ0, respectively. The measured results show good agreement with simulations. Return coefficients at both ports remain below -10 dB across 3.12.3.82 GHz (20%), fully covering 5G NR band 78 (3300.3800 MHz). Within this band, the antenna achieves a measured boresight gain greater than 8.12 dBi, an XPD exceeding 26 dB, and a port isolation above 22 dB. The demonstrated performance of the DLP-QHA highlights its potential as an alternative solution for 5G-NR applications, including microcell base stations and Internet of Things (IoT) systems, particularly in scenarios requiring multi-polarization, multibeam, multiband, pattern-reconfigurable, and diversity array configurations.

This letter proposes a new type of self-decoupled antenna, named as the self-decoupled coupled line antenna pair (CLAP). The theory of a lossy coupled line inspires the concept of CLAP as a two-port coupled line providing all-isolation characteristics. Thus, the two-port isolated lossy coupled lines are constructed by two closely spaced strip antennas and proper matching circuits, and a self-decoupled CLAP with good radiation efficiency, moderate matching bandwidth, and high isolation can be realized. CLAP has advantages such as superior spatial reuse, asymmetric structural self-isolation, multiple design freedom, and diversities design options. The measured results show that the CLAP with an inductive feeding circuit can achieve a high isolation better than 20 dB at the bandwidth of 3.4–3.6 GH, while the CLAP with a capacitive feeding circuit can achieve a high isolation of 12 dB at the bandwidth of 3.3–3.8 GHz. This new type of self-decoupled antenna pair is expected to provide the industry with more design options for multiple antennas in wireless terminals.

This letter presents a novel air-filled post-wall waveguide (PWW) in an advanced wafer-level planting process for millimeter-wave applications. This PWW, consisting of two metal plates and numerous regular copper columns, is implemented by an improved column grid array (CGA) bonding process with a high alignment accuracy of less than 50 μm. Since air is the only transmission medium, the CGA-PWW has a low-loss advantage over the traditional dielectric-filled substrate-integrated waveguide. For demonstration, the prototype CGA-PWW transmission lines with a standard waveguide transition are designed and fabricated by adopting the 8-inch wafer-level processing technology. An extremely low transmission loss of 0.0032 dB/mm is achieved in the entire V-band. A good agreement between the measured and simulated results verifies the process’s stability. Moreover, introducing the redistribution layer technology and the multilayer stacking process could significantly enhance the external integration capabilities. Hence, the CGA-PWW solution is appropriate for millimeter-wave radio-frequency components and system integrations.

This letter, for the first time, implements an air-filled glass-based double-sided gap waveguide (Glass-DS-GWG) using micropatterned adhesive bonding. This advanced bonding solves the challenge of uncertain gap height in conventional GWG-based devices. Meanwhile, the high-efficiency laser-induced wet etching (LIWE) removes most of the transmission medium. Extremely low-loss transmission and stable performance are obtained. Multiple $V$ -band transmission lines are fabricated in a 6-in glass wafer for demonstration. As the measured results, the transmission loss of 0.018–0.03 dB/mm, the average bend leakage of only 0.055 dB, and the isolation of better than 25 dB are achieved. Therefore, the proposed Glass-DS-GWG solution with the advantages of low loss, low cost, low profile, and high integration suits the fabrication and integration of radio frequency (RF) devices for millimeter-wave (mm-W) applications.

This article proposes a direction-of-arrival (DOA) estimation algorithm for a random sparse linear array based on a novel graph neural network (GNN). Unlike convolutional layers and fully connected layers, which do not interact well with information between different antennas, the GNN model can adapt to the goniometry problem of non-uniform random sparse linear arrays without any prior information by applying neighbor nodes’ aggregation and update operations. This helps the model in learning signal features under complex environmental conditions. We train the model in an end-to-end way to reduce the complexity of the network. Experiments are conducted on the uniform and sparse linear arrays for various signal-to-noise ratio (SNR) and numbers of snapshots for comparison. We prove that the GNN model has superior angle estimation performance on arrays with large sparsity that cannot be used by traditional algorithms and surpasses existing deep learning models based on convolutional or fully connected structures. The proposed algorithm shows excellent DOA estimation performance under the complex conditions of limited snapshots, low signal-to-noise ratio, and large array sparsity as well. In addition, the algorithm has a low time calculation cost and is suitable for scenarios that require low latency.