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The rise of artificial intelligence (AI) necessitates ultra-fast computing, with on-chip terahertz (THz) communication emerging as a key enabler. It offers high bandwidth, low power consumption, dense interconnects, support for multi-core architectures, and 3D circuit integration. However, transitioning between different waveguides remains a major challenge in THz systems. In this paper, we propose a THz band mode converter that converts from a rectangular waveguide (RWG) (WR-0.43) in TE10 mode to a substrate-integrated waveguide (SIW) in TE20 mode. The converter comprises a tapered waveguide, a widened waveguide, a zigzag antenna, and an aperture coupling slot. The zigzag antenna effectively captures the electromagnetic (EM) energy from the RWG, which is then coupled to the aperture slot. This coupling generates a quasi-slotline mode for the electric field (E-field) along the longitudinal side of the aperture, exhibiting odd symmetry akin to the SIW’s TE20 mode. Consequently, the TE20 mode is excited in the symmetrical plane of the SIW and propagates transversely. Our work details the mode transition principle through simulations of the EM field distribution and model optimization. A back-to-back RWG TE10-to-TE10 mode converter is designed, demonstrating an insertion loss of approximately 5 dB over the wide frequency range band of 2.15–2.36 THz, showing a return loss of 10 dB. An on-chip antenna is proposed which is fed by a single higher-order mode of the SIW, achieving a maximum gain of 4.49 dB. Furthermore, a balun based on the proposed converter is designed, confirming the presence of the TE20 mode in the SIW. The proposed mode converter demonstrates its feasibility for integration into a THz-band high-speed circuit due to its efficient mode conversion and compact planar design.

A novel design method based on a novel origami process that can create a solid structure swiftly and at a low cost is presented for rectangular waveguide-type microwave devices in this paper. A planar structure was fabricated by the lamination and laser cutting of polystyrene membranes and aluminum foils and was converted into a solid structure via origami in accordance with the selective absorption of infrared light. A rectangular waveguide, a rectangular waveguide-type coupler, and a power divider based on an origami structure with a multi-layer structure and a single-layer structure were fabricated and tested, demonstrating easy assembly and good microwave performance. The measured results of the rectangular waveguide indicated that the insertion loss was superior to −0.9 dB. Meanwhile, the results of the coupler showed that the coupling degree increased from −12.8 dB to −8.9 dB in the range of 11.0 GHz to 12.0 GHz. Correspondingly, the prepared power divider demonstrated that the return loss dwindled from −8.9 dB to −11.3 dB and that the insertion loss of one output port was approximate to that of the remaining one, varying between −3.5 dB and −5.2 dB in the range of 10.5 GHz to 11.5 GHz—verifying the effectiveness of the origami-based design method.

In this paper, a new approach to excite sharp asymmetric resonances using a single completely symmetric split-ring resonator (SRR) inside a rectangular waveguide is proposed. The method is based on an asymmetry in the excitation of a symmetric split-ring resonator by placing it away from the center of the waveguide along its horizontal axis. In turn, a prominent asymmetric resonance was observed in the transmission amplitude of both the simulated results and the measured data. Using a single symmetric SRR with an asymmetric distance of 6 mm from the center of a rectangular waveguide led to the excitation of a sharp resonance with a Q-factor of 314 at 6.9 GHz. More importantly, a parametric study simulating different overlayer analytes with various refractive indices revealed a wavelength sensitivity of 579,710 nm/RIU for 150 μm analyte thickness.

Recently, Kouzaev (J Comput Electron 20:169, 2021) proposed a novel rectangular waveguide with graphene inserts for light-pumped applications. However, the study has a serious error regarding the consistency between equations. Here, the error is specified.

In this paper, we present a novel structured THz BWO based on a rectangular waveguide grating with improved output characteristics. The circuit enabled, with a simple change, separation of the two sections without increasing the overall size. A conventional one-stage circuit with 45 grooves and a novel two-stage circuit with 15 and 25 grooves were quantitatively compared using the 3D MAGIC PIC code. The oscillation time could be drastically reduced, and the conversion efficiency could be increased by more than two times. Importantly, this structure enabled an output increase without increasing the circuit size. It can be expected to improve the output of a compact high-power THz source.

A methodology for characterizing dielectric materials frequently utilized in construction is presented. This approach entails assessing electromagnetic wave propagation properties within a waveguide containing the material under investigation, through the analysis of waveguide dimensions, measured parameters, and the implementation of calibration procedures. The method uses the Transmission/Reflection (T/R) technique to ascertain the complicated relative permittivity of various materials. A standard vector network analyzer is initially employed to estimate the Sij parameters within a rectangular waveguide containing the material under investigation in the X-band frequency spectrum (8.5 – 12.5 GHz). Subsequently, a numerical optimization process is applied to derive the complex permittivity, utilizing a MATLAB script designed to identify the complex relative permittivity of the dielectric material, aligning the measured and calculated values of the S-parameters. Specifically, two measures of transmission and reflection are employed: The preliminary measurement is performed using an empty sample holder or a dielectric reference. Conversely, in the second measurement, the sample holder is populated with the substance for characterization. The legitimacy of this approach is evidenced by experimental findings from various dielectric building materials, including Teflon, cellular concrete, and wood, in comparison with alternative ways, hence affirming the efficacy of the proposed strategy.

This paper researches the fabrication of a WR2.8 terahertz rectangular waveguide operating at the frequency ranging from 260 GHz to 400 GHz via UV-LIGA technology (UV-lithography, electroplating, and molding). In the process, megasonic agitation is applied to improve the mechanical properties and internal surface roughness of the WR2.8 rectangular waveguide. The effects of process parameters on the properties of structures are discussed, and optimized parameters are obtained to achieve accurate geometry dimensions. In addition, the highly crosslinked SU-8 is reliably removed from structures without damage through a synthesis method. The accuracy of the height and width of the WR2.8 rectangular waveguide is 5 µm and 2 µm, respectively, and the measured internal surface roughness is 79.6 nm. Moreover, experimental measurements and numerical simulations of the waveguide are conducted, and the difference between the two is also highlighted.

We present a compact dielectric lens integrated at the aperture of a WR90 rectangular waveguide, achieved using polytetrafluoroethylene (PTFE). This innovative configuration enables, for the first time in the X- and Ku-bands, the direct generation of a subwavelength electromagnetic jet from a guided structure. The beam exhibits the hallmark features of an electromagnetic jet: strong near-field focusing, a subwavelength beam width surpassing the diffraction limit, and a quasi-planar wavefront sustained over a propagation distance of about 2λ. The lens design was systematically optimized, and its performance was assessed through full-wave finite element simulations and experimentally validated on a fabricated prototype. Excellent agreement between the simulation and measurement confirms the robustness of the approach. Beyond its simplicity and low cost, this solution achieves state-of-the-art focusing performance compared to free-space and guided-wave alternatives. It offers strong potential for applications in high-resolution imaging, precision sensing, and material characterization, particularly in opaque or highly lossy environments.

Over the past decades Silicon on Insulator (SoI) technology has tantalized the interest of researchers in the design of numerous nonlinear Photonic Integrated Circuits (PIC’s) to provide a variety of devices. In this manuscript, four different types of optical add/drop resonators are proposed and compared using their simulated microcomb notch filter performance. The four types of resonators are (i) rectangular waveguide based conventional ring resonator, (ii) slot waveguide based ring resonator, (iii) rectangular waveguide based racetrack resonator, and (iv) slot waveguide based racetrack resonator, for variety of active/passive applications. The resonator parameters: Free Spectral Range (FSR), Full Width at Half Maximum (FWHM), Finesse (F) and Quality factor (Q-factor) are evaluated and compared for four resonators. The resonators are optimized for different parameters, such as ring radius (R), gap (g) between the waveguides and coupling length (L c ). The optimized R of ~ 30 μm with the power coupled ‘g’ of 55 nm is found after performing rigorous simulations for the entire optical conventional band (C-band) i.e., in 1530 nm  – 1565 nm using Finite Element Method (FEM). The manuscript provides valuable insights into the design considerations and performance trade-offs of different optical resonators in PICs showing symmetricity along x-axis and y-axis. These findings can guide the development of efficient and high-performance integrated photonic devices for various applications, including communication and computing systems.

A broadband right-angle transition from a substrate-integrated waveguide (SIW) to a rectangular waveguide (RWG) is proposed. A coupling aperture etched on the broad wall of the SIW and two stepped ridges embedded in the RWG flange are designed for good matching between both waveguides. A Ka-band prototype is designed and fabricated. Good agreement between the measured and simulated results is obtained. The measured results show an insertion loss <0.55 dB and a return loss below −15 dB from 31.3 to 38.35 GHz. This broadband transition may be used in microwave and millimetre-wave circuits and systems.