Search Results (199)

This paper presents a novel 1-to-N power division architecture combining overmoded ${\mathrm{TE}}_{10}$ mode waveguides and modular N-way waveguide-to-microstrip mode converters. By decomposing the ${\mathrm{TE}}_{10}$ mode field distribution along the narrow wall of a rectangular waveguide, the proposed design enables flexible power splitting into arbitrary output ports (even or odd numbers) through uniform sub-${\mathrm{TE}}_{10}$-mode waveguide pathways. To achieve the above function using microwave transmission lines, a tapered transition structure ensures wideband excitation of the overmoded waveguide, while linearly tapered slot antennas (LTSAs) serve as N-way mode converters. Prototypes with two-, three-, and four-channel outputs demonstrate excellent amplitude-phase uniformity (≤0.5 dB amplitude imbalance and ≤$5^{\circ }$ phase deviation) across 6.5–12 GHz, with return loss <−10 dB. The modular 1-to-N power divider enables the rapid reconfiguration of output channels by simply replacing the mode converter module. Full article

Ultra-wideband (UWB) technology is a crucial facilitator for high-data-rate wireless communication due to its extensive frequency spectrum and low power consumption. Simultaneously, multiple-input multiple-output (MIMO) systems have garnered considerable attention owing to their capability to enhance channel capacity and link dependability. This article discusses the development of small, high-performance MIMO UWB antennas with mutual suppression capabilities to fully use the benefits of both technologies. Additionally, the suggested antenna features a straightforward design and dual-band-notched characteristics. The antenna structure includes two radiating elements measuring 85 × 45 mm². These elements use a rectangular patch provided by a coplanar waveguide (CPW). Double U-shaped slots are incorporated into the rectangular patch to introduce dual-band-notched properties, which help mitigate interference from WiMAX and WLAN communication systems. The antenna is fabricated on a Mylar^® polyester film substrate of 0.3 mm in thickness, with a dielectric constant of 3.2. According to the measurement results, the suggested antenna functions efficiently across the frequency spectrum of 2.29 to 20 GHz, with excellent impedance matching throughout the bandwidth. Furthermore, it provides dual-band-notched coverage at 3.08–3.8 GHz for WiMAX and 4.98–5.89 GHz for WLAN. The antenna exhibits impressive performance, including favorable radiation attributes, consistent gain, and little mutual coupling (less than −20 dB). Additionally, the envelope correlation coefficient (ECC) is extremely low (ECC < 0.01) across the working bandwidth, which indicates excellent UWB MIMO performance. This paper offers an appropriate design methodology for future flexible and compact UWB MIMO systems that can serve as interference-resilient antennas for next-generation wireless applications. Full article

This study proposes a dual-element wideband circularly polarized (CP) slot-integrated multiple-input multiple-output (MIMO) antenna with an X-notch square-shaped artificial magnetic conductor (AMC) for dedicated short-range communications (DSRC) applications. The proposed antenna design consists of two substrate layers separated by an air gap. The upper layer features a dual-element coplanar waveguide-fed slot antenna and a defected ground structure decoupling isolator, while the lower layer comprises an 8 × 8 array of X-notch square-shaped elemental units, functioning as an AMC reflector. Characteristic mode analysis shows that circular polarization is produced by the dominant orthogonal mode pair (modes J₅ and J₆), whose modal significance exceeds 0.92 and whose characteristic angle separation is 82° around the 5.9 GHz DSRC band. An I-shaped slot embedded in the ground plane of the upper layer serves as a defected ground structure isolator to suppress mutual coupling between antenna elements. Meanwhile, the X-notch square AMC reflector enhances radiation characteristics and antenna gain. The measured return loss bandwidth and axial ratio bandwidth are 32% (4.72–6.61 GHz) and 21.18% (5.2–6.45 GHz), respectively. The dual-element antenna scheme achieves high isolation exceeding 19 dB, with a maximum gain of 8.6 dBic at 5.9 GHz. The envelop correlation coefficient remains below 0.003, while the diversity gain exceeds 9.98 dB. Full article

The development of compact, CMOS-compatible gas sensors is critical for advancing real-time environmental monitoring and industrial diagnostics. In this study, we present a detailed numerical investigation of integrated photonic waveguide designs—such as ridge and slot—optimized for overtone-based gas spectroscopy in the near-infrared range. By evaluating both the evanescent-field confinement and curvature-induced losses across multiple silicon-on-insulator platforms, we identify optimal geometries that maximize light–analyte interactions while minimizing bending attenuation. Our findings provide essential design guidelines for high-performance, low-footprint gas sensors. Full article

This paper presents the novel design of a printed, low-cost, dual-port, and dual-polarized slot antenna for microwave biomedical radars. The butterfly shape of the radiating element, with orthogonally positioned arms, enables simultaneous radiation of both vertically and horizontally polarized waves. The antenna is intended for full-duplex in-band applications using two mutually isolated antenna ports, with the CPW port on the same side of the substrate as the slot antenna and the microstrip port positioned orthogonally on the other side of the substrate. Those two ports can be used as transmit and receive ports in a radar transceiver, with a port isolation of 25 dB. Thanks to the bow-tie shape of the slots and an additional coupling region between the butterfly arms, there is more flexibility in simultaneous optimization of the resonant frequency and input impedance at both ports, avoiding the need for a complicated matching network that introduces the attenuation and increases antenna dimensions. The advantage of this design is demonstrated through the modeling of an eight-element dual-port linear array with an extremely simple feed network for high-gain biosensing applications. To validate the simulation results, prototypes of the proposed antenna were fabricated and tested. The measured operating band of the antennas spans from 2.35 GHz to 2.55 GHz, with reflection coefficients of less than—10 dB, a maximum gain of 8.5 dBi, and a front-to-back gain ratio that is greater than 15 dB, which is comparable with other published single dual-port slot antennas. This is the simplest proposed dual-port, dual-polarization antenna that enables straightforward scaling to other frequency bands. Full article

A self-diplexing, full-mode, substrate-integrated waveguide (SIW) rectangular cavity-backed antenna based on an inverted Z-shaped radiating slot with filtering characteristics is investigated in this work. The proposed design allows for individual control through the loading of four different slots, namely, a combination of horizontal and diagonal slots, called inverted Z-shaped slots. The two diagonal slots make 45° angles between them, and this flexible rotation gives the design flexibility regarding control of the bands. By combining these slots into a modified inverted Z-shaped slot, a SIW rectangular cavity is configured and energized with two separate 50 Ω microstrip feed lines to resonate at two different frequencies—11.63 GHz and 13.27 GHz—and TE₂₁₀ and TE₂₂₀ modes are obtained for X- and Ku-band wireless purposes. In an experimental analysis, reflection coefficients of S₁₁ < −10 dB were noted for both operating frequencies of 7.4% (11.23–12.09 GHz) and 3.0% (13.15–13.55 GHz), respectively. The average gain of the proposed antenna design in the two different operating conditions is 6.14 and 6.16 dBi, respectively. In addition, the proposed self-diplexing antenna attained high isolation, greater than 28 dB between both operating channels, and showed overall measured efficiency of 87.32%. Moreover, it features a single-layer structure, operates in dual bands, provides broadside linear polarization, and exhibits filtering capabilities. Full article

Integrated optical waveguide amplifiers, with their compact footprint, low power consumption, and scalability, are the basis for optical communications. The realization of high gain in such integrated devices is made more challenging by the tight optical constraints. In this work, we present efficient amplification in an erbium–ytterbium-based hybrid slot waveguide consisting of a silicon nitride waveguide and a thin-film active layer/electron-beam resist. The electron-beam resist as the upper cladding layer not only possesses the role of protecting the waveguide but also has tighter optical confinement in the vertical cross-section direction. On this basis, an accurate and comprehensive dynamic model of an erbium–ytterbium co-doped amplifier is realized by introducing quenched ions. A modal gain of above 20 dB is achieved at the signal wavelength of 1530 nm in a 1.4 cm long hybrid slot waveguide, with fractions of quenched ions f_q = 30%. In addition, the proposed hybrid waveguide amplifiers exhibit higher modal gain than conventional air-clad amplifiers under the same conditions. Endowing silicon nitride photonic integrated circuits with efficient amplification enriches the integration of various active functionalities on silicon. Full article

A millimeter-wave multi-layer and miniaturized multibeam antenna fed by an E-plane Butler matrix (BM) in substrate integrated waveguide (SIW) technology is proposed. For the beam-forming network (BFN), a folded E-plane 4 × 4 BM is proposed, whose basic components are stacked up along the vertical direction aiming to reduce the horizontal size by more than 75% compared with a single-layer BM. For the radiation portion, an unconventional slot antenna array arranged in a ladder type is adopted. The slot antenna elements are distributed in separate layers, making them more compatible with the presented BM and are arranged in the longitudinal direction to suppress the mutual coupling effect. Furthermore, the BM has been adjusted to accommodate the slot antenna array and obtain further miniaturization. The overall dimension of the designed multibeam antenna, taking the BFN into account, is 12 mm × 45 mm × 2 mm (1.2 λ × 4.5 λ × 0.2 λ), which is preferable for future 6G smartphone applications. The impacts of the air gap in fabrication are also taken into consideration to alleviate the error between simulated model and fabricated prototype. Full article

This work presents a novel $C{O}_2$ gas sensor based on a slotted polymer-phaseshift Bragg grating (SP-PSBG) waveguide filled with polyhexamethylene biguanide (PHMB) as the sensing medium. The transmission resonance, characterized by a narrow peak with a full width at half maximum (FWHM) of 1.6 nm within the Bragg grating bandgap, is highly responsive to refractive index changes in PHMB caused by variations in $C{O}_2$ concentration. Numerical simulations demonstrate a sensitivity of 14.4 pm/ppm, outperforming conventional gas sensors based on functional material coatings. This enhanced performance comes from the direct interaction between the PHMB-filled resonant structure and the cladding that contains $C{O}_2$ molecules, eliminating the need for polymer-coated cladding layers. The optimization approach employed in this design focuses on maximizing the optical confinement factor within the PHMB-filled slot, leading to an effective overlap between the guided optical mode and the sensing material. Full article

This paper presents a wideband circularly polarized (CP) substrate-integrated waveguide (SIW) cavity-backed slot antenna array arranged in a 2 × 2 configuration with differential feeding structures. The design features arc-shaped microstrips within the SIW cavity to excite the ${\mathrm{TE}}_{011}^x$/${\mathrm{TE}}_{101}^y$ and ${\mathrm{TE}}_{211}^y$/${\mathrm{TE}}_{121}^x$ modes. By overlapping the center frequencies of the two modes, wideband CP radiation is achieved. The introduction of four modified ring couplers composes a simple but efficient differential feeding network, eliminating the need for balanced resistors like baluns, making it more suitable for millimeter wave or even higher frequency applications. Experimental results show that the antenna array achieves a −10 dB impedance bandwidth of 32.6% (from 17.28 to 24.00 GHz), a 3 dB axial ratio (AR) bandwidth of 13.8% (from 17.05 to 19.57 GHz), a 3 dB gain bandwidth of 41.8% (from 15.39 to 23.51 GHz) and a peak gain of 10.6 dBi, with results closely matching simulation data. This study enhances the development of differential CP SIW cavity-backed slot antenna arrays, offering a potential solution for creating compact integrated front-end circuits in the millimeter wave or Terahertz frequency range. Full article

In recent years, research on light-matter interactions in silicon-based micro/nano cavity optomechanical systems demonstrates high-resolution sensing capabilities (e.g., sub-fm-level displacement sensitivity). Conventional 2D photonic crystal (PhC) cavity optomechanical sensors face inherent limitations: thin silicon layers (200–300 nm) restrict both the mass block (critical for thermal noise suppression) and optical Q-factor. Enlarging the detection mass in such thin layers exacerbates in-plane height nonuniformity, severely limiting high-precision sensing. This study proposes a 500 nm thick silicon-based 2D slot-type PhC cavity design for advanced sensing applications, fabricated on a silicon-on-insulator (SOI) substrate with optimized air slot structures. Systematic parameter optimization via finite element simulations defines structural parameters for the 1550 nm band, followed by 6 × 6 × 6 combinatorial experiments on lattice constant, air hole radius, and line-defect waveguide width. Experimental results demonstrate a loaded Q-factor of 57,000 at 510 nm lattice constant, 175 nm air hole radius, and 883 nm line-defect waveguide width (measured sidewall angle: 88.4°). The thickened silicon layer delivers dual advantages: enhanced mass block for thermal noise reduction and high Q-factor for optomechanical coupling efficiency, alongside improved ridge waveguide compatibility. This work advances the practical development of CMOS-compatible micro-opto-electromechanical systems (MOEMS). Full article

Terahertz (THz) antennas are among the critical components required for enabling the transition to sixth-generation (6G) wireless networks. Although research on THz antennas for 6G communication systems has garnered significant attention, a standardized antenna design has yet to be established. This study introduces the modeling of a full-metal transverse slotted waveguide antenna (TSWA) for 6G and beyond. The proposed antenna operates across the upper regions of the V-band and the entire W-band. Designed and simulated using widely adopted full-wave analysis tools, the antenna achieves a peak gain of 17 dBi and a total efficiency exceeding 90% within the band. Additionally, it exhibits pattern-reconfigurable capabilities, enabling main lobe beam steering between 5° and 68° with low side lobe levels. Simulations are conducted to assess the power handling capability (PHC) of the antenna, including both the peak (PPHC) and average (APHC) values. The results indicate that the antenna can handle 17 W of APHC within the W-band and 3.4 W across the 60–160 GHz range. Furthermore, corona discharge and multipaction analyses are performed to evaluate the antenna’s power handling performance under extreme operating conditions. These features make the proposed TSWA a strong candidate for high-performance space applications, 6G communication systems, and beyond. Full article

Millimeter-wave antennas have become more important recently due to the diversity of applications in 5G and upcoming 6G technologies, of which automotive systems constitute a significant part. Two crucial indices, detection range and angular resolution, are used to distinguish the performance of the automotive antenna. Strong gains and narrow beamwidths of highly directive radiation beams afford longer detection range and finer spatial selectivity. Although conventionally used, patch antennas suffer from intrinsic path losses that are much higher when compared to the waveguide antenna. Designed at 77 GHz, presented in this article is an 8-element slot array on the narrow side wall of a rectangular waveguide, thus being readily extendable to planar arrays by adding others alongside while maintaining the element spacing requirement for grating lobe avoidance. Comprising tilted Z-shaped slots for higher gain while keeping constrained within the narrow wall, adjacent ones separated by half the guided wavelength are inclined with reversed tilt angles for cross-polar cancelation. An open-ended external waveguide is placed over each slot for polarization purification. Equivalent circuit models of slotted waveguides aid the design. An approach for sidelobe suppression using the Chebyshev distribution is adopted. Four types of arrays are proposed, all of which show potential for different demands and applications in automotive radar. Prototypes based on designs by simulations were fabricated and measured. Full article

Despite significant progress, fabricating two-dimensional (2D) lithium niobate (LN)-based photonic crystal (PhC) cavities integrated with tapered and PhC waveguides remains challenging, due to structural imperfections. Notable, especially, are variations in hole radius (r) and inclination angle (°), which induce bandgap shifts and degrade quality factors (Q-factor). These fabrication errors underscore the critical need to address nanoscale tolerances. Here, we systematically investigate the impacts of key geometric parameters on optical performance and optimize a 2D LN-based cavity integrated with taper and PhC waveguide system. Using a 3D Finite-Difference Time-Domain (FDTD) and varFDTD simulations, we identify stringent fabrication thresholds. The a must exceed 0.72 µm to sustain Q > ${10}^7$; reducing a to 0.69 µm collapses Q-factors below ${10}^4$, due to under-coupled modes and bandgap misalignment, which necessitates ±0.005 µm precision. When an r < 0.22 µm weakens confinement, Q plummets to 2 × ${10}^4$ at r = 0.20 µm (±0.01 µm etching tolerance). Inclination angles < 70° induce 100× Q-factor losses, requiring ±2° alignment for symmetric modes. Air slot width (s) variations shift resonant wavelengths and require optimization in coordination with the inclination angle. By optimizing s and the inclination angle (at 70°), we achieve a record Q-factor of 6.21 ×${10}^6$, with, in addition, C-band compatibility (1502–1581 nm). This work establishes rigorous design–fabrication guidelines, demonstrating the potential for LN-based photonic devices with high nano-fabrication robustness. Full article

A high-gain circularly polarized (CP) magnetoelectric dipole (ME-dipole) radiating element is demonstrated at a millimeter-wave (MMW) 5G band of 37–43.5 GHz. Each ME-dipole radiating element, consisting of two pairs of ring-shaped and L-shaped metal posts is excited by a cross-shaped substrate-integrated waveguide (SIW) coupling slot to achieve CP radiation. Through the use of all-metal radiating structures with a height of 3.4 mm, high-gain and high-efficiency radiation performances are achieved. For proof of concept, a 4 × 4 antenna array with a SIW feeding network is designed, fabricated, and measured. The measured impedance bandwidth of the proposed 4 × 4 CP antenna array is 19.2% from 33.9 to 41.1 GHz for |S11| ≤ −10 dB. The measured 3 db AR bandwidth is 10.3% from 37 to 41 GHz. The measured peak gain is 20.3 dBic at 41 GHz. The measured and simulated results are in good agreement. Full article