Current Issue : July-September Volume : 2026 Issue Number : 3 Articles : 5 Articles
This paper proposes a compact, low-profile slot antenna integrated with a metasurface (MS) layer to realize wideband circular polarization and maintain a consistently high gain for IoT applications. The antenna element uses a C-shaped slot in the ground plane, excited by a microstrip feed to generate the circularly polarized waves. The metasurface layer incorporates mushroom-shaped outer cells and centrally placed slanted-slot elements to broaden the axial-ratio (AR) bandwidth and to maintain a consistently high gain. The metasurface consists of twelve adjacent cells arranged in a mushroom-shaped configuration, with a 45◦ slanted rectangular slots on four central cells. The simulated and measured results demonstrate strong agreement; the impedance-matching bandwidth is 26.7%, and the axial-ratio bandwidth is 15.7% at a central frequency of 6.8 GHz. Finally, the antenna consistently demonstrates a measurement gain exceeding 8 dBic across the AR bandwidth, with a peak measured gain of 9.6 dBic....
Here, we demonstrate that applying an external magnetic field to break time-reversal symmetry (TRS) induces topological phase transitions and topologically protected unidirectional edge state propagation in photonic crystals. We investigate nonreciprocal propagation in a square array of indium antimonide (InSb) rods embedded in air at terahertz frequencies. In photonic crystals, a modest external magnetic field applied to semiconductor rods creates gyroelectric (magneto-optical) anisotropy. This anisotropy breaks the TRS, which lifts the degeneracy at the Dirac-like point, opening a new nontrivial bandgap. The resulting edge modes supported by photonic crystals exhibit nonreciprocal propagation and remain immune to backscattering, even when encountering large obstacles, 90° sharp bends, and structural defects. The propagation direction of this state is determined by the magnetic field. A novel design approach for nonreciprocal terahertz topological devices is proposed, leveraging the strong correlation between the unidirectional edge mode properties and the Voigt effect. These findings offer promising potential for developing and fabricating advanced nonreciprocal terahertz topological devices....
A single-band-notched ultra-wideband (UWB) low-sidelobe planar array antenna for millimeter-wave (mmWave) applications is presented. The antenna element employs a planar dipole excited through an H-shaped coupling slot to achieve broadband impedance matching, while a centrally loaded parasitic patch acts as a half-wavelength resonator to generate a controllable notch band. Additional parasitic patches are introduced to recover the highfrequency matching without degrading the notch response. An 8×8 array is then developed using a Taylor-weighted feed network implemented with three classes of 1-to-4 microstrip power dividers. Measured results show that the array operates from 19.0 to 45.0 GHz with VSWR < 2, while providing a rejection band from 35.0 to 38.5 GHz. The notch suppresses the realized gain by about 5 dB around 37.0 GHz, the peak gain reaches 20.5 dBi in the passband, and average sidelobe levels better than −17 dB are obtained. The proposed design provides a practical approach for combining ultra-wide bandwidth, in-band interference rejection, and low-sidelobe radiation in a compact mmWave planar array....
A novel resonant-type defected ground structure (DGS) featuring a modified internal structure is proposed to enhance the suppression of cross-polarized (XP) radiation of rectangular microstrip antennas (RMAs) on slot-type DGS. Specifically, integrating periodic circular metal structure (PCS) into the slot-type DGS, which has been demonstrated to reduce RMA XP levels and minimize the space occupied by defects. As a resonant-type DGS, the embedding of the PCS enables the excitation of the entire DGS by the fringe field of the patch. The coupling between the fringe field and the PCS-type DGS results in a significant alteration of the field distribution of the high-order mode TM02, thereby effectively suppressing the XP radiation generated by TM02 mode. This structural concept originates from the unique control capabilities of periodic structures over electromagnetic field propagation, with the objective of optimizing the symmetry of the substrate field distribution inside the defect region. Compared to slot-type DGS, the periodic structure enables more electromagnetic fields to couple into the slot from the non-radiating side and disperse among each metal element, generating resonance in the TM02 mode field. Experiments demonstrate the H-plane co-cross polarization isolation exceeds 25 dB across an azimuth range exceeding 200◦, with peak XP suppression reaching 20 dB. This performance is at the forefront of resonant-type DGSs....
Substrate-free epidermal antennas promise imperceptible and long-term wearable sensing, yet their electromagnetic performance is fundamentally constrained by the properties of ultrathin conductors. In this work, gold nanomesh is employed for the first time as the radiating conductor of a substrate-free epidermal tattoo antenna operating in the UHF RFID band. Owing to its RF-thin nature, the nanomesh behavior is governed by sheet resistance rather than skin-depth effects, imposing a strict upper bound on achievable radiation efficiency. By combining surface-impedance modeling, full-wave simulations, and on-body experiments, we demonstrate that ohmic losses set a geometry-independent limit on the realized gain of on-skin antennas. An inductively coupled loop architecture is optimized to approach this bound while ensuring mechanical robustness and impedance stability. Measurements on phantoms and human subjects confirm the predicted performance limits within a few decibels, enabling reliable UHF RFID read ranges up to 30–40 cm under standard regulatory constraints....
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