Junhong Wang

This paper presents a low-profile compact cavity frequency scanning antenna that utilizes coupled characteristic modes to enable wide-angle beam scanning. The core advantage of this design lies in its utilization of characteristic mode analysis (CMA) to distinctly identify and excite both E-dipole and M-dipole modes within the structure. By integrating these modes into adjacent frequency bands and leveraging their coupling relationships and superposition, the array achieves continuous cross-quadrant scanning. By controlling the mode spectrum distribution through adjustable slots and coupling windows, the proposed antenna realizes a $103^{\circ }$ scanning range ($-60^{\circ }$ to $+43^{\circ }$) within a 7% bandwidth, a peak gain of 9.26 dBi, radiation efficiency of 77.6%, and a scanning rate of $15^{\circ }/\%$. This design overcomes the quadrant limitation of single-mode arrays and avoids high complexity, demonstrating the superiority of CMA for wide-angle frequency scanning antennas.

This paper develops a circularly polarized (CP) electronically-controlled beam-scanning leaky-wave antenna (LWA) in millimeter-wave band that can achieve wide angle scanning in both elevation and azimuth angles. The LWA comprises a bottom plate of the radial line slot array (RLSA), and a reconfigurable 1-bit amplitude modulated radiation elements (AMREs) array. The power amplitude of the AMREs array can be controlled via PIN diodes to modulate the aperture field distribution of the LWA. To achieve convenient wide-angle beam scanning, a binary holographic method (BHM) is developed, which employs the 1-bit AMREs array as the holographic surface (HS) to generate beams at different angles. Central feeding with a coaxial probe is adopted to suppress the beam squint. Measured results indicate that the LWA achieves beam scanning over a -50° to 50° range in elevation and a 0° to 360° range in azimuth. Furthermore, within the 25~27 GHz band, beam squint is suppressed within 2° across most of the scanning range except at large angles. The measured peak gain reaches 18.0dBi with good left-handed circular polarization (LHCP) property. The developed antenna shows significant potential for application in millimeter-wave mobile communications scenarios.

This paper proposes two types of phase gradient metasurfaces, named as non-centrosymmetric beam metasurface (NCSM) and centrosymmetric beam metasurface (CSM), which exhibit remarkable performance in reducing radar cross-section (RCS). For the NCSM, when a circularly polarized (CP) wave is incident, it scatters incident wave into 45 beams accompanied by polarization conversion. When a linearly polarized (LP) wave is incident, the NCSM can generate total of 90 beams, including 45 left-circularly polarized (LCP) beams and 45 right-circularly polarized (RCP) beams. In contrast, when either CP or LP waves are incident on a CSM, it scatters incident wave into 36 beams and simultaneously achieves polarization conversion. The NCSM achieves over 10 dB multi-polarization RCS reduction across frequency range from 14.3 GHz to 33.4 GHz (80.1% relative bandwidth). Similarly, the CSM achieves over 10 dB multi-polarization RCS reduction within a frequency range from 14.9 GHz to 33.5 GHz (76.8% relative bandwidth). The proposed metasurfaces provide an efficient way to achieve multi-polarization RCS reduction, which can be adapted to the complex radar detection environment.

This paper presents a beam-squint suppression method for an electronically beam-scanning leaky-wave antenna (LWA). The method utilizes a 66-element low-frequency slot array (LFSA) and a 72-element high-frequency slot array (HFSA). The two slot arrays simultaneously radiate to suppress the beam squint. A phase adjustment method is implemented by introducing two non-radiation sections and a radiation section, enabling the combination of the generated beams. A prototype is fabricated and measured, showing good agreement between the simulated and measured results. The proposed LWA achieves a beam-scanning range of 89° in the operating band from 14.8 GHz to 16.0 GHz (7.8% fractional bandwidth), while maintaining a relatively high gain (10.8dBi to 15.5dBi). Additionally, the minimal beam squint is only 2.4°, and the desired gains (gain at the desired angle) are above 10.1dBi. The fluctuation of the desired gain ranges from 1.4dB to 3.4dB, indicating stable and high desired gain performance. These results demonstrate the stable beam-scanning capabilities of the proposed LWA with suppressed beam squint.

This paper presents a novel dual-polarized leaky-wave antenna (LWA) that integrates dual-channel operation, polarization reconfigurability, and electronically controlled beam scanning into a simple structure. The architecture consists of a radiating superstrate, a 90° hybrid coupler, and gap waveguides (GWs). Two rows of patch elements on the superstrate are excited through orthogonal slots etched on a shared ground. PIN diodes and their electronically controlled network are placed beneath the slots to tune the radiation state of each element. The 90° hybrid coupler, implemented via a metal pin array, is integrated into the GWs to form the feed structure. A binary hologram control method based on the holographic principle is proposed, allowing real-time switching of polarization states and beam directions through the manipulation of PIN diodes. As a result, the antenna supports simultaneous dual-channel operation with four pairs of reconfigurable orthogonal polarizations—right-hand/left-hand circular polarization (RHCP/LHCP), LHCP/RHCP, horizontal/vertical polarization (HP/VP), and VP/HP—with independent beam scanning over a 100° range in each polarization state. A prototype is fabricated and measured, validating polarization switching among all four states and beam scanning from –50° to 50°. Owing to its dual-channel operation, polarization reconfigurability, and beam-scanning capability, the proposed antenna is a promising candidate for millimeter-wave applications.

A novel microstrip magnetic-current electronically steerable leaky-wave antenna (LWA) is proposed, capable of wide-angle two-dimensional (2-D) beam scanning over a broad band. The radiation mechanism is realized through a simple microstrip magnetic-current array. To enable dynamic beam control, each magnetic-current controlling unit is integrated with a PIN diode to allow operating state switching. Holographic method is employed to achieve real-time 2-D beam scanning in both azimuth and elevation planes. Besides, conventional LWAs often suffer from beam squint, which degrades the stability of signal strength in specific directions in the bandwidth. To address this issue, a center-fed substrate integrated waveguide is developed for the excitation of the microstrip magnetic-current array. This architecture effectively suppresses beam squint and stabilizes the gain across the signal bandwidth. A prototype is fabricated and measured, demonstrating 2-D beam scanning from 4.5 to 5.6 GHz. The antenna achieves a peak realized gain of 15.66dBi at 5.0 GHz. Measured gain drops are constrained to 3.90dB for scans up to ±50° and 5.18dB up to ±60°, with an average reduction of 3.75dB toward the band edges. Measured results show a good agreement with the simulated ones, validating the effectiveness of the proposed design. Due to its simple structure, low profile, low cost and lightweight, the antenna is suited for beam-scanning communication scenarios.

This paper presents a novel low cost, low-profile, wide-angle axial ratio, electronically controlled two-dimensional beam-scanning circularly polarized millimeter-wave antenna array. The antenna comprises Rogers RO5880 and Rogers RO4350B substrates. The Rogers RO4350B substrate ensures the mechanical robustness of the antenna array, while the lower-loss Rogers RO5880 substrate is utilized to minimize transmission loss. A reflective phase shifter loaded with two diodes is used to provide 0°/180° phase switching, and a mushroom-shaped electromagnetic bandgap structure is integrated beneath the phase shifter to suppress power leakage. A double-layer stacked patch structure is adopted for the circularly polarized element to broaden its bandwidth, while sequential rotation technique is implemented in the array to extend the beam scanning range with axial ratio < 3dB. Furthermore, the capability of the sequential rotation technique to suppress parasitic beams in 1-bit circularly polarized arrays is analyzed. Subsequently, a method of reducing antenna sidelobe levels is developed, which loads specific phase delays onto the antenna and optimizes them using genetic algorithm. Finally, an 8×8 prototype is fabricated and measured, achieving an axial ratio below 3dB over a ±50° beam-scanning range and a peak gain of 16.9dBic from 23 to 26 GHz. This design demonstrates promising application prospects for future wireless communication systems.

A low-cost, low-profile, electronically controlled millimeter-wave antenna array with two-dimensional wide-angle beam scanning capability is presented. It consists of a planar waveguiding structure and a 1-bit transmitting surface. The waveguiding structure, which is composed of a power divider and a coupling cavity array, provides equal-amplitude in-phase energy output. And a receive-transmit element loaded with diodes is utilized to achieve 1-bit phase switching. More importantly, theoretical analysis and simulated results demonstrate that the parasitic beams of a 1-bit phased array can be eliminated by incorporating specific phase delays. Moreover, the sidelobe level is effectively reduced by optimizing these delays using the Particle Swarm Optimization algorithm. In this design, substrate-integrated coaxial lines are integrated into the 1-bit element to implement specific phase delays. The effectiveness of this method has been thoroughly verified through both simulated and measured results. The final 16×16 antenna array successfully eliminates parasitic beams over the band from 25.5 to 28.5 GHz, and achieves a peak gain of 21.12dBi at 26.5 GHz. The design achieves a scanning range exceeding ±58° at 26.5 GHz in the φ = 0°, φ = 45°, and φ = 90° planes. Compared to existing digitally quantized antennas, this design enables 1-bit two-dimensional wide-angle beam scanning in the millimeter-wave band based on a planar antenna structure, demonstrating strong potential for millimeter-wave applications.

Reliable wireless communication is crucial for the safe operation of high‐speed trains, which is based on stable radio wave coverage in complex environments. The space along the railway can be categorized into three types: open space, confined space, and open‐confined mixed space. Predicting radio wave coverage in these environments is essential for designing reliable wireless communication systems for vehicles. This study focuses on the multitunnel connection environment along the railway, which falls into the category of open‐confined mixed space. Unlike conventional tunnel or open‐space environments, the propagation characteristics in such scenarios are more complex and influenced by multiple factors. Therefore, it is important to investigate the radio wave propagation characteristics in a multitunnel connection environment along a railway. By employing the parallel finite difference time domain (FDTD) technology, the influences of important factors such as antenna position, tunnel cross‐sectional shape, beam angle, and open‐space distance on radio wave coverage are analyzed, and the underlying mechanism is revealed. Simulation results show that the radio wave coverage is highly sensitive to the beam angle of the transmitting antenna, and the variation law of radio wave coverage with beam angle is related to the position of the transmitting antenna and tunnel cross‐sectional shape. Furthermore, the impact of trains on link reliability is quantitatively studied. These studies can provide concrete guidelines for antenna deployment optimization in railway vehicular communication systems.