This letter proposes a novel quadruple-mode beam-shaping method for microstrip antenna design using characteristic mode analysis (CMA). By simultaneously exciting two pairs of characteristic modes that respectively produce broadside and omnidirectional circularly polarized (CP) radiation patterns, the superposition thus forms the target saddle-shaped wide beam with enhanced half-power beamwidth (HPBW). An X-band prototype is fabricated and measured to validate the feasibility of the proposed method. The measured results confirm that the HPBW exceeds 116° and the axial-ratio beamwidth (ARBW) exceeds 119° in both orthogonal azimuth planes at the center frequency of 8 GHz. The proposed method achieves the wide-beam CP radiation with a low-profile and single-layer structure, offering a promising solution for space-constrained satellite applications.
Underwater electromagnetic localization can interpret propagation-model error as source displacement. We quantify this effect for single-frequency horizontal electric-dipole localization in vertically stratified marine media. The model hierarchy progresses from unbounded uniform water (H0), through bounded uniform water (W1), to profile-resolved water columns. A fast Fourier transform–Sommerfeld solver and variable-projection matched-field estimator separate boundary and vertical-profile effects while eliminating unknown source coefficients. At 30 dB, adding air and seabed reduces three-dimensional root-mean-square error from 23.079–27.584 m for H0 to 0.495–0.535 m for W1. Resolving the nominal eight-layer profile further lowers error from 0.486–0.575 to 0.094–0.108 m. The improvement is not pointwise monotone and becomes calibration-dependent. Under an independent WOA18 profile extending to 350 m, a seven-layer approximation reduces the circular-layout median from 1.224 to 0.749 m. It reduces the square-layout median from 1.010 to 0.628 m. Adverse pairs and a shared depth ambiguity remain. External boundaries therefore remove gross bias, whereas vertical resolution supplies a conditional correction governed by profile accuracy, frequency, geometry, and calibration.
This letter presents a two-dimensional (2-D) beam-scanning circularly polarized (CP) folded transmitarray antenna (FTA) based on the Risley prism principle. By constructing transmitarray elements capable of linear-to-circular and circular-to-circular polarization conversion, and introducing a polarization-converting reflectarray surface, continuous 2-D beam scanning is achieved with a low-profile and high-aperture efficiency structure. A 2×2 linearly polarized patch array is adopted as the feed, which improves structural integration while ensuring gain performance. A prototype was fabricated to validate the design. The measured results demonstrate that at 10 GHz, continuous scanning from 0° to 49° in elevation and 0° to 360° in azimuth are achieved with a maximum gain loss of less than 3.5 dB and good circular polarization maintained during scanning. Furthermore, the antenna achieves a measured gain of 23.8 dBic and an aperture efficiency of 42.1% with an overall profile of only 1.84 λ0.
A dual-linearly polarized high-gain Fabry–Pérot (F–P) resonant cavity antenna is proposed in this paper. The feed source adopts a dual orthogonal Y-shaped dipole structure connected by metallic posts to realize excitation of two independent linear polarizations. Four hollow resonant rings are loaded beneath the dielectric substrate to further expand the operating bandwidth. The F–P resonant cavity is composed of an upper dielectric substrate with dual-layer snowflake-shaped copper patches and a lower circular copper reflector. By placing the radiating elements inside the cavity, the impedance bandwidth and gain are simultaneously improved. Experimental results show that the impedance bandwidths of the two ports are 5.1–7.27 GHz and 5.3–7.4 GHz, corresponding to fractional bandwidths of 35.08% and 33.07%, respectively. The port isolation remains stably below −21 dB across the entire operating bandwidth. A maximum measured gain of 17.3 dBi is achieved for both polarizations at 5.8 GHz. The measured results agree well with the simulations, verifying the effectiveness of the proposed design.
Recent years have witnessed deep learning emerging as a pivotal tool for aiding metasurface design, reducing computational latency, and enhancing design efficiency. However, this application is hindered by two primary constraints: firstly, the scarcity of high-quality large-scale datasets for model training; secondly, the strongly nonlinear correlation between structural parameters and electromagnetic responses, which can induce unstable training dynamics and inadequate convergence performance. To address these issues, this paper proposes RFNet, which introduces Fourier-enhanced operations into the residual architecture, enabling the network to better capture long-range dependencies and incorporate global spectral information when datasets are insufficient.On a set of CST-simulated square-ring metasurface datasets, RFNet exhibits stable phase convergence and reduces the mean squared error of magnitude and phase by 88.5% and 55.9%, respectively, compared with a standard ResNet.
In this letter, an ultra-wideband polarization-multiplexed reconfigurable metasurface (MS) is proposed for simultaneous 1-bit programmable reflection and absorption. The unit cell is co-designed with an orthogonally symmetric topology and four triangular parasitic patches, enabling bandwidth enhancement in both the reflective and absorptive channels rather than a simple combination of two functional structures. Owing to the weak coupling between two orthogonal polarization channels, the PIN-controlled reflective response is achieved with little influence on the absorptive performance. The proposed MS provides a 1-bit phase bandwidth of 53.6% and an absorption bandwidth of 95.2%. A 10 × 10 prototype is fabricated and experimentally verified through dual-beam scattering, orbital angular momentum (OAM) vortex-beam generation, and radar cross section (RCS) reduction, demonstrating its capability for wideband polarization-decoupled wave control.
In this paper, an ultra-wideband millimeter-wave (mmWave) planar circularly polarized (CP) antenna array is reported. The proposed CP element is evolved from a center-fed long dipole. By bending the long dipole at its current null points, two orthogonal current components with an approximately 90° phase difference can be generated, thereby realizing CP radiation. To further broaden the axial-ratio (AR) bandwidth, the straight folded arms are evolved into Archimedean spiral arms. The spiral arm introduces an additional y-polarized field component for phase compensation, enabling the phase difference of around 90° over a wide frequency range. The operating principle has been analyzed in detail. The simulated results show that the proposed CP antenna achieves a 3-dB AR bandwidth of 56.6%. To meet the high-gain requirement, an 8 × 8 CP antenna array is designed, fabricated, and measured. The measured results show that the proposed CP antenna array achieves an overlapped bandwidth of 54.68% from 24.25 to 42.5 GHz, and a peak gain of 23.2 dBic. With its ultra-wide operating bandwidth, high gain, and planar configuration, the proposed CP antenna array is a promising candidate for 5G communications, satellite communications, and other broadband mmWave applications.
This letter presents a coupled-resonator frequency-scanning differential-beam antenna (FSDBA) with a high null scanning rate for short-range vibration sensing under strong static-reflection backgrounds. Magnetic coupling between adjacent resonators generates two frequency-scanned nulls, enabling a dual-null differential-beam scanning response. The fabricated prototype operates from 3.97 to 4.03 GHz with a measured null scanning rate of 22.67°%, substantially higher than those of the compared differential/null-scanning antennas. An actuator-vibration experiment is conducted under a controlled strong static-reflection background and compared with a higher-gain frequency-scanning directional receiver. The proposed differential receiver achieves a 5.11 dB higher maximum signal-to-clutter-plus-noise ratio (SCNR), demonstrating its potential for short-range vibration sensing in such scenarios.
Near-field power deposition in stratified lossy media is affected by layer-dependent phase accumulation, attenuation, and interfacial mismatch, limiting the accuracy of conventional free-space focusing. This letter presents a single-substrate, via-free transmissive Huygens metasurface (HMS) with stratified-medium phase compensation for superficial power deposition at 5.8 GHz. The HMS provides nearly 360° transmission-phase coverage and is implemented as a 15 × 15 aperture. Under identical excitation, full-wave simulations show that the stratified-medium-compensated HMS redirects the transmitted power flow toward the prescribed superficial region and increases the local electric field by approximately 2.39-fold at z = 1 mm and 4.86-fold at the prescribed z = 5 mm target depth. The corresponding SAR decreases rapidly with penetration depth. Ex vivo pork measurements show temperature rises of 3.7, 2.3, and 1.6°C at z = 1, 3, and 5 mm, respectively, consistent with the predicted superficial-dominant deposition trend. These results support the use of stratified-medium-compensated HMSs for superficial microwave power deposition in layered lossy tissue.
In this letter, a compact high-gain full-space beam scanning leaky-wave antenna based on dual-layer spoof surface plasmon polaritons (SSPPs) is proposed. By exploiting the asymmetric characteristics of the dual-layer SSPPs unit, the proposed antenna enables independent eigenmode dispersion tuning and effective open-stopband (OSB) suppression, while maintaining mode-1-dominant propagation. Moreover, lateral slots are introduced to redistribute the surface current and stabilize the leakage characteristics near broadside. Compared with equal-length-stub SSPP units, the proposed unit provides a higher phase constant, leading to an enhanced scanning rate. The antenna is fabricated and measured, and the measured results agree well with the simulations. With an overall length of 5.23λ0, the antenna achieves continuous full-space beam scanning over 7.53 − 11.31 GHz with a scanning rate of 4.67°/%. The realized gain ranges from 8.28 to 11.32 dBi, corresponding to a realized gain per unit length of 2.01 dBi/λ0. Owing to effective OSB suppression, the gain fluctuation around broadside is less than 0.5 dB, while the radiation-efficiency variation is below 5%. In addition, the radiation efficiency exceeds 70% across the entire operating band, and the sidelobe level remains below −8 dB.
A low-profile broadband tri-polarized metasurface (MTS) antenna is proposed in this paper. First, the performance of a 4×4 MTS with square unit cells is analyzed. Next, by etching a circular patch at the center, an omnidirectional vertically polarized mode is tuned to a lower frequency by modifying the corner patches into extended sector-shaped structures. A second omnidirectional mode is then introduced by loading circular parasitic patches and shifted to the lower frequency by shorting pins. Finally, a feeding network is designed to excite a pair of horizontal polarized degenerate modes and two vertically polarized omnidirectional modes. To validate the design, the proposed antenna was fabricated and measured. The measured tri-polarized operating bandwidth is 2.4–3.73 GHz (42.6%), which covers the Wi-Fi 2.4 GHz band and the fifth-generation (5G) NR N41/N78 bands. With the aid of characteristic mode analysis (CMA), the proposed tri-polarized antenna combines the low-profile advantage of coplanar radiator designs with the wideband characteristics of stacked radiator designs. This makes it suitable for indoor communication applications.
This letter presents a sequential rotation (SR) fed circularly polarized (CP) antenna with integrated filtering and duplexing functions. Unlike conventional cascaded forms, the proposed design systematically integrates open-/short-circuited coupled lines and triple-mode resonators in the feeding network for stable sequential-phase outputs and dual-channel filtering; whereas the antenna element, formed by dual patches with an H shaped slot and metallic vias, provides wideband 45° linearly polarized radiation. A 2×2 array based on this feeding network was fabricated and measured. The prototype exhibits stable CP radiation in both the lower and upper bands, with two radiation zeros near each passband, which significantly enhance frequency selectivity. Measured results show that the lower band (centered at 9.1 GHz) achieves an impedance bandwidth of 11.8%, a 3-dB axial-ratio bandwidth of 16.8%, and a realized gain of 9.52 dBic; the upper band (centered at 10.9 GHz) achieves 13.5%, 10.5%, and 9.38 dBic.
This letter presents an ultrawideband (UWB), large-curvature, wing-borne conformal (WBC) phased array that simultaneously achieves dual-polarized (DP) endfire radiation and transition-band (TB) scattering grating lobes suppression (SGLS). First, the generation of the TB scattering grating lobe is analyzed, and an effective SGLS approach is developed by optimizing the inter-element spacing along the array arrangement. To achieve the horizontally polarized (HP) endfire radiation, a new dual-element endfire (DEE) conformal array arrangement is proposed, utilizing only two broadside-radiated tightly coupled dipoles per unit cell. Based on the SGLS-driven inter-element spacing and the DEE arrangement, the HP conformal dipole is constructed accordingly. Furthermore, novel resistive overlapping ladder rings (ROLRs) are integrated into the HP conformal dipoles to mitigate the severe low-frequency impedance mismatch induced by the large curvature wing-borne skin (approximately 160 m-1). To validate this design, a 1×7 array prototype is fabricated and measured. Experimental results demonstrate operation from 0.4 to 2 GHz with a ±60° azimuth scan range, DP endfire radiation, and effective SGLS over the 2–3 GHz transition band.
An all-metal transmitarray (TA) unit cell optimized for X-band high-power microwave (HPM) applications is proposed in this Letter. Based on the Pancharatnam-Berry (PB) phase principle, the unit cell achieves a controllable phase shift covering the full 360° range by rotating the ridged through-hole. Full-wave simulations indicate that the unit cell achieves a cross-polarized transmission coefficient of −0.04 dB under normal incidence and −0.09 dB under 25.6° oblique incidence at 8 GHz. To verify its practical performance, two TA lens prototypes combined with a radial line slot array (RLSA) antenna were designed, fabricated, and tested. Low-power experimental results indicate a maximum gain of 32.5 dBi, with a beam steering range of ±60° and an aperture efficiency of 70.4%. High-power experiments confirm that the TA can withstand HPM power levels up to 1 GW and no RF breakdown or pulse shortening is observed. These results demonstrate that the proposed all-metal TA unit cell has broad application potential for high-power spatial phase modulation.
To address the narrow impedance bandwidth of high-$Q$ magnetoelectric (ME) antennas, a three-port annular ME antenna combining azimuthal segmentation with local stepped loading is proposed. The three ports share a continuous monolithic laminate, in which selective Au and Al$_{2}$O$_{3}$ loading produces three frequency-staggered local resonances, while port selection provides continuous combined impedance coverage. A hierarchical design procedure is established: acoustic transit time determines the initial layer thicknesses, local sensitivity controls the resonance locations, modified Butterworth–Van Dyke (MBVD) fitting coordinates impedance matching, and a multiport model verifies coupling. At a simulated center frequency of 371.125 MHz, a continuous combined $-10$ dB impedance bandwidth of 4.315 MHz is obtained, with all interport transmission coefficients below $-35$ dB. A fabricated prototype achieves a measured continuous combined impedance bandwidth of 3.159 MHz centered at 384.493 MHz, demonstrating the feasibility of integrating multiple local resonances and realizing combined coverage within a continuous monolithic structure.
Programmable metasurfaces provide a flexible electronic stirring approach for reverberation chambers (RCs). However, the selection of their coding states still largely relies on time-consuming full-wave simulations or measurement-based optimization. This letter presents a fast coding-sequence screening framework for programmable-metasurface RCs. The metasurface stirrer is first approximated as an array of electric dipole sources, and the chamber field is evaluated using a periodic Green's function. The resulting solver is then used to generate training data for a convolutional neural network (CNN), which serves as a fast field predictor. By embedding the trained CNN into a genetic algorithm (GA), coding sequences with low field correlation can be efficiently identified. A 1-bit programmable metasurface stirrer is used for proof-of-concept validation. The proposed method agrees well with full-wave simulations, reduces the field-evaluation time from tens of seconds to milliseconds, and yields coding-sequence sets with better field uniformity than random coding. These results indicate that the proposed CNN-GA framework is an efficient tool for rapid coding design in programmable-metasurface RCs.
This study proposes a block-based method aiming to rapidly achieve low peak sidelobe level (PSLL) for large sparse arrays. In the proposed method, the array elements are partitioned into several blocks and optimized alternately, reducing both computational complexity and runtime. Then, a novel block-wise adaptive upper bound descent strategy is introduced to enable larger reliable updates and thereby achieve substantially faster convergence. To alleviate the limitations of block-wise optimization, a global reconstruction strategy is periodically applied after every few block-wise iterations. Consequently, the proposed method achieves a PSLL comparable to that of full global optimization at a fraction of the runtime. Numerical examples are provided to demonstrate the effectiveness and superiority of this method in the synthesis of large sparse arrays.
A frequency- and pattern-reconfigurable wearable textile antenna with wide frequency turning range for body centric communications is proposed in this letter. The antenna is capable of dynamically switching between an omnidirectional radiation mode for on-body links and a broadside radiation mode for off-body communications. The wideband frequency agility and pattern reconfigurability are realized by synergistically utilizing one coplanar and one vertical reconfiguration module. To achieve these features, for each mode one of the two modules effectively operates as a switch that selects between two adjacent tuning ranges, which are controlled by the other module. By controlling the bias voltages of the varactor diodes loaded on these modules, the proposed antenna achieves extensive continuous fractional frequency tuning ranges of approximately 70.0% (from 1.74 to 3.56 GHz) in the broadside mode and 46.9% (from 2.12 to 3.42 GHz) in the omnidirectional mode. Measurement performed on a prototype of the antenna validates the approach.
This letter presents an adaptive mesh refinement method for physical optics (PO) under near-field source excitation. The method employs a piecewise-linear representation of the complex surface current. A hierarchical current error indicator is constructed from the discrepancy between the current interpolated from each parent facet and the PO current independently evaluated at its virtual subdivision nodes, followed by local refinement using Dörfler marking. Numerical results demonstrate that the proposed method improves the accuracy of total-field patterns computed using a coarse PO mesh while requiring significantly less computation time than the multilevel fast multipole method (MLFMM).
