Search Results (44)

Accurate Doppler frequency estimation for Low Earth Orbit (LEO)-based Signals of Opportunity (SoOP) positioning faces significant challenges from extreme dynamics (±40 kHz Doppler shift, 0.4 Hz/ms fluctuation) and severe SNR fluctuations induced by multi-beam switching. Empirical analysis reveals that phased-array beamforming generates three-tiered SNR fluctuation patterns during unpredictable beam handovers, rendering conventional single-algorithm solutions fundamentally inadequate. To address this limitation, we propose KDFE (KNN-Driven Fusion Estimator)—an adaptive framework integrating the Rife–Vincent algorithm and MLE via intelligent switching. Global FFT processing extracts real-time Doppler-SNR parameter pairs, while a KNN-based arbiter dynamically selects the optimal estimator by: (1) Projecting parameter pairs into historical performance space, (2) Identifying the accuracy-optimal algorithm for current beam conditions, and (3) Executing real-time switching to balance accuracy and robustness. This decision model overcomes the accuracy-robustness trade-off by matching algorithmic strengths to beam-specific dynamics, ensuring optimal performance during abrupt SNR transitions and high Doppler rates. Both simulations and field tests demonstrate KDFE’s dual superiority: Doppler estimation errors were reduced by 26.3% (vs. Rife–Vincent) and 67.9% (vs. MLE), and 3D positioning accuracy improved by 13.6% (vs. Rife–Vincent) and 49.7% (vs. MLE). The study establishes a pioneering framework for adaptive LEO-SoOP positioning, delivering a methodological breakthrough for LEO navigation. Full article

This paper presents a novel switchable branch-line coupler (BLC) designed to achieve variable phase shifts while maintaining a constant output power. The proposed design incorporates low stepwise phase shifters with incremental phase shifts of 10° to 20°, covering phase ranges from −3° to 150°. The initial structure is based on a 3 dB branch-line coupler with arm electrical lengths of 3λ_g/2. A novel delay line structure is integrated within the BLC arms, consisting of a λ_g/4 section bridged by a tapered stripline to accommodate a PIN diode switch, thereby altering the current path direction. Additionally, two interdigital capacitors (IDCs), uniquely mounted on a crescent-shaped extension, are implemented alongside the tapered line to elongate the current path when the PIN diode is in the OFF state. By controlling the PIN diode states, the delay time is differentially adjusted, resulting in variable differential phase shifts at the output ports. To validate the functionality, the proposed BLC was integrated with a two-element antenna array to demonstrate differential beam steering. The measurement results confirm that the phased array antenna can switch its main beam between −27° and 25° in the elevation plane, achieving an average realized gain of approximately 7 dBi. The BLC was designed and simulated using CST Microwave Studio and was fabricated on an RO4003C Roger substrate (ε_r = 3.55, 0.406 mm). The proposed design is well-suited for future Butler matrix-based beamforming networks in antenna array systems, particularly for 5G wireless applications. Full article

Terahertz reconfigurable reflectarray antennas (RRAs) hold significant promise for next-generation wireless communication systems by enabling dynamic beam control to mitigate severe path loss at high frequencies. This work presents a Complementary Metal-Oxide-Semiconductor (CMOS)-based RRA for terahertz amplitude control using tunable split-ring resonators. First, a terahertz switch in standard 65 nm CMOS process is designed, tested, and calibrated on the chip to extract the equivalent impedance, enabling precise RRA element design. Next, a reconfigurable element architecture is presented through the co-design of a split-ring radiator, control line, and a single switch. Experimental characterization demonstrates that the fabricated RRA achieves 3 dB amplitude variation at 0.290 THz with <8.5 dB element loss under 0.8 V gate bias. The measured results validate that the proposed single-switch topology effectively balances reconfigurability and loss performance in the terahertz regime. The demonstrated CMOS-compatible RRA provides a scalable solution for real-time beamforming in terahertz communication systems. Full article

Integrated sensing and communication (ISAC) can improve the energy harvesting (EH) efficiency of simultaneous wireless information and power transfer (SWIPT)-assisted IoT networks by enabling precise energy harvest. However, the transmit power is increased in the hybrid system due to the fact that the sensing signals are required to be transferred in addition to the communication data. This paper aims to tackle this issue by formulating an optimization problem to minimize the transmit power of the base station (BS) under a nonlinear EH model, considering the coexistence of power-splitting users (PSUs) and time-switching users (TSUs), as well as the beamforming vector associated with PSUs and TSUs. A two-layer algorithm based on semi-definite relaxation is proposed to tackle the complexity issue of the non-convex optimization problem. The global optimality is theoretically analyzed, and the impact of each parameter on system performance is also discussed. Numerical results indicate that TSUs are more prone to saturation compared to PSUs under identical EH requirements. The minimal required transmit power under the nonlinear EH model is much lower than that under the linear EH model. Moreover, it is observed that the number of TSUs is the primary limiting factor for the minimization of transmit power, which can be effectively mitigated by the proposed algorithm. Full article

Based on Digital Beamforming (DBF) technology, spaceborne SAR systems can achieve high-resolution and wide-swath (HRWS) imaging. When combined with reflector antennas, the DBF-SCORE (Digital Beamforming-SCan On REceive) system also features light weight and low cost, making it an important choice for spaceborne HRWS SAR. This paper firstly proposes an advanced Full-chain Real-time Internal Calibration (FRIC) scheme, where the calibration path covers the entire receive chain from the antenna feed port to the input port of the Analog-to-Digital Converter (ADC) and achieves high-precision internal calibration concurrently with data acquisition. Secondly, based on the L-band reflector antenna DBF-SCORE system architecture, the design of radio frequency (RF) front end, namely the Transmit-Receive-Calibration Module (TRCM), is carried out. We propose the implementation of azimuth encoding modulation of the calibration signal through periodic switch control within the TRCM. Subsequently, the calibration signal is extracted using waveform diversity technology and its Signal-to-Noise Ratio (SNR) is improved through azimuth coherent integration technology. In addition, a ground verification system is established using the TRCM to evaluate the comprehensive performance of transmitting, receiving, and real-time internal calibration. Experimental results verify the effectiveness of the FRIC scheme and provide valuable insights for future spaceborne DBF SAR systems. Full article

A medium- or large-scale receiving antenna array using digital beamforming can achieve high-resolution direction-of-arrival (DOA) estimation at the receiver. However, it typically suffers from high cost and complexity. This paper proposes an efficient reconfigurable digital beamformer that can achieve real-time angle estimation with high accuracy while making effective use of hardware resources. The digital beamformer operates in two modes: beamforming mode and angle estimation mode. In the angle estimation mode, the phase shift steps required for beam scanning can be flexibly adjusted according to the desired angular resolution. By dynamically switching operational modes and fine-tuning the granularity of processing tasks, this architecture maximizes the efficient use of Field-Programmable Gate Array (FPGA) resources, ensuring optimal performance and flexibility in real-time signal processing applications. Simulation results show that with an input signal-to-noise ratio of 10 dB, the beamformer can complete DOA estimation with an error of less than 1° within microsecond-level delay. Full article

Unmanned Aerial Vehicles (UAVs) are integral to the development of smart city infrastructures, enabling essential services such as real-time surveillance, urban traffic regulation, and cooperative environmental monitoring. UAV-to-UAV communication networks, despite their adaptability, have significant limits stemming from onboard battery constraints, inclement weather, and variable flight trajectories. This work presents a thorough examination of energy and spectral efficiency in UAV-to-UAV communication over four frequency bands: 2.4 GHz, 5.8 GHz, 28 GHz, and 60 GHz. Our MATLAB R2023a simulations include classical free-space path loss, Rayleigh/Rician fading, and real-time mobility profiles, accommodating varied heights (up to 500 m), flight velocities (reaching 15 m/s), and fluctuations in the path loss exponent. Low-frequency bands (e.g., 2.4 GHz) exhibit up to 50% reduced path loss compared to higher mmWave bands for distances exceeding several hundred meters. Energy efficiency (${\eta }_e$) is evaluated by contrasting throughput with total power consumption, indicating that 2.4 GHz initiates at around 0.15 bits/Joule (decreasing to 0.02 bits/Joule after 10 s), whereas 28 GHz and 60 GHz demonstrate markedly worse ${\eta }_e$ (as low as ${10}^{-3}$–${10}^{-4}\mathrm{bits}/\mathrm{Joule}$), resulting from increased path loss and oxygen absorption. Similarly, sub-6 GHz spectral efficiency can attain $4\times {10}^{-12}\mathrm{bps}/\mathrm{Hz}$ in near-line-of-sight scenarios, whereas 60 GHz lines encounter significant attenuation at distances above 200–300 m without sophisticated beamforming techniques. Polynomial-fitting methods indicate that the projected ${\eta }_e$ diverges from actual performance by less than 5% after 10 s of flight, highlighting the feasibility of machine-learning-based techniques for real-time power regulation, beam steering, or multi-band switching. While mmWave UAV communication can provide significant capacity enhancements (100–500 MHz bandwidth), energy efficiency deteriorates markedly without meticulous flight planning or adaptive protocols. We thus advocate using multi-band radios, adaptive modulation, and trajectory optimisation to equilibrate power consumption, ensure connection stability, and meet high data-rate requirements in densely populated, dynamic urban settings. Full article

Wireless Energy Transfer (WET) combined with Simultaneously Transmitting and Reflecting Reconfigurable Intelligent Surface (STAR-RIS) technology offers a promising approach to optimize the recharging of Internet of Things (IoT) devices. In this work, we propose the use of STAR-RIS in the WET context to enable efficient recharging of IoT devices, with the goal of minimizing the total system recharging time while ensuring that each IoT device meets its minimum energy requirement. The optimization is performed using the Particle Swarm Optimization (PSO) technique, including the beamforming configuration of the power beacon (PB) as well as the phase and amplitude coefficients of the STAR-RIS elements. We compare two STAR-RIS operating protocols: time switching (TS) and energy splitting (ES). Simulation results indicate that it is possible to charge devices efficiently using only statistical channel state information (S-CSI), even in the absence of direct link between the PB and the IoT devices. Full article

In this work, we unveil the advantages of synergizing cooperative rate splitting (CRS) with user relaying and simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR RIS). Specifically, we propose a novel STAR RIS-assisted CRS transmission framework, featuring six unique transmission modes that leverage various combinations of the relaying protocols (including full duplex-FD and half duplex-HD) and the STAR RIS configuration protocols (including energy splitting-ES, mode switching-MS, and time splitting-TS). With the objective of maximizing the minimum user rate, we then propose a unified successive convex approximation (SCA)-based alternative optimization (AO) algorithm to jointly optimize the transmit active beamforming, common rate allocation, STAR RIS passive beamforming, as well as time allocation (for HD or TS protocols) subject to the transmit power constraint at the base station (BS) and the law of energy conservation at the STAR RIS. To alleviate the computational burden, we further propose a low-complexity algorithm that incorporates a closed-form passive beamforming design. Numerical results show that our proposed framework significantly enhances user fairness compared with conventional CRS schemes without STAR RIS or other STAR RIS-empowered multiple access schemes. Moreover, the proposed low-complexity algorithm dramatically reduces the computational complexity while achieving very close performance to the AO method. Full article

In this study, we propose a smart transfer planer equipped with multiple antenna arrays to improve ground links for low Earth orbit (LEO) satellite communication. The STP features a symmetrical structure and is strategically placed on both ends of a window, serving both indoor and outdoor environments. Using the window glass as a medium, energy transmission occurs through a coupling mechanism between the planers. The design focuses on large array antenna design, beamforming networks, and coupler design on both sides of the glass. Beamforming networks enable the indoor and outdoor antenna arrays to switch beams in various directions, optimizing high-gain antennas with narrow beamwidths. Through electromagnetic induction and filter couplers, a robust signal transmission channel is established between indoor and outdoor environments. This setup significantly enhances communication efficiency, particularly in non-line-of-sight environments. Full article

In this paper, different concepts of reconfigurable RF-MEMS attenuators for beamforming applications are proposed and critically assessed. Capitalizing on the previous part of this work, the 1-bit attenuation modules featuring series and shunt resistors and low-voltage membranes (7–9 V) are employed to develop a 3-bit attenuator for fine-tuning attenuations (<−10 dB) in the 24.25–27.5 GHz range. More substantial attenuation levels are investigated using fabricated samples of coplanar waveguide (CPW) sections equipped with Pi-shaped resistors aiming at attenuations of −15, −30, and −45 dB. The remarkable electrical features of such configurations, showing flat attenuation curves and limited return losses, and the investigation of a switched-line attenuator design based on them led to the final proposed concept of a low-voltage 24-state attenuator. Such a simulated device combines the Pi-shaped resistors for substantial attenuations with the 3-bit design for fine-tuning operations, showing a maximum attenuation level of nearly −50 dB while maintaining steadily flat attenuation levels and limited return losses (<−11 dB) along the frequency band of interest. Full article

Wavelength selective switches (WSSs) are essential elements for wavelength division multiplexing (WDM) optical networks, as they offer cost-effective, high port-count and flexible spectral channel switching. This work proposes a new hybrid WSS architecture that leverages the beam shaping and steering features of uniform silicon nitride-based end-fire optical phased arrays (OPAs). By introducing beamforming to a WSS system, the spectral channels on the liquid crystal on silicon (LCoS) panel can be tailored and arranged properly, depending on the optical configuration, using the beam control capabilities of OPAs. Combining 3D-FDTD and ray tracing simulations, the study shows that, by reducing the input beam dimensions with proper sizing of the OPAs, the WSS design with a null-steering OPA layout and 4 × N_o switch size features increased spectral resolution. This extensive beamforming study on the steering-enabled layout reveals the acquirement of an even higher input channel number, matching the 8 × N_o WSS scheme, with flexible channel routing on the LCoS panel. Such implementation of beamsteerers can unlock an extra degree of freedom for the switching capabilities of hybrid WSS devices. The results show great promise for the introduction of OPAs in WSS systems and provide valuable insight for the design of future wireless communication links and WDM systems. Full article

Beam-switching antennas based on quasi-optical beamformers can provide cost-effective solutions for high-frequency communication applications. Here, we propose a wide-angle beam-switching planar lens antenna based on the recently presented virtual image lens. The antenna operates from 24 to 28 GHz and produces a beam that can be steered in a 100-degrees range in one plane with less than 2 dB simulated gain variation over the angular range and operational band. The performance of the presented antenna is similar to reported lens antennas with stable gain, but the proposed lens requires a smaller refractive index range to be realized, which alleviates the manufacturing. Full article

Optical beamforming in microwave photonics is promising for supporting broadband wireless communications. However, the current optical beamforming lacks freedom because of the fixed connection between radio frequency (RF) signal and antenna elements (AEs). This manuscript tackles this challenge by proposing a dynamical optical beamforming architecture that reconfigures the antenna subarray for signal transmission depending on the number of signals to be transmitted. The proposed architecture employs an optical switching and distributing network (SDN) to realize a flexible connection between signals and AEs. An instance of the proposed architecture in photonic integrated circuits, which enables three working modes and transmits four RF signals through sixteen AEs, was presented and numerically simulated. The optical field distribution and beam pattern plots illustrated the operational principle and validated the feasibility of the proposed SDN architecture. Furthermore, the impact of the introduced architecture on the signal amplitude–phase consistency and the comparison of the proposed dynamic architecture and conventional fixe architectures are analyzed and discussed. The results indicate that the proposed architecture exhibits variable beamforming gain with lower hardware complexity. Full article

In a beamforming circuit for a modern broadband phased-array system, high accuracy and compactness have received sufficient attention as they are directly related to side lobe level and fabrication cost, respectively. In order to meet the low phase error required, this paper proposed an ultra-broadband 6-bit digital step switched-type attenuator (STA) with capacitive/inductive compensation networks. Compared to the conventional methods, the proposed technique employs an improved simplified T-structure with capacitive compensation networks, which simultaneously achieves low insertion loss and high-accuracy amplitude/phase control. In addition, on-chip level shifting circuit is integrated to avoid complex control schemes. The strategy of prioritizing return loss is adopted to alleviate the performance degradation caused by impedance mismatch after cascade. As a proof-of-principle demonstration, a wideband 6-bit STA with core area of only 0.5 mm × 1.8 mm was designed via 0.15-micrometer GaAs pHEMT technology. It exhibits ultra-broadband operation with a 31.5 dB amplitude tuning range and a 0.5 dB tuning step. The insertion loss of the reference state is 4–5.3 dB. The return loss is better than 15 dB for all the 64 states. The RMS amplitude and phase errors are less than 0.2 dB and 2° over the 10 to 20 GHz. Full article