 Subjects -> AERONAUTICS AND SPACE FLIGHT (Total: 124 journals)
| A B C D E F G H I J K L M N O P Q R S T U V W X Y Z | | The end of the list has been reached or no journals were found for your choice. |
|
|
- The Journal of Miniaturized Air and Space Systems
-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Pages: C2 - C2
Abstract: null
PubDate:
MON, 24 FEB 2025 09:17:17 -04
Issue No: Vol. 6, No. 1 (2025)
- Cellular Connected UAV Anti-Interference Path Planning Based on PDS-DDPG
and TOPEM-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Authors:
Quanxi Zhou;Yongjing Wang;Ruiyu Shen;Jin Nakazato;Manabu Tsukada;Zhenyu Guan;
Pages: 2 - 18
Abstract: Due to the randomness of channel fading, communication devices, and malicious interference sources, uncrewed aerial vehicles (UAVs) face a complex and ever-changing task scenario, which poses significant communication security challenges, such as transmission outages. Fortunately, these communication security challenges can be transformed into path-planning problems that minimize the weighted sum of UAV mission time and transmission outage time. In order to design the complex communication environment faced by UAVs in actual scenarios, we propose a system model, including building distribution, communication channel, and antenna design, in this article. Besides, we introduce other UAVs with fixed flight paths and ground interference resources with random locations to ensure mission UAVs have better anti-interference ability. However, it is challenging for classical search algorithms and heuristic algorithms to cope with the complex path problems mentioned above. In this article, we propose an improved deep deterministic policy gradient (DDPG) algorithm with better performance compared with basic DDPG and double deep Q-network learning (DDQN) algorithms. Specifically, a post-decision state (PDS) mechanism has been introduced to accelerate the convergence rate and enhance the stability of the training process. In addition, a transmission outage probability experience memory (TOPEM) has been designed to quickly generate wireless communication quality maps and provide temporary experience for the post-decision process, resulting in better training results. Simulation experiments have proven that, compared to basic DDPG, the improved algorithm increases training speed by at least 50 %, significantly improves convergence rate, and reduces the episode required for convergence to 20 %. It can alsohelp UAVs choose better paths than basic DDPG and DDQN algorithms.
PubDate:
MON, 04 NOV 2024 09:19:03 -04
Issue No: Vol. 6, No. 1 (2024)
- A Low Profile Wideband Circularly Polarized Slotted Waveguide Antenna for
W-Band CubeSat Data-Links-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Authors:
Shilpi Singh;Shakti Singh Chauhan;Ananjan Basu;
Pages: 19 - 26
Abstract: This article presents a dual circularly polarized slotted waveguide leaky wave antenna for CubeSat communications at W-band. The proposed fully metallic, low profile, and high-performing antenna offers wideband operating bandwidth, which makes it suitable for space applications. To achieve circular polarization, an array of circular holes is perforated at an offset position from the narrow wall of the WR-10 waveguide. The prototype antenna provides a wide axial ratio bandwidth of 13% and an average half-power beamwidth of 4.5° on the elevation plane. At high frequencies, the thickness of the slot affects the emission through the slot, which is not typically encountered at low frequencies. Therefore, to increase the magnitude of the radiated power, the wall thickness of the hole is reduced. The proposed circular hole slotted waveguide antenna design provides superior tolerance, accuracy, and precision compared to any other structures. These characteristics eliminate fabrication challenges, especially within the W-band, and can seamlessly extend into the sub-THz domain as well. The proposed antenna is robust, easy to fabricate, and appropriate for integration into CubeSat. It can be adapted for W-band CubeSat LEO, intersatellite, and constellation missions.
PubDate:
TUE, 05 NOV 2024 09:16:50 -04
Issue No: Vol. 6, No. 1 (2024)
- Fragility-Rejection UAV Flight Control With Discrete-Time Constrained
Dynamics Endowing Preselected Qualities-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Authors:
Xiangwei Bu;Ruining Luo;Jiaxi Chen;Humin Lei;
Pages: 27 - 35
Abstract: Our objective is to explore a finite-time tracking control protocol with fragility-rejection for discrete-time systems subject to saturation constrained dynamics, specifically in the field of UAV flight control. This protocol is capable of imposing desired transient and steady-state behaviors on tracking errors, while introducing transformed errors utilizing finite-time performance functions and stabilizing them indirectly through feedback terms developed using these functions in a back-stepping-like control design. Our approach introduces a structure that distinguishes it from existing transformed-error-stabilization-based prescribed performance control (PPC) methods. Furthermore, we propose a compensated system to modify the final feedback term and address actuator saturation, effectively resolving the challenging fragility issue associated with existing PPC approaches caused by error fluctuation due to actuator saturation in discrete-time systems. Finally, comparative simulation results obtained for flight control applications validate the effectiveness of our design.
PubDate:
WED, 27 NOV 2024 09:17:19 -04
Issue No: Vol. 6, No. 1 (2024)
- An Assisted Method for Multitemporal SAR Image Registration
-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Authors:
Zhengyu Chen;Ruya Xiao;Xiaoyuan Gao;Dong Liang;Dezhi Zhang;Jingyi Sun;
Pages: 36 - 43
Abstract: Precise registration of multitemporal synthetic aperture radar (SAR) images is a crucial step in Interferometric SAR (InSAR) data processing and serves as the foundation for high-precision interferometric measurements. Regular SAR image registration methods rely on the coherence between images. However, when faced with decorrelation issues, these methods often fail to yield high-precision registration results, adversely affecting subsequent data processing and interferogram quality. In this article, we propose an assisted method for multitemporal SAR image registration that addresses the challenge. By introducing auxiliary scenes with favorable coherence conditions alongside the primary and secondary images, we establish a mathematical model for the assisted registration method based on geometric relationships. The registration precision of the assisted registration method is evaluated using three indicators: 1) consistency checks; 2) interferogram fringe quality; and 3) coherence coefficient distribution. Sentinel-1 SAR images of the mountainous area in southeastern China were used for the experiment, and results show that the offsets calculated using assisted registration method exhibit greater concentration, and root mean square errors (RMSEs) demonstrate improved accuracy in both range and azimuth directions compared to the regular method, with enhancements of 25.6% and 23.3%, respectively. Additionally, interferograms obtained from the assisted registration show clearer and more complete fringes in regions with low coherence. Notably, the number of samples with coherence coefficients exceeding 0.4 increased significantly by 58.1% in the assisted registration results. While the accuracy of the proposed assisted registration method is comparable to that of regular methods under high-quality conditions, it shows marked advantages in scenarios characterized by severe decorrelation.
PubDate:
TUE, 17 DEC 2024 09:20:15 -04
Issue No: Vol. 6, No. 1 (2024)
- A Wideband Flat Gain Circularly Polarized Transmitarray Utilizing LP-to-CP
Converter for Ka-Band CubeSat Applications-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Authors:
Javid Ahmad Ganie;Kushmanda Saurav;
Pages: 44 - 52
Abstract: This article presents a wideband millimeter-wave circularly polarized (CP) transmitarray utilizing the linear-to-circular polarization (LP-to-CP) converter for Ka-band CubeSat applications. The present design aims at combining the multiple band antennas into a single wideband design. The LP-to-CP converter employs a single-layer substrate, providing angular stability up to 50° and achieving a 3-dB axial ratio bandwidth of 29% over the frequency range of 29.5–39.5 GHz. The dimensions of the unit cell are $0.38\lambda \times 0.38\lambda \times 0.15\lambda $ , where $\lambda $ corresponds to a frequency of 30 GHz. A wideband 2-bit phase-quantized transmitarray is integrated with the proposed polarization converter, achieving the configuration of CP wideband transmitarray. The CP transmitarray is illuminated by a wideband linearly polarized (LP) Vivaldi antenna. The transmitarray surface consists of polarization rotating elements sized at $0.3\lambda \times 0.3\lambda \times 0.15\lambda $ ( $\lambda $ corresponding to a frequency of 30 GHz). This CP transmitarray antenna demonstrates an axial ratio and 1-dB gain bandwidth of 27.3% (29.5–39.5 GHz) and 24.5%(30–38.5 GHz), respectively, with a maximum gain of 21.4 dBic. Fabrication and measurements of both the LP-to-CP converter and the integrated CP transmitarray have been done. The simulated outcomes align well with the measured results.
PubDate:
MON, 23 DEC 2024 09:18:39 -04
Issue No: Vol. 6, No. 1 (2024)
|
Hybrid journal (It can contain Open Access articles)
