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The global fixed-time sliding mode control strategy is designed for the manipulator to achieve global fixed-time trajectory tracking in response to the uncertainty of the system model, the external disturbances, and the saturation of the manipulator actuator. First, aiming at the lumped disturbance caused by system model uncertainty and external disturbance, the adaptive fixed-time sliding mode disturbance observer (AFSMDO) was introduced to eliminate the negative effects of disturbance. The observer parameters can adaptively change with disturbances by designing the adaptive law, improving the accuracy of disturbance estimation. Secondly, the fixed-time sliding surface was introduced to avoid singularity, and the nonsingular fixed-time sliding mode control (NFSMC) design was put in place to ensure the global convergence of the manipulator system. Finally, the fixed time saturation compensator (FTSC) was created for NFSMC to prevent the negative impact of actuator saturation on the manipulator system, effectively reducing system chatter and improving the response speed of the closed-loop system. The fixed-time stability theory and Lyapunov method were exploited to offer a thorough and rigorous theoretical analysis and stability demonstration for the overall control system. Simulation experiments verify that the designed control scheme has excellent control effects and strong practicability. [ABSTRACT FROM AUTHOR]

A novel broadband circularly polarized square-slot antenna with parasitic elements is presented in this article. The proposed antenna with dimensions of 77.6 × 77.6 × 1.6 mm3 is composed of a L-shaped strip, a pair of rectangular slots, a L-shaped branch, and an inverted L-shaped feeding line. First, a pair of rectangular slots are used to excite an impedance resonance point that appears near 4.8 GHz and improve the axial ratio bandwidth (ARBW). Second, a L-shaped strip etched into the square-slot ground plane is used to enhance the ARBW. Third, a L-shaped branch is inserted into the inverted L-shaped feeding line to improve the impedance matching at high frequencies. At a result, the multiple circularly polarized (CP) resonant points could be excited by using these slot and strips as perturbation elements to alter the surface current distribution of the antenna. To demonstrate the design rationality, a designed antenna model is simulated, manufactured, and measured. The tested results show the proposed antenna has a wider −10-dB impedance bandwidth from 2.6 to 6.6 GHz (86.9%) and a broad 3-dB ARBW from 2.35 to 5.80 GHz (84.7%). In addition, the measured peak gain of the antenna is 4.8 dBi. The presented antenna has a potential application value in C band wireless communication. [ABSTRACT FROM AUTHOR]

In this article, a novel wideband circularly polarized (CP) square‐slot antenna with perturbation elements is proposed. The antenna comprises of an inverted L‐shaped feeding line, pairs of corner cuts, a rectangular slot, and a semi‐elliptical patch. The numerous CP resonant modes were excited simultaneously using these slots and patches as perturbation elements. To verify this concept, an antenna prototype was built and tested. The measured results indicate the −10‐dB impedance bandwidth (IBW) is 69.2% (2.42–4.98, 3.7 GHz) and 3‐dB axial ratio bandwidth (ARBW) is 59% (2.58–4.74, 3.66 GHz). Furthermore, the measured peak gain is 4.3 dBi, and the gain variation within the certain bandwidth is less than 1 dB. Therefore, the presented antenna features wide CPBW and stable gain characteristics. [ABSTRACT FROM AUTHOR]

In this paper, a novel 2 × 2 square slot wideband circularly polarized antenna array (CPAA) is proposed. The antenna consists of a sequential rotation feeding structure, four asymmetric U‐shaped feeding strips and a slotted ground plane formed by four square slots with cut corners, four rectangular slots, and four L‐shaped strips. In contrast to the traditional L‐shaped feeding strips used in CPAAs, an asymmetric U‐shaped feeding strip is, for the first time, presented to improve the antenna performance. By using these strips and slots as perturbation elements, the slotted CPAA is able to stimulate multiple circular polarized (CP) radiation modes, resulting in wideband CP radiation. The measured results revealed that the 3‐dB axial‐ratio (AR) bandwidth for AR < 3 reached 81.3% (1.75–4.15 GHz), whereas the −10‐dB impedance bandwidth (|S11| < −10 dB) reached 88.6% (1.96–5.08 GHz). [ABSTRACT FROM AUTHOR]

In this article, we propose a wide square-slot CPA loaded with a semi ellipse patch. The proposed antenna consists of a sequential rotation feeding structure, a square-slot ground-plane with corner cuts, and an asymmetric U-shaped feeding strip. In contrast to the traditional strips and slots etched into the square-slot ground-plane, semi ellipse patch is first inserted into the ground-plane to increase the antenna bandwidth. In addition, four rectangular slots are used to adjust the impedance matching. The slot CPAA could excite multipole CP resonant modes using these slots and patches, which result in the wideband radiation. The proposed slot CPAA has outstanding characteristics of 85.7% (2.0–5.0 GHz) −10-dB IBW and 68.3% (2.20–4.48 GHz) 3-dB ARBW, which would be a potential candidate in the wideband communication. [ABSTRACT FROM AUTHOR]