Antenna Pedestal Research Articles

Low-order finite element method for the static and vibration analysis of an antenna pedestal

In this work, an effective algorithm is developed for the static and vibration analysis of antenna pedestal, which can well balance the modelling efficiency and computational accuracy. At first, the antenna pedestal is discretized into a set of low-order tetrahedral elements that can be automatically generated. Then, the face-based smoothing domains are constructed based on the faces of the low-order tetrahedral mesh. With the help of strain smoothing technique, the system stiffness matrices are calculated in these smoothing domains and finally, the static and vibration responses of the antenna pedestal are obtained based on the related system equations. There is no need to add any penalty parameters or additional degrees of freedom. Numerical results demonstrate that the present algorithm can achieve much better accuracy and higher convergence rate than traditional FEM, which can be regarded as an efficient tool for the structural analysis of antenna pedestal.

Kinematic modeling and motion control of a parallel robotic antenna pedestal

AbstractThis paper deals with kinematic modeling and motion control of a novel antenna pedestal based on parallel robotic mechanism. Its active joints are two sliders equipped with DC motors on a circular rail. The synchronous and asynchronous motions of the two sliders enable the antenna to rotate in azimuth and pitch. In order to solve the problem of trajectory deviation caused by nonlinear friction and other uncertain disturbances, the structure of the antenna is described at the beginning, and then, the kinematic model is established based on geometry method. Then, the fuzzy PI (FPI) control system is designed based on the position feedback of the driving slider to realize the trajectory tracking of the desired curve. Finally, the parameters of the FPI controller are optimized and validated by Simulink simulation experiments. The tracking performance and the effectiveness of the control algorithm on prototype are verified by experiments of typical trajectory following control.

Pitch Angle Error Measurement Technology for Track and Control Equipment Based on Trajectory

Due to the large support span of the pitching mechanism of the Fork-arm antenna pedestal of large phased array track and control equipment, the antenna array was deflected downward by its self-weight load. When measuring the pitch angle error, the pitch axis and the normal pointing angle of the array fluctuated, which significantly interfered with the evaluation results of common measuring methods for pitch angle error such as electronic goniometer. In view of the above problems, this paper proposed a pitch angle error measurement technology of track and control equipment based on motion trajectory. In this method, Target point for measurement was set in the appropriate area of the end face of the array skeleton, and the laser tracker was used to track and capture the spatial coordinates and trajectory of the target point in the process of pitching motion. The geometric model of the pitch angle algorithm was constructed based on the circular motion trajectory, which eliminated the influence of the fluctuation of the pitch axis and the normal pointing angle of the array on the pitch angle. The pitch angle error algorithm and data processing model were established, and the programmed rapid calculation and evaluation of the pitch angle deviation of track and control equipment were realized.

Analysis of the PU-2UPS antenna parallel mechanism

In order to meet the requirements of the antenna pedestal for supporting and driving antenna to complete specific trajectory movement, the PU-2UPS parallel mechanism is proposed for antenna pedestal, where P, U and S represent the prismatic joint, universal joint and spherical joint, respectively. The screw theory is applied to analyze the mobility of the PU-2UPS antenna parallel mechanism (APM). Meanwhile, kinematic analysis of the mechanism is carried out based on the theory of twist and spatial acceleration. Based on the wrench and force balance relationship, the dynamic model of the PU-2UPS APM is established. Therefore, the actuation forces of each actuation joint are obtained. Afterward, the work-space of the PU-2UPS APM is constructed based on the boundary search method. Finally, the mathematical model of the PU-2UPS APM is established by MATLAB software, and the theoretical analysis of the PU-2UPS APM is verified by ADAMS software. The studies have been performed that the PU-2UPS APM is suitable for antenna pedestal in respect of mobility, kinematics and dynamics properties. This research results serve as a fundamental theoretical basis for design and analysis of the APM.

Topside radio frequency system consolidation with Gregorian parabolic antenna stacking

Shipboard platforms have numerous antennas crowding topside space. Consolidating these antennas would require having antennas with multi-frequency capabilities. A Gregorian parabolic stacked antenna provides multi-frequency capabilities on a single pedestal which reduces the number of antennas required on a US Navy shipboard platforms. This Letter depicts the simulated design and radiation pattern results of a 1.9 m Gregorian parabolic stacked antenna that is capable of operating at the X-, K-, Ka- and Q-band frequencies at VSWR values <2:1. These frequency band capabilities allow for satellite communication links where two antennas that are currently fielded are operating within. The dual Gregorian parabolic stacked antenna presented is capable of operating at the same frequencies on a single antenna pedestal which would reduce the number of antennas required on shipboard platforms.

Dynamic characteristics and influencing factors of azimuth axis of a new antenna pedestal

Based on the finite element method, the dynamic characteristics of the azimuth axis of an antenna pedestal were studied. With the help of modal analysis module of finite element software, the modal natural frequency and modal shape of the structure were obtained, and the influence of structural size parameters on its dynamic characteristics was also investigated. Through the research, it can be concluded that the first six natural frequency values of the azimuth axis are 220.21, 220.24, 1178.2, 1519.9, 1531.3, 1531.3 Hz. And the first six modes are shown as follows: the first and second order is the swing mode of the axis, the third order is the up and down stretching mode of the azimuth axis, the fourth order is the torsional vibration mode of the azimuth axis, and the fifth and sixth order are the first bending vibration mode of the azimuth axis. The first and second order natural frequencies of the axis decrease with the increase of size parameters d2 , l1 and l2 , and increase with the increase of size parameters d1 , d3 and d4 . The analysis results provide a theoretical basis for the optimization of the dynamic performance of the azimuth axis.

Static characteristics and influencing factors analysis of azimuth axis of a radar antenna pedestal

Azimuth axis is an important part of radar antenna support. Static characteristics were analyzed with the help of finite element software. And the stress and deformation distribution of the structure under the normal working load were obtained, and the influence of the size parameters of the azimuth axis structure on its static characteristics was also investigated. Through the analysis, it is found that the maximum stress value of the azimuth axis under the working load is less than the allowable stress of the material, and the strength meets the use requirements. With the increase of size parameter l3 and d11 , the maximum stress of the shaft decreases gradually, and increases with the increase of size parameter d32 . The analysis results provide data reference for further optimization of the azimuth axis.

Analysis and Correction of the Influence of Track Irregularity on the Antenna Pointing

According to the influence mechanism of the antenna track irregularity on the telescope pointing accuracy, the distribution of the track errors and their influence on the pointing of the Urumqi Nanshan 26 m telescope are reanalyzed after the antenna track was reformed by using the whole-body welding technology, and hereby the pointing error model is correspondingly revised. By using the moving least-squares method, the measured height errors of the antenna track plane are fitted with a closed curve, and the tilt of the antenna azimuth axis caused by the track irregularity can be determined accordingly. Comparing it with the measured deviation of the antenna azimuth axis caused by the deformation of antenna pedestal, it can be found that both deviations are strongly correlated. A new pointing error model is established in view of the gravity deformation of antenna pedestal, which includes the north-south and east-west components, as well as the antenna track irregularity. Finally, by scanning a known calibration radio source at different positions in the sky, the measured pointing errors are fitted with the new pointing error model. The result shows that the sinusoidal component of the model error can be well constrained by the new pointing correction model, indicating that the new model can reflect very well the antenna pointing error, and can amend it to a certain extend.

MIMO H∞ control of three-axis ship-mounted mobile antenna systems

ABSTRACTThe need for on-line information in any environment has led to the development of mobile satellite communication terminals. These high data-rate terminals require inertial antenna pointing error tolerance within fractions of a degree. However, the base motion of the antenna platform in mobile applications complicates this pointing problem and must be accounted for. Gimbaled motorised pedestals are used to eliminate the effect of disturbance and maintain uninterrupted communication. In this paper, a three-axis ship-mounted antenna on a pedestal gimbal system is studied. Based on the derived dynamic model of the antenna pedestal multi input-multi output PID and H∞ linear controllers are designed to stabilise the antenna to keep its orientation unaltered towards the satellite while the sea waves disturb the antenna. Simulation results are presented to show the stabilisation performance of the system with the synthesised controllers. It is shown through performance comparison and analysis that the proposed H∞ control structure is preferable over PID controlled system in terms of system stability and the disturbance rejection.

Modelling and stabilization of a three-axis ship-mounted mobile antenna system

A mobile satellite communication antenna is a device installed on a moving carrier for mobile satellite communication. Gimballed motorized pedestals are used to eliminate the effect of disturbance and maintain uninterrupted communication when the carrier is moving. Mobile satellite communication antennas are becoming increasingly more popular due many advantages of mobile satellite communication. In this paper, a three-axis ship-mounted antenna on a pedestal gimbal system is studied. We study the problem with a different perspective and method from the previous work for two-axis antenna pedestals. The former studies treat the subsystems to be isolated and design controllers separately, which neglect the coupling effects in the dynamics of two or three-axis antenna pedestal gimbals. We treat three sub-systems as a whole and derive the dynamic model of the system using the Newton–Euler method. Based on the dynamic model, linear PI controllers are designed to stabilize the antenna to keep its orientation towards the satellite. The design objective of the control system is to direct the on-board antenna toward a satellite and to keep its orientation unaltered despite the effect of sea waves disturbing the antenna. Simulation results are presented to show the stabilization performance of the system with the synthesized controllers.

Topology Optimization Design of Spacecraft Antenna Pedestal Structure under Random Excitations

The purpose of this paper is to demonstrate a topology optimization design of the spacecraft antenna pedestal structure to save the structural weight as well as maintain the dynamic performances. The dynamic responses under random acceleration excitations are analyzed firstly and then the peaks of acceleration response are equaled to be static inertial load in the topology optimization as an expedient method. The pseudo-density based topology optimization model considering stress under inertial load as constraint is then formulated, and then further detailed design of the pedestal is carried out according to the optimized structural topology. Compared with the initial design, the optimized structure is improved with the total weight saved and both the dynamic responses and static stress satisfied.

Optimization of Vehicle-Borne Radar Antenna Pedestal Based on Modified NSGA-II

This paper deals with application of Non-dominated Sorting Genetic Algorithm with elitism (NSGA-II) to solve multi-objective optimization problems of designing a vehicle-borne radar antenna pedestal. Five technical improvements are proposed due to the disadvantages of NSGA-II. They are as follow: (1) presenting a new method to calculate the fitness of individuals in population; (2) renewing the definition of crowding distance; (3) introducing a threshold for choosing elitist; (4) reducing some redundant sorting process; (5) developing a self-adaptive arithmetic cross and mutation probability. The modified algorithm can lead to better population diversity than the original NSGA-II. Simulation results prove rationality and validity of the modified NSGA-II. A uniformly distributed Pareto front can be obtained by using the modified NSGA-II. Finally, a multi-objective problem of designing a vehicle-borne radar antenna pedestal is settled with the modified algorithm.

Embedded System for the Command of a High-Gain Antenna Pedestal with GPS Coordinates

This paper develops and implements an embedded system for the command of a high-gain antenna pedestal. It is based on the use of GPS parameters transmitted by an aerospace vehicle via an RF link. These directional antennas allow to optimize the reception of high frequency radio link, increasing the scope and reducing the weight requirements of the onboard batteries. Equations are implemented by the system to transform GPS coordinates in pedestal commands.

Engineering Analysis and Research on Connection Plate of Vehicle Radar Antenna Pedestal

According to the usage of vehicle radar antenna pedestal connection plate, this article analyzes and compares the structure characteristic of welding and casting. We decide to adopt the casting structure and use cast aluminium ZL101A. Based on the connection plate of using conditions, we analyze the deformation and stress of connection plate by the finite element analysis software. The design is in line with the material allowable requirements and to meet the requirements of the system stiffness.

An Engineering Analysis and Research on Center Frame Structure Using Casting of Vehicle Radar Antenna Pedestal

According to the usage of vehicle radar antenna pedestal center frame, this article analyzes and compares the structure characteristic of welding and casting. We decide to adopt the casting structure and use special casting material ductile iron QT450-10. And we describe the casting material ductile iron QT450-10. Based on the center frame of using conditions, we analyze the deformation and stress of center frame by the finite element analysis software. The design is in line with the material allowable requirements and to meet the requirements of the system stiffness.

Structural Modeling and Analysis on Dynamic Characteristics of Antenna Pedestal in Airborne SAR

Structural Modeling and Analysis on Dynamic Characteristics of Antenna Pedestal in Airborne SAR

Modal and Transient Response Analysis for Complex Gear-Bearing System

The radar antenna pedestal is a complex gear-bearing system including three rotary motions, i.e. horizontal rolling, pitching rotation and azimuth rotation. In this paper, spring-dashpot elements and connection elements are applied to simulate gear meshing and bearing connection respectively. Moreover, the equivalent average stiffness and damping of teeth meshing and bearing connection are calculated. Then, quadrilateral shell elements, hexahedral elements, wedgy elements, connection elements and spring-dashpot elements are employed to build the finite element (FE) model of the gear-bearing system in Hypermesh software. Via intermediate file, the model is imported into ABAQUS software for modal analysis whose solutions agree well with experimental data. Then, impact acceleration is imposed on the three bolts of the underpan along the x-axis, y-axis and z-axis respectively. Dynamic stress distribution and regulation changing with time under impact load are obtained. From the numerical solutions, the regions where stress and deformation is lager are found. The method can provide significant reference to analysis and optimum design of the similar system.

Optical Measurements on Telstar to Determine the Orientation of the Spin Axis, and the Spin Rate

One plane mirror and two faceted mirrors were fitted to Telstar. A photoelectric telescope was mounted on a radar antenna pedestal. Appropriate recording gear was built. The 12-in. aperture Cassegrain photoelectric telescope could be pointed at the satellite directly from prediction tapes, and the pointing accuracy could on occasion be improved by homing on the microwave beacon on the satellite or by applying corrections from visual observation through other telescopes with apertures of up to 6 in. It has been possible to detect the flashes of sunlight reflected from the mirrors on Telstar at slant ranges up to 3,700 miles. Directly from pairs of these observations, or by combining this information with telemetry data from the solar sensors on the satellite, it has been possible to determine the orientation of the spin axis of Telstar and to examine how this is moving in time. This normal precession of the spin axis is due mainly to the interaction of the residual magnetic moment of the satellite with the magnetic field of the earth. It was also possible to study how the spin axis moved when the torque coil was operated. — Measurements have been made of the spin rate of the satellite and of its rate of decay. The spin rate will drop to 1/10 of its initial value in about 750 days. — Photographs of the glints have been taken, and a study is now being made of the feasibility of combining precise photoelectric observation of the time of the flashes with high-precision photographic observation of the instantaneous position of the satellite relative to the fixed star background.