Antenna Servo Research Articles

Re-Optimized Design for the ADR-Based Dual-Loop Controller of 100 m Class Aperture Radio Telescope

Pointing accuracy is a crucial performance index for a fully steerable large-aperture radio telescope and is subject to external and internal disturbances. Improvement of the antenna’s servo control performance is meaningful for pointing, especially for blind pointing of the antenna. This paper firstly establishes a multi-motor-driving four-degrees-of-freedom (DOF) model of an antenna servo system, then optimizes the original design consisting of the active disturbance rejection (ADR)-based velocity controller and lead–lag-based position controller, making the velocity controller a novel linear ADR-based controller coupled with a disturbance-velocity compensation (DLADRC) and the position controller the simplest proportional (P) controller. Simulation results based on a 100 m class radio telescope servo model indicate that the new control system’s velocity-loop response is smoother, the position-loop peak disturbance response is reduced by 17.8%, the position-loop dynamic performance with the short settling time and slight overshoot remains the same as the former PD-LADRC system, and the RMS pointing/tracking error is 2.16 arcsec under a mean wind of 3 m/s, less than the design specification of 2.5 arcsec RMS required.

Application of cell mapping to control optimization for an antenna servo system on a disturbed carrier

Abstract. The cell-mapping method, due to its global optimality, has been applied to solve multi-objective optimization problems (MOPs) and optimal control problems. However, the curse of dimensionality limits its application in high-dimensional systems. In this paper, the multi-parameter sensitivity analysis is investigated to reduce the parameter space dimension, which broadens the application of cell mapping to MOPs in high-dimensional parameter space. A post-processing algorithm for MOPs is introduced to help choose proper control parameters from the Pareto set. The proposed scheme is applied successfully in the control parameter optimization of an adaptive nonsingular terminal sliding-mode control for an antenna servo system on a disturbed carrier. Moreover, as the existing global optimal tracking control with an adjoining cell-mapping method may generate tracking-phase differences, an optimal-sliding-mode combined-control strategy is proposed. By using the combined-control strategy, the azimuth and pitch angles of the antenna system are controlled to catch up to a target trajectory with the minimum cost function and to keep high-precision tracking after that.

Active Disturbance Rejection-based Double-loop Control Design for Large Antenna's Servo System

Radio astronomical observations put stringent requirements on the tracking and pointing accuracy of radio telescope antennas. High inertia, low stiffness, underdamped, and multi-resonant frequencies of a large aperture radio telescope’s antenna make the high-accuracy control difficult. It is not easy to satisfy control performance using only conventional PID controllers. A low-order Active Disturbance Rejection-based double-loop controller for large antenna is designed in this paper and tested on the Green Bank Telescope model. First, the first-order Linear Active Disturbance Rejecting Controller (LADRC) cascading a first-order low-pass filter and a notch filter is designed for the antenna’s velocity loop to achieve the dual-objective optimal velocity tracking. Second, the position loop controller is designed to realize the antenna’s position-tracking control by combining the PD controller and a low-pass filter. Further optimization of the position-loop controller helps improve the dynamic performance of the system. The simulation results indicate that the response curves of the proposed PD-LADRC control are smother than those of the Quantitative Feedback Theory (QFT) based controller; the settling time of the PD-LADRC system is 10.1 s and reduces by about 8.2 s than that of the QFT. While using a better position controller reduces settling time to 5 s. The PD-LADRC system also has better wind-disturbance rejection; the worst disturbance response reduces at the gearbox by 68.3% and 60% at the dish, and the recovery time reduces by more than 15 s than the QFT-based controller. In addition, besides easier parameter tuning, the proposed PD-LADRC has better robustness to systematic parameter perturbations and minor tracking error rms in position tracking.

Using the Optical Pointing System to Build the Pointing Model of the Tianma 13 m Telescope

This paper describes the method of using the optical telescope to assist the Tianma 13 m radio telescope for pointing measurement and establishing the pointing error correction model. For small-aperture telescopes, there are few target sources for pointing and calibration, and it is difficult to establish a pointing model by radio method to cover the whole sky area. The Tianma 13 m radio telescope of Shanghai Astronomical Observatory is used to conduct optical-assisted pointing measurement research. A set of optical pointing system was installed on the back frame of Tianma 13 m antenna, which obtained a repeatable measurement accuracy better than 3”. In addition, through the analysis of the factors affecting the antenna pointing, a pointing error correction model containing 8 error terms, as well as the optical axis and electrical axis deviation models were established. The pointing model was brought into the antenna servo control system to cross-scan the calibration target radio source, and a pointing error of about 5” was obtained. This research can provide a reference method for high-precision pointing modeling.

Electromagnetic interference analysis and measures of the antenna servo system of ship-borne satellite communication

This paper analyzes the working principle of servo drive, introduces the interference source of electromagnetic interference, and summarizes the damage caused by electromagnetic interference. Based on the characteristics of the ship's electromagnetic environment, the suppression measures of the electromagnetic interference of the ship servo drive are proposed.

Observing the Microwave Radiation of the Sun during a Solar Eclipse with a Ground-Based Multichannel Microwave Radiometer

A ground-based multichannel microwave radiometer (GMR) is commonly used to observe the atmospheric radiation brightness temperature (TB) in order to retrieve atmospheric temperature and humidity profiles. At present, GMRs are used only in meteorology and climate monitoring. However, theoretical analysis showed that GMRs can be also used to observe the solar radiation. Therefore, we tried to improve the antenna servo control system of a GMR so that it could track and observe the sun, and the results showed that the GMR could respond to the variation of solar radiation. A further question was: can a GMR observe the variation of the sun during a solar eclipse? Fortunately, two solar eclipse events were captured by the GMR on 26 December 2019 and 21 June 2020 in Xi’an, China. We used the upgraded GMR to observe the variation of solar radiation during the two solar eclipses. The observation and analysis results showed that (1) the GMR could accurately track the sun and respond to the variation of solar radiation during the solar eclipse. We analyzed the variation features of the solar radiation by combining the solar phase during the two solar eclipses. (2) We found that the GMR could respond to the variation of the solar radiation arising from the Earth–Sun distance, and we further propose a novel method to measure the eccentricity of earth orbit with the GMR by using the passive solar observation. The results show that the eccentricity measured was 0.0169, which agreed quite well with the value of 0.0167 in the literature. (3) The average variation percentages of both the Earth–Sun distance and the intensity of the incident solar radiation throughout the year were estimated to be 3.44% and 6.6%, respectively. According to these results, the solar observation techniques can broaden the field usage of GMR.

Servo system control of satcom on the move based on improved ADRC controller

An improved active disturbance rejection controller (ADRC) based on particle swarm optimization (PSO) is proposed to solve the problems of control accuracy, response speed and parameter tuning in the current dynamic communication antenna servo system. Firstly, the models of antenna servo system and ADRC controller are established; Secondly, the structure of ADRC controller is simplified to reduce the parameters to be set in parameter setting; The particle swarm optimization algorithm is used to further adjust the relevant parameters in the original parameter setting method, and finally realize the control of the moving through antenna servo system. The simulation results show that compared with the control effect of traditional PID controller, the improved ADRC controller has the characteristics of small overshoot, fast response, high precision and strong anti-interference ability, and has good reliability and robustness.

Bi‐objective control design for vehicle‐mounted mobile antenna servo systems

This paper studies a high-performance control design for the servo system of a vehicle-mounted mobile satellite communication antenna. Considering the different requirements for tracking and disturbance attenuation in the servo system, a novel controller structure consisting of a central controller and a disturbance filter is proposed. Based on this controller structure, a bi-objective control design scheme is proposed: One is an optimal tracking design for the central controller, and the other is a disturbance attenuation design for the disturbance filter. It turns out that the resulting control system achieves an optimal tracking performance when the external disturbance is at a low level; meanwhile, the system achieves a robust disturbance attenuation performance when the disturbance is significant. Moreover, considering the trade-offs between performance and the robust stability of the closed-loop system, the weighting parameter selection in control design criteria is studied for a practical application. Furthermore, validation experiments and field tests are carried out to evaluate the effectiveness of this design, and their results show that the well-designed bi-objective controller significantly improves the dynamic pointing accuracy of the antenna in tracking a geostationary satellite when its carrier is driving off-road.

Measurement of Solar Absolute Brightness Temperature Using a Ground-Based Multichannel Microwave Radiometer

Ground-based multichannel microwave radiometers (GMRs) can observe the atmospheric microwave radiation brightness temperature at K-bands and V-bands and provide atmospheric temperature and humidity profiles with a relatively high temporal resolution. Currently, microwave radiometers are operated in many countries to observe the atmospheric temperature and humidity profiles. However, a theoretical analysis showed that a radiometer can be used to observe solar radiation. In this work, we improved the control algorithm and software of the antenna servo control system of the GMR so that it could track and observe the sun and we use this upgraded GMR to observe solar microwave radiation. During the observation, the GMR accurately tracked the sun and responded to the variation in solar radiation. Furthermore, we studied the feasibility for application of the GMR to measure the absolute brightness temperature (TB) of the sun. The results from the solar observation data at 22.235, 26.235, and 30.000 GHz showed that the GMR could accurately measure the TB of the sun. The derived solar TB measurements were 9950 ± 334, 10,351 ± 370, and 9217 ± 375 K at three frequencies. In a comparison with previous studies, we obtained average percentage deviations of 9.1%, 5.3%, and 4.5% at 22.235, 26.235, and 30.0 GHz, respectively. The results demonstrated that the TB of the sun retrieved from the GMR agreed well with the previous results in the literature. In addition, we also found that the GMR responded to the variation in sunspots and a positive relationship existed between the solar TB and the sunspot number. According to these results, it was demonstrated that the solar observation technique can broaden the field usage of GMR.

Improvement of center-correction reset between guide-model switching for shipborne radar

Antenna servo system of shipborne radar has added digital-guide model and mutual-guide model with the support of center correction in order to capture and track targets conveniently. However, the switching between these two models would create larger step change resulting from the non-reset of center-correction. To this point, this paper represents the working principle of digital guidance, mutual guidance and center correction, and analyses the reason of step change. Then an novel approach is presented to improve the reset of center-correction. The results of experiments indicate that it can avoid the step change caused by the existence of center-correction value, and it enhances the reliability of facility effectively.

Determination of Maintenance Time of Radar Seeker Based on ABC Method

According to the health state grade classification standard of seeker and the corresponding performance state description, the health state grade corresponding to the predicted value of performance index parameters of transmitter and antenna servo mechanism is evaluated. As a result, the health status grade of the seeker system is obtained. In order to determine the maintenance time of the seeker more accurately, the comprehensive performance index of the seeker in the stage of “deterioration” is divided by the application of ABC analysis rule. Finally, the best maintenance time of seeker is determined by calculation.

A Digital Implementation Method of Control Inner Loop of Ship-borne Servo System Based on PWM Power Amplifier

In order to realize the full digitalization and miniaturization of the ship-borne antenna servo system, a fully digital inner loop design method can be used to adjust the digital PID parameters through DA or AD conversion between signals. Large scale integrated circuits, such as PWM pulse width modulation amplifiers, can be used to achieve the desired antenna motion and response characteristics and achieve the acquisition and tracking of space targets and command control. The digital design scheme proposed below is simple, stable and reliable, and has certain universality.

Control Design of Antenna Servo Systems with Velocity Tracking Using LMIs

This paper considers controller design of large antenna servo systems, which is given by a new integral-type servo controller with gain-scheduled control for linear parameter-varying systems, while expanding to type-2 control with velocity tracking. An example of application is provided to demonstrate the effectiveness of the proposed method.

Variable step size tracking algorithm for the VICTS antenna

A variable step size tracking algorithm for the Variably Inclined Continuous Transverse Stub (VICTS) Antenna for Ku-band fixed-satellite service is proposed. The traditional step tracking algorithm is improved by using and the simulation analysis of the VICTS antenna to get the apposite step size. And the feasibility and superiority of the algorithm are verified by the failure rate of locking the satellite. The proposed algorithm provides a feasible method for the VICTS antenna servo system to achieve satellite communication on the move (SOTM).

Research on dynamic compensation method for nonlinear characteristics of large aperture antenna

The nonlinear characteristics are widely existed in all aspects of the Servo Drive System. The influence on pointing and tracking accuracy of high precision of large aperture radio telescope cannot be neglected. In this paper, the common non-linear characteristics are discussed, and the negative effects of these characteristics on the system are analyzed as well as the advantages and disadvantages of common non-linear compensation methods. Xinjiang 110-meter Radio Telescope (QTT) requires high pointing accuracy, which has high requirements for stability and reliability of equipment. Here, a non-linear dynamic compensation method is proposed to prevent the non-linear characteristics of antenna Servo Drive System, so as to reduce or eliminate the lag and error of tracking and pointing, improve the stability of the system and optimize the motion performance of large aperture antenna. Nonlinear dynamic compensation method has simple structure, strong robustness and high applicability. In this paper, the saturated non-linearity of large aperture antenna is simulated by combining computer simulation with semi-physical platform experiment. The actual compensation effect of the method is verified by taking the QTT antenna to be the controlled object. Finally, the further improvement direction of the non-linear dynamic compensation method is also discussed.

Design and performance analysis of a many-to-one configuration precise cable drive mechanism with high precision and large torque

Precise cable drive is a flexible frictional transmission method that transmits power from drive capstans to driven pulleys by a properly preloaded transmission medium. Since most of precise cable drive mechanism with high pointing precision proposed in previous studies suffer from low transmission stiffness and small output torque, this paper presents a novel many-to-one configuration precise cable drive mechanism (MCCDM) with high precision and large torque. The design methods of many-to-one configuration are studied including the system optimal design and cable wrapping design. The transmission characteristics of the developed configuration are analyzed, considering transmission capacity, transmission backlash, and transmission stiffness. The corresponding parameter sensitivities are also investigated. Moreover, a prototype of the MCCDM has been built, with which a series of experiments are carried out. It is noted that the developed mechanism has a motion range of ±2 rad. The steady-state error to a step reference of 1 rad amplitude is only 1.39 µrad and the position resolution is better than 0.5 µrad. This mechanism could achieve maximum output torque of 35 Nċm with compact size and light weight. It has reached a considerable toque-to-weight ratio of 8.997 N·m/kg. The experimental results show that the self-excited oscillation and backlash are dominant nonlinear effects in the MCCDM system. It shows that the self-excited oscillation is a function of the rotational displacement in such a system, with the highest peak at 0.1669 cycle/mrad and the amplitude of 34.63 µrad. The backlash could be measured about 60 µrad under exciting of a small amplitude and low frequency sinusoidal signal. The proposed technologies could have strong technological implications in some special applications such as antenna servo system.

Study on control strategies for an antenna servo system on a carrier under large disturbance

In this paper, control strategies and vibration isolation methods are investigated in order to enhance the attitude control accuracy of an antenna servo system on a carrier under large disturbance. First, the multi-body dynamical equations of the antenna servo system on a carrier incorporated with six wire-cable vibration isolators are derived. Then, an improved adaptive variable-rated exponential reaching law is proposed, and the non-singular terminal sliding mode control is designed based on the nonlinear multi-body model. Finally, simulations are carried out and results show that excellent control accuracies for both the azimuth and the pitch of the antenna can be achieved by the proposed control method, specifically with a shorten reaching time in the cases of holding a fixed angle and tracking a sinusoidal motion that is better than the existing adaptive variable-rated exponential reaching law. Furthermore, the six wire-cable vibration isolators with hysteretic characteristics of restoring forces are adopted that can effectively isolate the large disturbance transmitted from the carrier to the antenna servo system and are shown to be able to further improve the attitude control accuracy.

A Correction Method of Estimating the Pointing Error for Reflector Antenna

The pointing error caused by the structural deformation of large reflector antennas has become the most challenging problem of antenna servo control. Especially with the increase of the antenna diameter and the working frequency, environmental loads not only make the structure deformation more obvious, but also make the pointing accuracy influenced by deformation more sensitive. In order to solve this problem, accurately estimating the pointing error caused by the structural deformation is the key. Based on the dynamic model of antenna structure and the analyzing model of pointing error, using the displacement information of sampling points on reflector, this paper proposes a correction method to achieve the purpose of accurately estimating the pointing error caused by the structural deformation. Using a 7.3‐m Ka band antenna, the results show that the antenna maximum pointing error in theoretical model calculation is 0.0041° at 10m/s wind speed condition; however, the corrected pointing error would be about 0.0054° with considering the modeling error. After compensating the controller, the pointing error could be reduced to only 0.0008° and the performance of antenna pointing was improved.

Rapid Calculation Method Study and Realization for Wind Load of Ship-Borne Satellite Antenna

For antennas working in exposed environment, wind load is one of the main loads that must be taken into consideration. Wind load can not only directly impact on the structural strength of antenna, but also make actuating shaft of servo system bear wind torque disturbance which may indirectly affect the tracking accuracy of antenna servo system. This paper completed numerical computation on the wind loads of antenna at different wind speeds, angles of wind approach and angles of pitch based on method of computational fluid mechanics, hence the velocity fluid fields, pressure distribution on reflecting surface and moments of antenna under various posture situations were obtained and a sample database has been formed. According to the weather and ship navigation situation, rapid calculation of the wind load and moment born by antenna realized through ternary three-order curvilinear interpolation algorithm can effectively solve the problem of rapidly calculating the wind load of ship-borne satellite antenna. Moreover, with the sample database formed according to the images and moment data obtained from computation, the wind loads and moment parameters of antenna under all working conditions were obtained through ternary three-order interpolation algorithm, so as to realize the rapid calculation method for the wind loads of antenna under all working conditions.

Design of Radiation-Pattern-Reconfigurable Antenna With Four Beams

This letter presents a novel radiation-pattern-reconfigurable antenna that could operate in four directions without any antenna servo system. This is achieved by changing the wave director and wave reflector via appropriate p-i-n diodes. The reconfigurable antenna is incorporated within the four symmetrical wave detectors or wave reflectors to form the structure. The antenna can cover all directions in the azimuth plane ( $xy$ -plane) by controlling the states (on or off) of four p-i-n diodes. The achieved maximum gain of the antenna is 5.08 dB. A good agreement is found between the simulated and the measured results. Further advantages of the introduced antenna design are its easy fabrication process and its low cost.