Satcom-on-the-move Research Articles

0.78–1.22° RMS Phase Error, 0.14–0.32 dB RMS Gain Error, K-Band 4-Channel Phased Array Receiver IC for Satcom on the Move (SOTM)

0.78–1.22° RMS Phase Error, 0.14–0.32 dB RMS Gain Error, K-Band 4-Channel Phased Array Receiver IC for Satcom on the Move (SOTM)

Direct Closed-Loop Control Structure for the Three-Axis Satcom-on-the-Move Antenna

The traditional Satcom-on-the-Move (SOTM) mechanical structure consists of a dual-axis configuration with an azimuth axis and a pitch axis. In this structure, when the pitch angle is 90 degrees, the rotation of the azimuth axis cannot change the antenna’s direction. To solve this issue, a three-axis SOTM mechanical structure has been developed. The traditional three-axis SOTM servo control system adopts a closed-loop control scheme. In this scheme, due to the difficulty in directly obtaining the antenna’s rotation angle, the angles of rotation for each axis are typically selected to represent the antenna’s rotation angle. The closed-loop feedback includes the angles and angular velocities of the axes, which cannot completely capture the antenna’s motion state, essentially constituting an indirect closed-loop control. Addressing the shortcomings of this indirect closed-loop control, this paper first establishes the kinematic relations between the axes of the three-axis SOTM antenna using the Denavit–Hartenberg (DH) method. Subsequently, the relationship between antenna pointing and the rotational states of the three axes was derived using the Jacobian operator. Building upon this foundation, a direct closed-loop control structure for a three-axis SOTM antenna was designed. To enable the control system to achieve rapid convergence with minimal overshoot, an Active Disturbance Rejection Control (ADRC) algorithm based on smooth continuous functions is introduced as the inner and outer loop controller algorithms within the direct closed-loop control structure. To address the nonlinearity in the design scheme, a piecewise linearization method is proposed to reduce the demands on the microprocessor’s performance and enhance the engineering feasibility of the solution. Finally, the effectiveness of the proposed approach is validated through experiments. The experimental results demonstrate that compared to traditional indirect closed-loop control methods, utilizing the direct closed-loop control method for the three-axis SOTM antenna presented in this paper can lead to higher precision in pointing the antenna towards satellites and enhance communication effectiveness.

Distributed dynamic backup servo control for satcom-on-the-move systems

This paper proposes a distributed control system for the servo control of the Satcom-On-The-Move (SOTM) systems. The servo control system is designed based on a distributed structure, which divides the control system into four sub-systems according to their functions. Each sub-system is equipped with a dedicated controller, and the controllers are connected to sensors and actuators via a bus. The control tasks of each sub-system are carried out by their respective controllers. To mitigate the impact of controller failures on the control system during running, a backup sub-system is implemented, which dynamically adjusts its function and state to ensure the normal running of the control system. An analysis of the impact of the switch to the backup sub-system on the stability of the control system under fault condition is presented. Finally, experimental analysis is conducted, and the results demonstrate the feasibility and effectiveness of the proposed design.

Rapid Tracking Satellite Servo Control for Three-Axis Satcom-on-the-Move Antenna

To overcome the possible gimbal lock problem of the dual-axis satcom-on-the-move (SOTM) antenna, a three-axis tracking satellite SOTM antenna structure appears. The three-axis SOTM antenna is realized by adding a roll axis to the azimuth axis and pitch axis in the dual-axis SOTM structure. There is coupling among the azimuth axis, pitch axis and roll axis in the mechanical structure of the three-axis SOTM antenna, which makes the kinematic modeling of the antenna difficult. This paper introduces a three-axis SOTM antenna kinematic modeling method based on the modified Denavit–Hartenberg (MDH) method, named the new modified Denavit–Hartenberg (NMDH) method. In order to meet the modeling requirements of the MDH method, the NMDH method adds virtual coordinate systems and auxiliary coordinate systems to the three-axis SOTM antenna and obtains the kinematic model of the three-axis SOTM antenna. During the motion of the carrier, the SOTM antenna needs to adjust the antenna pointing in real time according to the changes of the location and attitude of the moving carrier. Therefore, this paper designs a servo control system based on the active disturbance rejection controller (ADRC), introducing a smooth and continuous ADRC fal function to enhance the tracking speed of the servo control system and reduce the overshoot of the output response. Finally, system experiments were carried out with a 60 cm caliber three-axis SOTM antenna. The experiment results show that the proposed servo control method achieves higher antenna tracking satellite accuracy and better communication effects.

Multi-Beam Satellite Seeking and Acquisition Method for Satcom-on-the-Move Array Antenna on a High Maneuverability Carrier

When the carrier of the Satcom-on-the-Move (SOTM) antenna is in a high maneuvering state of motion, the accuracy of the array antenna beam pointing towards the satellite may decrease, which may cause a decline in communication effectiveness for SOTM or even cause the antenna to deviate from the target satellite and lead to communication interruption. This paper proposes a multi-beam searching and capturing method for SOTM array antennas, which divides the array antenna into multiple parts to form multiple independent and controllable sub-beams. When the SOTM carrier is in a high maneuvering state of motion, multiple sub-beams are obtained by dividing the array antenna, thus obtaining multiple points in the radiation pattern. We designed an optimal pointing analyzer, which calculates the SOTM array antenna beam direction based on whether the SOTM antenna is pointing towards the satellite and utilizes different approaches for processing. Experimental verification was conducted for the proposed scheme. The experimental results show that if the antenna beam does not lose the satellite, the proposed scheme can obtain better communication quality compared to conventional schemes. If the SOTM antenna beam loses the satellite and causes communication interruption, the proposed scheme in this paper can capture the satellite faster than conventional schemes. The experimental results demonstrate the effectiveness of the proposed scheme.

A 35mW, 2.32dB NF, 1.1° Phase Error, 18-21.2GHz Beamforming Receiver IC for Satcom on the Move (SOTM) Phased Arrays

A 35mW, 2.32dB NF, 1.1° Phase Error, 18-21.2GHz Beamforming Receiver IC for Satcom on the Move (SOTM) Phased Arrays

A kinematic modeling scheme of three-axis "Satcom-on-the-Move" antenna based on modified Denavit-Hartenberg method

The current three-axes Satcom-on-the-Move(SOTM) antenna modeling method has some shortcomings, such as low model accuracy, poor portability and so on. In order to solve the above-mentioned shortcomings, a new modified Denavit-Hartenberg(NMDH) kinematics modeling scheme for the three-axes SOTM antenna was proposed. To overcome the modeling difficulties caused by the inherent mechanical structure of the antenna, and meet the requirements of the modified Denavit-Hartenberg(MDH) method, the virtual coordinate system and auxiliary coordinate systems are designed and added respectively on the basis of the MDH method, the forward kinematics model and inverse kinematics solution of the three-axes SOTM antenna are obtained. The correctness of the NMDH modeling scheme is verified by digital simulation. Finally, the system tests are carried out. The test results show that the NMDH modeling scheme proposed in this paper achieves good effect of antenna tracking satellite, and has stronger portability than the system identification modeling method commonly used in engineering.

A Compact and Simply-Constructed All-Metal Circularly Polarized Ridge-Waveguide Slotted Antenna Array for Vehicle Mounted Satcom on the Move (SOTM) Communication Application

In this paper, a novel circularly polarized (CP) ridge-waveguide slotted antenna array is proposed for vehicle used Satcom on the Move (SOTM) applications. The antenna array is designed closely following the required factors for generating the circular polarization. The proposed antenna array is constructed on a symmetrical single-ridge slotted waveguide. Each antenna element consists of a pair of inclined slots opened on the narrow walls, and longitudinal slots opened on the bottom of the U-shaped wall of the waveguide. The inclined slots and the longitudinal slots are able to radiate orthogonal electric-fields independently with a phase-difference of 90°. After a vector superposition in the far-field by using this design, the circular polarization could be realized with extremely low axial ratio theoretically. Several essential parameters affecting the CP performance are also studied in this paper. To verify the feasibility of the proposed approach, a four-element CP antenna array is simulated, fabricated and measured. Results show that the obtained prototype achieves a measured impedance bandwidth of 14.74% from 9.24 GHz to 10.71 GHz with S11 <−10 dB, and a 3-dB axial ratio bandwidth of 19.1% from 9.0 GHz to 10.9 GHz.

Synthetic Deviation Correction Method for Tracking Satellite of the SOTM Antenna on High Maneuverability Carriers

Using Satcom-On-The-Move (SOTM) antenna on moving carriers to track communication satellites is a rapidly developing technology. The normal running of the SOTM system requires its antenna beam to track the target communication satellite accurately at all times. However, due to the errors of the measurement system, tracking deviation will inevitably occur, especially when the moving carrier is in ahigh maneuvering state, which may cause communication failures. In this paper, we propose a synthetic deviation correction algorithm; when the carrier is in the high maneuvering state, the measurement error is converted into the deviation of the azimuth as well as the pitch of the antenna that needs to be corrected to correct the pointing of the SOTM antenna. Finally, the proposed algorithm is verified by experiments. The experimental results show that the proposed algorithm has a good isolation effect on the high maneuverability of the carrier, which means that the pointing to the communication satellite is more accurate and achieves better communication quality under the high maneuvering state. The effectiveness of the algorithm is illustrated.

A Novel Method of Parallel Computing Based North-Finding of the Satcom-On-The-Move System and Its Simulation

This paper presents a new north-finding method of the Satcom-On-The-Move (SOTM) system based on parallel computing. The characteristic of this method is that sets a range for the existence of north-pointing true value according to a piece of initial north-pointing information, selects several equally divided north-pointing value within this range. Take the value of each point as multiple initial north-pointing information, then calculate the position information accumulated over time, and compare the calculated position information with the position information obtained by the Global Navigation Satellite System (GNSS). Gradually reduce the value range of the true value of the north-pointing information until the position information obtained with the GNSS is less than a certain error range, then the initial north-pointing information value of the minimum error is obtained, which is approximately equal to the accurate value of the north-pointing information. The proposed algorithm is verified by a simulation case, and the simulation results show the effectiveness of the proposed algorithm.

Compact 2 × 2 Circularly Polarized Aperture-Coupled Antenna Array for Ka-Band Satcom-on-the-Move Applications

This paper presents a novel design of a wideband circular polarization 2 × 2 microstrip antenna array working at Ka-band frequencies, from 27.5 to 31 GHz. This module is highly integrable with new silicon beamformer chips, creating a unit cell that can be part of a large electronically steerable antenna for compact, ultra-low-profile, Satcom-on-the-move (SOTM) platforms. A multi-layer structure fabricated in standard printed circuit board (PCB) technology with high-yield substrates has been used. The radiating elements consist of double-stacked circular patches housed in a cavity and fed by H-shaped aperture coupling. It achieves a bandwidth of 16.5 % with a wide beam-width of 95° in the desired band, which is necessary for wide scanning angles in a large phased array. In the 2 × 2 unit cell, the antenna elements are distributed by means of a sequential rotation technique where the separation between two of them is 5.3 mm in the XY-plane. Broadside beam-widths ranging from 53.4° at 27.5 GHz to 42.1° at 31 GHz are achieved, with boresight directivities from 10.7 to 12.9 dBi, respectively, in both the RHCP and LHCP polarization. Moreover, mutual coupling levels below −20 dB and an axial ratio less than 3 dB in the whole band guarantee a good circular polarization purity.

A 1024-Element Ku-Band SATCOM Dual-Polarized Receiver With &gt;10-dB/K G/T and Embedded Transmit Rejection Filter

This article presents a 1024-element dual-polarized Ku-band (10.7–12.7 GHz) satellite communication (SATCOM) receive (RX) phased array. The array consists of four 16 $\times16$ subarray tiles, each of which comprises 64 eight-channel beamformer chips, 256 dual-channel low-noise amplifiers (LNAs), and 256 dual-polarized antennas built on an affordable printed circuit board (PCB). The antennas spaced at $\lambda $ /2 spacing at 12.2 GHz in an equilateral triangular grid allow scanning up to x±70° in all planes while maintaining a cross-polarization level $ dB. The use of LNAs just after the antennas enables a low-noise operation with an antenna gain-to-noise temperature (G/T) of 10.5 dB/K ( $T_{\mathrm {ant}} =20$ K) at broadside while maintaining a directivity of 34 dB at 11.7 GHz. Also, a two-pole/two-zero filter is placed between the LNA and the beamformer chip to greatly attenuate any transmit leakage signal at 14–14.5 GHz. The lightweight, low-cost PCB with all silicon chips and a thickness of 3.4 mm presents a viable candidate for Ku-band SATCOM ground and Satcom-On-The-Move (SOTM) terminals.

A 256-Element Ku-Band Polarization Agile SATCOM Transmit Phased Array With Wide-Scan Angles, Low Cross Polarization, Deep Nulls, and 36.5-dBW EIRP per Polarization

This article presents an ultralow-profile and lightweight Ku-band transmit phased array with 256 dual-polarized antenna elements for SATCOM on-the-move (SOTM) terminals. The antennas are placed in a square grid with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula> /2 spacing at 14 GHz. At normal incidence, the phased array results in a measured effective isotropic radiated power (EIRP) of 64.5 and 66.5 dBm at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\mathrm {1~dB}}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\mathrm {sat}}$ </tex-math></inline-formula> , respectively, per polarization. The measured patterns, in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$ </tex-math></inline-formula> - and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H$ </tex-math></inline-formula> -planes, show almost ideal patterns with a wide scanning range of ±60°, a 3-dB instantaneous bandwidth of 13.0–14.6 GHz, and a cross-polarization isolation of 27 dB up to ±45° and 23 dB at ±60° scan angles. In the circular polarization mode, the measured axial ratio (AR) is <1.1 dB at 14–14.5 GHz. The phased array is also capable of synthesizing deep nulls (−30 to −40 dB) over a wide range of angles, thereby reducing unintended radiation to geostationary orbit (GEO) satellites. Transmit noise analysis is presented and shows that the array signal-to-noise ratio (SNR) is dominated by the block upconverter (BUC) and not by the beamformers. An error vector magnitude (EVM) of 2.8%–3.5% was achieved over a wide scan range for QPSK, 8-PSK, and 16-PSK waveforms with 100-MHz bandwidth. The array near-ideal performance, compact size, low profile with 3.5-mm thickness, and ultralightweight of 212 g make it ideal for affordable Ku-band SATCOM terminals.

A 256-Element Ku-Band Polarization Agile SATCOM Receive Phased Array With Wide-Angle Scanning and High Polarization Purity

This article presents a Ku-band phased-array receive tile with 256 elements. The design is based on 64 dual-polarized beamformer chips assembled on a printed circuit board (PCB) with dual-polarized antennas and an integrated Wilkinson combiner network and can operate at any polarization (linear, rotated-linear, and circular). The 256 elements are spaced $0.52\lambda $ apart at 12.7 GHz in the $x$ - and $y$ -directions. The measured patterns show near ideal patterns with a wide beam scanning range of ±70° (V- and H-pol) and a high cross-polarization rejection of 27 dB. The array has a 3-dB instantaneous scanning bandwidth of 10.6–12.5 GHz. In circular polarization mode, the measured axial ratio (AR) is 0.5 dB at 11.75 GHz for both left- and right-hand circular polarizations. The tile design is scalable to allow large-scale phased-array construction with 1024 elements or higher. Extensive measurements are presented, showing the versatility of this approach. Also, the dual-polarization feeds can be optimized to result in very low cross-polarization for circular and slanted-linear polarizations at all scan angles. The array performance, compact size, ultralightweight of 258 g, and low profile with 3.5-mm thickness make it suitable for affordable mobile Ku-band SATCOM on the move (SOTM) terminals.

A Robust Multi-State Constraint Optimization-Based Orientation Estimation System for Satcom-on-the-Move

Current orientation estimation system (OES) approaches can meet the Satcom-on-the-move (SOTM) accuracy requirement in low dynamics using inertial measurement unit (IMU) without Global Navigation Satellite System (GNSS). However, the estimation accuracy will decrease significantly due to the influence of the high dynamics of the vehicle. This article addresses this issue by constructing a multi-state constraint optimization-based OES (MSCO-OES). Our first contribution is a high-precision incremental inertial constraint, which adds the influence of the earth's rotation to the rotation part of the pre-integration theory to maintain the integral gyro accuracy for a longer time. The second contribution is that the nonlinear optimization method is applied to orientation estimation, making better use of historical information and having higher estimation accuracy and robustness through batch optimization and iterating. In addition, we use the lie group theory to extend the weighted least square estimation algorithm to the manifold, which can update multiple historical states to the current state in real-time through incremental inertial constraints. Compared with state-of-the-art methods, the proposed orientation estimation method has higher estimation precision and a reasonable calculation amount. The performance of the proposed method is demonstrated by comparing tests and SOTM deploying tests. Several high-dynamic and long-range tests show that the proposed OES has acceptable orientation estimation precision and reliability, which meets the high-reliable SOTM system requirements.

Research on the Model of Formulating SOTM Satellite-switching Strategy Based on Probabilistic Visibility and Breadth-first Search

In order to let the Satcom-on-the-move (SOTM) users know the communication status of the current driving road in advance and avoid the blindness of the information transmission, a model of formulating SOTM satellite-switching strategy based on probabilistic visibility and breadth-first search is established. Firstly, through adapting JANUS visibility algorithm, a probabilistic visibility model based on terrain description error and interpolation algorithm is proposed to quantitatively represent the communication status of each road point on the whole road. Then, the breadth-first search algorithm is used to obtain the satellite- switching strategy on the condition of different satellite-switching time, and the appropriate satellite-switching strategy is selected for the user according to their requirements. Finally, the validity and practicability of the model are verified by an example.

A Nonlinear Observer for Attitude Estimation of Vehicle-Mounted Satcom-on-the-Move

In this paper, a low-cost attitude estimation system (AES) is designed to estimate the attitude information of the vehicle utilizing MEMS inertial measurement unit (MIMU) and single baseline global positioning system (GPS). The proposed AES adopts a nonlinear attitude observer to fuse different sensors and estimate the vehicle's attitude. With the help of single baseline GPS, a maneuver accelerations compensation algorithm is used to improve the accuracy of the attitude angles and gyro biases. Modified quaternions are also used for the attitude observer to separate the yaw angle from the gravity angles easily when the single baseline GPS information is absent. The proposed AES judges the maneuver state of the vehicle depending on a switch criteria and adjusts the gain of the observer during GPS outages. The rules can efficiently detect the maneuver state of the vehicle and make full use of the inertial sensor outputs than classical rules. The experimental tests show that the proposed AES has a good attitude estimation accuracy, which meets the requirements of the Satcom-on-the-Move (SOTM) systems.

Hybrid Beam Steerable Phased Array Antenna for Satcom OTM with 16 GHZ Feed Signal

Now a day there is a great demand for communication On the Move (OTM). OTM antenna is system which is mounted on a vehicle such as boat, train, car, flight, and this system is used to track the satellite link and maintain the link between the terminal and satellite even when the vehicle is moving. The antenna always steer to track the satellite link while motion. Phased array antenna with hybrid beam steering method is proposed in this paper to achieve effective communication. The beam Formed in phased array of 100 isotropic elements has a wide beam width. But, to fetch satellite communication applications, the beam width a narrow beam width is required. Hence a parabolic reflector is chosen to sharpen the beam. But, for the ease of simulation, in place of the array of antennas, a horn antenna design to operate at the same operating frequency, 16 GHz is given as a feed to the reflector antenna and the simulation is done using HFSS.

Pseudo-monopulse tracking method for low profile mobile satellite antenna system

A novel pseudo-monopulse tracking (PMT) method is presented for Ku-band Satcom-on-the-move (SOTM). An antenna architecture consisting of multiple distributed panels capable of moving back and forth mechanically is introduced firstly, which can effectively reduce the overall height. Two independent beams with hybrid beam steering approach are introduced to keep the excellent performance in terms of tracking accuracy and antenna gain over wide scan coverage. Then, a hybrid compensation method using switched delay lines and phase shifters is applied to solve the frequency scan effect. Finally, the tracking beam is sequentially scanned at a prescribed offset angle in different directions, and the pointing error is calculated by comparing the corresponding received beacon signal strengths. Simulation results confirm the veracity of the proposed tracking method.

A beam stabilization algorithm based on nonlinear observer for low cost satcom-on-the-move

A beam stabilization algorithm was proposed for low cost satcom-on-the-move (SOTM) to stabilize the vehicle-mounted antenna beam. The proposed algorithm utilizes the nonlinear observer to estimate the vehicle's attitude information based on inertial measurement unit. Then the estimated angles and angular velocities are used to stabilize the antenna beam. Experiment results show that the proposed algorithm can stabilize the antenna beam when the tracking information is available, indicating that it is competent to the SOTM system.