Abstract: This paper introduces a radar network measurement and control system based on CAN bus. The structure and basic principles of this CAN bus local area measurement and control network are analyzed, and the system hardware block diagram and software flow are presented. Experiments based on a certain type of radar show that the system has good reliability and accuracy. Keywords: CAN bus; radar; network; measurement and control system 1 Introduction With the rapid development of measurement and control technology, modern radar systems have increasingly higher demands for high-precision collaborative measurement, control , and tracking capabilities among multiple radars. However, most currently deployed radars do not possess this capability. Based on a certain type of radar, we developed a radar network measurement and control system based on the CAN bus. By installing this system on the radar, we constructed a local radar measurement and control network, realizing the sharing of target, status, and other related information among radars based on the CAN bus network. Using this information, the radars in the network can cooperate with each other, greatly improving the radar's detection and coordination capabilities. 2. Basic Structure and Principle of the Radar Network Measurement and Control System 2.1 Structure and Characteristics of the CAN Bus Measurement and Control Network Essentially, the radar network measurement and control system we designed belongs to a master-slave network test and control system. Compared with data networks, control networks have characteristics such as short data frames, frequent data exchange, and real-time constraints. At the same time, the electromagnetic environment of the radar itself is complex, and the relative distance is relatively long, all of which place high demands on the bus type used. In the past 20 years, control networks have developed rapidly, especially the fieldbus technology, which has formed a series of international standards. The CAN bus is one of the more influential fieldbus standards. The CAN bus is a multi-master serial communication bus with high bit rate, high resistance to electromagnetic interference, and the ability to detect various errors. When the signal transmission distance reaches 10km, CAN can still provide a data transmission rate of up to 50Kbit/s. At the same time, the CAN bus has high real-time performance and is widely used in industrial control, security protection, and other fields. Therefore, we chose the CAN bus to build the network. Figures 1 and 2 show the connection relationship between the radar network measurement and control system and the CAN bus, and the interconnection topology between the radars, respectively. [align=center] Figure 1 Connection between the network measurement and control system and the CAN bus[/align] [align=center] Figure 2 Radar network topology[/align] 2.2 System Principle Similar to other network measurement and control systems, the main working basis of the radar network measurement and control system is the acquisition and sharing of relevant data. In this network, depending on the actual working environment and actual needs, each radar can work as an independent unit or as a node in the network. When a radar works as a node in the network, it can coordinate with other radars in the network to track data based on the shared data. Under normal circumstances, the radars in the network work as independent nodes, and each radar in the network is equal. When special targets or other situations requiring coordinated tracking of the same target by multiple radars occur, the radar operator can issue a command to the network to enter network operation mode through the radar network telemetry and control system. Upon receiving the command, other radars within the network can choose to continue working independently or enter the network for collaborative operation, depending on the specific situation of that radar. The radars in the network have a master-slave relationship; the radar issuing commands and data is the master radar, and the radar receiving shared data is the slave radar. A radar operating in network mode can also exit network operation at any time. 3. System Hardware Structure From the above analysis of the system principle, it can be seen that the key technologies in the design of this system mainly include: acquisition and sharing of radar and target information, calculation and correction of target data, and target tracking based on the correction data. The system hardware design is also based on this. Figure 3 shows the hardware design block diagram of the system. As can be seen from the block diagram, the system mainly consists of a microcontroller module, a radar interface module, a communication and control module, an axis-angle conversion module, and a human-machine interface. The system microcontroller module uses the high-performance 51-compatible core microcontroller W77E58 from Winbond to implement system control. This microcontroller has two independent serial ports for easy communication with peripherals. It supports clock speeds up to 40MHz and features a frequency multiplication mode, meeting the requirements for calculating target and control information. The radar interface module extracts relevant signals from the radar via a signal conversion circuit and sends them to the interface signal processing circuit. The radar's digital signals are primarily processed by a CPLD. We used Altra's CPLD chip, EPM7128. Its first function is as a signal multiplexer and interface buffer. When the control system state changes, it switches between different data bus states based on the radar's state, while simultaneously latching or buffering data from the radar and microcontroller, enabling the radar and microcontroller to exchange correct data. Its second function is to generate interface logic and control logic for the control system. Using the clock signal, various timing signals, and status signals from the radar, it generates interface control signals to control data exchange and state transitions. Simultaneously, based on the address and control signals from the microcontroller, it synthesizes various control logics for the control system. [align=center] Figure 3 System Hardware Block Diagram[/align] The communication and control module is the interface for the processed information to interact with this radar and other radars. The status and target data of the control system are output from the microcontroller's serial port and then converted via MAX232 to be displayed on the human-machine interface (HMI) module. Control information from the HMI is also transmitted to the microcontroller through this interface. The interconnection between the control system and the CAN bus is also via an RS-232 interface, with the CAN communication module handling the conversion between RS-232 and CAN protocols, thus enabling long-distance, real-time communication with the remote radar. The target distance information calculated by the control system is acquired by the radar via the CPLD, while the target angle information undergoes D/A conversion, voltage isolation, and smoothing by the control module before being sent to the radar's antenna control system, directly driving the radar to track the target. Two double-precision azimuth and elevation angle conversion modules are used for radar antenna azimuth and elevation angle data extraction. When the radar antenna is controlled by the control system, this module forms the feedback branch of the radar control closed loop. The human-machine interface (HMI) module serves as the interface between the operator and the control system. Data and status information from the control system are displayed through the HMI module. The operator completes the setup and operation of the control system through the HMI interface. When a state transition occurs or a communication or operational error occurs, the HMI will issue a prompt or alarm. 4 System Software Design The system software design mainly focuses on three parts: system state design, system transition process, and data communication and processing process. 4.1 System State Design State design mainly addresses the various operating states of the control system and the corresponding operations on the system hardware. The system primarily sets three main states: stand-alone operating state, active operating state, and passive operating state. Before the network is established, each radar operates in stand-alone operating state, with each radar within the network operating independently and having equal relationships with the others. Once the network is established, the radars within the network will have different priorities. Among them, the radar providing target and radar information has the highest priority and operates in the active operating state, while other radars within the network operate in the passive operating state. In active mode, the radar is responsible for organizing the entire radar network, sending various target parameters and radar status information to the network. Passive radars acquire target and radar information from the network and control their operation accordingly until the active radar is removed from the network or the operator forces it to exit. This master-slave working mode ensures high network reliability. 4.2 System State Transition Flow Design The transition flow design mainly refers to the process design where the system automatically or passively transitions between various states based on the characteristics and properties of the target, operator commands, and instructions from other radars within the network. Figure 4 shows the system software state transition flow. As can be seen from the figure, the stand-alone working state is the system's default state. After the network is organized, the radar will enter either an active or passive state. The active or passive state is dynamic; depending on the different characteristics of the target, instructions from the network, and operator commands, the radar can switch between active and passive states, ensuring that the network is always organized by a single active radar. [align=center]Figure 4 System Software State Transition Flow[/align] 4.3 Data Communication and Processing Flow The data communication and processing flow is also an important part of the system software design. Figure 5 shows this flow chart. As can be seen from the figure, the active state radar starts and controls the entire communication process. The active state radar sends target [align=center]Figure 5 Data Communication and Processing Flow[/align] and radar status data to the network. After receiving the data, the passive state radar preprocesses it and sends a response signal to the active radar. If the data received by the passive state radar is erroneous due to interference or other reasons, it requests the active radar to retransmit it in the response signal. When there are too many communication errors, the passive radar will report the errors through the human-machine module and request the operator to handle them. A custom communication protocol is used in the communication to ensure highly reliable encrypted transmission. 5 Experimental Conclusions We used three radars that had been modified by the radar network measurement and control system to conduct radar network measurement and control experiments. From the current experimental results, the modified radar can achieve better communication and data exchange with other radars and can achieve better state switching. When active radar tracks a specific target, passive radar can perform relatively accurate joint positioning and tracking, basically achieving the expected design goals. This project innovatively constructed a radar local telemetry and control network based on the CAN bus, realizing the sharing of target, status and other related information between radars, as well as the collaborative work of radars in the network, improving radar efficiency and filling a gap in this field. References [1] Chen Youping et al., Scientific problems and application prospects of networked control systems, Control and Decision, 2004 (9): P962-966 [2] Li Dongxia, Research on networked radar technology (Doctoral dissertation), Beijing Institute of Technology, February 2002 [3] Zhu Lili, Wang Chaoxi, Research on networked guidance radar technology [J], Modern Radar, 2003 (7): 1-3 [4] Zhu Fei, Li Guanghui, Chen Zhiying, Design of intelligent nodes for distributed control network based on CAN bus, Microcomputer Information, 2003 (01) [5] Merrill I. Skolnik. Radar Handbook (Second Edition) [M]. New York. McGraw-Hill, 1990