With the continuous development of modern science and technology, new types of nautical instruments and equipments based on the informationization platform are constantly emerging. These new equipments have realized data fusion and information sharing with marine radar. Electronic Position Fixing System (EPFS) usually adopts GPS, BeiDou, GLONASS, etc. to provide ship position and time reference data for radar. Vessel Speed and Distance Measuring Equipment (SDME) is generally a range meter, which provides vessel speed to the radar, and AIS provides target identification information to the radar, including vessel identification information, dynamic data, and navigational data. AIS provides the radar with target identification information, including ship identification information, dynamic data and navigational data, etc. Transmitting Heading Devices (THD), such as gyrocompass, provide the radar with the ship's heading. Electronic Navigational Chart (ENC) or other vector charting systems provide chart data to the radar. The radar provides images and tracking target data to the Voyage Date Recorder (VDR) for record keeping. Other sensors, such as the bridge watch alarm system, can also be connected with the radar to form a multi-functional, multi-mission, high-precision navigation information system.

Depending on the form of subassembly, basic radar equipment can be categorized into below-mast (commonly known as three-unit) radars and above-mast (commonly known as two-unit) radars. The main body of a below-mast radar is divided into three boxes: antenna, transceiver and display. Of these, the antenna is mounted on the main mast or radar mast, the display is mounted in the pilothouse, and the transceiver is usually mounted in the chart room or in an equipment compartment near the pilothouse. If the transceiver is integrated with the antenna base and mounted on the mast, it is called a mast-up type radar. Below-mast radars are easy to maintain and are more commonly used on larger ships, and their transmitting power is usually higher. Small and medium-sized ships often use the above-mast configuration, which has lower transmit power and lower equipment costs, but is relatively more difficult to maintain.

The composition of the marine radar system is more complex and can be divided into antenna unit, transceiver unit, processor unit, display unit, control unit and power supply. From a functional point of view, the transceiver unit can be subdivided into four parts: timer, transmitting system, receiving system, and duplexer. Figure 1-1-1 shows the system components of a Furuno radar model.

Figure 1-1-1 System Components of a Furuno Radar Model

(1) Physical security

High voltage is generated when the radar is in operation. When maintaining the equipment, the operator should first cut off the power supply and discharge the high-voltage components before overhauling. If electric work is required, protective measures must be taken beforehand to prevent high-voltage electrocution accidents and to avoid electromagnetic radiation injury. Due to the strong magnetic field around the magnetron, maintenance personnel should keep objects such as watches, cell phones and ferromagnetic objects away from the magnetron during operation.

(2) Equipment safety

In order to prolong the service life of the magnetron, it must be fully warmed up for at least 3min when it is turned on, especially in the case that the radar is not used for a long time when the ship is docked in port, or in the case of cold and wet weather, the warming up time should be prolonged appropriately. In order to protect the magnetic properties of permanent magnets, it is strictly prohibited to bring ferromagnetic objects close to the magnetron, and non-ferromagnetic tools should be used when disassembling. Usually, the magnetron spare parts come in a special box. When using the magnetron, make sure that the magnetron is kept at a distance of more than 10 cm from other ferromagnetic materials and that the distance between two spare parts is more than 20 cm.

(3) Magnetron replacement and “seasoned” operation

When replacing magnetron spares, it is necessary to “season” the new magnetron to increase the vacuum level inside the tube and to prevent the tube from firing and damaging the cathode during operation. The specific method of “seasoning” is: the radar is set to ready (Standby) state, maintained for more than half an hour, and then more than 10 min of launch operations. In this process, the operator should observe the magnetron current changes, pay attention to the phenomenon of the screen display, and listen to the tube work sound. If the ammeter pointer is stable and not jittery, the screen scans evenly, and the tube works without discharge sound, then the machine can be turned off, the high-voltage adjustment to the normal value, so that the radar launch. Confirm that the magnetron current is smooth, even scanning, no abnormal sound emission, “seasoned” operation is over. Otherwise, it is necessary to extend the warm-up time of the radar in the ready state. If conditions permit, it is best to rotate the spare magnetron every six months.

1. Working band
The radars used in commercial vessels are of two wavelengths, 3cm and 10cm. The frequency range of 3cm wavelength radars is 2.9-3.1 GHz, and the frequency range of 10cm wavelength radars is 9.3-9.5 GHz.As the radar is used for longer periods of time, errors in the frequency of the radar's transmissions will occur. For X-band radars, the frequency drift is usually within ±55 MHz.

2. Pulse width
The duration of the RF pulse oscillations during each radar transmit cycle is called the pulse width and is often denoted by the symbol τ . To meet the radar observation requirements, the transmit pulse width varies depending on the selected range. A radar usually has several pulse widths, ranging from 0.04 to 1.2 μs.

3. Pulse Repetition Frequency
The number of pulses per second emitted by the radar is called the pulse repetition frequency, which can be expressed as fr, PRF (Pulse Repetition Frequency) or PPS (Pulses Per Second), the reciprocal of which is the pulse repetition period T. Generally, the radar pulse repetition frequency is 400~4000 Hz.

4. Transmit power
Radars using the pulsed regime typically have a peak transmit power of 4 to 30 kW.

Duplexers are also called transceiver switches. Because radar uses a common antenna for transmitting and receiving, it is possible to burn out the front-end circuits of the receiving system if a high-power pulse from the transmitter leaks into the receiving system. When the transmitting system works, the duplexer will connect the antenna with the transmitting system; after the end of the transmitting, the duplexer will automatically disconnect the antenna from the transmitting system, and re-establish the connection between the antenna and the receiving system, so as to realize the transceiver sharing function of the antenna. Therefore, the duplexer can prevent the transmitting pulse from entering the receiving system and protect the receiving circuit. At present, the duplexer mainly uses ferrite circulator (Ferrite Circulator).

1. Waveguide

Waveguides, often referred to simply as waveguides, are rectangular hollow tubes made of brass or copper with a high degree of internal finish. 23 mm x 10 mm is used for 3 cm radars, and 72 mm x 34 mm for 10 cm radars. When installing the waveguide, it is important that the flat connector faces the antenna and the choke connector faces the transceiver. This ensures the electrical continuity of the microwave even if there is no physical contact between the connectors. The waveguide should also be installed with the following points in mind:

Figure 1-1-7 Waveguide and Waveguide Elements

• (1) Cleanliness check: Waveguide spares are fitted with sealing caps at both ends which need to be opened before use. After opening, the inside of the waveguide should be carefully inspected for cleanliness and, if necessary, cleaned with pure alcohol.
• (2) Length and attenuation: Waveguide has certain attenuation effect on microwave, so the installation length should not exceed 20m, and the number of curved waveguide should not exceed 5. Too long waveguide will cause a significant increase in signal transmission loss.
• (3) Soft waveguide contraindication: Since soft waveguides are prone to deterioration, they are not suitable for outdoor installation.
• (4) Flange orientation and protection: During installation, it is necessary to face the plane flange toward the antenna, the choke flange toward the transceiver, and install the watertight rubber ring. The connecting bolts must be firmly fixed, and the installation should be painted after completion to prevent rusting.
• (5) Watertight intrusion: To prevent antenna leakage from flowing into the transceiver, the transceiver waveguide exit should be covered with a mica sheet.
• (6) Bracket fixing: When installing the waveguide to avoid the waveguide to withstand excessive external forces, every 1 ~ 2 m need to install fixed bracket. In the position where the waveguide is easy to contact and collision, a protective cover should be installed if necessary.

1. Directional characteristics: The ideal radiation beam of a radar antenna has a symmetrical scallop shape. Theoretically, the directionality diagram is commonly used to describe the radiation performance of the antenna. Radar radiation flap, the radiation of the stronger beam is called the main flap, its output power accounted for the total radar radiation power of 90% or more. Symmetrically distributed around the main flap are many weak side flap radiation, generally does not have a significant impact on the radar observation.

2. Beamwidth: The beamwidth of the antenna is defined as the angle between two half-power points on the main flap. To ensure the azimuthal accuracy and azimuthal resolution for radar target detection, the antenna'sHorizontal beamwidth (HBW)It is very narrow, usually 1°~2°. In order to avoid losing the sea surface target when the ship is swaying and other harsh environments, the radarVertical Beamwidth (VBW)Larger, about 20° to 30°.

3. Gain: Antenna directionality can also be expressed in terms of gain. Antenna gain is defined as the ratio of the signal power density produced by the actual antenna to that produced by the ideal radiating unit at the same point in space under the condition of equal input power.

The radar receiving system has good selectivity, high gain, wide passband and dynamic range, which can extract the useful target echo with large intensity variation from the mixed interference clutter and noise background, and process and amplify it to output a clear video signal to the display device.

(i) Basic components of a radar receiving system

The Furuno FAR-2827 radar's receiving system is located in the upper half of its transceiver unit, as shown in Figure 1-1-10. Its receiving system consists of a microwave integrated amplifier and inverter (MIC assembly), an intermediate frequency amplifier circuit (IF circuit board), and an RF control circuit board (RFC power supply circuit board).

Figure 1-1-10 Furuno FAR-2827 Radar Receiver System

(ii) Main technical specifications of the radar receiving system

• 1. IF frequency: Depending on the manufacturer of the equipment, radar IF is commonly used at 30 MHz, 60 MHz or 45 MHz.
• 2. Sensitivity and magnification: Sensitivity is usually expressed in terms of the minimum discernible signal power, Prmin, which is typically 10-¹²~10-¹⁴ W. The IF amplifier is required to have an amplification factor of 120~160 dB。
• 3. passband: Also known as bandwidth. The wider the passband, the less signal distortion and the higher the observation accuracy, but the more difficult it is to maintain sensitivity.

Modern radars use high-quality flat panel monitors (such as TFT, OLED, etc.) as radar information processing display terminals. Marine radar monitor display content, including color charts (if connected to ECDIS), plotting graphics, radar target echo, AIS target icons and system operation menu. The radar display includes input/output (I/O) interface, video processor, information processor, main controller and integrated display and operation control terminal.

(i) Controller: The main controller is the control center of the information processing and display system, which usually adopts high-performance industrial CPU chip, and coordinates the work of various parts of the system under the cooperation of bus, memory and other related parts.

(ii) Input/output interfaces and video processors: The synchronization unit (earlier known as the delay line) serves to coordinate the display with the transmitter and to eliminate systematic ranging errors. The coordinate converter converts the video echo in polar coordinates to video in right-angle coordinates to realize rasterized display. Video processing includes rain and snow interference suppression, co-frequency interference suppression, trailing display, scanning correlation processing, echo expansion, etc.

(iii) Information processors: It is responsible for comprehensively processing the information of each sensor, realizing target tracking and information fusion, and providing collision avoidance support for mariners.

(iv) Integrated display and operation control terminals: The operator can use tools such as moving range marker circles (VRMs), electronic bearing lines (EBLs), distance and bearing measurements (EBRLs), and bow lines (HLs) at the terminal. The graphical identification of the measurement tools is shown in Figure 1-1-12.

Figure 1-1-11 Integrated display control terminal |

Figure 1-1-12 Measuring Tool Graphic Identity

The Furuno FAR-2328W Radar Processor chassis, shown in Figure 1- 1- 13, contains the motherboard, power supply, network (LAN) signal converter, fan, terminal board (TB board), fuse, etc. The AC power supply is 100~230 V AC; the DC power supply is 24 V DC; the standard monitor power supply parameters are 100~230 V AC. The AC power supply is 100 to 230 V AC; the DC power supply is 24 V DC; the standard monitor power supply parameters are 100 to 230 V AC; the optional HUB power supply is 100 to 230 V AC.

Figure 1-1-13 FURUNO FRA-2328W Processor Chassis

The radar I/O interface is responsible for receiving external data through the microcontroller, and the modulation rate sets the baud rate (4800~38400 bit/s) according to the port characteristics. The external devices are shown in Figure 1-1-14, including gyrocompass, AIS, GPS, tachymeter, ECDIS, AMS and VDR. The data needs to satisfy IEC 61162 and AD-10 Formatting requirements.

Figure 1-1-14 External Sensor Topology Diagram

(i) Input interface: Twisted shielded wires should be used for interconnection. Modern instruments tend to use RS-232, RS-422 and RS-485.

The input interface feeds sensor information into the radar system. If the format of the information does not meet the requirements of the radar equipment, it needs to be converted via the interface and the equipment should be interconnected using twisted shielded cable.

Most modern marine instruments use digital interfaces, which do not require format conversion and are relatively easy to connect. For the serial communication protocol extension interface adopted by the radar, the common serial interfaces can be divided into RS-232, RS-422 and RS-485, etc. Some radars are also equipped with USB interface for data communication. Take the FURUNO FAR-28×7 series radar interface as an example, as shown in Figure 1-1-15. FURUNO FAR-28×7 series radar adopts RS-485 transceiver to receive data from the first direction sensor, and its transmission rate can be selected as 4800 bit/s or 38.4 kbit/s, as shown in Figure 1-1-15(a). The radar is connected to a trip meter or other navigational instrument as shown in Figure 1-1-15(b). Some models of radar and ECDIS can be used as inputs to each other, as shown in Figure 1-1-15(c).

(ii) Output interface: The radar must at least output to the VDR RGB format (1280 x 1024 pixels)Analog video signal or Ethernet/DVI interface signal.

The output interface is used to transmit radar video information to other navigation equipment or systems. According to the IEC Radar Performance Test Standard, the radar must have at least an interface to output an analog video signal to the VDR in RGB format (1280 x 1024 pixels). If the radar's display performance is not compatible with the RGB format, a DVI (Digital Visual Interface) or Ethernet interface is required, and the network bandwidth should support the transmission of a complete radar screen shot at least every 15s.

(iii) Sensor connection failure: Faults will trigger the Alert Box. For example, inconsistent baud rate settings can cause abnormal data transmission.

A sensor data transmission failure will trigger a radar alarm and the Alert Window (Alert Box) will display the specific alarm message. Some of the alarm messages associated with the radar sensor connection are shown in Table 1-1-3.

Table 1-1-3 Furuno Radar Sensor Connection Related Alarm Information

(iv) Examples of radar interfaces:

When wiring a radar system, use the manufacturer's supplied wiring in preference or ensure that the wiring meets the basic requirements of the radar installation instructions.

Take SPERRY VISIONMASTER FT marine radar as an example, its sensor configuration and parameter settings are shown in Table 1-1-1. It should be noted that the baud rate should be set according to the requirement, if the baud rate setting is not consistent, it will lead to abnormal data transmission.

Table 1-1-1 SPERRY VISIONMASTER FT Radar Sensor Configuration and Parameter Settings

The I/O configuration of the Furuno FAR-2××7 series radar with some of the sensors is shown in Table 1-1-2. The power supply of the radar is required to power the processor, display, control unit and antenna. The automatic mapping function is integrated in the signal processing unit and the performance monitor is integrated in the antenna unit as an option. The radar's built-in switch function operates via a LAN connection.

RS-422 communication is used between the antenna unit and the processor unit at a rate of 115.2 kbit/s, and RS-422 communication is used between the processor unit and the control unit at a rate of 19.2 kbit/s, both using asynchronous communication. Up to 8 radars of the same series can be connected via the HUB-100. The Inertial Navigation System (INS) supports both LAN and serial ports (RS-422/4800).

bit/s) connection.

Table 1-1-2 Furuno radar with some sensorsI/O configure

According to the 1974 SOLAS Convention, ships of 3,000 gross tons and above are required to install at least two radar systems, at least one of which is X-band. Multiple radars can be fitted with an Interswitch Unit for image sharing. The system has a single fail-safe mechanism.

(i) Dual radar system: They are categorized into same-frequency (both X-band) and heterodyne (X- and S-band) configurations. Transmitters, antennas, and transmission lines must be interchanged as a unit in a heterodyne system. Switching is accomplished through the interchange device shown in Figure 1-1-16.

Figure 1-1-16 Dual Radar System Architecture

(ii) Multi-radar systems: Three or more sets of radars can be passed HUB-3000 Perform network configuration. The IP address, subnet mask and gateway must be set correctly. After changing the IP address, all radars and related equipment connected to the LAN need to be restarted.

Figure 1-1-17 Multi-Radar and ECDIS Network Configuration