Marine radar structure
- Feb 05, 2019 -
It usually consists of an antenna, a transmitter, a receiver, a display, and a power supply.
Early use of parabolic reflector antennas has now been replaced by waveguide slot antennas. Antenna radiation is dominated by horizontal linear polarization; in order to improve the radar's ability to detect rain and snow, some antennas are equipped with circular polarization devices. Transmit and receive generally use one antenna, which is converted by a duplexer (transceiver switch). The antenna is driven by a motor for a 360° continuous ring sweep. In order to ensure azimuth measurement accuracy and azimuth resolution, the antenna beam has a narrow horizontal width, and many 3 cm navigation radars are within 1°. In order to prevent the target from being lost when the ship is swaying, the vertical width of the beam is wide, about 25°.
Adopt a pulse system. The pulse width is approximately 0.05 to 2 microseconds. Short-range pulses are used in close-range gears to improve range resolution; long-range gears use longer pulses to increase the range of action. The working band is dominated by X-band (9320~9500 MHz) and S-band (3000~3246 MHz). The radars of these two bands are usually called 3 cm radar and 10 cm radar respectively. In the case of the same antenna size, the former has a higher azimuth resolution, which is advantageous for close-range detection; the latter is less interfered by rain and snow clutter and sea clutter, and the electromagnetic wave is less attenuated by the rain zone if it is launched. The same power, high sensitivity at a long distance, is conducive to long-distance detection. The radar installs both bands at the same time, which can be used to complement each other.
The direct mixing super-heterodyne type is adopted, and a wave interference suppression circuit and a rain and snow interference suppression circuit are provided. In order to prevent radar interference in the same band, some radars have anti-synchronous interference circuits. The transmitter and receiver are assembled in the same cabinet, collectively called the transceiver.
The position of the plane is measured by the distance azimuth polar coordinates, and the scanning line and the antenna are rotated synchronously, and there are several distance ranges available. The range can be measured by the active distance or fixed distance; the measured orientation can be an electronic bearing line or a mechanical azimuth circle. The high-brightness display that appeared in the 1970s can be used without a hood, and can be observed by several people in the normal light of the bridge during the day. Some use color displays to represent different content in different colors to make the screen more eye-catching.
Early converters for marine radars, inverters are now widely used, and there are also direct use of ships.
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