Radio Detection and Ranging or Radar are one of the Electronic Navigation equipment that plays an important role in shipping. Basically, radar functions to detect and measure the distance of an object around the ship. Besides being able to provide clues to the presence of ships, buoys, shore positions, and other objects around the ship, this tool can also provide bearing and distance between the ship and these objects.

From the understanding of radar above, radar is very useful to know the position of other ships so that it can help avoid/prevent collisions at sea. Radar will be very useful during bad weather, foggy conditions, and sailing at night, especially when navigational instructions such as beacons, buoys, hills or buildings cannot be visually observed.

The main advantage of the radar compared to other navigation equipment is in its operation, the radar does not require transmitter stations.

Basically, how radar works using the principle of electronic wave emission. Where using a special transmitter that will emit short radio waves in a narrow path (narrow beam) by a directional antenna.

The movement of the waves generated by the radio is assumed to move in a straight line at a constant speed and if the pulse of the wave sent hits a target such as a ship, the coast of an island, or other object, the radio wave will be reflected again and received back by the receiver unit on the transmitting ship. Immediately.


The reflected echo is called a radio echo. By measuring the time difference between transmitting and receiving echoes and knowing the speed of radio wave propagation, the distance between the ship and the target can be known. This distance information will be shown on the radar screen by a cathode ray tube (CRT).

The radio wave pulses emitted will experience twice the distance, namely the distance from the observership (own ship) to the target when transmitting and the distance to return to the receiver from the target.

To determine the distance and position of the target, only half the travel time is taken into account. The radio waves emitted by a radar transmitter (Radar transmitter) move quickly so that the measurement uses microseconds (m/?s).

The propagation of radio waves travels at a speed of 300 m/?s. To calculate the distance from the ship to the target is very easy for example; the interval between sending and receiving radio waves is 100 s, the distance to and from the radio waves is 100 x 300 = 30,000 m and the distance between the two ships is half that is 15,000 m = 8.1 nautical miles.

The minimum range of the radar is the same as the distance that can be seen by the human eye and the maximum distance depends on the type and capability of the radar. However, the target behind the angle will not appear on the radar.


Information on targets such as islands and ships on the radar screen is shown in the form of a Plan Position Indicator (PPI). With this method target information such as islands, other ships, etc. Around the observership can be shown on the radar screen. Time measurement on the radar begins with the start of a trigger signal which is sent to the transmitter (magnetron) and cathode ray tube (CRT).

The magnetron consists of a high-strength magnet that can produce vibrations and very high frequencies that are very much needed by radar. High frequency will only be obtained if the modulator sends voltage to the magnetron repeatedly with an interval of 0.05 – 1 ?s (microseconds).

At the time of transmitting, radio waves will be transmitted through an antenna (scanner) through a waveguide which is controlled by an electronic transmit/receive switch (T/R electronic switch). Likewise, at the time of reception, radio echoes will be received by the receiver via the T/R electronic switch.

The Ship’s Radar Functions Are As Follows:

  1. To determine the position of the ship from time to time. Determining the position of the ship with radar can be done in several ways, namely using a bearing with a bearing, using a bearing with a distance, and using a distance with a distance.
  2. Guiding ships in and out of harbors or narrow waters. In the Head-Up position, the radar is very effective and efficient to assist the captains or pilots in navigating their ships in and out of ports, rivers, or narrow shipping lanes.
  3. Help find the presence or absence of a collision hazard. By looking at the Cathoda Ray Tube (CRT) screen there is a reflection or echo from thick clouds.
  4. Help predict the rain through the ship’s trajectory. By looking at the radar screen (Cathoda Ray Tube) there are reflections or echoes from thick clouds.

Ship Radar Parts

According to Arso Martopo, Capt, (1992: 65) then the parts of the radar or transmitter and receiver of a ship’s radio set are built-in units which can be distinguished as follows:

  1. Main Consule Is a box that contains units – units consisting of a transmitter, receiver, and button transmitter-receiver.
  2. Aerial Unit Is a unit consisting of a waveguide, a reflector with a motor to rotate it, and various schematic elements.
  3. Display Unit on the Radar Is a unitary unit consisting of a Cathoda Ray Tube (CRT) and various control buttons, usually placed on the bridge.

This is about what is meant by radar and the function of the ship’s radar, which is electronic navigation equipment on board