What Is Radar
What Is Radar
What Is Radar
We can see objects in the world around us because light (usually from the Sun) reflects off them
into our eyes. If you want to walk at night, you can shine a torch in front to see where you're
going. The light beam travels out from the torch, reflects off objects in front of you, and bounces
back into your eyes. Your brain instantly computes what this means: it tells you how far away
objects are and makes your body move so you don't trip over things.
Radar works in much the same way. The word "radar" stands for radio detection and ranging
and that gives a pretty big clue as to what it does and how it works. Imagine an airplane flying at
night through thick fog. The pilots can't see where they're going, so they use the radar to help
them.
An airplane's radar is a bit like a torch that uses radio waves instead of light. The plane
transmits an intermittent radar beam (so it sends a signal only part of the time) and, for the rest
of the time, "listens" out for any reflections of that beam from nearby objects. If reflections are
detected, the plane knows something is nearbyand it can use the time taken for the
reflections to arrive to figure out how far away it is. In other words, radar is a bit like the
echolocation system that "blind" bats use to see and fly in the dark.
Whether it's mounted on a plane, a ship, or anything else, a radar set needs the same basic set
of components: something to generate radio waves, something to send them out into space,
something to receive them, and some means of displaying information so the radar operator can
quickly understand it.
The radio waves used by radar are produced by a piece of equipment called a magnetron.
Radio waves are similar to light waves: they travel at the same speedbut their waves are
much longer and have much lower frequencies. Light waves have wavelengths of about 500
nanometers (500 billionths of a meter, which is about 100200 times thinner than a human hair),
whereas the radio waves used by radar typically range from about a few centimeters to a meter
the length of a finger to the length of your armor roughly a million times longer than light
waves.
Both light and radio waves are part of the electromagnetic spectrum, which means they're made
up of fluctuating patterns of electrical and magnetic energy zapping through the air. The waves
a magnetron produces are actually microwaves, similar to the ones generated by a microwave
oven. The difference is that the magnetron in a radar has to send the waves many miles,
instead of just a few inches, so it is much larger and more powerful.
It transfers the transmitter energy to signals in space with the required distribution and
efficiency. This process is applied in an identical way on reception.
It ensures that the signal has the required pattern in space. Generally this has to be
sufficiently narrow in azimuth to provide the required azimuth resolution and accuracy.
It has to provide the required frequency of target position updates. In the case of a
mechanically scanned antenna this equates to the revolution rate. A high revolution rate
can be a significant mechanical problem given that a radar antenna in certain frequency
bands can have a reflector with immense dimensions and can weigh several tons.
It must measure the pointing direction with a high degree of accuracy.
The antenna structure must maintain the operating characteristics under all environmental
conditions. Radomes are generally used where relatively severe environmental conditions are
experienced.
The basic performance of a radar can be shown to be proportional to the product of the
antenna area or aperture and the mean transmitted power. Investment in the antenna
therefore brings direct results in terms of system performance.
Taking into account these functions and the required efficiency of a radar antenna, two
arrangements are generally applied:
the parabolic dish antenna and
the array antenna.
speed, range, bearing, closest point of approach (CPA, and time to CPA (TCPA). 4. The ability
to display collision assessment information directly on the PPI, using vectors (true or relative) or
a graphical Predicted Area of Danger (PAD) display. 5. The ability to perform trial maneuvers,
including course changes, speed changes, and combined course/speed changes. 6. Automatic
ground stabilization for navigation purposes. ARPA processes radar information much more
rapidly than conventional radar but is still subject to the same limitations. ARPA data is only as
accurate as the data that comes from inputs such as the gyro and speed log.
ARPA Features
Acquires up to 20 targets automatically
Movement of tracked targets shown by true or relative vectors (Vector length 1 to 99 min.
selected in 1 min steps)
Setting of nav lines, buoy marks and other symbols to enhance navigation safety
On-screen digital readouts of range, bearing, course, speed, CPA, TCPA, BCR (Bow Crossing
Range) and BCT (Bow Crossing Time) of two targets out of all tracked targets.
Audible and visual alarms against threatening targets coming into operator-selected
CPA/TCPA limits, lost targets, two guard rings, visual alarm against system failure and target full
situation
Electronic plotting of up to 10 targets in different symbols (This function is disabled when ARPA
is activated)
Electronic parallel index lines
Interswitching (optional) built in radar or ARPA display unit
Enhanced visual target detection by Echo Average, Echo Stretch, Interference Rejector, and
multi-level quantization
Stylish display
Choice of 10,25 or 50 kW output for X-band; 30kw output for S-band, either in the transceiver
aloft (gearbox) or RF down (transceiver in bridge)
Exclusive FURUNO MIC low noise receiver
DISPLAY CONTROLS
MODE PANEL HM OFF Temporarily erases the heading marker.
ECHO TRAILS Shows trails of target echoes in the form of simulated afterglow.
MODE Selects presentation modes: Head-up, Head-up/TB, North-up, Course-up, and True
Motion.
GUARD ALARM Used for setting the guard alarm.
EBL OFFSET Activates and deactivates off-centering of the sweep origin.
BKGR COLOR Selects the background color.
INDEX LINES Alternately shows and erases parallel index lines.
X2 ZOOM enlarges a user selected portion of picture twice as large as normal. (R-type only)
CU, TM RESET Resets the heading line to 000 in course-up mode; moves own ship position
50% radius in stern direction in the true motion mode.
INT REJECT Reduces mutual radar interference