Read the text and translate it: Radar

Radar is an object-detection system which uses electromagnetic waves—specifically radio waves—to determine the range, altitude, direction, or speed of both moving and fixed objects such as aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish, or antenna, transmits pulses of radio waves or microwaves which bounce off any object in their path. The object returns a tiny part of the wave's energy to a dish or antenna which is usually located at the same site as the transmitter.

Practical radar was developed in secrecy during World War II by Britain and other nations. The term RADAR was coined in 1940 by the U.S. Navy as an acronym for radio detection and ranging. The term radar has since entered the English and other languages as the common noun radar, losing all capitalization. In the United Kingdom, the technology was initially called RDF (range and direction finding), using the same initials used for radio direction finding to conceal its ranging capability.

A radar system has a transmitter that emits radio waves called radar signals in predetermined directions. When these come into contact with an object they are usually reflected and/or scattered in many directions. Radar signals are reflected especially well by materials of considerable electrical conductivity—especially by most metals, by seawater, by wet land, and by wetlands. Some of these make the use of radar altimeters possible. The radar signals that are reflected back towards the transmitter are the desirable ones that make radar work. If the object is moving either closer or farther away, there is a slight change in the frequency of the radio waves, due to the Doppler effect.

Radar receivers are usually, but not always, in the same location as the transmitter. Although the reflected radar signals captured by the receiving antenna are usually very weak, these signals can be strengthened by the electronic amplifiers that all radar sets contain. The weak absorption of radio waves by the medium through which it passes is what enables radar sets to detect objects at relatively-long ranges—ranges at which other electromagnetic wavelengths, such as visible light, infrared light, and ultraviolet light, are too strongly attenuated. In particular, there are weather conditions under which radar works well regardless of the weather. Such things as fog, clouds, rain, falling snow, and sleet that block visible light are usually transparent to radio waves. Certain, specific radio frequencies that are absorbed or scattered by water vapor, raindrops, or atmospheric gases are avoided in designing radars except when detection of these is intended.

Post-text exercises:

1. Put the words in the right order to make a sentence:

1. Or, of, in, off, the, any, dish, microwaves, their, radar, pulses, radio, antenna, waves, object, or, which, path, transmits, bounce. 2. Fog, sleet, are, to, such, clouds, and, visible, transparent, waves, as, rain, snow, that, such, falling, block, things, light, usually, radio. 3. In, are, not, the, as, the, receivers, always, same, radar, usually, location, but, transmitter. 4. Has, directions, signals, a, called, radar, in, radio, that, system, emits, transmitter, waves, radar, predetermined. 5. Radar, Britain, in, during, and, practical, II, nations, was, World, other, War, developed, secrecy, by. 6. Has, English, radar, noun, all, the, since, languages, losing, term, entered, and, the, capitalization, common, other, as, radar. 7. Reflected, desirable, are, make, the, towards, radar, as, radar, back, transmitter, that, work, signals, the, ones, make. 8. With, into, they, are, or, in, when, contact, usually, scattered, directions, these, an, reflected, many, come, object, and.

2. Fill in the blanks with the following words:

Common, Doppler, acronym, reflected, range, secrecy, signals, regardless, weak, conductivity

1. Radar is an object-detection system which uses electromagnetic waves to determine the …, altitude, direction, or speed of both moving and fixed objects. 2. The … absorption of radio waves by the medium through which it passes is what enables radar sets to detect objects at relatively-long ranges. 3. The radar … that are reflected back towards the transmitter are the desirable ones that make radar work. 4. The term radar has since entered the English and other languages as the … noun radar, losing all capitalization. 5. In particular, there are weather conditions under which radar works well … of the weather. 6. Although the … radar signals captured by the receiving antenna are usually very weak, these signals can be strengthened by the electronic amplifiers that all radar sets contain. 7. Radar signals are reflected especially well by materials of considerable electrical …. 8. If the object is moving either closer or farther away, there is a slight change in the frequency of the radio waves, due to the … effect. 9. Practical radar was developed in … during World War II by Britain and other nations. 10. The term RADAR was coined in 1940 by the U.S. Navy as an … for radio detection and ranging.

3. Complete the following sentences using active vocabulary:

1. … transmits pulses of radio waves or microwaves which bounce off any object in their path. 2. … are avoided in designing radars except when detection of these is intended. 3. The radar signals that are reflected back towards the transmitter are …. 4. Radar receivers are usually, but not always, in …. 5. …, or speed of both moving and fixed objects such as aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. 6. The object returns a tiny part of the wave's energy to a dish or antenna which …. 7. The weak absorption of radio waves by the medium through which it passes is …. 8. There are weather conditions under which …. 9. Some of these make the use …. 10. … in secrecy during World War II by Britain and other nations.

4. Say if the following statements are true or false:

1. The radar dish, or antenna, transmits pulses of radio waves or microwaves which bounce off any object in their path. 2. The weak absorption of radio waves by the medium through which it passes is what enables radar sets to detect objects at relatively-long ranges. 3. Radar receivers are usually, but not always, in the different location as the transmitter. 4. The radar signals that are not reflected back towards the transmitter are the desirable ones that make radar work. 5. There are weather conditions under which radar works well regardless of the weather. 6. Such things as fog, clouds, rain, falling snow, and sleet that block visible light are not usually transparent to radio waves. 7. The object returns a tiny part of the wave's energy to a dish or antenna which is not usually located at the same site as the transmitter. 8. If the object is moving either closer or farther away, there is a slight change in the frequency of the radio waves, due to the Doppler effect. 9. When these come into contact with an object they are usually reflected and/or scattered in many directions. 10. Although the reflected radar signals captured by the receiving antenna are usually very weak, these signals can’t be strengthened by the electronic amplifiers that all radar sets contain.

5. Answer the following questions:

1. What things are usually transparent to radio waves? 2. Are there weather conditions under which radar works well regardless of the weather? 3. What is a radar? 4. What transmits pulses of radio waves or microwaves which bounce off any object in their path? 5. Does a radar system have a transmitter or a receiver that emits radio waves called radar signals in predetermined directions? 6. Who coined the term RADAR? 7. In what year was the term Radar coined? 8. Was Practical radar developed in secrecy during World War II or World War I by Britain and other nations? 9. Where are radar receivers located? 10. What radar receivers are the desirable ones that make radar work?

6. Match the first part (1-7) of the sentence with the second part (a-g):

1. Phase in waves is …

2. Antenna array is …

3. An azimuth (pronounced /ˈæzɪməθ/ (listen)) (from Arabic السمت (as‑simt), meaning "direction") is … in a spherical coordinate system.

4. Frequency is …

5. Electronic noise is…

6. The radar dish …

7. Radar signals…

a) … the number of occurrences of a repeating event per unit time.

b) … an angular measurement

c) …a random fluctuation in an electrical signal, a characteristic of all electronic circuits.

d) … a group of isotropic radiators such that the currents running through them are of different amplitudes and phases.

e) …the fraction of a wave cycle which has elapsed relative to an arbitrary point.

f) … are reflected especially well by materials of considerable electrical conductivity.

g) … transmits pulses of radio waves or microwaves which bounce off any object in their path.

7. Read the supplementary text, translate and entitle it:

A phased array is a group of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired direction. Phased array transmission was originally developed in 1905 by Nobel Laureate Karl Ferdinand Braun who demonstrated enhanced transmission of radio waves in one direction. An antenna array is a multiple of active antennas coupled to a common source or load to produce a directive radiation pattern. Usually the spatial relationship also contributes to the directivity of the antenna. Use of the term "active antennas" is intended to describe elements whose energy output is modified due to the presence of a source of energy in the element or an element in which the energy output from a source of energy is controlled by the signal input.

Phased array radar systems are also used by warships of many navies. Phased array radars allow a warship to use one radar system for surface detection and tracking (finding ships), air detection and tracking (finding aircraft and missiles) and missile uplink capabilities. Prior to using these systems, each surface-to-air missile in flight required a dedicated fire-control radar, which meant that ships could only engage a small number of simultaneous targets. Phased array systems can be used to control missiles during the mid-course phase of the missile's flight. During the terminal portion of the flight, continuous-wave fire control directors provide the final guidance to the target. Because the radar beam is electronically steered, phased array systems can direct radar beams fast enough to maintain a fire control quality track on many targets simultaneously while also controlling several in-flight missiles.

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