Radar

A

2

The Modulator

The next stage of a radar system is the modulator, which rapidly varies, or modulates, the signal from the oscillator. In a simple pulse radar system the modulator merely turns the signal on and off. The modulator should vary the signal, but not distort it. This requires careful design and engineering.

A

3

The Transmitter

The radar system’s transmitter increases the power of the oscillator signal. The transmitter amplifies the power from the level of about 1 watt to as much as 1 megawatt, or 1 million watts. Radar signals have such high power levels because so little of the original signal comes back in the return.

A

4

The Antenna

After the transmitter amplifies the radar signal to the required level, it sends the signal to the antenna, usually a dish-shaped piece of metal. Electromagnetic waves at the proper wavelength propagate out from the antenna as the electrical signal passes through it. Most radar antennas direct the radiation by reflecting it from a parabolic, or concave shaped, metal dish. The output from the transmitter feeds into the focus of the dish. The focus is the point at which radio waves reflected from the dish travel out from the surface of the dish in a single direction. Most antennas are steerable, meaning that they can move to point in different directions. This enables a radar system to scan an area of space rather than always pointing in the same direction.

B

Reception Elements

A radar receiver detects and often analyzes the faint echoes produced when radar waves bounce off of distant objects and return to the radar system. The antenna gathers the weak returning radar signals and converts them into an electric current. Because a radar antenna may both transmit and receive signals, the duplexer determines whether the antenna is connected to the receiver or the transmitter. The receiver determines whether the signal should be reported and often does further analysis before sending the results to the display. The display conveys the results to the human operator through a visual display or an audible signal.

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B

1

The Antenna

The receiver uses an antenna to gather the reflected radar signal. Often the receiver uses the same antenna as the transmitter. This is possible even in some continuous-wave radar because the modulator in the transmitter system formats the outgoing signals in such a way that the receiver (described in following paragraphs) can recognize the difference between outgoing and incoming signals.

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