Meteo

Radar Theory                                         

Radar term is the abbreviation of RAdio Detecting And Ranging, which it’s finding and positioning a target and determining the distance between the target and the source by using radio frequency.

                                      Figure 1. Simple overview of Radar Operation

Operation Principle of Radar

Operation principle of radar is very simple in theory and very similar to the way which bats use naturally to find their path during their flight (Figure 2). Bats use a type of radar system by emitting ultrasonic sounds in a certain frequency (120 KHz) and hearing the echoes of these sounds. These echoes make them enable to locate and avoid the objects in their path.

 

                               Figure 2. Bat using ultrasonic to detect an objects

In the radar systems, an electromagnetic wave generated by the transmitter unit is transmitted by means of an antenna and the reflected wave from the objects (echo) is received by the same antenna and after processing of the returned signal, a visual indication is displayed on indicators. After a radio signal is generated and emitted by a combination of a transmitter and an antenna, the radio waves travel out in a certain direction in a manner similar to light or sound waves. If the signals strike an object, the waves are reflected and the reflected waves travel in all directions depending of the surface of the reflector. The term reflectivity refers to the amount of energy returned from an object and is dependent on the size, shape and composition of the object. A small portion of the reflected waves return to the location of the transmitter originating them where they are picked up by the receiver antenna. This signal is amplified and displayed on the screen of the indicators, e.g. PPI (Plan Position Indicator). This simple approach can be achieved by means of many complex process including hardware and software components.

Block Diagram of Radar

Radar systems, like other complex electronics systems, are composed of several major subsystems and many individual circuits. Although modern radar systems are quite complicated, you can easily understand their operation by using a basic radar block diagram. Like it’s shown ai figure 3 below us.

  

                             Figure 3. Basic Block Diagram of Radar

A. Transmitter Assembly consist of 3 modules, that is Transmitter Module, Modulator and High Voltage Power Supply (HVPS).

     High Voltage Power Supply (HVPS) : module that serves to strengthen and refine the source of AC voltage into a DC high voltage to 4-7 kV which then becomes the source of input to the modulator. All the control and supervision necessary to operate and adjust the system lies in HVPS front panel. HVPS front panel is the starting point for identifying potential problems with the modulator during the radar operation. 

     Modulator: The purpose of modulator is to switch the transmitter ON and OFF and to provide the correct waveform for the transmitted pulse. That is, the modulator tells the transmitter when to transmit and for what duration.

     Transmitter Module : The source of the EM radiation emitted by radar is the transmitter. It generates the high frequency signal which leaves the radar.s antenna and goes out into the atmosphere.The transmitter generates powerful pulses of electromagnetic energy at precise intervals. The required power is obtained by using a high-power microwave oscillator (such as a magnetron) or a microwave amplifier (such as a klystron) that is supplied by a low- power RF source.

B. Receiver Assembly : The receiver is designed to detect and amplify the very weak signals received by antenna. Radar receivers must be of very high quality because the signals that are detected are often very weak. It’s consist of several components such as STALO ( Stable Oscilator ), LNA ( Low Noise Amplifier), and etc.

C.  Waveguide : shows that the connecting the transmitter and the antenna is waveguide. This is usually a hollow, rectangular, metal conductor whose interior dimensions depend upon the wavelength of the signals being carried. Waveguide is put together much like the copper plumbing in a house. Long piece of waveguide are connected together by special joints to connect the transmitter/receiver and the antenna.

D.  Antenna : The antennas are the device which sends the radar.s signal into atmosphere. Most antennas used with radars are directional; that is, they focus the energy into a particular direction and not other directions. An antenna that sends radiation equally in all directions is called isotropic antenna.

E.   Duplexer : kind of special intersection that being through the transmitted pulse and the received pulse.

F.   Transmit/Receive switch : is a special switch added to the radar system to protect the receiver from high power of the transmitter.

G.  Signal Processor & Data Processor : processing the received signal with several calculations and formulas to performing and displaying the data radar to the users.

H.   Controller : control all of the operational of the radar system. 

Reference sources

http://en.wikipedia.org/wiki/Weather_radar

http://www.wmo.int/pages/index_en.html

IOM-88_Training_Radar.pdf

The EEC. 2008. Schematic Diagram The EEC DWSR 2501C, U.S.A 

The EEC. 2008. Technical Manual The EEC DWSR 2501C, U.S.A