types of radars use some variations of these units, and we will explain those variations, as necessary in the next chapter. For now, let’s look at the block diagram in figure 1-4. Modulator You can see on the block diagram that the heart of the radar system is the modulator. It generates all the necessary timing pulses (triggers) for use in the radar and associated systems. Its function is to ensure that all subsystems making up the radar system operate in a definite time relationship with each other and that the intervals   between   pulses,   as   well   as   the   pulses themselves,  are  of  the  proper  length. Transmitter 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.  (You  can  review  the Figure 1-4.—Block diagram of fundamental radar system. construction  and  operation  of  microwave  components in NEETS module 11,  Microwave   Principles.) Duplexer The duplexer is essentially an electronic switch that permits a radar system to use a single antenna to both transmit and receive. The duplexer must connect the antenna to the transmitter and disconnect the antenna from the receiver for the duration of the transmitted pulse. As we mentioned previously, the switching time is called receiver recovery time, and must be very fast if close-in  targets  are  to  be  detected. Antenna  System The  antenna  system  routes  the  pulse  from  the transmitter, radiates it in a directional beam, picks up the returning echo and passes it to the receiver with a minimum of loss. The antenna system includes the antenna,  transmission  lines,  and  waveguide  from  the transmitter to the antenna, and transmission lines and waveguide  from  the  antenna  to  the  receiver. Receiver The receiver accepts the weak rf echoes from the antenna system and routes them to the indicator as discernible   video   signals.   Because   the   radar frequencies are very high and difficult to amplify, a superheterodyne receiver is used to convert the echoes to a lower frequency, called the intermediate frequency (IF), which is easier to amplify. Indicator The indicator uses the video output of the receiver to produce a visual indication of target information including  range  and  bearing  (or  in  the  case  of height-finding  indicators,  range  and  height). TYPES OF RADAR SYSTEMS Because  of  different  design  parameters,  no  single radar set can perform all the many radar functions required  for  military  use.    The  large  number  of  radar systems used by the military has forced the development of a joint-services classification system for accurate identification  of  radars. Radar  systems  are  usually  classified  according  to their  specific  function  and  installation  vehicle.  The joint-service  standardized  classification  system  divides these  broad  categories  for  more  precise  identification. 1-5


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