www.radartutorial.eu Radar Basics

Long Range / Short Range

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long range

Figure 1: Antenna pattern of a 3D-Radar using Long Range/Short Range templates

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long range

Figure 1: Antenna pattern of a 3D-Radar using Long Range/Short Range templates

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long range

Figure 1: Antenna pattern of a 3D-Radar using Long Range/Short Range templates

Figure 2: Maximum and minimum range are controlled by the dynamic pulse durations

Figure 2: Maximum and minimum range are controlled by the dynamic pulse durations

Figure 2: Maximum and minimum range are controlled by the dynamic pulse durations

Long Range / Short Range

Recent solid state transmitters aren't designed to provide a very high pulse power. The reachable pulse-power of transmitter modules in semiconductor techology is limited by voltage, current and temperature sensitive. Otherwise with help of the pulse compression method the radar doesn't need so very high pulse power. The frequency-modulated and relatively long pulses provide a respectable range also.

Unfortunately the long pulse duration deteriorates the minimal measuring range. During the transmitting time the receiver isn't connected with the antenna and cannot work in the event!

To compensate this disadvantage of the long pulses („long-range-pulses”) the radar can radiate shorter pulses for a dedicated schedule. There are three options for this method:

  1. A shorter frequency-modulated pulse (also pulse compressed) can be transmitted alternately. This method is typically for air-defense radars, whitch doesn't need a special characteristic in the minimal measuring range, like the RRP-117. This air defense radar uses pulses with a duration of 100 and 800 µs!
     
  2. The shorter pulse is an unmodulated very short pulse ( <1 µs). The limited pulse power causes a shorter maximum range in this period. This method is typically for air-traffic-control radars (ATC-radars), like the ASR-E).
     
  3. The needed pulse power is dynamically balanced in dependence on the chosen elevation angle. The pulse duration determines the maximum range therefore. So this radar reaches a stacked beam cosecant squared antennae pattern by interaction of a couple of pencil-beams.

The following figure is an example of a radar time line with frequency-modulated so called „Long-Range-Pulses” (pulse duration: 60 µs) interrupted by three very short peaks (pulse duration: 1 µs).

Figure 3: Radar time line with different pulse-durations

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Figure 3: Radar time line with different pulse-durations

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Figure 3: Radar time line with different pulse-durations

In the lower elevation the radar radiates three “Short-Range-Pulses” in series. This is required for pulse-pair processing practicable in close-up range only.