Aerodrome Surveillance Approach Radars

These are short range radars providing positional information up to 25 NM. Their wavelengths are 3 cm or 10 cm with pulse widths of 0.5 to 1 µs. They provide:

•Positional information and control of aircraft in the aerodrome vicinity, Approach Radar (RAD)

•Radar Vectoring to the ILS

•Surveillance Radar Approach (SRA)

Airport Surface Movement Radar (ASMR)

This is also known as AIRFIELD SURFACE MOVEMENT INDICATOR (ASMI) and is installed at major airfields to provide a very accurate radar display (in all weathers and conditions of visibility) of the aerodrome infrastructure, (taxi-ways, runways, aprons etc.), vehicular traffic and aircraft that are stationary, taxiing, landing or taking off.

ASMI radar is designed to provide a detailed, bright and flicker-free display of all aircraft and vehicles on runways and taxiways so that Air Traffic Control Officers can be certain that runways are clear of traffic before landings or take-offs, and to enable them to ensure the safe and orderly movement of traffic on taxiways. Processing can remove selected fixed features leaving targets on runways and taxiways, etc., clearly visible. This is shown in Figure 12.4; the aircraft taking off is a DC9.

The very high definition required by these radars is achieved by designing a radar with:

•a very narrow beam in the order of 0.2° to 1°.

•a scanner rotation rate of 60 rpm.

•a PRF in the order of 4000 to 20 000 pps.

•pulse widths in the order of 0.03 µs.

•frequencies of 15 to 17 GHz (SHF), 2 to 1.76 cm wavelengths.

•ranges of 2.5 to 6 NM in light precipitation.

The frequencies required for ASMI result in the transmissions being increasingly attenuated and absorbed as the intensity of precipitation increases. This has the effect of reducing the radar’s range, but this is not a significant problem as the radars are only required to cover the environs of the airfield. The EHF band is not suitable for an ASMI radar as the degree of attenuation in most types of precipitation reduces its effective operational range and capabilities.

Ground Radar 12

1.A primary radar has a pulse repetition frequency of 275 pps. The time interval between the leading edges of successive pulses is:

a.3.64 milliseconds

b.36.4 milliseconds

c.3.64 microseconds

d.36.4 microseconds

2.A primary radar system has a pulse repetition frequency of 450 pps. Ignoring pulse width and flyback at the CRT, the maximum range of the radar would be:

a.333 NM

b.180 NM

c.666 NM

d.360 NM

3.The frequency band and rate of scan of Airfield Surface Movement radars are:

4.A ground based radar with a scanner rotation of 60 rpm, a beamwidth in the order of 0.5° and a PRF of 10 000 pps would be:

a.an Airfield Surface Movement Indicator with a theoretical range of 8 NM

b.a Precision Approach Radar

c.an Airfield Surface Movement Indicator with a theoretical range of 16 NM

d.a high resolution Surveillance Approach Radar

Questions 12