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Target size (=Radar Cross Section) criteria are typically in the range 1 – 3 sq metres.
Even at airports handling large commercial transport aircraft, the primary radar is normally
required to detect and display intruding aircraft, which are of unspecified type.
A typical specification includes the ability to detect small targets (1sqm) with a probability
of detection of 90% and inevitably requires advanced processing to minimise the
probability of false alarms (10 -6 ). S band is also widely used by the military.
The general conclusion is that the basic operational requirement for civil approach/TMA
radar is unlikely to change significantly in the foreseeable future. An exception may be
that the requirement for a low false alarm rate may become more exacting. Also, the
probability is that as aviation expands, there is likely to be increased demand for primary
radar systems as more airports identify the need to have radar coverage to improve
expedition and safety of traffic.
3.2.3.4 Airport Surface Movement Radars
There are a total of 8 airport surface movement radars operating in the UK (5 at X band
and 3 at Ku band). Primary radar is the principle general purpose tool for monitoring
aircraft, vehicles and potential obstructions on the airport surface. Other sensors, such as
multilateration systems, are coming into use but they are likely to be complementary to
the basic surface movement radar. Security considerations are likely to increase the
demand for this type of radar.
Surface movement radars are limited to a maximum range of about 2.5nm although
operational requirements often specify the airport surface as the “range” requirement.
Minimum range is of the order of 0.05nm. They operate with aircraft and vehicles in close
proximity and are normally specified with a 60 RPM update rate.
Ground movement radars are usually required to provide coverage to an altitude of 350 ft
in order to display missed approaches, helicopter operations etc. Pulse widths are very
short – for example 40ns – to meet the requirement for high resolution of detail on the
airport surface. Given the requirement to monitor all aspects of the airport surface,
surface movement radars general have only very limited signal processing. Data
processing to provide correlation with other sensors and to track aircraft is becoming
common.
Monitoring of the airport surface is becoming increasingly important and some
enhancement to the operational requirement is likely in the future. This is likely to take the
form of more airports being equipped with surface movement radar and improved
coverage at airports where surface movement radar is already deployed.
3.2.3.5 En Route Services
There are a total of 12 L band en- route radars in the United Kingdom and two of them
are dual use (en route /airport). There are also two UHF radars. These radars support
ATC services to traffic flying in airways (the specific route structure established mainly for
commercial traffic and involving a mandatory ATC service) and off airways (traffic flying
outside the airways which is a mix of all classes of traffic) for most of the United Kingdom.
Secondary radar is the principle tool for the management of traffic flying airways although
the civil controllers use primary radar to monitor traffic which may not be transponder
equipped, traffic which has suffered transponder failure or other unidentified traffic. The
Military ATC authorities use the en route primary radar services to provide services to off
airways traffic. Mandatory carriage of SSR transponders is not required at low altitudes.
NATS has a contract with the MoD to provide and maintain the MoD share of en-route
primary radar services.
En route radars are characterised by long range performance and relatively low data
update rates. They are nearly always specified in conjunction with a secondary radar
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