FINAL REPORT - Stakeholders - Ofcom

L Band
Burrington
Figure 3-1: L Band Radar Station Locations
Claxby
Clee Hill
Debden
Gatwick
Great Dun Fell
Heathrow
Lowther Hill
Pease Pottage
Burrington 331 170 289 246 391 225 421 242 651 591
Claxby 178 136 225 195 195 294 234 404 502
Clee Hill 191 208 234 178 310 213 493 485
Debden 98 327 85 426 111 545 625
Gatwick 391 34 495 13 629 676
Great Dun Fell 361 98 400 258 311
Heathrow 451 38 604 640
Lowther Hill 496 204 209
Pease Pottage 634 681
Perwinnes Hill
Tiree
272
Table 3-5: Distances between L Band Radar Stations (Kilometres)
3.2.2 Primary Radar Technology
3.2.2.1 Primary Radar Background
This section gives primary radar technology background relevant to frequency and
bandwidth issues.
Primary radar is currently in wide spread use in air traffic control world-wide. It operates
independently of on board systems and is therefore the only system which detects non
co-operating targets or weather data. Non co-operating targets can include aircraft with
faulty transponders, light aircraft without any form of transponder or military aircraft that
are seeking to avoid detection. Security considerations have recently enhanced this role.
The basic principle of operation of primary radar is very easy to understand, however, the
theory can be quite complex.
The radar antenna illuminates the target with a microwave signal, which is then reflected
and picked up by a receiving device. The radar signal is generated by a powerful
transmitter and received by a highly sensitive receiver. The signal delivered by the
receiving antenna is called echo or return.
Lower microwave frequencies are less affected by weather conditions (particularly rain)
than high frequencies. Returns from rain present a significant problem and are a factor
in the choice of frequency for an ATC radar. However, low frequencies require much
bigger antennas to achieve a narrow beam.
A long range radar (with range up to 250 nm), may typically use frequencies in L band.
This type of radar requires a very large antenna to resolve targets at long range. Note,
however, that some long range radars operate on Channel 36 (UHF) and also in S band
(no civil ATC en-route radars operate in this band).
Typically, a short to medium range radar may use S band. This can be used to give a
sharper beam for a moderate sized antenna, giving good performance to medium ranges
(150 nm). An airport/terminal area radar, operating at shorter range (up to 80 nm), may
have a smaller antenna with wider beam width. A very narrow beam is not so critical for
shorter range applications.
In contrast, an airport surface movement radar, operating at very short range, will use a
higher frequency to achieve high resolution from a small antenna (a small antenna is
necessary to achieve the required high rotation speed). The high resolution enables
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Perwinnes Hill
Tiree