FINAL REPORT - Stakeholders - Ofcom

adars operating in their vicinity. Note, however, that all types of radar may suffer
front-end saturation from interfering signals thereby reducing sensitivity.
• Accuracy: Marine radars are characterised by very short pulse-widths which
improves resolution at the expense of occupied bandwidth.
• Range: Another difference between aeronautical and maritime radar lies in the
range of detection that is required. A typical maritime radar mounted 15 metres
above sea-level on a vessel has a range of only 30 miles. Ground-based radars
may have greater coverage but as they are tracking traffic at sea-level instead of
airborne, the range is still much more restricted than their aeronautical
counterparts.
• Coverage: Additionally, as the area of interest for a ground-based maritime radar
is out to sea, interference caused whilst it is sweeping inland areas is not a
significant problem 13 .
Primary maritime radars operate in the bands 2900 – 3100 MHz, 5460 – 5650 MHz and
9200 – 9500 MHz. These radars are used in both the mobile role on board ship and in a
fixed role for harbour and estuary control. The majority of fixed installations are in the 9
GHz band and provide a high resolution display due to the short pulse-widths employed.
Land based radars are used for a variety of shipping control and collision avoidance
purposes as well as general surveillance by coast guards. Using computer processing
and enhanced displays, the information derived from a group of these radars is displayed
as an aid to collision avoidance. It also provides information for future traffic control
systems.
Peak rated powers for maritime radars range from 1 to 100 kW. Pulse lengths range from
a maximum of 1.5µS down to 0.03µS for 3 GHz radars and 0.02µS for 9 GHz radars
(implying 3dB bandwidths up to 50 MHz). Figure 4-1 below shows the current out-of-band
emission mask for maritime radar (the same applies in all 3 bands, though note that it is a
percentage based mask, hence the actual skirt of the mask is wider for the higher
frequency bands).
Maritime radars in the 3 GHz band typically operate on a centre frequency of 3040 MHz;
radars in the 9 GHz band are centred around 9410 MHz. In the case of many lower cost
radars, no mechanism of frequency feedback control is used such that the transmit
frequency, once set at the point of manufacture or installation, may drift due to
temperature and other conditions.
Figure 4-1: Out-Of-Band Mask for Radars
13 And indeed sector blanking can be used to turn off radar transmitters and receivers
whilst they sweep areas of no interest.
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