| Type 281 | |
| Country: | United Kingdom |
| Introdate: | 1940 |
| Number: | 59 |
| Type: | Early-warning radar |
| Frequency: | 86–94 MHz |
| Prf: | 50 per second |
| Beamwidth: | 35° (horizontal) |
| Pulsewidth: | 2–3 μs or 15 μs |
| Range: | 115nmi |
| Altitude: | 30000feet |
| Power: | 350 kW–1 MW |
The Type 281 radar was a British naval early-warning radar developed during World War II. It replaced the Type 79 as the Royal Navy's main early-warning radar during the war.
The prototype system was mounted on the light cruiser in October 1940.[1] This radar used a frequency of 90 MHz, a beamwidth of 35°, and a wavelength of 3.5m (11.5feet). It required separate transmitting and receiving antennas that were rotated by hand. For long-range warning the radar used a 15 microsecond pulse at a power level of 350 kW that gave a detection range up to 110nmi for aircraft. For tracking surface targets it used a 2–3 microsecond pulse at 1 MW that gave a range up to . A second set was installed in January 1941 aboard the battleship and production began of another 57 sets with the first deliveries occurring the following month.[2] [3] This set also had a secondary aerial and surface gunnery capability and used a Precision Ranging Panel. The Type 281 ranging system allowed the user to select either a 2000yd to 14000yd or a 2000yd to 25000yd range display with range accuracies of 50yd or 75yd RMS, respectively. Aerial target ranges were passed directly to the HACS table (fire control computer).[4]
Type 281B consolidated the transmission and receiving antennas while the Type 281BP radar had the short-pulse feature removed. It was fitted with improved receivers that increased the maximum detection range for an aircraft at 20000feet to . At lower altitudes, ranges declined to at 10000feet and at 5000feet. The Type 281BQ was a Type 281BP fitted with power rotation, at 2 or 4 rpm, and equipped with a plan position indicator. After the end of the war, the Type 281 was replaced by the Type 960 radar.[5]