page_title: AI Mk. VIII radar
section_title: Description
hierarchical_section_title: AI Mk. VIII radar / Description
caption_attribution_description: English: Royal Air Force Radar, 1939-1945. Air interception radar: the installation of the AI Mark VIIIA receiver unit on the starboard side of the radar operator's position in a Bristol Beaufighter night fighter.
context_page_description: Airborne Interception radar, Mark VIII, or AI Mk. VIII for short, was the first operational microwave-frequency air-to-air radar. It was used by Royal Air Force night fighters from late 1941 until the end of World War II. The basic concept, using a moving parabolic antenna to search for targets and track them accurately, remained in use by most airborne radars well into the 1980s.
  Low-level development began in 1939 but was greatly sped after the introduction of the cavity magnetron in early 1940. This operated at 9.1 cm wavelength, much shorter than the 1.5 m wavelength of the earlier AI Mk. IV. Shorter wavelengths allowed it to use smaller and much more directional antennas. Mk. IV was blinded by the reflections off the ground from its wide broadcast pattern, which made it impossible to see targets flying at low altitudes. Mk. VIII could avoid this by keeping the antenna pointed upward, allowing it to see any aircraft at or above its own altitude.
  The design was just beginning to mature in late 1941 when the Luftwaffe began low-level attacks. A prototype version, the Mk. VII, entered service on the Bristol Beaufighter in November 1941.
context_section_description: The earlier Mk. VII radars were generally similar to Mk. VIII, but used a less powerful CV38 magnetron offering average power around 5 kW instead of 25 kW in the Mk. VIII's CV64. This reduced the normal operational range to about 3 miles (4.8 km), but the other performance measures were otherwise identical. Mk. VII lacked the alternate signal inputs needed to operate with IFF, beacons or AIBA, as described below. The rest of this description is based solely on the Mk. VIII.
caption: The Mk. VIIIA display was a complex but compact system, shown here installed on the starboard side of a Beaufighter.
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