Circularly disposed antenna array
Large circular antenna array for radio direction finding.
A circularly disposed antenna array (CDAA), sometimes called a circularly disposed dipole array (CDDA) or a wullenweber, is a large, ring-shaped antenna system built for radio direction finding. Military and government organizations use these arrays to triangulate radio signals for tasks like navigation, intelligence collection, search and rescue, and enforcing broadcast regulations. Because their massive circular reflecting screens look like round fences, some of these antennas have been nicknamed "elephant cages." The term "wullenweber" originated as a German cover name during World War II for their secret CDAA research program; it does not refer to any person involved in the work. Many nations operate CDAA systems, including Canada, Germany, Japan, Russia, the United Kingdom, and the United States.
**History**
**Origin in World War II Germany** The German navy’s communication research command, Nachrichtenmittelversuchskommando (NVK), along with Telefunken, developed CDAA technology during the early years of World War II as part of the Wullenweber project. The inventor was NVK group leader Dr. Hans Rindfleisch, who later became Technical Director for Norddeutscher Rundfunk (NDR) in northern Germany. Technical team leaders included Dr. Joachim Pietzner, Dr. Hans Schellhoss, and Dr. Maximilian Wächtler; Wächtler co-founded Plath GmbH in 1954 and later advised both Plath and Telefunken. The first Wullenweber was built during the war at Skibsby, northeast of Hjørring, Denmark. It featured 40 vertical radiator elements arranged along a circle 120 meters in diameter, with 40 reflecting elements placed behind them on an inner circle of 112.5 meters, suspended from wooden support poles. To simplify obtaining true geographic bearings, the north and south elements were aligned exactly on the north–south meridian.
**Post-war development** While Pietzner, Schellhoss, and Wächtler retired in West Germany, some of their second-tier technicians were taken to the Soviet Union after the war. At least 30 Krug (Russian for "circle") arrays were installed across the USSR and allied countries during the 1950s, well before the U.S. military pursued its own CDAA development. Several Krugs were placed in pairs less than 10 kilometers apart, apparently for radio navigation. At least four Krugs were installed near Moscow—to the north, east, and south of the city.
- First built
- World War II, at Skibsby, Denmark
- Diameter of first array
- 120 metres (390 ft)
- Number of radiator elements in first arr
- 40
- Number of reflecting elements in first a
- 40
- Inventor
- Dr. Hans Rindfleisch
- Technical team leaders
- Dr. Joachim Pietzner, Dr. Hans Schellhoss, Dr. Maximilian Wächtler
- Notable post-war arrays
- Krug (Soviet Union), AN/FRD-10 (U.S. Navy), AN/FLR-9 (U.S. Air Force)
Lore & Background
The technology was developed by the German navy communication research command, Nachrichtenmittelversuchskommando (NVK), and Telefunken during the early years of World War II. The inventor was NVK group leader Dr. Hans Rindfleisch. The first wullenweber was built at Skibsby, Denmark, using 40 vertical radiator elements on a 120-metre-diameter circle, with 40 reflecting elements on an inner circle of 112.5 metres. The term 'wullenweber' was the World War II German cover term for the secret research program; its name is unrelated to any person involved.
After the war, some second-echelon technicians were taken to the USSR, where at least 30 Krug arrays were installed in the 1950s. The U.S. disassembled a second array built at Langenargen/Bodensee and brought it to the U.S., where it became known as the 'Wullenweber' array. Professor Edgar Hayden led the reassembly and subsequent research at the University of Illinois, designing a large array with 120 vertical monopoles and a 1,000-foot-diameter circular screen. In the 1960s–1970s, the U.S. Navy deployed AN/FRD-10 arrays worldwide, and the U.S. Air Force deployed AN/FLR-9 systems. Many arrays have since been dismantled, though some remain in service.
Reader's Guide
The circularly disposed antenna array has been a cornerstone of military and government radio direction finding since its development in World War II. Its ability to triangulate signals for navigation, intelligence, search and rescue, and broadcasting law enforcement made it a critical asset for many nations, including Canada, Germany, Japan, Russia, the United Kingdom, and the United States. The post-war construction boom saw the U.S. deploy networks of AN/FRD-10 and AN/FLR-9 arrays at strategic locations worldwide, from Okinawa to Turkey, reflecting the Cold War emphasis on signals intelligence. The Soviet Krug arrays, installed earlier than their U.S. counterparts, were used to track early Sputnik satellites and locate re-entry vehicles. Although many arrays have been decommissioned or dismantled due to age, base closures, or geopolitical shifts, some survive—such as the Canadian Forces' FRD-10 arrays and the German Bundesnachrichtendienst facility at Gablingen. The technology's legacy continues in smaller, more economical designs like the Pusher CDAA, and in modern arrays such as the 410-metre-wide CDAA at Bramstedtlund, Germany, inaugurated in 1995.
Did You Know?
- The term 'wullenweber' was a World War II German cover term for the secret CDAA research program and is unrelated to any person.
- The first wullenweber was built at Skibsby, Denmark, with 40 radiator elements on a 120-metre-diameter circle.
- Soviet Krug arrays were used to track early Sputnik satellites using their 10 and 20 MHz beacons.
- The AN/FLR-9 at Clark AB, Philippines, was decommissioned after the Mt. Pinatubo volcano eruption in 1991 and later converted into an outdoor amphitheater.
Frequently Asked Questions
What is a Circularly disposed antenna array?
A CDAA is a massive ring-shaped antenna system built for radio direction finding, also known as a circularly disposed dipole array or a wullenweber. Its enormous circular reflecting screens resemble round fences, which is why operators nicknamed them "elephant cages."
What is a Circularly disposed antenna array's role in the story?
These arrays serve military and government organizations by triangulating incoming radio signals for navigation, intelligence collection, search-and-rescue operations, and enforcing broadcast regulations. They function as precision direction-finding instruments rather than simple transmitters.
Where does the Circularly disposed antenna array's origin story take place?
The first CDAA was erected during World War II at Skibsby, Denmark, with a 120-metre diameter and 40 radiator elements paired with 40 reflecting elements. Dr. Hans Rindfleisch is credited as the inventor, while Dr. Joachim Pietzner, Dr. Hans Schellhoss, and Dr. Maximilian Wächtler led the technical teams.
Why is the Circularly disposed antenna array important to the canon?
It represented a major leap in radio direction-finding capability during WWII, giving operators a far more accurate way to pinpoint signal sources than earlier directional designs. Its circular geometry and large reflecting screens made it a cornerstone of military and intelligence radio work.
Where does the nickname 'wullenweber' for the Circularly disposed antenna array come from?
The name originated as a German cover designation used during World War II, and it persisted as a colloquial shorthand for these ring-shaped arrays. Fans and operators alike still use it as a shorthand alternative to the full technical name.
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