Case Studies: First Gun-hardened GPS Antenna Array


In August 2005 Alliant Techsystems (NYSE: ATK) successfully “flew” a 155mm NATO round with a dummy payload and a GPS antenna array prototype attached. After the fuze body was located and excavated from the earth its antenna array was tested and found to function according to its design parameters. ATK advised Spectrum Microwave, Inc., that they had succeeded in supplying “the first gun-hardened GPS array in the free world.”

Bullets– Smart & Dumb

The M982 Excalibur is a GPS-guided 155mm artillery shell developed by Raytheon Missile Systems and BAE Systems Bofors. The specially designed “smart bullet” was demonstrated in Yuma, AZ, in September 2005. But Excalibur is expensive – the 2008 unit cost was US$85,000 (Wikipedia).

While Excalibur was in its development, some engineers at ATK had the idea to retrofit a precision guidance kit (PGK) to a conventional 155mm “dumb” round. But they didn’t have a GPS antenna, and didn’t know how to design one. They placed an urgent call to Spectrum Microwave, located in Columbia, MD at that time, asking for help. Mark W. Ingalls, currently Principal of Machine2Wireless LLC, was then Director of Technology (Antennas) at Spectrum. The engineers at PGK were not certain that a single GPS antenna would give them a “lock” on the GPS signal, so they requested a two-element array.

The Ingalls design featured Valox® covers press fit over each antenna element to act as radomes and also to hold the elements in place during the firing of the projectile.

“Armed” with a robust GPS array, ATK was able to develop the rest of their PGK system and win a shoot-off against their competition. They are now producing the PGK kits to turn dumb bullets into smart ones. (Defense Industry Daily)

Modified fuze body used to test antenna prototypes.

Modified fuze body used to test antenna prototypes.

Prototype array being tested in an anechoic chamber.

Prototype array being tested in an anechoic chamber.

M982 Excalibur (Wikipedia)

M982 Excalibur (Wikipedia)

Electromagnetic simulation used to design the PGK antenna array.

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