Early Days of Phased Array Radars for Ballistic Missile Detection and Tracking

In the early 1960s, the United States initiated development of an anti-ballistic missile (ABM) system that could counter the threat of intercontinental ballistic missiles. ABM quickly focused on planar phased arrays because the challenges of active missile defense would demand radar beam agility, power aperture, and wide-angle sensing capability. Lincoln Laboratory formed a team to push the development of phased arrays for a variety of missions, with ABM as the mission where the technology requirements were most stressing. At the time the nation did not yet have the capacity to produce reliable lowcost components that would be needed for active arrays. The country did however, have high power tubes and parametric amplifiers that could be incorporated into a phased array radar. Using this technology, Bell Telephone Laboratory and its industry partners developed several ABM radar designs that culminated in the SAFEGUARD system. A SAFEGUARD research and development prototype was installed at the Kwajalein missile test site in the Pacific. Lincoln Laboratory supported the ABM radar measurements program at Kwajalein with a number of dish radars that shared technology and components with the SAFEGUARD phased arrays. This historical paper summarizes the development of the initial ABM phased array radars, discusses the technical challenges that were faced and overcome, and illustrates how these early efforts laid the foundation for the long-range radars we have today.