Electromagnetic Implosion Using an Array

Summary form only given. This paper considers the use of a spherical array of sources producing a large fast-transient electromagnetic wave near the center of the sphere. The results here complement the results for an electromagnetic implosion due to reflector and lens types of implosion IRAs. There are at least three general ways to construct an IRA (impulse radiating antenna). The basic idea is to make a fast-rising pulse in the form of a plane wave on an antenna aperture. This can be done via a lens at the end of a TEM horn (lens IRA), a paraboloidal reflector driven by a TEM feed, typically four arms (a reflector IRA), and an array of very manv elements at or near the antenna aperture (an array IRA). Lately, IRA technology is being applied to focus a fast pulse on a small target (an IIRA, or implosion IRA). Much attention has been given to the reflector form. A similar effect can be achieved using a lens (which can be massive in a large structure). For completeness, let us consider an array as another alternative. Such is the subject of this paper. There are various forms that an array IRA can take. The array can be planar with the elements triggered in a sequence so as to produce a converging spherical wave. For convenience let us consider a spherical array of radius a on surface Sa . While the present result is for a full spherical distributed source, it can be applied to a half-covered sphere (say -pi/2 < phi < pi/2) using symmetry arguments. This will cut the delta function in half at the origin (when fields would otherwise be arriving from both sides of the target). This depends on the size of the target compared to ctmr . Note that we have not specified the characteristics of the target centered on r = 0. This will change the pulse amplitude based on reflection from the target. One can potentially improve matters with a special lens near the target". Here we do not go into the details of the design of the individual array elements. Note that on Sa - one can place conductors on contours of constant thetas. Array elements can be set in bands around the sphere connecting two adjacent such conductors. The element voltages can vary with thetas, and/or the spacing of the constant-thetas conductors can vary with thetas.