Daniel T. McGrath

Ultra-wideband arrays

There is a need for ultra-wideband phased arrays for military applications such as multifunction, EW, and ESM systems. This need was addressed on the DARPA reconfigurable aperture (RECAP) program, with a goal of a 10:1 bandwidth array aperture. Previous aperture designs covered 3 or 5:1 bandwidths [Hemmi, C, et al., March 1999, Chio, T.H., et al., Sept. 1999 and June 2000]. On this program we designed array radiating apertures tunable over a 10:1 bandwidth, using RF micro-electromechanical system (MEMS) switches. Design trades addressed multiple tunable approaches, but ultimately a 10:1 instantaneous-bandwidth approach, requiring no tuning, was selected for further development. An array aperture operating from 1.8 to 18 GHz (10:1), with dual polarization and wide-angle scan capability, was designed and demonstrated with hardware measurement.

Calculation of Coupling Coefficients for Arrays With Skewed Lattices From Infinite Array Scan Reflection Data

Calculation of array antenna mutual coupling coefficients may be accomplished using a Fourier transform of scan reflection coefficient data from an infinite array code provided that the limits of integration are defined appropriately. In most cases the limits extend outside visible space, imposing a requirement on the infinite array code that the boundary conditions be formulated in terms of u, v instead of thetas, phi. Further, when the array lattice is skewed, an additional change of variable is needed to form a rectangular integration region. This paper describes the method needed for mutual coupling coefficient calculation, and gives examples showing its versatility and accuracy.

Accelerated periodic hybrid finite element method analysis for integrated array element and radome design

A computational technique known as the periodic hybrid finite element method (McGrath et al., 1994) has been developed for finding the active reflection coefficient and active element gain of general phased array radiators. It uses periodic radiation conditions based on an integral equation, hence it is a hybrid of FEM and the periodic moment method (PMM). An extension of the method incorporates the effects of homogeneous dielectric cladding layers without including those layers in the FEM mesh. The result is an efficient means of modeling structures that include wide angle impedance matching sheets and planar radomes.

Wideband arrays and polarization synthesis

Array antennas may be required to produce arbitrary polarizations for best match to far field sources or receivers at arbitrary angles. A common presumption is that this requires radiating elements with phase center coincidence (PCC). This paper shows the results of extensive numerical experiments with three dual-polarization radiator types, two with phase center coincidence and one without. The three have comparable polarization performance as measured by the extent of the angular region and bandwidth over which low cross-polarization is maintained. Therefore, the added expense and/or loss of PCC radiating elements does not appear to be justified.