Light-weight phased array antennas for aerospace apph'cations require utilizing the same antenna aperture to provide multiple functions with dissimilar radiation pattern specifications (e.g., multi-band operation for communications and tracking). In this paper, we present a novel antenna element design for dual-band phased array configuration, comprising nested printed dipoles with balanced individual feeds for each band. The folded dipoles are assumed to be resonant at octave-separated frequency bands (1 GHz and 2 GHz for the design reported herein), and printed on photographic paper (dielectric constant of 3) using low-cost photolithography and ink-jet printing technology. In order to reduce the back-lobe and also to improve the impedance bandwidth, a ground plane is inserted 0.13 λ below the antenna substrate, where λ is the wavelength at 1 GHz. Each dipole is gap-fed in a balanced mode by voltage induced electro magnetically from a microstrip line on the other side of the substrate. The feed line includes a stub for improving the impedance match. Two high-band elements are each nested in one leg of a low-band folded dipole, with a spacing of half-wavelength at 2 GHz to produce an array pattern without grating lobes. This nested element configuration has been simulated, fabricated and measured, and excellent corroboration observed between simulated and measured data. The return loss shows well-centered low and high bands with 10-dB bandwidth of at least 5% for each, and isolation better than -15 dB between the bands. In both bands, the measured co-polarized gain is about 5.3 to 7 dBi in the two principal planes, with cross-polarization less than -25 dBi in the H-plane. Currently, this low-cost light-weight nested antenna element is being integrated into a dual-band phased array. The scan performance of this array will be reported in another paper.
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