Innovative Multi-Feed-Per-Beam Reflector Antenna for Space-Borne Conical-Scan Radiometers

We present an antenna for use on conical-scan space-borne radiometers in C band and demonstrate that stringent radiometric requirements can be met. The antenna consists of a 5 m offset reflector fed by a focal plane array in a multi-feed-per-beam configuration, so far never used in ocean observation missions. We use distinct element beams and two optimization routines for obtaining element excitation amplitudes and phases, and with either routine, and in both x- and y-polarization, compliant beams, with footprint < 20 km, distance to coast < 20 km and accuracy < 0:25 K, are obtained. These results may pave the way for use of focal plane arrays with digital beamforming in future radiometric ocean observation missions

Scaling of the Surface Plasmon Resonance in Gold and Silver Dimers Probed by EELS

The dependence of surface plasmon coupling on the distance between two nanoparticles (dimer) is the basis of nanometrology tools such as plasmon rulers. Application of these nanometric rulers requires an accurate description of the scaling of the surface plasmon resonance (SPR) wavelength with distance. Here, we have applied electron energy-loss spectroscopy (EELS) and scanning transmission electron I l microscopy (STEM) imaging to investigate the relationship between the SPR wavelength of gold and silver nanosphere dimers (radius R) and interparticle distance (d) in the range 0.1R < d < R. The choice of EELS enables probing the SPRs of E individual dimers, whose dimensions and separation distances are measured in situ with subnanometer resolution using STEM. We find that the decaying exponential description of the fractional SPR wavelength shift with d/2R holds valid only over a limited range of d. instead, within the range 0.1R < d < R the fractional SPR wavelength shift is found to be related to (2R/d)(n), with n similar to 0.9 determined for both gold and silver dimers. Despite this common power dependence, consistently larger SPR wavelength shifts are registered for silver for a given change in d, implying silver dimers to be more sensitive plasmon rulers than their gold counterparts