Carlos Vernich

The current space harness has limitations associated with the use of copper cables in the intra-satellite networks: mass, volume and limited data rate for a given link distance. To overcome these limitations the space community has identified fibre optics as a desired solution for payload and potentially for platform applications. EADS CASA Espacio and DAS Photonics have already been working developing an opto electronic conversion module to use fibre optic in control buses (MIL-STD-1553 and CAN BUS) and point-to-point links (SpaceWire, clocks, AOCS, TM/TC…) to serve as a drop–in replacement for present copper solutions. The mechanical design was done to fit conventional connectors plus backshell dimensions with similar mass. The use of optical fibre instead of copper allows for mass reduction of 25% in typical satellite. All of Engineering Model's (EM) employ 850 nm vertical cavity surface lasers, GaAs PIN photodiodes, radhard graded index multimode fibre (50/125 μm), space qualified optical and electrical connectors with all materials and processes suitable for space applications All modules survived the test campaign without performance degradation or failures. Based on test results, the transceivers are promising candidates to substitute copper harness in the short term, for communication protocols used in satellites at low and medium data rates.

It has come to our attention that in the original version of a paper published in Sensors recently, the names of four co-authors were misspelled with several hyphens missing.

The calibration of correlation radiometers, and particularly aperture synthesis interferometric radiometers, is a critical issue to ensure their performance. Current calibration techniques are based on the measurement of the cross-correlation of receivers’ outputs when injecting noise from a common noise source requiring a very stable distribution network. For large interferometric radiometers this centralized noise injection approach is very complex from the point of view of mass, volume and phase/amplitude equalization. Distributed noise injection techniques have been proposed as a feasible alternative, but are unable to correct for the so-called “baseline errors” associated with the particular pair of receivers forming the baseline. In this work it is proposed the use of centralized Pseudo-Random Noise (PRN) signals to calibrate correlation radiometers. PRNs are sequences of symbols with a long repetition period that have a flat spectrum over a bandwidth which is determined by the symbol rate. Since their spectrum resembles that of thermal noise, they can be used to calibrate correlation radiometers. At the same time, since these sequences are deterministic, new calibration schemes can be envisaged, such as the correlation of each receiver’s output with a baseband local replica of the PRN sequence, as well as new distribution schemes of calibration signals. This work analyzes the general requirements and performance of using PRN sequences for the calibration of microwave correlation radiometers, and particularizes the study to a potential implementation in a large aperture synthesis radiometer using an optical distribution network.