Calibration of correlation radiometers using pseudo-random noise signals

• Published in: Sensors (Basel, Switzerland) Vol. 9; no. 8; pp. 6131 - 6149
• Main Authors: Pérez, Isaac Ramos, Bosch-Lluis, Xavi, Camps, Adriano, Alvarez, Nereida Rodriguez, Hernandez, Juan Fernando Marchán, Domènech, Enric Valencia, Vernich, Carlos, de la Rosa, Sonia, Pantoja, Sebastián
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 03-08-2009; Molecular Diversity Preservation International (MDPI)
• Subjects: Bandwidths; Calibration; Code Division Multiple Access; correlation radiometers; PRN; Pseudo-Random Noise; Radiometers; Receivers & amplifiers; Sensors; Signal to noise ratio; Spectrum allocation; Spain; PRN; calibration; Pseudo-Random Noise; correlation radiometers
• ISSN: 1424-8220; 1424-8220
• DOI: 10.3390/s90806131

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.