Eduardo Artal, artale@unican.es: Universidad de Cantabria
"Broadband Back-End Modules for Planck-LFI radiometers at 30 and 44 GHz."
Eduardo Artal
Universidad de Cantabria
Abstract
Radiometers for the Low Frequency Instrument (LFI) of Planck mission are direct conversion receivers, without intermediate frequency stages. They use a differential scheme in order to cancel long term (slow) gain and noise temperature fluctuations, which appear as a systematic 1/f noise. Relative effective bandwidth requirement of each radiometer is 20%.
The Front End Module is a very low noise cryogenically cooled subsystem which uses state of the art InP HEMT devices in the Low Noise Amplifiers (LNA). These are integrated in a balanced structure containing 0º/180º phase switches. The Back End Module is operated at room temperature and contains LNAs based on GaAs HEMT MMICs, band pass filters, Schottky diode detectors and video amplifiers. Front End and Back End modules are connected by a rectangular waveguide about one meter length.
The proposed talk will present the block diagram of the radiometers at 30 and 44 GHz and a description of their function principles. Main test results performances of Back End Modules will be presented, among others: RF to DC response, effective bandwidth, equivalent noise temperature and linearity range. Analytical expressions to get those broadband parameters from test results will be commented. Finally simulated behaviour of the combination Front End Module, waveguide and Back End Module will be discussed, emphasizing the trade-offs and limitations found in the design and development phase.