||Compact Front-end for L-band Radiometer
||Jensen, Brian Sveistrup (Department of Electrical Engineering, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
||Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark
||This report concerns the design of a new compact analogue front-end (AFE) for the present fully polarimetric L-band (1400-1427 MHz) radiometer operated by the Technical University of Denmark (DTU). The radiometer uses the subharmonic principle to sample directly at the RF frequency. Using MMIC components and microstrip technology it is believed that the existing AFE can be made considerably smaller. This will give the opportunity to mount the AFE directly on the back of a patch antenna while the temperature stabilisation should be much easier. Using multiple antenna/AFE arrangements and a more complex digital processing it will be possible to construct an antenna array for synthesising a much larger antenna which can also be beem steered.
The basic radiometry theory is briefly discussed and a number of common radiometer configurations including the total power, Dicke and noise injection radiometers, are
presented. The radiometer is build and operated to support the ESA SMOS (European Space Agency - Soil Moisture and Ocean Salinity) mission with calibration data for their
MIRAS (Microwave Imaging Radiometer using Aperture Synthesis) instrument. A brief introduction to this mission is therefore given, in order to understand the radiometer
A new, much more compact, AFE prototype is developed and tested in order to determine sensitivity, linearity and stability. It includes an internal noise source for calibration purposes and interface directly to the old system control unit (SCU) and digital front-end (DFE). A noise temperature better than 78 K is obtained for both radiometer channels (horizontal and vertical), which is considerably better than for the old AFE. The sensitivity
is 0.1 K with an integration time just below 1 sec. Linearity is achieved and the long-term stability assessed to be good. As the temperature stabilisation of the test
setup was poor, it is belived that the long-term stability can be improved considerably, if a better temperature control is used.
Finally, a number of suggestions for future improvements is given, as the new AFE possesses the opportunity to become even more compact and less noisy.
||Technical University of Denmark (DTU) : Kgs. Lyngby, Denmark
||EMIRAD, L-band radiometer, Microwave radiometry, Microwave receivers, Polarimetry, Calibration, Sub-harmonic sampling, Radio Frequency Interference.
Creation date: 2009-10-30
Update date: 2009-10-30