A new generation of MMIC Direct Detection Radiometer Receivers in K and Ka bands
Trier, M¹; Goldstein, C²; Farre, R¹; Bayle, F¹; Granier, E^1
1EADS ASTRIUM Satellites; ²CNES

For the initial purpose of MADRAS (within MEGHA-TROPIQUES mission) Imager Radiometer and with modifications for the ALTI-KA Altimeter Radiometer, EADS ASTRIUM Satellites in France have developed a new generation of Direct Detection 18.7, 23.8, 36.5 and 37 GHz Radiometer Receivers. The work has been supported by the French Space Agency (CNES)

The Direct Detection architecture as compared to the heterodyne one, offers the advantage to save the need for a mixer and Local Oscillator chain, which indeed leads to significant improvements in mass, consumption and reliability and thus can greatly facilitate the accommodation of complex payloads with numerous frequency channels. The challenge for the development of such a solution is to design and qualify the microwave functions operating at the input frequency (instead of IF frequency)

The availability of space qualified low noise MMIC foundry gives the opportunity to obtain the high and stable gain, the stringent noise figures required for the achievement of competitive radiometric sensitivity and accuracy performances. The frequency selection of narrow band channels (down to 1% relative bandwidth e.g. 200 MHz at 18.7 GHz) is performed with low loss planar solution, thus permitting an easy integration with the other functions together with excellent selectivity.

Regarding the operating in conjunction with a radar transmitter, a RF blanking function has been implemented in order to prevent the radiometer from being dazzled during the transmitter time slot, thus guaranteeing the full radiometric performances during the receiving time slot.

ASTRIUM have developed and qualify under a common concept, a family of receivers sharing the same materials, processes and a maximum of EEE parts. The maximum frequency of use is compatible with ribbon interconnection and thus is not contradictory to a modular approach, interesting feature in the industrial phase where repair has to be envisaged.

ASTRIUM have delivered seven receiver flight models, five for MADRAS and two ALTI-KA. Achieved Noise figures are 2.2 dB (resp 2.5 and 3.7 dB) at 18.7 GHz (resp 23.8 and 37 GHz). Radiometric sensitivity down to less than 0.2 K are achieved thanks to excellent Short Term Gain Stability (ΔG/G)² measured at less than 30E-9 in the time frame of less than 10 s.

ASTRIUM plan to extend this solution to 89 and 150 GHz at space standard. A prototyping phase at 89 GHz achieved in the framework of E-GPM Technology Validation CCN, together with the output of ESA R&Ds on MMIC LNAs up to 200 GHz, show that the MMIC foundry and filter technologies are compatible.

Nevertheless the integration and interconnection will have to be matched to the growing frequency constraints thus involving flip-chip mounting and wiring. As well the square law detector with a Ge tunnel diode solution, as used in Ka band, will no longer be adapted and will have to be replaced by another low 1/f noise device such as zero bias Schottky or Tunnel diode.