Planck Pre-Launch Status Papers - APC - Université Paris Diderot ...

A&A 520, A4 (2010)Fig. 15. DAE biasing to a front-end LNA. Each LNA is composed offour to five amplifier stages driven by a common drain voltage, a dedicatedgate voltage to the first stage (most critical for noise performances),and a common gate voltage to the other stages.Fig. 13. Top:structureofa70GHzhalf-FEM.Ontherightsideofthemodule, one can see the small reference horn used to couple to the 4 Kreference load surrounded by quarter-wave grooves. The parts supportingthe amplifier chain assembly are dismounted and shown in the front.Bottom: pictureofLNAandphaseswitchwithina30GHzFEM.TheRF channel incorporating the four transistors runs horizontally in thisview. The phase switch is the black rectangular element on the left.Fig. 16. Picture of the reference loads mounted on the HFI 4 K box.On the top is the series of loads serving the 70 GHz radiometers, whilein the lower portion are the loads of the two 30 GHz FEMs and one ofthe 44 GHz FEMs. Each FEM is associated to two loads, each feedingaradiometerintheRCA.Fig. 14. A 4-stage InP HEMT MMIC low-noise amplifier usedin a flight model FEM at 70 GHz. The size of the MMIC is2.1 mm × 0.8 mm.Fig. 17. Schematics of the LFI composite waveguide design, showingrepresentative dimensions of the various sections as described inthe text.Conflicting constraints of thermal, electromagnetic, and mechanicalnature imposed challenging trade-offs inthedesign.The LFI waveguides must ensure good thermal isolation betweenthe FEM and the BEM, while avoiding excessive attenuationof the signal. In addition, their mechanical structure mustcomply with the launch vibration loads. The asymmetric locationof the FEMs in the focal plane and the need to ensure integrabilityof the HFI in the LFI main frame, as well as of theRAA on the spacecraft, impose complex routing with severaltwists and bends, which requiredadedicateddesignforeachindividualwaveguide.Acompositeconfigurationwasdevisedwithtwoseparatedsections: a stainless steel (SS) straight section connecting to theBEMs, and a copper (Cu) section incorporating all the twists andbends and connecting to the FEMs (Fig. 17). The two sectionsare connected via custom-designed multiple flanges, each servingthe four guides in each RCA.The SS sections essentially support the entire 20−300 Kthermal gradient. All 44 SS waveguides have the same lengthPage 14 of 21