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FAR-IR OPTICS DESIGN AND VERIFICATION EXPERIMENTAL SYSTEM AND RESULTS Final Meeting “Far-IR Optics Design and Verification”, Phase 2 27 November 2002, ESTEC, The Netherlands Willem Jellema National Institute for Space Research of the Netherlands (SRON) W.Jellema@sron.nl

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FAR-IR OPTICS DESIGN AND VERIFICATION OUTLINE OF PRESENTATION Test criteria and measurement concept System components Amplitude and phase measurement system Feasibility and upgrade of test facility Discussion of systematic errors Horn measurements Summary of as-validated test facility Mixer Sub-Assembly (MSA) measurements

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FAR-IR OPTICS DESIGN AND VERIFICATION TEST CRITERIA AND MEASUREMENT CONCEPT Test criteria: Resolve features with a characteristic scale of 1 mm at –20 dBc Measurement uncertainty smaller than 3 to 4 dB at –20 dBc Accuracy in main-beam better than 1 dB Dynamic range larger than 30 dB Measurement concept: Coherent narrow-band detection of output beam (phase is also measured) Signal chain based on harmonic mixer and phase-locked Gunn oscillator Field is sampled along linear cuts by a probe on a scanner system

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FAR-IR OPTICS DESIGN AND VERIFICATION SYSTEM COMPONENTS (1) Corrugated horn design: 2.5 mm aperture radius 15.4 mm slant length compliant with MSA optical I/F adapted waveguide dimensions optimised waveguide transition optimised corrugation diameters optimised corrugation widths minimum return loss low cross-polarisation good E/H symmetry

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FAR-IR OPTICS DESIGN AND VERIFICATION SYSTEM COMPONENTS (2) Pin flange waveguide I/F Chamfered corrugated horn

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FAR-IR OPTICS DESIGN AND VERIFICATION SYSTEM COMPONENTS (3) Probe design: Flared waveguide probe TE 10 mode + phase curvature Aperture of 1.0 x 1.4 mm Slant length of 10.7 mm Spatial resolution of ½ mm -1 Good E/H symmetry High polarisation purity Insertion loss of 11 dB for MSA Same flange design as for horn

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FAR-IR OPTICS DESIGN AND VERIFICATION SYSTEM COMPONENTS (4) Harmonic mixer and corrugated horn in MSAMSA on interface plate

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FAR-IR OPTICS DESIGN AND VERIFICATION SYSTEM COMPONENTS (5) Alignment mirrors in MSA plateAlignment windows in Gunn interface plate

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FAR-IR OPTICS DESIGN AND VERIFICATION SYSTEM COMPONENTS (6) Cross-hair in alignment windowGunn chain connected to scanner system

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FAR-IR OPTICS DESIGN AND VERIFICATION SYSTEM COMPONENTS (7) Gunn on scannerFinal assemblyAlignment MSA / scanner

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FAR-IR OPTICS DESIGN AND VERIFICATION SYSTEM COMPONENTS (8) Pitch alignment by shimmingRoll / yaw alignment by tilt units

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FAR-IR OPTICS DESIGN AND VERIFICATION SYSTEM COMPONENTS (9) SiC absorber around probeAbsorber on MSA I/F plate

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FAR-IR OPTICS DESIGN AND VERIFICATION PHASE AND AMPLITUDE MEASUREMENT SYSTEM Expected dynamic range is 30-40 dB / BW = 1 kHz / = 1 ms

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FAR-IR OPTICS DESIGN AND VERIFICATION FEASIBILITY AND UPGRADE OF TEST FACILITY (1) Gunn oscillator and subharmonic mixer with modified Potter horns

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FAR-IR OPTICS DESIGN AND VERIFICATION FEASIBILITY AND UPGRADE OF TEST FACILITY (2) Proof of concept: amplitude and phase detection with 30-40 dB dynamic range

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FAR-IR OPTICS DESIGN AND VERIFICATION FEASIBILITY AND UPGRADE OF TEST FACILITY (3) Upgrade: 2 HM’s + external diplexers, phase stable cables and an active IF tripler

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FAR-IR OPTICS DESIGN AND VERIFICATION DISCUSSION OF SYSTEMATIC ERRORS (1) Systematic error sources present in system: Multiple reflections / standing waves Stability Convolution with probe pattern Alignment errors Linearity Cross-talk and spurious signals

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FAR-IR OPTICS DESIGN AND VERIFICATION DISCUSSION OF SYSTEMATIC ERRORS (2) Multiple reflections: Scattering environment small Standing wave between horns: s(z) c(z) (1 + r 1 r 2 |c(z)| 2 exp(i2kz)) Considering only one roundtrip First-order correction: E c = (E 1 + E 2 exp(i /2)) / 2

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FAR-IR OPTICS DESIGN AND VERIFICATION DISCUSSION OF SYSTEMATIC ERRORS (3) Reduction > 10 dB

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FAR-IR OPTICS DESIGN AND VERIFICATION DISCUSSION OF SYSTEMATIC ERRORS (4) Typically 1% / hr Typically 5° / hr Stability

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FAR-IR OPTICS DESIGN AND VERIFICATION DISCUSSION OF SYSTEMATIC ERRORS (5) Convolution with probe pattern Example for GLAD

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FAR-IR OPTICS DESIGN AND VERIFICATION DISCUSSION OF SYSTEMATIC ERRORS (6) Alignment errors: Lateral: < 25-50 m Axial: < 0.1 – 0.2 mm Tilt (pitch and yaw): < 1 arcmin Tilt (roll): < 0.1° Planarity: < / 20 @ = 625 m Geometry is controlled within fractions of

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FAR-IR OPTICS DESIGN AND VERIFICATION DISCUSSION OF SYSTEMATIC ERRORS (7) Receiver linearity 45 dB

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FAR-IR OPTICS DESIGN AND VERIFICATION DISCUSSION OF SYSTEMATIC ERRORS (8) Cross-talk / spurious: Spurious avoided by frequency plan Cross-talk between reference and detector always present High isolation is needed: > 80 dB Cross-talk < noise level (BW = 10 Hz, = 10 s) Summary: Multiple reflections / standing waves biggest systematic error source Linear dynamic range of 45 dB with errors < 1 dB resp. 5

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FAR-IR OPTICS DESIGN AND VERIFICATION HORN MEASUREMENTS (1) Calculated and measured response for horn measured by probe

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FAR-IR OPTICS DESIGN AND VERIFICATION HORN MEASUREMENTS (2) Calculated and measured response for horn measured by probe

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FAR-IR OPTICS DESIGN AND VERIFICATION HORN MEASUREMENTS (3) Calculated and measured response for two identical horns

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FAR-IR OPTICS DESIGN AND VERIFICATION HORN MEASUREMENTS (4) Calculated and measured response for two identical horns

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FAR-IR OPTICS DESIGN AND VERIFICATION SUMMARY AS-VALIDATED TEST FACILITY We carefully designed several system components We developed a differential phase and amplitude measurement technique We demonstrated the measurement concept and proved feasibility We performed a detailed error analysis We quantified the systematic error contributions We developed a first-order standing wave correction We realized a system with known errors (< 1 dB resp. 5°) within a 45 dB range We are compliant with all previously defined criteria, requirements and objectives

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FAR-IR OPTICS DESIGN AND VERIFICATION MSA RESULTS (1) Symmetric, +5mm

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FAR-IR OPTICS DESIGN AND VERIFICATION MSA RESULTS (2) Symmetric, 0 mm

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FAR-IR OPTICS DESIGN AND VERIFICATION MSA RESULTS (3) Symmetric, -5mm

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FAR-IR OPTICS DESIGN AND VERIFICATION MSA RESULTS (4) Symmetric, -10mm

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FAR-IR OPTICS DESIGN AND VERIFICATION MSA RESULTS (5) Asymmetric, +5mm

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FAR-IR OPTICS DESIGN AND VERIFICATION MSA RESULTS (6) Asymmetric, +5 mm

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FAR-IR OPTICS DESIGN AND VERIFICATION MSA RESULTS (7) Asymmetric, 0 mm

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FAR-IR OPTICS DESIGN AND VERIFICATION MSA RESULTS (8) Asymmetric, 0 mm

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FAR-IR OPTICS DESIGN AND VERIFICATION MSA RESULTS (9) Asymmetric, -5mm

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FAR-IR OPTICS DESIGN AND VERIFICATION MSA RESULTS (10) Asymmetric, -5 mm

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FAR-IR OPTICS DESIGN AND VERIFICATION MSA RESULTS (11) Asymmetric, -10 mm

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FAR-IR OPTICS DESIGN AND VERIFICATION MSA RESULTS (12) Asymmetric, -10 mm

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FAR-IR OPTICS DESIGN AND VERIFICATION MSA RESULTS (13) Symmetric, +5mm

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FAR-IR OPTICS DESIGN AND VERIFICATION MSA RESULTS (14) Symmetric, 0 mm

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FAR-IR OPTICS DESIGN AND VERIFICATION MSA RESULTS (15) Symmetric, -5mm

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FAR-IR OPTICS DESIGN AND VERIFICATION MSA RESULTS (16) Symmetric, -10 mm

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FAR-IR OPTICS DESIGN AND VERIFICATION MSA RESULTS (17) Asymmetric, +5 mm

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FAR-IR OPTICS DESIGN AND VERIFICATION MSA RESULTS (18) Asymmetric, 0 mm

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FAR-IR OPTICS DESIGN AND VERIFICATION MSA RESULTS (19) Asymmetric, -5mm

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FAR-IR OPTICS DESIGN AND VERIFICATION MSA RESULTS (20) Asymmetric, -10 mm

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