FAR-IR OPTICS DESIGN AND VERIFICATION EXPERIMENTAL SYSTEM AND RESULTS Final Meeting “Far-IR Optics Design and Verification”, Phase 2 27 November 2002,

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)

[email protected]


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


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


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



Pin flangewaveguide I/F

Chamferedcorrugated

horn



Probe design:

• Flared waveguide probe

• TE10 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

90 45 0 45 9040

30

20

10

0

H-planeE-plane

Far-field angle (deg)

Rel

ativ

e In

tens

ity (

dB)



Harmonic mixer and corrugated horn in MSA MSA on interface plate



Alignment mirrors in MSA plate Alignment windows in Gunn interface plate



Cross-hair in alignment window Gunn chain connected to scanner system



Gunn on scanner Final assembly Alignment MSA / scanner



Pitch alignment by shimming Roll / yaw alignment by tilt units



SiC absorber around probe Absorber on MSA I/F plate


PHASE AND AMPLITUDE MEASUREMENT SYSTEM

Expected dynamic range is 30-40 dB / BW = 1 kHz / = 1 ms


FEASIBILITY AND UPGRADE OF TEST FACILITY (1)

Gunn oscillator and subharmonic mixer with modified Potter horns


-25 -20 -15 -10 -5 0 5 10 15 20 25-6

-5

-4

-3

-2

-1

0

[r

ad /

2]

x [mm]

-25 -20 -15 -10 -5 0 5 10 15 20 25

-50

-40

-30

-20

-10

0

ESA-TRP Contract: Far-IR Optics Design and Verification, Phase 2

Field coupling measured @ 480 GHz by scanning 2 modified Potter horns relative to each otherTest signal power 100 W, HM conversion loss -70 dB, IF detection BW of 10 Hz, S/N = 40 dB

Proof of Concept Amplitude and Phase Measurement

20 *

log

(E /

E0

) [dB

]

x [mm]

-25 -20 -15 -10 -5 0 5 10 15 20 25-6

-5

-4

-3

-2

-1

0

[r

ad /

2]

x [mm]

-25 -20 -15 -10 -5 0 5 10 15 20 25

-50

-40

-30

-20

-10

0

ESA-TRP Contract: Far-IR Optics Design and Verification, Phase 2

Field coupling measured @ 480 GHz by scanning 2 modified Potter horns relative to each otherTest signal power 100 W, HM conversion loss -70 dB, IF detection BW of 10 Hz, S/N = 40 dB

Proof of Concept Amplitude and Phase Measurement20

* lo

g (E

/ E

0 ) [

dB]

x [mm]


Proof of concept: amplitude and phase detection with 30-40 dB dynamic range



Upgrade: 2 HM’s + external diplexers, phase stable cables and an active IF tripler


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



2 1 0 1 210

9.5

9

8.5

8

CalculatedMeasured patternFirst-order correction

z (wavelengths)

Cou

plin

g ef

fici

ency

(dB

)

Multiple reflections:

• Scattering environment small

• Standing wave between horns:

s(z) c(z) (1 + r1r2|c(z)|2exp(i2kz))

• Considering only one roundtrip

• First-order correction:

Ec = (E1 + E2exp(i/2)) / 2



10 5 0 5 1020

15

10

5

0

E1E2Ec

First-order standing wave correction

x (mm)

Rel

ativ

e in

tens

ity (

dB)

15 10 5 0 5 10 150

0.1

0.2

0.3

0.4

0.5

0.6

0.7

E1E2Ec

First-order standing wave correction

x (mm)

Rel

ativ

e fie

ld m

agni

tude

Reduction > 10 dB



0 1 2 3 4 5 60.97

0.98

0.99

1

1.01

Elapsed time (hr)

Rel

ativ

e fi

eld

ampl

itude

(V

/m)

0 1 2 3 4 5 640

20

0

Elapsed time (hr)

Rel

ativ

e ph

ase

(deg

)

Typically 1% / hr

Typically 5° / hr

Stability



-0.03 -0.02 -0.01 0 0.01 0.02 0.03-80

-70

-60

-50

-40

-30

-20

-10

0Convolution with probe pattern

Example for GLAD



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


DISCUSSION OF SYSTEMATIC ERRORS (7)Receiver linearity

45 d

B



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


HORN MEASUREMENTS (1)

30 20 10 0 10 20 30

80

60

40

20

0

x (mm)

Rel

ativ

e In

tens

ity (

dB)

15 10 5 0 5 10 150

0.2

0.4

0.6

0.8

1

1.2

x (mm)

Rel

ativ

e fi

eld

ampl

itude

(V

/m)

Calculated and measured response for horn measured by probe


HORN MEASUREMENTS (2)Calculated and measured response for horn measured by probe

30 20 10 0 10 20 3014

12

10

8

6

4

2

0

x (mm)

Rel

ativ

e ph

ase

(per

iods

)


HORN MEASUREMENTS (3)Calculated and measured response for two identical horns

20 10 0 10 20100

80

60

40

20

0

x (mm)

Rel

ativ

e In

tens

ity (

dB)

10 5 0 5 100

0.2

0.4

0.6

0.8

1

x (mm)

Rel

ativ

e fi

eld

ampl

itude

(V

/m)


HORN MEASUREMENTS (4)Calculated and measured response for two identical horns

20 10 0 10 208

6

4

2

0

x (mm)

Rel

ativ

e ph

ase

(per

iods

)


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


MSA RESULTS (1)

Symmetric, +5mm

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

-10 -5 0 5 10off-axis distance (mm)

inte

nsity

(norm

alis

ed)

GLAD

CODE V

GRASP

Experiment


MSA RESULTS (2)

Symmetric, 0 mm

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

-15 -10 -5 0 5 10 15

off-axis distance (mm)

inte

nsi

ty (

norm

alis

ed)

GLAD

CODE V

GRASP

Experiment


MSA RESULTS (3)

Symmetric, -5mm

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

-20 -15 -10 -5 0 5 10 15 20


inte

nsity

(norm

alis

ed)

GLAD

CODE V

GRASP

Experiment


MSA RESULTS (4)

Symmetric, -10mm

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

-20 -15 -10 -5 0 5 10 15 20


inte

nsity

(norm

alis

ed)

GLAD

CODE V

GRASP

Experiment


MSA RESULTS (5)

Asymmetric, +5mm

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00


inte

nsity

(norm

alis

ed)

GLAD

CODE V

GRASP

Experiment


MSA RESULTS (6)

Asymmetric, +5 mm

0.E+00

1.E-01

2.E-01

3.E-01

4.E-01

5.E-01

6.E-01

7.E-01

8.E-01

9.E-01

1.E+00


field

(norm

alis

ed)

GLAD

CODE V

GRASP

Experiemnt


MSA RESULTS (7)

Asymmetric, 0 mm

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

-15 -10 -5 0 5 10 15


inte

nsity (

norm

alis

ed)

GLAD

CODE V

GRASP

Experiment


MSA RESULTS (8)

Asymmetric, 0 mm

0.E+00

1.E-01

2.E-01

3.E-01

4.E-01

5.E-01

6.E-01

7.E-01

8.E-01

9.E-01

1.E+00

-15 -10 -5 0 5 10 15


field

(norm

alis

ed)

GLAD

CODE V

GRASP

Experiment


MSA RESULTS (9)

Asymmetric, -5mm

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

-20 -15 -10 -5 0 5 10 15 20


inte

nsity

(nor

mal

ised

)

GLAD

CODE V

GRASP

Experiment


MSA RESULTS (10)

Asymmetric, -5 mm

0.E+00

1.E-01

2.E-01

3.E-01

4.E-01

5.E-01

6.E-01

7.E-01

8.E-01

9.E-01

1.E+00

-20 -10 0 10 20


field

(norm

alis

ed)

GLAD

CODE V

GRASP

Experiment


MSA RESULTS (11)

Asymmetric, -10 mm

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

-20 -10 0 10 20


inte

nsity (

norm

alis

ed)

GLAD

CODE V

GRASP

Experiment


MSA RESULTS (12)

Asymmetric, -10 mm

0.E+00

1.E-01

2.E-01

3.E-01

4.E-01

5.E-01

6.E-01

7.E-01

8.E-01

9.E-01

1.E+00

-20 -15 -10 -5 0 5 10 15 20off-axis distance (mm)

field

(n

orm

alis

ed

)

GLAD

CODE V

GRASP

Experiemnt


MSA RESULTS (13)

Symmetric, +5mm

-3

-2

-1

0

1

2

3

-5 -3 -1 1 3 5


phas

e (r

adia

ns)

GLAD

CODE V

GRASP

Experiment


MSA RESULTS (14)

Symmetric, 0 mm

-3

-2

-1

0

1

2

3

-10 -5 0 5 10


phas

e (r

adia

ns)

GLAD

CODE V

GRASP

Experiment


MSA RESULTS (15)

Symmetric, -5mm

-3

-2

-1

0

1

2

3

-10 -5 0 5 10


phase

(ra

dian

s)

GLAD

CODE V

GRASP

Experiment


MSA RESULTS (16)

Symmetric, -10 mm

-3

-2

-1

0

1

2

3

-20 -10 0 10 20


phas

e (r

adia

ns)

GLAD

CODE V

GRASP

Experiment


MSA RESULTS (17)

Asymmetric, +5 mm

-3

-2

-1

0

1

2

3

-5 -3 -1 1 3 5


phas

e (r

adia

ns)

GLAD

CODE V

GRASP

Experiment


MSA RESULTS (18)

Asymmetric, 0 mm

-3

-2

-1

0

1

2

3

-10 -5 0 5 10


pha

se (

radi

ans)

GLAD

CODE V

GRASP

Experiment


MSA RESULTS (19)

Asymmetric, -5mm

-3

-2

-1

0

1

2

3

-10 -5 0 5 10


phas

e (r

adia

ns)

GLAD

CODE V

GRASP

Experiment


MSA RESULTS (20)

Asymmetric, -10 mm

-3

-2

-1

0

1

2

3

-10 -5 0 5 10


phas

e (r

adia

ns)

GLAD

CODE V

GRASP

Experiment

Documents

FAR-IR OPTICS DESIGN AND VERIFICATION EXPERIMENTAL SYSTEM AND RESULTS Final Meeting “Far-IR Optics Design and Verification”, Phase 2 27 November 2002,