Development of the Dicke-switched WVR prototype for ALMA · Development of the Dicke-switched WVR...

WVR workshop, Wettzell, 2006 10 10 Miroslav Pantaleev

Development of the Dicke-switched WVR prototype for ALMA

Magne Hagström, Lars Pettersson and Leif Helldner

Collaboration with


Development of the Dicke-switched prototype for the ALMA WVR

• Radiometer design - Double Dicke

• Critical components

• Lab tests

• SMA - tests

• Single Dicke prototype


Optics layout - Double Dicke

M5

M5

C2

M4

C1

M3

• Chopper wheel to select between sky - calibration

• Measure all the time

• Cryo cooler as cold load

• Warm mixers and LNA


Calibration Hot and Cold

Solenoid Vane

Hot load


Chopper wheel function and design goals

• Reliable > 10 years of continuous running

• Small blade diameter – cut a small beam waist

• Phase locked to external square wave


Chopper blade

• Dynamically balanced chopper wheel

• No holes to avoid turbulences


Chopper support

• Bearings – SKF

• Lifetime – more than 25 years (depending on the operational rpm)

• Flexible coupling to dump vibrations


Chopper protective cover


Chopper blade positioning

Brushless motor3600 step encorder

S/Rinput

Choppercontrolelectronics


Chopper timingChopper speed = 10.42 Hz

48 ms

-36 dBbeam

Blanking = 3.2 ms 6.7 %

± Blade Jitter 0.2 ms

-.9 ms

89 A/D samples

Dicke radiometer Sampling rate and Chopper timing

Chopperedge

A/D sampling rate= 0.5 ms


Measured chopper data

Phase locked to external square wave. Switching rate 5-32 Hz (31 - 200 ms) Blanking time (-35 dB taper) 4.5 % (6.7 %) Blade jitter <0.5 ms Lock-in time 6-10 s Allowed external TTL jitter without affecting the blade jitter <0.5 ms

Chopper blade jitter


Block diagram Double Dicke

6 dB

LP 960 MHz

LP 2315 MHz

LP 3800 MHz

BP 3,95-6,45

BP 2,55-3,80

BP 1,56-2,32

BP 800-960

GunnIsolator91,6 GHz

Coupler

-3dB

-3dB

Harm.

Diplexer

6 dB

Ch 1

Ch 2

Phase lock6 dB

6 dB

6 dB

Mixer

G=47 dBG=32 dB

Powersupply

IF= .5 - 8 GHz

WVR Dicke version

0.048 dB/C 0.070 dB/C

LO power0.026 dB/C

0.017 dB/C -0.004 dB/C

Fixed Atten.

4 way P/S

Power Splitter

Phase Lock

Copper control

Calibration control

Temp. control

Micro- processor

-0.9 dBm / 10 GHz(1 dB Comp.= +14 dBm)

-23 dBm / ∆ B


Mixer


3 dB, 91.6 GHz power divider

• Waveguide branch type couplers – many section required to cover wide bandwidth

• Double probe structure is coupled to the E-field in a waveguideBy courtesy of V.Vassilev


DSB - Noise temperature Double Dicke


Sensitivity


Filter bands

0 1000 2000 3000 4000 5000 6000 7000

MHz

-30

-25

-20

-15

-10

-5

-0

dB

• The LO frequency is kept very close to line frequency.

• Mixers are double sideband.

• Four IF channels with larger bandwidth away from the centre of the line.


Filter and video assembly


Custom designed filters

• Bandpass filter B (1.565GHz – 2.315GHz)

•Ring resonators bandpass filter

• Compact, low insertion-loss, sharp-rejection, and wide-band application


Calibration reference loads

• Two reference temperatures with a ∆T ≈ 150 K,

one of them close to sky the temperature

• Peltier element - not possible to get below – 50 ºC

• Noise diode - only ≈ 4 dB ENR

Sterling cooler• Cool a microwave absorber to below 150 K.

• Stabilize the temperature of the absorber to < 0.05 K

• Absorber reflectivity > 30 dB at 183 GHz.

• Maintenance free time ≈ 10 years.


Cooling power

80 90 100 110 120 130 140 150 160

Cooled load in °K

200

300

400

500

600

700

800

mW

Airglass + PPA30

Polyurethane + PPA30

Hymatic cooling power

Hymatic cooling power vs.conductivity loss


Cooled load mount


Thermal stabilization

Insulation

Frame with Peltier cooler

IF temperature regulation


Single Dicke


Block diagram Single Dicke

6 dB

LP 960 MHz

LP 2315 MHz

LP 3800 MHz

BP 3,95-6,45

BP 2,55-3,80

BP 1,56-2,32

BP 800-960

GunnIsolator91,6 GHz

Coupler

-3dB

-3dB

Harm.

Diplexer

6 dB

Ch 1

Ch 2

Phase lock6 dB

6 dB

6 dB

Mixer

G=47 dBG=32 dB

Powersupply

IF= .5 - 8 GHz

WVR Dicke version

0.048 dB/C 0.070 dB/C

LO power0.026 dB/C

0.017 dB/C -0.004 dB/C

Fixed Atten.

4 way P/S

Power Splitter

Phase Lock

Copper control

Calibration control

Temp. control

Micro- processor

-0.9 dBm / 10 GHz(1 dB Comp.= +14 dBm)

-23 dBm / ∆ B


Optics layout - Comparison


Physical size comparison: Double -Single Dicke

Cost saving pre-production design work

• Single Dicke Receiver

• Replacement of the Hymatic Sterling cooler with a Peltier cooler

• Replacement of the cold load with a cool/hot load combination


Cold load

• Single Dicke Receiver

• Replacement of the Hymatic Sterling cooler with a Peltier cooler

• Replacement of the cold load with a cool/hot load combination


Current status


IF linearity

NoiseDiode

ENR=15.2 dB

Atten. 1:stIF

2:ndIF6 dB

SpectrumAnalyzer

(20 GHz bandpower)

Fixed

3 dB

Development of the Dicke-switched WVR prototype for ALMA · Development of the Dicke-switched WVR...

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