Group for Advanced Receiver Development (GARD)

Radio & Space Science Department

Chalmers University of Technology
S-412 96 Gothenburg, Sweden


RADIO CAMERA for OSO 20 m ANTENNA


Radio camera employs 4x4 diagonal horn array followed by 16 fix-tuned SIS mixers. The camera will operate at 85-115 GHz frequency band as SSB receiver.
Status: Ongoing / Recently the Group is working on "light" version of the camera (2x2 mixer array while optics and hardware is for the full version 4x4 mixers). The receiver have been installed on Onsala 20 m antenna during the November/December 1997 for evaluation.


FEATURES

Cassegrain Focal Number

f#cass = 4.7

Subreflector Edge Taper:

TE = -12 dB

Imaging Array Size

4x4 pack of diagonal horns

Beam Separation

angle, 54"

Beam Switch

Flipping mirrors*, fmax= 5 Hz

Beam Derotator

Software de-rotation

Frequency Range

85 - 115 GHz

IF Frequency

fIF = 3.4- 4.6 GHz

SSB System Noise Temperature

Tsys < 150 K**

** The SSB noise temperature below 150K has been achieved after improving optics and image load in lab (summer 1998).


OPTICAL LAYOUT**

** Optical layout shows previous design with a chopper wheel for beam switch. Recent design employs flipping mirrors and is more compact. We still need to work out vibration caused by the flipping mirror drivers.

Some terms from the picture above:
Kinoform is a like hologram plate (binary phase change) that converts a plane wave from mm-wave source into 16 partial beams (see for reference G. Delgado's Ph.D. thesis).
Attenuator is of quasioptical type, employs a semiconductor material sensitive to IR radiation. IR diodes used to modulate the electron density in the material that influences on "transparency" of the material for mm-radiation (see for reference G. Delgado's Ph.D. thesis).
RPI is Rotation Polarization Interferometer (see N. Erikson paper in Int. J. Infrared and MM Waves).

Two pictures shows the design of the RPI and its placement into the dewar;

The mixer assembly with cryogenics;

The whole dewar however without LO injection.


The cooler is 3 stage JT machine created by Bert Hansson. The machine cooling capacity isabout 2.25 W at ~4 K. Here you can see a picture of the machine.


All pictures have been taken by Bert Hansson


This page was last modified November 6, 1998, by Victor Belitsky. belitsky(a)oso.chalmers.se