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, f_max= 5 Hz**
Beam Derotator	Software de-rotation
Frequency Range	85 - 115 GHz
IF Frequency	f_IF = 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.

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