Three-module experimental radiometric matrix was designed and put in operation successfully. Flowchart of the one channel is shown in Figure 1. The receiver module is about the same, as for MARS-1 [1]. Some modification was made:

• new, more careful design was applied for the Hybride technology LNA, and it's noise temperature was reduced distinctly,
• frequency band was decreased down to 4 GHz ( the latter came out from the limited bandwidth of the input switch ).

Figure 1. MARS-2. Flowchart of the single channel.

The input switch is a latching WR-28 waveguide circulator, driven by alternate polarity current pulse sequence ( I = 8 - 10 A; t = 2 - 3 s; T = 5 - 10 ms ). Typical values for the switch are loss not more than 0.3 dB and isolation not less than 20 dB for frequency band 28 - 32 GHz. In figure 2 the receiver module and switch assembly is shown.
Engineering data for any of the three elementary radiometers of the matrix are as follows:

• central wavelength - 1 cm,
• frequency band - 28 - 32 GHz,
• overall gain - 65 dB,
• noise temperature - T_rec= 185 K,
• sensitivity realized - 6 mK/s^1/2,
• recorded Stokes parameter - Q.

Figure 2. The receiver module and switch assembly.

The elementary radiometers are combined ( figure 3 ) into the microwave unit ( one pair of horns shown is out of use ), where they integrated to use unified systems for calibration, power supply and temperature control.

Figure 3. HF part of the MARS-2 radiometric system.

The MARS-2 system was installed at the feed cabin No.1 of the RATAN-600 radio telescope ( figure 4 ).

Figure 4. The focal line of the RATAN-600 radio telescope ( feed cabin No.1 ).

To illustrate the results, two beam-switching recordings of the radio source are shown in figure 5. The first one is of MARS-2 uncooled elementary radiometer, the second was recorded at the regular cryoradiometer on near wavelength 1.38 cm during the same observing session.

Figure 5. Sensitivity comparison of the MARS-2 uncooled elementary radiometer and
of the cryoradiometer at nearest wavelength 1.38 cm.

The results of the MARS-2 investigation are used now as a basis for development of the next phase of the Project - 16 module matrix MARS-3 [2].

• 1. A.B. Berlin², G.M. Timofeeva², N.A. Nizhelskij¹, A.V. Bogdantsov¹, O.M. Pylypenko³, V.M. Chmil³, Yu.N. Meshkov, A.N. Zdor " MARS ( MAtrix Radiometric System ) Project ", Astron .& Astrophys.Transactions, vol.19, 3-4, pp. 558-565, 2000.
• 2. A.B. Berlin " MAtrix Radiometric System ( MARS ) ", Report SAO RAS, N 292, 2002 ( in Russian ).