A radiometer for two-frequency ranges, 1.45 and 2.35 GHz (with 100 MHz bandwidths), has been developed and integrated into the standard radiometric system of the SAO RAS RATAN-600 radio telescope. In accordance with the SAO RAS technical specification, a dual-band horn antenna with a shared phase center was designed and manufactured by Special Design Bureau of the Institute of Radio Engineering and Electronics of the Russian Academy of Sciences (Fig. 1).

Fig. 1. Dual-band horn antenna with a common phase center. Bands 1400-1500 and 2200-2300 MHz. Beamwidth at -10 dB level: 100 degrees, sidelobe level no more than -17 dB, losses < 0.2 dB.

    The radiometer features a new 1400-1500 MHz range and replaces the previous 1220-1270 MHz range requiring new uncooled low-noise amplifiers. These amplifiers, according to the SAO RAS specifications, were developed and manufactured by the Research and Production company Micran JSC (Tomsk) with a gain of 38 dB and a noise factor of 0.5 dB. New bandpass filters were also developed for the new frequency range. Directional couplers (insertion loss not exceeding 0.3 dB) were developed for both ranges to feed the signal of the calibration noise generator into the radiometer input path during gain calibration for each observation. The new radiometer has been integrated into routine operations (Fig. 2).

Fig. 2. New dual-band horn antenna (on the left) and radiometer installed on the focal line of secondary mirror No. 1.

Fig. 3. Observation of the calibration radio source 3C286 with the new radiometer. The red curve is the radiometer signal at 13.3 cm (2200-2300 MHz), the blue curve is the radiometer signal at 20.7 cm (1400-1500 MHz).

Fig. 4. Processing of observations and estimation of radiometer parameters from radio astronomical observations.

    Figure 3 shows the original records in each radiometer frequency range. The intrinsic noise, system temperatures (signal levels along the Y axis), and calibration signals are presented. The radio source passes through the telescope’s unmoving beam pattern simultaneously in both frequency ranges (antenna operation with a common phase center). Figure 4 shows the results of processing and estimation of the radiometer parameters in both frequency channels.

    Thus:

• a new two- frequency decimeter radiometer was developed, manufactured, and integrated into routine observations;
• the radiometer enabled resumption of RATAN-600 observations in decimeter bands with relatively high flux density sensitivity (10-20 mJy);
• the longest wavelength of 25 cm was replaced by 21 cm (20.6 cm). The quality of observations (signal-to-noise ratio, stability) has been improved significantly;
• the common phase center of the two ranges allows to conduct simultaneous observations in them (rather than sequentially, due to the spacing of the horns on the focal line, as before).

    Applications: astrophysical observations of cosmic radio sources of various nature - from Solar System objects to galactic objects and distant radio galaxies. In the near future, spectral observations of neutral hydrogen in the Milky Way and neighboring galaxies will be possible. Active digital interference suppression and observations of rapidly varying processes (pulsars, fast radio bursts) are planned.

Authors:
Tsybulev P.G., Nizhelsky N.A., Prizov P.V., Kratov D.V., Udovitsky R.Yu., Sotnikova Yu.V., Borisov A.N., Khapaev A.A. (SAO RAS)

This work was performed under the state assignment of SAO RAS (topic No. 225012903829).