Vladimir Khaikin

A wideband receiver-module for passive MM wave imaging array: Optimization and test results

Results of noise and impedance optimization of a W-band receiver-module are given. A wideband compact receiver-module for MM wave passive imaging array has been developed on the basis of InP MMIC LNA and a highly sensitive impedance matched low-barrier detector diode. Achieved bandwidth is 85–100 GHz, the gain factor is 30 dB that was sufficient to provide 15 mK/Hz1 temperature sensitivity of the receiver-module. Tests results of the receiver-module are presented.

Radiometric modules at 22 and 36 GHz for continuous monitoring of atmospheric opacity at RATAN-600 radio telescope

Continuous monitoring of atmospheric opacity at 22 GHz and 36 GHz, ground meteorological parameters and atmosphere models allow separating absorption in water vapor, oxygen and hydrometeors and predicting atmospheric opacity at RATAN-600 radio telescope in wide band. Design, features and parameters of radiometric modules at 22 and 36 GHz for effective continuous monitoring of atmospheric opacity are described.

Near and far field simulation of RATAN-600 radio telescope antenna using the MLPO algorithm

A fast and adaptive near-field physical optics algorithm is developed for the analysis of general multi-reflector antenna systems. The algorithm is applied to the radiation pattern computation of an extremely large antenna of RATAN-600 radio telescope operating at mm-wave frequencies. Near-field reflector to reflector field propagation and far-field radiation pattern computation results will be presented and compared with those obtained by geometrical optics with aperture integration.

Optimization of focusing optics of RATAN-600 radio telescope

Results of simulations of RATAN-600 radio telescope focusing optics are given. It is shown that due to suboptimal shape of the secondary mirror, the total energy loss amounts to 10%÷15% at low elevations and 2÷4% at high elevations. New ways of focusing optics optimization, which allow to compensate for up to 80% of the energy loss caused by the non-optimal shape of the secondary mirror, are proposed. The proposed solutions were verified by extensive simulations. These simulations used geometrical optics approximation (GO), supplemented by the calculation of the near and the far field with Projected Aperture (PA) and Physical Optics (PO) methods, thus taking the finite wavelength effects into account.

A compact highly sensitive radiometer for thermal sounding of atmosphere in 5 MM band

Design and characteristics of a compact highly sensitive direct detection MMIC radiometer of 5 MM wave band with a goal of atmosphere temperature profile determination are presented. The radiometer has bandwidth 56.6 plusmn 0.25 GHz and fluctuation sensitivity 35 mK/Hz1/2/65 mK/Hz1/2 in a ldquototal powerrdquo/modulation mode. The radiometer was successfully used for atmospheric temperature profile measurements with the thermal sounder MTP-5. Average deviation of a measured atmospheric temperature profile from the temperature profile constructed according to 11 probes was 0.2 C-0.4 C, average mutual difference of two devises was equal to or less than 0.2 C.

Analysis of very large radio telescope antennas using multilevel physical optics algorithm

Analysis of very large multi-reflector antennas like that of RATAN-600 radio telescope presents a formidable computational challenge. At mm-wave frequencies of interest, the RATAN-600 main reflector measures roughly 20,000 by 1000 square wavelengths. Such reflector antennas are often analyzed as quasi-optical systems in two main steps. In the first stage, the field is propagated from the feed to an equivalent aperture using geometrical optics (GO), while in the second, the radiation pattern is computed by aperture integration, which for planar apertures can be accelerated using the Fast Fourier Transform (FFT) (R.E. Collin, Antennas and Radio Wave Propagation, McGraw-Hill, 1985). This line of modeling completely neglects the wave phenomena involved in the inter-reflector propagation and introduces phase errors due to introduction of the artificial planar equivalent aperture required for the radiation pattern evaluation using the FFT.

Application of super-Rayleigh resolution in radio astronomy and passive radio imaging

Use of mathematical reduction method allows to achieve super-Rayleigh resolution of radio imaging with high enough S/N. It is demonstrated by processing of Sun and town building images obtained with help of microwave radiometric receivers.

Spline-profile smooth-walled horn as a feed of the multi-beam millimetre focal plane array

In this paper simulated and measured characteristics of an optimized smooth-walled spline-profile horn for two-dimensional multibeam focal plane array at RATAN-600 radio telescope are presented. The measured −10dB beamwidth is less than 45° in the H-and E-planes. The measured side-lobe levels of the radiation pattern are less than −18 dB in the both principal planes. The measured input reflection coefficient is better than −21dB in the frequency range 30GHz – 38GHz. The experimental results are in good agreement with simulated ones in the operational frequency band 34GHz – 38GHz.

An effective 34–38GHz feed horn for two-dimensional multibeam focal plane array at RATAN-600 radio telescope

In this paper simulated and measured characteristics of an optimized smooth-walled spline-profile horn for two-dimensional multibeam focal plane array at RATAN-600 radio telescope are presented. The measured −10dB beamwidth is less than 450 in the H- and E-planes. The measured side-lobe levels of the radiation pattern are less than −18dB in the both principal planes. The measured input reflection coefficient is better than −21dB in the frequency range 30GHz – 38GHz. The experimental results are in good agreement with simulated ones.

Alignment tolerances of antenna optics for KVN 21-m shaped cassegrain antenna

In this paper, gain loss of KVN (Korean VLBI Network) 21-m shaped Cassegrain antenna due to misalignment of antenna optics is calculated using ray-tracing method. It enables us to estimate alignment tolerances of feed and sub-reflector positioning. According to numerical results, KVN 21-m shaped Cassegrain antennas gain loss is more sensitive to positions of feed and sub-reflector than in case of the equivalent classical Cassegrain antenna. The result of calculation is believed to be utilized as a possible guideline when checking the performance of the antenna system.