A new spectral form of decameter type IIID radio bursts

The intensity-time profiles I(t) of narrow-band (δf/f≈10⁻²) radio bursts, which from the slanted dynamical spectrum (I_f,t) of type IIId emission, are strongly dependent on the heliolongitudes |l| of their coronal (quasi-monochromatic) sources. In the central sector (|l|<50°), each of these short-time (≈10 s), steep-front bursts generated at the second harmonic f=2f_p has a delayed echo-like component, and they usually have a slow exponential decay at the limb (|l|=90°). Using the UTR-2 antenna in the range 30>f>15 MHz, we have recently discovered another, previously unknown limb form of discontinuous type IIId spectrum. It is only the absence of the echo component that makes this spectrum different from the bimodal spectrum. It appears that fast-decaying limb bursts of short duration ≈1 s can be observed at considerable distances on the left and on the right of the solar disk. These bursts are similar in form to the leading pulses of the central binary bursts. According to the data from a 20-MHz radio heliograph, the apparent sources of unusually short-time limb bursts are nonstationary and do not tend to shift from the periphery to the central region of the corona. In the vicinity of the Sun, these sources can move over the celestial sphere at superluminal velocities along transversal global-scale trajectories. In such an event, the duration of radio-wave generation (at the plasma level f_p=10 MHz) is no more than 1s. It is quite probable that the actual compact radio source remains motionless. The behavior of the related dynamical source that is observed for several seconds indicates the existence of fairly dense coronal structures breaking the spherical symmetry of the solar atmosphere. These structures are successively illuminated during the burst and effectively alter the paths of some rays of the wave packet that were initially not directed to the Earth. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 5, pp. 403–417, May 1999     

Influence of ionospheric irregularities on decameter radio wave propagation: Mathematic modeling

Based on numerical simulation and using the Monte Carlo method, an investigation is carried out of the influence of random irregularities in the ionospheric F-region on short-wave propagation along one-hop radio paths.Irkutsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 11, pp. 1439–1446, November, 1994.     

Deviation of decameter radio waves from the great circle path at high latitudes

Variations in the azimuthal deviation of decameter radio wave trajectories from the great circle arc are considered for high-latitude ratio paths 7–9 thousand km long. Experimental data are compared to calculations with consideration of the specific properties of the high-latitude ionosphere.Arctic and Antarctic Scientific-Research Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 34, No. 2, pp. 119–122, February, 1991.     

A 110 GHz SIS receiver for radio astronomy

A 110 GHz superconductor insulator superconductor (SIS) tunnel junction receiver has been developed and used in regular astronomical observations on the 4m radio telescope at the Department of Astrophysics, Nagoya University. The SIS junction consists of a sandwich structure of Nb/AlOx/Nb, and is cooled to 4.2K with a closed cycle He-gas refrigerator. The receiver exhibits a best double side band noise temperature of 23±2 K at 110GHz. Additional measurements at 98–115 GHz indicate that the receiver has a good response over this input frequency range.     

A 691 GHz sis receiver for radio astronomy

We report the development of a low noise heterodyne receiver optimized for astronomical observations in the 650 GHz atmospheric window, and specifically for the CO(J=65) line at 691.5 GHz. The system is based on an open structure SIS heterodyne mixer pumped by a continuously tunable solid state oscillator. A niobium SIS junction double array is placed at the end of an integrated V-Antenna. For broad band impedance matching a combination of microstrip impedance transformer and radial stub was used. Receiver noise temperatures of 550 K DSB at 684 GHz were achieved at a 1.8 K physical temperature. The performance improved substantially when decreasing the temperature from 4.2 to 1.8 K. Comparison of model calculations and Fourier transform direct detection measurements of the tuning structure implies that this effect is likely due to the coincidence of operational frequency and the gap frequency of the niobium.     

Goniopolarimetry: Space-borne radio astronomy with imaging capabilities

The principles of space-based low-frequency radio astronomy (below 50 MHz) are briefly introduced. As the wavelength range considered does not allow the use of focusing systems, goniopolarimetric (or direction-finding) techniques have been developed. These inversion techniques provide the direction of the wave vector, the polarization state and the flux of the observed electromagnetic wave. In case of spatially extended sources, we can also infer an order of magnitude of the apparent source size. These techniques are presented, and their limitations are discussed. An example from a recent study illustrates the techniques and capabilities.     

A 345GHz SIS receiver for radio astronomy

A 345GHz superconductor insulator superconductor (SIS) tunnel junction receiver utilizing a full height rectangular waveguide mixer with two tuning elements, i.e. an E-plane and backshort tuner, has been constructed and installed on the Caltech Submillimeter Observatory 10m antenna on Mauna Kea, Hawaii. The receiver exhibits a best double side-band noise temperature response of 150K±20K (averaged over a 500 MHz IF bandwidth centered at 1.5GHz) at a design center frequency of 345GHz and at an ambient temperature of approximately 3.8K. Additional measurements show that the receiver has an excellent response at selected points within an RF input range of 280 to 363GHz.     

Cyclostationary approaches for spatial RFI mitigation in radio astronomy

Radio astronomical observations are increasingly corrupted by radio frequency interferences (RFIs), and real time filtering algorithms are becoming essential. In this article, it is shown how spatial processing techniques can limit the impact of the incoming RFIs for phased array radio telescopes. The proposed approaches are based on estimation of the RFI spatial signature. It requires the diagonalization of either the classic correlation matrix or the cyclic correlation matrix of the array. Different diagonalization techniques are compared. Then, RFI detection and RFI filtering techniques are illustrated through simulations on data acquired with the Low Frequency Array Radio telescope, LOFAR. The originality of the study is the use of the cyclostationarity property, in order to improve the spatial separation between cosmic sources and RFIs.     

Modern millimeter and submillimeter receiver systems for radio astronomy

In this review we consider the composition and placement of receiver complexes on millimeter and submillimeter wave radio telescopes as well as their components and circuitry. Examples of receiver complexes are given for both ground-based and space radio telescopes.     

On the optimal frequency of observation of Cherenkov radiation in the radio astronomy method for measuring superhigh-energy cosmic-ray particle flux

Possible reasons for the absence of direct observations of individual events in measuring the super-high-energy particle flux by the radio astronomy technique are considered. One of these reasons is probably associated with the choice of extremely high frequencies (∼1.5 GHz) for detecting radio pulses. Calculations show that the radiation intensity attains its peak value at frequencies ∼500–600 MHz and then sharply decreases so that it becomes three orders of magnitude lower even at a frequency of ∼1.5 GHz. The effectiveness of particle detection in the range of high (∼600 MHz) and low (∼60 MHz) frequencies is analyzed.