Multi-Frequency Synthesis in K-band
The Multi-Frequency Synthesis (MFS) permits to realize a good quality imaging of the continuum radio sources in short time. Switching between N values of frequency is equivalent at some assumptions to the switching between spatial frequencies and therefore equivalent to the operating simultaneously of N space radio telescopes distributed along the line Earth - RadioAstron. If two-element interferometer operate simultaneously at two frequencies, it is possible to measure the amplitudes and difference phases of two spatial frequencies.
The RadioAstron mission will operate one K-band circular polarized channel at fixed frequency 22,232 GHz. The second simultaneously operating channel with opposite circular polarization can switched in the band from 18,392 GHz to 25,112 GHz with fmax / fmin = 1,37. It permits to construct one-dimensional image in time determined the integration time for each channel multiplied on the number switching frequencies. Two-dimensional imaging is possible to make twice per orbit with maximum angular resolution and 1 - (fmin / fmax)2 = 46% of elliptic area on the UV plane. It is significant that this values are independent from the size and others parameters of the orbit. In general one K-band RadioAstron channel with fixed frequency will be unchanging and compatible with all the ground radio telescopes. The tunable K-band RadioAstron channel will be compatible with the EVLA K-band.
Some advantages of the MFS-method.
The observation modes can be selected for realization the mentioned above targets. The frequencies of tunable channel for MFS are 18.392, 19.352, 20.312, 21.272, 22.232, 23.192, 24.152, and 25.112 GHz. The band width of each frequency position is 32 MHz
Technical specification and more details about MFS-method may be see in Memo 3, ASC, 1999.