Chapter 3: Radio Observatory and DSN Fundamentals


5 March - 19 March
We discussed magnitude and phase of the visibility function. In particular we learned that the phase function
of the  visibility function determines the actual (observed) position of a source relative to the nominal position
used in the correlator. Then we focused on frequency standards, superheterodyne receivers and the block diagram
of a DSN station with VLBI equipment.

We  elaborated on the interferometer concept, found out that the interferometer response is a combination of a low-pass and a high-pass filter, introduced the terms "fringes" and "fringe spacing," and learned how the observed flux density of an interferometer changes with the brightness distribution of the source. We introduced the "visibility finction."

We  learned that an antenna is  a linear spatial filter.  The analogy to a filter in the time-frequency domain is apparent. Then we turned to the interferometer concept and  derived the spatial frequency spectrum of an interferometer.

We  learned about the spatial frequencies and the spatial frequency spectrum. We also looked a bit deeper into  the meaning of  the aperture distribution.  The  two-slit experiment to  demonstrate the wave nature of light can be seen as an experiment with an aperture distribution consisting of two delta functions. Then we saw how the spatial frequency spectrum can be derived from the aperture distribution through autocorrelatiomn.  We also looked at "tapering" to reduce sidelobes.


We continued with Chapter 3, did some Fourier gymnastics by changing the aperture distribution and figuring out how that changes the filed pattern and the beam pattern. We also introduced the terms, spatial frequency and spatial frequency spectrum and how the latter is related to the aperture distribution and the beam pattern.