A Michelson-type radio interferometer for university education

Abstract

We report development of a simple and affordable radio interferometer suitable as an educational laboratory experiment. The design of this interferometer is based on the Michelson and Pease stellar optical interferometer, but instead operates at the radio wavelength of $11 GHz ($2.7 cm), requiring much less stringent optical accuracy in its design and use. We utilize a commercial broadcast satellite dish and feedhorn with two flat side mirrors that slide on a ladder, providing baseline coverage. This interferometer can resolve and measure the diameter of the Sun, even on a day with marginal weather. Commercial broadcast satellites provide convenient point sources for comparison to the Sun's extended disk. The mathematical background of an adding interferometer is presented, as is its design and development, including the receiver system, and sample measurements of the Sun. Results from a student laboratory report are shown. With the increasing importance of interferometry in astronomy, the lack of educational interferometers is an obstacle to training the future generation of astronomers. This interferometer provides the hands-on experience needed to fully understand the basic concepts of interferometry.

Stellar interferometer experiment by measuring visibilities at different wavelengths

“…Given the challenges involved in implementing practical experiments in this field, students may perceive the subject as predominantly theoretical. In spite of these difficulties, several practical experiments have been developed for a better understanding of stellar interferometry, such as a simple experiment using streetlights [4], an outdoor radio interferometer for educational purposes to obtain the angular diameter of the sun [5], online visualization of experimental interference fringes as a function of baseline [6] or laboratory experiments simulating the Michelson interferometer's operation using polymer optical fibres (POFs) to simulate single and binary stars [7,8]. The latter activities involving POFs were designed for students enrolled in the master of space science and technology program at the University of the Basque Country [9].…”

A Two-element Interferometer for Millimeter-wave Solar Flare Observations

“…The sensitivity of the nulling interferometer is higher than that of a single-antenna radiometer with the same antenna diameter. The nulling interferometer detects the burst of small flares on the Sun with two small antennas with beamwidths covering the whole Sun; however, if each antenna is installed separately, the effective baseline distance varies with the Sun's time angle (Koda et al 2016). Therefore, the two antennas must be mounted in the same plane to ensure a stable effective baseline.…”

Practical training of stellar interferometry by measuring spectral fringes visibilities

“…Therefore, it is not an easy task to teach stellar interferometry to undergraduate and graduate students, especially if one wants to perform experimental activities related to this topic. Only a few experiments have been developed with the purpose of teaching the basic concepts of stellar interferometry: a Michelson-type radio interferometer, 3 interference methods, 4 and optical telescopes covered by a double-aperture lid that employ polymer optical fibers (POFs) illuminated by laser sources simulating stars. 5,6 These activities utilizing POFs were created for our students of the Master of Space Science and Technology of the University of the Basque Country.…”