ANTENTOP- 02- 2003, # 003

Jagadis Chandra Bose

touch, radiation propagates unhindered through both prisms. By introducing a small air gap, the combination becomes avariable attenuator to incident radiation; this is illustrated in Bose's original diagram, shown in Figure 13. Bose investigated this prism attenuator experimentally; his results were published in the Proceedings of the Royal Society in November, 1897 [8]. Schaefer and Gross [16] made a theoretical study of the prism combination in 1910; the device has since been described in standard texts.

At the National Radio Astronomy Observatory in Tucson, Arizona a new multiple-feed receiver, operating at a wavelength of 1.3 mm, has recently been built and installed on the 12 Meter Telescope at Kitt Peak [17].

Figure 13. Bose's 1897 diagram of the double-prism attenuator.

Figure 14. One of Bose's original double-prism attenuators, with adjustable air gap.

The system is an 8-feed receiver, where the local oscillator is injected into the superconducting tunnel junction (SIS) mixers optically. With an SIS mixer receiver the power level of the injected local oscillator is critical; each of the 8 mixers requires independent local oscillator power adjustment. This is achieved by adjustable prism attenuators. Figure 15 shows 4 of these 8 prism attenuators, installed on one side of the 8-feed system; this can be compared with Figure 14, which is a photograph taken at the Bose Institute in Calcutta in 1985, of an original prism system built by Bose.

CONCLUSIONS

Research into the generation and detection of millimeter waves, and the properties of substances at these wavelengths, was being undertaken in some detail one hundred years ago, by J.C. Bose in Calcutta. Many of the microwave components familiar today - waveguide, horn antennas, polarizers, dielectric lenses and

Figure 15. Four of the 8 double-prism attenuators used to control local oscillator injection into the NRAO 1.3-mm 8-beam receiver in use at the 12 Meter Telescope at Kitt Peak.

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