Oscillation is produced by sparking between 2 hollow hemispheres and
the interposed sphere. There is a bead of platinum on the inside
surface of each hemisphere. For some experiments, a lens of glass
or of sulphur was used to collimate the radiation - the first
waveguide-lens antenna. The lens was designed according to the
refractive index measured by Bose at the wavelength in use. Figure
3(b) shows Bose's drawing of such a radiator; the sparks
occur between the two outer spheres to the inner sphere, at the
focal point of the lens L at the right. Bose
was able to measure the wavelength of his radiation with a reflecting
diffraction grating made of metal strips [7].
Figure 4(a)
is a photograph of one of his radiating antennas; part
of the spark oscillations are generated inside the overmoded
circular waveguide. A polarizing grid is built into the antenna,
clearly visible at the radiating end of the waveguide. Figure
4(b) shows a closeup of the dual spark gaps used for the transmitter;
the sparks are generated between the 2 outer spheres and the inner
sphere. Figure 4(c) shows both a transmitting antenna (left) and
the receiver (right), with a dual prism in between set on the
experimental rotating table.
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Figure 3(b)
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Figure 3 Bose's diagrams of his radiators.
(a) shows the radiator used to generated
5-mm radiation, while (b) shows the arrangement with a lens L at the exit of the waveguide [2].
In some designs the mounting stems for the outer spheres could
be inclined to adjust the dimension of the spark gaps.
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