Millimetre-wave radar generates a narrower beam than conventional microwave radar. This makes it less vulnerable to antiradar missiles. (a) We have to calculate the angular width, from first minimum to first minimum, of the central “lobe” produced by a 220-GHz radar beam emitted by a 55-cm diameter circular antenna. (b) We have to calculate the same quantity for a ship’s radar with a wavelength of 1.57 cm, and a 2.33 m diameter antenna.
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Solution: Click For PDF Version The wavelength of radar waves of 220-GHz frequency is
In a diffraction pattern from a circular antenna of diameter d, the angular position of the first minima is given by the relation
As the diameter of the antenna is
we note that
Therefore,
the angular width of the central “lobe” will be
(b) In the second part of the problem the relevant data are
We have
The angular
width of the central “lobe” will be
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