05-03-2013, 03:48 PM
ANTENNAS:FOR ALL APPLICATIONS, THIRD EDITION.
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Approximate directivities.
Calculate the approximate directivity from the half-power beam widths of a
unidirectional antenna if the normalized power pattern is given by: (a) Pn = cos θ, (b) Pn
= cos2 θ, © Pn = cos3 θ, and (d) Pn = cosn θ. In all cases these patterns are unidirectional
(+z direction) with Pn having a value only for zenith angles 0° ≤ θ ≤ 90° and Pn = 0 for
90° ≤ θ ≤ 180°. The patterns are independent of the azimuth angle φ.
Effective aperture and beam area.
What is the maximum effective aperture (approximately) for a beam antenna having halfpower
widths of 30° and 35° in perpendicular planes intersecting in the beam axis?
Minor lobes are small and may be neglected.
Received power and the Friis formula.
What is the maximum power received at a distance of 0.5 km over a free-space 1 GHz
circuit consisting of a transmitting antenna with a 25 dB gain and a receiving antenna
with a 20 dB gain? The gain is with respect to a lossless isotropic source. The
transmitting antenna input is 150 W.
Mars and Jupiter links.
(a) Design a two-way radio link to operate over earth-Mars distances for data and picture
transmission with a Mars probe at 2.5 GHz with a 5 MHz bandwidth. A power of 10-19
W Hz-1 is to be delivered to the earth receiver and 10-17 W Hz-1 to the Mars receiver. The
Mars antenna must be no larger than 3 m in diameter. Specify effective aperture of Mars
and earth antennas and transmitter power (total over entire bandwidth) at each end. Take
earth-Mars distance as 6 light-minutes. (b) Repeat (a) for an earth-Jupiter link. Take the
earth-Jupiter distance as 40 light-minutes.