Question

A baseband signal of $3.5\text{MHz}$ frequency is modulated with a carrier signal of $3.5\text{GHz}$ frequency using amplitude modulation method. What should be the minimum size of antenna required to transmit the modulated signal?

• A. $21.4\text{mm}$
• B. $42.8\text{m}$
• C. $42.8\text{mm}$
• D. $21.4\text{m}$

Answer 1

The correct option is A $21.4\text{mm}$

$v_c=3.5\times {10}^9\text{Hz}$
$\therefore \lambda =\frac{c}{v_c}=\frac{3\times {10}^8}{3.5\times {10}^9}$
$\therefore$ Size of antenna $=\frac{\lambda }{4}$
$=\frac{8.57\times {10}^{-2}}{4}$
$=21.4\text{mm}$