Question

The minimum size of an antenna for transmitting electromagnetic waves at \(1500\ \text{MHz}\) is

• A. \(2\ \text{cm}\)
• B. \(5\ \text{cm}\)
• C. \(5\ \text{m}\)
• D. \(200\ \text{m}\)

Hint:

For transmission and reception of electromagnetic waves, the minimum practical antenna length is approximately \[ L=\frac{\lambda}{4}. \] First calculate the wavelength using \[ \lambda=\frac{c}{f}, \] and then divide by 4.

Answer 1

The Correct Option is B

Step 1: Find wavelength of 1500 MHz signal.
\( \lambda = \frac{c}{f} = \frac{3\times10^8}{1500\times10^6} = 0.2\text{ m} = 20\text{ cm} \).

Step 2: Minimum antenna size.
Minimum effective antenna length \( = \lambda/4 = 20/4 = 5\text{ cm} \).

\[ \boxed{\text{Minimum antenna size} = 5\text{ cm}} \]