Question

In the choke ring antenna there are concentric cylinders placed around the antenna that are of a certain depth to minimize the multipath effect. If the signal wavelength is \( \lambda \), then the depth of the cylinders in the choke ring antenna should be

• A. \( \text{exactly } \frac{\lambda}{4} \)
• B. \( \text{slightly more than } \frac{\lambda}{4} \text{ and far less than } \frac{\lambda}{2} \)
• C. \( \text{exactly } \frac{\lambda}{2} \)
• D. \( \text{slightly more than } \frac{\lambda}{2} \text{ and far less than } \lambda \)

Hint:

In choke ring antennas, remember the optimal choke depth lies between \( \frac{\lambda}{4} \) and \( \frac{\lambda}{2} \), just slightly above \( \frac{\lambda}{4} \), to cancel multipath interference effectively.

Answer 1

The Correct Option is B

Choke ring antennas are designed to minimize multipath effects by incorporating concentric metal rings (chokes) around the main antenna element. The depth of these rings is critical for optimal performance.

To effectively suppress multipath signals, the depth of the chokes is made:

Slightly more than \( \frac{\lambda}{4} \) to cause destructive interference with reflected signals,
But kept well below \( \frac{\lambda}{2} \) to avoid resonance and maintain the required suppression characteristics.

This specific depth causes reflected signals to undergo a phase shift that cancels their effect when they reach the antenna, improving signal clarity.