To radiate EM signal of wavelenth `lambda` with high efficiency, the antennas should have a minimum size equal to :

Options

A. `lambda/4`
B. `lambda`
C. `lambda/2`
D. `2lambda`

Answer

To determine the minimum size of antennas required to radiate an electromagnetic signal of wavelength \( \lambda \) with high efficiency, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Antenna Size Requirement**:
- Antennas are designed to efficiently radiate electromagnetic waves. The efficiency of radiation is significantly influenced by the size of the antenna relative to the wavelength of the signal being transmitted.

2. **Minimum Size of Antenna**:
- A common rule of thumb in antenna theory states that for efficient radiation, the size of the antenna should be at least a fraction of the wavelength. Specifically, the minimum size is often taken to be \( \frac{\lambda}{4} \).

3. **Evaluating the Options**:
- Given the options:
- (A) \( \frac{\lambda}{4} \)
- (B) \( \frac{\lambda}{2} \)
- (C) \( \frac{\lambda}{2} \)
- (D) \( \frac{\lambda}{2} \)
- Since we established that the minimum size for high efficiency is \( \frac{\lambda}{4} \), we can conclude that option (A) is correct.

4. **Final Conclusion**:
- Therefore, the minimum size of the antennas required to radiate an electromagnetic signal of wavelength \( \lambda \) with high efficiency is:
\[ \text{Minimum size} = \frac{\lambda}{4} \]

### Final Answer:
The correct option is (A) \( \frac{\lambda}{4} \).

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