Antenna Measurements Questions and Answers – Near Field and Far Field

This set of Antennas Multiple Choice Questions & Answers (MCQs) focuses on “Near Field and Far Field”.

1. The region greater than $$\frac{2D^2}{λ}$$ in an antenna with largest dimension D is called _____
a) Far field region
b) Near filed region
d) Reactive Field

Explanation: The characteristics of EM fields vary with distance from the antenna. It is divided into two regions. The region next to the antenna is the near field region and the region Far field region > $$\frac{2D^2}{λ}$$.

2. Which of the following is known as Non Radiative region?
a) Far field region
b) Near filed region
d) Reactive Field

Explanation: Radiative and reactive field regions are the parts of the near field region. The Far field region is greater than $$\frac{2D^2}{λ}$$and near field region is less than $$\frac{2D^2}{λ}$$. Reactive region is also known as non- Radiative region and is next to antenna. The Radiative region is also known as Fresnel region.

3. Which of the following is true?
a) Radiative Field < 0.62$$\sqrt{\frac{D^3}{λ}}$$
b) Reactive Field < 0.62$$\sqrt{\frac{D^3}{λ}}$$
c) Fresnel Field << 0.62$$\sqrt{\frac{D^2}{λ}}$$
d) Near field > $$\frac{2D^2}{λ}$$

Explanation: The characteristics of EM fields vary with distance from the antenna. It is divided into two regions. The region next to the antenna is the near field region and the region Far field region > $$\frac{2D^2}{λ}$$. Reactive field < 0.62$$\sqrt{\frac{D^3}{λ}} < \,Radiative\, field\, < \frac{2D^2}{λ}$$.

4. Radiative and Non Radiative fields are parts of which field region?
a) Near field
b) Fresnel field
c) Reactive field
d) Far field

Explanation: The Near field region is less than $$\frac{2D^2}{λ}$$ the Far field region is greater than$$\frac{2D^2}{λ}$$. Radiative and reactive field regions are the parts of the near field region. Reactive region is also known as non- Radiative region and is next to antenna. The Radiative region is also known as Fresnel region.

5. Near field is also known as inductive field.
a) True
b) False

Explanation: The region next to the antenna is the near field region and it is less than $$\frac{2D^2}{λ}$$. Near field has inductive effect hence it is also known as the inductive field. The far field is known as the radiating field as radiation is high in that region.
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Sanfoundry Global Education & Learning Series – Antennas.

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