wayground logo

Free Printable Worksheets

Font size

S
M
L
XL
Worksheets

Introduction to Half-Wave Dipole

Total questions: 10

Worksheet time: 5mins

Name
Class
Date
1.

For a half-wave dipole antenna in free space, what is the physical length of the conducting element relative to the wavelength?

a)

Approximately one full wavelength long

b)

Approximately half a wavelength long

c)

Approximately one-quarter wavelength long

d)

Approximately two wavelengths long

2.

A center-fed half-wave dipole is analyzed by assuming which current distribution along its length?

a)

Triangular current tapering to the center

b)

Uniform current along the entire length

c)

Sinusoidal current with nulls at the ends

d)

Piecewise constant current in two sections

3.

In the far-field approximation for a linear antenna, the distance from a current element to a distant point P is simplified as R ≈ r − z cosθ. What additional approximation is typically made for the denominator when integrating for Az at large r?

a)

Replace 1/R by 1/(r − z cosθ) exactly

b)

Replace R by r in magnitude only

c)

Keep R exact without approximation

d)

Replace R by r − z cosθ everywhere

4.

For a centre-fed dipole with total length l = 2h = λ/2 and phase constant β = 2π/λ, which trigonometric identities convert sinβ(h ± z) into functions of βz in the Az derivation?

a)

sinβ(h+z)=−cosβz and sinβ(h−z)=−cosβz

b)

sinβ(h+z)=sinβz and sinβ(h−z)=sinβz

c)

sinβ(h+z)=cos2βz and sinβ(h−z)=cos2βz

d)

sinβ(h+z)=cosβz and sinβ(h−z)=cosβz

5.

During simplification, the term ejβzcosθ+ejβzcosθe^{jβz cosθ} + e^{−jβz cosθ} appears inside the integral for Az. Which identity is used to replace this sum, and what does it become?

a)

Euler identity giving 2 sin(βz cosθ)

b)

Euler identity giving 2 cos(βz cosθ)

c)

De Moivre theorem giving cos(2βz cosθ)

d)

Phasor addition giving ej2βzcosθe^{j2\beta z \cos\theta}

6.

After applying the product-to-sum identity 2cosAcosB=cos(A+B)+cos(AB)2 \cos A \cos B = \cos(A+B) + \cos(A−B) and integrating from 0 to h with βh=π2\beta h = \frac{\pi}{2} , which final angular factor multiplies μImejβr/(2πβr)\mu I_m e^{-j\beta r}/(2\pi\beta r) in Az for the half-wave dipole far field?

a)

sin(π cosθ)/sinθ

b)

cos(π cosθ)/sinθ

c)

sin(π cosθ)/cosθ

d)

cos(π cosθ)/cosθ

7.

In free space, the intrinsic impedance η relates the magnitudes of the far‑field components as η = |Eθ|/|Hφ|. What numerical value of η is used to compute Eθ from Hφ in the notes?

a)

60π ohms approximately 188.5 ohms

b)

120π ohms approximately 377 ohms

c)

30π ohms approximately 94.2 ohms

d)

240π ohms approximately 754 ohms

8.

The maximum time‑average power density (W/m²) radiated by a short dipole is found using the Poynting vector. Which expression is used for the peak value before averaging?

a)

Pmax = |Eθ||Hφ| in the far field

b)

Pmax = |Eθ|²/η at any distance

c)

Pmax = η|Hφ|² in the near field

d)

Pmax = Re{Eθ·Hφ*}/2 everywhere

9.

For the given short dipole derivation, the radiation resistance is taken as which value?

a)

36.5 ohms for a monopole over ground

b)

50 ohms matching line impedance

c)

73 ohms for the thin half‑wave dipole

d)

120π ohms free‑space impedance

10.

Using Aem = V²/(4S Rrad) with V = Eλ/π and S = E²/η, the maximum effective aperture is obtained as Aem ≈ 0.13λ². What directivity value D follows from D = 4πAem/λ²?

a)

D ≈ 1.63 dimensionless

b)

D ≈ 2.50 dimensionless

c)

D ≈ 4.00 dimensionless

d)

D ≈ 0.50 dimensionless