WorksheetsIntroduction to Half-Wave Dipole
Total questions: 10
Worksheet time: 5mins
For a half-wave dipole antenna in free space, what is the physical length of the conducting element relative to the wavelength?
Approximately one full wavelength long
Approximately half a wavelength long
Approximately one-quarter wavelength long
Approximately two wavelengths long
A center-fed half-wave dipole is analyzed by assuming which current distribution along its length?
Triangular current tapering to the center
Uniform current along the entire length
Sinusoidal current with nulls at the ends
Piecewise constant current in two sections
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?
Replace 1/R by 1/(r − z cosθ) exactly
Replace R by r in magnitude only
Keep R exact without approximation
Replace R by r − z cosθ everywhere
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?
sinβ(h+z)=−cosβz and sinβ(h−z)=−cosβz
sinβ(h+z)=sinβz and sinβ(h−z)=sinβz
sinβ(h+z)=cos2βz and sinβ(h−z)=cos2βz
sinβ(h+z)=cosβz and sinβ(h−z)=cosβz
During simplification, the term ejβzcosθ+e−jβzcosθ appears inside the integral for Az. Which identity is used to replace this sum, and what does it become?
Euler identity giving 2 sin(βz cosθ)
Euler identity giving 2 cos(βz cosθ)
De Moivre theorem giving cos(2βz cosθ)
Phasor addition giving ej2βzcosθ
After applying the product-to-sum identity 2cosAcosB=cos(A+B)+cos(A−B) and integrating from 0 to h with βh=2π , which final angular factor multiplies μIme−jβr/(2πβr) in Az for the half-wave dipole far field?
sin(π cosθ)/sinθ
cos(π cosθ)/sinθ
sin(π cosθ)/cosθ
cos(π cosθ)/cosθ
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?
60π ohms approximately 188.5 ohms
120π ohms approximately 377 ohms
30π ohms approximately 94.2 ohms
240π ohms approximately 754 ohms
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?
Pmax = |Eθ||Hφ| in the far field
Pmax = |Eθ|²/η at any distance
Pmax = η|Hφ|² in the near field
Pmax = Re{Eθ·Hφ*}/2 everywhere
For the given short dipole derivation, the radiation resistance is taken as which value?
36.5 ohms for a monopole over ground
50 ohms matching line impedance
73 ohms for the thin half‑wave dipole
120π ohms free‑space impedance
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?
D ≈ 1.63 dimensionless
D ≈ 2.50 dimensionless
D ≈ 4.00 dimensionless
D ≈ 0.50 dimensionless
