With equal thin conductors at resonance, a folded dipole input resistance is roughly what multiple of a half-wave dipole?
A Four times
B Ten times
C One-half
D Twice
Answer: A. Four times. For equal thin conductors, the resonant folded dipole resistance is about four times that of a half-wave dipole.
Feed-point impedance is terminal voltage divided by?
A Frequency
B Current
C Power density
D Wavelength
Answer: B. Current. Input impedance is the voltage-to-current ratio at the antenna feed point.
VSWR for a perfect impedance match equals what?
A Infinite
B 1:1
C 2:1
D 3:1
Answer: B. 1:1. A perfect match has no reflected wave, giving VSWR equal to one.
Radome design aims for transparency to what?
A RF energy
B Visible sound
C Static charge
D Mechanical torque
Answer: A. RF energy. A radome protects the antenna while allowing its operating radio-frequency energy to pass.
Return loss in decibels is calculated as?
A 20 log₁₀ |Γ|
B 10 |Γ|
C −10 log₁₀ Γ
D −20 log₁₀ |Γ|
Answer: D. −20 log₁₀ |Γ|. Return loss is −20 log₁₀ of the reflection-coefficient magnitude.
Compared with its driven element, a Yagi reflector is usually?
A Longer
B Electrically absent
C Shorter
D Equal length
Answer: A. Longer. The reflector is typically slightly longer than the driven element.
Yagi-Uda directors are typically what length relative to the driven element?
A Longer
B Shorter
C Half wavelength
D Equal length
Answer: B. Shorter. Directors are typically slightly shorter than the driven element.
Horn antennas are widely used at?
A Power-line frequencies
B Audio frequencies
C DC frequencies
D Microwave frequencies
Answer: D. Microwave frequencies. Horn antennas are practical aperture antennas at microwave frequencies.
In a uniform in-phase broadside array, maximum radiation is perpendicular to its?
A Feed cable
B Reflector surface
C Ground plane
D Array axis
Answer: D. Array axis. A broadside array has its principal beam normal to the line of array elements.
Which direction describes an end-fire array's main lobe?
A Into the ground
B Perpendicular to axis
C Along array axis
D Toward its feed
Answer: C. Along array axis. The principal beam of an end-fire array points along its axis.
Equal orthogonal E components in quadrature produce?
A Zero field
B Linear polarization
C Unpolarized noise
D Circular polarization
Answer: D. Circular polarization. Equal orthogonal components with a 90-degree phase difference produce circular polarization.
Circular polarization has axial ratio equal to?
A Zero
B One
C Infinite
D Two
Answer: B. One. A circularly polarized wave has equal major and minor ellipse axes, so its axial ratio is one.
Omnidirectional antennas are nearly uniform in which plane?
A Azimuth
B Feed plane
C Elevation only
D Every direction
Answer: A. Azimuth. Omnidirectional commonly means approximately constant radiation around the azimuth plane.
HF skywave links can use refraction in the?
A Troposphere only
B Ground layer
C Stratosphere
D Ionosphere
Answer: D. Ionosphere. Ionospheric refraction can return suitable HF waves toward Earth for long-distance links.
Ground-wave propagation tends to follow the?
A Cloud tops
B Ionosphere
C Earth's surface
D Satellite orbit
Answer: C. Earth's surface. Ground waves travel along or near the Earth's surface.
Tropospheric ducting guides waves through what feature?
A Magnetic poles
B Metal cavities
C Refractive layers
D Vacuum gaps
Answer: C. Refractive layers. A refractive-index gradient can form a duct that guides radio waves in the troposphere.
Diffraction allows radio waves to bend around?
A Perfect matches
B Obstacles
C Feed points
D Carrier tones
Answer: B. Obstacles. Diffraction spreads wave energy into regions shadowed by obstacles.
Keeping the first Fresnel zone clear helps reduce what?
A Path obstruction
B Antenna noise
C Polarization
D Feed resistance
Answer: A. Path obstruction. Obstruction of the first Fresnel zone can add loss even when a geometric line of sight exists.
With frequency fixed, doubling link distance adds roughly how much free-space loss?
A +1 dB
B +6 dB
C +3 dB
D +12 dB
Answer: B. +6 dB. Free-space received power falls with range squared, so doubling distance adds about 6 dB loss.
Ideal linear antennas misaligned by 45° receive what power fraction?
A Three-quarters
B One-quarter
C One-half
D All power
Answer: C. One-half. The polarization factor is cos²(45°), equal to one-half.
Cross-polarization is oriented how relative to desired polarization?
A Parallel
B Longitudinally
C Randomly
D Orthogonally
Answer: D. Orthogonally. Cross-polarization denotes the field component orthogonal to the desired polarization.
Two nonzero orthogonal field components of unequal amplitude in quadrature produce which polarization?
A Unpolarized
B Linear
C Elliptical
D Circular
Answer: C. Elliptical. Unequal nonzero orthogonal components in quadrature trace an ellipse.
Far-field electric amplitude falls approximately how with range?
A Constant
B 1/R²
C 1/R
D R
Answer: C. 1/R. A spherical wave's field amplitude decays inversely with range; power density decays as 1/R².
Space-wave line-of-sight links are common in?
A ELF only
B VHF and above
C Audio bands
D DC systems
Answer: B. VHF and above. VHF, UHF, and microwave links commonly use space-wave line-of-sight propagation.
Beam steering in a phased array changes relative what?
A Element phases
B Carrier amplitude only
C Ground color
D Feedline length only
Answer: A. Element phases. Controlled phase differences between elements shift the array's constructive-interference direction.