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Antenna & Wave Propagation MCQs

Practice Antenna & Wave Propagation MCQs from fundamental concepts through intermediate, advanced and application-oriented questions. Each page contains up to 100 questions with answers and explanations where available.

Question 1
Antenna & Wave PropagationAntenna Fundamentals

The primary function of a transmitting antenna is to convert?

  • AGuided electromagnetic energy into radiated electromagnetic waves
  • BDC power directly into mechanical energy
  • CSound waves into heat only
  • DDigital data into resistance
Report an error
Correct Answer: A. Guided electromagnetic energy into radiated electromagnetic waves
Explanation: A transmitting antenna couples guided RF energy from a transmission system into electromagnetic waves that propagate through space.
Reference: Standard antenna and wave propagation: antenna fundamentals
Question 2
Antenna & Wave PropagationAntenna Fundamentals

A receiving antenna primarily converts incident electromagnetic waves into?

  • AElectrical signals available at its terminals
  • BMechanical rotation only
  • CDC resistance only
  • DOptical energy only
Report an error
Correct Answer: A. Electrical signals available at its terminals
Explanation: A receiving antenna intercepts electromagnetic energy and produces a corresponding electrical signal at its terminals.
Reference: Standard antenna and wave propagation: antenna fundamentals
Question 3
Antenna & Wave PropagationRadiation Pattern

The radiation pattern of an antenna describes the variation of its radiation properties with?

  • ADirection in space
  • BSupply voltage only
  • CConductor resistance only
  • DTime of day
Report an error
Correct Answer: A. Direction in space
Explanation: An antenna radiation pattern shows how radiation intensity, field strength or related quantities vary with direction.
Reference: Standard antenna and wave propagation: radiation pattern
Question 6
Antenna & Wave PropagationRadiation Pattern

A lobe other than the major lobe is generally called a?

  • AMinor lobe
  • BIsotropic lobe
  • CFeed lobe
  • DImpedance lobe
Report an error
Correct Answer: A. Minor lobe
Explanation: Side lobes and back lobes are collectively minor lobes because they are not the principal radiation lobe.
Reference: Standard antenna and wave propagation: radiation pattern
Question 7
Antenna & Wave PropagationIsotropic Radiator

An isotropic radiator is a hypothetical antenna that radiates?

  • AEqually in all directions
  • BOnly along one axis
  • COnly in the horizontal plane
  • DNo power
Report an error
Correct Answer: A. Equally in all directions
Explanation: An isotropic radiator is an ideal reference source with uniform radiation intensity in every direction.
Reference: Standard antenna and wave propagation: isotropic radiator
Question 8
Antenna & Wave PropagationDirectivity & Gain

The directivity of an isotropic radiator is?

  • A1 or 0 dBi
  • B2 or 3 dBi
  • C1.64 or 2.15 dBi
  • DInfinite
Report an error
Correct Answer: A. 1 or 0 dBi
Explanation: By definition, an isotropic radiator has directivity 1, corresponding to 0 dBi.
Reference: Standard antenna and wave propagation: directivity & gain
Question 9
Antenna & Wave PropagationDirectivity & Gain

Antenna directivity is the ratio of radiation intensity in a specified direction to?

  • AAverage radiation intensity over all directions
  • BInput current only
  • COhmic resistance
  • DWavelength squared only
Report an error
Correct Answer: A. Average radiation intensity over all directions
Explanation: Directivity compares radiation intensity in a given direction, usually its maximum, with the average radiation intensity.
Reference: Standard antenna and wave propagation: directivity & gain
Question 10
Antenna & Wave PropagationDirectivity & Gain

Antenna gain differs from directivity because gain also accounts for?

  • AAntenna efficiency
  • BOnly operating frequency
  • COnly polarization direction
  • DSpeed of light
Report an error
Correct Answer: A. Antenna efficiency
Explanation: Gain includes the effect of radiation efficiency, whereas directivity is based on the shape of the radiation pattern.
Reference: Standard antenna and wave propagation: directivity & gain
Question 12
Antenna & Wave PropagationDirectivity & Gain

A power gain of 10 corresponds to approximately?

  • A3 dB
  • B10 dB
  • C20 dB
  • D100 dB
Report an error
Correct Answer: B. 10 dB
Explanation: Gain in decibels is 10log10(10)=10 dB.
Reference: Standard antenna and wave propagation: directivity & gain
Question 14
Antenna & Wave PropagationBeamwidth

A narrower main beam generally indicates?

  • AHigher directivity
  • BLower directivity in every case
  • CZero gain
  • DNo radiation
Report an error
Correct Answer: A. Higher directivity
Explanation: Concentrating radiation into a narrower angular region generally increases antenna directivity.
Reference: Standard antenna and wave propagation: beamwidth
Question 15
Antenna & Wave PropagationAntenna Resistance

Radiation resistance is a fictitious resistance that represents?

  • APower radiated by the antenna
  • BOnly conductor heating loss
  • CDielectric breakdown
  • DFeed-line reactance only
Report an error
Correct Answer: A. Power radiated by the antenna
Explanation: Radiation resistance is defined so that the power attributed to it equals the antenna's radiated power for the specified current convention.
Reference: Standard antenna and wave propagation: antenna resistance
Question 16
Antenna & Wave PropagationAntenna Efficiency

Antenna radiation efficiency is commonly defined as radiated power divided by?

  • AAccepted input power
  • BIncident power density only
  • CReactive power only
  • DReflected power only
Report an error
Correct Answer: A. Accepted input power
Explanation: Radiation efficiency is the fraction of power accepted by the antenna that is actually radiated rather than dissipated as loss.
Reference: Standard antenna and wave propagation: antenna efficiency
Question 18
Antenna & Wave PropagationAntenna Impedance

For maximum power transfer between a transmission line and an antenna at a single frequency, the antenna input impedance should ideally be?

  • AMatched to the line impedance
  • BZero
  • CInfinite
  • DPurely capacitive regardless of the line
Report an error
Correct Answer: A. Matched to the line impedance
Explanation: Impedance matching minimizes reflection and permits efficient transfer of power from the line to the antenna.
Reference: Standard antenna and wave propagation: antenna impedance
Question 19
Antenna & Wave PropagationPolarization

The polarization of an antenna is normally defined by the polarization of the wave it?

  • ARadiates in a specified direction
  • BAbsorbs as heat only
  • CReflects from the ground only
  • DCarries inside a DC cable
Report an error
Correct Answer: A. Radiates in a specified direction
Explanation: Antenna polarization is described by the electric-field polarization of its radiated wave in the direction considered.
Reference: Standard antenna and wave propagation: polarization
Question 20
Antenna & Wave PropagationDipole Antennas

A vertically oriented half-wave dipole ideally produces what polarization in its broadside direction?

  • AVertical linear polarization
  • BHorizontal linear polarization
  • CCircular polarization automatically
  • DUnpolarized radiation
Report an error
Correct Answer: A. Vertical linear polarization
Explanation: The electric field of a thin dipole is oriented parallel to the dipole axis, giving vertical linear polarization for a vertical dipole.
Reference: Standard antenna and wave propagation: dipole antennas
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Question 26
Antenna & Wave PropagationDipole Antennas

The radiation pattern of an ideal half-wave dipole has maximum radiation in directions?

  • AAlong the dipole axis
  • BPerpendicular to the dipole axis
  • COnly at 45 degrees to the axis
  • DEqually in every direction
Report an error
Correct Answer: B. Perpendicular to the dipole axis
Explanation: A thin half-wave dipole has maximum radiation broadside to its axis and nulls along the axis.
Reference: Standard antenna and wave propagation: dipole antennas
Question 28
Antenna & Wave PropagationFriis Transmission

The Friis free-space transmission equation is primarily used to estimate?

  • AReceived power between antennas in free-space far-field conditions
  • BConductor skin depth
  • CAntenna mechanical strength
  • DIonospheric critical frequency only
Report an error
Correct Answer: A. Received power between antennas in free-space far-field conditions
Explanation: The Friis equation relates transmitted power, antenna gains, wavelength and separation to received power under ideal free-space far-field conditions.
Reference: Standard antenna and wave propagation: friis transmission
Question 29
Antenna & Wave PropagationFriis Transmission

In ideal free-space propagation, if the distance between transmitting and receiving antennas is doubled while all other factors remain unchanged, received power becomes?

  • ATwice
  • BHalf
  • COne-fourth
  • DOne-eighth
Report an error
Correct Answer: C. One-fourth
Explanation: The Friis equation gives received power proportional to 1/R², so doubling distance reduces received power to one-fourth.
Reference: Standard antenna and wave propagation: friis transmission
Question 30
Antenna & Wave PropagationAntenna Arrays

An antenna array is formed by using?

  • AMultiple radiating elements arranged and excited to obtain a desired radiation pattern
  • BA single resistor only
  • COnly one isotropic point with no feed
  • DA capacitor bank with no radiators
Report an error
Correct Answer: A. Multiple radiating elements arranged and excited to obtain a desired radiation pattern
Explanation: Arrays combine fields from multiple antenna elements to shape beam direction, gain and sidelobe behavior.
Reference: Standard antenna and wave propagation: antenna arrays
Question 31
Antenna & Wave PropagationAntenna Arrays

In a broadside linear array, the principal maximum is ideally directed?

  • AAlong the array axis
  • BPerpendicular to the array axis
  • COnly toward the feed point
  • DRandomly
Report an error
Correct Answer: B. Perpendicular to the array axis
Explanation: A broadside array is phased so that its main beam is normal to the array axis.
Reference: Standard antenna and wave propagation: antenna arrays
Question 32
Antenna & Wave PropagationAntenna Arrays

In an end-fire array, the principal radiation is directed approximately?

  • AAlong the array axis
  • BPerpendicular to the array axis
  • COnly vertically regardless of orientation
  • DEqually in all directions
Report an error
Correct Answer: A. Along the array axis
Explanation: An end-fire array is phased to produce its main beam along the array axis.
Reference: Standard antenna and wave propagation: antenna arrays
Question 33
Antenna & Wave PropagationAntenna Arrays

The array factor of an antenna array primarily depends on element?

  • APositions and relative excitation amplitudes/phases
  • BConductor color
  • CMechanical weight only
  • DDielectric breakdown voltage only
Report an error
Correct Answer: A. Positions and relative excitation amplitudes/phases
Explanation: Array factor is determined by the geometry and relative complex excitation of the elements, separate from the individual element pattern.
Reference: Standard antenna and wave propagation: antenna arrays
Question 34
Antenna & Wave PropagationYagi-Uda Antenna

A Yagi-Uda antenna normally consists of a driven element together with?

  • AA reflector and one or more directors
  • BOnly a parabolic dish
  • COnly a horn aperture
  • DTwo identical ground planes with no parasitic elements
Report an error
Correct Answer: A. A reflector and one or more directors
Explanation: A typical Yagi-Uda uses one driven element, usually a dipole, plus a reflector and one or more parasitic directors.
Reference: Standard antenna and wave propagation: yagi-uda antenna
Question 35
Antenna & Wave PropagationYagi-Uda Antenna

In a conventional Yagi-Uda antenna, the reflector is generally placed?

  • ABehind the driven element relative to the main radiation direction
  • BIn front of all directors
  • CAt the exact same position as the driven element
  • DOnly inside the feed cable
Report an error
Correct Answer: A. Behind the driven element relative to the main radiation direction
Explanation: The reflector is placed behind the driven element and helps reinforce radiation toward the directors.
Reference: Standard antenna and wave propagation: yagi-uda antenna
Question 36
Antenna & Wave PropagationYagi-Uda Antenna

Adding suitably designed directors to a Yagi-Uda antenna generally tends to?

  • AIncrease directivity in the forward direction
  • BMake it perfectly isotropic
  • CEliminate all impedance
  • DForce radiation only backward
Report an error
Correct Answer: A. Increase directivity in the forward direction
Explanation: Directors concentrate radiation in the forward direction and can increase Yagi-Uda directivity.
Reference: Standard antenna and wave propagation: yagi-uda antenna
Question 37
Antenna & Wave PropagationHorn Antenna

A horn antenna is commonly used at?

  • AMicrowave frequencies
  • BOnly audio frequencies
  • CDC only
  • DPower-line frequency only
Report an error
Correct Answer: A. Microwave frequencies
Explanation: Horn antennas are practical high-frequency aperture antennas widely used in microwave systems and as feeds for reflectors.
Reference: Standard antenna and wave propagation: horn antenna
Question 38
Antenna & Wave PropagationHorn Antenna

A major purpose of gradually flaring a waveguide into a horn is to?

  • AProvide a smoother transition from waveguide to free space
  • BCreate a DC short circuit
  • CStop all radiation
  • DIncrease conductor resistance intentionally
Report an error
Correct Answer: A. Provide a smoother transition from waveguide to free space
Explanation: The flare provides a gradual impedance transition and a larger radiating aperture, improving radiation into free space.
Reference: Standard antenna and wave propagation: horn antenna
Question 40
Antenna & Wave PropagationParabolic Reflector

A parabolic reflector antenna produces high directivity mainly because it?

  • AForms a large effective aperture and converts spherical wavefronts to approximately planar wavefronts
  • BRadiates equally in all directions
  • CUses only a resistive load
  • DHas zero physical aperture
Report an error
Correct Answer: A. Forms a large effective aperture and converts spherical wavefronts to approximately planar wavefronts
Explanation: With a feed near its focus, a paraboloid collimates radiation into a narrow beam, giving high gain/directivity.
Reference: Standard antenna and wave propagation: parabolic reflector
Question 41
Antenna & Wave PropagationDipole Antennas

The directivity of a half-wave dipole is approximately?

  • A1 or 0 dBi
  • B1.64 or 2.15 dBi
  • C3.28 or 5.16 dBi
  • D10 or 10 dBi
Report an error
Correct Answer: B. 1.64 or 2.15 dBi
Explanation: A half-wave dipole has maximum directivity about 1.64, corresponding to approximately 2.15 dBi.
Reference: Standard antenna and wave propagation: dipole antennas
Question 42
Antenna & Wave PropagationParabolic Reflector

For a parabolic reflector of fixed efficiency and wavelength, increasing the dish diameter generally?

  • AIncreases gain and narrows the beam
  • BDecreases gain and narrows the beam
  • CLeaves gain unchanged
  • DMakes the antenna isotropic
Report an error
Correct Answer: A. Increases gain and narrows the beam
Explanation: Reflector gain is approximately proportional to (D/lambda)², so a larger diameter gives higher gain and a narrower beam.
Reference: Standard antenna and wave propagation: parabolic reflector
Question 43
Antenna & Wave PropagationMonopole Antennas

The approximate directivity of a quarter-wave monopole over an ideal infinite conducting ground plane is?

  • A1 or 0 dBi
  • B1.64 or 2.15 dBi
  • C3.28 or 5.15 dBi
  • D10 or 10 dBi
Report an error
Correct Answer: C. 3.28 or 5.15 dBi
Explanation: An ideal quarter-wave monopole radiates into one hemisphere and has about twice the directivity of a half-wave dipole, approximately 3.28 or 5.15 dBi.
Reference: Standard antenna and wave propagation: monopole antennas
Question 44
Antenna & Wave PropagationEffective Aperture

For a receiving antenna, effective aperture Ae and gain G are related by?

  • AAe = G lambda²/(4 pi)
  • BAe = 4 pi G/lambda²
  • CAe = G/(4 pi lambda²)
  • DAe = lambda/(4 pi G)
Report an error
Correct Answer: A. Ae = G lambda²/(4 pi)
Explanation: For a matched receiving antenna, effective aperture is related to gain by Ae=Gλ²/(4π).
Reference: Standard antenna and wave propagation: effective aperture
Question 45
Antenna & Wave PropagationSky-Wave Propagation

Sky-wave propagation relies mainly on refraction/return of radio waves by the?

  • AIonosphere
  • BTropospheric ground surface only
  • COcean floor
  • DTransmission-line dielectric
Report an error
Correct Answer: A. Ionosphere
Explanation: In sky-wave communication, ionized atmospheric layers can bend suitable radio waves back toward Earth.
Reference: Standard antenna and wave propagation: sky-wave propagation
Question 46
Antenna & Wave PropagationSpace-Wave Propagation

Line-of-sight or space-wave propagation is especially important at?

  • AVHF and higher frequencies
  • BOnly very low frequency
  • CDC
  • DAudio frequency
Report an error
Correct Answer: A. VHF and higher frequencies
Explanation: At VHF, UHF and microwave frequencies, propagation is predominantly line-of-sight or space-wave because ionospheric return is generally not the normal mode.
Reference: Standard antenna and wave propagation: space-wave propagation
Question 47
Antenna & Wave PropagationSpace-Wave Propagation

If transmitting and receiving antenna heights are increased, the radio line-of-sight range generally?

  • AIncreases
  • BDecreases to zero
  • CRemains exactly unchanged
  • DBecomes independent of Earth curvature
Report an error
Correct Answer: A. Increases
Explanation: Increasing antenna heights extends the geometric/radio horizon and therefore generally increases line-of-sight range.
Reference: Standard antenna and wave propagation: space-wave propagation
Question 48
Antenna & Wave PropagationSpace-Wave Propagation

Which propagation mode is normally most appropriate for a terrestrial microwave point-to-point link?

  • ALine-of-sight space-wave propagation
  • BGround wave around the entire Earth
  • CIonospheric sky wave as the primary mode
  • DConduction through soil
Report an error
Correct Answer: A. Line-of-sight space-wave propagation
Explanation: Terrestrial microwave links generally use highly directional antennas and line-of-sight space-wave propagation.
Reference: Standard antenna and wave propagation: space-wave propagation
Question 50
Antenna & Wave PropagationWave Propagation

Ground-wave propagation is most useful at relatively?

  • ALow frequencies
  • BOnly optical frequencies
  • COnly millimeter-wave frequencies
  • DX-ray frequencies
Report an error
Correct Answer: A. Low frequencies
Explanation: Ground waves can follow Earth's surface effectively at lower frequencies, with losses increasing as frequency rises.
Reference: Standard antenna and wave propagation: wave propagation
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Question 51
Antenna & Wave PropagationAntenna Pattern Parameters

The front-to-back ratio of a directional antenna compares radiation in the main-beam direction with radiation?

  • AIn the opposite direction
  • BAt the half-power point
  • CAt 90 degrees only
  • DAt the feed terminals
Report an error
Correct Answer: A. In the opposite direction
Explanation: Front-to-back ratio compares forward radiation with radiation approximately 180 degrees behind the main beam.
Reference: Standard antenna and wave propagation: antenna pattern parameters
Question 55
Antenna & Wave PropagationParabolic Reflector

The approximate gain of a parabolic reflector is proportional to?

  • A(D/lambda)² times aperture efficiency
  • BD/lambda only
  • Clambda²/D
  • DD²lambda² only
Report an error
Correct Answer: A. (D/lambda)² times aperture efficiency
Explanation: A common reflector relation is G≈eta_a(pi D/lambda)², so gain scales with (D/lambda)² for fixed efficiency.
Reference: Standard antenna and wave propagation: parabolic reflector
Question 58
Antenna & Wave PropagationIonospheric Propagation

The D layer is particularly associated with significant absorption of?

  • ALower-HF and MF radio waves
  • BVisible light only
  • CAll microwave signals completely
  • DDC current
Report an error
Correct Answer: A. Lower-HF and MF radio waves
Explanation: Collisions in the lower ionosphere cause appreciable absorption, especially at lower radio frequencies.
Reference: Standard antenna and wave propagation: ionospheric propagation
Question 59
Antenna & Wave PropagationIonospheric Propagation

During daytime, the F region commonly separates into?

  • AF1 and F2 layers
  • BD1 and D2 only
  • CE1 and E2 only
  • DTwo tropospheric layers
Report an error
Correct Answer: A. F1 and F2 layers
Explanation: Under daytime solar ionization, the F region is commonly described as F1 and F2; they tend to merge at night.
Reference: Standard antenna and wave propagation: ionospheric propagation
Question 60
Antenna & Wave PropagationCritical Frequency

The critical frequency of an ionospheric layer is the highest frequency that is returned to Earth for?

  • AVertical incidence
  • BHorizontal incidence only
  • CAny angle without limit
  • DGround-wave propagation
Report an error
Correct Answer: A. Vertical incidence
Explanation: Critical frequency is defined for vertical incidence on a particular ionospheric layer.
Reference: Standard antenna and wave propagation: critical frequency
Question 61
Antenna & Wave PropagationMUF

The maximum usable frequency (MUF) for a given ionospheric path is generally?

  • AAt least as high as the relevant critical frequency and depends on path geometry
  • BAlways zero
  • CAlways lower than every critical frequency
  • DIndependent of ionosphere and path
Report an error
Correct Answer: A. At least as high as the relevant critical frequency and depends on path geometry
Explanation: For oblique incidence, frequencies above the vertical-incidence critical frequency may be returned; MUF depends on layer conditions and geometry.
Reference: Standard antenna and wave propagation: muf
Question 64
Antenna & Wave PropagationSkip Distance

Skip distance in sky-wave propagation is the minimum distance from the transmitter at which a wave of specified frequency is?

  • AReturned to Earth by the ionosphere
  • BAbsorbed completely by the antenna
  • CConverted to a ground current
  • DGuaranteed to have zero fading
Report an error
Correct Answer: A. Returned to Earth by the ionosphere
Explanation: Skip distance is the shortest ground distance at which a given sky wave returns to Earth under the prevailing ionospheric conditions.
Reference: Standard antenna and wave propagation: skip distance
Question 66
Antenna & Wave PropagationIonospheric Propagation

Virtual height of an ionospheric layer is the apparent reflection height inferred by assuming the radio wave?

  • ATravels at the speed of light along an equivalent straight path
  • BStops at the ionosphere
  • CTravels through a metallic cable
  • DHas zero propagation time
Report an error
Correct Answer: A. Travels at the speed of light along an equivalent straight path
Explanation: Virtual height is derived from propagation delay using an equivalent straight-line path assumption and is not necessarily the true physical layer height.
Reference: Standard antenna and wave propagation: ionospheric propagation
Question 69
Antenna & Wave PropagationAntenna Arrays

In a uniform linear array, increasing the number of similarly spaced elements while maintaining a comparable aperture arrangement generally tends to?

  • AIncrease directivity and narrow the main beam
  • BReduce directivity to zero
  • CMake all sidelobes disappear automatically
  • DMake element spacing irrelevant
Report an error
Correct Answer: A. Increase directivity and narrow the main beam
Explanation: More coherently combined elements generally provide a larger effective aperture, higher directivity and narrower main beam.
Reference: Standard antenna and wave propagation: antenna arrays
Question 71
Antenna & Wave PropagationAntenna Matching

A common purpose of impedance matching at an antenna feed is to reduce?

  • AReflected power
  • BRadiated power intentionally to zero
  • COperating wavelength
  • DSpeed of electromagnetic waves
Report an error
Correct Answer: A. Reflected power
Explanation: A good impedance match reduces the reflection coefficient and improves transfer of available power between feed line and antenna.
Reference: Standard antenna and wave propagation: antenna matching
Question 73
Antenna & Wave PropagationIonospheric Propagation

The ionosphere is important to HF communication because it contains?

  • AIonized particles capable of refracting radio waves
  • BOnly neutral particles with no electromagnetic effect
  • CA perfect metallic mirror
  • DNo free electrons
Report an error
Correct Answer: A. Ionized particles capable of refracting radio waves
Explanation: Solar radiation ionizes portions of the upper atmosphere, producing electrons and ions that affect radio-wave propagation.
Reference: Standard antenna and wave propagation: ionospheric propagation
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Question 77
Antenna & Wave PropagationGain Units

Antenna gain expressed in dBd is referenced to a?

  • AHalf-wave dipole
  • BIsotropic radiator
  • CParabolic reflector
  • DQuarter-wave transformer
Report an error
Correct Answer: A. Half-wave dipole
Explanation: dBd uses a half-wave dipole as the gain reference.
Reference: Standard antenna and wave propagation: gain units
Question 79
Antenna & Wave PropagationEIRP

Effective isotropic radiated power (EIRP) is the product of transmitter power delivered to the antenna and?

  • AAntenna gain relative to isotropic, including applicable feed losses when forming the link budget
  • BAntenna resistance only
  • COperating wavelength only
  • DReceiver sensitivity
Report an error
Correct Answer: A. Antenna gain relative to isotropic, including applicable feed losses when forming the link budget
Explanation: EIRP represents the equivalent power an isotropic radiator would need to produce the same power density in the direction of maximum antenna gain.
Reference: Standard antenna and wave propagation: eirp
Question 84
Antenna & Wave PropagationLink Budget

A received power of 0 dBm corresponds to?

  • A1 mW
  • B10 mW
  • C100 mW
  • D1 W
Report an error
Correct Answer: A. 1 mW
Explanation: By definition, 0 dBm is 1 milliwatt.
Reference: Standard antenna and wave propagation: link budget
Question 85
Antenna & Wave PropagationLink Budget

A received power of 30 dBm corresponds to?

  • A30 mW
  • B100 mW
  • C1 W
  • D30 W
Report an error
Correct Answer: C. 1 W
Explanation: 30 dBm=10^(30/10) mW=1000 mW=1 W.
Reference: Standard antenna and wave propagation: link budget
Question 88
Antenna & Wave PropagationAntenna Noise

The equivalent noise temperature of an antenna is related primarily to?

  • ANoise power received from the environment through its radiation pattern
  • BIts DC resistance only
  • CIts mechanical temperature in every case only
  • DTransmitter output power
Report an error
Correct Answer: A. Noise power received from the environment through its radiation pattern
Explanation: Antenna noise temperature represents environmental noise collected by the antenna, weighted by its directional response.
Reference: Standard antenna and wave propagation: antenna noise
Question 91
Antenna & Wave PropagationTropospheric Propagation

Tropospheric ducting can allow VHF/UHF/microwave signals to travel?

  • ABeyond the normal radio horizon
  • BOnly through underground conductors
  • COnly vertically upward
  • DOnly within an antenna feed line
Report an error
Correct Answer: A. Beyond the normal radio horizon
Explanation: Strong refractive-index gradients can trap radio waves in atmospheric ducts and extend propagation beyond the normal horizon.
Reference: Standard antenna and wave propagation: tropospheric propagation
Question 92
Antenna & Wave PropagationTropospheric Propagation

Troposcatter communication relies on?

  • AScattering from irregularities in the troposphere
  • BReflection from the ionospheric F2 layer only
  • CConduction along Earth wires
  • DReflection from a parabolic feed itself
Report an error
Correct Answer: A. Scattering from irregularities in the troposphere
Explanation: Tropospheric scatter uses small-angle scattering from refractive-index irregularities to communicate beyond line of sight.
Reference: Standard antenna and wave propagation: tropospheric propagation
Question 93
Antenna & Wave PropagationGain Units

A gain of 0 dBd is approximately equal to?

  • A0 dBi
  • B1 dBi
  • C2.15 dBi
  • D3 dBi
Report an error
Correct Answer: C. 2.15 dBi
Explanation: An ideal half-wave dipole has approximately 2.15 dBi gain, so 0 dBd≈2.15 dBi.
Reference: Standard antenna and wave propagation: gain units
Question 94
Antenna & Wave PropagationDiffraction

Diffraction is especially important in radio propagation when a wave encounters?

  • AAn obstacle or sharp edge near the propagation path
  • BA perfectly matched load only
  • CA DC power source
  • DAn ideal isotropic point with no obstacle
Report an error
Correct Answer: A. An obstacle or sharp edge near the propagation path
Explanation: Diffraction bends/spreads waves around edges and obstacles, enabling some reception even when direct line of sight is obstructed.
Reference: Standard antenna and wave propagation: diffraction
Question 95
Antenna & Wave PropagationFresnel Zone

The first Fresnel zone is important in a point-to-point radio link because excessive obstruction within it can cause?

  • AAdditional diffraction loss
  • BAutomatic gain increase
  • CZero path loss
  • DPerfect impedance matching
Report an error
Correct Answer: A. Additional diffraction loss
Explanation: Keeping much of the first Fresnel zone clear helps minimize diffraction loss and destructive interference.
Reference: Standard antenna and wave propagation: fresnel zone
Question 97
Antenna & Wave PropagationFresnel Zone

For good practical line-of-sight link clearance, a commonly used planning guideline is to keep at least about what fraction of the first Fresnel zone unobstructed?

  • A20%
  • B40%
  • C60%
  • D100% in every possible situation
Report an error
Correct Answer: C. 60%
Explanation: A widely used engineering guideline is about 60% first-Fresnel-zone clearance to limit diffraction loss.
Reference: Standard antenna and wave propagation: fresnel zone
Question 98
Antenna & Wave PropagationArray Phase

A two-element array has elements separated by lambda/2. To make their contributions add in phase in the direction along the array axis, the required progressive excitation phase can be chosen as approximately?

  • A0 degrees
  • B90 degrees
  • C180 degrees
  • D360 degrees only
Report an error
Correct Answer: C. 180 degrees
Explanation: A lambda/2 path difference produces 180 degrees propagation phase difference; an opposite 180 degrees excitation progression can compensate it for end-fire addition.
Reference: Standard antenna and wave propagation: array phase
Question 99
Antenna & Wave PropagationPolarization Matching

Polarization mismatch is minimized when transmitting and receiving antennas have?

  • AMatched polarization
  • BOrthogonal linear polarizations
  • CRandom polarization at all times
  • DZero gain
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Correct Answer: A. Matched polarization
Explanation: Maximum polarization coupling occurs when the receive antenna polarization matches that of the incident wave.
Reference: Standard antenna and wave propagation: polarization matching
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