Between a guided circuit and free space, an antenna serves as?
A A transducer
B A filter
C A mixer
D A modulator
Answer: A. A transducer. An antenna converts guided electrical energy to radiation and can receive it in reverse.
Radiation pattern describes antenna response versus?
A Time
B Temperature
C Frequency only
D Direction
Answer: D. Direction. A radiation pattern shows how radiated fields or power vary with direction.
Equal radiation in every direction defines what ideal source?
A Half-wave dipole
B Quarter-wave monopole
C Isotropic radiator
D Parabolic dish
Answer: C. Isotropic radiator. An ideal isotropic radiator has equal radiation in all directions.
Directivity compares peak radiation with an?
A Receiver reference
B Isotropic reference
C Grounded reference
D Feedline reference
Answer: B. Isotropic reference. Directivity compares maximum radiation intensity with that of an isotropic radiator having equal total radiated power.
Unlike directivity, antenna gain includes which factor?
A Cable length
B Feed voltage
C Radiation efficiency
D Receiver noise
Answer: C. Radiation efficiency. Gain accounts for antenna efficiency as well as directional concentration.
Linear polarization keeps electric-field orientation?
A Random
B Fixed
C Rotating
D Circular
Answer: B. Fixed. For linear polarization, the electric field oscillates along a fixed transverse direction.
For a thin resonant dipole, total length is approximately?
A One wavelength
B Quarter wavelength
C Two wavelengths
D Half wavelength
Answer: D. Half wavelength. A thin resonant dipole is approximately one-half wavelength long; practical length is slightly shorter.
Above a perfect ground plane, a quarter-wave monopole mirrors which radiator?
A Half-wave dipole
B Loop antenna
C Horn antenna
D Isotropic source
Answer: A. Half-wave dipole. Image theory makes the upper-hemisphere pattern equivalent to that of a half-wave dipole.
In the far field, angular pattern is nearly what?
A Time-invariant always
B Distance-independent
C Frequency-independent
D Zero everywhere
Answer: B. Distance-independent. In the far field, the normalized angular pattern is essentially independent of range.
Reactive near fields mainly store what?
A Only radiated power
B Thermal energy
C Static charge only
D Electromagnetic energy
Answer: D. Electromagnetic energy. Reactive near-field terms store energy around the antenna rather than carrying it away.
Half-power beamwidth spans directions at what power level?
A Twice maximum
B One-tenth maximum
C Half maximum
D Zero power
Answer: C. Half maximum. Its endpoints are the half-power, or approximately −3 dB, points around the main beam.
Gain referenced to an isotropic radiator is reported in?
A dBm
B dBd
C dBW
D dBi
Answer: D. dBi. The i in dBi denotes comparison with an isotropic radiator.
Lorentz reciprocity relates transmit and receive patterns when the medium obeys?
A Reciprocity
B Losslessness
C Isotropy
D Conductivity
Answer: A. Reciprocity. The reciprocity theorem requires reciprocal constitutive behavior; losslessness or isotropy alone does not establish it.
Effective aperture relates captured power to incident?
A Phase velocity
B Power density
C Frequency shift
D Input voltage
Answer: B. Power density. Received power equals incident power density times effective aperture for a matched polarization.
Free-space wavelength is c divided by?
A Power
B Frequency
C Impedance
D Aperture
Answer: B. Frequency. The free-space relation is λ = c/f.
At fixed wave speed, increasing frequency makes wavelength?
A Shorter
B Unchanged
C Longer
D Infinite
Answer: A. Shorter. Because λ = v/f, wavelength decreases as frequency rises.
The main lobe points toward peak?
A Absorption
B Reflection
C Attenuation
D Radiation
Answer: D. Radiation. The main lobe contains the direction of maximum radiation.
At a pattern null, radiation is?
A Maximum bandwidth
B Zero radiation
C Maximum gain
D Perfect match
Answer: B. Zero radiation. A null is a direction where the idealized radiation pattern falls to zero.
Radiation efficiency divides radiated power by?
A Input power
B Reactive power
C Stored energy
D Bandwidth
Answer: A. Input power. Radiation efficiency is radiated power divided by power accepted at the antenna terminals.
Usable antenna bandwidth spans frequencies meeting a?
A Fixed wavelength
B Single direction
C Performance specification
D Ground condition
Answer: C. Performance specification. Bandwidth is the frequency range over which stated performance requirements are met.
Which equivalent resistance accounts for radiated power?
A Load resistance
B Leakage resistance
C Radiation resistance
D Surface reactance
Answer: C. Radiation resistance. Radiation resistance models radiated power as an equivalent feed-point resistance.
For a uniform plane wave, E, H, and travel direction are mutually?
A Perpendicular
B Parallel
C Collinear
D Unrelated
Answer: A. Perpendicular. A uniform plane wave has mutually perpendicular electric field, magnetic field, and propagation direction.
Under which condition does Friis transmission apply?
A Blocked path
B Reactive near field
C Far-field line of sight
D Static fields
Answer: C. Far-field line of sight. The standard Friis equation assumes a far-field free-space link with aligned, matched antennas.
Which Yagi-Uda element connects to the feedline?
A Driven element
B Reflector
C Director
D Boom
Answer: A. Driven element. The driven element is connected to the feedline; parasitic elements are not.
Large parabolic reflectors primarily provide?
A Low directivity
B Wide nulls
C Low aperture
D High gain
Answer: D. High gain. A large effective aperture concentrates radiation into a narrow, high-gain beam.