Q.1 Which of the following is the primary principle behind the operation of a dipole antenna?
Reflection of electromagnetic waves
Resonant standing waves on a conductor
Magnetic flux confinement
Electrostatic induction
Explanation - A dipole antenna works by supporting a half‑wavelength standing wave of current, which radiates electromagnetic energy.
Correct answer is: Resonant standing waves on a conductor
Q.2 In a rectangular waveguide, the TE10 mode has its electric field maximum at:
The centre of the broad wall
The centre of the narrow wall
The walls of the waveguide
All points equally
Explanation - For the dominant TE10 mode, the electric field varies sinusoidally across the broad dimension and is maximum at its centre.
Correct answer is: The centre of the broad wall
Q.3 The characteristic impedance of a lossless coaxial cable is given by Z₀ = (60/√ε_r)·ln(b/a). What do ‘a’ and ‘b’ represent?
Inner and outer radii of the conductors
Length and diameter of the cable
Permittivity and permeability of the dielectric
Frequency and wavelength of the signal
Explanation - ‘a’ is the radius of the inner conductor and ‘b’ is the inner radius of the outer conductor; they determine the geometry of the coaxial line.
Correct answer is: Inner and outer radii of the conductors
Q.4 Which electromagnetic phenomenon is primarily exploited in a microwave oven?
Magnetic resonance of iron
Dielectric heating of water molecules
Inductive coupling of metals
Electrostatic discharge
Explanation - Microwave ovens use 2.45 GHz radiation to cause polar water molecules to rotate, producing heat through dielectric loss.
Correct answer is: Dielectric heating of water molecules
Q.5 A microstrip line is fabricated on a dielectric substrate. Which parameter most strongly influences its effective dielectric constant (ε_eff)?
Thickness of the metal strip
Width of the strip relative to substrate height
Conductivity of the metal
Frequency of operation
Explanation - ε_eff depends on the field distribution, which is governed by the ratio of strip width to substrate thickness.
Correct answer is: Width of the strip relative to substrate height
Q.6 The radar cross‑section (RCS) of an object measures:
The physical size of the object
The amount of reflected electromagnetic energy
The absorption coefficient of the material
The frequency bandwidth of the radar
Explanation - RCS quantifies how detectable an object is by radar, i.e., how much incident power is scattered back toward the source.
Correct answer is: The amount of reflected electromagnetic energy
Q.7 In electromagnetic compatibility (EMC), the term ‘radiated emission’ refers to:
Conducted noise on power lines
Unwanted electromagnetic energy emitted into space
Desired signal transmission
Shielding effectiveness of a enclosure
Explanation - Radiated emissions are unintended electromagnetic fields that can interfere with other equipment.
Correct answer is: Unwanted electromagnetic energy emitted into space
Q.8 A Fabry‑Pérot resonator in optics is analogous to which microwave component?
A waveguide bend
A coaxial cable
A cavity resonator
A directional coupler
Explanation - Both consist of two reflecting surfaces that form standing wave patterns at resonant frequencies.
Correct answer is: A cavity resonator
Q.9 Which law describes the power radiated by an accelerating charge?
Ohm’s law
Faraday’s law
Larmor formula
Coulomb’s law
Explanation - The Larmor formula gives the total power radiated by a non‑relativistic accelerating point charge.
Correct answer is: Larmor formula
Q.10 In a leaky‑wave antenna, the main beam direction can be steered by:
Changing the substrate permittivity
Varying the frequency of operation
Adjusting the ground plane size
Modifying the feed line length
Explanation - The beam angle of a leaky‑wave antenna depends on the phase constant, which varies with frequency.
Correct answer is: Varying the frequency of operation
Q.11 What is the primary advantage of using a phased‑array antenna over a mechanically steered antenna?
Lower cost
Higher gain at all angles
Instantaneous beam steering without moving parts
Simpler feed network
Explanation - Phased arrays adjust the relative phase of elements electronically, enabling rapid beam direction changes.
Correct answer is: Instantaneous beam steering without moving parts
Q.12 The skin depth δ in a good conductor at angular frequency ω is given by δ = √(2/ωμσ). Which material property will increase δ?
Higher conductivity σ
Higher permeability μ
Higher frequency ω
Lower conductivity σ
Explanation - Skin depth is inversely proportional to √σ; lower conductivity results in a larger penetration depth.
Correct answer is: Lower conductivity σ
Q.13 In the context of electromagnetic wave propagation, ‘dispersion’ refers to:
Attenuation of the wave amplitude
Variation of phase velocity with frequency
Reflection from a surface
Conversion of electric to magnetic energy
Explanation - Dispersion occurs when different frequency components travel at different speeds, causing waveform distortion.
Correct answer is: Variation of phase velocity with frequency
Q.14 A dielectric resonator antenna (DRA) primarily stores energy in:
Magnetic fields within a metal cavity
Electric fields inside a high‑ε_r dielectric
Surface currents on a metal patch
Radiated fields only
Explanation - DRAs confine electromagnetic energy within a dielectric, where the electric field dominates the stored energy.
Correct answer is: Electric fields inside a high‑ε_r dielectric
Q.15 Which of the following transmission lines is most suitable for frequencies above 10 GHz?
Twisted pair cable
Coaxial cable
Microstrip line
Parallel plate waveguide
Explanation - Microstrip lines have low loss and easy integration at millimeter‑wave frequencies, unlike coaxial or twisted pair.
Correct answer is: Microstrip line
Q.16 The Friis transmission equation predicts received power. Which parameter is NOT part of the equation?
Transmitting antenna gain
Receiving antenna gain
Distance between antennas
Polarization mismatch loss
Explanation - The basic Friis formula includes gains, wavelength, and distance, but does not account for polarization loss unless explicitly added.
Correct answer is: Polarization mismatch loss
Q.17 In a waveguide, the cutoff frequency for TE_mn mode is given by f_c = (c/2)·√((m/a)²+(n/b)²). What happens when the operating frequency is below f_c?
The mode propagates with reduced loss
The mode becomes evanescent and does not propagate
The waveguide acts as an antenna
The field pattern changes to TM mode
Explanation - Below cutoff, the propagation constant becomes imaginary, leading to exponential attenuation (evanescent mode).
Correct answer is: The mode becomes evanescent and does not propagate
Q.18 Which type of antenna is most commonly used for GPS receivers?
Yagi‑Uda antenna
Helical antenna
Patch (microstrip) antenna
Horn antenna
Explanation - Compact, low‑profile patch antennas are ideal for handheld GPS devices.
Correct answer is: Patch (microstrip) antenna
Q.19 The Poynting vector S = E × H represents:
Energy density of the field
Power flow per unit area
Magnetic flux density
Electric potential
Explanation - The cross‑product of electric and magnetic fields gives the instantaneous power density vector.
Correct answer is: Power flow per unit area
Q.20 In electromagnetic shielding, the term ‘SE’ stands for:
Signal Enhancement
Shielding Effectiveness
Surface Emissivity
Static Electricity
Explanation - SE quantifies how well a material attenuates incident electromagnetic fields.
Correct answer is: Shielding Effectiveness
Q.21 A quarter‑wave monopole antenna over a perfect ground plane is equivalent to:
A half‑wave dipole antenna
A loop antenna
A horn antenna
A patch antenna
Explanation - The image of the monopole creates a virtual half‑dipole of length λ/2.
Correct answer is: A half‑wave dipole antenna
Q.22 The term ‘ground wave’ in radio propagation refers to:
Waves reflected from the ionosphere
Waves traveling along the surface of the Earth
Waves emitted by satellites
Waves that are completely absorbed by the ground
Explanation - Ground waves follow the curvature of the Earth, especially at low frequencies.
Correct answer is: Waves traveling along the surface of the Earth
Q.23 In a parallel‑plate waveguide, the dominant mode is:
TE₁₀
TM₁₀
TEM
TE₀₁
Explanation - Parallel plates support a TEM mode where both electric and magnetic fields are transverse to the direction of propagation.
Correct answer is: TEM
Q.24 A Smith chart is primarily used for:
Antenna pattern plotting
Transmission line impedance matching
Field distribution visualization
Frequency spectrum analysis
Explanation - The Smith chart maps complex impedance (or reflection coefficient) to facilitate matching calculations.
Correct answer is: Transmission line impedance matching
Q.25 Which material is commonly used as a dielectric in microwave printed circuit boards due to its low loss tangent?
FR‑4
Rogers RO4003
Polycarbonate
Aluminum
Explanation - Rogers substrates have low dielectric loss, making them suitable for high‑frequency applications.
Correct answer is: Rogers RO4003
Q.26 The main radiation mechanism of a loop antenna is:
Electric dipole moment
Magnetic dipole moment
Quadrupole radiation
Surface wave propagation
Explanation - A small loop behaves like a magnetic dipole, radiating due to circulating current.
Correct answer is: Magnetic dipole moment
Q.27 In an RF power amplifier, the term ‘gain compression point (P1dB)’ indicates:
The frequency where gain is maximum
The input power at which output power deviates 1 dB from linearity
The point where the amplifier stops conducting
The maximum voltage rating of the device
Explanation - P1dB is a standard metric for non‑linear behavior in amplifiers.
Correct answer is: The input power at which output power deviates 1 dB from linearity
Q.28 Which of the following is a key advantage of using a horn antenna at microwave frequencies?
Very low cost
Compact size
High gain and good impedance matching
Broad bandwidth without any matching network
Explanation - Horn antennas provide a smooth transition from waveguide to free space, offering high gain and low VSWR.
Correct answer is: High gain and good impedance matching
Q.29 The term ‘near‑field’ in antenna theory refers to:
The region within one wavelength from the antenna
The region where the radiation pattern is formed
The region where reactive fields dominate
The region where only magnetic fields exist
Explanation - In the near field, stored electric and magnetic energy is significant, and fields do not behave as pure radiating waves.
Correct answer is: The region where reactive fields dominate
Q.30 Which of the following best describes a metamaterial?
A naturally occurring dielectric
A material engineered to have negative permittivity or permeability
A superconductor at room temperature
A polymer with high tensile strength
Explanation - Metamaterials obtain unusual electromagnetic properties from sub‑wavelength structuring, not from their composition alone.
Correct answer is: A material engineered to have negative permittivity or permeability
Q.31 In a cavity resonator, the quality factor Q is defined as:
Stored energy divided by power loss per radian
Ratio of resonant frequency to bandwidth
Ratio of electric to magnetic field strengths
Product of permittivity and permeability
Explanation - Q = f₀/Δf, indicating how sharply the cavity resonates.
Correct answer is: Ratio of resonant frequency to bandwidth
Q.32 For a transmission line, the condition for maximum power transfer to a load is:
Load impedance equals source resistance
Load impedance equals the complex conjugate of source impedance
Load impedance is purely resistive
Load impedance is much larger than source impedance
Explanation - Maximum power transfer occurs when Z_L = Z_S* (complex conjugate matching).
Correct answer is: Load impedance equals the complex conjugate of source impedance
Q.33 The ‘Bragg reflector’ in a distributed Bragg reflector (DBR) laser works by:
Absorbing specific wavelengths
Reflecting light due to periodic refractive index variations
Amplifying light via stimulated emission
Changing polarization of the beam
Explanation - Alternating high‑ and low‑index layers create constructive interference for certain wavelengths.
Correct answer is: Reflecting light due to periodic refractive index variations
Q.34 The term ‘effective aperture’ of an antenna is:
Physical size of the antenna
Area over which the antenna collects power from an incoming wave
Cross‑sectional area of the feed line
Frequency bandwidth of the antenna
Explanation - Effective aperture relates the received power to the power density of the incident wave.
Correct answer is: Area over which the antenna collects power from an incoming wave
Q.35 In the context of SAR (Specific Absorption Rate), a higher value indicates:
More efficient antenna performance
Greater absorption of RF energy by biological tissue
Lower electromagnetic interference
Higher transmission power
Explanation - SAR measures the rate at which energy is absorbed per mass of tissue, important for safety limits.
Correct answer is: Greater absorption of RF energy by biological tissue
Q.36 Which of the following is true about a balanced transmission line (e.g., twin‑lead)?
It requires a ground plane for operation
It has equal potentials on both conductors
It carries signals with opposite polarity on the two conductors
It is immune to external electromagnetic fields
Explanation - Balanced lines have equal magnitude but opposite sign currents, reducing radiation and susceptibility to noise.
Correct answer is: It carries signals with opposite polarity on the two conductors
Q.37 In a Faraday cage, the shielding effectiveness improves when:
The mesh size is much larger than the wavelength
The cage is made of a dielectric material
The mesh size is much smaller than the wavelength of the incident wave
The cage is placed near a ground plane
Explanation - A fine mesh prevents the wave from penetrating because the openings are too small for the wavelength to pass.
Correct answer is: The mesh size is much smaller than the wavelength of the incident wave
Q.38 The term ‘beamwidth’ of an antenna is defined as:
The physical width of the antenna aperture
The angular separation between the half‑power points of the main lobe
The frequency range over which the antenna operates
The distance at which the antenna gain drops by 3 dB
Explanation - Beamwidth (often expressed in degrees) is measured between points where the radiation intensity falls to half its maximum.
Correct answer is: The angular separation between the half‑power points of the main lobe
Q.39 A TEM mode cannot exist in a single‑conductor waveguide because:
There is no return path for current
The frequency is too low
The conductor material is not magnetic
TEM requires two conductors to support equal and opposite currents
Explanation - TEM fields need a pair of conductors; a single conductor cannot sustain a transverse electromagnetic mode.
Correct answer is: TEM requires two conductors to support equal and opposite currents
Q.40 In satellite communications, the term ‘rain fade’ refers to:
Signal loss due to atmospheric humidity
Signal loss caused by precipitation scattering microwave signals
Doppler shift caused by satellite motion
Interference from other satellites
Explanation - Rain droplets absorb and scatter high‑frequency (e.g., Ku‑band) signals, reducing received power.
Correct answer is: Signal loss caused by precipitation scattering microwave signals
Q.41 The wave impedance of free space (Z₀) is approximately:
120 π Ω
377 Ω
50 Ω
75 Ω
Explanation - Z₀ = √(μ₀/ε₀) ≈ 377 Ω; sometimes expressed as 120π Ω.
Correct answer is: 377 Ω
Q.42 In a standing wave ratio (SWR) measurement, an SWR of 1:1 indicates:
Maximum power transfer
Total reflection
Perfect impedance match
High attenuation
Explanation - SWR = 1 means no reflected wave; the line is perfectly matched to the load.
Correct answer is: Perfect impedance match
Q.43 The primary function of a balun in antenna systems is to:
Amplify the signal
Convert balanced to unbalanced transmission lines
Filter out unwanted frequencies
Provide mechanical support
Explanation - Baluns (balanced‑to‑unbalanced transformers) match impedance and prevent unwanted currents.
Correct answer is: Convert balanced to unbalanced transmission lines
Q.44 Which of the following is a key reason why waveguide losses are lower than coaxial cable losses at microwave frequencies?
Waveguides use superconducting material
Waveguides have no dielectric filling
Waveguides support higher-order modes
Waveguides have larger cross‑sectional area reducing conductor loss
Explanation - Absence of dielectric reduces dielectric loss; metallic walls also have lower skin‑effect loss at high frequencies.
Correct answer is: Waveguides have no dielectric filling
Q.45 In electromagnetic theory, the continuity equation ∇·J + ∂ρ/∂t = 0 expresses:
Conservation of charge
Conservation of energy
Magnetic flux linkage
Relation between E and H fields
Explanation - It states that the rate of charge density change in a volume equals the net current flowing out of the volume.
Correct answer is: Conservation of charge
Q.46 A leaky‑wave antenna typically radiates most efficiently when:
The phase constant equals the free‑space wavenumber
The attenuation constant is zero
The wave is below cutoff
The operating frequency matches the waveguide cutoff frequency
Explanation - Radiation occurs when the guided wave’s phase constant matches the propagation constant in free space, allowing energy to leak out.
Correct answer is: The phase constant equals the free‑space wavenumber
Q.47 Which parameter determines the beam steering capability of a reflectarray antenna?
Size of the feeding horn
Phase shift provided by each element
Material conductivity
Operating temperature
Explanation - By adjusting the phase of individual elements, the overall reflected wavefront can be steered.
Correct answer is: Phase shift provided by each element
Q.48 In a resonant LC circuit, the resonant frequency f₀ is given by:
1/(2πLC)
1/(2π√(LC))
2π√(LC)
√(L/C)
Explanation - f₀ = 1/(2π√(LC)) is the frequency where inductive and capacitive reactances cancel.
Correct answer is: 1/(2π√(LC))
Q.49 What is the main advantage of using a dielectric lens in a microwave antenna system?
Increased bandwidth
Reduced weight compared to metal reflectors
Higher gain and beam focusing without metal losses
Simpler feeding network
Explanation - Dielectric lenses refract microwave energy, focusing it similarly to optical lenses while avoiding conductor losses.
Correct answer is: Higher gain and beam focusing without metal losses
Q.50 In the context of antenna arrays, the term ‘grating lobe’ appears when:
Element spacing exceeds half a wavelength
The array is fed with unequal amplitudes
The array is placed near a conductive surface
The operating frequency is too low
Explanation - Spacing > λ/2 causes additional maxima (grating lobes) in the radiation pattern.
Correct answer is: Element spacing exceeds half a wavelength
Q.51 A surface wave propagating along a dielectric‑metal interface is known as:
Zenneck wave
Sommerfeld wave
Mie scattering
Rayleigh wave
Explanation - Zenneck (or surface) waves travel bound to the interface, decaying exponentially away from it.
Correct answer is: Zenneck wave
Q.52 Which of the following statements about the Friis transmission equation is correct?
It is valid only for near‑field distances
It assumes isotropic antennas
It includes polarization loss factor
It requires line‑of‑sight propagation
Explanation - The equation assumes free‑space, far‑field, line‑of‑sight conditions between antennas.
Correct answer is: It requires line‑of‑sight propagation
Q.53 In a TEM transmission line, the ratio of electric to magnetic field magnitudes (|E|/|H|) equals:
The speed of light c
The intrinsic impedance η
The characteristic impedance Z₀
The propagation constant γ
Explanation - For a TEM wave, |E|/|H| = η = √(μ/ε), which equals the medium’s intrinsic impedance.
Correct answer is: The intrinsic impedance η
Q.54 The term ‘polarization mismatch loss’ in a wireless link occurs when:
The transmit and receive antennas have different gains
The antennas are oriented with orthogonal polarizations
The frequency of operation changes
The link distance exceeds the Fresnel zone
Explanation - Mismatched polarizations reduce the effective received power, quantified by the cosine squared of the angle between them.
Correct answer is: The antennas are oriented with orthogonal polarizations
Q.55 In a frequency‑selective surface (FSS), the stop‑band behavior is primarily caused by:
Resonant electric dipoles
Magnetic coupling between elements
Surface roughness
Dielectric losses
Explanation - Arrays of resonant elements reflect or absorb specific frequencies, creating stop‑band characteristics.
Correct answer is: Resonant electric dipoles
Q.56 Which type of antenna is inherently circularly polarized?
Half‑wave dipole
Helical antenna (axial mode)
Monopole over ground
Log‑periodic dipole array
Explanation - When the helix dimensions satisfy axial mode conditions, the radiation is circularly polarized.
Correct answer is: Helical antenna (axial mode)
Q.57 The term ‘mutual coupling’ between antenna elements refers to:
Energy loss due to conductor resistance
Interaction of currents causing altered input impedance
Radiation pattern narrowing
Frequency shift of each element
Explanation - Coupled elements exchange power, which changes the effective impedance and pattern of each antenna.
Correct answer is: Interaction of currents causing altered input impedance
Q.58 When a waveguide is operated in the dominant TE10 mode, the cutoff wavelength λ_c is:
2a
2b
a
b
Explanation - For TE10, λ_c = 2a (where a is the broader dimension of the rectangular waveguide).
Correct answer is: 2a
Q.59 In a radar system, the maximum unambiguous range is determined by:
Pulse width
Pulse repetition frequency (PRF)
Antenna gain
Operating frequency
Explanation - Maximum unambiguous range = c/(2·PRF); higher PRF reduces the range before echoes overlap.
Correct answer is: Pulse repetition frequency (PRF)
Q.60 Which of the following best describes a ‘smart antenna’?
An antenna that changes its shape physically
An antenna system that uses signal processing to adapt its radiation pattern
An antenna made of superconducting material
An antenna with built‑in amplification
Explanation - Smart antennas employ algorithms (e.g., beamforming) to dynamically steer beams and suppress interference.
Correct answer is: An antenna system that uses signal processing to adapt its radiation pattern
Q.61 A wave traveling in a lossless transmission line has a voltage standing wave ratio (VSWR) of 3:1. What is the magnitude of the reflection coefficient |Γ|?
0.33
0.5
0.66
0.75
Explanation - VSWR = (1+|Γ|)/(1‑|Γ|); solving for |Γ| gives |Γ| = (VSWR‑1)/(VSWR+1) = (3‑1)/(3+1) = 0.5.
Correct answer is: 0.5
Q.62 In electromagnetic wave propagation, the term ‘group velocity’ refers to:
The velocity of individual wave fronts
The speed at which the overall envelope of a pulse travels
The speed of light in vacuum
The phase velocity divided by the refractive index
Explanation - Group velocity = dω/dk; it determines the speed of energy and information transport.
Correct answer is: The speed at which the overall envelope of a pulse travels
Q.63 Which phenomenon is exploited in a frequency‑modulated continuous‑wave (FMCW) radar?
Doppler shift
Time‑delay measurement using frequency sweep
Pulse compression
Phase array scanning
Explanation - FMCW radars measure distance by correlating frequency differences caused by propagation delay.
Correct answer is: Time‑delay measurement using frequency sweep
Q.64 The effective relative permittivity (ε_eff) of a microstrip line is always:
Greater than the substrate permittivity ε_r
Less than the substrate permittivity ε_r
Equal to the substrate permittivity ε_r
Independent of the substrate permittivity
Explanation - Part of the field propagates in air, reducing the effective permittivity below the bulk substrate value.
Correct answer is: Less than the substrate permittivity ε_r
Q.65 A ‘travelling‑wave tube’ (TWT) amplifies RF signals by:
Resonant standing wave interaction
Electron beam interacting with a slow‑wave structure
Magnetic confinement of plasma
Thermal heating of a semiconductor
Explanation - In a TWT, the RF wave travels synchronously with an electron beam, transferring energy and providing broadband amplification.
Correct answer is: Electron beam interacting with a slow‑wave structure
Q.66 In the context of antenna theory, the term ‘effective length’ of a dipole antenna is:
The physical length of the dipole
Half the physical length
The length that would produce the same radiation resistance as the actual dipole
The length of the feed line
Explanation - Effective length accounts for current distribution, providing a simplified model for radiation calculations.
Correct answer is: The length that would produce the same radiation resistance as the actual dipole
Q.67 The primary cause of dielectric loss in a transmission line is:
Magnetic hysteresis
Conduction currents in the dielectric
Molecular dipole rotation lagging the applied field
Skin effect in conductors
Explanation - Dielectric loss arises from the lag (phase angle) between the electric field and the polarization response of the material.
Correct answer is: Molecular dipole rotation lagging the applied field
Q.68 Which antenna type is most suitable for satellite TV reception on a residential rooftop?
Yagi‑Uda antenna
Parabolic dish antenna
Log‑periodic antenna
Helical antenna
Explanation - Parabolic dishes provide high gain and directivity needed for weak satellite signals.
Correct answer is: Parabolic dish antenna
Q.69 The ‘Brewster angle’ is the incidence angle at which:
Reflection coefficient for parallel polarization becomes zero
Both polarizations are reflected equally
Transmission is completely blocked
Total internal reflection occurs
Explanation - At Brewster’s angle, the reflected wave for the parallel component vanishes, leading to polarization by reflection.
Correct answer is: Reflection coefficient for parallel polarization becomes zero
Q.70 A waveguide filled with a dielectric of relative permittivity ε_r has its cutoff frequency:
Increased by √ε_r
Decreased by √ε_r
Unchanged
Increased by ε_r
Explanation - Cutoff frequency f_c ∝ 1/√(ε_r); higher permittivity lowers the cutoff frequency.
Correct answer is: Decreased by √ε_r
Q.71 The term ‘dispersion’ in a waveguide leads to:
All frequency components traveling at the same speed
Signal distortion because different frequencies travel at different phase velocities
Higher attenuation at low frequencies
Improved bandwidth
Explanation - Dispersion causes pulse spreading as spectral components propagate with varying velocities.
Correct answer is: Signal distortion because different frequencies travel at different phase velocities
Q.72 In a phased‑array radar, the beam steering angle θ is given by sinθ = λ·Δφ/(2π·d). What does ‘d’ represent?
Distance between the radar and target
Spacing between adjacent array elements
Diameter of the antenna aperture
Depth of the feed network
Explanation - Δφ is the progressive phase shift; d is the element spacing, determining steering angle via the array factor.
Correct answer is: Spacing between adjacent array elements
Q.73 Which of the following is a common method for measuring the dielectric constant of a material at microwave frequencies?
Using a Wheatstone bridge
Resonant cavity perturbation technique
Four‑point probe method
Thermal conductivity test
Explanation - Inserting a sample into a resonant cavity shifts its resonant frequency, allowing extraction of ε_r.
Correct answer is: Resonant cavity perturbation technique
Q.74 In antenna terminology, the term ‘aperture efficiency’ accounts for:
Losses due to surface roughness only
The ratio of effective area to physical area
The polarization purity
The bandwidth of the antenna
Explanation - Aperture efficiency includes illumination, spill‑over, and phase errors, comparing actual gain to ideal.
Correct answer is: The ratio of effective area to physical area
Q.75 The ‘K factor’ in ionospheric propagation indicates:
The level of attenuation caused by rain
The deviation of the ionospheric refractive index from unity
The power of solar flares
The speed of electromagnetic waves in vacuum
Explanation - K = 1 – (N_e/N_critical); it quantifies the ionosphere’s effect on wave propagation.
Correct answer is: The deviation of the ionospheric refractive index from unity
Q.76 A microstrip patch antenna primarily radiates due to:
Fringing fields at the edges of the patch
Currents on the ground plane
Surface waves in the substrate
Magnetic dipole moments inside the dielectric
Explanation - Radiation occurs where the field lines extend beyond the patch edges, creating an effective aperture.
Correct answer is: Fringing fields at the edges of the patch
Q.77 Which type of waveguide mode is cut‑off free (i.e., can propagate at any frequency)?
TE₁₀
TM₀₁
TEM
TE₁₁
Explanation - TEM mode, present in coaxial and parallel‑plate guides, has no cutoff frequency.
Correct answer is: TEM
Q.78 In a lossy transmission line, the attenuation constant α (in nepers per meter) depends on:
Only the line’s geometry
Both conductor resistance and dielectric loss
Only the frequency of operation
Only the characteristic impedance
Explanation - α includes contributions from conductor (skin effect) and dielectric (tan δ) losses.
Correct answer is: Both conductor resistance and dielectric loss
Q.79 The primary benefit of using a ‘corrugated waveguide’ over a smooth‑wall waveguide is:
Lower manufacturing cost
Reduced mode conversion and improved polarization purity
Higher power handling capability
Simpler connector interface
Explanation - Corrugations suppress higher‑order modes and maintain linear polarization over a wide bandwidth.
Correct answer is: Reduced mode conversion and improved polarization purity
Q.80 In the context of radar cross‑section reduction, the technique of ‘frequency selective surfaces’ is used to:
Absorb incident waves at specific frequencies
Reflect all incident waves
Amplify radar returns
Focus radar beams
Explanation - FSS can be designed as absorbers that attenuate reflected energy at targeted radar bands.
Correct answer is: Absorb incident waves at specific frequencies
Q.81 Which of the following equations correctly expresses the relationship between wavelength λ, frequency f, and the speed of light c?
λ = c·f
λ = c/f
f = λ·c
c = λ·f²
Explanation - The fundamental wave relation is λ = c / f.
Correct answer is: λ = c/f
Q.82 The term ‘rain attenuation’ in satellite links is most severe at:
VHF frequencies
UHF frequencies
C‑band (4–8 GHz)
Ka‑band (26–40 GHz)
Explanation - Higher frequencies experience greater scattering and absorption by rain droplets.
Correct answer is: Ka‑band (26–40 GHz)
Q.83 A waveguide with dimensions a = 2 cm and b = 1 cm will have its dominant TE10 cutoff frequency at approximately:
7.5 GHz
15 GHz
30 GHz
45 GHz
Explanation - f_c = c/(2a) ≈ (3×10⁸)/(2×0.02) = 7.5 GHz.
Correct answer is: 7.5 GHz
Q.84 Which parameter of a rectangular waveguide determines the wave impedance for the TE10 mode?
Waveguide height b
Operating frequency f
Guide wavelength λ_g
Material permeability μ
Explanation - The TE mode impedance depends on the ratio of guide wavelength to free‑space wavelength.
Correct answer is: Guide wavelength λ_g
Q.85 The main reason why a dielectric resonator antenna (DRA) can be made very low‑profile is:
It uses a metal reflector
Its resonant volume is comparable to wavelength
It stores energy in magnetic fields only
It requires no feeding network
Explanation - DRAs achieve resonance in a small dielectric block whose dimensions are a fraction of the wavelength, allowing thin structures.
Correct answer is: Its resonant volume is comparable to wavelength
Q.86 In a transmission line model, the reflection coefficient Γ at the load is given by (Z_L‑Z₀)/(Z_L+Z₀). If Z_L = 2Z₀, what is |Γ|?
0.33
0.5
0.67
0.75
Explanation - Γ = (2Z₀‑Z₀)/(2Z₀+Z₀) = Z₀/3Z₀ = 1/3 ≈ 0.33.
Correct answer is: 0.33
Q.87 Which type of wave is primarily used in ground‑penetrating radar (GPR) systems?
Very low frequency (VLF)
Ultra‑high frequency (UHF)
Microwave (X‑band)
Infrared
Explanation - GPR typically operates in the 100 MHz–1 GHz range (UHF) to achieve sufficient penetration and resolution.
Correct answer is: Ultra‑high frequency (UHF)
Q.88 A 'split‑ring resonator' (SRR) is used in metamaterials to achieve:
Negative permeability
High thermal conductivity
Superconductivity
Enhanced dielectric constant
Explanation - SRRs exhibit magnetic resonance that can produce an effective negative μ over a narrow band.
Correct answer is: Negative permeability
Q.89 In a waveguide with perfect electric conductor walls, the tangential component of the electric field at the wall is:
Maximum
Zero
Equal to the normal component
Undefined
Explanation - Boundary condition for PEC walls forces the tangential electric field to vanish.
Correct answer is: Zero
Q.90 The term ‘link budget’ in a wireless system accounts for:
Only transmitter power
All gains and losses from transmitter to receiver
Antenna polarization only
Atmospheric noise only
Explanation - Link budget sums transmitter power, antenna gains, path loss, and other margins to predict received power.
Correct answer is: All gains and losses from transmitter to receiver
Q.91 In a coaxial cable, the dominant mode is:
TEM
TE11
TM01
HE11
Explanation - Coaxial lines support a transverse electromagnetic mode as the fundamental mode.
Correct answer is: TEM
Q.92 The ‘effective conductivity’ of a composite material is primarily determined by:
The volume fraction and conductivity of its constituents
Its magnetic permeability
Its thermal expansion coefficient
Its color
Explanation - Mixing rules (e.g., Maxwell‑Garnett) relate overall conductivity to the proportion and conductivity of each phase.
Correct answer is: The volume fraction and conductivity of its constituents
Q.93 A waveguide with a rectangular cross‑section can support a TE01 mode. What is the field variation of this mode along the a‑dimension (broad side)?
Sinusoidal with one half‑wave variation
Uniform (no variation)
Two half‑wave variations
Complex exponential decay
Explanation - TE01 varies only along the narrow side (b) and is constant along the a‑dimension.
Correct answer is: Uniform (no variation)
Q.94 Which of the following statements is true about the Poynting vector in a lossless medium?
It points opposite to the direction of wave propagation
Its magnitude is zero
It represents the instantaneous power flow per unit area
It depends on the conductivity only
Explanation - S = E × H gives the direction and magnitude of power transport in the field.
Correct answer is: It represents the instantaneous power flow per unit area
Q.95 In a microstrip line, the dominant mode is:
TEM
TE10
TM01
Quasi‑TEM
Explanation - Microstrip supports a quasi‑TEM mode because fields are not completely confined, but it behaves similarly to TEM at low frequencies.
Correct answer is: Quasi‑TEM
Q.96 Which factor most directly influences the bandwidth of a patch antenna?
Substrate thickness
Feed point location
Operating temperature
Ground plane material
Explanation - Increasing substrate height raises the Q factor, thereby broadening the resonant bandwidth.
Correct answer is: Substrate thickness
Q.97 The term ‘far‑field’ region of an antenna begins at a distance roughly equal to:
λ/2
2D²/λ, where D is the largest dimension of the antenna
λ
D
Explanation - The Fraunhofer distance defines the far‑field start: R ≈ 2D²/λ.
Correct answer is: 2D²/λ, where D is the largest dimension of the antenna
Q.98 In electromagnetic scattering, the term ‘Mie scattering’ applies when:
Particle size is much smaller than wavelength
Particle size is comparable to wavelength
Particle is a perfect conductor
Scattering occurs only in vacuum
Explanation - Mie theory describes scattering from spheres whose dimensions are on the order of the incident wavelength.
Correct answer is: Particle size is comparable to wavelength
Q.99 For a rectangular aperture antenna, the first null in the radiation pattern occurs at an angle θ where:
sinθ = λ/a
sinθ = 2λ/a
cosθ = λ/a
tanθ = λ/a
Explanation - The first null of a uniformly illuminated rectangular aperture occurs when the path difference equals one wavelength.
Correct answer is: sinθ = λ/a
Q.100 Which of the following is a characteristic of a horn antenna’s ‘aperture efficiency’?
It is always 100 %
It decreases with increasing frequency
It depends on the flare angle and tapering
It is independent of the horn dimensions
Explanation - Proper flare angle and smooth taper reduce phase errors and spill‑over, improving aperture efficiency.
Correct answer is: It depends on the flare angle and tapering
Q.101 A dielectric waveguide can support which type of mode at frequencies well above its cutoff?
TEM
TE0m
TM0m
Hybrid (HE/EH) modes
Explanation - Dielectric waveguides, lacking a metallic boundary, support hybrid modes where both electric and magnetic fields have longitudinal components.
Correct answer is: Hybrid (HE/EH) modes
Q.102 In a radar system, increasing the transmitted pulse width primarily affects:
Maximum unambiguous range
Range resolution
Doppler resolution
Antenna beamwidth
Explanation - Longer pulses degrade range resolution because they spread the returned echo over a longer time.
Correct answer is: Range resolution
Q.103 Which material property is most critical for minimizing loss in a high‑frequency waveguide?
High electrical conductivity
High magnetic permeability
High dielectric constant
High thermal conductivity
Explanation - Low resistive (skin) loss in the walls is essential for efficient waveguide operation at microwave frequencies.
Correct answer is: High electrical conductivity
Q.104 In a parallel‑plate waveguide with plate separation d, the cutoff frequency for the TE1 mode is:
c/(2d)
c/d
c/(πd)
Zero (no cutoff)
Explanation - The TE1 mode has half‑wavelength variation across the gap, giving f_c = c/(2d).
Correct answer is: c/(2d)
Q.105 The 'radiation pattern' of an antenna is usually expressed in terms of:
Voltage versus time
Gain versus angle
Current versus frequency
Impedance versus temperature
Explanation - A radiation pattern plots the relative field strength (or gain) as a function of direction.
Correct answer is: Gain versus angle
Q.106 For a uniform linear array (ULA) with N elements spaced λ/2 apart and uniform excitation, the directivity D (in linear scale) is approximately:
N
2N
N²
√N
Explanation - Uniformly excited λ/2 spaced linear arrays have directivity roughly equal to the number of elements.
Correct answer is: N
Q.107 Which of the following is a common technique to reduce mutual coupling in a tightly spaced antenna array?
Increasing feed voltage
Adding decoupling networks or neutralization lines
Using higher frequency operation
Reducing antenna element size
Explanation - Decoupling circuits introduce counteracting currents that mitigate coupling between elements.
Correct answer is: Adding decoupling networks or neutralization lines
Q.108 In a cavity resonator, the resonant frequency for the TM₁₁₀ mode in a rectangular cavity of dimensions a, b, d is given by:
c/2·√((1/a)²+(1/b)²+(1/d)²)
c·√((1/a)²+(1/b)²+(1/d)²)
c/π·√((1/a)²+(1/b)²+(1/d)²)
c/2π·√((1/a)²+(1/b)²+(1/d)²)
Explanation - Resonant frequencies follow f_mnp = (c/2)·√((m/a)²+(n/b)²+(p/d)²) for rectangular cavities.
Correct answer is: c/2·√((1/a)²+(1/b)²+(1/d)²)
Q.109 A 'quarter‑wave transformer' is used to match two transmission lines of characteristic impedances Z₁ and Z₂. Its characteristic impedance Z₀ should be:
√(Z₁·Z₂)
(Z₁+Z₂)/2
Z₁·Z₂
max(Z₁, Z₂)
Explanation - A λ/4 transformer with Z₀ = √(Z₁Z₂) provides an impedance match between the two lines.
Correct answer is: √(Z₁·Z₂)
Q.110 The phenomenon of ‘standing wave ratio (SWR)’ is a measure of:
Impedance mismatch between line and load
Propagation speed in a medium
Magnetic field strength
Thermal noise level
Explanation - SWR quantifies the ratio of maximum to minimum voltage along a line, indicating mismatch.
Correct answer is: Impedance mismatch between line and load
Q.111 In an antenna array, a progressive phase shift of 180° between adjacent elements will produce:
Broadside radiation
End‑fire radiation
Null in the broadside direction
Circular polarization
Explanation - A 180° phase difference causes destructive interference at broadside, steering the main beam off‑axis.
Correct answer is: Null in the broadside direction
Q.112 Which of the following best describes the purpose of a ‘frequency selective surface’ (FSS) used as a radome?
To reflect all incident frequencies
To allow passage of desired frequencies while reflecting others
To convert linear to circular polarization
To amplify incoming signals
Explanation - FSS radomes act as filters, transmitting specific bands and blocking others for protection and stealth.
Correct answer is: To allow passage of desired frequencies while reflecting others
Q.113 In a lossy dielectric, the loss tangent tan δ is defined as:
Ratio of conductivity to permittivity
Ratio of imaginary to real part of permittivity
Ratio of magnetic to electric field strength
Ratio of phase velocity to group velocity
Explanation - tan δ = ε''/ε' quantifies dielectric losses due to lagging polarization.
Correct answer is: Ratio of imaginary to real part of permittivity
Q.114 Which antenna type inherently provides a broad bandwidth without requiring matching networks?
Log‑periodic dipole array
Half‑wave dipole
Horn antenna
Monopole over ground
Explanation - Its geometry scales logarithmically, giving frequency‑independent impedance and wide bandwidth.
Correct answer is: Log‑periodic dipole array
Q.115 For a plane wave incident on a perfectly conducting flat surface, the reflected electric field is:
Equal in magnitude and in phase with the incident field
Equal in magnitude and 180° out of phase with the incident field
Zero
Half the magnitude of the incident field
Explanation - The boundary condition forces the tangential electric field to zero, resulting in a reflected wave with opposite phase.
Correct answer is: Equal in magnitude and 180° out of phase with the incident field
Q.116 The ‘beam squint’ effect in a phased‑array antenna becomes significant when:
The array operates over a very narrow bandwidth
The element spacing is much less than λ/2
The array is fed with a true‑time‑delay network rather than phase shifters
The operating frequency deviates from the design frequency
Explanation - Phase‑shifter based beam steering causes the beam direction to change with frequency, known as beam squint.
Correct answer is: The operating frequency deviates from the design frequency
Q.117 Which of the following best describes the 'near‑field' region of a loop antenna?
Region where the fields fall off as 1/r²
Region where the fields fall off as 1/r³
Region beyond the Fraunhofer distance
Region where only radiated fields exist
Explanation - In the reactive near field of a small loop, the magnetic field dominates and decays with 1/r³.
Correct answer is: Region where the fields fall off as 1/r³
Q.118 A waveguide with a corrugated wall is primarily used to:
Increase mechanical strength
Support higher power levels
Suppress higher‑order modes and improve polarization purity
Reduce the weight of the waveguide
Explanation - Corrugations act as a periodic structure that stabilizes the dominant mode and reduces cross‑polarization.
Correct answer is: Suppress higher‑order modes and improve polarization purity
Q.119 Which of the following is the correct expression for the wave number k in a lossless medium?
k = ω·√(με)
k = ω/(c·√(με))
k = √(ω·μ/ε)
k = 1/√(με)
Explanation - In a lossless medium, the propagation constant γ = α + jβ reduces to β = ω√(με) = k.
Correct answer is: k = ω·√(με)
Q.120 The term ‘radiation resistance’ of an antenna refers to:
The physical resistance of the antenna material
The part of the input resistance that accounts for power radiated as electromagnetic waves
The resistance of the feed line
The resistance measured at DC
Explanation - Radiation resistance models the power loss from the source into free space as an equivalent resistance.
Correct answer is: The part of the input resistance that accounts for power radiated as electromagnetic waves
Q.121 In a satellite communication link, the ‘link margin’ is:
The difference between transmitted and received power
The extra power budget to overcome unforeseen losses and maintain reliable communication
The bandwidth allocated to the link
The frequency offset between uplink and downlink
Explanation - Link margin provides a safety buffer above the minimum required signal‑to‑noise ratio.
Correct answer is: The extra power budget to overcome unforeseen losses and maintain reliable communication
Q.122 A cavity resonator made of a rectangular metal box exhibits its lowest resonant frequency when:
All dimensions are equal
One dimension is much larger than the others
The cavity is filled with a high‑ε_r dielectric
The walls are made of a magnetic material
Explanation - The lowest mode (TE101) depends on the largest dimension; making one side long lowers the resonant frequency.
Correct answer is: One dimension is much larger than the others