Difficulty: Easy & Basic
Circuit dimensions become electrically significant at microwave frequencies. Which engineering field studies these systems?
A Power electronics
B Microwave engineering
C Structural design
D Audio engineering
Answer: B. Microwave engineering. Microwave engineering studies electromagnetic circuits and systems at microwave frequencies.
Why can a circuit stop behaving as a simple lumped network at microwave frequencies?
A Size nears wavelength
B Voltage becomes zero
C Current stops flowing
D Resistance disappears
Answer: A. Size nears wavelength. Distributed effects matter when component dimensions are a significant fraction of wavelength.
What does a hollow metallic waveguide carry?
A Only DC current
B Sound pressure
C Electromagnetic energy
D Optical fibre modes
Answer: C. Electromagnetic energy. A waveguide confines and guides electromagnetic waves.
Which mode is dominant in a standard rectangular waveguide?
A TM00
B TEM00
C TE10
D TE33
Answer: C. TE10. The lowest-order propagating mode is usually TE10.
In a transverse-electric mode, which field component is zero along propagation?
A Transverse electric field
B Longitudinal electric field
C Longitudinal magnetic field
D Both transverse fields
Answer: B. Longitudinal electric field. TE means the electric field has no longitudinal component.
What is absent along propagation in a transverse-magnetic mode?
A Transverse magnetic field
B Longitudinal electric field
C Both transverse fields
D Longitudinal magnetic field
Answer: D. Longitudinal magnetic field. TM means the magnetic field has no longitudinal component.
Why can a hollow single-conductor waveguide not support a TEM mode?
A No magnetic field
B No electric field
C No cutoff frequency
D No second conductor
Answer: D. No second conductor. TEM propagation requires two conductors to support transverse fields.
Below a mode’s cutoff frequency, its field in the guide is what?
A Evanescent
B Unattenuated
C TEM
D Radiating freely
Answer: A. Evanescent. Below cutoff, the propagation constant is imaginary and the field decays along the guide.
For a selected mode, what happens above its cutoff frequency?
A It becomes static
B It propagates
C It is always reflected
D It turns into DC
Answer: B. It propagates. A waveguide mode can propagate when its frequency exceeds cutoff.
For an air-filled rectangular guide, TE10 cutoff depends mainly on which dimension?
A Broad wall width
B Guide length
C Wall thickness
D Narrow wall height
Answer: A. Broad wall width. The TE10 cutoff is c/(2a), where a is the broad internal dimension.
At a perfectly matched load, what is the input reflection coefficient?
A Zero
B One
C Minus one
D Infinite
Answer: A. Zero. An ideal match produces no reflected wave at the input.
What VSWR corresponds to a perfect impedance match?
A 2:1
B 0:1
C 1:1
D Infinite
Answer: C. 1:1. With zero reflection, incident and standing-wave amplitudes are equal everywhere.
Which S-parameter measures input reflection at port 1?
A S11
B S21
C S12
D S22
Answer: A. S11. S11 is the reflection coefficient looking into port 1.
Which S-parameter describes forward transmission from port 1 to port 2?
A S21
B S11
C S12
D S22
Answer: A. S21. S21 measures forward transmission through a two-port network.
Which instrument measures a component’s S-parameters across frequency?
A Spectrum analyzer
B Signal generator
C Vector network analyzer
D Power supply
Answer: C. Vector network analyzer. A VNA measures reflected and transmitted waves at calibrated reference planes.
What display plots normalized impedance and reflection coefficient together?
A Eye diagram
B Constellation map
C Waterfall plot
D Smith chart
Answer: D. Smith chart. The Smith chart relates normalized impedance to reflection coefficient.
Which instrument displays signal amplitude versus frequency?
A Vector network analyzer
B Spectrum analyzer
C Oscilloscope probe
D Frequency counter
Answer: B. Spectrum analyzer. A spectrum analyzer shows signal power across frequency.
Within a cavity resonator, what form of energy is stored?
A Mechanical torque
B Chemical fuel
C Electromagnetic energy
D Audio pressure
Answer: C. Electromagnetic energy. A cavity supports resonant electromagnetic fields.
What does a resonator’s quality factor Q relate?
A Frequency to wavelength
B Power to voltage
C Gain to bandwidth only
D Stored energy to loss
Answer: D. Stored energy to loss. Q measures stored energy relative to energy dissipated per cycle.
In a three-port circulator, power entering port 1 is routed primarily to which port?
A Port 1
B Port 2
C Port 3
D All ports equally
Answer: B. Port 2. An ideal circulator routes energy sequentially from port 1 to port 2.
How does a microwave isolator protect a source?
A Amplifies every reflection
B Blocks reverse power
C Converts RF to DC
D Splits frequency bands
Answer: B. Blocks reverse power. An isolator passes power forward while attenuating reverse-traveling power.
What is the main purpose of a microwave attenuator?
A Generate oscillations
B Measure phase
C Reduce signal power
D Change polarization
Answer: C. Reduce signal power. An attenuator introduces a specified reduction in RF power.
To monitor traveling microwave power, which port samples a directional coupler’s signal?
A Isolated port only
B DC port
C Ground plane
D Coupled port
Answer: D. Coupled port. A coupler extracts a known fraction of forward or reverse traveling power.
The input RF changes which electron-beam property in a klystron?
A Waveguide width
B Magnetic permeability
C Cavity temperature
D Electron velocity
Answer: D. Electron velocity. An RF cavity velocity-modulates electrons, which then bunch and transfer energy.
Which device uses crossed electric and magnetic fields with a resonant anode structure?
A Magnetron
B Klystron
C Schottky mixer
D PIN attenuator
Answer: A. Magnetron. A magnetron is a crossed-field microwave oscillator.