Question 1

Q.1. Write down the applications of microwaves.

Accepted Answer

Microwaves (roughly 1-300 GHz) are used in radar, satellite communication, terrestrial microwave links, mobile/wireless networks, RFID/GPS, microwave heating, and biomedical (diathermy) applications.

Question 2

Q.2. List out the differences between the TE mode and TM mode.

Accepted Answer

TE mode has Ez=0, Hz≠0 (electric field fully transverse); TM mode has Hz=0, Ez≠0 (magnetic field fully transverse) — both propagate in a waveguide above a mode-dependent cutoff frequency, with TE10 typically the dominant (lowest-cutoff) mode.

Question 3

Q.3. What is a phase shifter?

Accepted Answer

A phase shifter is a two-port microwave device that introduces a controllable (fixed or variable) phase shift to a signal passing through it, without significantly altering its amplitude, used for beam-steering in phased arrays and for tuning matching networks.

Question 4

Q.4. Why are the S-parameters used in microwaves?

Accepted Answer

S-parameters (scattering parameters) are used in microwaves because voltage and current are difficult to measure directly at microwave frequencies, whereas S-parameters directly relate measurable incident and reflected power/wave amplitudes, and remain well-defined even for active or distributed (non-lumped) high-frequency networks.

Question 5

Q.5. What is a slow wave structure?

Accepted Answer

A slow-wave structure is a periodic or helical waveguide-like structure designed to reduce the phase velocity of an electromagnetic wave to near the drift velocity of an electron beam, enabling sustained energy exchange in travelling-wave microwave tubes (TWT).

Question 6

Q.6. What is Gunn effect?

Accepted Answer

The Gunn effect is the generation of periodic microwave-frequency current oscillations in certain bulk semiconductors (GaAs, InP) when a DC electric field above a threshold value is applied, arising from electron transfer between conduction-band valleys of differing mobility (negative differential resistance).

Question 7

Q.7. What are the applications of MMICs?

Accepted Answer

MMICs (Monolithic Microwave Integrated Circuits) are applied in cellular/wireless handset front-ends, satellite communication payloads, radar transmit/receive modules (phased-array T/R modules), and low-cost mass-produced RF systems requiring small size and high reliability.

Question 8

Q.8. What is VSWR?

Accepted Answer

VSWR (Voltage Standing Wave Ratio) is the ratio of maximum to minimum voltage magnitude of the standing-wave pattern on a mismatched transmission line, VSWR = Vmax/Vmin = (1+|Γ|)/(1−|Γ|), a dimensionless measure of impedance match quality ranging from 1 (perfect match) to ∞ (total mismatch).

Question 9

Q.9. Describe various radar applications.

Accepted Answer

Radar applications include air-traffic control, military surveillance/tracking, weather monitoring, marine navigation, automotive collision-avoidance, and remote sensing (synthetic aperture radar for terrain mapping).

Question 10

Q.10. What is RFID and GPS?

Accepted Answer

RFID (Radio Frequency Identification) uses radio waves to wirelessly identify and track tagged objects via reader-tag communication; GPS (Global Positioning System) uses timed microwave signals from orbiting satellites to determine a receiver's precise position, velocity and time.

Question 11

Q.1. Explain the stripline and microstripline.

Accepted Answer

Stripline is a planar transmission line with a centre conductor fully sandwiched between two ground planes in a homogeneous dielectric (pure TEM mode); microstripline has a centre conductor on top of a single-sided dielectric substrate over one ground plane, exposed to air above (quasi-TEM mode) — microstrip is easier to fabricate and access, stripline offers better shielding and no dispersion.

Question 12

Q.2. An air-filled rectangular waveguide has dimensions: a = 6 cm and b = 4 c…

Accepted Answer

For a = 6 cm, b = 4 cm air-filled waveguide: fc(TE10) = c/2a = 2.5 GHz (propagates at 4 GHz), fc(TM11) = (c/2)√[(1/a)²+(1/b)²] ≈ 4.507 GHz (does not propagate at 4 GHz).

Question 13

Q.3. What is 'Magic' associated with a Magic Tee? Draw a neat sketch of a Mag…

Accepted Answer

A Magic Tee is a 4-port hybrid waveguide junction combining an E-plane and H-plane Tee; its 'magic' property is complete isolation between the E-arm and H-arm ports, used as a duplexer, mixer, and balanced bridge for impedance measurement.

Question 14

Q.4. Derive the S-matrix for an ideal 3 dB directional coupler.

Accepted Answer

For an ideal, matched, lossless, reciprocal 3 dB (quadrature) directional coupler, unitarity and symmetry constraints reduce the S-matrix to S13=S24=1/√2, S14=S23=j/√2 (or similarly with the 90° phase split assigned to the coupled port), with all other elements zero.

Question 15

Q.5. Derive the equation of velocity modulation for a Two-Cavity Klystron amp…

Accepted Answer

In a two-cavity klystron, the input (buncher) cavity's gap voltage modulates the velocity of electrons passing through it; in the field-free drift space this velocity modulation converts into density (bunching) modulation, described by v(t0) = v0[1 + (V1/2V0)sin(ωt0)] for electrons entering the gap at time t0.

Question 16

Q.6. Explain the principle of operation of an IMPATT diode.

Accepted Answer

An IMPATT (Impact Avalanche and Transit Time) diode operates by combining avalanche-multiplication-induced current delay with drift-region transit-time delay in a reverse-biased p-n junction, together producing a total current-to-voltage phase delay near 180°, yielding negative resistance and microwave oscillation/amplification.

Question 17

Q.7. Describe the microwave power measurement.

Accepted Answer

Microwave power is measured using bolometers/thermistors (resistance change from RF heating, used with a Wheatstone bridge), thermocouples (RF-heating-induced thermoelectric EMF), and calorimetric methods for high power — all converting RF power into a measurable thermal or electrical effect, since direct high-frequency voltage/current measurement is impractical.

Question 18

Q.1. Derive the expression for cut-off frequency, phase constant and phase ve…

Accepted Answer

For a circular waveguide of radius a, the TE and TM mode fields satisfy the Helmholtz equation in cylindrical coordinates with Bessel-function solutions; cutoff wavenumbers are set by the zeros of Jn (TM) or Jn′ (TE), giving fc = kc·c/2π, with phase constant β=√(k²−kc²) and phase velocity vp=ω/β exactly as in rectangular waveguide but with Bessel-function-derived cutoff values.

Question 19

Q.2. Explain the working principle of an 8-cavity cylindrical magnetron. Deri…

Accepted Answer

An 8-cavity cylindrical magnetron uses crossed static E (radial) and B (axial) fields to force electrons from a central cathode into cycloidal paths past 8 resonant cavities in the surrounding anode block, inducing RF oscillation via synchronism between electron rotation and the cavity π-mode field pattern; the Hartree voltage sets the minimum anode voltage for oscillation onset at a given magnetic field.

Question 20

Q.3. Explain the construction of the Gunn diode using RWH and two-valley theo…

Accepted Answer

The Gunn diode's negative differential resistance is explained by the Ridley-Watkins-Hilsum (RWH) two-valley theory (electron transfer from a high-mobility lower valley to a low-mobility satellite valley above threshold field); Gunn diodes operate in transit-time (Gunn), delayed, quenched, or LSA modes, and are used as low-power microwave/millimetre-wave oscillator sources.

Question 21

Q.4. Design a bandpass filter having a 0.5 dB equal-ripple response, with N=3…

Accepted Answer

Using standard 0.5 dB-ripple Chebyshev lowpass-prototype g-values for N=3 (g1=1.5963, g2=1.0967, g3=1.5963), the bandpass filter is realized via lowpass-to-bandpass transformation (series elements become series LC, shunt elements become shunt LC) scaled to fc=5 GHz, FBW=10%, Z0=75 Ω, giving the required inductor/capacitor (or equivalent coupled-line/resonator) values for each of the three resonators.

Question 22

Q.5. Draw the block diagram of the radar and explain each block. Derive the r…

Accepted Answer

A radar system's block diagram comprises transmitter, duplexer/T-R switch, antenna, receiver (mixer/IF amplifier/detector), signal processor, and display; the radar range equation, derived from the two-way inverse-square power spreading plus target radar cross-section, gives Rmax = [PtG²λ²σ/((4π)³Smin)]^(1/4).

Microwave Theory And Techniques