Question 1

Q.1. Define Rectangular Waveguide.

Accepted Answer

A rectangular waveguide is a hollow metallic conductor of rectangular cross-section (dimensions a × b) used to guide electromagnetic waves at microwave frequencies via successive reflections from its walls, supporting only TE and TM modes (no TEM).

Question 2

Q.2. What do you mean by VSWR?

Accepted Answer

VSWR (Voltage Standing Wave Ratio) is the ratio of maximum to minimum voltage magnitude along a mismatched transmission line, VSWR = Vmax/Vmin = (1+|Γ|)/(1−|Γ|), ranging from 1 (perfect match) to ∞ (total mismatch).

Question 3

Q.3. Define Phase Velocity.

Accepted Answer

Phase velocity is the speed at which a point of constant phase (e.g., a wave crest) travels along the direction of propagation, vp = ω/β; in a waveguide it exceeds the free-space speed of light c.

Question 4

Q.4. What are the basic laws of electromagnetics?

Accepted Answer

The basic laws of electromagnetics are Coulomb's law, Gauss's law, Faraday's law of induction, Ampere's (circuital) law, and the continuity equation — unified by Maxwell's four equations.

Question 5

Q.5. If the cut-off frequency of an air-filled waveguide is 10 GHz and it sup…

Accepted Answer

For an air-filled waveguide supporting TE01 mode with cutoff frequency 10 GHz, the cutoff depends only on the narrow dimension b: fc = c/(2b), giving b = c/(2fc) = 1.5 cm.

Question 6

Q.6. What do you mean by monopole and dipole antenna?

Accepted Answer

A monopole antenna is a single straight conductor fed against a ground plane, radiating a hemispherical pattern; a dipole antenna is two collinear conducting arms fed at the centre, radiating a doughnut-shaped pattern, and behaves like two monopoles joined end to end.

Question 7

Q.7. Define the radiation resistance of an antenna.

Accepted Answer

Radiation resistance is the equivalent resistance that would dissipate the same power as is actually radiated by the antenna, defined by Prad = I₀²Rrad/2 (or I₀²Rrad for rms current), representing the antenna's coupling of circuit power into electromagnetic radiation.

Question 8

Q.8. Write the name of two impedance matching techniques used in Transmission…

Accepted Answer

Two common impedance matching techniques for transmission lines are single-stub matching and quarter-wave transformer matching (double-stub matching and lumped L-network matching are also widely used).

Question 9

Q.9. What is the centre of the constant VSWR circle in a Smith chart?

Accepted Answer

On a Smith chart, the centre point (Γ = 0) is the common centre of all constant-VSWR circles; it represents a perfectly matched load (Z = Z0), and each constant-VSWR circle is centred there with radius |Γ| = (VSWR−1)/(VSWR+1).

Question 10

Q.10. Write the unit of Poynting vector.

Accepted Answer

The Poynting vector S = E×H represents power flow per unit area and has SI unit watt per square metre (W/m²).

Question 11

Q.1. Why is TEM mode not possible inside a waveguide? Explain the reasons sup…

Accepted Answer

TEM mode requires both Ez = 0 and Hz = 0 simultaneously; substituting this condition into Maxwell's equations for a hollow single-conductor waveguide forces the transverse fields to vanish as well (they would need a static-like solution impossible for a source-free hollow guide), so TEM cannot exist inside a waveguide — only TE (Ez=0) or TM (Hz=0) modes are possible.

Question 12

Q.2. Explain any four antenna parameters and also write their units.

Accepted Answer

Four key antenna parameters are: gain (dimensionless, dB), directivity (dimensionless, dB), beamwidth (degrees), and radiation resistance (ohms) — each characterizing a different aspect of how an antenna concentrates and couples radiated power.

Question 13

Q.3. State the radiation properties of an isotropic radiator.

Accepted Answer

An isotropic radiator is a hypothetical, lossless point source that radiates equally in all directions with a perfectly spherical radiation pattern, unit (0 dB) directivity, and serves as the universal reference for defining antenna gain and directivity.

Question 14

Q.4. Distinguish between near and far fields of a Hertzian dipole. State thei…

Accepted Answer

Near-field (reactive/radiating) regions surround a Hertzian dipole within roughly r < λ/2π, dominated by reactive, non-radiating, rapidly-decaying (1/r², 1/r³) field terms; the far field (r >> λ) has only the slowly-decaying 1/r radiating terms that carry real power to infinity, with E and H in phase and transverse to r.

Question 15

Q.5. Design a single stub of a Transmission line which is terminated with a l…

Accepted Answer

For ZL = 20+j50 Ω on a Z0 = 100 Ω line at 100 MHz, normalizing gives zL = 0.2+j0.5; using the Smith chart procedure, the stub is placed where the normalized admittance has unit real part (y = 1±jb), and a short-circuited stub of the appropriate length is added in shunt to cancel ±jb, achieving a match.

Question 16

Q.6. Explain Maxwell's equations in various forms.

Accepted Answer

Maxwell's equations exist in differential (point) form, integral form, phasor (time-harmonic) form, and free-space/source-free form, each expressing the same four physical laws (Gauss's electric/magnetic law, Faraday's law, Ampere-Maxwell law) in a different mathematically convenient representation.

Question 17

Q.7. Explain transmission lines and their applications.

Accepted Answer

A transmission line is a distributed-parameter conductor pair (coaxial cable, twin-lead, microstrip, etc.) that guides electromagnetic energy with characteristic impedance Z0, used in power transmission, telecommunication signal routing, RF/microwave interconnects, matching networks, and as circuit elements (stubs, resonators, delay lines).

Question 18

Q.1. Explain the following: (a) How are microstrip lines better than waveguid…

Accepted Answer

(a) Above ~60 GHz, waveguide dimensions shrink to impractically small, hard-to-manufacture sizes while microstrip remains easy to fabricate photolithographically and integrates directly with active devices, so microstrip is preferred; (b) between 1-30 GHz, waveguides handle far higher power with much lower loss than microstrip, so waveguides are preferred for high-power, low-loss links in that range.

Question 19

Q.2. Explain wave propagation in a conducting medium and derive an expression…

Accepted Answer

In a conducting (lossy) medium the propagation constant γ = α+jβ is complex; solving the wave equation with a general complex permittivity gives frequency-dependent α, β, and hence phase velocity vp = ω/β and group velocity vg = dω/dβ, both differing from the lossless free-space value c and from each other, showing the medium is dispersive.

Question 20

Q.3. Explain the radiation solution for the potential function.

Accepted Answer

Solving the inhomogeneous wave equation for the magnetic vector potential A with a time-varying source at position r' and observation point r (retarded time t−R/c) gives the retarded potential A(r,t) = (μ/4π)∫[J(r',t−R/c)/R]dv', from which the radiated E and H fields of any antenna are derived by differentiation.

Question 21

Q.4. Explain different types of waveguides briefly.

Accepted Answer

Common waveguide types are rectangular waveguide (TE/TM modes, most widely used), circular waveguide (TE/TM modes with Bessel-function field patterns, used for rotary joints and low-loss circular polarization), ridge waveguide (wider single-mode bandwidth), and elliptical waveguide (flexible, used for long antenna feeder runs).

Question 22

Q.5. Explain Smith Chart with diagram. Also explain applications of Smith Chart.

Accepted Answer

The Smith chart is a polar plot of the normalized impedance/admittance (constant-r and constant-x circles) mapped onto the unit reflection-coefficient circle; it is used graphically to convert between Γ and Z, find VSWR, and design impedance-matching networks (single/double-stub, quarter-wave) without complex-number arithmetic.

Electromagnetics Waves