Waveguides, Optical Fibres and Antennas - Electromagnetics - Electronics & Communication Engineering Previous Year Questions

1

2007 · Electronics & Communication Engineering · Electromagnetics · Waveguides, Optical Fibres and Antennas

Electronics & Communication Engineering (EC) 2007

An air-filled rectangular waveguide has inner dimensions of \(3 \text{ cm} \times 2 \text{ cm}\). The wave impedance of the \(TE_{20}\) mode of propagation in the waveguide at a frequency of 30 GHz is (free space impedance \(\eta_0 = 377 \Omega\))

A

308 \(\Omega\)

B

355 \(\Omega\)

C

400 \(\Omega\)

D

461 \(\Omega\)

Check answer

Open complete paper

2

2007 · Electronics & Communication Engineering · Electromagnetics · Waveguides, Optical Fibres and Antennas

Electronics & Communication Engineering (EC) 2007

The \(\vec{E}\) field in a rectangular waveguide of inner dimensions \(a \times b\) is given by \[ \vec{E} = \frac{\omega\mu}{h^2} \left(\frac{\pi}{a}\right) H_0 \sin\left(\frac{2\pi x}{a}\right) \sin(\omega t - \beta z) \hat{y} \] where \(H_0\) is a constant, and \(a\) and \(b\) are the dimensions along the x-axis and the y-axis respectively. The mode of propagation in the waveguide is

A

\(TE_{20}\)

B

\(TM_{11}\)

C

\(TM_{20}\)

D

\(TE_{10}\)

Open complete paper

3

2007 · Electronics & Communication Engineering · Electromagnetics · Waveguides, Optical Fibres and Antennas

Electronics & Communication Engineering (EC) 2007

A λ/2 dipole is kept horizontally at a height of λ/2 above a perfectly conducting infinite ground plane. The radiation pattern in the plane of the dipole (E plane) looks approximately as

A

B

C

D

Open complete paper

4

2008 · Electronics & Communication Engineering · Electromagnetics · Waveguides, Optical Fibres and Antennas

Electronics & Communication Engineering (EC) 2008

For a Hertz dipole antenna, the half power beam width (HPBW) in the E-plane is

A

\(360^\circ\)

B

\(180^\circ\)

C

\(90^\circ\)

D

\(45^\circ\)

Open complete paper

5

2008 · Electronics & Communication Engineering · Electromagnetics · Waveguides, Optical Fibres and Antennas

Electronics & Communication Engineering (EC) 2008

A rectangular waveguide of internal dimensions (a = 4 cm and b = 3 cm) is to be operated in TE₁₁ mode. The minimum operating frequency is

A

6.25 GHz

B

6.0 GHz

C

5.0 GHz

D

3.75 GHz

Open complete paper

6

2008 · Electronics & Communication Engineering · Electromagnetics · Waveguides, Optical Fibres and Antennas

Electronics & Communication Engineering (EC) 2008

In the design of a single mode step index optical fiber close to upper cut-off, the single-mode operation is NOT preserved if

A

radius as well as operating wavelength are halved

B

radius as well as operating wavelength are doubled

C

radius is halved and operating wavelength is doubled

D

radius is doubled and operating wavelength is halved

Check answer

Open complete paper

7

2008 · Electronics & Communication Engineering · Electromagnetics · Waveguides, Optical Fibres and Antennas

Electronics & Communication Engineering (EC) 2008

At 20 GHz, the gain of a parabolic dish antenna of 1 meter diameter and 70% efficiency is

A

15 dB

B

25 dB

C

35 dB

D

45 dB

Open complete paper

8

2009 · Electronics & Communication Engineering · Electromagnetics · Waveguides, Optical Fibres and Antennas

Electronics & Communication Engineering (EC) 2009

Which of the following statements is true regarding the fundamental mode of the metallic waveguides shown ?
P: Coaxial, Q: Cylindrical, R: Rectangular

A

Only P has no cutoff-frequency

B

Only Q has no cutoff-frequency

C

Only R has no cutoff-frequency

D

All three have cut-off frequencies

Open complete paper

9

2011 · Electronics & Communication Engineering · Electromagnetics · Waveguides, Optical Fibres and Antennas

Electronics & Communication Engineering (EC) 2011

The modes in a rectangular waveguide are denoted by TE_mn/TM_mn where m and n are the eigen numbers along the larger and smaller dimensions of the waveguide respectively. Which one of the following statements is TRUE?

A

The TM₁₀ mode of the waveguide does not exist

B

The TE₁₀ mode of the waveguide does not exist

C

The TM₁₀ and the TE₁₀ modes both exist and have the same cut-off frequencies

D

The TM₁₀ and the TE₀₁ modes both exist and have the same cut-off frequencies

Open complete paper

10

2012 · Electronics & Communication Engineering · Electromagnetics · Waveguides, Optical Fibres and Antennas

Electronics & Communication Engineering (EC) 2012

The magnetic field along the propagation direction inside a rectangular waveguide with the cross-section shown in the figure is \( H_z = 3 \cos(2.094 \times 10^2 x) \cos(2.618 \times 10^2 y) \cos(6.283 \times 10^9 t - \beta z) \) The phase velocity \( v_p \) of the wave inside the waveguide satisfies

A

\(v_p > c \)

B

\(v_p = c \)

C

\(0 < v_p < c \)

D

\(v_p = 0 \)

Open complete paper

11

2016 · Electronics & Communication Engineering · Electromagnetics · Waveguides, Optical Fibres and Antennas

Electronics & Communication Engineering (EC) 2016 [Session 1]

The far-zone power density radiated by a helical antenna is approximated as:
\[ \vec{W}_{rad} = \vec{W}_{average} \approx \hat{a}_r C_0 \frac{1}{r^2} \cos^4 \theta \]
The radiated power density is symmetrical with respect to \(\phi\) and exists only in the upper hemisphere: \(0 \le \theta \le \frac{\pi}{2}; 0 \le \phi \le 2\pi\); \(C_0\) is a constant. The power radiated by the antenna (in watts) and the maximum directivity of the antenna, respectively, are

A

1.5C₀, 10dB

B

1.256C₀, 10dB

C

1.256C₀, 12dB

D

1.5C₀, 12dB

Open complete paper

12

2016 · Electronics & Communication Engineering · Electromagnetics · Waveguides, Optical Fibres and Antennas

Electronics & Communication Engineering (EC) 2016 [Session 2]

Light from free space is incident at an angle \( \theta_i \) to the normal of the facet of a step-index large core optical fibre. The core and cladding refractive indices are \( n_1 = 1.5 \) and \( n_2 = 1.4 \), respectively.
The maximum value of \( \theta_i \) (in degrees) for which the incident light will be guided in the core of the fibre is ______

Check answer

Open complete paper

13

2016 · Electronics & Communication Engineering · Electromagnetics · Waveguides, Optical Fibres and Antennas

Electronics & Communication Engineering (EC) 2016 [Session 3]

Consider an air-filled rectangular waveguide with dimensions \(a = 2.286\) cm and \(b = 1.016\) cm. At 10 GHz operating frequency, the value of the propagation constant (per meter) of the corresponding propagating mode is __________

Check answer

Open complete paper

14

2016 · Electronics & Communication Engineering · Electromagnetics · Waveguides, Optical Fibres and Antennas

Electronics & Communication Engineering (EC) 2016 [Session 3]

Consider an air-filled rectangular waveguide with dimensions \(a = 2.286\) cm and \(b = 1.016\) cm. The increasing order of the cut-off frequencies for different modes is

A

\(TE_{01} < TE_{10} < TE_{11} < TE_{20}\)

B

\(TE_{20} < TE_{11} < TE_{10} < TE_{01}\)

C

\(TE_{10} < TE_{20} < TE_{01} < TE_{11}\)

D

\(TE_{10} < TE_{11} < TE_{20} < TE_{01}\)

Open complete paper

15

2017 · Electronics & Communication Engineering · Electromagnetics · Waveguides, Optical Fibres and Antennas

Electronics & Communication Engineering (EC) 2017

Standard air-filled rectangular waveguides of dimensions a = 2.29 cm and b = 1.02 cm are designed for radar applications. It is desired that these waveguides operate only in the dominant TE10 mode with the operating frequency at least 25% above the cutoff frequency of the TE10 mode but not higher than 95% of the next higher cutoff frequency. The range of the allowable operating frequency f is

A

8.19 GHz ≤ f ≤ 13.1 GHz

B

8.19 GHz ≤ f ≤ 12.45 GHz

C

6.55 GHz ≤ f ≤ 13.1 GHz

D

1.64 GHz ≤ f ≤ 10.24 GHz

Open complete paper

16

2018 · Electronics & Communication Engineering · Electromagnetics · Waveguides, Optical Fibres and Antennas

Electronics & Communication Engineering (EC) 2018

The cutoff frequency of TE01 mode of an air filled rectangular waveguide having inner dimensions a cm × b cm (a > b) is twice that of the dominant TE10 mode. When the waveguide is operated at a frequency which is 25% higher than the cutoff frequency of the dominant mode, the guide wavelength is found to be 4 cm. The value of b (in cm, correct to two decimal places) is ______.

Check answer

Open complete paper

17

2019 · Electronics & Communication Engineering · Electromagnetics · Waveguides, Optical Fibres and Antennas

Electronics & Communication Engineering (EC) 2019

The dispersion equation of a waveguide, which relates the wavenumber \(k\) to the frequency \(\omega\), is \(k(\omega) = (1/c)\sqrt{\omega^2 - \omega_0^2}\), where the speed of light \(c = 3 \times 10^8\) m/s, and \(\omega_0\) is a constant. If the group velocity is \(2 \times 10^8\) m/s, then the phase velocity is

A

\(1.5 \times 10^8\) m/s

B

\(2 \times 10^8\) m/s

C

\(3 \times 10^8\) m/s

D

\(4.5 \times 10^8\) m/s

Open complete paper

18

2019 · Electronics & Communication Engineering · Electromagnetics · Waveguides, Optical Fibres and Antennas

Electronics & Communication Engineering (EC) 2019

A rectangular waveguide of width \(w\) and height \(h\) has cut-off frequencies for \(TE_{10}\) and \(TE_{11}\) modes in the ratio 1:2. The aspect ratio \(w/h\), rounded off to two decimal places, is ____.

Check answer

Open complete paper

19

2020 · Electronics & Communication Engineering · Electromagnetics · Waveguides, Optical Fibres and Antennas

Electronics & Communication Engineering (EC) 2020

For an infinitesimally small dipole in free space, the electric field \(E_\theta\) in the far field is proportional to \((e^{-jkr}/r)\sin\theta\), where \(k = 2\pi/\lambda\). A vertical infinitesimally small electric dipole (\(\delta l \ll \lambda\)) is placed at a distance \(h (h > 0)\) above an infinite ideal conducting plane, as shown in the figure. The minimum value of \(h\), for which one of the maxima in the far field radiation pattern occurs at \(\theta = 60^\circ\), is

A

\(\lambda\)

B

\(0.5\lambda\)

C

\(0.25\lambda\)

D

\(0.75\lambda\)

Open complete paper

20

2021 · Electronics & Communication Engineering · Electromagnetics · Waveguides, Optical Fibres and Antennas

Electronics & Communication Engineering (EC) 2021

The refractive indices of the core and cladding of an optical fiber are 1.50 and 1.48, respectively. The critical propagation angle, which is defined as the maximum angle that the light beam makes with the axis of the optical fiber to achieve the total internal reflection, (rounded off to two decimal places) is __________ degree.

Check answer

Open complete paper