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

1

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

\(45^\circ\)

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2

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

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3

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

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4

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

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5

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

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6

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

\(v_p = 0 \)

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7

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

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8

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 ______

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9

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 __________

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10

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

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

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11

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

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12

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 ______.

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13

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

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14

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 ____.

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15

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

\(0.75\lambda\)

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16

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.

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17

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

Electronics & Communication Engineering (EC) 2021

A standard air-filled rectangular waveguide with dimensions \(a = 8\) cm, \(b = 4\) cm, operates at 3.4 GHz. For the dominant mode of wave propagation, the phase velocity of the signal is \(v_p\). The value (rounded off to two decimal places) of \(v_p/c\), where \(c\) denotes the velocity of light, is __________.

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18

2022 · Electronics & Communication Engineering · Electromagnetics · Waveguides, Optical Fibres and Antennas

Electronics & Communication Engineering (EC) 2022

A waveguide consists of two infinite parallel plates (perfect conductors) at a separation of 10^-4 cm, with air as the dielectric. Assume the speed of light in air to be 3 × 10^8 m/s. The frequency/frequencies of TM waves which can propagate in this waveguide is/are ______.

A

6 × 10^15 Hz

B

0.5 × 10^12 Hz

C

8 × 10^14 Hz

D

1 × 10^13 Hz

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19

2026 · Electronics & Communication Engineering · Electromagnetics · Waveguides, Optical Fibres and Antennas

Electronics and Communication Engineering (EC) 2026

The cutoff frequency (in GHz) for the dominant \(TE_{10}\) mode of an air-filled rectangular waveguide of inner dimension 0.28 inch × 0.14 inch is __.
(rounded off to two decimal places).

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