Transmission Lines - Electromagnetics - Electronics & Communication Engineering Previous Year Questions

1

2008 · Electronics & Communication Engineering · Electromagnetics · Transmission Lines

Electronics & Communication Engineering (EC) 2008

One end of a loss-less transmission line having the characteristic impedance of 75Ω and length of 1cm is short-circuited. At 3GHz, the input impedance at the other end of the transmission line is

A

0

B

Resistive

C

Capacitive

D

Inductive

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2

2010 · Electronics & Communication Engineering · Electromagnetics · Transmission Lines

Electronics & Communication Engineering (EC) 2010

A transmission line has a characteristic impedance of 50 Ω and a resistance of 0.1 Ω/m. If the line is distortionless, the attenuation constant (in Np/m) is

A

500

B

5

C

0.014

D

0.002

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3

2010 · Electronics & Communication Engineering · Electromagnetics · Transmission Lines

Electronics & Communication Engineering (EC) 2010

In the circuit shown, all the transmission line sections are lossless. The Voltage Standing Wave Ratio (VSWR) on the 60 Ω line is

A

1.00

B

1.64

C

2.50

D

3.00

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4

2011 · Electronics & Communication Engineering · Electromagnetics · Transmission Lines

Electronics & Communication Engineering (EC) 2011

A transmission line of characteristic impedance 50 \(\Omega\) is terminated by a 50 \(\Omega\) load. When excited by a sinusoidal voltage source at 10 GHz, the phase difference between two points spaced 2 mm apart on the line is found to be \(\pi/4\) radians. The phase velocity of the wave along the line is

A

\(0.8 \times 10^8 m/s\)

B

\(1.2 \times 10^8 m/s\)

C

\(1.6 \times 10^8 m/s\)

D

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

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5

2011 · Electronics & Communication Engineering · Electromagnetics · Transmission Lines

Electronics & Communication Engineering (EC) 2011

A transmission line of characteristic impedance $50\,\Omega$ is terminated in a load impedance $Z_L$. The VSWR of the line is measured as 5 and the first of the voltage maxima in the line is observed at a distance of $\lambda/4$ from the load. The value of $Z_L$ is

A

$10\,\Omega$

B

$250\,\Omega$

C

$(19.23 + j46.15)\,\Omega$

D

$(19.23 - j46.15)\,\Omega$

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6

2012 · Electronics & Communication Engineering · Electromagnetics · Transmission Lines

Electronics & Communication Engineering (EC) 2012

A coaxial cable with an inner diameter of 1 mm and outer diameter of 2.4 mm is filled with a dielectric of relative permittivity 10.89. Given \(\mu_0 = 4\pi imes 10^{-7}\) H/m, \(\epsilon_0 = rac{10^{-9}}{36\pi}\) F/m, the characteristic impedance of the cable is

A

330 Ω

B

100 Ω

C

143.3 Ω

D

43.4 Ω

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7

2012 · Electronics & Communication Engineering · Electromagnetics · Transmission Lines

Electronics & Communication Engineering (EC) 2012

A transmission line with a characteristic impedance of 100 \( \Omega \) is used to match a 50 \( \Omega \) section to a 200 \( \Omega \) section. If the matching is to be done both at 429 MHz and 1 GHz, the length of the transmission line can be approximately

A

82.5 cm

B

1.05 m

C

1.58 m

D

1.75 m

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8

2013 · Electronics & Communication Engineering · Electromagnetics · Transmission Lines

Electronics & Communication Engineering (EC) 2013 [Session 1]

The return loss of a device is found to be 20 dB. The voltage standing wave ratio (VSWR) and magnitude of reflection coefficient are respectively

A

1.22 and 0.1

B

0.81 and 0.1

C

-1.22 and 0.1

D

2.44 and 0.2

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9

2014 · Electronics & Communication Engineering · Electromagnetics · Transmission Lines

Electronics & Communication Engineering (EC) 2014 [Session 1]

For a parallel plate transmission line, let \(v\) be the speed of propagation and \(Z\) be the characteristic impedance. Neglecting fringe effects, a reduction of the spacing between the plates by a factor of two results in

A

halving of \(v\) and no change in \(Z\)

B

no changes in \(v\) and halving of \(Z\)

C

no change in both \(v\) and \(Z\)

D

halving of both \(v\) and \(Z\)

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10

2014 · Electronics & Communication Engineering · Electromagnetics · Transmission Lines

Electronics & Communication Engineering (EC) 2014 [Session 3]

In the following figure, the transmitter Tx sends a wideband modulated RF signal via a coaxial cable to the receiver Rx. The output impedance \( Z_T \) of Tx, the characteristic impedance \( Z_0 \) of the cable and the input impedance \( Z_R \) of Rx are all real.
Which one of the following statements is TRUE about the distortion of the received signal due to impedance mismatch?

A

The signal gets distorted if \(Z_0 \neq Z_R \), irrespective of the value of \(Z_T \)

B

The signal gets distorted if \(Z_T \neq Z_0 \), irrespective of the value of \(Z_R \)

C

Signal distortion implies impedance mismatch at both ends: \(Z_T \neq Z_0 \) and \(Z_R \neq Z_0 \)

D

Impedance mismatches do NOT result in signal distortion but reduce power transfer efficiency

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11

2016 · Electronics & Communication Engineering · Electromagnetics · Transmission Lines

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

The propagation constant of a lossy transmission line is (2 + j5) m⁻¹ and its characteristic impedance is (50 + j0) Ω at ω = 10⁶ rad s⁻¹. The values of the line constants L, C, R, G are, respectively,

A

L = 200 /m, C = 0.1 /m, R = 50 Ω/m, G = 0.02 /m

B

L = 250 /m, C = 0.1 /m, R = 100 Ω/m, G = 0.04 /m

C

L = 200 /m, C = 0.2 /m, R = 100 Ω/m, G = 0.02 /m

D

L = 250 /m, C = 0.2 /m, R = 50 Ω/m, G = 0.04 /m

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12

2016 · Electronics & Communication Engineering · Electromagnetics · Transmission Lines

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

A lossless microstrip transmission line consists of a trace of width \(w\). It is drawn over a practically infinite ground plane and is separated by a dielectric slab of thickness \(t\) and relative permittivity \(\epsilon_r > 1\). The inductance per unit length and the characteristic impedance of this line are \(L\) and \(Z_0\), respectively.
Which one of the following inequalities is always satisfied?

A

\(Z_0 > \sqrt{\frac{Lt}{\epsilon_0\epsilon_r w}}\)

B

\(Z_0 < \sqrt{\frac{Lt}{\epsilon_0\epsilon_r w}}\)

C

\(Z_0 > \sqrt{\frac{Lw}{\epsilon_0\epsilon_r t}}\)

D

\(Z_0 < \sqrt{\frac{Lw}{\epsilon_0\epsilon_r t}}\)

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13

2016 · Electronics & Communication Engineering · Electromagnetics · Transmission Lines

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

A microwave circuit consisting of lossless transmission lines \(T_1\) and \(T_2\) is shown in the figure. The plot shows the magnitude of the input reflection coefficient \(|\Gamma|\) as a function of frequency \(f\). The phase velocity of the signal in the transmission lines is \(2 \times 10^8\) m/s.
The length \(L\) (in meters) of \(T_2\) is ________

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14

2017 · Electronics & Communication Engineering · Electromagnetics · Transmission Lines

Electronics & Communication Engineering (EC) 2017

A two-wire transmission line terminates in a television set. The VSWR measured on the line is 5.8. The percentage of power that is reflected from the television set is ________

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15

2018 · Electronics & Communication Engineering · Electromagnetics · Transmission Lines

Electronics & Communication Engineering (EC) 2018

The points \( P, Q \) and \( R \) shown on the Smith chart (normalized impedance chart) in the following figure represent:

A

P: Open Circuit, Q: Short Circuit, R: Matched Load

B

P: Open Circuit, Q: Matched Load, R: Short Circuit

C

P: Short Circuit, Q: Matched Load, R: Open Circuit

D

P: Short Circuit, Q: Open Circuit, R: Matched Load

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16

2018 · Electronics & Communication Engineering · Electromagnetics · Transmission Lines

Electronics & Communication Engineering (EC) 2018

A lossy transmission line has resistance per unit length \(R = 0.05\ \Omega/m\). The line is distortionless and has characteristic impedance of \(50\Omega\). The attenuation constant (in Np/m, correct to three decimal places) of the line is ______.

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17

2020 · Electronics & Communication Engineering · Electromagnetics · Transmission Lines

Electronics & Communication Engineering (EC) 2020

The impedances \(Z = jX\), for all \(X\) in the range \((-\infty, \infty)\), map to the Smith chart as

A

a circle of radius 1 with centre at (0, 0).

B

a point at the centre of the chart.

C

a line passing through the centre of the chart.

D

a circle of radius 0.5 with centre at (0.5, 0).

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18

2020 · Electronics & Communication Engineering · Electromagnetics · Transmission Lines

Electronics & Communication Engineering (EC) 2020

A transmission line of length 3λ/4 and having a characteristic impedance of 50 Ω is terminated with a load of 400 Ω. The impedance (rounded off to two decimal places) seen at the input end of the transmission line is __________ Ω.

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19

2020 · Electronics & Communication Engineering · Electromagnetics · Transmission Lines

Electronics & Communication Engineering (EC) 2020

For a 2-port network consisting of an ideal lossless transformer, the parameter \(S_{21}\) (rounded off to two decimal places) for a reference impedance of 10 \(\Omega\), is __________.

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20

2023 · Electronics & Communication Engineering · Electromagnetics · Transmission Lines

Electronics & Communication Engineering (EC) 2023

The standing wave ratio on a 50 \(\Omega\) lossless transmission line terminated in an unknown load impedance is found to be 2.0. The distance between successive voltage minima is 30 cm and the first minimum is located at 10 cm from the load. \(Z_L\) can be replaced by an equivalent length \(l_m\) and terminating resistance \(R_m\) of the same line. The value of \(R_m\) and \(l_m\), respectively, are

A

\(R_m=100\ \Omega,\ l_m=20\ \text{cm}\)

B

\(R_m=25\ \Omega,\ l_m=20\ \text{cm}\)

C

\(R_m=100\ \Omega,\ l_m=5\ \text{cm}\)

D

\(R_m=25\ \Omega,\ l_m=5\ \text{cm}\)

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