ECE QUESTION BANKS - TRANSMISSION LINES AND WAVEGUIDES - Anna University|JNTU UNIVERISTY|KERALA UNIVERSITY

ECE QUESTION BANKS - TRANSMISSION LINES AND WAVEGUIDES - Anna University

MODEL REGULATION 2004
Time: Three hours
Maximum: 100 marks
PART A — (10 x 2 = 20 marks)

1. Define propagation constant of a transmission line.
2. Calculate the characteristic impedance of a transmission line if the following measurements have been made on the line Zoc= 550 /__-60 degree ohm and Z sc = 500/__30 degree.
3. What are the applications of the quarter—wave line?
4. A 50 ohm line is terminated in load ZR =90+j60 ohm. Determine the reflection coefficient.
5. What are the characteristics of principal wave?
6. Define the cut—off frequency of a guide.
7. A rectangular waveguide with dimensions a = 8.5 cm and b = 4.3cm is fed by 5 GHz carrier. Will a TE11 mode be propagated?
8. Define wave impedance and write the expression for wave impedance of TE waves in rectangular guide.
9. What are the applications of cavity resonators?
10. Write Bessel's function of first kind of order zero.

PART B — (5 x 16 = 80 marks)

11. (a) (i) Derive the expressions for the input impedance of a transmission line. (10)
(ii) A cable has the following parameters:
R: 48.75 ohm/km, L: 1.09 mH/km, G: 38.75 MU/km and C: 0.059 uf/km.
Determine the characteristic impedance, propagation constant and wavelength for a source of f: 1600 Hz and Es: 1.0 volts. (6)

Or

(b) (i) A cable has been uniformly loaded by an inductance such that wl >> R . Assuming leakage conductance to be nil, deduce an expression for attenuation and phase constant without neglecting R.
(ii) A transmission line has the following parameters per km R: 15 ohm, C: 15 uf, L: 1 mH and G: 1 uU. Find the additional inductance to give distortion-less transmission. Calculate attenuation and phase constant for the loaded line. ( 8 )

12. (a) (i) Deduce the expression for constant — S circle for the dissipation-less line and explain. ( 8 )
(ii) A transmission line is terminated in ZL. Measurements indicate that the standing wave minima are 102 cm apart and that the last minimum is 35 cm from the load end of the line. The value of
standing wave ratio is 2.4 and R0 :250 ohm. Determine wave length and load impedance. ( 8 )

Or

(b) (i) Explain the procedure of double stub matching on a transmission line with an example. ( 8 )
(ii) Determine the length and location of a single short circuited stub to produce an impedance match on a transmission line with R0 of 600 Q and terminated in 1800 Q. ( 8 )

13. (a) (i) Derive the expressions for the field components of TM waves between parallel plates, propagating in Z direction. (10)
(ii) For a frequency of 6 GHz and plane separation = 7 cm. Find the following for the TE1o made z
(1) Cutoff frequency
(2) Phase and group velocity. (6)

Or

(b) (i) Explain wave impedance and obtain the expressions of wave impedance for TE and TM waves guided along parallel planes, Also sketch the variation of wave impedance with frequency. (10)
(ii) For a frequency of 5 GHz and plane separation of 8 cm in air, find the following for TM mode (6)
(1) Cut-off wave length
(2) Characteristic impedance and
(3) Phase constant.

14. (a) (i) Obtain the solution of Electric and Magnetic fields of TM waves guided along rectangular wave guide. (10)
(ii) A rectangular waveguide measures 3 >< 4.5 cm internally and has a 10 GHz signal propagated in it. Calculate the cut-off wavelength, the guide wavelength and the characteristic wave impedance for the TE mode. (6)

Or

(b) (i) Discuss the attenuation of electromagnetic wave s guided along rectangular waveguide. ( 8 )
(ii) What are the dimensions of a waveguide with the following specifications?
(1) At a frequency of 9959.5 MHz, the guide wavelength for TE mode is 87.57% of the cut-off wavelength
(2) TEao and TEiz mode have the same cut-off frequency. ( 8 )

15. (a) (i) Determine the solution of electric and magnetic fields of TM waves guided along circular waveguide. (10)
(ii) A circular waveguide has an internal diameter of 4 cm. For a 10 GHZ signal propagated in it in the TEn mode, calculate cut—off wavelength, guide wavelength and characteristic impedance. Uhm: 1.84 (6)

Or

(b) (i) Obtain the expression for resonant frequency of circular cavity resonator. ( 8 )
(ii) Calculate the resonant frequency of a rectangular resonator of dimensions a: 3 cm, b: 2 cm and d = 4 cm if the operating mode is TEioi. Assume free space within the cavity. (8 )




MODEL PAPER 2


EC335 - Transmission Lines and Waveguides

Total Marks:100
Maximum Hours:3 Hrs

This is exam consists of two sections Part A and Part B
Part A questions carry 2 marks each
Part B questions carry 15 marks

Answer all

PART - A (10 x 2 = 20 Marks)

1. Why frequency and phase distortion occur in transmission line? Write the condition of no distortion in terms of line parameters.
2. What is meant by reflection loss and insertion loss in a transmission line?
3. An air-filled coaxial transmission line has outer and inner conductor radii equal to 6 cm and 3cm, respectively. Calculate the values of a) inductance per unit length, b) capacitance per unit length and c) characteristic impedance of the line.
4. A loss less transmission line with Z0 = 50 ohm is terminated in an impedance equal to 50+j50 ohm. What is the reflection coefficient and VSWR on the line.
5. A 100-ohm load is to be matched to a 50-ohm line. Determine the characteristic impedance of a quarter wavelength matching section
6. State the reasons, which necessitate the use of stub matching in practice.
7. What is the function of the m-derived section in a composite filter?
8. Sketch the variation of characteristic impedance of a low-pass constant K filter as a function of frequency.
9. What is the function of delay equalizer? Where it is used.
10. Show under what condition a symmetrical lattice network with series arm impedances Z1 and diagonal impedances Z2 will be a constant resistance network.

PART - B (5 x 16 = 80 Marks)

11.a) Derive the expressions for the voltage and current at any point on the transmission line in terms of propagation constant, length and characteristic impedance of the line. (or)
11.b)deduce an expression for input impedance in terms of reflection coefficient.

12.a) What are the special considerations of radio frequency lines? A radio frequency line with Z0 = 70 ohm is terminated by ZL = 115 - j80ohm at attentuation constant = 2.5m. Find the VSWR & the maximum and minimum line impedances. Derive the formula used.(or)
12.b) A loss less line has a standing -wave ratio of 4. The Ro is 150 ohm and the maximum voltage measured on the line is 135 V. Find the power being delivered to the load. Derive the equation used.

13.a) A loss less line with Z0 = 300 ohm in operated at 200 MHz. The line is terminated with a load ZL to produce VSWR = 4.48, the first voltage minimum occurs at 6cm from the load end. Determine two stubbing positions nearest to the load and the corresponding lengths of short-circuited stubs having a characteristic impedance of 300 ohm for matching.(or)
13.b) A 50 ohm line feeds an inductive load Z = 35+j35 ohm. Design a double stub tuner to match this load to the line (make use of a Smith's chart).

14.a) Design a composite low-pass filter with a cutoff frequency of 10KHz for a load resistance of 500 ohm. It should have high attenuation at 10.65 KHz.(or)
14.b) Design a composite high-pass filter with a cutoff frequency of 10KHz for a load resistance of 500 ohm with high attenuation at 9.39 KHz.

15.a) Design a symmetrical 600ohm bridged - T resistance attenuator to have an attenuation of 20dB.(or)
15.b) A length of telephone cable is driven from a 600 ohm resistance. The measured insertion loss in dB is tabulated:
f(Hz) --> 30 100 500 1000 2000 4000 6000 loss(dB) --> 3.8 3.8 4.6 6.6 10.5 16.4 20.7 Design a lattice network to equalize the cable within 2dB from 30 to 4000 Hz. The overall insertion loss of the cable and equalizer must not exceed 20dB.


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