GITAM University 2006 B.E Electronics & Tele-Communication Engineering Transmission Lines & Waveguides - Question Paper

College of Engineering
Gandhi Institute of Technology and Management, Visakhapatnam
(Affiliated to Andhra University)

B.E.(Electronics and Communications Engineering)
2nd Year 2nd Semester exams 2005-2006
(Autonomous Stream)

EC 226: Transmission Lines & Waveguides

Time: three Hours Max. Marks: 60


1. Answer ques. No. one ( Part – A) and any 4 of the remaining 7 (Part – B)
2. All parts of a ques. must be answered in 1 place, otherwise they will not be valued.
3. Figures in the right hand margin indicate marks allotted.



PART – A

1. Answer the subsequent in 1 or 2 phrases each (10x2=20)
a) Write the expressions for characteristic impedance and propagation constant, in terms of the primary constants of a transmission line.
b) A 50 O line of length ?/8 is terminated in 20+j40 O. What is the magnitude of the input impedance?
c) Sketch the standing wave trend for voltage on open and short circuited lines.
d) What distance is normally maintained ranging from the 2 stubs in double stub matching and why?
e) What is the significance of the centre point on the Smith chart?
f) Show that TEM wave can not propagate in a waveguide.
g) Define Q-factor for a cavity resonator. What is its significance?

h) Sketch the electric and magnetic field lines in the cross-section of a balanced strip line.
i) What is a re-entrant cavity?
j) Wavegudes are not used at low frequencies- why?



PART – B


ans any 4 of the subsequent. If you attempt more than 4 questions, only the 1st 4 in order will be valued


2. a) Give the equivalent circuit of a part of a transmission line. (2)
b) Derive expressions for voltage and current on a transmission line in terms of the receiving end parameters. (6)
c) Deduce the expression for the input impedance of a lossless line, terminated in ZR. (2)
3. a) Determine the characteristic impedance of a lossless coaxial line with inner diameter of outer conductor = 1.2 cm and outer diameter of inner conductor = 0.4 cm, and filled with polyesterence( e r = 2.5) (5)
b) Why does a signal get distorted on a transmission line? State the condition for no distortion. (5)
4. a) Explain the construction of Smith chart. (5)
b) A transmission line of 50 ohm characteristic impedance is terminated in an impedance of 100+j100 ohm. compute i) the impedance at 3?/8 distance from load. Ii) the VSWR on the line. (5)
5. a) Derive the relationship ranging from free space wavelength, guide wavelength and cut off wavelength in a rectangular waveguide. (5)

b) Find the cut off frequency of TE11 mode in a circular wave guide having a radius of 2.5 cm. Also obtain guide wavelength and wave impedance. (5)
6. a) Show that, when a cylindrical cavity is operated in the waveguide TE11 mode, the resonant frequency depends on the radius and length of the cavity. (5)
b) An air filled cavity resonator has cross-sectional dimensions of 2.3 cm x 1.0 cm and is five cm long. obtain its resonant frequency. In which mode does it resonate? (5)
7. a) Distinguish ranging from strip and microstrip transmission lines in structure and properties. (5)
b) Explain the concept of stub matching. (5)
8. Write short notes on:
a) Measurement of impedance (5)
b) Phase and group velocities (3)
c) Special features of R.F. lines. (2)

Earning:   Approval pending.