ELECTROMAGNETIC WAVES AND GUIDE STRUCTURE
BSc in electrical & Computer engineering IV BSc I Semester
Time: 3 hours Max Marks: 50
Answer all Questions
Part I: Answer ALL questions
1. A quarter wave transformer matches a 100 ohms load to a transmission line with
L=1.35μH/m and C=60pF/m .calculate the characteristic impedance of matching
transformer. (3pts).
2. A distortionless line operating at 120 MHz has R = 20 Ω/m, L = 0.3 μH/m, and C = 63
pF/m. How far will a voltage wave travel before it is reduced to 20% of its initial
magnitude?(2pts).
3. Calculate the VSWR for short circuited, open circuited and matched line. (2pts).
4. At 50 MHz, a lossy dielectric material is characterized by ε = 3.6ε0, μ = 2.1μo, and
σ = 0.08 S/m. If E, = 6e-γx az V/m, compute: (a) γ, (b) η. (2pts).
5. A uniform plane wave propagating in a medium has E = 2e-αz sin (108t - βz) ay V/m.If the
medium is characterized by εr = 1, μr = 20, and σ = 3 mhos/m, find α and β. (2pts).
6. Determine the phase and group velocities for a rectangular guide of 2.5 cm. x 1.0 cm.
cross-section, for the TE20mode at 15 GHz. (2pts).
7. What is impossibility of TEM wave in rectangular waveguide? (2pts).
Part II Answer any FIVE questions 7*5=35
1. A)in an air filled rectangular waveguide the cutoff frequency of TE10 mode is 6GHz
where that of TE01 mode is 10GHz calculate the cutoff frequency of next higher TE
modes and the cutoff frequency of TE11 mode if the guide is filled with a lossless
material having εr=4 and μr=2.(4pts).
b)a certain transmission line operating at w=106rad/sec has α=10dB/m, β=1rad/m and
Zo=50+j30Ω and 2m long .if the line is connected to a source of 10∟0V Zg=50Ω and
terminated by load of 25+j40Ω then determine the input impedance and the current at the
middle of the line (3pts).
2. A) Obtain an expression for the Input Impedance of lossless line of length ‘l’ with Z0as
characteristic Impedance and terminated by a load ZL.(4pts).
b) A rectangular wave guide is designed to propagate the dominant mode TE10 at a
frequency of 5MHz.the cutoff frequency is 0.8 of signal frequency .the ratio of the guide
height to the width is 2.calculate the dimensions of guide.(3pts).
3. a)A manufacturer produces a ferrite material with μ = 750μo, ε = 5εo, and σ=10-6S/m at
10MHz. (a)Would you classify the material as lossless, lossy, or conducting, determine
the phase difference between two points separated by 2 m.(b) Calculate β and intrinsic
impedance (4pts)
b) What is distortion on a line and derive a condition for Distortion less transmission in
terms of line parameters.(3pts).
4. a)A uniform plane wave propagating in a medium has
E = 2e-αz sin (108t - βz) ay V/m. If the medium is characterized by εr = 1, μr = 20, and σ =
3 mhos/m, find α, β, and H.(4pts).
b) For an air-filled rectangular guide cavity resonator of 4 cm x 2 cm. cross-section and 5
cm. axial length, determine the resonant frequency of the lowest 3 possible modes.(3pts).
5. a)An air-filled cubical cavity operates at a resonant frequency of 2 GHz when excited at
the TE1O1 mode. Determine the dimensions of the cavity. (3pts).
b) Derive the field expressions for TM wave propagation. (4pts).
6. a) For a rectangular guide of 7.2 cm x 3.4 cm., determine m, n and all the propagation
characteristics for the lowest possible TM mode at 6 GHz (no derivations). Can a TE
mode exist for such m and n? If so, what will be the change in propagation characteristics
for such a TE mode? (4pts).
b) A 30-m-long lossless transmission line with Z0 = 50Ω operating at 2 MHz is
terminated with a load ZL = 60 + j40 Ω0. If u = 0.6c on the line, find (a) The
reflection coefficient Γ and standing wave ratio S (b) The input impedance. (3pts).
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