ANNA UNIVERSITY :: CHENNAI – 600 025
MODEL QUESTION PAPER
B.E. ELECTRONICS AND COMMUNICATION ENGINEERING
SEMESTER - 7
EC432 MICROWAVE ENGINEERING
Time: Three Hours Maximum : 100 Marks
Answer All The Questions
PART - A (2 x 10 = 20 Marks)
1. With the help of electronic admittance diagram explain the modes of a reflex
klystron oscillator.
2. A two-cavity klystron operates at 10 GHz with I0 = 3.6 mA, V0 = 10KV. The
drift space length is 2 cms, the output cavity total shunt conductance is Gsh = 20 µ
mho and the beam coupling coefficient β2 = 0.92. Find the maximum voltage
gain.
3. Explain the use of a PIN device as a single switch and a double switch circuits.
4. Give the comparison between IMPATT, TRAPATT and BARITT diodes
considering their performance characteristics and applications.
5. Establish the relation between Z and S matrices of a two-port network.
6. Derive the scattering matrix of a H plane T.
7. Explain the concept of choke flange and how it is realized in microwave joint.
8. Explain the use of magic T in a balanced microwave mixer.
9. Explain the principle of the power meter double bridge circuit for microwave
power measurement.
10. A crystal detector generates a signal of 10 m V for an incident microwave power
of -25 dBm. What is the detector sensitive in mV/ mW ? Why is the microwave
signal amplitude modulated by a 1 KHz square wave before it is applied to a
crystal detector?
PART - B (5 x 16 = 80 Marks)
11. Derive the expressions for power output and efficiency of a reflex klystron
oscillator.
A reflex klystron operators at frequency 5 KHz with repeller space L =- 0.5 cm,
dc beam voltage V0 =300V, beam current I0 = 20 mA, repeller voltage - VR volt
for 1¾ mode. Calculate (i) maximum power output (ii) repeller voltage, (iii) the
bandwidth for the range of ∆VR = 1V, (iv) efficiency.
12.a) Explain with the help of neat diagram the construction and amplification process
in TWTA. Draw the rf power output and gain characteristic curves.
A helix TWT operates at 5 GHz under a beam impedance 8KV and beam current
400 mA. The helix impedance is 20 ohm and the interaction length is 25 cm. Find
the output power gain in dB.
(OR )
12.b) Draw the schematic diagram of a cylindrical magnetron tube oscillator. If a & b
are outer & inner radii of the cathode and anode cylinders respectively, derive the
expression for the cut off magnetic field Bc. Give three important application of
magnetron with power and frequency specifications.
A cylindrical magnetron with 16 resonators is operated at 1 GHz with a = 3 cm,
b= 5 cm, V0= 20 KV, B0 = 0.1 Tesla. Find the Hartree voltage.
13.a) Draw the electrical equivalent circuit of a Gunn diode explaining the parameters.
Explain with diagram how a Gunn diode oscillator can be designed using
rectangular waveguide in X-band. Give typical power output and frequency
tuning range achievable. What is the difficulty in obtaining very high power?
The drift velocity of electrons is 3 x107 cm/s, through the active region of length
20 x 10-4 cm. Calculate the natural frequency of the diode and the critical voltage
for GaAs. Critical field for GaAS is 3.2 KV / cm.
(OR)
13.b) Explain how Varactor diode is used as frequency multiplier, State and explain
Man1ey Rowe relations with the help of the circuit diagram.
A sinusoidal input signal at frequency fs and pump signal at frequency fp are
applied across a varactor diode. If the output circuit is a bandpass filter with
resistive series load at frequency fs + fp, calculate the power gain.
14.a) What are the properties of S parameters of a perfectly matched, lossless,
reciprocal microwave network?
A matched magic-T is terminated at collinear ports 1&2 and difference port 4 by
impedances of reflection coefficients Γ1 = 0.5, Γ2 = 0.6 & Γ4 = 0.8 respectively. If
I-watt power is fed at a sum port 3, calculate the power reflected at port 3 &
power transmitted to other three ports.
OR
14.b) Explain with a schematic diagram. The working principle of a four part circulator
and how it is achieved. A three port circulator has an insertion loss of dB,
isolation 30 dB and VSWR = 1.5. Find the S-matrix.
15.a) Why VSWR> 20 is not measured directly by VSWR meter? Explain the theory
of double minimum method of experimentally determining high VSWR of a load
by using w/g-slotted line. What are the possible errors in the slotted line method?
OR
15.b) Define antenna test ranges. Explain with a schematic diagram the antenna gain
measurement with three-antenna method. How do you predict about the
polarization of the signal from the measured output voltage pattern?
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