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Max. Marks: 100

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00000EC40312 190%176:
APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY

Seventh semester B.Tech degree examinations (S), September 2020

Course Code: EC403
Course Name: MICROWAVE & RADAR ENGINEERING

PART A
Answer any two full questions, each carries 15 marks.
What are re-entrant cavities? Show that they support infinite number of resonant
frequencies.
Derive power output and efficiency of a reflex klystron.
A reflex klystron operates under the following conditions:
Vo = 600V, Rg, =15KQ, f= 9 GHz, L=1 mm, e/m = 1.759 x 10"! (MKS system)
The tube is oscillating at fr at the peak of the n = 2 or 13 mode. Assume that the

transit time through the gap and beam loading to be neglected. Determine:-
1. The value of the repeller voltage Vr.
2. The direct current necessary to give a microwave gap voltage of 200 V.
3. The electronic efficiency under this condition.
Derive an expression for velocity modulation in two cavity Klystron with the
help of a neat diagram.
A two cavity klystron amplifier has the following parameters:
Vo=700V 1-100 kQ 1,=30mA f=3GHz
Gap spacing in either cavity d=l1mm, spacing between the two cavities L=Scm
and shunt impedance ‏تيآ‎
‎Determine:
‎1. Input gap voltage to give maximum voltage V>
2. Voltage gain , neglecting the beam loading in the output cavity
3. Efficiency of the amplifier, neglecting beam loading.
4. Beam loading conductance and show that it can be neglected.
With the help of neat sketches and sufficient equations explain the working of a

cylindrical magnetron.

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Duration: 3 Hours

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