# Microwave Engineering December-2011

UNIT – I

1. (a) Derive the TEmn field equations in a rectangular waveguides.

(b) An air filled waveguide with a cross section 2×1 cm transports energy in the TE10 mode at the rate of 0.5 hp. The impressed frequency is 30 GHz. What is the peak value of the electric field occurring in the guide ?

OR

1. (a) Derive the field equations of TMnp modes in a circular waveguide.

(b) An air filled circular waveguide has a radius of 1.5 cm and is to carry energy at a frequency of 10 GHz. Find all TE and TM modes for which transmission is possible.

UNIT – II

2. Describe the following using scattering matrix representation : .

(a) Magic Tees

(b) Hybrid Rings

OR

2. Describe the following using scattering matrix representation:

(a) Directional coupler

(b) Microwave circulars.

UNIT – III

3 (a) Describe the working of two cavity Klystron using Applegate diagram.

(b) A two cavity amplifier Klystron has the following parameters :

Beam voltage vo = 900 V Beam current Io = 30 mA Frequency f = 84 GHz

Gap spacing in either cavity d = 1 mm effective shunt impedance Rsh = 40 Kq

Determine :

(i) The electron velocity

(ii) The dc electron transit time

(iii) The input voltage for maximum output voltage

(iv) The voltage gain in dB

OR

3 (a) Explain the working and operation of reflex Klystron.

(b) A reflex Klystron operates at the peak mode of n = 2 with Beam voltage Vo = 300 V Beam current Io = 20 mA Signal Voltage V1 = 40 V Determine :

(i) The input power in watts

(ii) The output power in watts

(iii) The efficiency

UNIT – IV

4. (a) Explain the construction, operation and practical consideration of helix type TWT.

(b) A TWT has the following characteristics :

Beam voltage Vo = 2 kV

Beam current I = 4″ mA

(c) Frequency f = -8 GHz Circuit length N = 50 Characteristic impedance Zo =    20 ft Determine :

(i)  The gain parameter C

(ii) The power gain in decibels

OR

4. (a) Write brief note on following :

(i)  Pulsed dual mode TWT

(ii) Coupled cavity TWT

(b) A TWT operates under the following parameters :

Beam current I = 50 mA

Peam voltage Vo = 2.5 kV

(c) Characteristics impedance of helix Zo = 6.75 q Circuit length N = 45 Frequency f = 8 GHz Determine :

(i)  All four propagations constant

(ii) The wave equation for all four modes in exponential form.

UNIT – V

5 (a) Explain the construction and operation of travelling wave magnetron.

(b) A linear magnetron has the following parameters :

Anode Voltage Vo = 20 KV Anode current I = 17 A

Magnetic flux density Bo = 0.01 Wb/m2 Distance between cathode and anode d = 6 cm Calculate :

(i)  The Hull cut off voltage for a fixed Bo

(ii) The Hull cutoff magnetic flux density for a fixed Vo.

OR

5 (a) Explain the working of backward cross-field oscillator.

(b) A CFA operates under the following parameters :

Anode dc voltage Vao = 1.80 kV Anode dc current I = 1.30 A

Electronic efficiency rje = 22% ‘

RF input power Pin = 70 W Calculate :

(i)  The indirect RF power

(ii) The total RF output power

(iii) The power gain in dB