**RTU Previous Question Papers BE EC 5th Sem **

**Microwave Engineering December-2011**

**UNIT – I**

1. (a) Derive the TE_{mn} field equations in a rectangular waveguides.

(b) An air filled waveguide with a cross section 2×1 cm transports energy in the TE_{10} 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 TM_{np} 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 R_{sh} = 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 V_{o} = 300 V Beam current I_{o} = 20 mA Signal Voltage V_{1} = 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 V_{o} = 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 V_{o} = 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 V_{o} = 20 KV Anode current I = 17 A

Magnetic flux density B_{o} = 0.01 Wb/m^{2} 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 V_{o}.

**OR**

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

(b) A CFA operates under the following parameters :

Anode dc voltage V_{ao} = 1.80 kV Anode dc current I = 1.30 A

Electronic efficiency rj_{e} = 22% ‘

RF input power P_{in} = 70 W Calculate :

(i) The indirect RF power

(ii) The total RF output power

(iii) The power gain in dB