## Microwave & Radar Engineering - May 2012

### Electronics & Telecomm. (Semester 7)

TOTAL MARKS: 80

TOTAL TIME: 3 HOURS
(1) Question 1 is compulsory.

(2) Attempt any **three** from the remaining questions.

(3) Assume data if required.

(4) Figures to the right indicate full marks.
**1 (a)** Solution for magnetic vector potential (5 marks)
**1 (b)** Microstrip transmission lines.(5 marks)
**1 (c) ** Power dividers(5 marks)
**1 (d)** Gryotrons.(5 marks)
**2 (a)** Derive plane wave equations and explain the significance(10 marks)
**2 (b)** Derive the expression for reflection and transmission coefficient of finite length (10 marks)
**3 (a)** Derive the electro magnetic equations for TE modes in rectangular waveguide.(10 marks)
**3 (b)** A TE_{11} mode propogating through a circular waveguide. The radius of the guide is 5 cm and the guide contains a air dielectric.

(i) Determine the cut off frequency

(ii) Determine the guid wavelength for an operating frequency of 3 GHz

(iii) Determine the wave impedance in the guide(10 marks)
**4 (a)** Explain various types of microwave solid state devices along with their applications(10 marks)
**4 (b)** A Silicon n-p-n bipolar transistor operates in common-base mode at 300°K and has the following parametes:

Silicon instrinsic density : n_{1}=1.5 ×10^{10} cm^{-3}

Acceptor density in base region : N_{a}=5 ×10^{16} cm^{-3}

Donor density in emitter region : N_{d}=5 × 10^{18} cm^{-3}

Hole Lifetime : ?_{p}=1 ?s

Electron Lifetime : ?_{n} = 1 ?s

Cross Section : A= 10^{-4} cm^{2}

Base width : w=10^{-3} cm

Emitter length : L_{E} = 10^{-2} cm

Determine : -

(i) The mobilities μ_{n} and μ_{p}

(ii) The diffusion coefficients D_{n} and D_{p}

(iii) The emitter efficiency factor y

(iv) The transport factor β

(v) The current gain α(10 marks)
**5** Explain various avalanche transit-time devices with reference to construction, operation and applications.(20 marks)
**6 (a)** A two cavity amplifier Klystron has the following characteristics :

Voltage gain : 15 dB

Input power : 5 mW

Total shunt inpedance of input cavity R_{sh} : 30 k?

Total shunt impedance of output cavity R_{sh} : 40 ?

Load impedance at o/p cavity R_{L} : 40?

Determine :-

(i) The input Voltage (Vms)

(ii) The output Voltage (Vms)

(iii) The power delivered to the load in watts(10 marks)
**6 (b) ** Explain the concept velocity madulation and explain cylindrical magnetron.(10 marks)
**7 (a) ** Microwave filters (5 marks)
**7 (b) ** Travelling wave tube(5 marks)
**7 (c) ** Measurement of impedance .(5 marks)
**7 (d)** Hybrid junctions.(5 marks)