## Microwaves & RADAR - Jun 2015

### Electronics & Communication (Semester 5)

TOTAL MARKS: 100

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

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

(3) Assume data wherever required.

(4) Figures to the right indicate full marks.
**1 (a)** Derive:

1) Voltage and current equations on a transmission line.

2) The Characteristic impedance of the line.

3) Propagation constant.

4) Phase velocity.

5) The relative phase velocity factor.(12 marks)
**1 (b)** What is impedance matching? Explain single stub matching and double stub matching.(8 marks)
**2 (a)** Derive TE_{mn} field equation in rectangular waveguide and define cut off wave number, cut-off frequency, propagation constant, phase velocity, character wave impedance and wave length in the guide.(10 marks)
**2 (b)** Explain why TEM mode is not possible in waveguides.(2 marks)
**2 (c)** Explain faraday rotation and discuss microwave circulator.(8 marks)
**3 (a)** Discuss the criterion for classifying the modes of operation for Gunn effect diodes. For a transit time domain made; the domain velocity is equal to the current drift velocity is 10^{7} cm/s. Determine the drift length of the diode of a frequency of 8GHz(7 marks)
**3 (b)** Explain how carrier current I_{0}(t) and external current I_{e}(t) are generated when a read diode is mounted in a microwave resonant circuit, with the aid of diagrams for structure of read diode, field distribution, applied ac voltage and I_{0} (t) and I_{e}(t).(7 marks)
**3 (c)** Write equivalent circuit for a parametric amplifier. AN up-converter parametric amplifier has the following parameters:

i) Figure of merit; γQ=8

ii) Ratio of output frequency over signal frequency f_{0}/f_{δ}=δ

iii) Factor of merit figure;γ=0.2

iv) Diode temperature T_{d}=300°t.

Calculate : i) The power gain in dB; ii) The noise figure in dB; iii) Bandwidth.(6 marks)
**4 (a)** What is a reciprocal network? For a reciprocal microwave N-port network prove that the admittance and impedance matrices are symmetrical.(7 marks)
**4 (b)** State and prove the following properties of S-parameters

i) Symmetry property for a reciprocal network.

ii) Unitary property for a lossless junction.(8 marks)
**4 (c)** The impedance matric of a passive network is given by $$Z=\begin{bmatrix}
4 &3 \\1
&2
\end{bmatrix}$$, find scattering matrix.(5 marks)
**5 (a)** Why are co-axial connectors and adaptors used? List six types of co-axial connectors with their frequency ranges.(5 marks)
**5 (b)** What are waveguide tees? Explain with the aid of neat diagram, E-plane tree and H-plane tree.(9 marks)
**5 (c)** List four applications of Magic T. Explain Magic-Tee as a microwave mixer.(6 marks)
**6 (a)** Show that for a micro trip line, the quantity factors is Q_{c}$$Q_{c}=0.636\sqrt[h]{\sigma f_{CH_{2}}}$$.(7 marks)
**6 (b)** A gold parallel strip line has the following parameters

Relative dielectric constant of polyethylene ε_{rd}2.25.

Strip width; W=25mm

Separation width; d=5mm

Calculate:

i) Characteristic impedance of the strip line

ii) Strip-line capacitance

iii) Strip-line inductance

iv) Phase velocity.(8 marks)
**6 (c)** Write a note on coplanar stripline.(5 marks)
**7 (a)** What is radar? With a neat block diagram explain the operation of radar.(8 marks)
**7 (b)** Explain the various forms of radar equation.(6 marks)
**7 (c)** Discuss the application the radar.(6 marks)
**8 (a)** With a neat block diagram, explain CW Doppler radar.(8 marks)
**8 (b)** Explain a simple MTI delay line canceller.(8 marks)
**8 (c)** Discuss the difference between MTI and Doppler radar.(4 marks)