MU Advanced Microwave Engg - May 2015 Exam Question Paper

MU Electronics and Telecom Engineering (Semester 8)
Advanced Microwave Engg
May 2015

Total marks: --
Total time: --

INSTRUCTIONS
(1) Assume appropriate data and state your reasons
(2) Marks are given to the right of every question
(3) Draw neat diagrams wherever necessary

1 (a) Find S-parameter of two port series-network with Z=100 ω and Zo=50ω.

5 M

1 (b) Derive the expression of overall noise figure in three cascades stages of amplifiers.

5 M

1 (c) Define stability. List the various criteria for stability.

5 M

1 (d) What are the characteristics of power amplifiers?

5 M

2 (a) A BJT with Ic=30mA and V_CE=10V is operated at a frequency of 1.0 Ghz in a 50Ω system.
Its S-parameters are:
S₁₁=0.73 ∠ 175° ;
S₂₂=0.21 ∠ -80°
S₁₂=0.0;
S₂₁=4.45 ∠ 65°
Determine whether the transistor is unconditionally stable. If yes, calculate the optimum terminations.
Gs, max, G_L, max and G_TU, max.

10 M

2 (b) Explain using suitable diagrams two methods of designing broad band amplifier.

10 M

3 (a) Determine stability of GaAs FET that has the following S-parameter at 2GHz in a 50Ω system both graphically and mathematically.

$S= \begin{bmatrix} 0.89 \angle - 60^\circ & 0.02 \angle 62^\circ \\ 3.1 \angle 123 ^\circ & 0.78 \angle -27 ^\circ \end{bmatrix}$

10 M

3 (b) Derive the transducer power gain as:

$G_T = \dfrac {P_L}{P_{avg}} = \dfrac {|s_{21}|^2 \left (1-|\Gamma s|^2 \right ) \left ( 1-|\Gamma L |^2 \right )}{|1-\Gamma s \Gamma in|^2 |1-ss_{22} \Gamma L |^2}$

10 M

4 Design a transistor oscillator at 6GHz using an FET in C^G configuration driving a 50ω load drain side. The S parameters at 50 Ω are

$S= \begin{bmatrix} 0.9 \angle 150^\circ &0.2 \angle - 156\circ \\2.6 \angle 50 ^\circ & 0.5 \angle 105^\circ \ \ \ \ \end{bmatrix}$ Calculate and plot output stability circle for

$|\Gamma in | >> 1, \ choose \ \Gamma T \ so \ that \ |\Gamma in | >> 1$ Design load and terminating networks.

20 M

5 (a) Discuss various mixer topologies. Compare performance of various topologies.

10 M

5 (b) Compare microwave amplifier with microwave oscillators.

10 M

6 (a) A GaAs FET is biased for minimum noise figure and has following S parameter and noise parameter at 4 Ghz (z_o=50Ω)

$S= \begin{bmatrix} 0.6 \angle -60 ^\circ & 0.05 \angle 26^\circ \ \ \\ 1.9 \angle 81 ^\circ \ \ \ \ & 0.5 \angle - 60^\circ \end{bmatrix}$ Fmin=1.6 dB, Γopt=0.62 ∠ 100°, R_N=20Ω.
Design an amplifier with 2 dB noise figure and maximum gain compatible with this noise figure. Assume device is unilateral.

15 M

6 (b) Prove that scattering matrix is symmetrical and reciprocal.

5 M

7 (a) Noise figure test equipment.

5 M

7 (b) 1 dB compression point.

5 M

7 (c) Amplifier linearisation methods.

5 M

7 (d) Single ended diode mixer.

5 M

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