Advanced Microwave Engg - Dec 2013

Electronics & Telecomm. (Semester 8)

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) What are the causes of low frequency noise and high frequency noise associated with the mixer?(5 marks) 1 (b) Find S-parameters of two port series network Z=50Ω and Z_O=100Ω network.(5 marks) 1 (c) What are the characteristics of power amplifiers?(5 marks) 1 (d) Explain 1dB Compression point.(5 marks) 2 (a) A BJT with I_C = 30 mA and V_CE = 10V is operated at a frequency of 1 GHz in a 50Ω system. Its S-parameters are -
S₁₁=0.73∠175°
S₁₂=0
S₂₁=4.45∠65°
S₂₂=0.21∠-80°
Determine whether the transistor is unconditionally stable. If yes, calculate optimum terminations, G_Smax, G_Lmax, G_TUmax. (10 marks) 2 (b) Explain using suitable diagrams two methods of designing broad band amplifier.(10 marks) 3 (a) A BJT has the following s-parameters -
S₁₁=0.65∠-95°
S₁₂=0.035∠40°
S₂₁=5∠115°
S₂₂=0.8∠–35°
Is this transistor unconditionally stable? Draw input and output stability circles.(10 marks) 3 (b) Determine the stability of GaAs FET that has the following S-parameters at 2 GHz in a 50Ω systems both graphically and mathematically -
S₁₁=0.89∠-60°
S₁₂=0.02∠62°
S₂₁=3.1∠123°
S₂₂=0.7∠-27°(10 marks) 4 (a)

Derive the Transducer Power gain as
$G_T = \dfrac {|S_{21}|^2 (1-|\tau_S|^2) (1-|\tau_L|^2)}{|1-\tau_S\tau_{in}|^2 |1 - S_{22}\tau_L|^2}$