Advanced Microwave Engg - May 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) Explain Large Signal characterization with reference to load pull contours. How is it measured? (5 marks) 1 (b) What are the causes of low frequency noise and high frequency noise associated with the mixer? (5 marks) 1 (c) Define and explain with neat diagram noise correlation matrix for general noisy two port network. (5 marks) 1 (d) What is unilateral figure of merit of an amplifier?(5 marks) 2 (a) If the transistor has following S-parameters at 5Ghz with 50Ω impedance.
S₁₁=0.6∠–175°
S₁₂=0.02∠20°
S₂₁=2.2∠35°
S₂₂=0.6∠-95°
Determine the stability criteria and plot the stability circles. (10 marks) 2 (b) Derive the parameters of an Amplifier:
(i) Power gain (G)
(ii) Available gain (GA)
(iii) Transducer gain (GT)(10 marks) 3 (a) Explain using suitable diagrams two methods of designing broadband amplifier.(10 marks) 3 (b) 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) 4 (a) A certain GaAs MESFET has following noise figure parameters measured at V_ds = 50, I_ds = 20 mA with 50Ω resistor once for frequency of 9 GHz,
F_min = 4dB, Γ_opt=0.55∠175, R₀= 4Ω.
Plot noise figure circles for given values of f₁ at 2, 2.5, 3.5, and 4.5 dB. (15 marks) 4 (b) Define stability. List the various criteria for stability.(5 marks) 5 (a) If a one port microwave diode has Γ_in=1.5∠60° with respect to Z₀=50Ω. Design an oscillator for desired frequency of 10GHz.(12 marks) 5 (b) For a two port oscillator at steady state oscillations prove that if τ_Lτ_in=1 then τ_inτ_out=1(8 marks) 6 A certain MESFET is biased for large signal class A operation with following small signal S-parameters at 5GHz:
S₁₁=0.55∠-150°
S₁₂=0.04∠20°
S₂₁=3.5∠170°
S₂₂=0.45∠-30°
The large signal forward transmission coefficient S₂₁ is measured to be S₂₁=2.1∠180°. Design a large-signal class A amplifier with maximum transducer gain in a 50Ω system. Assume (±)0.5dB error in gain. What is the high-power amplifier gain? (20 marks) 7 (a) Write a note on optimal loading used in 1+PA design.(10 marks) 7 (b) A wideband amplifier (2-4 GHz) has gain of 10dB, an O/P power gain of 10dBm and a noise figure of 4dB at room temperature. Find the output noise power in dBm.(10 marks)