Advanced Microwave Engg : Question Paper May 2012 - Electronics & Telecomm. (Semester 8)

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Advanced Microwave Engg - May 2012

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 the properties of S-parameter.(5 marks) 1 (b) Explain Stability circles and its importance in amplifier design.(5 marks) 1 (c) Explain how noise parameters at microwave frequencies can be determined.(5 marks) 1 (d) Explain 1dB compression point.(5 marks) 2 (a) Find S parameters of 3 dB attenuator shown in Figure -
(10 marks) 2 (b) Derive the Transducer Power gain as
(10 marks) 3 (a) Define the figure of merit in unilateral microwave amplifiers. If unilateral gain of microwave amplifier is

show that

where G_T is the transducer gain and G_TU is the transducer gain in unilateral case.(10 marks) 3 (b) A BJT has the following S-parameters as a function of three frequencies. Determine in which of these cases, device is unconditionally stable and which has the greatest stability.

Frequency (MHz)	S₁₁	S₁₂	S₂₁	S₂₂
500	0.7∠-57⁰	0.04∠47⁰	10.5∠136⁰	0.79∠-33⁰
750	0.56∠-78⁰	0.05∠33⁰	8.6∠122⁰	0.66∠-42⁰
1000	0.46∠-97⁰	0.06∠22⁰	7.1∠112⁰	0.57∠-48⁰

(10 marks) 4 Design a transistor oscillator at 4 GHz using FET in a common gate configuration. An inductor of value 5nH is placed in series with the gate to increase stability. Choose a Terminating network to match a 50Ω load and an appropriate tuning network. The S-parameters of the transistor in a common gate configuration are:
S₁₁=2.18∠-35°
S₁₂=1.26∠18°
S₂₁=2.75∠96°
S₂₂=0.52∠155°(20 marks) 5 (a) For a two port oscillator at steady state oscillations prove that if, τ_L τ_in=1 then τ_Tτ_OUT=1(10 marks) 5 (b) Discuss microwave amplifiers versus microwave oscillators.(10 marks) 6 GaAs FET has the following scattering and noise parameters at 4 GHz measured with 50Ω systems:
S₁₁=0.6∠-60°
S₁₂=0.05∠26°
S₂₁=1.9∠81°
S₂₂=0.5∠-60°
and F_min=1.6dB, R_N=20Ω and Γ_opt = 0.62°100°
Assuming the FET to be unilateral, design an amplifier using open circuited shunt stubs and transmission line lengths for a maximum possible gain and a noise figure no more than 2.0dB. Estimate the error introduced in G_T due to this assumption.(20 marks)

Write shorts notes any two of the following:-

7 (a) Balanced FET mixer.(10 marks) 7 (b) Power Distributed Amplifiers.(10 marks) 7 (c) Microwave Resonators.(10 marks)

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