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SEMESTER I - FINAL EXAMINATION - 2021/2022

EEEN3019J - RF Electronics

Question 1 (Total Marks: 20)

(i) Use the Smith chart to find the following quantities for the transmission line circuit shown in the figure below:         [60%]

(a) The SWR on the line.

(b) The reflection coefficient at the load.

(c) The load admittance.

(d) The input impedance of the line.

(e) The distance from the load to the first voltage minimum.

(f) The distance from the load to the first voltage maximum.

(ii) A three-port network has the scattering matrix shown as follows (Z0 = 50 Ω).     [40%]

(a) Is this network lossless? (Explain your answer)

(b) Is this network reciprocal? (Explain your answer)

(c) What is the return loss seen at port 1 if port 2 and 3 are terminated with matched loads?

Question 2 (Total Marks: 20)

(i) Find the scattering parameters, S12 and S13, of the following lossless 90◦ hybrid coupler network. (Note: you can normalize all impedances to the characteristic impedance Z0 during the calculation.)     [75%]

(ii) What is the coupling factor of this 90◦ hybrid coupler? What is the reflection coefficient seen at port 1 if port 3 is terminated with a short circuit and all other ports are terminated with matched load?        [25%]

Question 3 (Total Marks: 20)

Design a passive fourth-order Butterworth low-pass filter, and implement such design using only shunt stubs and microstrip lines with 50 Ω characteristic impedance at the input and output. The cutoff frequency is 8 GHz.