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GATE : Transmission lines questions

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1) Two very long loss-less cables of characteristic impedances of 50 \Omega and 100 \Omega respectively are to be joined for reflection less transmission. If the quarter wave transformer is used for matching, what should be the value of its impedance(in ohms)?

a) 70.7
b) 35.7
c) 50
d) 2

2) A transmission line with a characteristic impedance of 100 \Omega is used to match a 50 \Omega section to a 200 \Omega section. If the matching is to be done both at 429MHz and 1GHz, the length of the transmission line can be approximately

a) 82.5cm
b) 1.05m
c) 1.58m
d) 1.75m

3) Impedance of a transmission line repeats itself every

a) \lambda/4
b) \lambda/2
c) \lambda
d) 2\lambda

4) If Z_{open} is the impedance of a open circuited transmission line and Z_{short} is the impedance of a short circuited transmission line whose characteristic impedance is Z_o. Then which of the following relationship is true?

a) Z_o =\frac{Z_{open}}{Z_{short}}
b) Z_o =Z_{open} * Z_{short}
c) Z_o =\sqrt{\frac{Z_{open}}{Z_{short}}}
d) Z_o =\sqrt {Z_{open}*Z_{short}}

5) A transmission line of characteristic impedance 50 \Omega is terminated by a 50 \Omega load. When excited by a sinusoidal voltage source at 10 GHz, the phase difference between two points spaced 2 mm
apart on the line is found to be π/4 radians. The phase velocity of the wave along the line is

a) 0.8* 10^8 m/s
b) 1.2*10^8 m/s
c) 1.6*10^8 m/s
d) 3*10^8 m/s

A transmission line of characteristic impedance 50 \Omega is terminated in a load impedance . The
VSWR of the line is measured as 5 and the first of the voltage maxima in the line is observed at a
distance of \lambda/4 from the load. The value of Z_L is
(A) 10 \Omega
(B) 250 \Omega
(C) (19.23 + j46.15) \Omega
(D) (19.23 – j46.15) \Omega

….

1-a, 2-c , 3-b, 4-d

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