1
GATE ECE 1991
Subjective
+10
-0
In the radiation pattern of a 3-element array of isotropic radiators equally spaced at distances of $${\lambda /4}$$ it is required to place a null at an angle of 33.56 degrees off the end-fire direction. Calculate the progressive phase shifts to be applied to the elements. Also calculate the angle at which the main beam is placed for this phase distribution.
2
GATE ECE 1991
+2
-0.6
A silicon sample is uniformly doped with 1016 phosphorous atoms/cm3 and 2 ×1016 boron atoms/cm3. If all the dopants are fully ionized, the material is
A
n-type with carrier concentration of 1016/cm3
B
p-type with carrier concentration of 1016/cm3
C
p-type with carrier concentration of 2 ×1016/cm3
D
n-type with carrier concentration of 2 ×1016/cm3
3
GATE ECE 1991
+2
-0.6
The small signal capacitances of an abrupt P+−N junction is 1 nF at zero bias. If the built-in voltage is 1 volt, the capacitance at a reverse bias voltage of 99 volts is equal to
A
100
B
0.1
C
0.01
D
10
4
GATE ECE 1991
Numerical
+2
-0
Referring to the figure. The switch S is in position 1 initially and steady state conditions exist from time t = 0 to t = t0. At t = t0, the switch is suddenly thrown into position 2. The current I through the 10K resistor as a function of time t, from t = 0 is (in mA) _____________.

(Give the sketch showing the magnitudes of the current at t = 0, t = t0 and t = $$\infty$$ )

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