# Multiple choice question for engineering

## Set 1

1. 180^{0} hybrid is a network in which there is a phase shift of 180^{0} between the input signal applied and the output taken.

a) true

b) false

### View Answer

^{0}hybrid is a four port network that has one input port and two output ports. The phase difference between the 2 output ports is 180

^{0}.

2. Port 1 and port 4 of 180^{0} hybrid are called sum and difference ports respectively because of their behavior and action mechanism.

a) true

b) false

### View Answer

^{0}hybrid is used as a combiner, with input signals applied at port 2 and port 3, the sum of the inputs will be formed at port 1, while the difference will be formed at port 4. Hence they are referred to as sum and difference ports.

3. S matrix of 180^{0} hybrid consists of all diagonal elements zero.

a) true

b) false

### View Answer

^{0}hybrid are properly matched, no power is reflected back to the same port. Hence all the diagonal elements of the S matrix, S

_{ii}=0.

4. In 180^{0} hybrid, different power levels can be received at the two output ports of the hybrid.

a) true

b) false

### View Answer

^{0}hybrid is a symmetrical coupler. Hence, the input power applied at the input port can be divided equally and obtained at the 2 output ports. Unequal division of power is not possible in 180

^{0}hybrid.

5. 1800^{0} ring hybrid with system impedance of 50 Ω has to be designed. Then the characteristic impedance of the arms of the 180^{0} hybrid is:

a) 50 Ω

b) 70.70 Ω

c) 100 Ω

d) none of the mentioned

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6. In a waveguide magic-T there is no coupling of power between port 1 and port 4.

a) true

b) false

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_{10}mode incident at port 1. There is odd symmetry about guide 4. Because the field lines of a TE

_{10}mode in guide 4 would have even symmetry, hence there is no coupling between port 1 and port 4.

7. When a TE_{10} wave is incident on port 4 of a magic-T, all the power is coupled to port 1.

a) true

b) false

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^{0}.

8. The tapered coupled line 180^{0} hybrid can provide an arbitrary power division at the 2 output ports of the coupler.

a) true

b) false

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9. The plot of frequency V/s S_{11} parameter for a tapered line coupler has a dip at the frequency at which it is designed.

a) true

b) false

### View Answer

_{11}value is almost zero or negligibly small and hence has a dip at the designed frequency.

10. For a tapered line coupler, the curves of S_{12} and S_{13} are identical and have the same magnitude at all frequencies.

a) true

b) false

### View Answer

_{12}and S

_{13}curves are not identical since the power outputs are not equal.

## Set 2

1. Transistor multipliers are more efficient compared to diode multipliers from all operational aspects.

a) True

b) False

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2. A major characteristic property required by frequency multipliers for frequency multiplication to happen is:

a) High gain

b) High conversion efficiency

c) Non linearity

d) None of the mentioned

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3. If the input power for a frequency doubler is 10.7 mW and the output measured after the frequency doubling process is 21 mW, then the conversion gain for the frequency doubler is:

a) 4.5 dB

b) 8.4 dB

c) 9.8 dB

d) 2.9 dB

### View Answer

_{2}/P

_{avail}. Here P

_{2}is the power measured at the output of the frequency doubler and P

_{avail}is the power input. Substituting the given values in the equation, the conversion gain is 2.9 dB.

4. An ideal _______ produces an output consisting of the sum and difference frequencies of the two input signals.

a) Mixer

b) Amplifier

c) Product modulator

d) Phase modulator

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5. A mixer consists of a non-linear device that produces various harmonics of the input frequency.

a) True

b) False

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6. A mixer can be used for both up conversion and down conversion at the transmitter and receiver respectively.

a) True

b) False

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7. A mixer having high conversion loss is said to have very high:

a) Gain

b) Loss

c) Bandwidth

d) None of the mentioned

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8. The IS-54 digital cellular telephone system uses a receive frequency band of 869-894 MHz, with a first IF frequency range of 87 MHz, one possible range of local oscillator frequency is:

a) 956 to 981 MHz

b) 750 to 784 MHz

c) 869 to 894 MHz

d) None of the mentioned

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9. The curve of FET transconductance v/s gate-to-source voltage is a straight line through origin.

a) True

b) False

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10. RF input matching and RF-LO isolation can be improved through the use of:

a) Balanced mixer

b) Single-ender diode mixer

c) Single ended FET mixer

d) Image reject mixer

### View Answer

## Set 3

1. Lumped elements can be used to make resonators that rare to be operated at microwave frequencies.

a) True

b) False

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2. Short circuited λ/2 transmission line has a quality factor of:

a) β/2α

b) 2β/α

c) β/α

d) Z0/ZL

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3. Quality factor of a coaxial cable transmission line is independent of the medium between the wires of the transmission line.

a) True

b) False

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4. A coaxial cable is air filled with air as dielectric with inner and outer radius equal to 1 mm and 4 mm. If the surface resistivity is 1.84*10-2Ω,then the attenuation due to conductor loss is:

a) 0.011

b) 0.022

c) 0.11

d) 0.22

### View Answer

_{s}(a

^{-1}+b

^{-1})/2ln (b/a). Here ‘a’ and ‘b’ are the inner and outer radii of the coaxial cable. is the intrinsic impedance of the medium, for air is 377Ω. Substituting the given values in the equation, conductor loss is 0.022 Np/m.

5. An air coaxial cable has attenuation of 0.022 and phase constant of 104.7, then the quality factor of a λ/2 short circuited resonator made out of this material is:

a) 2380

b) 1218

c) 1416

d) Insufficient data

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6. The equivalent resistance of a short circuited λ/4 transmission line is independent of the characteristic impedance of the transmission line.

a) True

b) False

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7. A microstrip patch antenna has a width of 5.08mm and surface resistivity of 1.84*10^{-2}. Then the attenuation due to conductor loss is:

a) 0.0724

b) 0.034

c) 0.054

d) None of the mentioned

### View Answer

_{s}/Z

_{0}W. Substituting the given values, attenuation due to conductor loss is 0.0724 Np/m.

8. If the attenuation due to dielectric loss and attenuation due to conductor loss in a microstrip transmission line is 0.024Np/m and 0.0724 Np/m, then the unloaded quality factor if the propagation constant is 151 is:

a) 150

b) 783

c) 587

d) 234

### View Answer

9. The equivalent capacitance of a short circuited λ/4 transmission line is dependent on the characteristic impedance of the transmission line.

a) True

b) False

### View Answer

_{0}Z

_{0}.

10. Inductance of an open circuited λ/2 transmission line is dependent on the characteristic impedance of the transmission line.

a) True

b) False

### View Answer

_{0}

^{2}c, C is the equivalent capacitance of the open circuited line. C has the expression π/4ω

_{0}Z

_{0}.

## Set 4

1. ABCD matrix is used:

a) When there is two or more port networks in the cascade

b) To represent a 2 port network

c) To represent a 2 port network

d) To represent the impedance of a microwave network

### View Answer

2. The voltage equation for a 2 port network that can be represented as a matrix is:

a) V_{1}=AV_{2} + BI_{2}

b) V_{1}=CV_{2} + DI_{2}

c) V_{1}=BV_{2} +AI_{2}

d) V_{1}=DV_{2}+CI_{2}

### View Answer

_{1}is the voltage measured at port 1 and V

_{2}is the voltage measured at port 2 and I

_{2}is the current measured at the second port. A and B are the network constants.

3. ABCD matrix of the cascade connection of 2 networks is equal to:

a) Product of ABCD matrices representing the individual two ports

b) Sum of the ABCD matrices representing the individual two ports

c) Difference of the ABCD matrices representing the individual two ports

d) Sum of transpose of ABCD matrices representing the individual two ports

### View Answer

4. For simple impedance Z, the ABCD parameters are:

a) A=1, Z=B, C=0, D=1

b) A=0, B=1, C=1, D=0

c) A=Z, B=1, C=1, D=0

d) A=1, B=0, C=Z, D=1

### View Answer

5. For a simple admittance Y, the ABCD parameters are:

a) A=1, B=0, C=Y, D=1

b) A=Z, B=1, C=1, D=0

c) A=1, B=0, C=Z, D=1

d) A=1, Y=B, C=0, D=1

### View Answer

6. C parameter for a transmission line of characteristic impedance Zₒ, phase constant β and length ‘l’ is:

a) j Yₒ Sin βl

b) j Zₒ Sin βl

c) j Zₒ tan βl

d) j Yₒ tan βl

### View Answer

7. For a 2 port network if Z₁₁=1.5 and Z₁₂=1.2, A parameter for the same 2 port network is:

a) 1.5

b) 1.25

c) 0.75

d) 1.75

### View Answer

_{11}and the impedance Z

_{12}. Substituting in this equation,’ A’ parameter of the network is 1.25.

8. For a 2 port network, if the admittance parameter Y₁₂=0.4, then B among the ABCD, parameters for the 2 port network is:

a) 2.5

b) 4.5

c) 5

d) 6

### View Answer

_{12}. Taking the reciprocal of the given value, the B parameter of the network is 2.5.

9. If D=1.6 and B=2.8 for a 2 port network, then Y₁₁=?

a) 0.5714

b) 0.987

c) 0.786

d) 1.75

### View Answer

_{11}of the network is defined as the ratio of B parameter to the D parameter of the network. Taking the ratio of the given values, admittance Y

_{11}is 0.5714.

10. If A=2.8 and B=1.4 for a 2 port network then Z₁₁=?

a) 0.5

b) 2

c) 4.2

d) 2.7

### View Answer

_{11}parameter of a two port network is the ratio of the A parameter of the network to the B parameter of the network. Taking the ratio of the given values, Z

_{11}is 2.

## Set 5

1. The power gain G of a two port network is independent of the source impedance of the two port network.

a) True

b) False

### View Answer

2. __________ is defined as the ratio of power available from the two port network to the power available from the source.

a) Transducer power gain

b) Available power gain

c) Power gain

d) None of the mentioned

### View Answer

_{S}, not Z

_{L}.

3. Transducer power gain of a two port network is dependent on :

a) Z_{S} and Z_{L}

b) Z_{S}

c) Z_{L}

d) Independent of both the impedances

### View Answer

_{S}and Z

_{L}.

4. For a two port network the voltage reflection coefficient seen looking towards the load, Г_{S} is:

a) (Z_{S} –Z_{0})/ (Z_{S} –Z_{0})

b) (Z_{S} +Z_{0})/ (Z_{0} – Z_{0})

c) Z_{S} / (Z_{S} –Z_{0})

d) Z_{0}/ (Z_{S} –Z_{0})

### View Answer

_{S}–Z

_{0})/ (Z

_{S}–Z

_{0}). Here Z

_{S}is the input impedance of the transmission line and Z

_{0}is the characteristic impedance of the transmission line.

5. In a two port network, the source impedance was measured to be 25 Ω and the characteristic impedance of the transmission line was measured to be 50 Ω. Then the reflection coefficient at the source end is:

a) -0.33333

b) -0.1111

c) 0.678

d) 0.2345

### View Answer

_{S}–Z

_{0})/ (Z

_{S}–Z

_{0}). Substituting the given values in the above equation, reflection coefficient at the source end is -0.3333.

6. For a unilateral transistor, the S parameter that is zero is:

a) S_{11}

b) S_{12}

c) S_{21}

d) S_{22}

### View Answer

_{12}is sufficiently small and can be ignored. Also for a unilateral transistor the reflection coefficients reduce to Гin=S

_{11}and Гout=S

_{22}.

7. Gain of an amplifier is independent of the operating frequency.

a) True

b) False

### View Answer

^{2}or 6dB per octave.

8. Gain of a conjugate matched FET amplifier is given by the relation:

a) R_{ds} (f_{T})^{2}/ 4R_{i} (f)^{2}

b) 4R_{i} (f)^{2}/R_{ds} (f_{T})^{2}

c) R_{ds}/ R_{i}

d) None of the mentioned

### View Answer

_{ds}(f

_{T})

^{2}/ 4R

_{i}(f)

^{2}. Gain depends on the drain to source resistance, input resistance and also on the frequency of operation of the amplifier.

9. When both input and output of an amplifier are matched to zero reflection (in contrast to conjugate matching), the transducer power gain is:

a) │S_{21}│^{2}

b) │S_{22}│^{2}

c) │S_{12}│^{2}

d) |S_{11}│^{2}

### View Answer

_{L}=0 and Г

_{S}=0. This reduces the complex transducer gain equation to the s parameter of the amplifier S

_{21}. S

_{21}signifies the power at port 2 due to input applied at port 1.

10. If the load impedance of a two port network is 40 Ω and the characteristic impedance is 50 Ω, then the reflection coefficient of the two port network at the load end is:

a) -0.111

b) -0.333

c) -0.987

d) None of the mentioned

### View Answer

_{L}-Z

_{0})/ (Z

_{L}+Z

_{0}). Z

_{L}is the load impedance and Z

_{0}is the characteristic impedance. Substituting, reflection at load end is -0.1111.