Category: Microwave Engineering Objective Questions

250+ TOP MCQs on Coupled Line Directional Couplers and Answers

Microwave Engineering Multiple Choice Questions on “Coupled Line Directional Couplers “.

1. In coupled line directional couplers, power from one line to another is transmitted through a microstrip line running between them.
A. true
B. false
Answer: B
Clarification: In coupled line couplers, the power is transmitted between the 2 lines by coupling from one line to another due to the interaction of the electromagnetic fields. Hence, wireless power transmission occurs here.

2. The number of conductors used in the construction of coupled line couplers is fixed.
A. true
B. false
Answer: B
Clarification: Since the method of power transmission in coupled line couplers is wireless power transmission by the interaction of electromagnetic fields, any number of wires can be used. But as a standard, 3 lines are used in the construction of these couplers.

3. The mode of propagation of propagation supported by coupled line couplers is:
A. TM mode
B. TE mode
C. TEM mode
D. quasi TEM mode
Answer: C
Clarification: Coupled transmission lines are assumed to operate in TEM mode of propagation. TEM mode of propagation is mostly valid for coaxial and stripline structures while microstrip lines support quasi TEM mode of propagation.

4. Coupled line couplers are:
A. symmetric couplers
B. asymmetric couplers
C. in phase couplers
D. type of hybrid coupler
Answer: a
Clarification: Coupled line couplers are symmetric three line couplers. Symmetric here means that the lines are of equal width and thickness. Their position with respect to ground is identical.

5. For coupled line coupler, if the voltage coupling factor is 0.1 and the characteristic impedance of the microstrip line is 50 Ω, even mode characteristic impedance is:
A. 50.23 Ω
B. 55.28 Ω
C. 100 Ω
D. 80.8 Ω
Answer: B
Clarification: Even mode characteristic impedance of coupled line coupler is Z0√ (1+C. /√ (1-C..here C is the voltage coupling coefficient. Substituting the given values, even mode characteristic impedance is 55.28 Ω.

6. If the coupling coefficient of a coupled line coupler is 0.1 and the characteristic impedance of the material is 50 Ω, then the odd mode characteristic impedance is:
A. 45.23 Ω
B. 50 Ω
C. 38 Ω
D. none of the mentioned
Answer: A
Clarification: Odd mode characteristic impedance of a coupled line coupler is Z0√ (1-C./ √ (1+C.. C is the voltage coupling co-efficient. Substituting the given values, odd mode characteristic impedance is 45.23.

7. Dielectric and conductor loss have no effect on the directivity of the coupled line coupler.
A. true
B. false
Answer: B
Clarification: Both dielectric loss and conductor loss reduce the directivity of the coupled line coupler. In the absence of loss under matched conditions, the directivity of a coupler could be up to 70 dB.

8. Multisection couplers have a very narrow operational bandwidth which is a major disadvantage.
A. true
B. false
Answer: B
Clarification: Multisection couplers have very high operational bandwidth. This high bandwidth can be achieved only when the coupling levels are low. In order to achieve these low coupling levels, stripline are used in their construction.

9. Three section binomial couplers have very low directivity as compared to other coupler designs.
A. true
B. false
Answer: B
Clarification: Three section binomial couplers have very low conductor and dielectric losses. This low loss can be achieved by efficient design. Since the losses are low for a binomial coupler, they have directivity greater than 100 dB.

10. The capacitance per unit length of broadside parallel lines with width W and separation d is:
A. ∈W/d
B. ∈d/W
C. dW/∈
D. none of the mentioned
Answer: A
Clarification: The capacitance of the line used in the construction of a coupled line coupler is directly proportional to the width of the line. As the width increase, capacitance increases. Capacitance varies inversely with distance d. as the separation increases, capacitance decreases.


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250+ TOP MCQs on Heterojunction BJT – 1 and Answers

Microwave Engineering Multiple Choice Questions on “Heterojunction BJT – 1”.

1. BJTs are bipolar junction transistors. The name bipolar is given because:
A. they are made of n type and p type semiconductor
B. they have holes as charge carriers
C. they have electrons as charge carriers
D. none of the mentioned
Answer: D
Clarification: In bipolar junction transistors, both electrons and holes are charge carriers and both of them together constitute current flow in transistors. Since both carriers result in current, they are called bipolar devices.

2. BJTs are suitable for RF applications because:
A. good performance in terms of frequency
B. power capacity
C. noise characteristics
D. all of the mentioned
Answer: D
Clarification: BJTs designed to operate at certain frequency can be operated over a wide range of frequencies hence offering higher bandwidth. Also they have high power handling capacity and very good noise characteristics.

3. Bipolar junction transistors have _______ 1/f characteristics hence making them suitable for oscillators.
A. high
B. low
C. constant
D. decreasing exponential
Answer: B
Clarification: Bipolar junction transistors have very low 1/f noise. 1/f noise is nothing but thermal noise. Hence BJTs are not very temperature and can be used at high temperature applications as well.

4. Silicon junction transistors are used as amplifiers at frequency range of about:
A. 5-10 MHz
B. 2-10 GHz
C. 40-50 MHz
D. 12-45 GHz
Answer: B
Clarification: Silicon junction transistors have unconditional stability as a two port device at a wide range of frequencies. They are more suitable as amplifiers in the frequency range of about 2-10 GHz. Junction transistors when used as oscillators are used in the frequency range of about 20 GHz.

5. At frequency range of about 2-4 GHz, BJTs are preferred over FETs.
A. true
B. false
Answer: A
Clarification: At about 2-4 GHz frequency range, BJTs have higher gain as compared to FETs, power capacity is high and biasing can be done using a single power supply. Because of these advantages, BJTs are preferred over FETs.

6. One major disadvantage of BJTs over FETs is that:
A. they have low gain
B. they do not have a good noise figure
C. low bandwidth
D. none of the mentioned
Answer: B
Clarification: Bipolar junction transistors are subject to shot noise as well as thermal noise effects, so their noise figure is not as good as that of FET. Noise figure can pose serious problems at high operating frequencies.

7. Bipolar junction transistor is a ________ driven device.
A. current
B. voltage
C. power
D. none of the mentioned
Answer: A
Clarification: Bipolar junction transistor is a current driven device where the collector output current directly depends on the input base current. Base current modulates the collector current of the device.

8. The upper frequency limit of BJT depends on the:
A. collector length in the transistor
B. base length
C. emitter length
D. driving voltage
Answer: B
Clarification: The upper operating frequency limit of a BJT depends on the base length of the transistor. Typical base length of a transistor is in the range of a 0.1 µm. the operating frequency is a few GHz for this base length.

9. In the hybrid –π model of a BJT, the capacitance Cc between the base and collector in the hybrid –π model is ignored.
A. true
B. false
Answer: A
Clarification: The capacitance Cc in the hybrid –π model is small and can be neglected. This has the effect of making the S12 parameter of the BJT equal to zero, implying that the power flows only in one direction through the device.

10. with the increase in the operating frequency of a BJT, the S22 parameter of the transistor:
A. increases
B. decreases
C. remains constant
D. none of the mentioned
Answer: B
Clarification: With increase in the operating frequency of the transistor, S22 parameter of the transistor decreases. S22 parameter signifies the voltage reflected back to port 2. S22 parameter has a value of about 0.93 at 0.1 GHz frequency and 0.33 at 4 GHz frequency.


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250+ TOP MCQs on Oscillator Phase Noise and Answers

Microwave Engineering online quiz on “Oscillator Phase Noise”.

1. A practical oscillator has a frequency spectrum consisting of a single delta function at its operating frequency.
A. True
B. False
Answer: B
Clarification: An ideal oscillator has a frequency spectrum consisting of a single delta function at its operating frequency, but a practical oscillator has a spectrum in the form of a Gaussian curve consisting of some noise component.

2. ____________ due to random fluctuations caused by thermal and other noise sources appear as broad continuous distribution localized about the output signal.
A. Phase noise
B. White noise
C. Thermal noise
D. Shot noise
Answer: A
Clarification: Phase noise is defined as the ratio of power in one phase modulation sideband to the total signal power per unit bandwidth at a particular offset fm. phase noise due to random fluctuations caused by thermal and other noise sources appear as broad continuous distribution localized about the output signal.

3. The phase variation for an oscillator or synthesizer is given by:
A. ∆f*sin ωmt/ fm
B. ∆f / fm
C. Sin ωmt/ fm
D. None of the mentioned
Answer: A
Clarification: The phase variation for an oscillator or synthesizer is given by ∆f*sin ωmt/ fm. here, fm is the modulating signals frequency, ∆f is the change in the frequency.

4. The expression for phase noise in an oscillator is given by:
A. θrms2
B. θrms2/√2
C. θrms2/2
D. θrms2/ 3
Answer: C
Clarification: The expression for phase noise in an oscillator is given by θrms2/2. θrms is the rms value of the phase deviation. Phase noise is directly proportional to the square of the RMS value of the phase deviation. Greater the deviation, higher is the phase noise.

5. Phase noise at the output of an oscillator is given by:
A. kBFGT0
B. kT0F/Pc
C. kT0F/Pc
D. None of the mentioned
Answer: B
Clarification: Phase noise at the output of an oscillator is given by kT0F/Pc. here k is the Boltzmann’s constant. B is the operating bandwidth of the system, here the equation is considered for a bandwidth of 1 Hz as per the definition of phase noise. F is the figure of merit of system.

6. Noise power versus frequency for an amplifier has spikes at the operating frequency without the application of an input voltage.
A. True
B. False
Answer: B
Clarification: Noise power versus frequency for an amplifier has spikes at the operating frequency with the application of an input voltage. When an input voltage is applied to the amplifier, noise component also is added. Along with the signal, noise is also amplified and peaks at the operating frequency.

7. An idealized power spectral density of amplifier has a straight line parallel to X axis and the noise is constant at all frequencies.
A. True
B. False
Answer: B
Clarification: The curve has a negative slope up to a frequency called fα due to the thermal noise also called as 1/f noise. Above this frequency, the graph is a straight line parallel to X axis.

8. At higher frequencies of operation of an oscillator, induced noise is mostly:
A. Thermal noise
B. White noise
C. Shot noise
D. Flicker noise
Answer: A
Clarification: At higher frequencies of operation of an oscillator, induced noise is mostly thermal, and constant with frequency. This noise is also proportional to the noise figure of the amplifier.

9. A GSM cellular telephone standard requires a minimum of 9 dB rejection of interfering signal levels of -23 dBm at 3 MHz from the carrier, -33 dBm at 1.6 MHz from the carrier, and -43 dBm at 0.6 MHz from the carrier, for a carrier level of -99 dBm. Determine the required local oscillator phase noise at 3 MHz carrier frequency offset.
A. -138 dBc/Hz
B. -128 dBc/Hz
C. -118 dBc/Hz
D. None of the mentioned
Answer: A
Clarification: Phase noise is given by the expression C (dBm)-S (dB. –I (dBm)-10log (B.. Substituting the given values in the above expression, the oscillator phase noise is -138.

10. The most affected parameter of a receiver by the phase noise is signal to noise ratio.
A. True
B. False
Answer: B
Clarification: The effect of phase noise in a receiver is to degrade both the signal to noise ratio and the selectivity. Of these, the most severely affected is the selectivity. Phase noise degrades the receiver selectivity by causing down conversion of signals located near by the desired signal frequency.


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250+ TOP MCQs on Lossy Transmission Lines and Answers

Microwave Engineering Multiple Choice Questions on “Lossy Transmission Lines”.

1. For a low loss line when both conductor and di-electric loss is small, the assumption that could be made is:
A. R < < ωL and G < < ωC
B. R > > ωL and G > >ωC
C. R < <ωC and G < < ωL
D. R > >ωC and G > >ωL
Answer: A
Clarification: For a low loss line, the real part of impedance and admittance, that is resistance and conductance must be very small compared to the complex part of admittance and impedance for maximum power transfer. Hence R < <ωL and G < < ωC.

2. Expression for α(attenuation constant) in terms of R , G, L and C of a transmission line is:
A. (R√(C/L)+G√(L/C.)0.5
B. (R√(C/L)+G√(L/C.)
C. (R√(L/C.+G√(C/L))
D. (R√(L/C.+G√(C/L))0.5
Answer: A
Clarification: For a low loss line, the real part of impedance and admittance, that is resistance and conductance must be very small compared to the complex part of admittance and impedance for maximum power transfer. Hence R < <ωL and G < < ωC, with this assumption, modifying the expression for propagation constant, the simplified expression for attenuation constant α is (R√(C/L)+G√(L/C.)0.5.

3. Expression for characteristic impedance Zₒ of a transmission line in terms of L and C the transmission line is:
A. √(C/L)
B. √(CL)
C. √(L/C.
D. 1/√(LC.
Answer: C
Clarification: For a low loss line, the real part of impedance and admittance, that is resistance and conductance must be very small compared to the complex part of admittance and impedance for maximum power transfer. HenceR < <ωL and G < < ωC, with this assumption, modifying the expression for characteristic impedance√(((R+jωL))/√(G+jωC.), the ratio reduces to √ (L/C..

4. If the inductance and capacitance of a loss line transmission line are 45 mH/m and10 µF/m, the characteristic impedance of the transmission line is:
A. 50Ω
B. 67.08Ω
C. 100Ω
D. none of the mentioned
Answer: B
Clarification: The expression for characteristic impedance of a transmission line in terms of inductance and capacitance of a transmission line is√((L)/C.. Substituting the given values in this equation, the characteristic impedance of the transmission line is 67.08Ω.

5. If the characteristic impedance of a transmission line is 50 Ω, and the inductance of the transmission line being 25 mH/m, the capacitance of the lossy transmission line is:
A. 1µF
B. 10 µF
C. 0.1 µF
D. 50 µF
Answer: B
Clarification: The expression for characteristic impedance of a transmission line in terms of inductance and capacitance of a transmission line is√((L)/C.. Substituting the given values in this equation, and solving for C, value of C is 10µF.

6. If R = 1.5Ω/m, G = 0.2 mseimens/m, L = 2.5 nH/m, C = 0.1 pF/m for a low loss transmission line, then the attenuation constant of the transmission line is:
A. 0.0.158
B. 0.0523
C. 0.0216
D. 0.0745
Answer: A
Clarification: The expression for attenuation constant of a low loss transmission line is (R√(C/L)+G√(L/C.)0.5. Substituting the given values in the above expression, the value of attenuation constant is 0.0158.

7. A lossy line that has a linear phase factor as a function of frequency is called:
A. distortion less line
B. terminated lossy line
C. loss less line
D. lossy line
Answer: A
Clarification: A distortion less transmission line is a type of a lossy transmission line that has a linear phase factor as a function of frequency. That is, as the frequency of operation changes, the phase variation is linearly dependent.

8. The condition for a distortion less line is:
A. R/L=G/C
B. R/C=G/L
C. R=G
D. C=L
Answer: A
Clarification: The special case of a lossy transmission line that has a linear phase factor as a function of frequency is called distortion less line. The relation between the transmission line constants for such a distortion less line R/L=G/C.

9. For a distortion less line, R= 0.8Ω/m, G= 0.8 msiemens/m, L= 0.01µH/m then C is:
A. 10 pF
B. 1pF
C. 1nF
D. 10nF
Answer: A
Clarification: The special case of a lossy transmission line that has a linear phase factor as a function of frequency is called distortion less line. The relation between the transmission line constants for such a distortion less line R/L=G/C. substituting the given values in the equation, we get 10pF.

10. For a lossy transmission line, γ=0.02+j0.15 and is 20m long. The line is terminated with an impedance of a 400Ω. Then the input impedance of the transmission line given that the characteristic impedance of the transmission line is 156.13+j11.38Ω is:
A. 100+j50 Ω
B. 228+j36.8 Ω
C. 50+36.8j Ω
D. none of the mentioned
Answer: B
Clarification: The relation between source impedance, propagation constant and characteristic impedance is given by ZS= Z0 (ZLcosh(γl) + Z0 sinh(γl))/( Z0cosh(γl) + ZL sinh(γl)). Substituting the given values in the above equation, input impedance of the transmission line is 228+j36.8 Ω.


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250+ TOP MCQs on Quarter Wave Transformer(Smith Chart) and Answers

Microwave Engineering Multiple Choice Questions on “Quarter Wave Transformer(Smith Chart)”.

1. A quarter wave transformer is useful for matching any load impedance to a transmission line.
A. True
B. False
Answer: B
Clarification: Quarter wave transformers are a simple circuit that can be used to match real load impedance to a transmission line. Quarter wave transformers cannot be used to match complex load impedances to a transmission line.

2. Major advantage of a quarter wave transformer is:
A. It gives proper matching
B. It gives high gain
C. Broader bandwidth
D. None of the mentioned
Answer: C
Clarification: Quarter-wave transformers can be extended to multi section designs in a methodical manner to provide a broader bandwidth.

3. If a narrow band impedance match is required, then more multi section transformers must be used.
A. True
B. False
Answer: B
Clarification: If a narrow band impedance match is required, then a single section of quarter wave transformer is used. When a wideband impedance match is required, then multi-section quarter wave transformers must be used for impedance matching.

4. The major drawback of the quarter wave transformer that it cannot match complex load to a transmission line cannot be overcome.
A. True
B. False
Answer: B
Clarification: The major drawback of the quarter wave transformer that it cannot match complex load to a transmission line can be overcome by transforming complex load impedance to real load impedance.

5. Complex load impedance can be converted to real load impedance by:
A. Scaling down the load impedance
B. By introducing an approximate length of transmission line between load and quarter wave transformer
C. Changing the operating wavelength
D. None of the mentioned
Answer: B
Clarification: By introduction of a transmission line of suitable length between the load and the quarter wave transformer, the reactive component of the load that is the complex value can be nullified thus leaving behind only real load impedance to be matched.

6. Converting complex load into real load for impedance matching has no effect on the bandwidth of the match.
A. True
B. False
Answer: B
Clarification: Adding a length of line to the transmission line between the load and quarter wave transformer alters the frequency dependence of the load thus altering the bandwidth of the match.

7. If a single section quarter wave transformer is used for impedance matching at some frequency, then the length of the matching line is:
A. Is different at different frequencies
B. Is a constant
C. Is λ/2 for other frequencies
D. None of the mentioned
Answer: A
Clarification: The length of the matching section is λ/4 for the frequency at which it is matched. For other frequencies, the electrical length varies. For multi section transformers, a wide bandwidth can be achieved.

8. Quarter wave transformers cannot be used for non-TEM lines for impedance matching.
A. True
B. False
Answer: A
Clarification: For non-TEM lines, propagation constant is not a linear function of frequency and the wave impedance is frequency dependent. These factors complicate the behavior of the quarter wave transformer for non-TEM lines.

9. The reactances associated with the transmission line due to discontinuities:
A. Can be ignored
B. Have to matched
C Discontinuities do not exist
D. None of the mentioned
Answer: B
Clarification: Reactance due to discontinuities in the transmission line contribute to the impedance, they can be matched by altering the length of the matching section.

10. If a load of 10Ω has to be matched to a transmission line of characteristic impedance of 50Ω, then the characteristic impedance of the matching section of the transmission line is:
A. 50Ω
B. 10Ω
C. 22.36Ω
D. 100Ω
Answer: C
Clarification: Characteristic impedance of the matching section of a transmission line is given by Z1=√Zₒ.ZL. Substituting the given impedance values, the characteristic impedance of the matching section is 22.36 Ω.


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250+ TOP MCQs on Lange Coupler and Answers

Microwave Engineering Multiple Choice Questions on “Lange Coupler”.

1. The major disadvantage of coupled line coupler is:
A. complex construction
B. low power gain
C. higher loss
D. none of the mentioned
Answer: D
Clarification: Coupling in a coupled line coupler is too loose to achieve coupling factors of 3 or 6 dB. Since higher efficiency is not achievable, this a major disadvantage. One method of improving coupling is designing in such a way that the fringing field contributes to coupling.

2. Lange couplers consist of four parallel lines that are ______ coupled.
A. tightly
B. loosely
C. partially
D. none of the mentioned
Answer: A
Clarification: Lange couplers consist of four parallel lines. These parallel lines are tightly coupled to achieve 3 dB coupling ratio. Achieving 3dB coupling implies that 70% of the applied power is coupled.

3. Lange coupler is a type of Quadrature hybrid.
A. true
B. false
Answer: A
Clarification: Lange coupler ha two output ports. The output voltage measured at these ports is 900 out of phase with one another. Hence, they are called a type of Quadrature hybrid.

4. A major disadvantage of Lange coupler is:
A. high power loss
B. complex construction
C. low gain
D. none of the mentioned
Answer: B
Clarification: The main disadvantage of Lange coupler is probably practical, as the lines are very narrow and close together, and the required bonding wires across the lines increases complexity.

5. For even mode excitation of a Lange coupler, all the four lines of the Lange coupler are at:
A. equal potential
B. zero potential
C. unequal potential
D. negative potential
Answer: A
Clarification: during the analysis of Lange coupler, when they are excited in the even mode, all the four conductors of the coupler are at equal potential. Hence the capacitance Cm has no effect and need not be considered for further analysis.

6. Even mode characteristic impedance of a Lange coupler:
A. (Vp.Cep)-1
B. Vp.Cep
C. (Vp.Lep)-1
D. Vp.Lep
Answer: A
Clarification: The even mode characteristic impedance of a Lange coupler is given by (Vp.Cep)-1. Here Vpp is the phase velocity and Cep is the capacitance of any of the four conductors of the Lange coupler measured during even mode of analysis.

7. In a Lange coupler having 4 lines, the adjacent lines are connected so as to act as two conductors in parallel.
A. true
B. false
Answer: B
Clarification: In a Lange coupler consisting of 4 lines, the alternating lines are connected together. This simplifies the computation effort for finding equivalent capacitance and the construction is simpler. Also ports are easily distinguished and helps in flow of power in required direction.

8. For a 4 wire Lange coupler, if the odd mode and even mode capacitances are 12pF and 9pF respectively, then the equivalent capacitance in terms of two wired coupled line in even mode is:
A. 15.1 pF
B. 16.7 pF
C. 12 pF
D. 9 pF
Answer: B
Clarification: Equivalent capacitance in terms of two wired coupled model is Ce (3Ce+C0)/(Ce+C0), Where Ce and C0 are the equivalent capacitances in even mode and odd mode for 4 wire model. Substituting the given values in the above expression, the equivalent capacitance is 16.7 pF.

9. For a 4 wire Lange coupler, if the odd mode and even mode capacitances are 12pF and 9pF respectively, then the equivalent capacitance in terms of two wired coupled line in odd mode is:
A. 18.56 pF
B. 25.71 pF
C. 42 pF
D. 31.6 pF
Answer: B
Clarification: Equivalent capacitance in terms of two wired coupled model is C0 (3C0+Ce)/ (Ce+C0), Where Ce and C0 are the equivalent capacitances in even mode and odd mode for 4 wire model. Substituting the given values in the above expression, the equivalent capacitance is 25.71 pF.

10. The phase velocity of the waves in both even and odd mode of a Lange coupler is equal.
A. true
B. false
Answer: B
Clarification: The phase velocity of the waves in the even mode and odd mode are not practically equal and there are lot of variations. But only for theoretical analysis, they are assumed to be equal.


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