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Microwave Engineering MCQs Set-6

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1. Advantage of chebyshev matching transformers over binomial transformers is:




2. There are passband ripples present in the chebyshev characteristic curve.




3. Chebyshev matching transformers can be universally used for impedance matching in any of the microwave networks.




4. Chebyshev polynomials do not obey the equal-ripple property.




5. For values of x greater than 1, the chebyshev polynomial in its trigonometric form cannot be determined.




6. A single section tapered line is more efficient in impedance matching than a multisection tapered line for impedance matching.




7. Passband characteristics of tapered lines differ from one type of taper to another.




8. The value of constant ‘a’ for an exponentially tapered line of length 5 cm with load impedance being 100Ω and characteristic impedance of the line is 50Ω is:




9. Reflection co-efficient magnitude response is an exponential curve for tapered line.




10. Triangular taper is the best solution for any impedance matching requirement.




11. For any load impedance, perfect match can be obtained and the minimum reflection co-efficient achieved can be zero.




12. For a given load (a fixed RC product), a broader bandwidth can be achieved with a low reflection co-efficient in the passband.




13. A perfect match can be obtained in the passband for any impedance matching circuit around the center frequency for which it is defined.




14. In a series LCR circuit, at resonance point the energy stored in the inductor and capacitor in the form of magnetic and electric energies are equal.




15. Quality factor-Q of a resonant circuit signifies:




16. The total energy stored in a series RLC circuit is equal to the energy stored in the inductor.




17. Higher the quality factor of a series LCR circuit, greater is the operating bandwidth of the resonant circuit.




18. The plot of input impedance magnitude v/s frequency has a peak at the resonant frequency.




19. For a parallel resonance circuit, the plot of input impedance magnitude v/s frequency has a dip at the resonant frequency.




20. The relation between unloaded Q and external Q is:




21. Loaded Q and External Q are 2 different parameters.




22. The bandwidth of a series RLC circuit is 200 Hz. Then the quality factor of the circuit is:




23. If a parallel RLC circuit is excited with a source of 8v, 50 Hz and the circuit has an inductor of 1mH, capacitor of 1µF and a resistor of 50Ω, then the power loss that occurs in the circuit is:




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




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




26. 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:




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




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




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




30. Microwave resonators can be constructed from open sections of waveguide.




31. There is no energy stored inside a rectangular waveguide cavity resonator.




32. A dielectric resonator is considered to be closed at both the ends.




33. A dielectric material in the form of a small cube or disc can be used as a resonator.




34. The level of coupling required between a resonator and its attached circuitry is a standard and independent of the application where coupling is required.




35. A measure of the level of coupling between a resonator and a feed is given by:




36. To obtain maximum power transfer between a resonator and feed line, the resonator should be matched to the load at:




37. Coupling coefficient Q can be defined as the ratio of unloaded Q to external Q.




38. When the coupling coefficient is lesser than one, the resonator is over coupled to the feed line.




39. Direct measurement of the unloaded Q of a resonator is not possible.




40. For practical applications cavity resonators can be modified as per the requirement of the application where it is used.




41. When coupling coefficient is 1, the resonator is ________ to the feed line.




42. In aperture coupling, a small aperture in the transverse wall of the waveguide acts as:




43. One of the most commonly used dielectric materials is:




44. Dielectric resonators use materials that are less lossy.




45. The resonant frequency of a dielectric resonator cannot be mechanically tuned.




46. Q factor does not exist for dielectric resonator.




47. The direction of propagation is in z direction outside the dielectric in the resonator.




48. A T junction has a 3×3 ‘s’ matrix.




49. If all the ports of a microwave network are matched, then the diagonal elements of the S matrix of the network is zero.




50. A lossless reciprocal 3 port network can be matched at all the three ports.




51. A circulator is a 3 port network that allows energy flow in clockwise direction only.




52. The diagonal elements of the S matrix of an improperly matched circulator is zero.




53. Coupling factor of a directional coupler must be maximum and is a key factor that determines the performance of the coupler.




54. Directivity of a directional coupler signifies the direction of power flow in the coupler.




55. Insertion loss is the power delivered to the through port.




56. In a symmetric coupler, the power delivered to the through port and output port are equal.




57. A T junction power divider can be used only for division of power.




58. The lossless T junction dividers can be can all be modeled as a junction of three transmission lines.




59. For the realization of lossless T-junction power divider using transmission lines, the characteristic impedance of the transmission line has to be real.




60. Hybrid couplers are also a type of directional couplers.




61. A lossy T junction can be matched at all the three ports.




62. The diagonal elements of the s matrix of a resistive T junction are:




63. The power delivered to the input port of a resistive power divider is equal to the source voltage applied.




64. The power input at the port 1 of resistive T junction is equally divided among the 2 output ports of the T junction.




65. S12 curve of a Wilkinson coupler when plotted versus frequency is a line passing through origin.




66. The plot of S23 v/s frequency has the same curve as that of S11 v/s frequency.




67. The plot of frequency v/s S11 parameter of a Wilkinson coupler has a dip at the frequency at which it is designed to operate.




68. A Wilkinson coupler designed can be operated at any frequency.




69. Wilkinson power divider is an equal split power divider.




70. Branch-line couplers are also popular as Quadrature hybrids.




71. A branch-line coupler is an asymmetric coupler.




72. The plot S11 v/s frequency for a branch-line coupler has a straight line characteristic for a wide range of frequency around the designed frequency range.




73. The curve of S14 for a branch-line coupler is similar to that of the S11 curve of the branch-line coupler.




74. S12 and S13 curves for branch-line couplers are almost a straight line parallel to X –axis. Both the curves are similar and follow same path.




75. If the branch-line impedance of a coupler designed to operate at 1 GHz is 70.70 Ω, then the characteristic impedance of the material of the arms of the branch-line coupler is:




76. In coupled line directional couplers, power from one line to another is transmitted through a microstrip line running between them.




77. The number of conductors used in the construction of coupled line couplers is fixed.




78. 1800 hybrid is a network in which there is a phase shift of 1800 between the input signal applied and the output taken.




79. Port 1 and port 4 of 1800 hybrid are called sum and difference ports respectively because of their behavior and action mechanism.




80. S matrix of 1800 hybrid consists of all diagonal elements zero.




81. In 1800 hybrid, different power levels can be received at the two output ports of the hybrid.




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




83. The tapered coupled line 1800 hybrid can provide an arbitrary power division at the 2 output ports of the coupler.




84. Moreno crossed-guide coupler is a waveguide directional coupler consists of four waveguides at right angle.




85. Ribblet short-slot coupler consists of two waveguides that are separated by a distance “d”.




86. Symmetric tapered coupled line couplers offer higher bandwidth when compared to other forms of couplers.




87. The coupling and directivity of couplers with apertures in planar lines can be adjusted as per the requirement of the application.




88. Reflectometer can also be used as a frequency meter.




89. A basic Reflectometer circuit can be used to measure the _____________ magnitude of the unknown load.




90. ________ is a three-port microwave device that can be lossless and matched at all spots.




91. There exists no difference between the construction of GaAs MESFET and silicon MOSFET except for the material used in their construction.




92. MOSFETs can provide a power of several hundred watts when the devices are packaged in:




93. High electron mobility transistors can be constructed with the use of single semiconductor material like GaAs that have high electron mobility.




94. The curve of IDS v/s VDS of an FET does not vary with the gate to source voltage applied.




95. High-power circuits generally use higher values of:




96. High drain current at RF levels is achieved with the biasing and decoupling circuitry for a dual polarity supply.




97. Since multiple layers of semiconductor materials is used in high electron mobility transistors, this results in:




98. A major disadvantage of high electron mobility transistor is that:




99. HEMT fabricated using GaN and aluminum gallium nitride on a silicon substrate can be used in :




100. The scattering parameter S11 for GaN HELMT increases with increase in frequency of operation