# (Paper) Transmission Lines and Waveguides - Objective Questions

**Paper : Transmission Lines and Waveguides - Objective Questions**

** :: Transmission Lines and Waveguides ::
**

1. In a transmission line terminated with a load equal to the characteristic impedance, the reflection coefficient is

a) + 1 b) ? 1 c) 0 d) ?

2. Short circuited stubs are preferred to open-circuited stubs because the latter are

a) more difficult to make and correct

b) made of a transmission line with a different ZO

c) liable to radiate

d) incapable of giving a full range of reactance

3. For electromagnetic waves traveling in free space, the power carried by the waves changes with distance ?d? in proportion to

a) d b) 1/d c) 1/d2 d) d2

4. Decibel is a logarithmic unit expressing

a) noise levels b) current c) voltage d) power ratio

5. Input impedance of a shorted lossless line of length ? / 4 is

a) 0 b) 1 c) ZO d) ?

6. On a transmission line withstanding waves, the distance between a voltage maxima and adjacent current maxima is

a) ? / 4 b) ? / 8 c) ? / 4 d) ?

7. Stub matching eliminates standing waves on

a) load side b) transmitter side c) both sides of stub d) none

8. Electromagnetic waves are reflected back by ionosphere due to their interaction with

a) Electrons d) Protons c) Ultra-violet rays d) Neutrons

9. For a transmission line with ?L << R and ?C << G, attenuation constant ? is

a) proportional to frequency b) constant

c) inversely proportional to frequency d) proportional to velocity

10. When power ratios are expressed in dbm, the reference power is

a) 1 W b) 1 mW c) 1 ?W d) 1 MW

11. In a distortion less line, attenuation constant is

a) directly proportional to frequency b) inversely proportional to frequency

c) independent of frequency d) independent of primary constants

12. Impedance matching over wide frequency range can be obtained by using

a) double stubs b) single stubs c) quarter wave transformer d) none

13. Loading is used in cables to

a) reduce distortion b) increase power handling capacity

c) increase load resistance d) increase distortion

14. Input impedance of an open circuited loss-less line of length ? is

a) infinity b) finite capacitive reactance

c) finite inductive reactance d) zero

15. A matching stub should be

a) nearest to load b) nearest to transmission end

c) mid-way between both d) anywhere between two

16. If the spacing between the wires of a transmission line is increased, its characteristic impedance will

a) increase b) decrease c) is unchanged d) none

17. For a transmission line with ?L >> R and ?C >> G, propagation constant ? is

a) ? b) ?2 c) d) 0

18. The reflection coefficient on a lossless transmission line

a) is always purely imaginary b) is always purely real

c) is always complex d) can be anyway

19. There will be no reflection in an transmission line if it is terminated by an impedance

a) equal to characteristic impedance

b) less than the characteristic impedance

c) equal to twice the characteristic impedance

d) equal to square root of its characteristic impedance

20. Among the following lines, the simplest one to construct is

a) strip line b) microstrip line c) coaxial cable d) optical fibre

21.The unit of magnetic field of electromagnetic radiation at any point is usually expressed in

a) ampere/metres b) volts/metre c) watts/metre d) watt/metre2

22. The intrinsic impedance of free space is

a) 50 ohms b) 377 ohms c) 73 ohms d) 83 ohms

23. The velocity of electromagnetic waves in a dielectric (? = 4) is

a) 3 x 108 m/sec b) 1.5 x 108 m/sec c) 6 x 108 m/sec d) 2 x 108 m/sec

24. The propagation constant of a transmission line is

a) b)

c) d)

25. The induction field of a short current element varies as

a) b) c) d)

26. The guide wavelength in a rectangular waveguide in TE10 mode is

a) greater than free-space wavelength b) less than free-space wavelength

c) equal to free-space wavelength d) double the free-space wavelength

27. The dominant mode in a cylindrical wavelength is

a) TM11 b) TE11 c) TE10 d) TM10

28. The MKS unit for ? is

a) farads per square metre b) farads per metre

c) henrys per metre d) henrys per square metre

29. If the frequency is 10 MHz, the wavelength of a plane electromagnetic wave in free space will be

a) 30 metres b) 100 metres c) 60 metres d) 90 meters

30. The velocity of EM waves in free-space with respect to that in an RF cable with air dielectric is

a) increased b) decreased c) unchanged d) none

31. The propagation constant in a lossless line is given by

a) b) c) j? d)

32. VSWR in a short-circuited line equals

a) infinity b) unity c) zero d) none

33. A rectangular waveguide is

a) resonant circuit b) high pass filter

c) low pass filter d) band pass filter

34. The intrinsic impedance of free space is

a) 1 ohm b) 4 ohms c) 120 ohms d) 3 x 108 ohms

35. In a rectangular waveguide, the phase velocity

a) increase with increasing frequency b) decrease with increasing frequency

c) is independent of frequency d) none of these

36. A (75 ? j 50) load is connected to a coaxial transmission line of ZO = 75 ohms at 10 GHz, the best method of matching consists in connecting

a) a short-circuited stub at the load

b) an inductance at the load

c) a capacitance at some specific distance from the load

d) a short-circuited stub at some specific distance from the load

37. To couple a coaxial line to a parallel wire line, it is best to use a

a) slotted line b) balun

c) directional coupler d) quarter wave transformer

38. In rectangular waveguides

a) vg vp = c2 b) vg vp = 1 c) vg vp = 2c2 d) vg = vp

39. A microstrip transmission line is

a) a thin metal strip placed within a waveguide

b) a thin metal strip placed within a circular coaxial line

c) a thin metal strip placed on a dielectric with a ground plane

d) a transmission line consisting of two parallel thin metal strips

40. Waveguide impedance ZO of a rectangular waveguide for TE10 mode is

a) directly proportional to the width of the guide

b) inversely proportional to the width of the guide

c) does not depend on the width of the guide

d) directly proportional to double the width of the guide

41. ZO of a parallel wire transmission line______ with increase in distance between the conductors.

a) increases b) decreases

c) does not change d) none of these

42. The characteristic impedance ZO equals

a) ZOC / ZSC b) ZSC / ZOC c) (ZSC / ZOC)? d) (ZSC.ZOC)?

43. A Smith chart is used for solving

a) propagation problems b) transmission problems

c) antenna problems d) attenuation problems

44. To specify a mode in rectangular a rectangular waveguide, its electric field has to be defined in

a) one axis b) two axes c) three axes d) four axes

45. If a loss less line of 50 ohms terminated in a load Zl has VSWR = 2.0 and the voltage maxima occurs with the load, the Zl is

a) 25 ohms b) 50 ohms c) 100 ohms d) 150 ohms

46. A lossless line will be distortion less if the phase shift constant

a) is constant with frequency

b) varies directly with frequency

c) varies inversely with frequency

d) has nothing to do with distortion on a lossless line.

__Mark the wrong statements in the following:
__

47. The VSWR of a transmission line is infinity, the line is terminated in

a) a complex impedance b) open line c) a pure reactance d) short line

48. When an ideal transmission line is terminated in its character impedance, the first minimum is formed at the load end.

49. Transmission lines can be used for impedance matching.

50. Loading of cables reduces transmission loss.

51. Propagation in waveguides is below the critical frequency and independent of waveguide dimensions.

52. A rectangular waveguide supports TEM mode.

53. The input impedance of an infinite transmission line is equal to Characteristic impedance ZO.

54. A loaded coil behaves like a low pass filter.