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# Important Short Questions and Answers: Guided Waves

Transmission Lines and Waveguides - Impedance Matching in High Frequency Lines - Important Short Questions and Answers: Guided Waves

GUIDED WAVES

68.            What are guided waves? Give examples

The electromagnetic waves that are guided along or over conducting or dielectric surface are called guided waves.

Examples: Parallel wire, transmission lines

69. What is TE wave or H wave?

Transverse electric (TE) wave is a wave in which the electric field strength E is entirely transverse. It has a magnetic field strength Hz in the direction of propagation and no component of electric field Ez in the same direction

70. What is TH wave or E wave?

Transverse magnetic (TM) wave is a wave in which the magnetic field strength H is entirely transverse. It has a electric field strength Ez in the direction of propagation and no component of magnetic field Hz in the same direction

71. What is a TEM wave or principal wave?

TEM wave is a special type of TM wave in which an electric field E along the direction of propagation is also zero. The TEM waves are waves in which both electric and magnetic fields are transverse entirely but have no components of Ez and Hz

.it is also referred to as the principal wave.

72. What is a dominant mode?

The modes that have the lowest cut off frequency is called the dominant mode.

73.            Give the dominant mode for TE and TM waves

Dominant mode: TE10 and TM10

74.            What is cut off frequency?

The frequency at which the wave motion ceases is called cut-off frequency of the waveguide.

75. What is cut-off wavelength?

It is the wavelength below which there is wave propagation and above which there is no wave propagation.

76.            Write down the expression for cut off frequency when the wave is propagated in between two parallel plates.

The cut-off frequency, fc = m/ (2a (µE)1/2)

77.            Mention the characteristics of TEM waves.

a)It is a special type of TM wave

b)It doesn’t have either e or H component

c) Its velocity is independent of frequency

d)Its cut-off frequency is zero.

78. Define attenuation factor

Attenuation factor = (Power lost/ unit length)/(2 x power transmitted)

79.            Give the relation between the attenuation factor for TE waves and TM waves aTE = aTM (fc/f)2

80.            Define wave impedance

Wave impedance is defined as the ratio of electric to magnetic field strength Zxy= Ex/ Hy in the positive direction

Zxy= -Ex/ Hy in the negative direction

81. What is a parallel plate wave guide?

Parallel plate wave guide consists of two conducting sheets separated by a dielectric material.

82.Why are rectangular wave-guides preferred over circular wave-guides?

Rectangular wave-guides preferred over circular wave guides because of the following reasons.

a) Rectangular wave guide is smaller in size than a circular wave guide of the same operating frequency

b)It does not maintain its polarization through the circular wave guide

c) The frequency difference between the lowest frequency on dominant mode and the next mode of a rectangular wave-guide is bigger than in a circular wave guide.

83.Mention the applications of wave guides

The wave guides are employed for transmission of energy at very high frequencies where the attenuation caused by wave guide is smaller. Waveguides are used in microwave transmission.Circular waveguides are used as attenuators and phase shifters

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Transmission Lines and Waveguides : Impedance Matching in High Frequency Lines : Important Short Questions and Answers: Guided Waves |