SUBJECT CODE & NAME: EC3551 & TRANSMISSION LINES &RF SYSTEMS
YEAR/SEMESTER: III/V BATCH: 2021-2025 ACADEMIC YEAR: 2023-2024 (ODD)
UNIT IV
WVAEGUIDES
PART A 10x2=20 Marks
1. Justify why TM01 and TM10 modes in the rectangular waveguide do not exit.
(APRIL/MAY 2019)
For TM modes in rectangular waveguides, neither m nor n can be zero because all the fields
equations vanish. If m=0,n=1 or m=1,n=0 no fields are present. Hence TM01 and TM10 mode in a
rectangular wave guide do not exist.
2. What is dominant mode? (APRIL/MAY 2018, NOV/DEC 2017)(NOV/DEC 2022)
The mode which has lowest cut off frequency or highest cut of wavelength is called dominant mode.
3. Write the expression for cut off wavelength of the wave which is propagated in between two
parallel planes. (NOV/DEC 2017)
The cutoff wavelength 𝜆𝑐=2𝑎/m
4. Define TEM wave.
The Transverse Electromagnetic (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 called the principal wave.
5. An air filled rectangular waveguide of inner dimensions 2.286*1.016 in centimeters operates
in the dominant TE10 modes. Calculate the cut off frequency and phase velocity of a wave in
the guide at a frequency of 7 GHz. (N/OVDEC 2016)
Refer Notes II(Page no.4)
1
6. A waveguide is generally operated at f = 1.5 fc where fc is the cutoff frequency. assuming that
the broader dimension is twice the other dimension in a rectangular waveguide, calculate the
dimension if it operates in TE10 mode at 6 GHz. (APRIL /MAY 2021)
Refer Notes (Page no.142)
7. What is degenerate mode in rectangular waveguide?
The higher order modes which are having the same cut off frequency are called degenerate modes. In
a rectangular waveguide, TEm,n and TMm,n modes (both m = 0 and n = 0) are always degenerate
mode.
8. What is an evanescent mode?
When the operating frequency is lower than the cut-off frequency, the propagation constant becomes
real. So the wave cannot be propagated for that frequency. This non- propagating mode is known as
evanescent mode.
9. Write the expression for cut off wavelength of the wave which is propagated in rectangular
Waveguide.(APRIL/MAY 2022)
Refer Notes (Page no.125)
10. Define group and phase velocity. (APRIL /MAY 2021)
Waves can be in a group and such groups are called wave packets, so the velocity with which
a wave packet travels is called group velocity. The velocity with which the phase of a wave travels is
called phase velocity.
PART B 5X13=65 Marks
1. Derive the expression TE waves in parallel plane perfectly conducting planes for the field
Components. (APRIL/MAY 2019) (APRIL /MAY 2022) (APRIL/MAY 2021)
Refer Notes (Page no.102-107)
TE waves derivation parallel plane
2. Write the expression for TM and TE waves in circular wave guides. (NOV/DEC 2018)
Refer Notes (Page no.135-139)
TE waves derivation for circular waveguide
TM waves derivation for circular waveguide
3. Derive an expression for the TM waves between parallel perfectly conducting planes for the
field components.
Refer Notes (Page no.108-111)
TM waves derivation parallel plane
2
4 A rectangular waveguide is to be designed to operate at a frequency 10 gHz. it is desired that
the frequency of operation be 15% above the cutoff frequency of the operating frequency and
20% below the cutoff frequency of the next higher mode, determine the dimensions of the
waveguide. Determine the propagation constant, phase velocity and group velocity at 10 gHz.
represent the Electric and magnetic field distribution at 10 gHz in the waveguide. (APRIL /MAY
2021)
Refer notes II(Page no.42)
5. Discuss the characteristics of cutoff frequency, cutoff wavelength, phase velocity, group
velocity, wave impedance for TE, TM, TEM waves between two conducting planes.
(NOV/DEC 2022)
Refer Notes (Page no.111-120)
Characteristics of TE and TM waves
Velocity of propagation
Characteristics of TEM waves
PART C 1x15=15 Marks
1. An air filled circular waveguide having an inner radius of 1cm is excited is dominant mode
at 10ghz.Find the cutoff frequency of the dominant mode at 10 ghz. The guide wavelength wave
impedance. Also find the bandwidth for operation in the dominant mode only.
Refer Notes II (Page no.07)
2. Derive an expression for the TM waves in rectangular waveguide for the field components.
Refer Notes (Page no.121-126)
TM waves derivation for rectangular waveguide
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