Donot consider circular waveguide questions

Two mark Questions

1. What is the importance of aspect ratio of 2:1 in rectangular waveguide
2. How does ridging improve performance of waveguide?
3. TEM mode does not exist in hollow metallic waveguide. Justify.

6 Define dominant mode and degenerate mode in waveguides

7 What takes place inside a waveguide if a signal of wavelength greater than cutoff wavelength
is applied to the waveguide. Why?

8 A rectangular waveguide is 5.1 cm by 2.4cm and the number of half wavelengths to be

established is 2. Calculate the cut off wavelength.
9 Why are re-entrant cavities used even though cavity resonators are available?

10 Why must impedances/admittances be normalized before being plotted on smith

chart?

11. What is stub? Why are short circuited stubs preferred to open circuited stubs? 12 Give
two ways of coupling energy to a cavity resonator.
13. What is the value of obtained VSWR and ideal VSWR after impedance matching?
Justify.

15. Microwaves have the advantage of high bandwidth and transparency. Justify.

16. List two applications of microwaves in industry and two applications in medical field.

17. Waveguide behaves as a High Pass filter. Justify

2 marks Questions
Differentiate between Rectangular and Circular waveguide with at least two points.

Justify why waveguide does not support TEM propagation.

Define group velocity and phase velocity and give mathematical representation.

Justify why TE10 mode is the overall dominant mode in rectangular waveguide.

2 Marks questions

1. Difference between Rectangular and Circular waveguide.

2. Justify why waveguide does not support TEM propagation.
3. What is a Rat-race junction?
4. Explain the advantages of microwaves and what are the different microwave
frequency bands.
5. Differentiate between group velocity and phase velocity.
6. State 4 properties of Scattering parameters?
7. Why TE10 mode is the overall dominant mode in rectangular waveguide.
8. Problem based on modes in cavity resonator.
9. Explain why Y,Z and ABCD parameters cannot be used at microwave frequencies?
10. What is a Faraday’s rotation in ferrites?
11. What is the guide wavelength? Is it greater than or less than free space
wavelength?
12. How can you change the cut-off frequency of a waveguide without altering its
dimensions?
13. What is the condition on length for a cavity resonator to resonate?
 5marks Questions

14. Calculate the position and length of short circuited stub design to match (200+j300) Ω
load to a transmission line whose characteristic impedance is 300Ω. Use a smith chart.
15. Design Circulator using Magic Tee's.
16. Explain the operation of a two hole directional coupler with S-Matrix.
17. Draw a rectangular waveguide and brief note on its operation.
18. Derive S-matrix for E-Plane / H-Plane / Hybrid Tee junctions.
19. What is a Circulator? Explain its working using 3dB couplers.
20. Explain the operation of Isolator using Faraday's rotation principle.
21. What is a Directional Coupler? Explain the terms:
a. Coupling Factor
b. Directivity
c. Isolation
22. Problem based on modes, cut off frequency, phase velocity and phase constant.

5 Marks Questions
Derive the equations for the propagation of TE/TM mode in rectangular waveguides.

Explain the various advantages and disadvantages of microwaves?

Design a single shunt short circuited stub to match the load impedance ZL=(90-j25)Ω to a 50Ω
transmission line.

(d1=0.12𝝺, l1=0.152𝝺, d2=0.318𝝺, l2= 0.34𝝺)

1. A lossless line of characteristics impedance Ro=50Ὡ is to be matched to a load

Zl=50/[2+√3]Ω by means of a lossless short-circuited stub. The characteristics impedance
of the stub is 100Ω. Find the stub position and length so that a match is obtained.

2. The terminating impedance ZL=100+j100Ω and the characteristic impedance Z0 of the line
and the stub is 50Ω. The first stub is placed at 0.40λ away from load. The spacing
between the two stubs is 3/8λ. Determine the length of the short-circuited stubs when the
match is achieved.

3. Match a load impedance of ZL=100+j80 Ω to a 50Ω line using a single series open
circuited stub.
4. A rectangular waveguide is filled by dielectric material of Ԑr=9 and has inside dimension
of 7×3.5cm. It operates in the dominant TE10 mode

a) Determine the cutoff frequency

 b) Find the phase velocity in the guide at a frequency of 2Ghz
c) Find the guided wavelength at the same Frequency.
5. The dominant mode TE10 is propagated in a rectangular waveguide of dimensions a = 6cm
and b = 4 cm. The distance between a maximum and a minimum is 4.47 cm. Determine
the signal frequency of the dominant mode.

6. An air-filled circular waveguide is to be operated at a frequency of 6GHz and is to have

dimensions such that fc=0.8f for the dominant mode. Determine diameter of the guide and
guide wavelength.

7. An air-filled circular waveguide has a radius of 1.5cm and is to carry energy at a frequency
of 10GHz. Find all TE and TM modes for which transmission is possible.

8. A TE11 wave is propagating through a circular waveguide . The diameter of the guide is
10cm, and the guide is air filled.

a) Find the cutoff frequency

b) Find wavelength λg in the guide for a frequency of 3GHz.

c) Determine wave impedance in the guide.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

List of Important Questions And Numericals

Subject: Microwave Engineering (171001)

Chapter-1 Inroduction to microwaves

1. What is a microwave? Explain its advantages and its applications?

2. “Vessels in microwave oven should be made of dielectric material.” Justify with

proof.

Chapter-2 Microwave transmission

lines and waveguides:
 (A) Transmission lines
1. Describe following terms with necessary equations

a. Tranmission co-efficient

b. Reflection co-efficient

c. Standing waves

d. Standing wave ratio

e. Propagation constant

f. Attenuation constant

g. Phase constant

h. Characteristics impedance

2. Derive the expression for Reflecton coefficient, Transmision coefficient, and

input impedance of transmission line.

3. Draw and explain the equivalent circuit of a general transmission line and derive V and I
equations for the same.

4. What is stub? Explain the principle of stub matching.How stub matching is achieved
using single stub and double stub?

(B) Smith Charts

1. Explain impedance matching and smith chart.

2. A lossless line of characteristic impedance Ro of 50 Ohm is to be matched with a load of Zl=

50 / [ 2 + j(2 + sqrt(3))] ohm by means of lossless short circuited stub. The characteristic
impedance of the stub is 100 Ohm. Find the stub position (Closest to the load) and length using
Smith chart so that match is obtained.

3. A losseless transmission line is having characteristics impedance of 50 ohm is to be

terminated by load impedance of 200 – j50 ohm. Using Smith chart find

a. Line impedance at d=1.2λ

b. Line admittance at d=1.0λ

 c. SWR and SWR circle

d. Distance of first Vmax and Vmin from the load

e. Smallest line length at which real part becomes 50 Ohm

4. A 5.2 cm length of lossless 200 ohm line is terminated in a load impedance of 60 + j100
ohm. Using smith chart

(i) Determine ‫׀‬τL‫( ׀‬Reflection coefficient), φL (phase or

angle of reflection coefficient) and SWR along the line.

(ii)Determine the Z and Y at the input and at a point 2.0 cm from the load end.
The signal frequency is 750 MHz and λ = λ0 (means to find λ use c=3 X
108.)

(C) Waveguide analysis:

1. Sketch circular and rectangular waveguide and compare their dominant

modes, advantages and disadvantages.

2. What do you mean by modes in waveguide? Define TE, TM, TEM, Hybrid and
degenerate modes. Explain TE10 mode in case of a rectangular waveguide.Why it is called
dominant mode? Why TEM mode can not propagate through rectangular waveguide?

3. Explain the following terms in case of waveguide.

a.

Phase veocity

b. Group velocity

c. Cutoff wavelength

d. Cutoff frequency

4. What is micro strip line? Derive expression of characteristics impedance of micro

strip line using comparative or alternative method.

5. Write shortnote on various microstrip lines.write equation of its

characteristics impedance

Chapter-3 Microwave components &

their s-parameters:
1. Explain requirements and significance of S-parameters for microwave frequency
analysis. What is S-matrix? Write its properties.

2. What do you mean by reciprocal network? Draw and explain series tee and shunt tee
junction and find its simplified S-matrix using S-parameter.

3. Explain the operation of magic tee with its S-parameters. Enlist applications of
Magic Tee and explain any two of them.

4. What is ferrite device? What is Faraday’s rotation? Explain basic principle of ferrite device.

5. Explain principle working of isolator and circulator.How to construct four port circulator
using two magic tees.

6. Explain working principle of four port directional coupler.Note down significance of each
port and associated parameter.

7. Draw and explain waveguide band, corners and twist in detail with their applications.

Chapter 4: Microwave Tubes and

Circuits
1. Conventional tubes suffer from various limitations at high frequency.Enlist them
and discuss with justification.

2. Explain velocity modulation with apple gate diagram. Draw a neat diagram of two cavity
Klystron amplifier and explain each port.

3. Explain how Klystron device can work as an oscillator. Explain construction of reflex
Klystron with neat diagram

4. Draw different slow wave structures and write why slow wave structures are used in
traveling wave tubes? Also explain working of helixtype of TWT with neat sketch.

5. What do you mean by favorable electrons? Draw crosss sectional view of cavity
magnetron and discus field inside the interaction gap.How it can works as an
oscillator.

6. Explain following terms.

a. Electron bunching

b. Strapping

c. Frequency pushing

d. Frequency pulling

e. Phase focusing effect

Chapter 5: Semiconductor
microwave devices and Circuits
1. Explain Gunn Effect using two valley theory.Describe the constructional details of
Gunn diode and mention its performance chracteristics and applications.
2. Explain the Tunnel diode characteristics with the aid of Energy band diagram.

3. Describe the working of parametric amplifier with the help of equivalent circuit and write
the basic difference from the conventional amplifier.

4.

Explain IMPATT Diode and TRAPATT diode with its construction, working and
application.

5. Explain BARRIT Diode with application.

6. How PIN diode works? Enlist its applications.

7. Write shortnote on Schotkky and varactor diode.

 NUMERICALS:

1. An open wire transmission line has following constants. R=4 ohm/Km, L=3.5 mH/Km,
C=9pF/Km and G=0.29 micro mho/Km, operating frequency = 10 KHz. Find characteristic
impedance, attenuation constant, phase constant and phase velocity.

2. A crtain transmission line has a characteristics impedance of 75 + j0.01 Ohm and is

terminated in a load impedance of 70 + j50 ohm. Compute

a. The reflection coefficient

b. The transmission coeffiecient

3. For a rectangular waveguide of dimensions ( 3 X 4.5 ) cm operating at 1 GHz in TE10

mode find

a. Vg and Vp

b. Zo

c. Cutoff wavelength

d. Guided wavelength

4. A rectangular waveguide has dimension of 2.29 cm and 1.02 cm. It is desired that this
waveguide is to be operated only in dominant mode and operating frequency is at least 25%
above cut off frequency of dominant mode and not higher than 95% of the next cut off
frequency. What is allowable operating frequency?

5. The dimension of a waveguide is 2.5X1cms.The frequency is 8.6GHz Find the

possible modes that can propagate through the waveguide also find the cutoff
frequencies for the same.
6. A rectangular waveguide is filled by dielectric material of Є =9, with inside
dimension of 7X3.5cm. It operates in the dominant TE10 mode.

Determine (i) cutoff frequency (ii) phase velocity at a frequency of 2 GHz (iii) guided
wavelength at the same frequency.

7. A typical transmission line has a resistance of 6 ohm /km, inductance of 2.2mH/km, a

capacitance of 0.005 μF/km and a conductance of 0.05μmho/km. Calculate the characteristic
impedance, attenuation constant and phase constant of the transmission line at a frequency of
1kHz.Also calculate the phase velocity of the signal.