10-04-2017, 08:46 PM
microwave engineering viva questions and answers pdf free download
MICROWAVE ENGINEERING
Ques 1. What is Microwave Engineering?
Ans. Microwave engineering is the study and design of microwave circuits , components , and systems. Fundamental principles are applied to analysis , design and measurement techniques in this field.The short wavelengths involved distinguish this discipline from electronic engineering . This is because there are different interactions with circuits, transmissions and propagation characteristics at microwave frequencies.
Ques 2. Define s-matrix and its properties?
Ans. In a microwave junction there is an interaction of three or more components.There will be an output port, in addition there may be reflection from the junction of other ports. Totally there may be many combination, these are represented easily using a matrix called S matrix.
Properties of s- matrix
1. it possess symmetric properties sij=sji
2. it possess unitary property
3. [s][s]*=[i]
Microwave
Microwave Components
Ques 3. Write the applications of microwave engineering?
Ans. Following are the applications of microwave engineering-
1. Antenna gain is proportional to the electrical size of the antenna. At higher frequencies, more antenna gain is therefore possible for a given physical antenna size, which has important consequences for implementing miniaturized microwave systems.
2. More bandwidth can be realized at higher frequencies. Bandwidth is critically important because available frequency bands in the electromagnetic spectrum are being rapidly depleted.
3. Microwave signals travel by line of sight are not bent by the ionosphere as are lower frequency
signals and thus satellite and terrestrial communication links with very high capacities are possible.
Ques 4. Why is s-matrix used in MW analysis?
Ans. Matrix is used in MW analysis to overcome the problem which occurs when H,Y & Z parameter are used in high frequencies.
Ques 5. What are the advantages of ABCD matrix?
Ans. The advantages of ABCD matrix are as follows-
1. They are used in power transmission lines
2. They are helpful in case of cascade networks.
MICROWAVE ENGINEERING LAB
VIVA QUESTIONS AND ANSWERS
1.Why can t conventional tubes be used at microwave frequencies?
A:Conventional tubes can t be used at microwave frequencies because of transit time effect. Lead inductance and inter electrode capacitance of the devices will finally limit the output which may even be zero.
2.What is transit time?
A:It is the time taken by the electrons to travel from cathode to anode.
3.What is the operating principle of reflex klystron?
A:It works on the principle of velocity modulation and current modulation.
4. What is velocity and current modulation in a reflex klystron?
A:Variation in velocities of the electrons in the electron beam is called velocity modulation; variation in the current density of the electron beam is referred to as current modulation.
5. How does bunching occur in a reflex klystron?
A:A reference electron passing the gap when the gap voltage is zero travels with no change in velocity. An electron leaving the gap earlier during slightly positive voltage would travel further into repeller space and hence would take longer time then the reference electron to return to the gap. An electron leaving the gap later will face slightly negative voltage and gets retarded. So it returns back after a shorter travel in the repeller space. Thus all the electrons would arrive back to the gap in bunches. Bunching around reference electron takes place once per cycle of RF oscillations.
6. Why do different modes of operation exist for a reflex klystron?
A:There are several combinations of repeller voltage and anode voltage that provide favorable conditions for bunching. Accordingly there are several modes of operation, expressed by N + where N is an integer.
7. What modes are generally used in a reflex klystron?
A:1 and 2 are the most commonly used modes in a practical reflex klystron.
8. What is the operating frequency and power output of a reflex klystron?
A:Frequency range: 4GHz 200GHzOutput power: maximum 3W in X-band to 10mW at220GHz
9. What is the maximum theoretical efficiency of the reflex klystron?
A:22.7% for 1 mode.
10. What is mechanical tuning and electronic tuning in a reflex klystron?
A:Variation in frequency of resonance of cavity by varying its dimension by a mechanical method like adjusting screws is called mechanical tuning. Variation of frequency by adjusting repeller voltage is called electronic tuning.