Important viva questions on microwave engineering with answers

Basic Microwave Engineering VIVA Questions and Answers:

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 techniin 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.a

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]

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.

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.

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.

6. What are junctions ? Give some example
 Ans. A microwave circuit consists of several microwave devices connected in some way to achieve the desired transmission of MW signal. The interconnection of two or more microwave may be regarded as MW junction.
E.g.: TEE, HYBRID RING

7. What are non-reciprocal devices ?Give two examples?
Ans. The devices which are having the properties that the forward characteristics are not equal to the reverse characteristics are called non-reciprocal devices.

8. What are the applications of reflex klystron?
Ans. The main applications of a reflex klystron are as follows-
1. Signal source in MW generator
2. Local oscillators in receivers
3. It is used in FM oscillator in low power MW links.
4. In parametric amplifier as pump source.

9. What is the purpose of slow wave structures used in TWT amplifiers?
Ans. Slow wave structures are special circuits that are used in microwave tubes to reduce wave velocity in a certain direction so that the electron beam and the signal wave can interact. In TWT, since the beam can be accelerated only to velocities that are about a fraction of the velocity of light, slow wave structures are used.

10.Give two examples for two port junctions?
Ans. Following are the two examples of two port junctions-
1. The junction of two rectangular guides of unequal height
2. A symmetrical junction consisting of two similar rectangular guides joined by an Intermediate guide of greater width.