Microwave Engineering Interview Questions & Answers

  1. Question 1. What Is Microwave Engineering?

    Answer :

    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.

  2. Question 2. Define S-matrix And Its Properties?

    Answer :

    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]
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  4. Question 3. Write The Applications Of Microwave Engineering?

    Answer :

    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.
  5. Question 4. Why Is S-matrix Used In Mw Analysis?

    Answer :

    Matrix is used in MW analysis to overcome the problem which occurs when H,Y & Z parameter are used in high frequencies.

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  7. Question 5. What Are The Advantages Of Abcd Matrix?

    Answer :

    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.
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  9. Question 6. What Are Junctions ? Give Some Example?

    Answer :

    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.


  10. Question 7. What Are Non-reciprocal Devices ?give Two Examples?

    Answer :

    The devices which are having the properties that the forward characteristics are not equal to the reverse characteristics are called non-reciprocal devices.

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  12. Question 8. What Are The Applications Of Reflex Klystron?

    Answer :

    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.
  13. Question 9. What Is The Purpose Of Slow Wave Structures Used In Twt Amplifiers?

    Answer :

    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.

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  15. Question 10. Give Two Examples For Two Port Junctions?

    Answer :

    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.
  16. Question 11. What Is Microwave?

    Answer :

    Electromagnetic waves having frequencies between 1 GHz to 300 GHz (it may be 300 MHz to 300 GHz) are called microwaves.

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  18. Question 12. What Are The Properties Of Microwaves?

    Answer :

    Microwave are unidirectional. This means that when an antenna transmits microwaves, they travel in one direction. That is why microwave propagation is line of sight (LOS) propagation. They are not reflected by ionosphere. High frequency microwaves can not penetrate an object like wall.

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  20. Question 13. What Are The Merits And Demerits Of Microwaves?

    Answer :

    Due to above properties  microwaves have following advantages and disadvantages:

    1. Due to line of sight propagation, a pair of antennas can be  aligned without interfering with another pair of aligned antennas.
    2. Due to wide frequency bandwidth, high data transfer rate is possible.
    3. Due to line of sight propagation, it can be transmitted long distance. But a problem is faced due to its penetration properties.It can not be transfer inside a bound area. Also its transformation has obstacles like hills trees, mountains, earth curvature etc. That is why we need repeaters or tall towers for long distance transmission.
    4. As they are not reflected by ionosphere, they can be used for space transmission.
  21. Question 14. What Are The Applications Of Microwave?

    Answer :

    They are used in several applications. Some of these are:

    1. Communication (astronomy, satellite, WLAN, mobile,cellular, radar, TV etc)
    2. Remote sensing and navigation (prediction/monitoring/guidence- traffic control, weather, missile, aircraft etc)
    3. Medical applications (cautery imaging, heart stimulation, therapy etc)
  22. Question 15. What Are The Reasons For Using Microwave In Communication?

    Answer :

    1. Wider bandwidth due to higher frequency
    2. Better resolution due to smaller wavelength
    3. Higher speed of operation
    4. Higher antenna gain (size reducing)
    5. As the production of  frequency in microwave range by natural resources are less , it is more available and less crowed frequency spectrum. 
    6. Lower interference due to lower signal crowding.
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  24. Question 16. What Is Velocity Of Microwave?

    Answer :

    All electromagnetic wave has velocity of light. (Light,microwave,radio wave, infrared ray all are electromagnetic wave).

  25. Question 17. What Is Microwave Systems?

    Answer :

    A microwave system normally consists of a transmitter subsystem, including a microwave oscillator, waveguides, and a transmitting antenna, and a receiver subsystem that includes a receiving antenna, transmission line or waveguide, a microwave amplifier, and a receiver.

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  27. Question 18. What Is Pointing Theorem?

    Answer :

    It states that the total complex power fed into a volume is equal to the algebraic sum of the active power dissipated as heat, plus the reactive power proportional to the difference between time-average magnetic and electric energies stored in the volume, plus the complex power transmitted across the surface enclosed by the volume.

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  29. Question 19. What Are Boundary Conditions?

    Answer :

    There are four basic rules for boundary conditions at the surface between two different materials:

    1. The tangential components of electric field intensity are continuous across the boundary.
    2. The normal components of electric flux density are discontinuous at the boundary by an amount equal to the surface-charge density on the boundary.
    3. The tangential components of magnetic field intensity are discontinuous at the boundary by an amount equal to the surface-current density on the boundary.
    4. The normal components of magnetic flux density are continuous across the boundary.
  30. Question 20. Why Uniform Wave Is A Tem Wave?

    Answer :

    A uniform plane wave is a wave whose magnitude and phase are both constant. Electromagnetic waves in free space are typical uniform plane waves. The electric and magnetic fields are mutually perpendicular to each other and to the direction of propagation of the waves. The phases of the two fields are always in time phase and their magnitudes are always constant. The stored energies are equally divided between the two fields, and the energy flow is transmitted by the two fields in the direction of propagation. Thus a uniform plane wave is a transverse electromagnetic wave or a TEM wave.

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  32. Question 21. What Is Non-uniform Wave ?

    Answer :

    A non-uniform plane wave is a wave whose amplitude (not phase) may vary within a plane normal to the direction of propagation. Consequently, the electric and magnetic fields are no longer in time phase.

  33. Question 22. What Is Wave Propagation In Free Space?

    Answer :

    The electromagnetic wave being propagated in free space near the surface of the earth is divided into two parts: 

    1. Ground wave: Classified as direct wave, earth-reflected wave and surface wave
    2. Sky wave or ionosphere wave. 
  34. Question 23. What Are The Properties Of Tem Modes In A Lossless Medium?

    Answer :

    1. Its cutoff frequency is zero.
    2. Its transmission line is a two-conductor system.
    3. Its wave impedance is the impedance in an unbounded dielectric.
    4. Its propagation constant is the constant in an unbounded dielectric.
    5. Its phase velocity is the velocity of light in an unbounded dielectric.
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  36. Question 24. What Is Terminated Line?

    Answer :

    A transmission line terminated in its characteristic impedance Zo is called a properly terminated line. Otherwise it is called an improperly terminated line.

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  38. Question 25. What Is Dominant Mode?

    Answer :

    The mode having the lowest resonant frequency.

  39. Question 26. What Is Microwave Junction?

    Answer :

    The point of interconnection of two or more microwave devices is called a junction. Commonly used microwave junctions include such waveguide tees as the E-plane tee, H -plane tee, magic tee, hybrid ring (rat-race circuit), directional coupler and the circulator.

  40. Question 27. What Is Tee Junction?

    Answer :

    In microwave circuits a waveguide or coaxial-line junction with three independent ports is commonly referred to as a tee junction.

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  42. Question 28. What Is E-plane Tee (series Tee)?

    Answer :

    An £-plane tee is a waveguide tee in which the axis of its side arm is parallel to the E field of the main guide.

  43. Question 29. What Is H-plane Tee (shunt Tee)?

    Answer :

    An H-plane tee is a waveguide tee in which the axis of its side arm is “shunting” the E field or parallel to the H field of the main guide.

  44. Question 30. What Is Magic Tees (hybrid Tees)?

    Answer :

    A magic tee is a combination of the £-plane tee and H -plane tee.  The magic tee is commonly used for mixing, duplexing, and impedance measurements.

  45. Question 31. How To Use Waveguide Corners, Bends, And Twists?

    Answer :

    These are normally used to change the direction of the waveguide through an arbitrary angle.

  46. Question 32. What Is Waveguide Twist?

    Answer :

    Waveguide twists are used to change the plane of polarization of a propagating wave.

  47. Question 33. What Is Directional Couplers?

    Answer :

    A directional coupler is a four-port waveguide junction. Several types of directional couplers exist, such as a two-hole directional coupler, four-hole directional coupler, reverse-coupling directional coupler (Schwinger coupler), and Bethe-hole directional coupler.

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  49. Question 34. What Is Hybrid Couplers?

    Answer :

    Hybrid couplers are interdigitated microstrip couplers consisting of four parallel striplines with alternate lines tied together.  Hybrid couplers are frequently used as components in microwave systems or subsystems such as attenuators, balanced amplifiers, balanced mixers, modulators, discriminators, and phase shifters.

  50. Question 35. What Is Microwave Isolators?

    Answer :

    An isolator is a nonreciprocal transmission device that is used to isolate one component from reflections of other components in the transmission line.

  51. Question 36. Why Isolator Is Uniline?

    Answer :

    An ideal isolator completely absorbs the power for propagation in one direction and provides lossless transmission in the opposite direction. Thus the isolator is usually called uniline.

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  53. Question 37. How Does Isolator Increase Frequency Stability ?

    Answer :

    Isolators are generally used to improve the frequency stability of microwave generators, such as klystrons and magnetrons, in which the reflection from the load affects the generating frequency. In such cases, the isolator placed between the generator and load prevents the reflected power from the unmatched load from returning to the generator. As a result, the isolator maintains the frequency stability of the generator.

  54. Question 38. What Is Non Reciprocal Devices?

    Answer :

    Non reciprocal devices are defined as devices having different forward and reverse propagating characteristics.

  55. Question 39. What Is Cavity Resonator?

    Answer :

    It is a metallic enclosure that confines the electromagnetic energy. Some cavity resonators:  rectangular-cavity resonator, circular-cavity resonator, and reentrant-cavity resonator etc.

  56. Question 40. What Is The Need Of Quality Factor Q?

    Answer :

    Quality factor Q which is a measure of the frequency selectivity of a cavity.

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  58. Question 41. What Is The Function Of Input And Output Matching Networks?

    Answer :

    Input and output matching networks are needed to reduce undesired reflections and improve the power flow capabilities.

  59. Question 42. What Is Transferred Electron Effect?

    Answer :

    When GAAs is biased above a threshold value of the electric field, it exhibits a negative differential mobility. The electrons in the lower energy band will be transferred into the higher energy band. This behavior is called transferred electron effect.

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  61. Question 43. What Is Saturated Drift Velocity?

    Answer :

    Maximum velocity of charge carriers in a semiconductor is called saturation drift velocity.

  62. Question 44. What Is Homo- Junction Transistor?

    Answer :

    When the transistor junction is joined by two similar materials such as silicon- to silicon or germanium-to-germanium, it is called a homo junction transistor.

  63. Question 45. What Is Hetero Junction Transistor?

    Answer :

    When the transistor junction is joined by two different materials such as Ge to GaAs, then it is called a homo junction transistor.

  64. Question 46. What Is The Need Of Diffusion And Ion Implantation?

    Answer :

    Diffusion and ion implantation are the two processes used in controlling amounts of dopants in semiconductor fabrications.

  65. Question 47. What Is Insertion Loss?

    Answer :

    It is a measure of the loss of the energy in transmission through a line or device compared to the direct delivery of energy without the line or device.

  66. Question 48. What Is Unconditional Stability?

    Answer :

    It refers to the situation where amplifier remains stable for any passive source and load at the selected frequencies and bias conditions.

  67. Question 49. What Is Available Power Gain?

    Answer :

    Available power gain is defined as the power available from the microwave network to that of the product from the source.

  68. Question 50. What Is Power Gain Of An Amplifier?

    Answer :

    It is defined as the ratio of power delivered to the load to that of the power from the source into an amplifier.

  69. Question 51. What Is Reflection Loss?

    Answer :

    The reflection loss is a measure of power loss during transmission due to the reflection of the signal as a result of impedance mismatch.

  70. Question 52. What Is Zero Property Of S Matrix?

    Answer :

    It states that, “ for a passive lossless N- port network, the sum of the products of each term of any row or any column multiplied by the complex conjugate of the corresponding terms of any row or column is zero”.