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.
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:
o
it possess symmetric properties sij=sji
o
it possess unitary property
o
[s][s]*=[i]
3.
Write The Applications Of
Microwave Engineering?
Answer :
Following are the applications of
microwave engineering:
o
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.
o
More bandwidth can be realized at higher frequencies. Bandwidth is
critically important because available frequency bands in the electromagnetic
spectrum are being rapidly depleted.
o
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?
Answer :
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?
Answer :
The advantages of ABCD matrix are as follows-
o
They are used in power transmission lines
o
They are helpful in case of cascade networks.
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.
E.g.: TEE, HYBRID RING
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.
8.
What Are The Applications Of
Reflex Klystron?
Answer :
The main applications of a reflex
klystron are as follows:
o
Signal source in MW generator
o
Local oscillators in receivers
o
It is used in FM oscillator in low power MW links.
o
In parametric amplifier as pump source.
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.
10.
Give Two Examples For Two Port
Junctions?
Answer :
Following are the two examples of two
port junctions:
o
The junction of two rectangular guides of unequal height
o
A symmetrical junction consisting of two similar rectangular guides
joined by an Intermediate guide of greater width.
2.
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.
3.
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.
4.
What Are The Merits And
Demerits Of Microwaves?
Answer :
Due to above properties
microwaves have following advantages and disadvantages:
o
Due to line of sight propagation, a pair of antennas can be
aligned without interfering with another pair of aligned antennas.
o
Due to wide frequency bandwidth, high data transfer rate is possible.
o
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.
o
As they are not reflected by ionosphere, they can be used for space
transmission.
5.
What Are The Applications Of
Microwave?
Answer :
They are used in several
applications. Some of these are:
o
Communication (astronomy, satellite, WLAN, mobile,cellular, radar, TV
etc)
o
Remote sensing and navigation (prediction/monitoring/guidence- traffic
control, weather, missile, aircraft etc)
o
Medical applications (cautery imaging, heart stimulation, therapy etc)
6.
What Are The Reasons For Using
Microwave In Communication?
Answer :
o
Wider bandwidth due to higher frequency
o
Better resolution due to smaller wavelength
o
Higher speed of operation
o
Higher antenna gain (size reducing)
o
As the production of frequency in microwave range by natural
resources are less , it is more available and less crowed frequency
spectrum.
o
Lower interference due to lower signal crowding.
7.
What Is Velocity Of Microwave?
Answer :
All electromagnetic wave has velocity of light.
(Light,microwave,radio wave, infrared ray all are electromagnetic wave).
8.
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.
9.
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.
10.
What Are Boundary Conditions?
Answer :
There are four basic rules for
boundary conditions at the surface between two different materials:
o
The tangential components of electric field intensity are continuous
across the boundary.
o
The normal components of electric flux density are discontinuous at the
boundary by an amount equal to the surface-charge density on the boundary.
o
The tangential components of magnetic field intensity are discontinuous
at the boundary by an amount equal to the surface-current density on the
boundary.
o
The normal components of magnetic flux density are continuous across the
boundary.
o 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.
o
1.
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.
2.
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:
o
Ground wave: Classified as direct wave, earth-reflected wave and surface
wave
o
Sky wave or ionosphere wave.
3.
What Are The Properties Of Tem
Modes In A Lossless Medium?
Answer :
o
Its cutoff frequency is zero.
o
Its transmission line is a two-conductor system.
o
Its wave impedance is the impedance in an unbounded dielectric.
o
Its propagation constant is the constant in an unbounded dielectric.
o
Its phase velocity is the velocity of light in an unbounded dielectric.
4.
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.
5.
What Is Dominant Mode?
Answer :
The mode having the lowest resonant
frequency.
6.
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.
7.
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.
8.
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.
9.
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.
10.
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.
11.
How To Use Waveguide Corners,
Bends, And Twists?
Answer :
These are normally used to change the
direction of the waveguide through an arbitrary angle.
12.
What Is Waveguide Twist?
Answer :
Waveguide twists are used to change
the plane of polarization of a propagating wave.
13.
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.
14.
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.
15.
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.
16.
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.
17.
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.
18.
What Is Non Reciprocal
Devices?
Answer :
Non reciprocal devices are defined as
devices having different forward and reverse propagating characteristics.
19.
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.
20.
What Is The Need Of Quality
Factor Q?
Answer :
Quality factor Q which is a measure
of the frequency selectivity of a cavity.
21.
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.
22.
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.
23.
What Is Saturated Drift
Velocity?
Answer :
Maximum velocity of charge carriers
in a semiconductor is called saturation drift velocity.
24.
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.
25.
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.
26.
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.
27.
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.
28.
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.
29.
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.
30.
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.
31.
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.
32.
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”.
