Antenna all units

ANTENNAS &
MICROWAVE
ENGINEERING

Introduction to Microwave Systemsand Antennas
Antennas :-
Antenna is an electrical Device
which converts electrical Energy into
radio waves and Vice versa.
▪ Microwaves Microwave
frequencies range between
109 Hz (1 GHz) to 1000 GHz
with respective wavelengths of
30 to 0.03 cm.
▪ Radio frequency
The frequency at 1 m is 300 MHz.
(wavelengths above 1 m)

Types!
Wire Antennas – Monopole and Dipole
Yagi uda Antenna
ParabolicAntenna
Horn Antennas
Microstrip Antenna
Father of Antenna

MONOPOLE DIPOLE
PARABOLIC
Yagi
Microstrip Horn
Example
Pictures
of
Antenna

Isotropic antennas
Antenna Radiates Equally in all directions
Anisotropic antennas
anisotropic antenna is a
directional antenna; the power level is not the
same in all directions.

Physical conceptof radiation
▪ Radiation is a energy in the form of electromagnetic waves
or particles , travelling in the air

Radiation Pattern
▪ Graphical representation of the radiation
properties of the antenna as a function of space
coordinates.
▪ Refers to the directional (angular) dependence of
the strength of the radio waves from the antenna

▪ Practically energy radiated from an antenna does not have same
strength in all directions
▪ Its maybe more in one direction or zero in other direction.
▪ Radiation pattern of the antenna is expressed in terms of the
field strength (E) or Power
▪ Field radiation pattern & Power Radiation Pattern
Radiation Pattern

Radiation Pattern
Main Lobe
The main lobe, or main
beam, is the lobe
containing the
higher power.
Side Lobe
A radiation lobe in any
direction other than the
intended lobe (Main
lobe)
Back Lobe
The sidelobe in the opposite
direction from the main
lobe is called the
"backlobe".
FB Ratio
Main lobe max. Value to
back lobe .value ratio • The Front to Back Ratio (F/B Ratio) of an antenna is the
ratio of power radiated in the front/main radiation lobe
and the power radiated in the opposite direction (180
degrees from the main beam).

Near Field
Radiation field that is closed to the
antenna.
Power in this field is continusly
radiated and returned back to the
antenna
Energy Confined
(Very small amount Propogates)
Field Regions
Fair Field
Radiation field that is far from the
antenna.
Power the far field continues to
radiate outward and is never returned
to the antenna
Energy Propogates Infinity

Field Regions
▪ An antenna is usually subdivided into 3 regions.
• Reactive Near field, Radiating Nearfield(Fresnel Regions),Farfield
(Fraunhofer Regions)
➢ Reactive near field Reactive near field energy stored not radiated
λ= wavelength D= largest dimension of the antenna
➢ Radiating near field (Fresnel) Radiating near field (Fresnel) radiating
fields predominate pattern still depend on R radial component may still be
appreciable

Field Regions
➢ Far field Far field (Fraunhofer) field distribution
independent of R field components are essentially
transverse

Directivity
▪ The ratio of the maximum radiation intensity in a given direction
from the antenna to the radiation intensity averaged over all
directions.
▪ Directivity is a measure of maximum radiation intensity in
the particular direction.
▪ Directivity of an antenna is the ratio of radiation density in the direction of
maximum radiation to the radiation density averaged over all the directions.

Directivity of Antenna
▪ Directivity of Large Antenna
▪ Directivity of Small Antenna
D=
4∗
180
п
2
θ𝐸θ𝐻
Convert radiance to Degree =
Multiply By
𝟏𝟖𝟎
п
𝟐
Note: According to Elliott, a better
number to use in the Kraus formula is
32,400 (Eq. 2-271 in Balanis). In fact,
the 41,253 is really wrong (it is derived
assuming a rectangular beam footprint
instead of the correct elliptical one).

A antenna with low side lobes has HPBWof 220 and 230 in E- and H-
principal planes.

Gain
Gain of an antenna (in a given direction) is defined as
“the ratio of the intensity, in a given direction” to the
radiation intensity that would be obtained if the power
accepted by the antenna were radiated isotropically.
Ratio of transmit / Receive power in a particular
direction, to that of an isotropic antenna
Antenna gain indicates how strong a signal
an antenna can send or receive in a specified
direction.

Efficiency
▪ To describe how efficiently an antenna transmits and receives
RF signals
▪ The ratio of the total power radiated by an antenna to the total
input power received from the generator.

Polarisation
▪ Linear Polarisation
(change of electric field along one direction or single axis )
▪ Circular Polarisation
(change of electric field all directions & Magnitude of field components
equal in all directions)
▪ Elliptical Polarisation
(change of electric field all directions & Magnitude of field components not equal in all
directions)
Vertical Polarization
Horizontal Polarization
Orientation of Electric field is called polarisation

HPBW is the angle
between two vector
s from the pattern
orgin to the points
of the major lobe
where the radiation
intensity is
maximum.
HPBW
(Half Power Beam Width)
-3dB
-2dB
-1dB
HPBW
(Half Power Beam Width)

First Null Beam Width (FNBW)
is defined as the angular
difference between the two nulls
enclosing the main beam
Angle Between two null points of
Main Beam is called FNBW or
Null to Null Beam Width
FNBW = 2.25*HPBW
FNBW
(First Null Beam Width)

HPBW
(-3 dB) from the peak of
the main beam
Pattern decreases to -3 dB
at 77.7 and 102.3 degrees.
Hence the HPBW is
102.3-77.7 = 24.6 degrees.
FNBW – Null to Null
Beam Width
The pattern goes to
zero at 60 degrees and
120 degrees. Hence,
the Null-Null
Beamwidth is 120-
60=60 degrees.

Bandwidth
Bandwidth = [ (f2-f1) / f0 ] *100

TA parameter that describes how much noise an antenna
produces in a given environment.
The noise power received from an antenna at
temperature can be expressed in terms of the bandwidth (B)
the antenna (and its receiver) are operating over.
PTA =KTAB
Antenna Noise Temperature

K- Boltzmanns constant = 1.38x 10-23 J/K
TA - Antenna Temperature
Radiation Pattern

Impedancematching,
VSWR stands for Voltage Standing Wave Ratio, and is also referred to as
Standing Wave Ratio (SWR). VSWR is a function of the reflection coefficient,
which describes the power reflected from the antenna. If the reflection
coefficient is given by , then the VSWR is defined by the followingformula:
Reflection Coefficient

Friis transmission equation
Friss transmission formula used to obtain power received by the receiver

The power density p (in Watts per square meter) of the plane wave incident on the receive antenna a
distance R from the transmit antenna is given by:
If the transmit antenna has an antenna gain in the direction of the receive antenna given by then the
power density equation above becomes:
Assume now that the receive antenna has an effective aperture given by Then the power received by this
antenna is given by:
Since the effective aperture for any antenna can also be expressed as

The resulting received power can be written as:

A GSM1800 cell tower antenna is transmitting 20W of power in the frequency range of 1840 to
1845MHz. The gain of the antenna is 17dB. Find the power density at a distance of (a) 50m and (b)
300m in the direction of maximum radiation.

Aperture Efficiencyand Effective Area
The Effective antenna aperture/area is a theoretical value which is a measure of how effective an antenna is at
receiving power. The effective aperture/area can be calculated by knowing the gain of the receiving antenna.
Effective Aperture =Area over which the antenna extracts the power from the incident wave
Ae = Effective Antenna Aperture
λ = Wavelength = c/f (where f = frequency, C = speed of light)
G= Antenna gain (Linear Value)
Ae = Aphy * ή

Aperture Efficiencyand Effective Area
Ae = Aphy *η
η= Ae/ Aphy
η- Aperture Efficiency of the antenna
Always Effective aperture (Ae )less than the physical aperture (Aphy)

Link Budged& Link Margin
The difference betweenthe minimum received signal level and the actual received
power is called the link margin.
In a wireless communication system, the link margin (LKM), measured in dB, is the
difference between the minimum expected power received at the receiver's end, and the
receiver's sensitivity.
link budget, where each of the factors can be individually considered in terms of its net
effect on the received power
Link budget is a way of quantifying the link performance

Link Budged
The received power in an wireless link is determined by three factors: transmit power, transmitting antenna
gain, and receiving antenna gain.
‣If that power, minus the free space loss of the link path, is greater than the minimum received signal level
of the receiving radio, then a link is possible.
Path loss is defined (in dB) as

Examplelink budget calculation
Let’s estimate the feasibility of a 5 km link, with one access point and one
client radio.
The access point is connected to an antenna with 10 dBi gain, with a
transmitting power of 20 dBm and a receive sensitivity of -89 dBm.
The client is connected to an antenna with 14 dBi gain, with a transmitting
power of 15 dBm and a receive sensitivity of -82 dBm.
The cables in both systems are short, with a loss of 2dB at each side at the
2.4 GHz frequency of operation.

The access point is connected to an antenna with 10 dBi gain, with a transmitting power of 20 dBm
and a receive sensitivity of -89 dBm.
The client is connected to an antenna with 14 dBi gain, with a transmitting power of 15 dBm and a
receive sensitivity of -82 dBm.
The cables in both systems are short, with a loss of 2dB at each side at the 2.4 GHz frequency of
operation.

Link Budgetcalculation (AccessPoint to client)

Noise Characterization of a Receiver

The equivalent noise temperature of the receiver can be found as
The transmission line connecting the antenna to the receiver has a loss LT , and is at a physical
temperature Tp.
we find that the noise temperature of the transmission line (TL) and receiver (REC) cascade is
the noise temperature of the antenna is given

The noise power at the antenna terminals, which is also the noise power delivered to the transmission line, is
Si is the received power at the antenna terminals, then the input SNR at the antenna terminals is Si /Ni . The
output signal power is
where GSYS has been defined as a system power gain. The output noise power is

A 1 km long microwave link uses two antennas each having 30dB gain. If the power transmitted by
one antenna is 1 W at 3 GHz, the power received by the otherantenna is approximately

Considera lossless antenna with a directive gain of +6 dB. If 1 mW of power is fed to it the
total powerradiated by the antenna will be

For an 8 feet (2.4m) parabolic dish antenna operating at 4 GHz, the minimum distance required
for far field measurement is closest to

“ ▪ RADIATION MECHANISMS AND
DESIGN ASPECTS

Wire Antenna
▪ Dipole antenna,
▪ Monopole antenna,
▪ Helix antenna,
▪ Loop antenna

Dipole
Dipole consists of two terminals or poles into which radio frequency current flows.
The current and the associated voltage causes electromagnetic or radio signal to be radiated.
It is simply an open-circuited wire, fed at its center.

Centre fed with Various length
The current amplitude of such antenna is maximum at center and decreases uniformly to zero

Short Dipole
• A short dipole is a physically feasible dipole formed by two conductors with total length L
• L is very small compared to wavelength λ(A current element whose length is λ /50 < l < λ /10 is called
small dipole antenna )
• Two conducting wires feed at center of the dipoles
• The current is maximal at center and linearly decrease to zero.
• Consider current is flowing through the short dipole (same length) the it radiates one quarter of the
power.

Mono Pole
• A Monpole radiates only through the hemispherical surface which is above the reflecting plane
• Mono pole - Half of the radiated by a short dipole

Half Wave Dipole (λ/2 Dipole)
• Half wave Length ( λ/2 ) Dipole
• Hertz antenna
• Symmetrical antenna in which two ends are equal at potential relative to midpoint.
• Dipole is feed at centre there fore Maximum current at center .

WHY MICROSTRIP PATCH ANTENNA ?
▪ Possible to design any kind of shape depends upon application
▪ Impedance matching fairly simple.
▪ Microstrip patch antenna occupy a very small volume during installation (Compact Size)
▪ They are manufactured very inexpensively and easily using modern printed circuit technology.
APPLICATIONS
▪ Satellite & Microwave Communications
▪ Cellphone antennas & GPS antennas
▪ Radar & Military Applications
▪ Beam Steering and Forming
▪ Telemedicine applications

Merits and Demerits Microstrip Patch antenna
▪ Merits
▫ Conformability to a Shaped surface
▫ Capable to operate Multi band
▫ Compact Size & Low fabrication Cost
▫ Compatibility with integrated circuit technology and easy fabrication.
▫ Supports for Both Linear and Circular Polarization
▫ Demerits
▫ Narrow Bandwidth
▫ Less Gain and Efficiency
▫ Only used for microwave frequencies and above , because the substate become to
larger at low frequencies

Necessities of subsequent for Microstrip patch antenna design
▪ Selection of substrate type
▪ Substrate thickness
▪ Selection of patch shape
▪ Determining the Dimension of patch
▪ Type of Feeding mechanism
▪ Centered frequency

MICROSTRIP PATCH ANTENNA
▪ Microstrip patch antenna consists of three layers i.e. Ground plane, Substrate and
Patch.
▪ Radiating metallic patch mounted on top of dielectric substrate which has ground
plane on other side.
▪ The height of the substrate is denoted by h and 𝜀𝑟 represents its dielectric constant.
▪ A thicker substrate will increase the radiation power, reduce conductor loss and
improve Bandwidth.

Various shapes in Microstrip Patch antenna
▪ There are variety shapes of the patch of the antenna, but rectangular, square and
circular are the most common shapes.

Microstrip Feeding Techniques
a). Microstrip feeding
b). Microstrip inset feeding
c). Coaxial feeding
d). Aperture coupled feeding
e). Proximity coupled feeding
Microstrip Feeding Microstrip Inset Feeding Aperture Coupled Feeding Coaxial Feeding
Proximity Coupled Feeding

Fringing fields
Radiation from MSA can occurs from the fringing fields
between periphery of patch and ground plane
To Enhance the fringing fields from patch which account for
radiation width of patch is increased or dielectric constant is
decreased or substance thickness is increased
Radiations occurs two width sides of the antenna.
With decrease in εr Both L and W increase, which increases fringing fields and aperture area , hence both
Bandwidth and gain Increase

Fringing effect
▪ Fringing in this case makes the microstrip line look wider electrically compared
to its physical dimensions. Since some of the waves travel in the substrate and
some in air, an effective dielectric constant ε reff is introduced to account for
fringing and the wave propagation in the line

▪ Bandwidth is Inversional proportional to dielectric substrate
▪ Bandwidth is Directly proportional to substrate thickness h.
▪ Narrow Bandwidth
▪ The permittivity of the substrate controls the fringing fields
▪ Lower permittivity's have wider fringes and therefore better radiation.
▪ Decreasing the permittivity also increases the antenna’s Bandwidth and
Efficiency

Design Equations of Patch Antenna
▪ Calculation of the Width (W)
▪ Calculation of the Effective Dielectric Constant
▪ Calculation of the Effective length
▪ Calculation of the length extension ΔL
▪ Calculation of actual length of the patch

DesignEquations of Patch Antenna
1. Design a Rectangular microstrip patch antenna using a substrate with dielectric constant
of 2.2, h=0.1588cm so as to resonance at 900 MHz
Calculation of the Width (W)
W=(3 × 10^2) ÷ (2 × 900 × 10^6)(√(3.2 ÷ 2))
W=0.131761 metre (m)
W=131.76157Millimetre (mm)
Calculation of the Effective Dielectric Constant.
= ((2.2 + 1) ÷ 2) + ((2.2 - 1) ÷ 2)(1 + (12 × 1.588 ÷ 131.76157)^-0.5)
=3.777719

▪ Calculation of the Effective length
L eff =159.38
▪ Calculation of the length extension ΔL
▪ Calculation of actual length of the patch
L=111.699mm

Aperture Antenna
Aperture means to opening in an closed surface
• Slot Antenna
• Horn Antenna
• Reflector Antenna
• Lens Antenna

Slot Antenna
▪ A slot antenna consists of metal surface, Usually a flat
plate, with a slot cut.
▪ It has Longer distance communication with respect to
dipole antenna.
▪ It has enhanced impedance with space
▪ It has higher mechanical stability with respect to dipole
antenna

Slot Antenna
▪ A Slot Length is λ/2 is cut in the conducting sheet.
▪ The flat strip is take out of the slot can be treated as short dipole
▪ The complementary of the slot antenna is the dipole
▪ Slot antenna Perfectly conductor to E field (σ= ∞)
▪ Complementary Slot or Dipole Slot antenna Perfectly conductor to
H field (H= ∞)
▪ If Dipole is vertically placed ,Vertical Polarization or horizontally
place Horizontal Polarization.
▪ If slot is vertically place , it has Horizontal Polarization or Vice
versa

Slot Antenna
▪ For Horizontal polarization there is maximum
attenuation by earth. So signal cannot move long
distance and it have higher mechanical stability
▪ For Vertical Polarization , the signal can travel long
distance but lower mechanical stability
▪ Slot antenna with Horizontal slot it provides vertical
polarization, it has longer distance communication
with higher mechanical stability.

HORNAntenna
▪ Horn antenna are constructed by
flaring of wave guide.
▪ One End of the wave guide excited
and the other end is kept open.
▪ Improves Impedance matching.
▪ Utilized for Long Distance
communications.

HORNAntenna
▪ Flaring Done in the Direction of Electric
field
▪ Flaring Done in the Direction of Magnetic
field
▪ Flaring Done in along the both walls of
rectangular wave Guide
▪ Flaring Done uniformly

HORNAntenna
▪ L- flaring Length
▪ Өe-Flaring angle with E Plane
▪ 𝛿e- flaring difference

L- flaring Length
Өe-Flaring angle with E Plane
𝛿e- flaring difference
By neglecting 𝛿e
2
2 𝛿eL= A2 /4
L=A2 /8𝛿e

𝛿E < 0.25 λ & 𝛿H < 0.4 λ

Ap = AE * BH
AE =BH =λ = 1m therefore directivity of rectangular
horn is εap=0.6

Reflector Antenna:
• Modify the radiation pattern of a radiating element
• Backward Radiation eliminatedwith a plane sheet reflector
• Highly Directional antenna
• Long Distance communicationsuch as satellite communication
• → Active Element (Feed antenna )
• → Parasitic Element (Reflector antenna)

Types Reflector Antenna:
Plane Reflector
Corner Reflector
Parabolic Reflector

Advantages
Less cross polarization
Disadvantages
Difficult to use low noise application due to
isolation
Blockage Due to feed
Advantages
No Blockage
Disadvantages
Cross Polarization

Lens Antenna
➢ Consists of Electromagnetic lens with a feed
➢ Lens is parasitic element and feed is active element
➢ Converges spherical wave form to planner wave form
➢ Typically thicker and difficult to construct
➢ Advantage is blockage is not happening

• Lens is not an antenna it’s a parasitic
element thatis used to improve radiation
pattern
• SphericalWave to planner end at Sender
• Planner to Sphericalwave at receiver end
Transmitter Lens
Receiver Lens

➢ It consists of two types
▪ ConductingType of E Lens
▪ Dielectric Type
Accelerating
Deaccelerating

Advantages:-
More EM receivedwith Respect to Parabolic
Reflector
Higher Gain Comparedwith ParabolicReflector
No Blockage due to feed and Feed support
Low Noise
Disadvantages
Lens are heavy
Complex to construct
Costlier
Stepped Dielectric types

Loop Antenna
▪ A loop antenna is a coil carrying radio frequency
current.
▪ It may be in any shape such as circular, rectangular,
triangular, square or hexagonal according to the designer’s
convenience.
▪ Types
▫ Small Loop antennas
▫ Large Loop antennas

Small Loop Antenna
When overall length of loop is Less than λ/10 it is called small Loop antenna
For N umber of turns
N(2пr) < λ /10
Properties
Null at perpendicular to plane of loop
Less radiation resistance
Less radiation Efficiency
Large Loop Antenna
When overall length of loop is about λ it is called Large Loop antenna

APPLICATIONS
• HF
• VHF
• UHF
• Microwave frequency

Arrays
An array antenna is a set of multiple antennas (more
than one antennas) connected which work together as a
single antenna
➢ Increase the overall gain and directivity antenna
➢ Minor lobes are reduced much
➢ To improve the Signal to Noise Ratio (SNR)
Ant 1 Ant 2 Ant 3 Ant 4
Axis

Radiation Pattern of the array
Depends on following influences :-
1. Types of Individual Elements
2. Total number of elements
3. Orientation of elements
4. The relative displacement between the elements
5. The excitation amplitude and Phase of the individual elements
6. The relative pattern of the individual elements

Types of the array
▪ Broad side Array
▪ End fire array

Broadside arrays
Elements with equal space
Axis
900
900
00
1800
Maximum Radiation Pattern exists perpendicular to the axis

Ordinary End-fire Array
Elements with equal space
Axis
00
1800
900 900
Maximum radiation pattern exists along the axis

Array of Two Point sources
(i) Two point sources with currents of equal magnitude and same phase
(ii) Two point sources with currents of equal magnitude with opposite phase
(iii) Two point sources with currents of unequal magnitudes with opposite phase

Two Point sources with Equal in Magnitude and Phase

Two point sources with currents of equal magnitude with opposite phase

Unit IV
PASSIVE AND ACTIVE MICROWAVE DEVICES

DirectionalCoupler
A Directional coupler is a 4-port device that is used to sample a small amount of input signal power for
measurement purposes.
Port 1 is the input port, port 2 is the output port, port 3 is the coupled port and port 4 is the
isolated/terminated port.
When an input signal travels from port 1 to port 2, a part of this signal is coupled to port 3. The portion
of the power coupled to port 3 depends on the coupling value of the coupler being used.

if we use a 3 dB coupler, the power split between port 2 and port 3 would be 50%, however, if we use a 10
dB coupler, then this power split would be 9:1.
Port 4 of the directional coupler is known as the isolated port. In an ideal directional coupler, no signal
should appear at the isolated port, however practically, a small amount of power called back power is
obtained at Port 4.

Coupling FactorC
Directivity D
Isolation I
Three Characteristicsof Directional Coupler

HYBRID JUNCTIONS
Wave guide tees are 3-port components,It is used in microwave technologies when
power in wave guide need to be splitted or combined.
Tee—Junction:-
In a microwave circuits a waveguide with 3 independent ports is commonlyreferred
to as a TEE Junction.
They are used to connect a branch or section of the waveguide in serious or parallel
with the main waveguide transmissionline for providingmeans of splitting and also
of combining poweris a wave guide

E Plane Tee
The arms of rectangular waveguides make two ports called collinear ports i.e., Port1 and
Port2,
while the new one, Port3 is called as Side arm or E-arm.
This E-plane Tee is also called as Series Tee.
Here
Port 1 & Port 2 are collinear arm.
Port 3 is side arm.
Axis of its side arm is parallel to the electric field of main guide.
If power feed into port 3 is equal divided into arms 1 and 2. the output power appearing at
port 1 & Port 2 of collinear arm will be equal in magnitude and 180o out of phase with
each other.

If two inputs are feed into port 1 and port2 , The output wave at port 3 will be difference
between port 1 and port 2. its also known as differences.
H Plane Tee
• it is also called as shunt tee
• Axis of its side arm is parallel to the H field of main guide
Here
Port 1 & Port 2 are collinear arm.
Port 3 is side arm.
If power feed into port 3 is equal divided into arms 1 and 2. the output power appearing at
port 1 & Port 2 of collinear arm will be equal in magnitude and In phase with each other.
If two input waves are feed into port 1 & port 2, the output wave at port 3 will be In-phase
and additive.

The Schottky diode or Schottky Barrier Diode unlike
the semiconductor diode that has a P-N juntion, has an N-
Metal junction. These diodes are characterized by their
switching speed and low voltage drop when they are forward
biased (typically 0.25 to 0.4 volts).

For the construction of this diode semiconductor material normally doped with the N, the material
is combined with metals such as silver, gold, or platinum.
In this diode, there is no PN junction like other diodes but it has semiconductor to a metal junction.
•The metallic part of this diode functions as anode and N part is a cathode that mean current can
move from metallic part to semiconductor according to the conventionaldirection of the current.
•The Schottky barrier of this diode sources the high-speed switching and less loss of forward
biased voltage.
•The forward voltage required for diode depends on the metal and semiconductor material used.
Both N and P-type semiconductor material can be used to make Schottky barrier but forward
biased voltage for P-type material is less.
•With the decrement in forward biased voltage reverse leakage current increases that so voltage
value for P-type material is kept in the range of 0.5 to 0.7 volts.

The characteristic curve of Schottky diode is similar to the normal diode with the difference is that forward
biased voltage for Schottky diode is less than the general diode.
•The voltage drop for forward-biased Schottky diode is 0.2 to 0.3 volts while for a silicon diode is 0.6 to
0.7V.
•The reverse saturation current for Schottky diode is less than the normal diode.

PIN Diodes
A Pin diode is a special type of diode that contains an undoped intrinsic semiconductor between the p-
type semiconductor and n-type semiconductor regions.
It differs from a normal diode in the sense that it has an extra layer in between the p and the n
junctions. By an intrinsic layer, we mean a pure crystal of silicon or germanium without any doping in
it.
This layer does not conduct electric current well. The p-type and n-type layer is heavily doped as they
are used for ohmic contacts.

The working principle of the PIN diode exactly same as a normal diode. The main
difference is that the depletion region, because that normally exists between both the P & N
regions in a reverse biased or unbiased diode is larger. In any PN junction diode, the P
region contains holes as it has been doped to make sure that it has a majority of holes.
Likewise the N-region has been doped to hold excess electrons.
The layer between the P & N regions includes no charge carriers as any electrons or holes
merge As the depletion region of the diode has no charge carriers it works as an
insulator. The depletion region exists within a PIN diode, but if the PIN diode is forward
biased, then the carriers come into the depletion region and as the two carrier types get
together, the flow of current will starts.

When the PIN diode is connected in forward biased, the charge carriers are very much higher than the
level of intrinsic carrier’s attention. Due to this reason the electric field and the high level injection
level extends deeply into the region.
This electric field assists in speeding up of the moving of charge carriers from P to N region, which
consequences in quicker operation of the PIN diode, making it an appropriate device for high
frequency operations.

When the diode is kept forward biased, the charges are continuously injected into the I-region
from the P and N-region. This reduces the forward resistance of the diode, and it behaves like a
variable resistance.
The charge carrier which enters from P and N-region into the i-region are not immediately
combined into the intrinsic region. The finite quantity of charge stored in the intrinsic region
decreases their resistivity.
Consider the Q be the quantity of charge stored in the depletion region. The τ be the time used
for the recombination of the charges. The quantity of the charges stored in the intrinsic region
depends on their recombination time. The forward current starts flowing into the I region.
Forward Bias

Reverse Bias
When the reverse voltage is applied across the diode, the width of the depletion region increases. The
thickness of the region increases until the entire mobile charge carrier of the I-region swept away from
it. The reverse voltage requires for removing the complete charge carrier from the I-region is known as
the swept voltage.
In reverse bias, the diode behaves like a capacitor. The P and N region acts as the positive and
negative plates of the capacitor, and the intrinsic region is the insulator between the plates.

Gunn Diodes
Gunn diodes are fabricated from a single piece of n-type semiconductor. The most common materials
are gallium Arsenide, GaAs and Indium Phosphide, InP. However other materials including Ge, CdTe,
InAs, InSb, ZnSe). and others have been used. The device is simply an n-type bar with n+ contacts. It
is necessary to use n-type material because the transferred electron effect is only applicable to
electrons and not holes found in a p-type material.

186
• As the field increases, the
electron drift velocity in
gallium arsenide reaches a
peak and then decreases.
• As the E-field increases, the
energy of the electron
increases & the electron can
be scattered into the upper
valley, where the density of
states effective mass is 0.55
m0

Transferred Electron Devices (Gunn Diode)
E(GaAs) = 0.31 eV
Effective Mass increases
upon transfer under bias

On applying a DC voltage across the terminalsof the Gunndiode, an electric field is developed
across its layers, most of which appears across thecentral active region. At initial stages, the
conduction increases due to the movement of electrons from the valence bandinto the lower valley
of theconduction band.
Theassociated V-I plot is shown by the curve in the Region 1 (colored in pink) of Figure 2. However,
after reaching a certain threshold value (Vth), the conduction current through the Gunndiode
decreases as shown by thecurve in the Region 2 (colored in blue)
This is because, at higher voltages the electrons in the lower valley of the conduction band move into
its higher valley where their mobility decreases due to an increase in their effective mass. The
reduction in mobility decreases the conductivity which leads to a decrease in the curren flowing
through the diode.
As a result the diode is said to exhibit negative resistance region (region spanning from Peak point to
Valley Point) in the V-I characteristic curve. This effect is called transferred electron effect and thus
the Gunndiodes are also called Transferred Electron Devices.

For the generation and amplification of Microwaves, there is a need of some special tubes called
as Microwave tubes.
Klystron majorly consists of two elements
➢ Electron beams and
➢ Cavity resonators
➢ Electron beams are produced from a source and the cavity klystrons are employed to amplify
the signals.
➢ A collector is present at the end to collect the electrons.
Microwave Tubes

The electrons emitted by the cathode are accelerated towards the first resonator. The collector at the end is at
the same potential as the resonator.
Hence, usually the electrons have a constant speed in the gap between the cavity resonators.
Initially, the first cavity resonator is supplied with a weak high frequency signal, which has to be amplified.
The signal will initiate an electromagnetic field inside the cavity.

➢ Themagnetron is a high-powered vacuum tube that works as a self-excited
microwave oscillator.
➢ Thisis multi Cavity Device
➢ Its available with 8 to 20 cavity mdoel
➢ Crossed electron and magnetic fields are used in the magnetron to produce the high-
power output required in radar equipment.
➢ Frequency 0.6GHZto30 GHZ
Magnetron

➢ There are 8 cavities
➢ All cavity are 180 degree phase shift each
other
➢ Coaxial connection used to feed RF Input
➢ Cathode is connected with filaments

Magnetic field is zero from cathode to anode cavity
electron will directly move.
Magnetic field which excite F this much amount of
force so electron tilted.

Unit V
MICROWAVE DESIGN PRINCIPLES

RF and Microwave Amplifier Design,

Low-Noise Amplifier Design
Besides stability and gain, another important design consideration for a microwave amplifier is its noise
figure.
In receiver applications especially it is often required to have a preamplifier with as low a noise figure as
possible since
the first stage of a receiver front end has the dominant effect on the noise performance of the overall
system.
Generally it is not possible to obtain both minimum noise figure and maximum gain for an amplifier, so
some sort of compromise must be made.
This can be done by using constant-gain circles and circles of constant noise figure to select a usable
trade-off between noise figure and gain
the noise figure of a two-port amplifier can be expressed as

Microwave Mixer
➢ Microwave Mixer is a device that performs the task of frequency conversion, by multiplying two signals
➢ A mixer is a three-port component,which performs the task of frequency conversion. Mixers
translate the frequency of an input signal to a different frequency.
➢ This functionality is vital for a wide range of applications, including military radar, satellite-
communications (satcom), cellular base stations, and more.
➢ Mixers are used to perform both frequency up conversion and down conversion.

➢ Two ports serve as inputs, while the third port serves as an output port. An ideal mixer produces an
output that consists of the sum and difference frequencies of its two input signals.
fout = fin1 ± fin2
➢ The three ports of a mixer are known as the intermediate-frequency (IF), radio-frequency (RF), and
local-oscillator (LO) ports. The LO port is usually an input port.
➢ The RF and IF ports can be used interchangeably, depending on whether the mixer is being used to
perform up conversion or down conversion.
➢ The LO signal is typically the strongest signal injected into a mixer.
Down Conversion
➢ An input signal enters the RF port and an LO signal enters the LO port. These two input signals
produce an output signal at the IF port.
➢ The frequency of this output signal is equal to the difference of the RF input signal’s frequency and
the LO signal’s frequency.

An input signal enters the IF port and an LO signal enters the LOport.
These two input signals produce an output signal at the RF port. The frequency of this output
signal is equal to the sum of the IF input signal’s frequency andthe LOsignal’s frequency.

Single Diode Mixer (Single Ended Diode Mixer)
The simplest mixer consists of a single diode with a large signal LO and a small signal RF combine at the
anode
An “ideal” single diode mixer assumes that the LO is significantly stronger than the RF such that only
the LO affects the diode’s transconductance.
The “mixing” process is due to the switching response of the diode I-V curve to the strong LO signal. As
the diode is opened and closed by the LO, the smaller signal RF is “chopped”.
fIF = nfLO + fIF

Single-Ended FET Mixer
There are several FET parameters that offer nonlinearities that can be used for mixing, but the strongest is the
transconductance,gm, when the FET is operated in a common source configuration with a negative gate bias.
Fig shows the variation of transconductance with gate bias for a typical FET. When used as an amplifier, the
gate bias voltage is chosen near zero, or slightly positive, so the transconductance is near its maximum value,
and the transistor operates as a linear device.
When the gate bias is near the pinch-off region, where the transconductance approaches zero, a small positive
variation of gate voltage can cause a large change in transconductance, leading to a nonlinear response.

BalancedMixer
➢ RF input matching and RF-LO isolation can be improved through the use of a balanced mixer, which
consists of two single-ended mixers combined with a hybrid junction.
➢ The basic configuration, with either a 90◦ hybrid or a 180◦ hybrid junction
➢ a balanced mixer using a 90◦ hybrid junction will ideally lead to a perfect input match at the RF port
over a wide frequency range, while the use of a 180◦ hybrid will ideally lead to perfect RF-LO
isolation over a wide frequency range.
➢ In addition, both mixers will reject all even-order intermodulation products

Double Balanced Mixer
It provides good isolation between all three ports, as well as rejection of all even harmonics of
the RF and LO signals.
This leads to very good conversion loss, but less than ideal input matching at the RF port. The
double-balanced mixer also provides a higher third-order intercept point than either a single-
ended mixer or a balanced mixer.

Microwave Oscillator
Oscillator

Transistor Oscillatorsor Two Port Oscillator Design
The circuit model of a transistor oscillator is shown in Figure
In this circuit, the RF output port is part of the load network on the output side of the transistor, but
it is also possible to use the terminating network to the left of the transistor as the output port.
In the case of an amplifier, we preferred a device with a high degree

Thanks!
Any questions?
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