B & B Institute of Technology-Vallabh Vidyanagar

Electronics & Communication Engineering Department

Microwave & Radar Communication (4351103)

Notes
Unit-2:- Microwave Propagation and Components

(1) Transmission Line and Waveguide comparison.

Feature Transmission Line Waveguide

Consists of two conductors (e.g.,

Structure Typically, a hollow metallic tube
coaxial cable, twisted pair)

Supports TE (Transverse Electric) and TM

Modes of Supports TEM (Transverse
(Transverse Magnetic) modes, but not TEM
Propagation Electromagnetic) mode
mode

Can transmit all frequencies, Primarily used for microwave frequencies

Frequency
typically effective up to several (above 1 GHz) and only above a certain cut-off
Range
GHz frequency

Power Generally lower power handling High power handling capacity due to larger
Handling capacity surface area

Reflections occur from the walls of the

Reflections occur mainly due to
Reflections waveguide; less susceptible to reflections
impedance mismatches
overall

Characteristic impedance is
Wave impedance is frequency-dependent and
Impedance defined and varies with physical
varies with the mode of propagation
parameters

Bandwidth Typically has a wider bandwidth Limited bandwidth due to cut-off frequencies

Lower dielectric and conductor losses, making

Higher dielectric and conductor
Losses them more efficient for high-frequency
losses
applications

Used in RF communication, audio Used in radar, satellite communications, and

Applications signals, and general data microwave transmission due to their efficiency
transmission at high frequencies

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(2) Propagation of microwaves through waveguide and derivation of the cut off
wavelength.

Figure 1 - Plane waves at a conducting surface

Consider Figure 1, which shows wave fronts incident on a perfectly conducting plane (for
simplicity, reflection is not shown). The waves travel diagonally from left to right, as indicated, and
have an angle of incidence θ.

If the actual velocity of the waves is Vc, then simple trigonometry shows that the velocity of the
wave in a direction parallel to the conducting surface Vg and the velocity normal to the wall, Vn
respectively, are given by,
𝑽𝒈 = 𝑽𝒄 𝐬𝐢𝐧 𝜽 (1)
𝑽𝒏 = 𝑽𝒄 𝐜𝐨𝐬 𝜽 (2)

As should have been expected, Equations (1) and (2) show that waves travel forward more slowly
in a waveguide than in free space. In Figure 1, it is seen that the wavelength in the direction of
propagation of the wave is shown as λ, being the distance between two consecutive wave crests in
this direction.

The distance between two consecutive crests in the direction parallel to the conducting plane, or
the wavelength in that direction is λp, and the wavelength at right angles to the surface is λn. So,
𝝀 𝝀
𝝀𝒑 = 𝐬𝐢𝐧 𝜽 (3) 𝝀𝒏 = 𝐜𝐨𝐬 𝜽 (4)
This shows not only that wavelength depends on the direction in which it is measured, but also
that it is greater when measured in some direction other than the direction of propagation.
The velocity of light, 𝑽𝒄 = 𝝀 𝒇 (5)

For Figure 1, it is indicated that the velocity of propagation in a direction parallel to the conducting
surface is 𝑉𝑔 = 𝑉𝑐 sin 𝜃, as given by Equation 1. It is also shown that the wavelength in this
𝜆
direction is 𝜆𝑝 = sin 𝜃 given by Equation 3.

If the frequency is f, it follows that the velocity (called the phase velocity) with which the wave
changes phase in a direction parallel to the conducting surface is given by the product of the two.
𝝀𝒇 𝑽𝒄
Thus, phase velocity 𝑽𝒑 = 𝝀𝒑 𝒇 = 𝐬𝐢𝐧 𝜽 = 𝐬𝐢𝐧 𝜽 (6)

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 Figure 2 - Placement of second short circuit on transmission line

Three suitable positions for the second short circuit are indicated in Figure 2. It is seen that ·each
of them is at a point of zero voltage on the line, and each is located at a distance from the first
short circuit that is a multiple of half-wavelengths.

The presence of a reflecting wall does to electromagnetic waves what a short circuit did to waves
on a transmission line. A pattern is set up and will be destroyed unless the second wall is placed in
a correct position.

Figure 3 - Reflections in a parallel-plane waveguide

The situation is illustrated in Figure 3, which shows the second wall, placed three half-
wavelengths away from the fast wall, and the resulting wave pattern between the two walls.

In waveguide, the wavelength normal to the walls is not the same as in free space, and thus 3λn/2
here, as indicated. Here "the signal arranges itself so that the distance between the walls becomes
an integral number of half-wavelengths." The arrangement is accomplished by a change in the
angle of incidence, so as long as this angle is not required to be ''more perpendicular than 90°."

2𝜆𝑛 𝜆𝑛
Here, the second wall might have been placed (as indicated) so that 𝑎′ = or 𝑎′′ = without
2 2
upsetting the pattern created by the first wall.

If a second wall is added to the first at a distance “a” from it, then it must be placed at a point
where the electric intensity due to the first wall is zero, i.e., at an integral number of half-
wavelengths away.

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 𝒎𝝀𝒏
Putting this mathematically, we have 𝒂 = (7), where
𝟐
a = distance between walls
𝜆𝑛 = wavelength in a direction normal to both walls
m = number of half-wavelengths of electric intensity to be established between the walls (an integer)

𝑚𝜆 𝒎𝝀
Substituting for 𝜆𝑛 from Equation (4) gives 𝑎 = 2 cos 𝜃 , so 𝐜𝐨𝐬 𝜽 = (8)
𝟐𝒂

Equation (8) shows that for a given wall separation, the angle of incidence is determined by the
free-space wavelength of the signal, the integer m and the distance between the walls. It is now
possible to use Equation (8) to eliminate 𝜆𝑛 from Equation (3), giving a more useful expression
for𝜆𝑝, the wavelength of the travelling wave which propagates down the waveguide.

𝝀 𝝀 𝝀
We then have 𝝀𝒑 = 𝐬𝐢𝐧 𝜽 = = (9)
𝟏−𝒄𝒐𝒔𝟐 𝜽 𝒎𝝀 𝟐
𝟏−
𝟐𝒂

From Equation (9), it is easy to see that as the free-space wavelength is increased, there comes a
point beyond which the wave can no longer propagate in a waveguide with fixed a and m.

The free-space wavelength at which this takes place is called the cut-off wavelength and is defined
as the smallest free-space wavelength that is just unable to propagate in the waveguide under
given conditions.

This implies that any larger free-space wavelength certainly cannot propagate, but that all smaller
ones can. From Equation (9), the cut-off wavelength is that value of λ for which λp becomes
infinite, under which circumstances the denominator of Equation (9) becomes zero, giving

𝒎𝝀𝒐 𝟐 𝒎𝝀𝒐 𝟐𝒂
𝟏− =𝟎 =𝟏 𝝀𝒐 = (10)
𝟐𝒂 𝟐𝒂 𝒎

Where λ0 = cut-off wavelength. The largest value of cut-off wavelength is 2a, when m = 1. This
means that the longest free-space wavelength that a signal may have and still be capable of
propagating in a parallel-plane waveguide, is just less than twice the wall separation.

(3) Definitions (i) Cut-off wavelength (ii) Guided Wavelength (iii) Dominant Mode (iv)
Group Velocity (v) Phase Velocity (vi) Characteristics wave impedance (vii) TE & TM
modes (viii) S Parameters

(i) Cut-off wavelength

 The cut-off wavelength (𝜆𝑜 or 𝜆𝑐) is the longest wavelength at which a mode can propagate in a
waveguide. For wavelengths above the cut-off wavelength, the mode will not propagate and will
instead attenuate.

 For a rectangular waveguide, the cut-off wavelength for a given mode can be calculated using,
2𝑎
𝜆𝑐 = Where ‘a’ is the width of the waveguide and m is the mode number (for example, for the
𝑚
dominant TE10 mode, m=1).

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(ii) Guided Wavelength

 The guided wavelength (often denoted as λg) refers to the distance that a wave travels in a
waveguide to undergo a phase shift of 2π radians. This concept is essential for understanding how
electromagnetic waves propagate within waveguides.

 The guided wavelength is always longer than the wavelength in free space. This difference arises
due to the boundary conditions imposed by the waveguide structure, which affects how
electromagnetic waves propagate.

𝜆
 Mathematically, 𝜆𝑔 =
𝜆 2
1−
𝜆𝑐

(iii) Dominant Mode

 The dominant mode refers to the mode of propagation in a waveguide that has the lowest cut-off
frequency or the highest cut-off wavelength. This mode is crucial because it allows for the most
efficient transmission of microwave signals with minimal attenuation.

 In rectangular waveguides, the dominant mode is typically the TE10 mode. In circular waveguides,
the dominant mode is often the TE11 mode.

(iv) Group Velocity

 Group velocity is defined as the velocity at which the envelope of a wave packet or group of waves
travels through a medium. It is particularly relevant in the context of wave propagation in
dispersive media, where different frequencies travel at different speeds.
𝑑𝜔
 Mathematically, the group velocity can be expressed as, 𝑉𝑔 = , Where ω is the angular
𝑑𝑘
frequency and k is the wave number.
𝜆 2
 Also, 𝑉𝑔 = 𝑉𝑐 1 − 𝜆𝑐

 The group velocity is significant in telecommunications and optics, as it determines how quickly
information can be transmitted through a medium.

(v) Phase Velocity

 Phase velocity is the speed at which a particular phase of the wave propagates through space. It is
𝑑𝜔
defined as the ratio of the angular frequency to the wave number,𝑉𝑝 = where ω is the angular
𝑑𝑘
frequency and k is the wave number.

𝑉𝑐
 Also, 𝑉𝑝 =
𝜆 2
1−
𝜆𝑐

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(vi) Characteristics wave impedance

 Characteristic wave impedance refers to the impedance associated with the propagation of
electromagnetic waves in a waveguide. It is defined as the ratio of the electric field to the
magnetic field in the transverse direction of the waveguide.

120𝜋
 Mathematically, 𝑍𝑜 =
𝜆 2
1−
𝜆𝑐

 Where 120𝜋 is characteristic wave impedance of free space

(vii) TE & TM modes

 In TE (Transverse Electric) Modes, the electric field is entirely transverse to the direction of
propagation, meaning there is no electric field component in the direction of wave travel (z-
direction).
 However, the magnetic field can have a component along the direction of propagation.

 The electric field component Ez is zero: Ez=0 & Hz≠0

 In TM (Transverse Magnetic) modes, the magnetic field is entirely transverse to the direction of
propagation, meaning there is no magnetic field component in the direction of wave travel.

 The electric field can have a component along the direction of propagation.

 The magnetic field component Hz is zero: Hz=0 & Ez≠0

(viii) S Parameters

 S-parameters, or scattering parameters, are a set of measurements that describe the electrical
behaviour of linear electrical networks when subjected to high-frequency signals. They are
particularly useful for analyzing the performance of RF (radio frequency) and microwave circuits.

 S-parameters characterize the relationship between incident and reflected power waves at the
ports of a network. Each S-parameter is a complex number that represents the amplitude and
phase of the wave.

𝑆11 𝑆12
 For a two-port network, the S-parameter matrix is represented as:
𝑆22 𝑆21

S11: Reflection coefficient at port 1 (input power reflected back).

S21: Forward transmission coefficient from port 1 to port 2.
S12: Reverse transmission coefficient from port 2 to port 1.
S22: Reflection coefficient at port 2.

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(4) TEM mode cannot be propagated in a rectangular waveguide. Reasons.

The TEM (Transverse Electromagnetic) mode cannot propagate in a hollow rectangular waveguide
for the following reasons:

 Field Configuration: TEM mode requires both the electric field (E) and magnetic field (H) to be
entirely transverse (no longitudinal components). In a hollow rectangular waveguide, there is no
central conductor to support this configuration.

 Cut-Off Frequency: TEM mode has a cut-off frequency of zero, meaning it can theoretically
propagate at any frequency. However, waveguides need a structure that supports non-zero cut-off
frequencies, which is not possible for TEM in a hollow waveguide.

 Waveguide Structure: A rectangular waveguide is a hollow metallic tube without a central

conductor, making it impossible to establish the necessary electric and magnetic fields for TEM
propagation.

 Mode Support: Rectangular waveguides can only support TE (Transverse Electric) and TM
(Transverse Magnetic) modes because these modes allow for one field component to exist along
the direction of propagation.

 In summary, TEM mode cannot propagate in a hollow rectangular waveguide due to the absence
of a central conductor and the structural limitations that only allow TE and TM modes.

(5) Draw TE10, TE20 and TE30 modes for rectangular waveguide.

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 (6) Comparison of rectangular and circular waveguides.

Feature Rectangular Waveguide Circular Waveguide

Hollow metallic tube with a Hollow metallic tube with a circular
Shape
rectangular cross-section cross-section
Dominant Mode TE10 mode TE11 mode
Defined by dimensions (a, b) with Defined by radius (a) with specific
Cut-Off Frequency
specific modes (e.g., TE10, TE11) modes (e.g., TE11, TM01)
Varies based on mode; e.g., TE11 has
Varies based on mode; e.g., TE10 has a
Cut-Off Wavelength a cut-off wavelength of 1.706d,
cut-off wavelength of 2a
where d is the diameter
Supports TE and TM modes; no TEM
Mode Support Supports TE and TM modes
mode
Manufacturing Generally more complex due to
Easier to manufacture
Complexity precise dimensions
Polarization Can support different polarizations Limited polarization control
Commonly used in radar, couplers, Used in applications requiring
Applications
isolators rotational symmetry and low loss
Typically lower attenuation for given Generally low attenuation but can
Attenuation
dimensions and frequencies vary with mode
Larger size for the same frequency
Smaller size for specific frequencies
Size for Given Frequency compared to rectangular
compared to circular waveguides
waveguides

(7) Isolator

 An isolator is a two-port device that transmits microwave or radio frequency power in one
direction only. The non-reciprocity observed in these devices usually comes from the interaction
between the propagating wave and the material, which can be different with respect to the
direction of propagation.

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 It is used to shield equipment on its input side, from the effects of conditions on its output side;
for example, to prevent a microwave source being detuned by a mismatched load.

 An isolator is a non-reciprocal device, with a non-symmetric scattering matrix. An ideal isolator

transmits all the power entering port 1 to port 2, while absorbing all the power entering port 2, so
that to within a phase-factor its S-matrix is
0 0
𝑆=
1 0

 To achieve non-reciprocity, an isolator must necessarily incorporate a non-reciprocal material.

 At microwave frequencies, this material is usually a ferrite which is biased by a static magnetic
field but can be a self-biased material. Isolators are typically constructed with Ferrite Material.

 This material exhibits unique magnetic properties that allow it to interact differently with signals
depending on their direction of travel. The ferrite is often biased by a static magnetic field, which
enhances its non-reciprocal behaviour.

 The ferrite is positioned within the isolator such that the microwave signal presents it with a
rotating magnetic field, with the rotation axis aligned with the direction of the static bias field. The
behaviour of the ferrite depends on the sense of rotation with respect to the bias field, and hence
is different for microwave signals travelling in opposite directions.

 Depending on the exact operating conditions, the signal travelling in one direction may either be
phase-shifted, displaced from the ferrite or absorbed.

(8) Circulator

 A circulator is a non-reciprocal passive microwave device that allows microwave signals to flow in
a specific direction among its ports. The fundamental principle behind a circulator is based on the
Faraday rotation effect, where the polarization plane of electromagnetic waves is rotated when
they pass through a magnetized ferrite material. This rotation ensures that a signal entering one
port exits through the next port in a predetermined sequence, effectively preventing any signal
from returning to its source.

 Circulators can be constructed in various configurations; most common designs include typically
three or four ports arranged at equal angles (120° for three-port and 90 ° for four-ports).

 Ferrite Material: A ferrite disk or rod is used to provide the necessary Faraday rotation. The ferrite
is placed in a magnetic field created by permanent magnets.

 Waveguide or Microstrip Configuration: Circulators can be designed as waveguide devices or

microstrip circuits on printed circuit boards.

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 Working of Circulator

 Signal Input: When a microwave signal is applied to one port (e.g., Port 1), it travels through the
ferrite material.

 Faraday rotation: As the signal passes through the ferrite under the influence of the magnetic
field, its polarization rotates by 45° (or another specified angle depending on design).

 Directional Propagation: The rotated signal exits through the next adjacent port (e.g., Port 2). This
process continues such that: A signal entering Port 2 exits through Port 3, A signal entering Port 3
exits back to Port 1.

 Isolation from Reflections: If any reflections occur at one port, they are absorbed or redirected
due to the circulator's design, ensuring they do not return to the original input port.

 Non-reciprocal Behaviour: Signals can only travel in one direction among ports.

 Isolation Levels: Typically provides isolation ranging from 10 dB to 25 dB, depending on design and
frequency.

Applications of Circulators

 Transmitter-Receiver Systems: In radar and communication systems, circulators facilitate

simultaneous transmission and reception by directing signals appropriately.

 Signal Routing: They are used for routing signals in complex RF systems without interference.

 Protective Devices: Circulators can protect sensitive components from reflected signals, similar to
isolators.

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(9) E-Plane Tee & H-Plane Tee.

 An E-Plane Tee junction is formed by attaching a simple waveguide to the broader dimension of a
rectangular waveguide, which already has two ports.

 The arms of rectangular waveguides make two ports called collinear ports i.e., Port 1 and Port 2,
while the new one, Port 3 is called as Side arm or E-arm.

 This E-plane Tee is also called as Series Tee.

 As the axis of the side arm is parallel to the electric field, this junction is called E-Plane Tee
junction. This is also called as Voltage or Series junction. The ports 1 and 2 are 180° out of phase
with each other.

 An H-Plane Tee junction is formed by attaching a simple waveguide to a rectangular waveguide

which already has two ports.

 The arms of rectangular waveguides make two ports called collinear ports i.e., Port 1 and Port 2,
while the new one, Port 3 is called as Side arm or H-arm.

 This H-plane Tee is also called as Shunt Tee.

 As the axis of the side arm is parallel to the magnetic field, this junction is called H-Plane Tee
junction. This is also called as Current junction, as the magnetic field divides itself into arms.

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(10) Magic Tee / Hybrid Tee/ E-H Plane Tee

 An E-H Plane Tee / Hybrid Tee / Magic Tee junction is formed by attaching two simple waveguides
one parallel and the other series, to a rectangular waveguide which already has two ports.

 This is also called as Magic Tee, or Hybrid or 3dB coupler.

 The arms of rectangular waveguides make two ports called collinear ports i.e., Port 1 and Port 2,
while the Port 3 is called as H-Arm or Sum port or Parallel port.

 Port 4 is called as E-Arm or Difference port or Series port.

 The cross-sectional details of Magic Tee can be understood by the following figure.

 The following figure shows the connection made by the side arms to the bi-directional waveguide
to form both parallel and serial ports.

Characteristics of Magic Tee

 If a signal of equal phase and magnitude is sent to port 1 and port 2, then the output at port 4 is
zero and the output at port 3 will be the additive of both the ports 1 and 2.

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 If a signal is sent to port 4, E−arm then the power is divided between port 1 and 2 equally but in
opposite phase, while there would be no output at port 3. Hence, S34 = 0.

 If a signal is fed at port 3, then the power is divided between port 1 and 2 equally, while there
would be no output at port 4. Hence, S43 = 0.

 If a signal is fed at one of the collinear ports, then there appears no output at the other collinear
port, as the E-arm produces a phase delay and the H-arm produces a phase advance. So, S12 = S21
= 0.

Applications of Magic Tee

 Magic Tee is used to measure the impedance − A null detector is connected to E-Arm port while
the Microwave source is connected to H-Arm port. The collinear ports together with these ports
make a bridge and the impedance measurement is done by balancing the bridge.

 Magic Tee is used as a duplexer − A duplexer is a circuit which works as both the transmitter and
the receiver, using a single antenna for both purposes. Port 1 and 2 are used as receiver and
transmitter where they are isolated and hence will not interfere. Antenna is connected to E-Arm
port. A matched load is connected to H-Arm port, which provides no reflections. Now, there exists
transmission or reception without any problem.

 Magic Tee is used as a mixer − E-Arm port is connected with antenna and the H-Arm port is
connected with local oscillator. Port 2 has a matched load which has no reflections and port 1 has
the mixer circuit, which gets half of the signal power and half of the oscillator power to produce IF
frequency.

(11) Hybrid Ring

 This microwave device is used when there is a need to combine two signals with no phase
difference and to avoid the signals with a path difference.

 A normal three-port Tee junction is taken and a fourth port is added to it, to make it a rat race
junction.

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 All of these ports are connected in angular ring forms at equal intervals using series or parallel
junctions.

 The mean circumference of total race is 1.5λ and each of the four ports is separated by a distance
of λ/4. The following figure shows the image of a Rat-race junction.

 Let us consider a few cases to understand the operation of a Rat-race junction.

Case 1
 If the input power is applied at port 1, it gets equally split into two ports, but in clockwise direction
for port 2 and anti-clockwise direction for port 4. Port 3 has absolutely no output.

 The reason being, at ports 2 and 4 the powers combine in phase, whereas at port 3, cancellation
occurs due to λ/2 path difference.

Case 2
 If the input power is applied at port 3, the power gets equally divided between port 2 and port 4.
But there will be no output at port 1.

Case 3
 If two unequal signals are applied at port 1 itself, then the output will be proportional to the sum
of the two input signals, which is divided between port 2 and 4. Now at port 3, the differential
output appears.

Applications
 Rat-race junction is used for combining two signals and dividing a signal into two halves.

(12) Two-hole Directional Coupler

 A Directional coupler is a device that samples a small amount of Microwave power for
measurement purposes.

 Directional coupler is used to couple the Microwave power which may be unidirectional or bi-
directional.

 This is a directional coupler with same main and auxiliary waveguides, but with two small holes
that are common between them.

 These holes are λg/4 distance apart where λg is the guide wavelength. The following figure shows
the image of a two-hole directional coupler.

 A two-hole directional coupler is designed to meet the ideal requirement of directional coupler,
which is to avoid back power. Some of the power while travelling between Port 1 and Port 2,
escapes through the holes 1 and 2.

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 The magnitude of the power depends upon the dimensions of the holes. This leakage power at
both the holes are in phase at hole 2, adding up the power contributing to the forward power Pf.
However, it is out of phase at hole 1, cancelling each other and preventing the back power to
occur. Hence, the directivity of a directional coupler improves.

 Ideally, the output of Port 3 should be zero. However, practically, a small amount of power called
back power is observed at Port 3. The following figure indicates the power flow in a directional
coupler.

 Pi = Incident power at Port 1

 Pr = Received power at Port 2
 Pf = Forward coupled power at Port 4
 Pb = Back power at Port 3

Following are the parameters used to define the performance of a directional coupler.

Coupling Factor C
 The Coupling factor of a directional coupler is the ratio of incident power to the forward power,
measured in dB.
𝑃𝑖
𝐶 = 𝑙𝑜𝑔10
𝑃𝑓
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 Directivity D
 The Directivity of a directional coupler is the ratio of forward power to the back power, measured
in dB.
𝑃𝑓
𝐷 = 𝑙𝑜𝑔10
𝑃𝑏
Isolation
 It defines the directive properties of a directional coupler. It is the ratio of incident power to the
back power, measured in dB.
𝑃𝑖
𝐼 = 𝑙𝑜𝑔10
𝑃𝑏
 Isolation in dB = Coupling factor + Directivity

(13) Cavity Resonators

 Here are some types of cavity resonators

 Re-entrant cavity resonator
 Rectangular cavity resonator
 Circular cavity resonator
 Dielectric resonator

 A cavity resonator is a device used to resonate electromagnetic waves at specific frequencies. A

cavity resonator is typically a hollow metallic structure (like a box or cylinder) with conductive
walls. These walls reflect electromagnetic waves, allowing them to bounce back and forth inside
the cavity.

 Resonance: When an external source injects electromagnetic waves into the cavity at a frequency
matching one of its resonant frequencies, the waves interfere constructively. This means that the
waves reinforce each other, creating standing waves within the cavity.

 Standing Waves: Standing waves are formed when waves travelling in opposite directions overlap.
The points where the waves reinforce each other are called antinodes, and the points where they
cancel each other out are called nodes.

 Resonant Frequency: The specific frequencies at which these standing waves occur depend on the
dimensions of the cavity.

 The resonant frequency is typically determined by the size and shape of the cavity, and it can be
tuned by adjusting these dimensions or by inserting tuning elements like dielectric materials or
probes.

 High Q Factor: Cavity resonators have a high quality factor (Q factor), meaning they can store
energy efficiently with minimal loss.

 This allows them to act as narrow band pass filters, selectively allowing certain frequencies to pass
while blocking others.

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(14) Duplexer

 Duplexer is an essential electronic device used in communication systems, particularly in radar and
radio applications. It functions as a switch that allows a single antenna to be used for both
transmitting and receiving signals, effectively managing the flow of signals between the
transmitter and receiver.

Working of a Duplexer as a Switch

 Signal Path Management: The duplexer connects the antenna to either the transmitter or the
receiver based on the operational mode (transmits or receive).

 During transmission, the duplexer routes the signal from the transmitter to the antenna, allowing
the antenna to send out the signal.

 During reception, it switches to connect the antenna to the receiver, allowing it to pick up
incoming signals.

 Isolation: The duplexer isolates the transmitter from the receiver to prevent high-power signals
from damaging sensitive receiver components. This isolation is critical because, without it,
transmitted signals could overload or destroy the receiver.

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