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Q.1Compare rectangular and circular waveguides.

Feature Rectangular Circular wave

wave
Cross-sectional Rectangular Circular
Shape
Mode of Dominant mode Dominant mode is
propagation isTE10 TE11
Ease of fabrication Easier to fabricate More deficult to
And connect manufacture
precisely
Mode separation Better mode Poor mode
separation separation; May
support more modes
Application Common in radar and Used in rotating
microwave system Joints and satellite
system

Q.2Define cut-off frequency and cut-off wavelength.

Cut-off Frequency:
It is the minimum frequency below which a wave cannot propagate
through a waveguide.

Cut-off Wavelength:
It is the maximum wavelength above which a wave cannot propagate
in a waveguide.
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Q.3Sketch field patterns of TE modes.

TE₁₀ Mode in a rectangular waveguide:

E-field:
Varies along the broader side (a), no variation along the narrower
side (b), shown as straight horizontal arrows.

H-field:
Forms circular loops around the E-field lines.
TE₁₀ means 1 variation along 'a' and 0 along 'b'.
It’s the dominant mode with the lowest cut-off frequency.
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Q.4Draw Magic Tee + Applications.

Definition:
A Magic Tee is a 4-port waveguide junction that combines the features
of both E-plane Tee and H-plane Tee.

Applications:
Mixers: Combining RF and LO signals.
Duplexers: Separate transmit and receive paths.
Phase Shifters: Creating phase difference in outputs.

Q.5Gunn Diode
Construction + Working of Gunn Diode.
Gunn Diode
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Construction:

Made of n-type semiconductor (like GaAs or InP).

It has three layers: n⁺ – n – n⁺.

n⁺ layers: Highly doped for ohmic contacts.

Middle n-layer: Lightly doped and is the active region.
No p-n junction is present, unlike regular diodes.

Working:

Based on the Gunn Effect discovered by J.B. Gunn.

When a voltage is applied across the diode, electrons accelerate.

At a certain threshold voltage, electrons shift to a higher energy band

(conduction band satellite valley) with lower mobility.

This causes negative differential resistance (NDR)—as voltage

increases, current decreases.

Due to NDR, the diode oscillates and generates microwave

frequencies (1–100 GHz).

Applications:

Microwave oscillators
Radar systems
Speed guns
Microwave transmitters

Q.6Derive/Explain RADAR Range Equation.

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The standard form of Radar range equation is also called as simple
form of Radar range equation. Now, let us derive the standard form of
Radar range equation.

We know that power density is nothing but the ratio of power and
area. So, the power density, Pdi
at a distance, R from the Radar can be mathematically represented
as-
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Q.7CW Doppler RADAR with Block Diagram.

CW Doppler Radar

Definition:
A CW Doppler radar continuously transmits a wave and detects
moving targets by measuring the Doppler shift in the reflected signal.
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Block Diagram:

Transmitter:
Generates continuous RF signal.
Antenna:
Transmits and receives signals.
Duplexer/Circulator:
Separates transmitted and received signals.
Mixer:
Compares transmitted and received signals to detect frequency shift.
Bandpass Filter:
Filters out unwanted frequencies.
Detector:
Measures Doppler shift.
Output/Display:
Shows target speed.

Working:

The radar transmits a continuous wave.

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A moving target reflects the wave with a Doppler frequency shift.
The shift is proportional to the velocity of the target.
The receiver detects this shift to measure speed.

Applications:

Speed detection (e.g., traffic radar)

Heartbeat/breathing monitors
Industrial automation

Q.8Compare TWT & Klystron.

Feature TWT(Travelling Klystron

Wave Tube)
Working principle Continuous Velocity modulation
interaction of of electron beam
electron beam with
RF wave
Bandwidth Very wide(up to Narrow bandwidth
several GHz)
Gain Moderate(40-60 dB) High(up to 70 dB)
Efficiency Lower(20-40%) Higher(up to 60%)
Construction Helix or coupled Cavity resonator
cavity structure based(two or more
cavities)
Power output Suitable for low and Suitable for high
medium power power application
application
Application Satellite Radar,TV transmitters
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communication, Praticle
Wideband system accelerators

Q.9Applications of IMPATT Diode.

Applications of IMPATT Diode:

1. Microwave Transmitters
Used in microwave communication systems due to high-power and
high-frequency capabilities.

2. Radar Systems
Suitable for low-power radar applications, especially in the X-band
and Ku-band.

3. Local Oscillators
Used in microwave receivers as a local oscillator source.

4. Alarms and Sensors

Employed in motion detectors, intrusion alarms, and proximity
sensors.

5. Telecommunication
Used in point-to-point communication links due to high-frequency
operation (up to 200 GHz).

Q.10.Define the term antenna scanning. State its

types.
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Antenna Scanning:
It is the process of changing the direction of the antenna beam to
cover a specific area for communication or detection.

Types:

1. Mechanical Scanning –
Beam direction is changed by physically moving the antenna.

2. Electronic Scanning –
Beam is steered electronically using phase shifts.

3. Hybrid Scanning –
Combines mechanical and electronic methods.

Q.11Two-Hole Directional Coupler.

Two-Hole Directional Coupler

A two-hole directional coupler is a passive microwave device used to

sample a small amount of microwave power for measurement or
monitoring, without disturbing the main power flow.

Construction:

It consists of two parallel transmission lines or waveguides placed

close to each other.
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These lines are connected through two small holes (apertures) drilled
at a distance of λ/4 (quarter wavelength) apart.

Ports:

1. Input port (Port 1)

2. Transmitted port (Port 2)
3. Coupled port (Port 3)
4. Isolated port (Port 4)

Working Principle:

When a signal is applied at Port 1:

Most power flows to Port 2.
A small amount is coupled to Port 3.
Ideally, no power reaches Port 4 (isolated port).

The two holes produce two waves that interfere constructively at the
coupled port and destructively at the isolated port, due to the λ/4
spacing.

Key Parameters:

Directivity: Measures how well the coupler isolates the coupled and
isolated ports.
Coupling factor: Ratio of input power to coupled power.
Insertion loss: Power loss from input to output.

Applications:
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Power monitoring
Signal sampling
VSWR measurement
Isolating components in microwave systems

Q.12Working + Applications of PIN Diode.

PIN Diode – Working and Applications

Working:

A PIN diode is a semiconductor device with three regions:

P-type layer (P)
Intrinsic (undoped) layer (I)
N-type layer (N)

Working principle:

Forward-biased condition:
The diode behaves like a variable resistor.
The intrinsic region gets filled with charge carriers, reducing
resistance.
It allows RF and microwave signals to pass through with low loss.

Reverse-biased condition:

The intrinsic layer is depleted of carriers.

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The diode acts as a high impedance (open switch), blocking RF
signals.

Because of the wide intrinsic layer, the diode stores and releases
charge slowly, which makes it ideal for switching and attenuating
high-frequency signals.

Applications:

1. RF and Microwave Switches:

Acts as an ON/OFF switch in high-frequency circuits.

2. Attenuators:

Controls signal amplitude by changing resistance in response to bias

current.

3. Phase Shifters:
Used in phased array antennas to adjust the phase of RF signals.

4. Limiters and Protectors:

Protects sensitive circuits from high-power RF pulses.
5. Modulators and Detectors:
Useful in analog and digital modulation systems.

6. Isolators and Circulators (with ferrite):

Enhances directional flow in microwave systems.

Q.13Compare TE and TM modes.

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Q14.Explain bunching in magnetron + applications.

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Bunching in Magnetron

Magnetron is a high-power microwave oscillator commonly used in

radar and microwave ovens. It uses the principle of velocity
modulation and electron bunching to generate microwaves.

What is Bunching?

In a magnetron, electrons are emitted from a central cathode and

move toward the anode, which has resonant cavities.
A perpendicular magnetic field causes the electrons to follow spiral
paths instead of straight lines.
Due to interaction with the RF field in the cavities, some electrons
slow down and others speed up, depending on their phase.
Over time, these electrons form groups or "bunches"—areas of high
electron density.
These bunches transfer kinetic energy to the RF field in the resonant
cavities, sustaining microwave oscillations.

Significance:

Bunching is essential for efficient energy transfer from the electron

stream to the RF field.
Without bunching, the magnetron would not sustain oscillations.

Applications of Magnetron

1. Microwave Ovens – Used to generate microwave energy for

cooking.
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2. Radar Systems – Used in military, weather, and air traffic control
radars.
3. Industrial Heating – For drying, melting, and processing materials.
4. Medical Therapy – In some types of cancer treatment and
diathermy.

Q.15.Calculate cut-off wavelength for a=4.5cm, b=3cm

at 9GHz
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Q.16Calculate cut-off frequency for a=4cm, b=3cm at

5GHz.
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Q.17.Calculate max RADAR range for P =1MW,
σ=3m²"
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Q.18.Calculate max range for P =600kW, σ=20m²
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.Q.19.Explain directional coupler principle.

Directional Coupler – Principle of Operation

A directional coupler is a 4-port passive microwave device that

samples a small amount of power from a transmission line without
disturbing the main power flow.

Ports:

1. Input (Port 1) – where the signal enters.

2. Output (Port 2) – where the main signal exits.
3. Coupled (Port 3) – samples a fraction of the forward signal.
4. Isolated (Port 4) – ideally receives no power.

Working Principle:

It operates based on electromagnetic coupling between two

transmission lines placed close together. When a signal enters the
input port, most of it goes to the output port, and a small, known
fraction is coupled to the coupled port. Due to phase relationships
and field direction, almost no power reaches the isolated port.

Key Concepts:
Forward Coupling:
Only a small portion of power is coupled to port 3 in the same
direction as the input.
Isolation:
Port 4 is isolated from port 1; minimal power flows here.
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Reverse Operation: If power is sent into port 2, port 4 becomes the
coupled port, and port 1 becomes isolated.

Applications:

Power monitoring
Signal sampling
VSWR measurement
Isolating and combining signals in RF systems

Q.20Draw magnetron construction + applications.

1. Microwave Ovens
Used to generate microwave radiation for heating and cooking food.

2. Radar Systems
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Employed in military and weather radars for generating high-power
microwave pulses.

3. Industrial Heating
Used in drying, welding, and material processing applications.

4. Medical Equipment
Applied in microwave diathermy machines for deep tissue heating.

5. Communication Systems (older)

Previously used in early microwave relay and satellite links.