Electronic Systems and Technologies

Microwave
Communications
Lectured by:
Timothy M. Amado

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Microwave
MICROWAVES are UHF, SHF and EHF
radio signals in the frequency range from
1 to 300 GHz.

ITU-R Rec V.431-6

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Waveguides
A hollow metal pipe with a circular or
rectangular cross section used for carrying
microwave signals from one place to
another.

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Waveguides
Waveguides acts as high-pass filter.

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Example Problem
A rectangular waveguide has a width of 0.65 in
and a height of 0.38 in. What is the cutoff
frequency?
Typical operating freq
fo = fc/0.7

9 GHz
Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Example Problem
Calculate the group velocity of a 4 cm x 2 cm
waveguide operating at 10 GHz.

2.78 x 108 m/s

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Phase and Group Velocity
Group Velocity
✓ Actual velocity of the wave inside the
waveguide

Phase velocity
✓ Waves require an apparent velocity greater
than the velocity of light in space. This is
called as phase velocity

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Microwave Tubes
Cavity Resonator
✓ A cavity resonator is a hollow conductor
blocked at both ends and along which an
electromagnetic wave can be supported. It can
be viewed as a waveguide short-circuited at
both ends
✓ It serves as parallel-tuned circuit and filter

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Microwave Tubes
Magnetron
✓ A cross-field microwave tube oscillator in
which electrons circle around the cathode
under the influence of magnetic field
✓ The oldest microwave tube design
✓ It serves as a microwave oscillator

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Example Problem
A pulsed magnetron with an average power of 1.2
kW and a peak power of 18.5 kW. One pulse is
generated every 10 ms. Find the length of a pulse.

0.65 ms
Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Microwave Tubes
Klystron
✓ A type of linear beam tube that uses velocity
modulation of the electron beam, used for
microwave amplification and oscillation.

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Semiconductor Devices
Gunn Diode
✓ a microwave semiconductor device used to
generate microwave energy.
✓ When combined with a microstrip, stripline or
resonant cavity, simple low power oscillators
with frequencies up to 50 GHz are easily
implemented.

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Semiconductor Devices
Varactor Diodes
✓ Widely used as microwave frequency
multipliers. Multiplication factors of 2 and 3
are common with power levels up to 20 W and
efficiencies up to 80 percent.

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Semiconductor Devices
Step Recovery Diodes
✓ Also used as frequency multipliers with
multiplication factors up to 10, power ratings
up to 50 W and efficiencies approaching 80
percent.

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Semiconductor Devices
Schottky (Hot Carrier) Diodes
✓ widely uses as mixers in microwave equipment
as they have low capacitance and inductance.

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Couplers
Isolator
✓ a waveguide device that has low loss in one
direction and high in the other, providing
isolation

Circulator
✓ is a device with three or more parts that allows
an input on one port to emerge only at next
port in order

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Terrestrial Microwave Communications

TERRESTRIAL COMMUNICATIONS use

microwave frequencies to transmit information
in a line-of-sight or space wave propagation.

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
PATH PROFILE
Types of Path
• Line of sight – the straight path between a
transmitting and receiving antenna
unobstructed by the horizon.
• Grazing path – the microwave beam barely
touches the obstruction (zero clearance)
• Obstructed path – the microwave beam is
hindered by an obstruction

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Parameters

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Example Problem
Determine the radio horizon in miles given that
the antenna heights in site A and site B are equal
to 80 ft.

25.3 mi
Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Example Problem
If the line-of-sight distance for an optical beam is
12 km, what would it be, approximately, for a
microwave beam?
A. 9 km B. 16 km C. 20 km D. 24 km

16 km
Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Parameters

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
k-factor

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Example Problem
The k-factor under normal atmospheric conditions
in a microwave radio data profile calculation is

4/3
Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Parameter

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Example Problem
Calculate the earth bulge 2 miles away from a
transmitter for a 25 mile microwave link. Assume
a k of 4/3.

23 ft
Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Parameter
Fresnel Zone
A region near an object where diffraction effects
are significant, this is one of the conical zones
that exist between microwave transmitting and
receiving antennas due to cancellation of some
portions of the wavefront by other portions that
travel different distances

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Parameter

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Parameter

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Example Problem
Line-of-sight microwave link operating at 4 GHz
has a separation of 40 km between antennas. An
obstacle in the path is located midway between
the two antennas. By how much must the beam
clear the obstacle?

16.4 m
Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Link Budget
A theoretical calculation of end-to-end
performance for a communications path under
specific set of conditions

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Link Calculations
✓ Transmitter Power Output (Po)
✓ Effective Isotropic Radiated Power (EIRP)
✓ Free Space Loss (FSL)
✓ Isotropic Receiver Level (IRL)
✓ Receive Signal Level (RSL)
✓ Receiver Noise Threshold
✓ Carrier-to-Noise Ratio (C/N)
✓ Fade Margin (FM)

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Link Calculations

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Transmitter Power Output (Po)

This refers to the output power transmitted by

the microwave radio, usually 1-10W and
expressed in dBm or dBW

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Review Question
A transmitter has an output power of 2 W and is
connected to a 100 m antenna with an
attenuation coefficient of 0.03 dB/m. Determine
the power level in dBm that actually reaches the
antenna?

30 dBm
Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Effective Isotropic Radiated Power (EIRP)

EIRP is defined as the power radiated by

an antenna in its favored direction, taking
the gain of the antenna into account as
referenced to the isotropic radiator.

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Example Problem
Compute the EIRP in dBm where the transmitter
output power is 200 mW at the waveguide flange,
the transmission line losses are 4.7 dB, and the
antenna gain is 37.3 dB.

55.6 dBm
Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Free Space Loss (FSL)
Loss incurred by an electromagnetic wave
as it propagates in a straight line through a
vacuum with no absorption or reflection of
energy from nearby objects.

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Example Problem
What is the free-space loss, in dB, between two
microwave parabolic antennas 38.0 kilometers
apart operating at 7.0 GHz?

140.89 dB
Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Isotropic Receive Level (IRL)

The RF signal level impinging on the far

end receive antenna as if it were an
isotropic antenna.

This is the signal level at the receiving

antenna, i.e., it is the EIRP minus the total
path loss.

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Example Problem
Calculate the IRL of a radiolink where the EIRP
is 28 dBW, the FSL is 137.25 dB, and the
atmospheric gaseous absorption loss is 0.6 dB

-109.85 dBW
Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Received Signal Level (RSL)
It is simply the level of signal at the
receiving end of the transmission.

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Example Problem
A transmitter and receiver operating at 6 GHz
are separated by 40 km. How much power (in
dBm) in delivered to the receiver if the
transmitter has an output power of 2 W, the
transmitting antenna has a gain of 20 dBi, and
the receiving antenna has a gain of 25 dBi?

–62 dBm
Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Receiver Noise Threshold
This is the noise threshold brought to by the
receiver.
The RSL must be greater than this level by a
several decibels (which is the unfaded C/N at this
case) to ensure proper link connectivity.

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Example Problem
Determine the noise threshold (in dBW) for a
link, having a bandwidth of 10 MHz and a noise
figure of 10 dB.

-124 dBW
Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Fade Margin (FM)
A fudge factor included in the system gain
equation that considers the practical and
non-ideal less predictable characteristics of
radio propagations such as multipath
propagation and terrain sensitivity.

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Fade Margin (FM)

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Example Problem
Determine the fade margin for a link whose RSL
in dBW is -85.56, having a bandwidth of 10 MHz
and a noise figure of 10 dB.

38.44 dB
Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Outage Time
The time that the microwave system will
not meet the necessary requirement/ full
connectivity in a given period of time.

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Example Problem
What is the outage time per year of a microwave
link that has a reliability of 99.9999%

32 secs
Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Diversity
Diversity suggests that there is more than
one transmission path or method or
transmission available between a
transmitter and a receiver.
➢Frequency Diversity
➢Space Diversity
➢Polarization Diversity
➢Hybrid Diversity
➢Quad Diversity

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Frequency Diversity
It is simply modulating two different RF carrier
frequencies with the same IF intelligence, then
transmitting both RF signals to a given
destination.

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Space Diversity
The output of the transmitter is fed to two or
more antennas that are physically separated by
an appreciable number of wavelengths.

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Polarization Diversity
A single RF carrier is propagated with two
different electromagnetic polarization
either vertical or horizontal.
It used in conjunction with space diversity.

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Hybrid Diversity
✓ Consists of standard frequency-diversity
path where the two transmitter/receiver
pairs at one end of the path are
separated from each other and connected
to antennas that are vertically separated
as in space diversity.

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Quad Diversity
✓ Provides the most reliable transmission.
✓ It combines frequency, space,
polarization, and receiver diversity into
one system.

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Diversity and Hot Standby
Hot Standby protection
• Each working radio channel has dedicated backup or
spare channel.
Diversity protection
• A single back-up channel is made available to as
many as 11 working channels.

Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE
Example Problem
Determine the gain of a 6 ft parabolic dish
operating at 1800 MHz.

28.17 dB
Technological University of the Philippines Electronics Engineering Department Timothy M. Amado, ECE