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Terrestrial Microwave Link Design
‗Abdulrahman1, Ong Sin Yee2, Nurul Shafikah3, Mohamud Mire mohamud 4
Radar Communication Laboratory, Faculty of Electrical Engineering
Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia
Abstract—Microwave links provide the bulk of the
interconnectivity between sites in telecommunications networks
(especially mobile voice and data networks) because they are
rapidly deployable, relatively small and require less
infrastructure outlay than technologies such as fibre
transmission. Typical applications of microwave link includes
mobile backhaul links - between 2G/3G base stations and
WiMAX/LTE backhaul links. The basic components required for
operating a radio link are the transmitter, towers, antennas, and
receiver. To achieve point-to-point radio links, antennas are
placed on a tower or other tall structure at sufficient height to
provide a direct, unobstructed line-of-sight (LOS) path between
the transmitter and receiver sites. Before a microwave link can
be installed, an analysis and calculation of the microwave link
must be made first. The analysis should take place before the site
survey itself to get a clear idea about the dimensions of the
antennas. Our analysis consists in this paper consists of Free
space loss calculation and Link budget calculation.
Keywords— transmitter design, receiver design, point-to-point
microwave link, frequency of 9, 15 and 18 GHz, system level.
A microwave link fundamentally consists of a transmitter
and a receiver. The transmitter and the receiver are each
connected to an antenna. This is typically a parabolic dish
antenna connected to the transmitter, and also typically a dish
antenna on the receiver. Based on operating 3G point-to-point
microwave link system which functioning frequency 9, 15 and
18 GHz only. The receiver always needs to be typically within
the range of kilometres of the transmitter, but the distance is
very much dependent on the path between the transmitter and
receiver, as in .
Before we discuss the different types of antennas, this is the
objectives as follows:
To understand the project and problem statement given.
To design a terrestrial microwave link system.
To analysis and discuss on the performance of the
To determine the appropriate operating frequency to be
engaged in this microwave link system.
To do analysis on actual overall costing for the
microwave link design.
We should have a quick look at the subject of polarization,
as it is relevant to antennas used in terrestrial microwave
communications. Signals transmitted in any frequency band
have a property termed polarization, and this relates to the
geometric plane in which the electromagnetic waves are
transmitted or received. Hence polarization describes the
orientation of the electric field radiated from the antenna, as in
There is little fundamental difference between transmitting
antennas and receiving antennas, since the same antenna is
often used for both purposes. While some antennas can be as
simple as a wire thrown out of a window, for the best
performance the right type of antenna needs to be used. The
most important properties of an antenna are its radiation
pattern and its gain (the magnitude of the signal), whether it is
being used at the transmitter or receiver. In the case of a
transmitting antenna, the radiation pattern is a plot of the
power strength radiated by the antenna in different directions.
As a consequence of its radiation pattern, power radiated by
an antenna may be concentrated in a particular direction, and
this directivity is expressed in terms of power gain, as in .
In order to design terrestrial point-to-point link system,
there are several technical choices that we considered for
instance the microwave LOS link , the link budget , free space
path loss and its accuracy on the link analyses. The choice of
the transmission media is one the most important actions we
took, always at the first stages of the design of a
communication system. This section describes briefly the
different choices for establishing a link between two locations,
and the different advantages and drawbacks of each
II. POINT TO POINT MICROWAVE LINKS
Point-to-Point (PTP) Microwave technology provides
dedicated, point-to-point connectivity using directional
antennas. A microwave link is a communications system that
uses a beam of radio waves in the microwave frequency range
to transmit video, audio, or data between two locations, which
can be from just a few meters to several kilometres apart. PTP
links typically require clear Line of Sight (LOS) between the
A. Microwave Line-of-Sight Systems
Microwave frequencies range from 300 MHz to 30 GHz,
corresponding to wavelengths of 1 meter to 1 cm. These
frequencies are useful for terrestrial and
communication systems, both fixed and mobile.
important to realize that ITU-R recommendations are usually
adopted on a worldwide basis.
"Line-of-sight" is a term used in radio system design to
describe a condition in which radio device antennas can
actually see each other. High frequency radios, such as those
used in Spread Spectrum Radio require line-of-sight between
antennas, as shown in Fig. 1, as in .
So, in our case, which is specifies the minimum
performance parameters for terrestrial fixed service digital
radio communications equipment‘s operating in the 13 GHz,
15 GHz and 18 GHz frequency bands. Systems considered are
able to respect ITU-R national or international grade
performance objectives, i.e. ITU-R Recommendations F.1189
for national, F.1092 for international and ITU-R
Recommendation G.826. We also respect to the ITU-R P.53012 – Propagation data and prediction methods required for the
design of terrestrial line-of-sight systems.
ATPC power level definitions and limits are shown in
In the case of point-to-point radio links, antennas are placed
on a tower or other tall structure at sufficient height to provide
a direct, unobstructed line-of-sight (LOS) path between the
transmitter and receiver sites, as in .
We also make use of the Automatic Transmit Power
Control (ATPC) range in our project. ATPC is defined as the
power interval from the maximum (including tolerances)
output power level to the lowest transmitter output power
level. If implemented, the ATPC range shall not be less than
ATPC set manually to a fixed value for system
performance. Other than that, ATPC also set at maximum
provide power for Transmit (TX) performance.
VALUE OF LINK BUDGET
Fig. 1 Line of sight of point-to-point application
Each country has a varying requirement for the licensing of
microwave radio links. In most cases this license only
addresses the transmitter, but in the same instance, it offers
regulatory protection to any interference that may affect the
In the United States, radio channel assignments are
controlled by the Federal Communications Commission (FCC)
National C. Microwave Link Structure
Telecommunications and Information Administration (NTIA)
The basic components required for operating a radio link
for government systems.
are the transmitter, towers, antennas, and receiver. Transmitter
The FCC's regulations for use of spectrum establish functions typically include multiplexing, encoding,
eligibility rules, permissible use rules, and technical modulation, up-conversion from baseband or intermediate
specifications. FCC regulatory specifications are intended to frequency (IF) to radio frequency (RF), power amplification,
protect against interference and to promote spectral efficiency. and filtering for spectrum control. Receiver functions include
Equipment type acceptance regulations include transmitter RF filtering, down-conversion from RF to IF, amplification at
power limits, frequency stability, out-of-channel emission IF, equalization, demodulation, decoding, and demultiplexing.
To achieve point-to-point radio links, antennas are placed on a
limits, and antenna directivity.
tower or other tall structure at sufficient height to provide a
The International Telecommunications Union Radio direct, unobstructed line-of-sight (LOS) path between the
Committee (ITU-R) issues recommendations on radio channel transmitter and receiver sites, as shown in Fig. 2, as in .
assignments for use by national frequency allocation agencies.
Although the ITU-R itself has no regulatory power, it is
Radio transmitters are described in terms of power output
expressed in watts. The power output may also be expressed
in terms of decibels of gain (dB). Radio receivers are rated in
terms of sensitivity (ability to receive a minimal signal). The
rating is listed in terms of milliwatts (mW), or decibels of gain
(dB). Antenna cable is rated in terms of signal loss per foot
and expressed as dB of loss per foot. The antenna is rated in
terms of gain (dB). There are a number of software programs
that will calculate path loss by frequency and use the
specifications of the system hardware to help determine the
overall system feasibility.
Fig. 2 Point-to-point microwave link structure
III. MICROWAVE LINK DESIGN
A block diagram of a transmitter base station is shown in
Fig. 3. The transmitter base station of digitalization and
encoding, WCDMA Generation (modulator), and transmitter.
A block diagram of a receiver base station is shown in Fig. 4.
The transmitter base station of receiver, demodulator, and
digitalization and encoding.
to analogue. Encoding using orthogonal coding, spreading,
and correlation that W-CDMA uses a variable length code.
The length of spreading code is also known as the spreading
factor. Base station that receives a transmitted data sequence
and attempts to demodulate it using the ―wrong‖ orthogonal
code, would interpret the information as noise.
2) Transmitter: The transmitter produces a microwave
signal that carries the information to be communicated. The
transmitter has two fundamental functions: generating
microwave energy at the required frequency and power level,
and modulating it with the input signal so that it conveys
meaningful information. Modulation is accomplished by
varying some characteristic of the energy in response to the
3) Transmission Line: The transmission line carries the
signal from the transmitter to the antenna and, at the receiving
end of the link, from the antenna to the receiver. At
microwave frequencies, coaxial cables and, especially, hollow
pipes called waveguides are used as transmission lines.
4) W-CDMA Generation (Modulator): The access
technology, W-CDMA (Wideband Code Division Multiple
Access), is termed UTRA (UMTS Terrestrial Radio Access).
The information that was modulated onto the carrier from the
carrier itself. It could be audio and/or video information, or
other data. The modulator accomplished by puts the
information or intelligence onto a carrier wave at the
5) Receiver: The receiver extracts information from the
microwave signal and makes it available in its original form.
To accomplish this, the receiver must demodulate the signal to
separate the information from the microwave energy that
carries it. The receiver must be capable of detecting very
small amounts of microwave energy, because the signal loses
much of its strength on its journey.
Fig. 3 Transmitter base station block diagram
Fig. 4 Receiver base station block diagram
D. Description of the Purpose and Operation of All the Major
Components of Base Stations
1) Digitalization and Encoding: using ADC at transmitter
to convert the information from analogue to digital and it
using DAC at receiver to convert the information from digital
6) Demodulator: Demodulator is a circuit used in AM
(amplitude modulation) and FM (frequency modulation)
receivers to separate the information that was modulated onto
the carrier from the carrier itself. It could be audio and/or
video information, or other data. A demodulator is the
analogue of the modulator. The demodulator pulls it off so it
can be processed and used on the other end.
E. Brief Description of the Basic Operation of Transmitter
A block diagram of a transmitter is shown in Fig. 5. The
transmitter of mixer with local oscillator, band pass filter, RF
amplifier, cable and antenna. A block diagram of a receiver is
shown in Fig. 6. The transmitter of antenna, cable, receiver,
lower noise amplifier, band pass filter and mixer with local
conversion, also referred to as heterodyning, produces the sum
and difference frequencies of the frequency of the local
oscillator and frequency of the input signal of interest. These
are the beat frequencies. Normally, the beat frequency is
associated with the lower sideband, the difference between the
Fig. 5 Transmitter block diagram
Fig. 6 Receiver block diagram
1) Lower Noise Amplifire (LNA): LNA is an electronic
amplifier used to amplify possibly very weak signals (for
example, captured by an antenna). It is usually located very
close to the detection device to reduce losses in the feedline.
An LNA is a key component which is placed at the frontend
of a radio receiver circuit. Per Friss‘ formula, the overall noise
figure (NF) of the receiver‘s front-end is dominated by the
first few stages. A good LNA has a low NF (e.g. 1 dB), a very
large enough gain (e.g. 20 dB) and should have large enough
intermodulation and compression point. The gain of the LNA
is 22 dB and the NF is 2.5 dB.
2) RF Amplifier: RF Amplifier (power amplifier) is a type
of electronic amplifier used to convert a low-power radiofrequency signal into a larger signal of significant power,
typically for driving the antenna of a transmitter. It is usually
optimized to have a high efficiency, high output power
compression, good return loss on the input and output, good
gain and optimum heat dissipation.
3) Band Pass Filter (BPS): Band Pass Filter is a device
that passes frequencies within a certain range and rejects
frequencies outside that range. An ideal band pass filter would
have a completely flat passband (e.g. with no gain/attenuation
throughout) and would completely attenuate all frequencies
outside the passband. Additionally, the transition out of the
passband would be instantaneous in frequency. In practice, no
bandpass filter is ideal. The filter does not attenuate all
frequencies outside the desired frequency range completely; in
particular, there is a region just outside the intended passband
where frequencies are attenuated, but not rejected. This is
known as the filter roll-off, and it is usually expressed in dB
of attenuation per octave or decade of frequency.
4) Local Oscillator: To generate a signal normally for the
purpose of converting a signal of interest to a different
frequency using a mixer. This process of frequency
5) Cable: The cable is to provide power from a power
source to some piece of equipment or tool. The basic and sole
purpose of a power cable is to transport electrical energy from
the source of the electricity to the device.
6) Antenna: The last part of the microwave system is the
antennas. On the transmitting end, the antenna emits the
microwave signal from the transmission line into free space.
At the receiver site, an antenna pointed toward the
transmitting station collects the signal energy and feeds it into
the transmission line for processing by the receiver. Antennas
used in microwave links are highly directional, which means
they tightly focus the transmitted energy, and receive energy
mainly from one specific direction. By concentrating the
received signal, this characteristic of microwave antennas
allows communication over long distances using small
amounts of power.
7) Microwave tower: A microwave tower is a structure
built to enhance wireless communication. For them to work,
they have to cover large areas using an interconnecting pattern
and they can be located anywhere. Most of them are located
close to where people habit and to power supply areas.
F. Signal spreading in W-CDMA transmitter and receiver
The process start with IF input 350 MHz then convert to 9
GHz or 15 GHz or 18 GHz. The data is then "spread‖ using a
code which is running at either 9 GHz or 15 GHz or 18 GHz
code rate. The resulting spread bits are called chips and the
resulting transmitted spread rate is expressed as either 9 GHz
or 15 GHz or 18 GHz. The distance is fixed to 10km. The
receiver of base station will see this spread signal together
with noise, interference, and messages on other code channels
in the same RF frequency slot. The interference can come
from other signal. The base station‘s demodulator then
reapplies the code and recovers the original data signal. The
signal spreading as shown in Fig. 7.
Fig. 7 Signal spreading in W-CDMA transmitter and receiver
G. Signal spreading in W-CDMA transmitter and receiver
The typical technical characteristics of microwave point to
point transmission links as follows:
Range: microwave point to point links use 10 km.
Microwave radio communication requires clear line-ofsight (LOS) between the respective endpoints. Increase
in range typically requires higher antenna heights to
account for the ―earth bulge‖.
Data Rate: Microwave PTP systems can support up to
Frequency Bands: Microwave PTP links operate in
Licensed and Unlicensed frequency bands
Licensed frequency bands require expensive license.
However there are multiple benefits associated with
using licensed frequencies including
High system availability
Secure as compared to unlicensed band
Optimum system performance due to lack of
Lower long term operational cost
Considerations with licensed band
Microwave PTP can be used for a very wide range of
applications. Currently mostly PTP Microwave systems are
used for cellular backhaul application, for example Mobile
backhaul links between 2G/3G base stations. Cellular
companies utilize PTP microwave links for their equipment
Enterprise networks utilize microwave PTP system for
Internet/Intranet access, corporate voice, File transfers, Videoconferencing. PTP systems are commonly used for last mile
access to the PSTN and other voice and data networks.
PTP microwave system are widely used for increasing rural
telephony and network extensions.
IV. LINK ANALYSIS AND BUDGET
A. Free space loss path calculation
The Free Space Path Loss (FSPL) measures the power loss
in free space without any obstacles. So for end-users, it is
important to know the approximate frequency between the
transmitter and receiver while maintaining a certain link
quality at different data transfer rates.
FSPL depends on two parameters:
Frequency of radio signals
Wireless transmission distance
In our task, we choose to fix the parameter distance and
varied the frequency. The following formula can reflect the
relationship between them as follows:
d = distance (10 km)
f = frequency (9 GHz, 15 GHz, 18 GHz)
K= constant that depends on the units used for d and f
If d is measured in kilometres, f in MHz, the formula is:
1) FSPL (dB) of 9 GHz
2) FSPL (dB) of 15GHz
3) FSPL (dB) of 18 GHz
B. Link Budget Calculation
A wireless link budget for a point-to-point radio link
accounts for all the gains and losses from the transmitter,
through cables, antennas and free space to the receiver.
The link budget values are shown in Table 2.
Estimating the value of the "power" in the different parts of
the radio link is necessary to be able to make the best design
and the most adequate choice of equipment. The equation of
link budget as follow:
Link Budget = Tx power (dBm) + Tx Antenna Gain (dBi) +
Rx Antenna Gain (dBi) – Tx Cable losses (dB)
– Rx Cable Losses (dB) –FSPL
VALUE OF LINK BUDGET
*For Tx Power is assumed to be equal to 18dBm for all the
frequency. For others, the value is taken from the data sheet.
1) Link Budget (dB) of 9 GHz
2) Link Budget (dB) of 15 GHz
3) Link Budget (dB) of 18 GHz
*For Rx sensitivity (minimum received signal) to be assumed = 110 dB
RG405 U Cable
Coax 0.5-20 GHz
The performance of any communication link depends on
the quality of the equipment being use. The receive power or
the link budget is determined by transmit power, transmitting
antenna gain, receiving antenna gain and some losses. With
that value, we have to minus with Free Space Path Loss of the
link path and make a comparison with the receiver sensitivity.
The difference between the minimum received signal level
and the actual received power is called the link margin. The B. Cost Budget for Transmitter and Receiver using 15 GHz
link margin must be positive, and should be maximized.
No Component Name and Picture Gain NF Quantity Total Price
Based on the calculation on the Free Space Path Loss and
Link Budget Calculation the frequency of 9 GHz is the most
appropriate frequency compare to 15 GHz and 18 GHz
because of the lowest value of losses (131.52 dB) and it
receive the highest power (based on link budget). Moreover,
the link margin for 9 GHz is 20.28 dB which the link margin
should be maximized for reliable link.
A. Cost Budget for Transmitter and Receiver using 9 GHz
K&L S/N 1 9SB107000/T4000-O/O
No Component Name and Picture Gain NF Quantity
1 Mixer with
V. COST BUDGET
14.4 – 15.35 GHz
RG405 U Cable
Coax 0.5-20 GHz
C. Cost Budget for Transmitter and Receiver using 18 GHz
No Component Name and Picture Gain NF Quantity
1 Mixer with
Based on the cost budget of 9 GHz is the most appropriate
compare to 18 GHz and 15 GHz because of the lowest cost
Microwave link design is a specific sort of engineering in
the broader field of communications. Most installers know
that clear line of sight is required between two antennas, but
there is a lot more to it than that. To have some certainty as to
whether your wireless link will be reliable, an RF path
analysis needs to be performed. Our main objective was to
understand and design terrestrial microwave link system and
also to analyse the performances of design system whether,
Link budge, Free Space Loss and line of sight. Furthermore
our designing link system to be operating these frequencies 9,
15 and 18GHz after analysis we were able to meet the needed
appropriate operating frequency, lastly therefore we were
able to make a terrestrial microwave link system. To get the
good performance should use the 9 GHz because based on the
calculation on the Free Space Path Loss and Link Budget
Calculation the frequency of 9 GHz is lowest value of losses
(131.52 dB) and lowest Cost Budget that is RM101,764.28.
We would like to express our deepest gratitude and
appreciation to our laboratory instructor‘s Prof .Madya
Dr .Mohamad Ngasri Bin Dimon and Dr. Kamaludin bin
Mohd Yusof for their excellent guidance, caring, patience,
suggestions and encouragement who helped usto coordinate
our project especially to design the link. We would also like to
acknowledge with much appreciation to all those who gave us
the possibility to complete this project. A special thanks goes
to the crucial role of the staff of the Radar communication
Laboratory. Last but not least, again we would like to say
many thanks go to our laboratory instructors, Prof .Madya
Dr .Mohamad Ngasri Bin Dimon and Dr. Kamaludin bin
Mohd Yusof, who are given as full effort guiding in our team
to make the goal as well as the panels especially in our project
presentation that has improved our presentation skills by their
comment and tips.
RG405 U Cable
Coax 0.5-20 GHz
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