Aircraft Radar Systems Analysis

This assignment examines the characteristics and performance of aircraft radar systems. It delves into antenna types, specifications (peak power, pulse width, PRF), performance factors, and applications. A key component involves calculating the average power output of a Boeing 737's radar system based on provided parameters. Additionally, the assignment explores the calculation of Pulse Repetition Frequency (PRF) for specific pulse widths and rest times.

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RESEARCH PAPER ON THE AIRCRAFT RADAR SYSTEM
A Research Paper on Aircraft By
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INTRODUCTION
This research paper focuses on evaluation and comparison of two different aircraft
radar systems with reference to their antennas used, specification, performance and factors
affecting their performance, as well as their applications. The other section discussed in this
paper include elapsed time for a radar pulse, distance travelled by a radar pulse, and the PRF
for a pulse.
A radar is an object-detection system which utilises radio waves to find out the
velocity, angle, and range of objects. An aircraft radar system is used to detect aircraft is
space by continuously sending radio waves for the transmitter to be reflected by the object
and then return to the receiver to provide the information concerning the speed and location
of the object. A radar system is composed of processor and receiver which determines the
properties of the object, a receiving antenna, a transmitting antenna, and a transmitter which
produces electromagnetic waves in the microwaves or radio domain (Ali, 2013).
There are to different aircraft radar systems that are currently being used, these are
primary radars and secondary radars. The secondary radars produce pulses and listen for the
special response of emitted digital data by a transponder of the aircraft as a response. The
primary radars are a classical radar which reflects every category of echoes, such as clouds
and aircraft (Bagad, 2016).
Primary radar systems
A primary radar system is a radar sensor which illuminates a huge portion of space by
the use of electromagnetic wave and receives the waves reflected from the object within the
space. The primary radar system utilizes antenna of low vertical resolution but perfect
horizontal resolution. This system is different from the secondary radar which receives extra
data from the transponder of the target (Charvat, 2010).

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Specification
The primary radar system sends pulses of the high frequency which are reflected by
the target such as an aircraft and then the signal is received back in form of an echo. This
system can be described as a passive system since the aircraft does not require any extra
equipment for the system to function. Some of the basic components making up the primary
radar system include the transmitter, mixer, detector, analogue to digital converter, signal
processing, and display (Jones, 2014). The figure below shows the schematic of the Primary
radar:
Figure 1: Schematic of Primary radar (Kingsley, 2012)
Performance
A transmitter produces the radio signal by the use of an oscillator like magnetron or
klystron and the controls its period by the use of a modulator. The primary radar system
functions on the echolocation principle. Electromagnetic pulses of huge power produced by
the antenna radar are changed into the wavefront that is narrow which propagates at the
velocity of light. The aircraft will then reflect the wave and then received again by the
rotating antenna on its own axis. The person operating the system will then hear the echoes
from any reflection and then continuously perform listening and transmission to cover 360o
space (Kolawole, 2012). The primary radar system results in measurements and detection of

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the location in case there is the presence of an object through recognition of important signal.
The basic radar measurements by the primary radar system include:
 Radial velocity by the use of Doppler Effect
 The angle ϴ based on the antenna direction in azimuth
 The distance D at the time of wave transit to/from the path (Lacomme, 2014).
Antennas used
The primary radar system utilizes antenna of low vertical resolution but perfect
horizontal resolution. The primary radar system locates an aircraft on a quarter circle in the
plane that is vertical, however, it is difficult to know its altitude if it is using the fan-beam
antenna. Some of the antenna systems that are currently being used in the primary radar
systems include dual polarizers with circular and linear polarization or double-curvature
antenna reflector with two beams (Lynn, 2013).
Factors Affecting Performance
Some of the factors affecting the performance of the primary radar system include
transmitter power, antenna size, receiver noise, target size, clutter, and atmospheric effect.
Huge amounts of power must be radiated to ensure returns from the target. Due to the minute
amount of energy returned at the receiver, the return signals may be disrupted easily because
of factors such as signal attenuation as a result of atmospheric conditions like heavy rainfall
or changes in the attitude of the target (Mahapatra, 2013).
Secondary Radar System
A secondary radar system is a system which apart from measuring and detecting the
position of the aircraft, an additional information is also reflected from the aircraft itself like
altitude and identity (Meikle, 2015).
Specifications

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There are slight differences between the secondary and primary radar system since
there is need of aircraft to possess a transponder so as to respond to the interrogations from
the transmitter of the secondary radar system. This system can be described as an active
system since there is need of the aircraft to have a transponder for the system to function. The
secondary radar system relies on equipped target with a transponder of the radar which
response to every signal of interrogation by conveying a response containing data encoded
(Tooley, 2014).
Figure 2: Secondary radar schematics (Wyatt, 2011)
Performance
The two basic transponders categories include Mode C and Mode A. Mode C report
the altitude of the aircraft while Mode A reports the ID number of the aircraft. The secondary
radar is attached on top of the primary radar system, and with the combination of the received
data between secondary and primary radar, the operator is able to acquire a full picture of the
location of the aircraft. The ground unit is normally known as the interrogator and it functions
by sending a coded pulse to the transponder. After the pulse have been received, it is
decoded, and a reply is conveyed back down to the station to the ground (Kolawole, 2012).

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Antennas used
The antenna at the ground has a horizontal 3dB beamwidth of 2.5oC which limits the
precision in evaluating the aircraft’s bearing. This accuracy can be enhanced through making
numerous interrogations as the antenna beam scans an aircraft and a perfect estimation can be
gotten by putting into consideration where the responses began and where terminated and
taking the centre of responses as the aircraft’s direction. The antenna that was used
previously was known as hog trough which had a huge horizontal dimension to generate a
horizontal beam that is narrow and a minute vertical length to give cover from nearly
overhead to close to horizontal (Charvat, 2010).
Factors Affecting Performance
Some of the factors affecting the performance of the primary radar system include
interference, atmospheric effects, clutter, and receiver noise. Interference can be caused by
signals from nearby radars and other transmitters which can be the strength to get into a radar
receiver and generate spurious responses. Atmospheric effects such as rain and other forms of
precipitation may lead to echo signals that mask the target echoes that are desired. Clutters
are caused by echoes from meteors, auroras, insects, birds, hail, snow, rain, sea, and land and
affects the performance of the secondary radar system by limiting the capability of a radar
system. The secondary radar system also requires a target aircraft to carry an operating
transponder hence it is a dependant radar system (Bagad, 2016).
Task 2
a. Find the elapsed time for a radar pulse to travel 82.5 NM
Radar operates by broadcasting a high-frequency radio-wave pulse which is reflected from an
object targeted. A reflected signal is detected at the original source.

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The distance of the object from the radar antenna, D = 82.5*10-9M
The total distance that would be covered by the signal = 82.5*10-9*2 = 165*10-9M
Taking speed of the signal to be equivalent to that of light = 299,792,458 m/s
Elapsed time = Distance /Speed
= 165*10-9/299,792,458
= 0.000550 microseconds
b. The elapsed time for a radar pulse to travel 87.3 Nm
The distance of the object from the radar antenna, D = 87.3*10-9M
The total distance that would be covered by the signal = 87.3*10-9*2 = 174.6*10-9M
Taking speed of the signal to be equivalent to that of light = 299,792,458 m/s
Elapsed time = Distance /Speed
= 174.6*10-9/299,792,458
= 0.000582 microseconds
c. The distance a radar pulse has travelled after a time of 12460 microseconds
The distance of the object from the radar antenna, D =?
Time elapsed round trip = 12460 *10-6 seconds
Taking speed of the signal to be equivalent to that of light = 299,792,458 m/s
Distance of the object from the radar antenna = 12460 *10-6 * 299792458/2
Distance, D = 1,868,707.014m
d. The distance a radar pulse has travelled after a time of 60.37 microseconds
The distance of the object from the radar antenna, D =?
Time elapsed round trip = 60.37 *10-6 seconds
Taking speed of the signal to be equivalent to that of light = 299,792,458 m/s
Distance of the object from the radar antenna = 60.37 *10-6 * 299792458/2
Distance, D = 9049.24m
e. A Boeing 737 has the following specifications. Peak Power = 15Kwatts, Pulse Width =
4microseconds and PRF = 400. Calculate the average power.
Peak transmitted power, Pt = 15000W

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Pulse width = 0.004s
Pulse repetition frequency (PRF) = 400
Pulse energy, E = Peak power * Pulse width
= 15000*0.004
= 60J
Duty cycle, d = PRF * Pulse width
= 400*0.004
= 1.6
Power average = Pt * Duty cycle
= 15000*1.6
= 24000W
f. The PRF for a pulse width of 45 microseconds and a rest time of 23.5 microseconds
Pulse width = 45*10-6
Rest time = 23.5*10-6
Rest time = PRF – Pulse width
PRF = Rest time + Pulse time
= 45*10-6 + 23.5*10-6
= 68.5*10-6
= 6.85*10-5
Conclusion
This research paper is about an evaluation and comparison of two different aircraft
radar systems with reference to their antennas used, specification, performance and factors
affecting their performance, as well as their applications. An aircraft radar system is used to
detect aircraft is space by continuously sending radio waves for the transmitter to be reflected
by the object and then return to the receiver to provide the information concerning the speed
and location of the object.

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Bibliography
Ali, B., 2013. Aircraft Surveillance Systems: Radar Limitations and the Advent of the Automatic
Dependent Surveillance-Broadcast. Sydney: Taylor & Francis.
Bagad, V., 2016. Radar System. Perth: Technical Publications.
Charvat, G., 2010. Small and Short-Range Radar Systems. Michigan: CRC Press.
Jones, J., 2014. Manuals Combined: Electronic Warfare and Radar Systems Engineering Handbook.
Colorado: Principles of Naval Weapons Systems.
Kingsley, S., 2012. Understanding Radar Systems. Melbourne: SciTech Publishing.
Kolawole, M., 2012. Radar Systems, Peak Detection and Tracking. Chicago: Elsevier.
Lacomme, P., 2014. Air and Spaceborne Radar Systems: An Introduction. New York: Institution of
Electrical Engineers.
Lynn, P., 2013. Radar Systems. Paris: Springer Science & Business Media.
Mahapatra, P., 2013. Aviation Weather Surveillance Systems: Advanced Radar and Surface Sensors
for Flight Safety and Air Traffic Management. New York: Institution of Electrical Engineers, American
Institute of Aeronautics and Astronautics.
Meikle, H., 2015. Modern Radar Systems. London: Artech House.
Tooley, M., 2014. Aircraft Digital Electronic and Computer Systems, 2nd ed. Toledo: Routledge.
Wyatt, D., 2011. Aircraft Communications and Navigation Systems. Colorado: Routledge.