Introduction to Radar System & Component Tests

Introduction to Radar System and
Component Tests
White Paper
This White Paper provides a general overview of
various military and commercial radar systems.
It also covers some typical measurements on such
systems and their components.
RolandMinihold,DieterBues
11_2013-1MA207-1e
WhitePaper

Table of Contents
1MA207-1e Rohde & Schwarz Introduction to Radar System and Component Tests 2
Table of Contents
1 Abstract ............................................................................................... 3
2 Overview of Typical Radar Application and Radar Types............... 4
2.1 Typical Radar applications .........................................................................................4
2.2 Radar Frequencies, Bands, Wavelength and Applications.....................................5
3 Radar Equation ................................................................................... 6
4 Common Radar Types........................................................................ 7
4.1 Pulse Radar ..................................................................................................................7
4.2 Pulse Doppler Radar ...................................................................................................8
4.3 Pulse Compression Radar ..........................................................................................9
4.4 Continuous Wave Radar ...........................................................................................10
4.5 Frequency Modulated Continuous Wave Radar.....................................................11
4.6 Frequency Agile Radar..............................................................................................11
4.7 Stepped Frequency Radar ........................................................................................12
4.8 Moving Target Indicator Radar.................................................................................13
4.9 Synthetic Aperture Radar .........................................................................................13
4.10 Bistatic Radar.............................................................................................................14
4.11 Passive Radar ............................................................................................................15
4.12 Multimode Radar........................................................................................................15
4.13 Angular Measurement Techniques..........................................................................16
4.13.1 Mono-Pulse..................................................................................................................16
4.13.2 Phased Array, Digital Beamforming and Active Electronically Scanned Array ...........17
4.14 Future of Radar Systems ..........................................................................................19
A Common Radar Abbreviations.................................................................................20

Abstract
Typical Radar applications
1 Abstract
RAdio Detection And Ranging (RADAR), much like SOund Navigation And Ranging
(SONAR) is a technical equivalent of what nature blueprinted with the navigation and
imaging used by bats. Incepted at the beginning of the 20th century, radar technology
was developed in earnest the first time for a military purpose during World War II.
Today, more than half a century later, there are much wider radar application areas
beyond the military one. Radar is needed for weather forecast, airport traffic control
and automotive applications such as adaptive cruise control (ACC), blind spot
detection (BSD) and active pedestrian safety.
Radar technology was made affordable on a mass production basis due to highly
integrated signal processing components which make it possible to detect even low
power signals in applications where in former times much more RF energy was
needed. Low power radar components as a side effect reduce cost and size. In
addition there are a lot of Computer-Aided Design (CAD) tools available nowadays to
deal with high frequencies of up to 110 GHz and beyond.
This White Paper gives an overview on radar systems and addresses some important
measurements. An additional White Paper 1MA239 explains more advanced kinds of
waveform for both A&D and automotive radar systems in detail and mentions future
waveform trends briefly.
A corresponding application note 1MA127 goes into more detail explaining radar test
technology along with the specific Rohde & Schwarz products that can be used to
perform test and measurement.
Documents 1MA127, 1MA207 and 1MA239 and associated videos also address
students who want to become familiar with radar techniques as well as the related test
and measurement tasks.

Overview of Typical Radar Application and Radar Types
Typical Radar applications
2 Overview of Typical Radar Application and
Radar Types
2.1 Typical Radar applications
Typical radar applications are listed to give an idea of the huge importance of radar:
ı Surveillance: Military and civil air traffic control, ground-based, airborne, surface
coastal, satellite-based
ı Searching and tracking: Military target searching and tracking
ı Fire control: Provides information (mainly target azimuth, elevation, range and
velocity) to a fire-control system
ı Navigation: Satellite, air, maritime, terrestrial navigation
ı Automotive: Collision warning, adaptive cruise control (ACC), collision avoidance
(CA), blind spot detection (BSD), pedestrian protection and active safety
ı Level measurements: Monitoring e.g. fill levels of liquids
ı Proximity fuses: Guided weapon systems require a proximity fuse to trigger the
explosive warhead
ı Altimeter: Aircraft or spacecraft altimeters for civil and military use
ı Terrain avoidance: Airborne military use
ı Secondary radar: Transponder in target responds with coded reply signal
ı Weather: Storm avoidance, wind shear warning, weather mapping
ı Space: Earth surveillance, ground mapping, and exploration of space environment
ı Security: Hidden weapon detection, military earth surveillance, ground or through
the wall penetration

Overview of Typical Radar Application and Radar Types
Radar Frequencies, Bands, Wavelength and Applications
2.2 Radar Frequencies, Bands, Wavelength and Applications
Radar Bands, -Frequencies, -Wavelengths and their Applications
Band Frequency Wavelength Application
HF 3 - 30 MHz 10 m – 100 m Coastal radar systems, over-the-horizon (OTH) radars;
'high frequency'
P 30 - 300 MHz 1m – 10 m applied retrospectively to early radar systems; 'P' for
'previous’
UHF 300 - 1000 MHz 0.3 m – 1 m Very long range (e.g. ballistic missile early warning),
ground penetrating, foliage penetrating; 'ultra high
frequency'
L 1 - 2 GHz 15 cm – 30 cm Long-range air traffic control and surveillance; 'L' for
'long'
S 2 - 4 GHz 7.5 cm – 15 cm Terminal air traffic control, long-range weather, marine
radar; 'S' for 'short'
C 4 – 8 GHz 3.75 cm – 7.5 cm Satellite transponders, weather radar; a compromise
(hence 'C') between X and S bands
X 8 – 12 GHz 2.5 cm – 3.75 cm Missile guidance, marine radar, weather, medium-
resolution mapping and ground surveillance; in the
USA the narrow range 10.525 GHz ± 25 MHz is used
for airport radar. Named X band because the frequency
was kept secret during World War 2.
Ku 12 – 18 GHz 1.67 cm – 2.5 cm High-resolution mapping, satellite altimetry; frequency
just under K band (hence 'u')
K 18 – 27 GHz 1.11 – 1.67 cm K band is used by meteorologists for detecting clouds
and by police for speed enforcement. K band radar
guns operate at 24.150 ± 0.100 GHz. Automotive radar
uses 24 – 26 GHz
Ka 27 – 40 GHz 0.75 cm – 1.11
cm
Mapping, short range, airport surveillance, photo radar,
used to trigger cameras that take pictures of license
plates of cars running red lights, operates at 34.300 ±
0.100 GHz; frequency just above K band (hence 'a')
mm 40 - 300 GHz 1 mm – 7.5 mm Millimeter band, subdivided as below. The letter
designators appear to be random, and the frequency
ranges dependent on waveguide size. Multiple letters
are assigned to these bands by different groups, i.e.
frequencies around 75 and 85 GHz are also referred to
as Lower and Upper E-band, respectively.
Q 40 - 60 GHz 5 mm – 7.5 mm Used for military communications
V 50 - 75 GHz 4 mm – 6 mm Very strongly absorbed by the atmosphere
W 75 to 110 GHz 2.7 mm – 4 mm 76 GHz LRR and 79 GHz SRR automotive radar, high-
resolution meteorological observation and imaging

Radar Equation
Radar Frequencies, Bands, Wavelength and Applications
3 Radar Equation
Radar allows to detect and measure range, radial velocity and angular information.
While range is measured by signal propagation time, radial velocity is measured due to
Doppler frequency shift.
Figure 3-1 shows the basic principle of radar transmitting an electromagnetic wave of
power and receiving the radar echo, partly reflected by a target after a certain time
delay. By time delay and speed of light range is estimated.
Figure 3-1: Radar principle
Receiving a radar echo signal of sufficient signal-to-noise (SNR) is the main task and
together biggest challenge of radar systems, as SNR determines detection probability
and measurement accuracy of any target. The “Radar Equation” describes the echo
signal power according to the following parameters:
( )
● : The power transmitted by the antenna. e.g. 20 dBm for 24 GHz
Automotive Radar
● : Gain of the transmitting and receiving antenna (hence squared in the
equation). e.g. 12 dBi for a BiQuad antenna and 70 dBi for a highly focusing
parabolic antenna.
● : wavelength of the transmitted signal, which is directly calculated from the
carrier frequency. e.g. 0.03 m for 10 GHz
● : Radar cross section (RCS), is a virtual area representing the intensity of
the reflection and describes somehow the e.g. material, reflection area in terms of
wavelength of the target. Depending on wavelength e.g. 12 for a commercial
plane, 1 for a person or 0.01 for a bird. Refer to [18], page 6665 for further
examples.
● : Range between the transmitting antenna and the reflecting object.

Common Radar Types
Pulse Radar
4 Common Radar Types
In any radar system range is measured using the delay caused by signal propagation
time between transmit and receive signal. The signal propagation time describes the
elapsed time the transmitted radar signal takes to travel to an object in range R, where
it reflects and travels back to its origin.
A technical strength of radar is to measure the exact radial velocity of an object by
using the Doppler-effect (named after physicist Christian Doppler). The Doppler-effect
describes the apparent change in frequency of a signal emitted or reflected to an
observer if an object is moving relative towards or away from its observer. In the
special case of radar, the observer is also the emitter of the signal, see Figure 4-1
where the radar transmits a wave and observes a moving object where the frequency
in the direction of motion is increases or decreases in opposite direction.
Figure 4-1: Principal operation of radial velocity measurement.
The following sub-sections list the most common types of radar systems with brief
explanations. More detailed information about certain waveforms can be found in the
White Paper "1MA239 Radar Waveforms for A&D and Automotive Radar".
4.1 Pulse Radar
Pulse radar estimates range by measuring the time difference between the
transmission and reception of a single pulse. While pulse width determines range
resolution, pulse repetition frequency (PRF) determines the range where measurement
results are unambiguous.
Figure 4-2: Pulse radar principle.
Angular information such as elevation and azimuth is measured using a narrow
transmit antenna beam and mechanical steering. By the known position of the antenna
beam azimuth angle is estimated.
R

Common Radar Types
Pulse Doppler Radar
Important measurements on (non-coherent) radar equipment are range accuracy and
resolution, Automatic Gain Control (AGC) settling time of the receiver, peak power,
frequency stability, phase noise of the local oscillator (LO) and all pulse parameters.
The AGC circuit of the receiver protects the radar from overload conditions due to
nearby collocated radars or jamming countermeasures. The attack and decay time of
the AGC circuit can be varied based on the operational mode of the radar. Since the
roundtrip of a radar signal travels approximately 150 meters per microsecond, it is
important to measure the response of the AGC for both amplitude and phase response
when subject to different overload signal conditions. The measured response time
influences the minimum detection range of the radar (the so-called "blind range").
4.2 Pulse Doppler Radar
Pulse Doppler radar transmits consecutive pulses and measures the phase difference
in-between their received echoes to provide radial velocity in addition to range
measurement.
In case of coherent operation of the radar transmitter and receiver, radial velocity is
derived from the pulse-to-pulse phase variations.
Pulse Doppler radar systems normally use various pulse repetition frequencies ranging
from several hundred Hz up to hundreds of kHz and change during operation in order
to solve range and Doppler ambiguities. Important criteria to achieve good
performance in pulse Doppler radar include very low LO phase noise, low receiver
noise and low I/Q gain phase mismatch (to avoid "false target indication") in addition to
the measurement parameters listed above.
When measuring the performance of a pulse Doppler radar transmitter the uncertainty
of the measurement system for accurate Doppler measurements is influenced by
several parameters:
● Signal-to-noise ratio (SNR) of the radar echo signal: signals with high SNR can be
detected with higher probability and allow deriving target parameters more
accurately.
● Signal bandwidth (BW): bandwidth of the IF acquisition system must be sufficient
to accurately represent the rise time of the pulsed signal. Bandwidth is also directly
related to range resolution.
● Reference clock stability.
● Jitter or uncertainty due to the measurement point of the rising edge of the signal:
rising edge interpolation or signals that have changing edges.
● Overshoot and preshoot of rising and falling edges: any ringing on the rising and
falling edges can impact the measurement points adversely on a pulse-to-pulse
basis. It is important that the measurement point, or the average set of
measurement points, are sufficiently far spaced in time from the leading and falling
edges of a pulse. Applying a Gaussian filter to smooth the impact of the rising and
falling edges can reduce this phenomena and is often implemented in the Doppler
filter of a radar receiver.

Common Radar Types
Pulse Compression Radar
● Time between measured signals: due to the Pulse Repetition Interval (PRI) of the
measured signal, the close-in phase noise of the measurement system needs to
be considered due to integration time at lower offset frequencies.
● The same variables can also contribute to the uncertainty in the signal generator
when testing the receiver circuit and Doppler measurement accuracy.
4.3 Pulse Compression Radar
Classical pulse and pulse Doppler radar transmit extremely short pulses. On the one
hand, by increasing the pulse width the radar system achieves greater ranges as there
is much more power in the pulse. On the other hand decreasing the width of the
transmit pulses provides better range resolution of the radar system. However, there
are also technical boundaries which limits the maximum transmit power. Pulse
compression combines the power-related benefits of very long pulses (long range) with
the benefits of very short pulses (high range resolution), Figure 4-3.
Figure 4-3: Pulse Compression Radar using LFM.
For pulse compression several different modulation techniques are used.
● Linear frequency modulation (LFM)
● Non-linear frequency modulation (NLFM)
● Encoded pulse phase modulation (e.g. Barker code)
● Polyphase modulation and time-frequency coded modulation
Next to these advantages of pulse compression radar, a drawback is an increased
blind range due to longer pulse duration. As this would be a major disadvantage
especially in air traffic control, some radars use both compressed and uncompressed
techniques. Some ATC radars switch between frequency-modulated pulses of high
average power for long range measurement and very short uncompressed pulses to
cover the area nearby.
● LFM is most common in older radar systems, e.g. air-defense radar RRP-117 [4].
● NLFM is becoming more widespread due to various practical benefits such as
inherently low range side lobes [16].
● Encoded pulse phase modulation, particularly Barker codes with lengths of 11 and
13 [15].
f
t
f2
f1
Transmitted
Signal

Common Radar Types
Continuous Wave Radar
● Polyphase pulse compression is also used increasingly with special codes in
advanced military radar systems [14].
As to measurements, pulse compression radar signals require
● baseband IQ collection of the signal covering the bandwidth of the pulse rise time,
● wideband analog FM demodulation or vector demodulation,
● display for analysis (amplitude, frequency, and phase vs. time), and
● demodulation including EVM measurement for BPSK/QPSK modulations.
4.4 Continuous Wave Radar
A continuous wave (CW) radar system with a constant frequency is used to measure
radial velocity. However, it does not provide any range information.
A signal at a certain frequency is transmitted via an antenna. It is then reflected by a
target moving with a certain speed relative to the receiver beam. This causes Doppler
frequency shift in the radar echo signal. Comparing the transmitted frequency with the
received frequency radial velocity can be determined, see Figure 4-1. Note that any
tangential component will not be taken into account; hence a plane travelling at high
speed in an exact circle around a rotating radar antenna would record a zero result for
radial velocity.
Radar speed traps operated by law enforcement use CW radar technology. They
typically are compact handheld units or completely automatic systems with an
integrated camera to take a picture if a certain speed is exceeded, example see Figure
4-4.
Figure 4-4: Mobile traffic monitoring radar, MultaRadar CD – Mobile speed radar for speed
enforcement from Jenoptic
Radar motion sensors, i.e. for anti-burglary use, are based on the same principle, but
they must also be capable of detecting slow changes in the received field strength due
to variable interference conditions and possible very slow target movement.
In military applications, CW radars are also used for target "illumination". The radar
beam is kept pointing at a moving target by linking it to a target tracking radar for
range, radial velocity and angle information estimation.
CW radars are somewhat hard to detect, which is why they are classified as low-
probability-of-intercept radars.

Common Radar Types
Frequency Modulated Continuous Wave Radar
CW radar also lends itself well to detecting low-flying aircraft that attempting to
overcome an enemy's air defense. The reason for this is that pulse radar has
difficulties in discriminating between ground clutter and low-flying aircraft. CW radar
can close this gap because it is blind to slow-moving ground clutter [7].
4.5 Frequency Modulated Continuous Wave Radar
Constant-frequency CW radar measures radial velocity with high accuracy and
resolution due to long illumination. However, one drawback of CW radar systems is
they cannot measure range due to a missing timing reference.
For measuring range and radial velocity simultaneously, Frequency Modulated
Continuous Wave (FMCW) radar can be used. This waveform is a signal whose
frequency changes. A received radar echo signal will have
● a delay like in pulse radars,
● a Doppler frequency shift like in CW radars.
Range and radial velocity can be measured in case of a single target and multiple
frequency measurements. Frequency patterns with triangular form and periodic
repetition are transmitted to resolve range and radial velocity. However, ambiguities
can occur in a multi-target situation, which is why different patterns are transmitted,
Figure 4-5, (please see White Paper 1MA239 for more detailed information on this
waveform).
Figure 4-5: Basic principle of FMCW radar.
FMCW radar is used in aircraft as radio altimeter or as ground tracking radar to
measure altitude above ground. Because ground can be considered a single fixed
target in these applications, FMCW can unambiguously measure range.
FMCW radar is also commonly used commercially for measuring distances e.g. as
used in level indicators. Some automotive radar sensors also apply FMCW, e.g. for
Adaptive Cruise Control (ACC).
4.6 Frequency Agile Radar
Frequency hopping is an effective technique for a radar system to avoid system
dropout by enemy jamming. Hence Frequency Agile Radar (FAR) is primarily used in
military radar applications.

Common Radar Types
Stepped Frequency Radar
Due to the frequency hopping, ground clutter effects may increase as it cannot be
suppressed well anymore. Reason is that a change of carrier frequency changes the
radar cross section of a target, thus the radar echo signal power and hence the
amplitude of the clutter is not constant through consecutive measurements anymore.
Sub-microsecond switching times and bandwidths ranging from several hundred MHz
in the X-Band to over 2 GHz at 95 GHz are typical for FAR systems.
Measurement parameters that are relevant in FAR include
● frequency switching/settling time,
● hopping sequence,
● switching spurious measurement, and
● broadband amplitude and phase stability.
FAR should be tested across the whole BW of interest. Oscilloscopes with FFT
analysis often need to be employed to assess hopping performance and anomalies
due to the frequency hopping modes.
4.7 Stepped Frequency Radar
Stepped Frequency Radar (SFR) applies bandwidth from a few MHz up to several GHz
to reach the desired range resolution. One application of SFR is Synthetic Aperture
Radar (SAR) for ground mapping [17].
The SFR waveform increases frequency by a fixed step size from pulse to pulse
up to N steps/pulses, Figure 4-6.
Figure 4-6: Stepped Frequency Radar
The individual bursts typically consist of pulse sequences up to e.g. 128 or 256 pulses.
As in FMCW radar, there is no need for large capture bandwidth in SFR. Due to the
wide RF bandwidth of the transmitter and receiver, these subsystems must exhibit
excellent stability in order to obtain the desired high resolution.
SFR measurements with regard to testing each pulse require highly precise tools for
pulse-to-pulse coherence analysis (magnitude and phase stability is most important).
As in frequency agile radar, the settling time of the local oscillator is also an important
measurement parameter.
f
t
fN
f1
fstep
Tp

Common Radar Types
Moving Target Indicator Radar
4.8 Moving Target Indicator Radar
The idea behind a moving target indicator (MTI) radar is to suppress radar echo
signals from stationary or slow-moving targets such as buildings, mountains, waves,
clouds, etc. and thus obtain an indication of the moving targets of interest.
Figure 4-7: Radar echo and MTI filter response
Unwanted radar echo signals are generally referred to as clutter, which is normally
distributed around zero Doppler frequency and multiples of the pulse repetition
frequency, Figure 4-7. One possible implementation of a MTI is a delay line canceler,
which stores the last radar echo in order to be subtracted from the actual radar echo.
In case of a stationary target the difference value becomes zero, while for the
remainder represents the moving targets.
Optimizing MTI requires the use of staggered PRF (variable PRF) in order to offset
"blind velocities" or in order to make them visible.
Important measurement parameters in optimizing MTI or clutter suppression include:
● Pulse-to-pulse phase and amplitude stability of the transmit signal,
● LO phase stability and generally a low phase and broadband noise in the radar
system,
● Lowest close-to-carrier phase noise particularly in low radial velocity applications.
4.9 Synthetic Aperture Radar
Synthetic Aperture Radar (SAR) is a coherent radar system often mounted on satellites
or aircrafts. It provides very high image resolution by using the flight path to simulate
an extremely large antenna aperture.
A technique referred as Inverse SAR (ISAR) uses the same technique, but utilizes the
motion of a target rather than that of the emitter, by which the synthetic aperture is then
created.
Due to its all-weather and day-or-night capability SAR is used for surveillance, terrain
mapping (interferometry using two receive antennas), ground penetration and many
other applications where it shows advantages over optical sensor systems while
offering high resolution.
The basic principle behind SAR is similar to a phased array antenna. But unlike parallel
antenna array elements, SAR uses parts of the (virtual) antenna area in time multiplex.
The antenna position is known precisely, and moves perpendicularly to the radiation

Common Radar Types
Bistatic Radar
direction over time. All radar echo signals containing their respective amplitude and
phase components are stored over time and processed.
Today's SAR systems apply a signal bandwidth of several GHz in order to achieve a
resolution of centimeters. Some SAR systems also use stepped carrier frequency,
polarization switching and other complex techniques (e.g. intra-pulse beam steering,
multi-aperture recording in azimuth, spatiotemporal waveform encoding, e.g. in the
TerraSAR X), see [5], [6], [19] for more details.
Figure 4-8: Synthetic Aperture Radar (SAR)
Requirements for successful SAR processing are an extremely stable "fully coherent"
transmitter, powerful signal processing and the exact knowledge of flight path and ego
velocity.
Test challenges are the bandwidth of interest for the SAR's generation and analysis
tools. There is a trade-off between stepped frequency vs. single frequency operation
e.g. effort for coherent pulse-to-pulse analysis vs. amount of analysis bandwidth
required.
4.10 Bistatic Radar
Radar systems where transmitter and receiver are located at the same position are
called monostatic radar. In bistatic radars, one transmitter and one receiver of the
radar system are located at different positions. Their distance is typically chosen to be
comparable to the expected target distance.
An advantage of bistatic radar sites is an easier detection of stealth targets, as these
targets typically are designed to minimize reflection of power into the direction of the
source. Bistatic receivers thus may detect stealth targets. These systems also have
practical applications in weather radar, see [9].
Bistatic radars by their nature rely on enhanced accuracy in timebase and network
synchronization. Measurement systems must have best synchronization and lowest
clock jitter performance in order to yield meaningful measurement results. This gets
even more important in low-phase noise applications i.e. if slow-moving target
detection is an extra requirement.
Azimuth
Range
3
2
1
Height
Footprint
Swath
Aperture

Common Radar Types
Passive Radar
4.11 Passive Radar
In conventional radar, the system is formed of at least one transmitter and at least one
receiver section. Passive radar does not actively transmit electromagnetic energy in
order to detect targets.
Instead, reflections and Doppler frequency shift of targets caused by known broadcast
transmitters, mobile radio transmitters and other systems are evaluated, Figure 4-9.
Therefore the signal from a known transmitter is measured. Echoes from targets
illuminated by chance are also measured. Passive radar systems are difficult to locate,
since they do not transmit any signals. This is a decisive advantage in military
applications, next to the ability to detect stealth aircrafts, which is very limited with
existing active radar technology [10].
Signal collection systems need to cover the BW of the signals of opportunity that
should be analyzed. For instance, signal collection equipment with 80 MHz BW
mounted close to airports can cover most kinds of cellular infrastructure for a given
cellular band.
Other variants of passive radars use FM radio stations, while some also make use of
new digital video signals (DVB) which must be collected over wider spans.
The collection of passive radar signals is continually evolving as new wireless cellular
infrastructure, digital video, and digital audio terrestrial broadcast stations are deployed
worldwide.
For test of passive radar known signals have to be recorded or generated to test e.g.
signal processing and hardware.
4.12 Multimode Radar
Many radar systems used nowadays in airborne applications (e.g. from
reconnaissance, to maritime helicopter to airstrike jets) are multimode radar systems
and handle a wide range of different tasks, such as target searching and tracking,
Commercial TX
e.g. DVB-T, FM, LTE,
WiMAX
Reference RX
Remote RX
RX
Figure 4-9: Passive Radar

Common Radar Types
Angular Measurement Techniques
weapon guidance, air-to-ground ranging, high-resolution ground mapping, weather
detection, terrain following and avoidance, electronic counter-countermeasures
(ECCM) etc..
Therefore radar systems use various frequency bands ranging from 100 MHz to 100
GHz, switch between different PRF modes, including FM chirp, Barker phase
modulation or complex modulation and SAR processing. These radars often use
frequency hopping over a very wide range and intra-pulse polarization to avoid
jamming.
Growing areas are Active Electronically Scanned Array (AESA) antennas, radars that
steer their antenna beams flexibly.
Testing a multimode radar system of this sort is complex and costly. Fast, fully
automated test systems are needed. Test & Measurement needs are equivalent to the
aggregate of what has been described in the preceding sections.
4.13 Angular Measurement Techniques
Angular measurement in radar techniques can be performed using several different
approaches by single transmit signal. Azimuth α and elevation angle β is measured as
an additional target parameter next to range and radial velocity. Due to azimuth
information target tracking accuracy is improved.
Some radar systems apply mechanical rotation to steer a very narrow antenna beam
into the direction of targets. Azimuth angle is then determined by the angle of the
antenna position. Other possibilities are
● sequential lobing,
● amplitude or phase mono-pulse and phased arrays,
● active electronically scanned arrays (AESA),
are common and their alternative or combined use depends on the application. Fighter
jets or naval radars for example use AESA technique to steer a beam of nearly
arbitrary shape into any arbitrary desired direction. Automotive radars are more likely
to apply phased array or mono-pulse techniques [20].
4.13.1 Mono-Pulse
Mono-pulse radar systems are characterized by the use of at least two spatially
distributed antenna groups [13].
One approach is to compare the amplitudes of a single target at two receive antennas.
Another approach is to estimate the phase difference from a radar echo signal at these
two receive antennas while azimuth angle is then determined by trigonometry.
In case of amplitude mono-pulse radar, two antennas illuminate a symmetrically but
displaced focal point, see Figure 4-11. A radar echo signal with a certain azimuth angle
will cause different receive amplitudes so that the direction of arrival can be calculated.
Phase mono-pulse divides the aperture and produces two sub apertures with identical
amplitude vs. angle pattern response, Figure 4-10.

Common Radar Types
In case of a received radar echo signal under a certain azimuth angle amplitude will be
the same, but time of arrival will be different, which is measured in phase difference.
By knowing the wavelength and distance between two or more receive antennas the
azimuth angle is estimated.
Measurement challenges include the fact that antenna beam patterns haves to be
known exactly. Channel matching of the different channels is important in mono-pulse
radar systems and must be characterized next. Multi-channel phase-coherent
synthesizers with adjustable phase offsets are typically used for this purpose. Phase
coherent multichannel analysis e.g. by means of a high performance digital
oscilloscope with IQ interface becomes important for testing the transmitter coherence.
4.13.2 Phased Array, Digital Beamforming and Active Electronically
Scanned Array
Radar applications desire dynamic beam steering, as the area of a static
electromagnetic beam is not wide enough to cover the entire area of interest,
especially within A&D applications. In classical radar systems mechanical devices
have been used in order to move the radar beam to cover a certain area, e.g. the 360-
degree rotating antenna in air surveillance systems. Older fighter jets also are using
mechanically rotating radar antennas. However, mechanical systems are both, heavy
and failure-prone, which can be serious drawbacks for equipment being used in safety-
critical applications.
High performance Digital Signal Processing along with affordable and small, highly
integrated hardware systems have made digital beamforming (DBF) possible. DBF
always relies on antenna arrays which allow steering the beam in a desired direction
by adjusting phase and amplitude of each single transmitter / receiver [2]. Therefore
each antenna element is equipped with a complete up- and down-converter unit.
RX1 RX2
TX
d
α
Figure 4-10: Mono-Pulse Technique (Phase)
Diff Difference
Diagram
Sum
RX1
Sum
Diagram
RX2
Figure 4-11: Mono-Pulse Technique (Amplitude)

Common Radar Types
Figure 4-12: 360-degree rotating antenna (left) of an air surveillance system and electronically
steered antenna (right)
In the example shown in Figure 4-13 signals of electrical energy supply several
isotropic antennas. Each single isotropic antenna is radiating equally in all directions if
no phase shift is applied. The resulting power of the radiated sum beam in forward
direction is very close to the sum of the sine signals. Depending on the phase shift
between the transmit antenna signals, the beam can be steered into a certain direction.
The phase shift of the antenna signals causes the final signal to be reduced in
amplitude as compared to a signal being added up in forward direction without phase
shift.
Phase shift of antenna array signals can be generated in various ways. One way is to
use supply cables of different lengths. Another method is to implement phase-shifting
elements in the appropriate antenna supply circuits, see Figure 4-13.
Figure 4-13: Basic Principle of DBF
Application Note 1MA127 describes an integrated circuit performing digitally controlled
phase shifting. It is also shown how such phase shifters can be controlled digitally by
test instruments such as network analyzers.
A high performance digital scope is highly suited to test the transmitted delay between
up to 4 channels of T/R modules if the skew between the scope channels is sufficiently
low (<< 1 ns).
Phased-array radar antennas have hundreds or even thousands of individual radiating
elements (as opposed to a reflector antenna with a single radiator). The magnitude and
phase of the power fed to the elements can be individually controlled, making it
possible for the overall antenna to generate wave-fronts with nearly any desired shape.
In real-world operation, the pattern can be turned by about ±60°. The efficiency of the
antenna drops at larger angles. Unlike a conventional antenna that is moved
mechanically, a phased array can rotate its pattern in space with practically no delay.

Common Radar Types
Future of Radar Systems
Since phased-array antennas are very costly, they are used primarily in military and
SAR satellite applications. The current state of the art is an active phased array radar
(or AESA) based on many individual, small Transmit/Receive (TRX) modules, whereas
the passive variant (PESA) uses a common shared RF source whose signal is
modified using digitally controlled phase shifter modules.
Important in AESA is the uniformity of the different modules in terms of amplitude and
phase, which involves considerable test and calibration effort. Very fast automated test
systems are required to align an array of hundreds, sometimes thousands of TRX
elements to achieve very good radar performance.
4.14 Future of Radar Systems
In the future, multisensory systems that combine radar and infrared (or other) systems
will be encountered. These techniques combine the benefits of the different types of
systems while suppressing certain weaknesses [11]. Military onboard radar systems
will be increasingly confronted with improved stealth technology of future aircrafts. The
contradiction between different requirements imposed on aircraft must be solved (i.e.
planes should exhibit stealth properties while not revealing their position through the
use of onboard radar). One possibility could involve bistatic radar systems using a
separate illuminator and a receiver on-board the aircraft. Another option is passive
radar which provides anti-stealth defense options.
In today's radar antenna research there is a huge trend towards AESA antennas. The
next generation of AESA radars used on-board of aircraft will likely have more than
one fixed array and an increased number or TRX modules. Also there could be
additional integration of antenna structures onto the aircraft body, wings, ship's hull or
other platforms. This is also partly driven due to technology like Unmanned Aerial
Vehicles (UAV) where radar is used.
Radar sensors allowing vision through a building wall applying extremely wide
bandwidth to gather very good resolution will be an additional demand.
For many new radar systems transmit and receive modules using semiconductor
materials such as gallium arsenide (GaAs) or gallium nitride (GaN) could take the
place of magnetrons while increasing performance, shrinking system size / weight and
allowing more flexible filtering of transmit signals. These systems are supported by
integrated circuits employing Direct Digital Synthesis (DDS) which allow a more flexible
generation of radar signals. Future price drops in DDS will lower the barrier to apply
DDS also in automotive radar sensors.
Performance requirements on the digital back-end equipment used for processing
radar raw data increases. Through parallel processing, throughput as needed for high-
resolution radar operating modes can be provided [12].
Additional challenges to radar detection caused by wind farms or increased mobile
communication using Long Term Evolution (LTE) will have to be covered by radar
system processors. Impacts on ATC radar through LTE equipment have already been
measured and shown to be an issue. The huge variety of radar systems and
applications causes a wide area of demand for suitable measurement equipment.

Common Radar Types
Appendix
A Common Radar Abbreviations
Common Radar Abbreviations
Abbreviation Meaning
ACC Adaptive Cruise Control
AESA Active Electronically Scanned Array
AEW Airborne Early Warning
AFC Automatic-Frequency-Control
AGC Automatic Gain Control
APAR Active Phase Array Radar
ASR Airport Surveillance Radar
ASR-S Airport Surveillance Radar Mode-S (Mode S is an extension to
secondary radar. Mode S makes it possible to query additional
information, e.g. the speed of the aircraft.)
ATC Air Traffic Control
BARDS Baseband Radar Detection Sensor
BSD Blind Spot Detection
BW Bandwidth (or Beamwidth)
CFAR Constant False Alarm Rate
CMOS Complementary Metal-Oxide Semiconductor
COHO Coherent Local Oscillator
DOA Direction of Arrival
DoD Department of Defense
DTM Digital Terrain Model
ECCM Electronic Counter-Countermeasures
EIRP Effective Isotropic Radiated Power
ELINT Electronic Intelligence (electronic acquisition of radar parameters)
EMPAR European Multifunction Phased Array Radar
EMV Electromagnetic Vulnerability
ESA Electronically Steerable Array

Common Radar Types
Common Radar Abbreviations
Abbreviation Meaning
ESM Electronic Warfare Support Measures
FCW Forward Collision Warning
FFT Fast Fourier Transform
FMCW Frequency Modulated Continuous Wave
GCA Ground-Controlled Approach
LPI Low Probability of Intercept
LRR Long Range Radar
MTD Moving Target Detection
OTH Over-The-Horizon
PAR Phased-Array-Radar
PDF Pulse Desensitization Factor
PESA Passive Electronically Scanned Array
PRF Pulse Repetition Rate or Frequency
PRI Pulse Repetition Interval
PRT Pulse Repetition Time
RCS Radar Cross-Section
RDF Range and Direction Finding
RS Ramp Slope
SAR Synthetic Aperture Radar
SRR Short Range Radar
SSR Secondary Surveillance Radar
TBD Track-Before-Detect
TRM Transmitter-Receiver Module
ULA Uniform Linear Array

Common Radar Types
Literature
[1] Merrill I. Skolnik,1990, Radar Handbook, Second Edition McGraw-Hill
[2] Merrill I. Skolnik,1990, Radar Handbook, Second Edition McGraw-Hill, Chapter 7
[3] http://www.radartutorial.eu/index.en.html
[4] http://www.radartutorial.eu/rrp.117.html
[5] http://de.wikipedia.org/wiki/Synthetic_Aperture_Radar
[6] http://keydel.pixelplaat.de/uploads/File/vorlesung07-08/SAR.pdf
[7] http://www.h2g2.com/approved_entry/A743807
[8] http://www.armedforces.co.uk/releases/raq43f463831e0b7
[9] http://www.pa.op.dlr.de/poldirad/BISTATIC/index.html
[10] Silent Sentry™Passive Surveillance
[11] http://defense-update.com/20110721_super-hornets-future-eo-radar
[12] radar-technology-looks-to-the-future.html
[13] http://www.radartutorial.eu/06.antennas/an17.en.html
[14] http://dl.acm.org/citation.cfm?id=1294551
[15] http://en.wikipedia.org/wiki/Barker_code
[16] http://prod.sandia.gov/techlib/access-control.cgi/2006/065856.pdf
[17] www.google.com/patents/US6965341.pdf
[18] David M. Pozar, Microwave Engineering, Third Edition, Wiley
[19] Inverse Synthetic Aperture Radar Imaging.pdf, retrieved September 2013,
http://users.ece.utexas.edu/~bevans/courses/ee381k/projects/fall98/li/literatureSurvey.
pdf
[20] Smartmicro GmbH, UMRR Automotive Sensor Data Sheet, Project Title:
Automotive Sensor, May 28, 2013, retrieved September 2013,
http://www.smartmicro.de/images/smartmicro/automotive/UMRR Automotive Type 29
Data Sheet.pdf

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Introduction to Radar System & Component Tests

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