2016 IEEE Radar Conference (RadarConf)

Dual-polarization DVB-T Passive Radar:

Experimental Results
M. Conti, C. Moscardini, A. Capria
RaSS National Laboratory
CNIT (National Inter-University Consortium for Telecommunications)
Pisa, Italy
{michele.conti, christian.moscardini, amerigo.capria}@cnit.it

Abstract— The present work is going to investigate the range and Doppler resolutions [8]. A PBR receiver generally
potential benefits obtainable by taking advantage of the presents at least two receiving channels denoted as reference
polarization diversity in a Passive Bistatic Radar (PBR) system and surveillance channels. The reference channel is used to
exploiting Digital Video Broadcasting - Terrestrial (DVB-T) capture the direct signal from the IO and provides the reference
signals. In particular, a PBR demonstrator equipped with a signal to be compared with the target return received from the
surveillance array antenna able of simultaneously receiving both surveillance channel. The comparison is usually carried out by
horizontal and vertical polarizations has been used to cross-correlating the reference signal and the target signal,
experimentally assess the radar performances as a function of the which actually represents the basic process to detect targets
received polarization. The results obtained in a maritime
with a passive radar system. The target echo signal generally
scenario show a different target Signal-to-Interference-plus-Noise
Ratio (SINR) variation as a function of the surveillance channel
exhibits amplitude values tens of dB lower than the direct
receiving polarization. Therefore, the availability of receiving signal ones coming from the IO, therefore a passive radar
both Horizontal (H) and Vertical (V) polarizations might system should be able to operate in a high dynamic range
improve the target detection performance if a suitable method of signal environment and to make use of effective interferences
combining the signals received at different polarization is cancellation signal processing algorithms.
adopted. Studies about the advantages of exploiting different
polarizations in passive radars have been recently published
Keywords—passive radar; PBR; dual-polarization; DVB-T. [9]-[10]. In these works a number of results have been shown
to point out the possibility of using the polarization diversity in
I. INTRODUCTION order to mitigate the effects of the interferences and to enhance
the detection performance of FM-based PBRs.
Passive Bistatic Radar (PBR) systems have been The present work is going to investigate the potential benefits
developing both in terms of signal processing and system obtainable by taking advantage of the polarization diversity in a
maturity (demonstrators and prototypes). Several non- PBR system exploiting DVB-T signals.
cooperative transmitters, also known as Illuminators of In particular, a PBR demonstrator equipped with a
Opportunity (IOs) can be used by this family of radars in order surveillance array antenna able of simultaneously receiving
to achieve targets localization. Ground-based broadcast both horizontal and vertical polarizations has been used to
transmitters such as Frequency Modulation (FM) [1]-[2] and experimentally asses the radar performances as a function of
Digital Audio Broadcasting (DAB) radio [3], as well as the received polarization.
analogue [4] and digital television [5] have been largely
exploited to demonstrate their capability to perform air and
coastal surveillance [6]-[7]. The performance of a passive radar II. EXPLOITING POLARIZATION DIVERITY
system strongly depends on the transmitted power and on the Under the assumption of operating with a PBR able to
characteristics of the used IO, which is used as a reference exploit different receiving polarizations on the surveillance
signal [4]. The exploitable signals can be divided in two main antenna, a number of potential benefits can be foreseen:
classes: analogue and digital waveforms. It is worth noting that
1. The suppression of the interference caused by the
the ambiguity function of analogue sources (e.g.: FM radio or
reception of the direct signal coming from the IO can
analogue TV) is unpredictable as it is the result of a time-
be enhanced if the surveillance antenna operates in
varying signal structure, which typically produces a content
cross-polarization with respect to the polarization
dependent signal bandwidth. On the contrary, digital
used in transmission by the exploited IO;
waveforms exhibit a stationary ambiguity function with a
thumb-tack shape and constant bandwidth. Among the digital 2. The target echoes collected by the PBR exhibit a
IOs, the terrestrial digital television, e.g. DVB-T, represents a random polarization, therefore the availability of
very attractive opportunity for passive radar applications. As a receiving both H and V polarizations might increase
matter of fact, the DVB-T transmissions generally exhibit high the information available, hence improving the target
radiated power levels and a signal structure standard which Signal to Noise Ratio (SNR).
turns into good waveform performance both in terms of radar

978-1-5090-0863-6/16/$31.00 ©2016 IEEE

The first mentioned advantage is of great interest especially from National Instruments, the NI USRP-2922: it is a
when the bistatic geometry is not favourable, which means that versatile transceiver with on-board Field Programmable
the surveillance antenna is steered towards the direction of the Gate Array (FPGA) processing capabilities; it can
IO. In this case a very strong DPI (Direct Path Interference) operate on a wide frequency band: 400MHz-4.4GHz;
might be experienced and it could lead to the Radio Frequency the sampling resolution is equal to 14 bits.
(RF) amplification chain or Analog-to-Digital Converter
(ADC) saturation. • Synchronization signal generator: in order to form a
synchronized and coherent multichannel system, 9
The other expected advantage, resulting from the usage of a USRP-2922 are fed with ad hoc reference signals (i.e.:
dual polarization PBR receiver, might be experienced as a 10 MHz clock and PPS).
target SNR improvement which can enhance the target
detection performance if a suitable method of combining the
signals received at different polarization is adopted. IV. SCENARIO GEOMETRY
The SMARP demonstrator has been installed in Livorno on
III. SMARP DEMONSTRATOR the roof of the CSSN-ITE “Istituto Vallauri”. A number of
measurement campaigns have been carried out to perform
The PBR demonstrator used for the purpose of this work is
detection of various vessels both arriving and departing from
named SMARP (Software-defined Multiband Array Passive
the Livorno harbour, by exploiting the DVB-T signal. The
Radar) and it has been conceived in the framework of the
Italian National Plan for Military Research by the Radar and surveillance antenna was directed towards an area of sea in
Surveillance Systems Laboratory (RaSS Lab.) of the Italian front of the receiver site at an angular direction of about 260°
National Inter-university Consortium for Telecommunications as shown in Fig. 2. A building which limits the surveillance
(CNIT). The SMARP system is shown in Fig. 1 and the main area toward North is located at the direction of about 275°. The
technical specifications are reported in the following: transmitter of opportunity (see Fig. 2) is a DVB-T transmitter
located on “Monte Serra” in Pisa (around 32 km far from the
receiver). For this installation the effect of the DPI is very
limited thanks to the surveillance antenna which is directed
almost in the opposite direction of the IO and to the presence of
a wall behind the array antenna further reducing the direct
signal.

Fig. 1 SMARP demonstrator pictures

• Antenna system: multiband receiving array antenna for

the surveillance channel, working in UHF (470-790
MHz) and S-band (2100-2200 MHz) with dual
polarization reception (H/V); four linear arrays, two for
each band, composed of eight Logarithmic Periodic
Dipole Antenna (LPDA) patch antennas; a separate
antenna is used for reference signal acquisition.
• The RF-Front-End #1 and Calibration Network: it
contains the system input filters used to reject the
interferences out of the working frequency band, and
the Low Noise Amplifier (LNA) used to amplify the
desired signal with a limiting effect on the system noise
figure. The calibration routine estimates the constant
phase offsets and amplitude imbalances, and generates
the correction coefficients to be applied to the signal
samples before the digital beamforming techniques.
• The RF-Front-End #2: it contains the multichannel
receiver which is based on a Software Radio System
Fig. 2 Scenario geometry
 V. EXPERIMENTAL RESULTS been possible to exploit all 30 acquisitions because the target
In this section the preliminary results obtained during the was detectable only in the first 18 acquisitions.
measurement campaign are presented. The trajectories of non-
cooperative vessels have been acquired with Automatic
Identification System (AIS) receiver to be used as validation
for the detection and tracking functionalities of the system.
According to Fig. 3, in the considered experiment, two
dual polarized antennas, one horizontally polarized (channel
4) and one vertically polarized (channel 5), have been used as
surveillance channels. Regarding the reference channel, a
dedicated horizontal polarized antenna, with the same
characteristics of the array elements, has been used. The
carrier frequency of the DVB-T signal transmitted in horizontal
polarization was 546 MHz.
In [11] the main characteristics of the non-cooperative
vessels exploited during the experiment can be found and are
reported in TABLE I.

Fig. 4 Plot sequences in the Range Doppler map for 30 consecutive

acquisitions with Ref-H and Surv-H

The simplest possible processor can be implemented by

using the single polarimetric-channel. In this case, the detector
simply compares the magnitude of the HH or HV channels to
the detection threshold. Specifically the blue and red lines
represent the SINR values evaluated on H channel and V
channel respectively. The green line represents the SINR
values after a simple combination of the signals received at
different antennas. Precisely the range-Doppler maps obtained
Fig. 3 Array antenna geometry at the two surveillance channels are incoherently integrated
[13]. In relation to the SINR values, it is important to point out
TABLE I. TARGETS CHARACTERISTICS that for some acquisitions the values on HV channel are higher
Target MMSI Name Type Size than HH channel, this behaviour is particularly evident for
target #3. Regarding the green line, it is worth nothing that it
#1 229970000 Excellent Cargo 125m x 20m follows the HH channel more closely than the HV channel in
terms of SINR values. This is entirely due to the fact that
Anna Sophie
#2 304317000
Dede
Cargo 135m x 23m power levels of the target and the clutter in the HH channel are
higher than the ones in the HV channel. In Fig. 8 and Fig. 9
Corsica
#3 247552000
Marina
Passenger 120m x 20m the power of the target echo and the power of the considered
range-Doppler map floor relative to the target#3 are shown.
These results allow us to state that the polarization diversity
Fig. 4 reports the overlapped range-Doppler maps obtained
might be exploited in DVB-T passive radar to improve the
for 30 consecutive acquisitions after the application of
detection performance and to increase the coverage of the
common PBR processing architecture [12].
systems. To do this a study on polarimetric target detection
The integration time was 1s and the time between two
algorithms and on polarimetric clutter model applied to the
consecutive acquisitions is around 1 minute. The positions of
PBR case will be further investigated.
the three targets described before are highlighted with white
From the point of view of the array antenna element,
ellipses. We propose a solution to estimate the SINR from the
during this demonstration phase it has been decided to use
acquired range-Doppler maps. Using the position of the target
separate elements for each linear polarization in order to better
in the range-Doppler maps as a reference, the SINR was
characterize the two possibilities. The future upgrades of the
evaluated for each acquisition as the ratio between the power
system are going to consider also a new design of the single
of the target echo and the power of the considered range-
receiving element; different approaches will be taken into
Doppler map floor. To avoid corrupting this estimate with
account, as combining in the same structure the two linearly
power leaks coming from the target itself, the cells
polarized receiving antennas or using a circular polarized
immediately adjacent to the target peak are normally ignored.
antenna. The most suitable solution will be chosen considering
In Fig. 5, Fig. 6 and Fig. 7 the SINRs relative to the three
the requirements coming from the application of interest.
targets of interest are shown. Regarding target #3, it has not
Fig. 5 SINR of the target #1 Fig. 8 Power of the Target #3

Fig. 6 SINR of the target #2 Fig. 9 RD Map floor power of the Target #3

VI. CONCLUSION
The present work has been focused on the preliminary
investigation of the potential benefits obtainable by taking
advantage of the polarization diversity in a PBR system
exploiting DVB-T signals. In particular, a PBR demonstrator
equipped with a surveillance array antenna able of
simultaneously receiving both horizontal and vertical
polarizations has been used to experimentally asses the radar
performances as a function of the received polarization. The
results obtained in a maritime scenario show a different target
SINR variation as a function of the surveillance channel
receiving polarization. Therefore, the availability of receiving
both H and V polarizations might improve the target detection
performance if a suitable method of combining the signals
received at different polarization is adopted. Furthermore the
suppression of the interference caused by the reception of the
Fig. 7 SINR of the target #3 direct signal coming from the IO can be enhanced if the
surveillance antenna operates in the cross-polarization with
respect to the polarization used in transmission by the exploited [13] R.D. Chaney, M.C., Bud, L.M. Novak, "On the performance of
polarimetric target detection algorithms," in Aerospace and
IO. This additional advantage can be used when operating in an Electronic Systems Magazine, IEEE , vol.5, no.11, pp.10-15,
unfavourable bistatic geometry, which means that the Nov.1990
surveillance antenna is steered towards the direction of the IO.
In this case a very strong DPI might be experienced therefore
operating in the cross-polarization will reduce the possibility of
saturating the RF amplification chain or the ADC.
ACKNOWLEDGMENT
The authors would like to thank the Centro di Supporto e
Sperimentazione Navale - Istituto per le Telecomunicazioni e
l’Elettronica “Giancarlo Vallauri” (CSSN-ITE), an
experimental facility of the Italian Navy, for technical and
logistic support given during the experiment that took place in
Livorno. A special acknowledgement goes to the “V Reparto”
of Segredifesa, which is the department of the Italian MoD in
charge of the Technological Innovation, for funding the
SMARP project, together with CNIT, within the contract
number 20008.

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