Ww 
| D à 
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| 2 | QD 
À BISTATIC PARASITICAL RADAR 
(BIPAR) 
by 
Philipp Hartl, University of Stuttgart 
and 
Hans Martin Braun, Dornier System, Friedrichshafen 
FRG 
ABSTRACT 
After decades of remote sensing from aircrafts and satellites with cameras and 
other optical sensors Earth observation by imaging radars become more and more 
suitable because of their night and day and all weather operations capability 
and their information content being complementary to those of optical sensors. 
The major problem with microwave sensors (radars) is that there are not many of 
them presently in operation and therefore not enough data available for effec- 
tive radar signature research for civil applications. 
This paper shows that airborne bistatic real aperture radar receivers can be 
operated with spaceborne transmitters of opportunity. Famous candidates for 
those systems are high power communications or direct TV satellites illuminat- 
ing the Earth surface with a power density of more than 10-12 Watt per square- 
meter. The high sophisticated status of signal processing technology today 
allows the realization of receivers correlating the received direct path signal 
from a communications satellite with its unavoidable reflection on the ground. 
Coherent integration can improve the signal to noise ratio up to values where 
the radiometric resolution can satisfy users needs. 
The development of such "parasitical" radar receives could even provide a cost 
effective way to open up new frequency bands for radar signature research. 
Advantages of these quiet systems for the purpose of classical radar reconais- 
sance are evident. 
Is INTRODUCTION 
Bistatic radars are defined as systems in which spatial separation exists be- 
tween the transmitting and the receiving radar chain. The fundamental prin- 
ciples of bistatic surveillance radar systems have been known from the 
beginning of radar history. However, interest in them declined early, doubt- 
less driven by the desire of users, particularly military users, to have radars 
capable of being operated from a single site. Therefore, up to now, monostatic 
radars have been developed to a very sophisticated state, whereas bistatic and 
multistatic radar systems laid dormant for about more than two decades. How- 
ever, these systems received new interest, when the development of advanced 
radar processing techniques allowed bistatic radars to deploy their advantages. 
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