Communications: directive radio wave systems and devices (e.g. – Directive – Including a steerable array
Reexamination Certificate
1999-12-09
2001-11-06
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a steerable array
C342S375000
Reexamination Certificate
active
06313792
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application relates to French Patent Application 98-07240 incorporated by reference herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention regards an optical control device for broadband radar transmission and reception. It is applicable to the control of broadband electronic scanning antennas to ensure both the formation of a beam for transmission and the reception of a beam reflected by a target.
2. Discussion of the Background
An electric scanning antenna comprises many radiating elements that ensure both the transmission and the reception of an ultrahigh frequency signal. A transmission or reception beam is formed by all the signals transmitted or received by each element. To orient a beam in a given direction &thgr;, it is necessary to create time delays between signals transmitted or received by the various radiating elements. To obtain an analogous effect, it is known how to create a phase delay between these signals. The phase difference &phgr;
1
−&phgr;
2
between the signals transmitted or received by two radiating elements is given by the following equation:
Φ
1
-
Φ
2
=
d
sin
θ
c
×
2
π
f
(
1
)
where d represents the distance between the two radiating elements, f represents the frequency of the signals and c represents the speed of the light, the time delay created being
T
1
-
T
2
=
d
sin
θ
c
.
The phase difference &phgr;
1
−&phgr;
2
is equal to 2&pgr;f(T
1
−T
2
).
The preceding equation (1) highlights a major disadvantage residing in the fact that the phase difference depends on the frequency. Consequently, if the frequency varies, the sighting angle varies as well. This method for orienting a beam is therefore not suited to broadband radar. However ultrahigh frequency techniques do not allow us to create a time delay between the signals other than through the creation of the preceding phase difference, except to implement a device that is prohibitive from a size and cost standpoint. Effectively, a theoretically simpler solution would be to create a delay directly between the signals supplied to the different radiating elements, but that would require cumbersome and costly ultrahigh frequency circuits, due more particularly to the unavoidable dimensions imposed by the wavelengths in question.
The use of optical techniques allows us to overcome the aforementioned disadvantage by controlling the radiating elements directly through time delays, without requiring the artifice of phase differences, these delays being created in the optical domain. To that effect, optical control solutions for electronic scanning antennas have already been implemented. With regard to transmission, numerous optical control architectures have already been proposed in order to control the radiation pattern during transmission. An example of optical architecture is given in French patent No. 90 03386.
With regard to reception, beam formation using time delays requires a very significant dynamic of all the delays, still inaccessible to the optical components. A direct architecture based on the bi-directional operation of the control developed for transmission therefore does not seem possible in the short- or intermediate-term. To mitigate this disadvantage, a correlation architecture was defined in particular in accordance with the description of French patent No. 94 11498. However, this type of architecture is restricted to radars with a small bandwidth, typically 10 MHz.
SUMMARY OF THE INVENTION
The disadvantage of a correlation architecture stems particularly from the fact that the use of complementary delays is incompatible with local oscillator signal frequencies and remote transmission signal frequencies, for example 500 MHz, which characterize broadband radar. This frequency difference is unavoidable for the proper operation of a radar system, particularly in order to avoid problems linked to aliasing.
One goal of the invention is more particularly to allow an architecture of the aforementioned type to function for a radar with a large bandwidth. To this end, the aim of the invention is an optical control device for electronic scanning antenna comprising radiating elements for controlling this device comprising a set of optical circuits for creating delays, each receiving a first light beam, polarized according to a first direction and having a first wavelength, this first beam being affected by an appropriate delay; and a second light beam, polarized according to a second direction, with a second wavelength. Each optical delay circuit induces complementary delays with respect to a determined time value on the light of the first and second beams that it receives, a chromatic separator is situated at the output of each delay circuit and separates the light with the first wavelength from the light with the second wavelength, and each radiating element of the antenna is coupled to the output of a delay circuit by a first photodetector. As the two beams are modulated at the transmission frequency, for each receiving signal of a radiating element, the local oscillator is supplied at the output of a first ultrahigh frequency mixer by mixing the transmission frequency and an intermediate frequency, then the frequency of the receiving signal supplied to the radar processing means, at an intermediate frequency augmented by the Doppler frequency of the signal received, is obtained at the output of a second ultrahigh frequency mixer by mixing the local oscillator frequency with the frequency of the signal received.
In an embodiment variation of a device according to the invention, as the two beams are modulated at the transmission frequency, for each receiving signal of a radiating element the local oscillator frequency is supplied at the output of a photo-mixer by mixing the frequency of the signal received carried by the optical wave and an intermediate frequency, then the frequency of the receiving signal supplied to the radar processing means, at an intermediate frequency augmented by the Doppler frequency of the signal received, is obtained at the output of an ultrahigh frequency mixer by mixing the local oscillator frequency with the transmission frequency.
The main advantages of the invention are that the invention makes it possible to avoid the transposition of the receiving signal on an optical carrier, while benefiting from the broadband processing offered by a time-delay architecture, and that it is simple to implement.
REFERENCES:
patent: 5231405 (1993-07-01), Riza
patent: 5235463 (1993-08-01), Broussoux et al.
patent: 5298740 (1994-03-01), Ayral et al.
patent: 5307073 (1994-04-01), Riza
patent: 5307306 (1994-04-01), Tournois et al.
patent: 5428697 (1995-06-01), Dolfi et al.
patent: 5430454 (1995-07-01), Refregier et al.
patent: 5475525 (1995-12-01), Tournois et al.
patent: 5936484 (1999-08-01), Dolfi et al.
patent: 6031201 (2000-02-01), Amako et al.
patent: 0 708 491 (1996-04-01), None
N.A. Riza, et al., Applied Optics, vol. 36, No. 5, pp. 983-996, “Phased-Array Antenna, Maximum-Compression, Reversible Photonic Beam Former with Ternary Designs and Multiple Wavelengths,” Feb. 10, 1997.
Dolfi Daniel
Maas Olivier
Merlet Thomas
"Thomson-CSF"
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Phan Dao
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