ELECTRONIC DEFLECTION DEVICE FOR A MICROFREQUENCY BEAM.

Abstract

This electronic deflection device is characterized in that the ferrite body is in the form of a plate forming part of a planar waveguide in which the incident, deflected and elastic wave beams propagate, and in that the incident beam and the elastic wave are chosen so that their wave vectors (ki and K) and the wave vector (kd) of the deflected beam form a right triangle, the vector (K) of the elastic wave and that (kd) of the deflected beam forming a right angle.

Description

The present invention relates to a certificate of addition concerning an improvement made to the deflection device described in the main patent. The deflection device described in this main patent comprises a magnetostrictive ferrite body disposed in the path of a microwave beam and subjected to magnetic polarization and means for generating at least one elastic wave in the body to create in it a network of stresses generating a phase network, in order to deflect the beam. As explained in the main patent, when one wishes to obtain a single deflected beam, that is to say in the case of diffraction of BRAGG, a network of scanning transducers must be used to vary the direction of the wave vector K of the elastic wave at the same time as its frequency. The purpose of this certificate of addition is to improve this device in order to obtain a single deflected beam by varying only the frequency of the elastic wave in the body, thereby eliminating the scanning transducer array. To this end, the invention relates to an electronic deflection device for a microwave beam according to any one of claims 1, 2, 3, 5, 6, 7, 8, 9, 10, 11, 13 or 14 and 15 of the main patent, characterized in that the ferrite body is in the form of a plate forming part of a planar waveguide in which the incident and deflected beams and the elastic wave propagate, and in that the incident beam and the elastic wave are chosen so that their wave vector and the wave vector of the deflected beam form a right triangle, the wave vector of the elastic wave and that of the deflected beam forming a right angle. Advantageously, varying the frequency of the elastic wave is used to vary the direction of the deflected beam. Also advantageously, the magnetic polarization Mo must satisfy the relation 0.3 Ms S Mo S 0.9 Ms where Ms represents the saturation magnetization of the ferrite satisfying the relation Ms < 0.8 w ygyro x po where w is the angular frequency of the microwave, ygyro the gyromagnetic ratio, and po the permeability of a vacuum. Finally, and according to another characteristic, a magnetic bridge parallel to the direction of magnetization is formed between the corresponding faces of the body to close the magnetic circuit. The invention will be better understood with the aid of the following description, given solely by way of example and made with reference to the accompanying drawings, on which - Fig. 1 illustrates the wave vectors of the incident and deflected beams and of the elastic wave implemented in the device according to the invention; and - Fig.2 represents an embodiment of a device according to the invention. It has already been indicated in the main patent that by using guided waves, the elastic power and the volume of ferrite required to make the device according to the invention are reduced. The purpose of this certificate of addition is to propose an improvement concerning planar waveguides. In the following description, a waveguide is defined as a stack of homogeneous layers all parallel to the same plane P. A detailed description of these planar waveguides can be found, for example, in "Theory of Electromagnetic Waveguides," Chapter III by C. Vassallo, edition EYROLLES, for microwave modes and "Acoustic fields and waves in solids" chapter X by PAAULD, G.WILEZ edition and SONS for elastic modes. In the device according to the invention, at least one of these layers consists of a magnetically polarized magnetostrictive ferrite plate in accordance with the explanations given in the main patent. As can be seen with regard to Fiv.1, the incident and deflected beams and the elastic wave propagate in the plane P defined by this waveguide, and the incident beam and the elastic wave are chosen so that their wave vector, respectively ki and K, and the wave vector kd of the deflected beam form a right triangle, the vector K of the elastic wave and that of the deflected beam kd forming a right angle, for the elastic or acoustic center frequency Fo. It should be noted that this condition implies that the guided wavelengths Ai and Ad respectively of the incident mode or beam and of the diffracted mode or beam are different, which is relatively easy to achieve by using guided modes whose field configurations are different. Thus, while the main patent indicated that to obtain a single deflected beam, i.e., in the case of Bragg diffraction, a scanning transducer array must be used to vary the direction of the elastic wave vector K along with its frequency, in the present device, the diffraction condition of BRAGG, kd = ki + K is conserved over a wide frequency band AF around Fo without changing the direction of the vector K and therefore without requiring a network of transducers. We therefore obtain a single beam deflected over a wide angular range AE with a single control of the frequency F instead of those required to control the phase shifters of the transducer network, which greatly simplifies the device. With regard to the diffracted intensity, which is a function of the coupling coefficient between the incident mode and the diffracted mode by the elastic wave in the ferrite, one of the conditions for the effectiveness of the device is that the structure of the planar guide and the choice of modes optimize this coupling coefficient as will be given in more detail later. It should also be noted that, in order to improve the characteristics and performance of the device according to the invention, the magnetic polarization Mo must satisfy the relation 0.3 Ms S Mo S 0.9 Ms where Ms represents the saturation magnetization of the ferrite satisfying the relation Ms < 0.8 w ygyro x po where w represents the angular frequency of the microwave, xgyro the gyromagnetic ratio, and ijO the permeability of a vacuum. This allows, on the one hand, for a reduction in magnetic losses and, on the other hand, for the piezomagnetic tensor d of the ferrite to be maximized in order to increase the efficiency of the device. Furthermore, a magnetic bridge parallel to the direction of magnetization can also be formed between the corresponding faces of the body to close the magnetic circuit. This virtually eliminates demagnetizing fields, which further reduces the polarizing magnetic field. This field can be, as explained in more detail in the main patent, either a coercive field from the magnetostrictive ferrite, a field created by permanent magnets arranged in the magnetic circuit, or a field created by a coil surrounding the bridge of the magnetic circuit. In the last two examples mentioned, it is possible to ensure very good independence of Mo from temperature, either by choosing permanent magnets with very high Curie temperatures, or by controlling the current in the coil so as to keep Mo constant. If we now refer to Fig.2, which represents a perspective view of a device according to the invention, operating in the KA band around a frequency f = 30 GHz, we can see that it comprises a planar waveguide 1 made of a magnetostrictive ferrite ceramic plate of composition NixZn 1-x Fe2O4 with x = 0.5. This plate, for example, has dimensions of 110 mm x 145 mm and a thickness of 2 mm. In this example, the body then has the following characteristics ygyropo Ms = 0.5 w Magnetic losses are therefore low. The incident mode and the TE mode 10 Ai = 3.4 mm, the diffracted mode and the TM mode 10 Ad = 4 mm and the angle EI (Fig.1) between the wave vector of the incident beam and that of the diffracted beam for the center frequency, is equal to 30-. To produce this incidence, a ceramic wedge 2, composed of Al2O3 and with an angle n of 34° and a thickness of 2 mm, is placed on the input face of the microwave beam in the ferrite plate. The elastic mode is the 5H shear mode, and the elastic center frequency Fo is 510 kHz. o This elastic mode is produced by transducers 3 made of lead titanozirconate ceramic, for example type X5105 from the company PONS, polarized in a direction normal to the electrodes and excited according to the d33 mode. These transducers are powered by a single frequency control source F and designated by reference 4 in this figure. These transducers are glued or welded onto the corresponding edge of the ferrite, which has a flare 5 to facilitate the attachment of the transducers by widening the junction surface. A corresponding flare 6 is also formed on the opposite side of the ferrite to bond a silicone resin absorption device 7, enabling the progressive elastic wave to be produced. The ferrite plate is magnetically polarized along OX3, and as explained previously, the magnetic circuit is closed using a soft ferrite bridge 8 (manganese and zinc ferrite) into which a slice of permanent magnet 9 can be inserted, creating a magnetostrictive magnetic field polarizing the ferrite plate with a value of Mo = 0.7 Ms. The device according to the invention also includes a standard rectangular waveguide R320 10 feeding a radiating source 11 formed of a sectoral horn in the plane E corrected by a dielectric lens of composition Al2O3 (Er = 10) and matching elements of the same composition designated by reference 12 on this figure at the entrance of the body for the incident mode and in Teflon, 13, at the exit of the body for the deflected mode. Under these conditions and with a relative bandwidth of the transducers, AF / F = 1 / 2 around Fo, we obtain a 30 scan on each side of OXI with a single deflected beam, a switching time of 40 ps and an electrical control power of 10 Watts, with insertion losses on the order of 3 dB.

Claims

DEMANDS 1. Electronic deflection device of a microwave beam according to any one of claims 1,2,3,5,6,7,8,9,10,11,13 or 14 and 15 of the main patent, characterized in that the ferrite body (1) is in the form of a plate forming part of a planar waveguide in which incident and deflected beams and the elastic wave propagate, and in that the incident beam and the elastic wave are chosen so that their wave vector (ki and K) and the wave vector (kd) of the deflected beam form a right triangle, the vector (K) of the elastic wave and that (kd) of the deflected beam forming a right angle.

2. Device according to claim 1, characterized in that the frequency (F) of the elastic wave is varied to vary the direction of the deflected beam.

3. A device according to any one of the preceding claims, characterized in that the magnetic polarization Mo satisfies the relation 0.3 Ms S Mo 4 0.9 Ms where Ms represents the saturation magnetization of the ferrite satisfying the relation Ms < 0.8 w ygyro x po where w is the angular frequency of the microwave, ygyro the gyromagnetic ratio, and po the permeability of a vacuum.

4. Device according to any one of the preceding claims, characterized in that a magnetic bridge (8) parallel to the direction of the magnetization is formed between the corresponding faces of the body (1) to close the magnetic circuit.

5. Device according to claim 4, characterized in that means (9) for generating magnetic polarization are arranged in the magnetic bridge (8).

6. Device according to claim 5, characterized in that the means for generating the magnetic polarization are formed by a permanent magnet (9) inserted in the bridge.

7. Device according to claim 5, characterized in that the means for generating the magnetic polarization are formed by a coil arranged around the bridge.