CIRCUIT WITH CIRCULATOR FUNCTION WITH SIW TECHNOLOGY, CORRESPONDING TRANSMIT / RECEIVE CHANNEL AND RADAR

Description

[0001] The present invention relates to the field of radiofrequency circuits and, more particularly, to that of circuits making it possible to perform a circulator function, for example with a view to an application in a monostatic radar.

[0002] The document D'ORAZIO W et al. “Substrate-Integrated-Waveguide Circulators Suitable for Millimeter-Wave Integration”, IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, PLENUM, USA, vol. 54, no. 10, October 1, 2006 (2006-10-01), pages 3675-3680, the document CHEN JX et al, "DEVELOPMENT OF A LOW COST MICROWAVE MIXER USING A BROAD-BAND SUBSTRATE INTEGRATED WAVEGUIDE (SIW) COUPLER", IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS, IEEE SERVICE CENTER, NEW YORK, NY, US, vol. 16, no. February 2, 2006 (2006-02-01), pages 84-86, and document US 2018 / 159192 A1 respectively disclose a circuit performing a circulator function intended to be mounted between a transmitter and a receiver, on the one hand, and an antenna element, on the other hand, said circuit being produced in “substrate-integrated waveguide” - SIW technology.

[0003] There figure 1 is a functional diagram of a transmission / reception channel of a monostatic radar comprising a transmitter E and a receiver R, which are coupled to an antenna element A through a circulator 5, so that the radar can transmit and receive simultaneously.

[0004] Circulator 5 directs the signal delivered by transmitter E (or transmission signal) towards antenna element A, while it directs the signal received by antenna element A (or antenna signal) towards receiver R.

[0005] Circulator 5 therefore makes it possible to address the antenna element in transmission without the receiver being disturbed by the emitted wave.

[0006] Known circulators are essentially magnetic type circulators, using magnetic fields, magnets and ferrites.

[0007] Circulators made from printed circuits carrying electronic components are also known.

[0008] Thus, all known solutions involve electrical or electronic components so that known circulators have a significant footprint, which is not compatible with the necessary integration, for example, in multi-channel radar antennas, used in particular for electronic scanning.

[0009] In addition, the presence of the circulator 5 is the source of a coupling (of the order of at least twenty decibels) between the transmitter E and the receiver R. This coupling causes a leak of the transmission signal towards the receiver R.

[0010] Therefore, the signal applied to the input of the receiver R (or reception signal) results from the superposition of the antenna signal, which alone constitutes the useful signal, and a leakage signal, which is an unnecessary signal disturbing the processing of the antenna signal.

[0011] To cancel the leakage signal, it is known to take a replica of the transmission signal and, after modifying its phase and amplitude, to reinject the cancellation signal thus obtained on the receiver input to cancel the leakage signal.

[0012] To generate such a cancellation signal, one can for example, as shown in the figure 1 , taking a fraction of the transmission signal by means of a first coupler 6 interposed between the transmitter and the coupler 5. The replica thus taken is then shaped by means of a phase shifter 7, suitable for adapting the delay of the cancellation signal, and an attenuator 8, suitable for adapting the amplitude of the cancellation signal. The replica thus shaped is applied to one of the inputs of a second coupler 9, interposed between the coupler 5 and the receiver R, which generates the cancellation signal and superimposes it on the signal coming from the coupler 5 before applying it to the input of the receiver R. By adapting the amplitude and the phase of the cancellation signal, it is possible to cancel the leakage signal so that the reception signal corresponds to the antenna signal alone.

[0013] Therefore, electronic components must be added to the known couplers to cancel the leakage signal, which has a negative effect on the overall size of the circulator function.

[0014] The aim of the present invention is to solve this problem, in particular by proposing a circuit making it possible to carry out the circulator function in a particularly compact manner.

[0015] For this purpose, the invention relates to a circuit in SIW technology performing a circulator function, a transmission / reception channel, and a radar according to the appended claims.

[0016] The invention and its advantages will be better understood upon reading the following detailed description of a particular embodiment, given solely as a non-limiting example, this description being made with reference to the appended drawings in which: [ Fig 1 ] there figure 1 is a functional diagram of a transmission / reception channel of a monostatic radar, which integrates a circuit according to the invention; [ Fig 2 ] there figure 2 is a schematic representation in top view of a first hybrid component of the circuit according to the invention; [ Fig 3 ] there figure 3 is a graph representing, as a function of frequency, the gain on each of the ports of the hybrid component of the figure 2 when injecting a signal on an input port; [ Fig 4 ] there figure 4 is a schematic representation in top view of a coupling component of the circuit according to the invention; [ Fig 5 ] there figure 5 is a graph representing, as a function of frequency, the gain on each of the ports of the coupling component of the figure 4 when injecting a signal on an input port; [ Fig 6 ] there figure 6 is a schematic representation in top view of the circuit according to the invention associating the hybrid component of the figure 2 and the coupling component of the figure 4 ; [ Fig 7 ] there figure 7 is a graph representing, as a function of frequency, the gain on each of the terminals of the circuit of the figure 6 when injecting a transmission signal; [ Fig 8 ] there figure 8 is a representation of the amplitude of the electric field in the circuit of the figure 6 when injecting a transmission signal; [ Fig 9 ] there figure 9 is a graph representing, as a function of frequency, the gain on each of the terminals of the circuit of the figure 6 when injecting an antenna signal; and, [ Fig 10 ] there figure 10 is a representation of the amplitude of the electric field in the circuit of the figure 6 when injecting an antenna signal.

[0017] There figure 1 is a functional diagram of a transmission / reception channel 100 of a monostatic radar.

[0018] It includes a transmitter E capable of generating a transmission signal.

[0019] It comprises an antenna element A capable of emitting an electromagnetic signal into the environment as a function of the transmission signal and of generating an antenna signal from the electromagnetic signal captured in the environment.

[0020] It includes a receiver R capable of processing a reception signal ideally corresponding to the antenna signal.

[0021] The transmission / reception channel 100 comprises a circuit 110 which performs at least one circulator function and, possibly, a leakage signal cancellation function.

[0022] The circuit 110 is produced using “substrate integrated waveguide” (SIW) technology. In a manner known per se, a circuit using SIW technology comprises a substrate, made of a dielectric material and of low thickness, and first and second conductive layers, made of a material that conducts electric current, the first and second layers covering the two large faces of the substrate. The circuit also comprises a plurality of metallized holes, each metallized hole forming a via between the first and second conductive layers. The circuit behaves like a waveguide delimited, according to the thickness, between the first and second conductive layers and, according to the width, between the plurality of metallized holes.The plated holes locally modify the boundary conditions that constrain the propagation of the electromagnetic field in the substrate, i.e. the properties of the waveguide that constitutes the circuit. The pattern formed by the plurality of plated holes therefore defines the function performed by the circuit.

[0023] The transmitter E is connected to a first terminal 1 of the circuit 110; the antenna element A is connected to a second terminal 2 of the circuit 110; the receiver R is connected to a fourth terminal 4 of the circuit 110 and a third terminal 3 of the circuit 110 is connected to a load 103 adapted for example to 50 Ohms or 75 Ohms. This can also serve as an access point for tests or self-tests.

[0024] The circulator function performed by the circuit 110 functionally comprises a circulator 5 allowing, in transmission, to connect the transmitter E to the antenna element A and, in reception, the antenna element A to the receiver R.

[0025] Advantageously, the circulator function performed by the circuit 110 is increased by a function of canceling the leakage signal between the transmitter E and the receiver R. The cancellation function functionally comprises a first coupler 6, a phase shifter 7, an attenuator 8 and a second coupler 9.

[0026] The first coupler 6 is arranged between terminal 1 and circulator 5 so as to take a fraction of the transmission signal. The fraction of the signal thus taken is transmitted to means 7 and 8 so as to adjust its phase and amplitude. The replica of the transmission signal thus shaped is applied to the second coupler 9. The latter, arranged between circulator 5 and terminal 4 of circuit 110, injects a cancellation signal whose characteristics make it possible to cancel the leakage signal. Thus, only the antenna signal is transmitted to the receiver R.

[0027] In the preferred embodiment described here, the circuit 110 integrates, on the same substrate, a hybrid component 10, playing the role of circulator 5 and first coupler 6. It comprises a phase shift component 30 playing the role of phase shifter 7. Finally, the circuit 110 comprises a coupling component 50 playing the role of attenuator 8 and second coupler 9.

[0028] The hybrid component 10 will now be described in more detail in connection with the figures 2 And 3 .

[0029] The hybrid component 10 is produced using SIW technology. It is shown schematically in top view on the figure 2 . It has a length of L10 and a width of W10.

[0030] The vias of the hybrid component 10 form a pattern which is symmetrical along a longitudinal axis X10 of the component and along a transverse axis Y10.

[0031] The hybrid circuit 10 comprises four ports 11 to 14: a first port 11 intended to be coupled to the first terminal 1 of the circuit 110 and consequently to the transmitter E; a second port 12 intended to be coupled to the second terminal 2 and consequently to the antenna element A; a third port 13 intended to be coupled to a port of the phase shift component 30; and a fourth port 14 intended to be coupled to a port of the coupling component 50.

[0032] The hybrid component 10 comprises a first waveguide 15 between the ports 11 and 12. This first waveguide is delimited by a lower row of vias 17 and a central row of vias 19. The width of the waveguide 15 at each of its ports is noted a1.

[0033] The hybrid component 10 comprises a second waveguide 16 between the ports 14 and 13. This second waveguide 16 is delimited by an upper row of vias 18 and the central row of vias 19. The width of the waveguide 16 at each of its ports is preferably chosen to be equal to a1.

[0034] The central row 19 is for example made up of a double row of vias. Alternatively, this row could be made up of a single row of vias.

[0035] The central row of vias 19 comprises a central portion 20, which is devoid of vias, and two end portions 21 and 22, on either side of the central portion 20. The central portion 20 defines an opening of length L20 making it possible to establish a coupling between the first and second waveguides 15 and 16.

[0036] The row of vias 17 is made up of the association of a plurality of via segments. Each segment is rectilinear, arranged parallel to the central row 19, but at a distance from the latter which differs from one segment to another so as to form a constriction at the level of the central portion 20.

[0037] Thus, for example, the lower row 17 consists of five segments, the first and fifth segments of which are arranged at a distance W1 / 2 from the longitudinal axis X, the second and fourth segments are arranged at a distance W2 / 2 from the longitudinal axis X and the third segment is arranged at a distance W3 / 2 from the longitudinal axis X.

[0038] The choice of the quantities W1, W2 and W3 contributes to the adjustment of the coupling value by forcing the electric field to converge towards the coupling zone at the level of the opening delimited by the central portion 20.

[0039] A similar description could be made of the top row of vias 18.

[0040] Knowing that the distance between a pair of vias laterally delimiting a waveguide makes it possible to adjust the frequency gain of this waveguide, the distance W3 between the third segment of the lower row 17 and the third segment of the upper row 18 makes it possible to adjust the frequency of the maximum of the coupling.

[0041] The amplitude and phase behavior of the hybrid component 10, when an input signal is applied to port 11 and port 13 is connected to a suitable load (50 or 75 Ohms for example), is as follows.

[0042] The phase shift D ij of the signal between two ports i and j is given by the following relations: D 11 − 12 = D 12 − 13 = D 13 − 14 = π 2 And D 11 − 14 = 3 π 2 .

[0043] There figure 3 is a graph representing, as a function of frequency, the gain on the different ports of the hybrid component 10 when a signal is applied to port 11. A gain G ij is defined as the ratio of the amplitude of the outgoing signal on port j to the amplitude of the signal applied to port i.

[0044] So, for example for the frequency value 13.3 GHz (which belongs to the radio frequency domain - RF), the gain G 11-11 between port 11 and port 11 is about -29 dB, the gain G 11-12 between port 12 and port 11 is about -3 dB, the gain G 11-13 between port 13 and port 11 is about -4 dB and the gain G 11-14 between port 14 and port 11 is about -31 dB.

[0045] It is noted that the behavior of the hybrid component 10 is reminiscent of that of a state-of-the-art ring circulator.

[0046] The circuit according to the invention could be limited to the single hybrid component 10, port 11 then being connected to terminal 1 and to the transmitter, port 12 being connected to terminal 2 and to the antenna, port 13 being connected to terminal 3 and to a suitable load (for example with an impedance of 50 or 75 Ohms) and port 14 connected directly to terminal 4 and to the receiver R. This would perform the sole circulator function.

[0047] Terminal 3 can be used as an access point for testing or self-testing.

[0048] On the other hand, it would be desirable, in transmission, to reduce the leakage on terminal 14 and possibly, in reception, to maximize the power transmitted to terminal 14. That is to say, to associate a leakage cancellation function with that of circulator.

[0049] For this, the hybrid component 10 is advantageously associated with the phase shift component 30 and the coupling component 50.

[0050] The coupling component 50 will now be described in more detail in connection with the figures 4 And 5 .

[0051] The coupling component 50 is produced using SIW technology. It is shown schematically in top view on the figure 4 . It has a length L50 and a width W50.

[0052] The vias of the coupling component 50 form a pattern which is symmetrical along a longitudinal axis X50 of the component and along a transverse axis Y50.

[0053] The coupling circuit 50 comprises four ports 51 to 54: a first port 51 intended to be connected to port 13 of the hybrid component; a second port 52 intended to be connected to terminal 3 of the circuit 110 and consequently to a suitable load (for example 50 or 75 Ohms); a third port 53 intended to be connected to terminal 4 of the circuit 110 and consequently to the receiver R; and a fourth port 54 intended to be coupled to port 14 of the hybrid component 10.

[0054] The coupling component 50 comprises a first waveguide 55 between the ports 51 and 52. This first waveguide is delimited by a lower row of vias 57 and a central row of vias 59. The width of the waveguide 55 at each of its ports is noted a5.

[0055] The coupling component 50 comprises a second waveguide 56 between the ports 54 and 53. This second waveguide 56 is delimited by an upper row of vias 58 and the central row of vias 59. The width of the waveguide 56 at each of its ports is preferably chosen to be equal to a5.

[0056] The lower row 57 and upper row 58 are straight and parallel to the central row 59. They have a uniform pitch between their respective vias.

[0057] The central row 59, for example consisting of a single thickness of vias, comprises a central portion 60, the density of which is reduced, and two end portions, 61 and 62, on either side of the central portion 60, the density of which is greater and for example identical to that of the upper and lower rows 67 and 68.

[0058] The central portion 60 creates a leak between the first and second waveguides 55 and 56, establishing a coupling between the electromagnetic fields established in these waveguides.

[0059] The pitch separating two successive vias and the length L60 of the central portion 60 makes it possible to adapt the value of the coupling between the waveguides 55 and 56.

[0060] More generally, the behavior of the coupling component 50 depends on the geometric parameters of the pattern formed by the vias.

[0061] The amplitude and phase behavior of the coupling component 50, when an input signal is applied to port 51 and port 53 is connected to a suitable load, is as follows.

[0062] The phase shift D ij of the signal between two ports i and j is approximately 90°.

[0063] There figure 5 is a graph representing, as a function of frequency, the gain on each of the ports of component 50 when an input signal is applied to port 51.

[0064] For example, for the value of 13.3 GHz, the G 51-51 gain between port 51 and port 51 is of the order of -34 dB, the G 51-52 gain between port 52 and port 51 is of the order of -0.4 dB, the G 51-53 gain between port 53 and port 51 is of the order of -24 dB and the G 51-54 gain between port 54 and port 51 is of the order of -48 dB.

[0065] We therefore see that by applying an input signal to port 51, most of the power is transmitted to port 52 and, to a lesser extent, to port 53. On the other hand, the signal on port 54 is strongly attenuated.

[0066] There figure 6 is a representation, seen from above, of the circuit 110 according to the invention, which is preferably entirely produced using SIW technology, the various components being produced on the same substrate. For example, the circuit 110 has a length of 80mm and a width of 27mm.

[0067] On the figure 6 we find the hybrid component 10 whose port 11 is connected by a waveguide to terminal 1 of the circuit 110 intended to be connected to the transmitter E; port 12 is connected by a waveguide to terminal 2 of the circuit 110 intended to be connected to the antenna A; port 14 coincides with port 54 of the coupling component 50; and port 13 is connected to port 51 of the coupling component 50 through the phase shift component 30.

[0068] We also find the coupling component 50, whose port 53 is connected by a waveguide 106 to terminal 4 of the circuit 110 intended to be connected to the receiver R; port 52 is connected by a waveguide 107 to terminal 3 of the circuit 110 intended to be connected to a suitable load.

[0069] Finally, we find the phase shift component 30.

[0070] This consists of a "U"-shaped waveguide which extends between an input port 31, which coincides with the port 13 of the hybrid component 10, and an output port 32, which coincides with the port 51 of the coupling component 50.

[0071] The phase shift component comprises a first rectilinear waveguide portion 102, which opens into a second rectilinear waveguide portion 104, arranged at 90° relative to the first waveguide portion 102. The second waveguide portion 104 opens into a third rectilinear waveguide portion 103, arranged at 90° relative to the second waveguide portion 104. The first and third waveguide portions are parallel but oriented in opposite directions.

[0072] Advantageously, the component 30 has a pattern for guiding the electromagnetic field in a hairpin circuit. For example, the lower and upper corners of the second waveguide portion 104, opposite the first and third portions, have vias to assist in the propagation of the field.

[0073] The lengths of the first and third waveguide portions make it possible to adjust the phase shift between the signal applied to the input port 31 and the signal delivered to the output port 32.

[0074] The phase shift adjustment is made so that the signal injected into port 51 of the coupling component 50 is 180° out of phase with the signal injected into port 54 of the coupling component 50 in order to be able to cancel it.

[0075] There figure 7 is a graph representing, as a function of frequency, the gain on each of the terminals of circuit 110 when a transmission signal is applied to terminal 1. Still for the considered frequency of 13.3 GHz, the gain G 1-1 between input 1 and input 1 is approximately -18 dB, the gain G 1-2 between input 2 and input 1 is of the order of -3.6 dB, the gain G 1-3 between terminal 3 and terminal 3 is of the order of -5.8 dB and finally the gain G 1-4 between terminal 4 and terminal 1 is of the order of -46.8 dB.

[0076] Thus, in transmission, circuit 110 allows maximum power to be transmitted from terminal 1 to terminal 2, while strongly attenuating the leakage signal on terminal 4. It will be noted that the gain between terminal 1 and terminal 4 is -46.8 dB, while the gain G 11-14 between port 14 and port 11 was -31.2 dB on the figure 3 . There is therefore a strong attenuation of the leakage signal with the interposition of the coupling component 50 between port 14 of the hybrid component and terminal 4 of the circuit.

[0077] There figure 8 represents the amplitude of the electric field in the circuit 110 operating in transmission. In particular, it can be seen that a replica of the transmission signal is delivered to port 13 of the hybrid component, which is then injected, after phase shift, into the coupling component to cancel the leakage signal on terminal 4, while the latter was still visible at port 14 of the hybrid component.

[0078] There figure 9 is a graph representing, as a function of frequency, the gain on each of the terminals of circuit 110 when an antenna signal is applied to terminal 2 of circuit 110. This is therefore the reception behavior of circuit 100.

[0079] So on the figure 9 , for the frequency of 13.3 GHz, the gain G 2-2 between terminal 2 and terminal 2 is of the order of -34 dB, the gain G 2-1 between terminal 2 and terminal 1 is of the order of -3.6 dB; the gain G 2-4 between terminal 4 and terminal 2 is of the order of -4.8 dB and the gain G 2-3 between terminal 3 and terminal 2 is of the order of -17 dB.

[0080] There figure 10 represents the amplitude of the electric field in the circuit 110 operating in reception. It can therefore be seen that the antenna signal applied to terminal 2 is essentially distributed between terminal 1 connected to the transmitter and terminal 4 connected to the receiver. The presence of the coupling component 50 slightly reduces the gains on terminal 2 and terminal 4, but marginally.

[0081] In the above, all the functionalities associated with the circulator are gathered in a single component 110. This therefore has very high integrability, its dimensions being reduced.

[0082] Alternatively, only some of the functionalities could be implemented using SIW technology or by combining different components using SIW technology.

[0083] For example, a hybrid component in SIW technology could constitute a first circuit associated with electronic components to perform attenuation, phase shift and secondary coupling functions. Optionally, these last two functions could be performed by a coupling component in SIW technology.

[0084] Those skilled in the art will understand that adjusting the topology of the patterns of the components produced using SIW technology makes it possible to precisely adjust the value of the characteristics of the function(s) produced.

[0085] The present invention finds its application in radar systems requiring high integration of the acquisition electronics so as to allow integration in the immediate vicinity of the radiating element, preferably at the rear of the latter. This is particularly well suited for network type antennas.

Claims

1. A circuit (110) performing a circulator function intended to be mounted between a transmitter (E) and a receiver (R), on the one hand, and an antenna element (A), on the other hand, said circuit being made from substrate integrated waveguide, SIW, technology, said circuit further performing a function of canceling a leakage signal, the circuit (110) includes: - a hybrid component (10), made up of a first waveguide (15) between a first port (11) and a second port (12), and a second waveguide (16) between a third port (13) and a fourth port (14), the first and second waveguides of the hybrid component being mutually coupled; the circuit being characterized in that it includes: - a phase shift component (30), made up of a U-shaped waveguide (102, 103, 104) between an input port (31) and an output port (32); and - a coupling component (50), made up of a first waveguide (55) between a first port (51) and a second port (52), and a second waveguide (56) between a third port (53) and a fourth port (54), the first and second waveguides of the coupling component being mutually coupled, the first port (11) of the hybrid component being coupled to the transmitter (E), the second port (12) of the hybrid component being coupled to the antenna element (A), the third port (13) of the hybrid component being coupled to the first port (51) of the coupling component through the phase shift component (30), the second port (52) of the coupling component being coupled to a suitable charge, and the third port (53) of the coupling component being connected to the receiver (R) and the fourth port (54) of the coupling component coinciding with the fourth port (14) of the hybrid component (10).

2. The circuit (110) according to claim 1, including a substrate, made from a dielectric material, and first and second conductive layers, made from a conductive material, the first and second layers covering two opposite faces of the substrate, the circuit including a plurality of metallized holes, each metallized hole forming a via between the first and second conductive layers through the substrate, the plurality of metallized holes forming a pattern able to guide the electromagnetic waves in the substrate so as to confer the circulator function on the circuit.

3. The circuit (110) according to claim 1 or claim 2, wherein the hybrid component (10) behaves as a conventional circulator of the ring resonator type.

4. The circuit (110) according to any one of claims 1 to 3, wherein the hybrid (10), phase shift (30) and coupling (50) components are made on a same substrate.

5. A transmission / reception channel (100) including a transmitter (E), a receiver (R) and an antenna element (A), characterized in that it includes a circuit (110) according to any one of the preceding claims mounted between the transmitter (E) and a receiver (R), on the one hand, and an antenna element (A) on the other hand.

6. A radar including an antenna made up of a plurality of antenna elements, each antenna element being associated with a transmission / reception channel, characterized in that each transmission / reception channel is according to the transmission / reception channel of claim 5.