EP0013222B1 - Diode phase shifter for microwaves and electronic scanning antenna comprising same - Google Patents

Description

The present invention relates to a microwave phase shifter with diodes. More particularly, this phase shifter can be produced in a flat structure on a substrate of high dielectric constant and is capable of giving four phase states.

There are different kinds of diode phase shifter, using those of the PIN type, such as disturbance phase shifters which are characterized by high power handling and wide bandwidth and line section phase shifters, such as the switching phase shifter, which characterized compared to the previous ones by a smaller footprint and constant losses as a function of the phase shift. These two types of phase shifters, with disturbance and line sections, lend themselves well to being produced in a flat structure, and it is on the criteria of number of phase shift diodes, standing wave rate (TOS), losses integration and power handling, whether the choice is for one or the other type.

However, these phase shifters pertaining to the prior art, involving propagation line lengths, therefore have phase shift, loss and TOS characteristics varying as a function of frequency.

The object of the invention is a microwave phase shifter with PIN diodes, the structure of which makes it possible to avoid the drawbacks previously mentioned. This structure combines the advantages of perburbation structures which conveniently give constant phases, but at the cost of a large number of diodes, and those of line segment structures which use few diodes, but whose phase shift varies linearly in the frequency band envisaged.

According to the invention, the phase shifter is advantageously produced by the combination of two identical elementary phase shifters with diodes commonly called O-π phase shifters, as they are known for example from document FR ― A ― 2379 196, producing a structure giving four steps phase, while presenting only two different electrical states. Such a structure gives the advantage of a simple development.

According to the invention, on the one hand, the phase shift of ₇ r between two positions - (O, π) and (ϕ, ϕ + π) - is created by the invention of the field obtained in the coupling zone of a line with an asymmetric field structure such as a slit line from a line with a symmetrical field structure, such as a ribbon line or a coplanar line, also achievable in planar structure on ceramic substrate of high dielectric constant; on the other hand, the phase shift of ₇ r is obtained by changing the structure of the line ensuring the transmission of the wave.

According to a characteristic of the invention, the phase shifter considered comprises a first phase shifter O-π acting in the coupling zone of two lines with different electric field structures, and a second phase shifter O-π identical to the first, located at a determined distance first, the connection between the two phase shifters being established by two propagation lines with different electric field structures, different propagation constants and coincident or parallel propagation axes, the two lines then being located in two parallel planes and the propagation axes defining a plane orthogonal to the planes of the lines.

• - la figure 1, un dephaseur à quatre pas de appelé aussi à deux bits, réalisé entre une ligne à ruban et une ligne à fente, vu de dessus;
• - la figure 2, un autre type de réalisation d'un déphaseur à deux bits réalisé entre une ligne à ruban et une ligne à fente, vu de dessus;
• - la figure 3, le déphaseur de la figure 1 vu en coupe;
• - la figure 4, une variante vue en coupe du déphaseur de la figure 1;
• - la figure 5, un déphaseur à deux bits réalisé entre une ligne coplanaire et une ligne à fente, vu de dessus;
• - la figure 6, une ligne coplanaire vue en coupe, transmettant un mode de réalisation à structure de champ électrique symétrique;
• - la figure 7, une ligne coplanaire, vue en coupe, transmettant un mode de propagation à structure de champ électrique dissymétrique.

The invention will be better understood in the description which follows of embodiments given with the aid of the figures which represent:

• - Figure 1, a four-phase dephaser also called two-bit, produced between a ribbon line and a slotted line, seen from above;
• - Figure 2, another embodiment of a two-bit phase shifter made between a ribbon line and a slotted line, seen from above;
• - Figure 3, the phase shifter of Figure 1 seen in section;
• - Figure 4, a variant sectional view of the phase shifter of Figure 1;
• - Figure 5, a two-bit phase shifter made between a coplanar line and a slotted line, seen from above;
• - Figure 6, a coplanar line seen in section, transmitting an embodiment with symmetrical electric field structure;
• - Figure 7, a coplanar line, sectional view, transmitting a propagation mode asymmetric electric field structure.

As indicated in the introduction, the invention proposes to produce a phase shifter giving four phase steps, also called two-bit phase shifter, with PIN diodes, using the absence of coupling which exists between two superposed parallel lines, of which one has a symmetric field structure and the other an asymmetric field structure, these two lines having parallel propagation axes belonging to the same plane orthogonal to the planes of the lines. The connection between the two identical phase shifters O-π is made by such lines, produced in planar structure on ceramic substrate, and of which another characteristic is that they have different propagation constants β ₁ , and P2, such that the difference (β ₁ , - β ₂ ) is constant in the selected frequency band. The difference between the propagation constants may well be due to the very nature of the lines, or may be obtained using high pass filters in one line and low pass filters in the other.

It will be recalled briefly in what follows, what is meant by slotted line, ribbon line and coplanar line whose field structures are different.

A slotted line is a propaga line tion consisting of an opening in a ground plane, deposited on a dielectric substrate. The dielectric support provides the mechanical strength of the metal conductors, generally produced by photoengraving or photolithography. It is a line with asymmetrical field structure.

In a slotted propagation line, almost all of the energy propagates in the dielectric and is concentrated between the edges of the slit. The thickness of the dielectric material is related to its nature and the width of the slotted line then determines the characteristic impedance of the line.

A ribbon propagation line, known by the term microstrip line in the English language, comprises a dielectric plate placed between a metallic ribbon and a metallic plane, the latter called ground plane. Here too, almost all of the energy is concentrated in the dielectric. It is a line with a symmetrical field structure.

A coplanar line is made up of a thin metal strip deposited on the surface of a dielectric 90 with two ground electrodes placed in parallel on either side of the strip. When the dielectric constant is high, most of the energy is stored in the dielectric. The coplanar line is a line capable of transmitting two propagation modes represented by FIGS. 6 and 7: a mode with symmetrical field structure and a mode with asymmetric field structure.

According to the invention, it is a question of phase shifting the microwave electromagnetic field established in a transmission line considered, at a localized point of this line. The object of the invention is achieved by combining, by at least two diodes, two phase shifters with O-π diodes as described in document FR-A-2 379 196.

According to the different combinations of the polarities of each of the diodes of this device, the coupling between the line to be asymmetrical field structure and the line symmetrical field structure is at either of the first phase shifter 0- ₇ r or the second; and in these conditions the transmission of energy is done in one or the other case in a line or in the other.

Figure 1 shows an example of phase shifter to two bit diodes according to the invention, comprising two phase shifters 0- ₇ r microwave diodes, realized in the coupling area of a slot line and a strip line , and linked together by two lines with different electric field structures, a slotted line which extends on both sides by the slotted lines of the two O-π phase shifters thus constituting line 3, and a ribbon line which is extended at one of its ends by the ribbon line of the second phase shifter O-π, thus constituting line 2.

The ribbon lines 1 and 2, the longitudinal axes of which coincide, are obtained by depositing a conductive ribbon of a certain length on a ceramic substrate 90, located above a ground plane 10. The line to slot 3 is cut in this ground plane and its axis of propagation is parallel to the longitudinal axis of the ribbon lines 1 and 2, and defines with the latter a plane orthogonal to the plane of the lines. The adaptation between the lines is obtained, on the one hand by the fact that the slit line 3 extends towards the ribbon line 1 with a length of  / 4, and on the other hand by a diode 9 which can be short -circuit the slotted line 3 at a distance close to A / 4 from the end of the ribbon line 2.

At the end of the strip line 1 are placed on either side two diodes, generally of the PIN type, 4 and 5. One of the terminals of a diode, 4 for example, is fixed on the one hand to a ribbon line 44 open quarter wave produced in the plane of the substrate 90, on which the ribbon lines 1 and 2 are deposited, and on the other hand to the source 43 of bias voltage, by the conductor 434. The another terminal of the diode 4 is connected to an edge 41 of the strip line 1 by a conductor 410. An identical arrangement is made for the diodes 5, 6 and 7, one terminal of which is respectively fixed on the one hand to the lines to ribbon 54, 64 and 74 quarter wave open, and on the other hand to the sources 53, 63 and 73 of bias voltage by conductors 534, 634 and 734, and of which the other 'bounded is connected respectively to the edges 51 , 62 and 72 of the ribbon lines 1 and 2 by the conductors 410, 510, 620 and 720. The microwave frequency adaptation of the ribbon line 1 is done by a quarter-wave line open erte 11, placed at a distance of JL / 4 from the ribbon line 1; this quarter wave line 11, equivalent in microwave to a short circuit in its plane, brings an infinite impedance in the plane of the ribbon line 1.

It will be noted that the diodes can be fixed directly by soldering to the strip lines 1 and 2, if the dimensions thereof allow it, and connected to the quarter wave lines by a conductor.

To ensure the transmission of energy from the ribbon line 1 to the ribbon line 2, or to the slit line 3, a diode 8 is fixed directly by brazing to the ribbon line 2 and connected to the ribbon line 1 by a conductor 81. The polarization of this diode is done by means of a quarter-wave ribbon line 21, connected to the edge 72 of the ribbon line 2 by a conductor 212 and to the voltage source 83 of polarization by a conductor 210.

To ensure the transmission of energy from the ribbon line 2 to the slit line 3, a diode 9 is fixed by brazing under the ground plane 10 and connected by a conductor 994, to a capacitor 94, itself connected to a bias voltage source 93 by a conductor 934.

To collect the signal from the depha In general, a coaxial socket P is generally used, the connection of which with a ribbon line is easier than with a slotted line, because of the radial arrangement of the field lines in a coaxial socket. This is why the slit line 3 is coupled at its end to a ribbon line 100, so that the energy propagating in the slit line exits through the ribbon line 100.

We briefly recall the realization of the coupling between the two lines with different field structures that are for example the ribbon line 1 or 2 and the slotted line 3, located in two coincident or parallel planes, of coincident or parallel propagation axes. defining a plane orthogonal to the planes of the lines. Each quarter-wave ribbon line element 44 or 54 or 64 or 74 brings, in the plane perpendicular to its plane of connection to the edge of the ribbon line, an effect equivalent to a short circuit between the edge considered of the ribbon line and a slit line edge. Thus, an electric field E perpendicular to the ribbon line 1 or 2 induces an electric field in the slotted line 3.

To demonstrate the operation, the different phase states we will consider that the invention allows to obtain, the electrical lengths of the lines denoted by Φ ₁ and Φ ₂ representing areas outside the phase shifters 0- ₇ r and whose phase shift is constant. When diodes 4, 5, 6, 7, 8 and 9 are mounted as shown in the description and Figure 1, they behave as a first approximation, according to their polarity, either as a short circuit equivalent to a low value inductance , or as an open circuit, equivalent to a low value capacity.

puisque l'énergie se propage sur une longueur 1 de la ligne à fente 3, dont la constante de propagation est β₂.Under these conditions, state 0 is defined by reverse biasing the diodes 5, 6, 7, 8 and 9 and direct the diode 4. Thus the strip line 1 is connected by the conductive diode 4 to the slotted line 3, as described above. As the diode 8, between the two ribbon lines 1 and 2, is blocked, the energy is not transmitted in the ribbon line 2 but in the slotted line 3. The electric field É _o , applied to the line ribbon 1, induced in the slit line 3, an electric field E4, in a determined direction and this field is maximum, the short-circuit of the tent line being placed, as has been indicated, at a length close to λ / 4 below the ribbon line. The blocking of diodes 6 and 7 makes it impossible to couple the ribbon line 2 and the slotted line 3. The transmission phase is then:

since the energy propagates over a length 1 of the slotted line 3, the propagation constant of which is β ₂ .

We also define the state φ, in reverse biasing the diodes 4, 5 and 7 and direct diodes 6, 8 and 9. In this case, the first phase shifter 0- ₇ r does not work and the diode 8 is conductive , the energy propagates from the ribbon line 1 to the ribbon line 2 to the conductive diode 6, where it is then transmitted in the slit line 3. The diode 9 in conduction short-circuits the slit line 3 to λ / 4 from the end of the ribbon line 2 and ensures its adaptation. The electric field E ₆ , created in the slotted line is of the same value as E ₄ , but their directions form an angle between them (p.

puisque l'énergie se propage sur la longueur 1 de la ligne à ruban 2 de constante de propagation β1.This time, the transmission phase is

since the energy propagates over the length 1 of the ribbon line 2 of propagation constant β1.

The differential phase shift with respect to state 0 is therefore:

The third state 7r works in the same way as state 0, this time with the diode 5 in conduction instead of the diode 4. Thus, in the slotted line 3, the electric field Eg has a value identical to E ₄ but its meaning is reversed.

The differential phase shift with respect to state 0 is:

Finally, the last state cp + π works like the state (p, with diode 7 in conduction instead of diode 6. The electric field E ₉ , created in the slotted line 3, has a value identical to E ₆ but its meaning is reversed.

Consequently, the differential phase shift compared to state 0 is:

A variant of the invention is presented in FIG. 2, in which the ribbon line 2 is formed by two distinct sections T ₁ and T ₂ . The microwave link between this two sections is provided by a capacitor 200 of very large value. On the other hand, continuously this capacitor insulates the two sections, avoiding any spurious propagation of the diode control signals. The polarization of the diode 8 takes place via an open quarter wave line 21, which on one side is connected to it by a conductor 212 and on the other is connected to the bias voltage source 83 by a conductor 210. The microwave frequency adaptation of the second section T, of the ribbon line 2 is ensured by an open quarter wave line 221, placed at a distance of λ / 4 from the line 2.

Figure 3 shows in simplified section a part of the first phase shifter of Figure 1, showing more clearly how are made the connections of a phase shifter diode. The diode 4, for example, is on the one hand fixed by brazing to the ribbon of the quarter-wave line 44 by one of its electrodes, the same which connects it to a source of non-drawn bias voltage, and on the other hand part, connected by its other electrode to the ribbon line 1 by means of the conductor 410 ..

In the variant shown in section only in FIG. 4, the quarter-wave line 44 is eliminated and the contact with the slotted line is made through the substrate 90. In the drawing embodiment, the substrate is cut directly above the ribbon line 1. In the slot thus produced and in the ground plane 10 there is a diode 4 on a base 40, by which the polarization of this diode takes place. A dielectric disc 41, metallized on its two faces is brazed on the ground plane 10 and on the base of the diode. The conductor 410 directly connects an electrode of the diode to an edge of the strip line 1.

5 shows another example of phase shifting two bits following the diodes invention, consisting of two elements 0- ₇ r microwave diodes, realized in the coupling area of a slot line and a coplanar line, and interconnected both by a coplanar line extending at one of its ends by the coplanar line of the second phase shifter O- _T r and constituting with it line 13, and also by a slotted line divided into two parallel sections 14 and 15 located on either side of the central metal strip of the coplanar line 13.

The coplanar lines 12 and 13, the longitudinal axes of which coincide, are obtained by depositing a conductive tape of a certain length, lying between two ground planes 16 and 17, on a ceramic substrate.

As we have seen previously, the coplanar line is capable of transmitting two modes of propagation, therefore it has two propagation constants: y, for the mode with symmetric field structure and γ ₂ for the mode with asymmetric field structure.

This is why, when the coplanar line, formed by the central conductor 13 and the two ground planes 16 and 1.7, transmits the propagation mode with symmetrical field structure, it can be likened to a slotted line, constituted by the two slots 14 and 15 made between the metal conductors. Here again, the adaptation between the lines is obtained by the fact that, on the one hand, the slotted line 14-15 extends towards the coplanar line 12 with a length close to λ / 4 up to the conductor 30 and on the other hand, a diode 601 can short-circuit the slotted line at a distance close to λ / 4 from the end of the coplanar line 13.

As in Figure 1, there is a diode system, 101, 201, 301, 401, 501 and 601 connected on the one hand, by conductors 102, 202, 302, 402, 502 and 602, respectively, to the voltage sources polarization 103, 203, 303, 403, 503 and 603 and on the other hand to lines 12 and 13 by conductors 104, 204, 304, 404 and 504 and to the ground plane 17 by a conductor 604. To highlight the operation of this two-bit phase shifter, we will study the different phase states that the invention makes it possible to obtain.

pu sque l'énergie se propage sur une longueur L de la ligne à structure de champ dissymétrique, dont la constante de propagation est y₂.State 0 is defined by reverse biasing the diodes 201, 301, 401, 501 and 601 and direct diode 101. Thus the coplanar line 12 is at the same potential as the ground plane 16 in the plane of the diode 101 which excites a mode with asymmetric field structure beyond this diode to the plane containing the diodes 301 and 401. Between these two planes, the transmission phase is:

since the energy propagates over a length L of the line with an asymmetric field structure, the propagation constant of which is y ₂ .

We also define the state p, by reverse biasing the diodes 101, 201 and 401 and direct the diodes 301, 501 and 601. Then the first phase shifter does not work, and the diode 501 being conductive, the energy propagates from the coplanar line 12 to the coplanar line 13 to the conductive diode 601, where it is transmitted in the slotted line.

puisque l'énergie se propage sur la longueur L de la ligne de champ symétrique.This time, the transition phase is:

since the energy propagates over the length L of the symmetrical field line.

Compared to state 0, the differential phase shift is:

The third state π is defined in the same way as state 0, but this time the diode 201 in conduction instead of the diode 101. Thus, the coplanar line 12 is set to the potential of the ground plane 17 in the plane of diode 201, thus exciting, beyond this plane, an asymmetrical mode in phase opposition with respect to that of state 0. With respect to the latter, the differential phase shift is:

Finally, the last state p + π is established as the state ϕ, with the diode 401 in conduction instead of the diode 301.

et le déphasage différentiel par rapport à l'état 0 est:

The energy propagates from the coplanar line 12 to the coplanar line 13 to the plane of the diode 601. The transmission phase is:

and the differential phase shift with respect to state 0 is:

In these three examples of phase shifters, we will note a particular case, that where ϕ = π / 2, making it possible to obtain the four symmetrical phase shifts 0, π / 2, π, 3π / 2. We obtain rp = π / 2 by using, as connection between the two phase shifters 0-n, lines with different electric field structures of length 1, and whose propagation constants β1 and β ₂ (or γ ₁ and γ ₂ ) are as

Two embodiments of broadband two-bit diode phase shifters have thus been described, produced in a flat structure on a ceramic substrate of high dielectric constant and established in the coupling zone of two transmission lines with different electric field and axis structures. of coincident or parallel propagation, the two lines then being located in two parallel planes and the propagation axes defining a plane orthogonal to the planes of the lines. These phase shifters have several advantages, in particular a small variation of the phase shift in the frequency band considered, which can have a large width. The superimposition of lines with different field structures, having parallel propagation axes, makes it possible to produce phase shifters of reduced bulk.

It will be noted that in the examples described, the width of the strip, the width of the slot, and the thickness of the substrate are conditioned by the value of the characteristic impedance of the transmission line upstream and downstream of the plane of the diodes. The line is charged by this characteristic impedance so that a maximum transmitted power is obtained with a low TOS, which may be close to 1.

We will also note an interesting application of these phase shifters. These, which are particularly reliable and have a small variation in phase shift, attenuation and the standing wave ratio in a large frequency band, are advantageously. used in electronic scanning antennas, being connected directly to the radiating element mainly if the latter is slit on the substrate. In this case, referring to FIG. 5 for example, it is possible to connect a radiating element R to the slotted line 14-15 and connect the coplanar line 12 to an energy source H.

Claims (17)

1. Ultra-high frequency diode phase changer having at least one ultra-high frequency O-π diode phase changer made of a plane structure on a ceramic substrate, characterized in that it comprises a second O-π phase changer, connected to the first one by at least two transmission lines of different electric fields, of the length I, with mingled or parallel, superimposed propagation axes, with said lines having propra- gation constants β₁, and β₂ which are different in that their difference (β₁ β₂) is constant in the utilized frequency band, and at least one diode being provided at one of the ends of each of said lines, with means for commuting their state.

2. Phase changer according to claim 1, characterized in that it has two 0-₇r ultra-highfrequency diode phase changers, each comprising a strip line and a slit line with parallel superimposed axes of propagation, separated by a dielectric substrate (90), with said two phase changers being interconnected, on the one hand, by a section of hollow slit line in the mass plane extending at each end by the slit line of the two phase changers, with a diode (9) being directly fixed onto the mass plane by one of its electrodes and the other electrode being connected by a conductor (994) with capacitor (94), connected with a polarized voltage source (93) and, on the other hand, by a section of strip line arranged on the ceramic substrate (90), whose one end extends by the strip line of the second phase changer O―π and on the other end of which a diode (8) is fixed by one of its electrodes, with the other electrode being fixed to the strip line of the first phase changer 0-₇r by a conductor (81 with the diode being polarized by means of a quarter wave length strip line (21), connected on one side by a conductor (212) to the strip line (2) and on the other side by a conductor (210) to a polarized voltage source (83).

3. Phase changer according to claim 2, characterized in that the diode (9) is placed at a distance of .1/4 from the end of the second phase changer 0-₇r.

4. Phase changer according to claim 2, characterized in that the slit line (3) extends at a length equal to one fourth of the wave length under the strip line (1).

5. Phase changer according to claim 2, characterized in that the diode (8) which assures the transmission of electric energy from the first phase changer O-π to one or the other of the two transmission lines, is fixed directly by soldering onto the strip line (1) of the first phase changer O-π and connected by a conductor to the strip line (2).

6. Phase changer according to one of claims 1 to 3, characterized in that it comprises a strip line (100), connected at its output end to the slit line (3) of the second phase changer 0-₇r.

7. Phase changer according to one of claims 1 to 6, characterized in that the strip line (2) which connects the two phase changers O―π, is divided into two sections T₁ and T₂, interconnected by a capacitor (200), with an open quarter wave length line (221) being placed at a distance of λ/4 of the line (2).

8. Phase changer according to claim 1, characterized in that it comprises two phase changers 0-₇r, each having a coplanar line arranged on the same side of a ceramic substrate of parallel propagation axes provided between two mass planes (16 and 17), with the two phase changers O-π being interconnected, on the one hand, by a section of slit line (14-15), with a diode (601) being directly fixed onto one of said mass planes by one of its electrodes which connects it with a polarized voltage source (603) and the other electrode being connected to a second mass plane by a conductor (604), with said diode (601) short- circuiting the slit line (14-15) and, on the other hand, by a section of the coplanar line (13) whose one end extends by the coplanar line of the second phase changer 0-₇r and on the other end of which a diode (501) is attached by the same electrode which connects it with a polarized voltage source (503) and the other electrode connects it with the coplanar line (12) of the first phase changer 0-₇r.

9. Phase changer according to claim 8, characterized in that the diode (601) is placed at a distance which equals one fourth of the wave length at the end of the second phase changer O-π.

10. Phase changer according to one of claims 1 to 5, characterized in that each of the diodes is fixed directly onto a support (40) which is mounted in the slits of the slit lines, associated with the ribbon lines and the coplanar lines by one of its electrodes, whereas the other electrode of the diode is connected by a conductor (410) through the substrate of the ribbon lines and the coplanar lines and to the polarized voltage source.

11. Phase changer according to one of claims 1 to 10, characterized in that one of the diodes of the first phase changer O-π is directly polarized, with all the other diodes of the two bits - phase changer being inversely polarized, thus defining the phase state called O.

12. Phase changer according to one of claims 1 to 10, characterized in that one of the two diodes of the first phase changer O-π which is inversely polarized in the state of the phase 0, is directly polarized, with all the other diodes of the two bits - phase changer being inversely polarized, thus defining the phase state called π.

13. Phase changer according to one of claims 1 to 10, characterized in that the two diodes of the first phase changer O-π and one of the two diodes of the second phase changer 0-π are inversely polarized, with all the other diodes of the two bits - phase changer being directly polarized, and the propagation constants β₁ and β₂ of the two connecting lines between the two phase changers 0-₇r being such that (β₁ - β₂). I = Φ, thus defining the phase state called Φ.

14. Phase changer according to one of claims 1 to 10, characterized in that the two diodes of the first phase changer O- and the diode of the second phase changer, which is directly polarized in the state Φ, are inversely polarized, with all the other diodes being directly polarized and the propagation constants of the two phase changers 0-₇r being such that (β₁ - β₂). 1= Φ, thus defining the phase state called I + 7r.

15. Phase changer according to claims 13 or 14, characterized in that the connecting lines between the two phase changers O-π are such that (β₁, -β₂) . I =π/2.

16. Phase changer according to any of the claims 1 to 15, characterized in that it is utilized in an electronic scanning antenna, with the output of the phase changer being connected to a radiating element and the strip line (1) or the coplanar line (12) being connected to an energy source.

17. Electronic scanning antenna utilizing the phase changers according to claims 1 to 16.

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