EP0335788A1 - Microwave phase shifter - Google Patents

Abstract

The phase-shifter circuit is constructed with the aid of strip lines (16, 17 and 18) arranged in candlestick form on one face (14) of a substrate (10) and of a slotted line (12) which is disposed on the other face (13). The lengths of the branches (17 and 18) of the candlestick differ by b/4, b being the wavelength, and the ends (19, 20) of the said branches are short-circuited, or not, by PIN diodes (21, 22) which may be forward or reverse biased. The invention is applicable to radars. <IMAGE>

Description

The invention relates to microwave phase shifting circuits and, more particularly, microwave phase shifting circuits which perform elementary phase shifts under the control of electrical signals and which can be grouped to obtain phase shifts which are integral multiples of the elementary phase shifts. In microwave, propagation lines are used which can take different forms and FIGS. 1 to 4 are respectively views which respectively represent a slotted propagation line and a ribbon propagation line better known by the name of microstrip line.

A slotted line (Figures 1 and 2) consists of an opening 1 made in a metal layer 2 deposited on a dielectric substrate 3. The dielectric support provides the mechanical strength of the metal conductors and constitutes the medium for propagation of the microwave wave. whose energy is concentrated between the edges 4 and 5 of the slit. In FIG. 2, lines of force of the electric field E have been shown in dotted lines and those of the magnetic field in solid lines. The thickness of the dielectric material is related to its nature and the width of the slotted line determines the characteristic impedance of the line.

The ribbon propagation line (FIGS. 3 and 4) comprises a dielectric plate 7 disposed between a ribbon 6 and a metallic plane 8 also called the ground plane. As with the slotted line in Figures 1 and 2, almost all of the energy is concentrated in the dielectric 7. In FIG. 4, the lines of force of the electric field E have been shown in dotted lines. The dielectric material used in the two slit or ribbon lines can be polytetrafluoroethylene, beryllium oxide, aluminum ceramic, quartz or ferrite.

In addition to a propagation function, the slit or ribbon lines can separately perform a phase shift function by configuring them in different ways. Thus, by implementing a technology of the ribbon line type, it is possible to produce the so-called line switching, disturbance phase shifters or with 3 db / 90 ° couplers.

For a description of these phase shifters of the prior art, whether they are of the slotted line or ribbon line type, reference may be made to numerous articles in the review IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES and in particular an article by Elio A MARIANI and others - Vol MTT-l7 n ° 12 - December 1969 pages 1091 to 1096 entitled "Slot Line Characteristics" as well as an article by JF WHITE March 1965 pages 232 to 242 entitled "High Power, pin Diode Controlled Microwave Transmission Phase Shifters ".

In certain applications, it is necessary to switch from one type of line to another, and numerous coupling devices have been proposed for this purpose. These coupling devices are generally not intended to simultaneously produce a phase shifting circuit whose value of the phase shift would be controlled. When a determined phase shift must be introduced, the circuit is modified to insert a phase shift circuit of any known type before or after the coupling device, which increases the losses, complicates the circuit and makes it more voluminous.

There is therefore a need for coupling devices with incorporated phase shifter or vice versa for phase shifting devices incorporated in coupling devices.

An object of the present invention is therefore to achieve, in the same structure, a change of propagation line and a controlled phase shift of the incident wave, which leads to a reduction in losses and bulk.

The invention relates to a microwave phase shifting circuit characterized in that it comprises:
- a substrate of dielectric material, one of the faces of which has a slotted line while the other side of which has a ribbon line in the form of a candlestick with two parallel branches connected by a transverse arm perpendicular to the direction of the slit line , the lengths of the branches of the candlestick being different from b / 4 if b is the wavelength of the microwave signals.
- two PIN diodes each connected between the end of a branch and the ground potential,
- Means for making the PIN diodes simultaneously passing or blocked so as to introduce an identical impedance variation in each branch and thus obtaining a determined phase variation between the input wave applied to a line and the output wave appearing on the other line, when the state of said diodes changes.

• - la figure 1 est une vue de dessus d'une ligne à fente ;
• - la figure 2 est une vue en coupe de la ligne à fente suivant la ligne II-II de la figure 1 ;
• - la figure 3 est une vue de dessus d'une ligne à ruban ou ligne microstrip ;
• - la figure 4 est une vue en coupe de la ligne à ruban suivant la ligne IV-IV de la figure 3 ;
• - la figure 5 est une vue en perspective cavalière d'un circuit déphaseur hyperfréquence selon l'invention, et
• - les figures 6,7 et 8 sont des schémas qui permettent de comprendre le fonctionnement du circuit déphaseur hyperfréquence selon l'invention.

Other characteristics and advantages of the present invention will appear on reading the following description of a particular embodiment, said description being made in relation to the accompanying drawings in which

• - Figure 1 is a top view of a line to slit;
• - Figure 2 is a sectional view of the slotted line along line II-II of Figure 1;
• - Figure 3 is a top view of a ribbon line or microstrip line;
• - Figure 4 is a sectional view of the ribbon line along line IV-IV of Figure 3;
• FIG. 5 is a perspective view of a microwave phase shifting circuit according to the invention, and
• - Figures 6,7 and 8 are diagrams which allow to understand the operation of the microwave phase shifting circuit according to the invention.

Figures 1 to 4 have been described succinctly in the preamble to define the field of the invention, that is to say that of slit and ribbon lines.

Figure 5 is a perspective view which schematically shows a microwave phase shifting circuit which comprises a substrate 10 of dielectric material similar to that bearing the reference 3 or 7 in Figures 2 and 4. The underside of the substrate 10 is covered with 'a metal layer 11 in which is made a straight slot 12 of a certain width d, for example by chemical action, so as to produce a slot line of the type described in relation to Figures 1 and 2. This slot 12 does not extend over the entire length of the substrate and ends at one end 40 with a short circuit constituted by the metal layer 11. The other end 41 of the slotted line is open.

The upper face 14 of the substrate 10 comprises a strip 15 called a microstrip, having a particular shape. It comprises a central arm 16 and two lateral arms 17 and 18 which are connected to the central arm 16 by a transverse arm 23, the set of arms providing a structure in the form of a candlestick with two branches of unequal length. The arm 17, for example, has a length which is b / 4 greater than that of the arm 18 for reasons which will be explained below, b being the wavelength of the microwave signals transmitted by the line.

The ends 19 and 20 of the arms 17 and 18 are each connected to the cathode of a PIN diode 21 and 22, the anode of which is connected to ground. These diodes 21 and 22 have been shown in their electrical form, but it can be understood that in practice they are in the form of a component which is wired to the substrate 10 by connecting the output terminals, one at the end of a branch 17 or 18 and the other at ground potential.

These diodes 21 and 22 are biased by conventional type bias circuits which include, for the diode 22 for example, a shock coil 30 and a decoupling capacitor 31 for the cathode of the diode and a shock coil 32 and a decoupling capacitor 33 for the anode of the diode. The bias voltage Vp is applied between points 34 and 35 of the bias circuits.

In FIG. 5, the diodes 21 and 22 are shown connected in a certain direction between the end of the branch and the ground potential. Of course, they can be connected in the other direction, the important thing being that they can be conductive or blocked according to the bias voltage Vp which is applied to them.

The positions of the slit line 12 and the ribbon line must be such that the slit line is aligned with the central arm 16 and its end 30 terminates under the arm 16 so as to obtain the best possible coupling. Furthermore, the lengths of the transverse arm 23 on either side of the central arm 16 are equal.

The operation of the microwave phase shifting circuit which has just been described in relation to FIG. 5 will now be explained with the aid of FIGS. 6, 7 and 8. The arms 16, 17 and 18 produce a power divider for the incident wave transmitted by line 16 like a magic tee. It is known that in a magic tee (FIG. 6), the incident wave 25 at the input 26 is divided into two waves of amplitudes A and equal phases φ on the channels 27 and 28, the channel 29 being decoupled. It is also known (FIG. 7) that two waves of the same amplitude A but in phase opposition which are applied to the channels 27 and 28 combine in phase on the channel 29, the channel 26 being decoupled.

In the case of the phase shifting circuit of FIG. 5, as a result of the arm 17, which has a length greater by b / 4 than the length of the arm 18 (FIG. 8), the incident wave at 16, after sharing in the two arms lateral, is reflected by the ends 19 and 20 of said arms but the waves reflected have a phase difference of 180 ° due to a difference in length of the paths equal to b / 2. As a result, they cannot exit through the inlet 16 but through the slotted line 12, the coupling with the latter being carried out by means of the transverse arm 23.

By way of illustration, FIG. 5 shows the directions of the electric fields e1 and e2 in the substrate 10 under the transverse arm 23 and the electric field e3 resulting from their combination in the slotted line 12. The operation of the phase shifting circuit has been described for a certain direction of propagation - ribbon line to slotted line - but it is clear that the circuit phase shifter also works in the other direction of propagation - slotted line to substrate.

The variation of the phase shift between the wave entering by the strip line 16 and the wave leaving by the slit line 12 depends on the variation in impedance presented by the diodes 21 and 22 depending on whether they are simultaneously blocked or conductive, their state depending on the bias voltage Vp applied to them. It should be noted that there is a certain phase shift between the input and output waves for a certain state of the diodes and that this phase shift is modified when the diodes pass into the other state so that this results in a variation. of the phase shift between the two successive states of the diodes.

More precisely, the variation in the phase shift to be obtained is calculated as a function of the line impedance, the length of the line and the capacity of the diode, the calculations being carried out in accordance with known prior art such as that cited in the preamble. It is thus possible to produce phase shifting circuits which introduce elementary phase shifts of 22.5 ° 45 ° or 90 ° in frequency bands of 10%.

Furthermore, these elementary phase shift circuits can be assembled to make different combinations of elementary phase shifts. Each elementary phase shift is obtained by making the diodes 21 and 22 simultaneously conducting or blocked.

The phase-shifting circuits of a group can be assembled in various ways and one of them consists in using the same substrate on which the different slit line / ribbon line transitions are made. The coupling between the adjacent phase-shifting circuits can be achieved in various ways, by for example a line to slot / line to line coupling, or a line to tape / line to line coupling, or even a line to slot / line to line coupling and vice versa.

Claims (6)

1. Microwave phase shifter circuit of the type comprising a hybrid junction, two accesses of which are connected to ground via semiconductor diodes located at distances differing from b / 4, where b is the wavelength of the microwave signals, characterized in what said phase shifting circuit comprises:
a substrate (10) of dielectric material, one of the faces of which has a slotted line (12) while the other side of which has a strip line (16, 17, 18) in the form of a candlestick with two parallel branches ( 17, 18) connected by a transverse arm (23) perpendicular to the direction of the slit line (12), the lengths of the branches of the candlestick being different from b / 4 if b is the wavelength of the microwave signals;
-two PIN diodes (21, 22) each connected between the end (19 or 20) of a branch (17 or 18) and the ground; and
means for making the PIN diodes (21, 22) simultaneously on or blocked so as to introduce an identical variation in impedance in each branch and thus obtain a determined phase variation between the input wave applied to a line and the output wave appearing on the other line when the state of said diodes changes. 2. phase-shifting circuit, characterized in that it comprises several phase-shifting circuits according to claim 1 arranged in series, each phase-shifting circuit being designed to introduce a determined phase variation when the state of said diodes changes. 3. phase-shifting circuit according to claim 2, characterized in that said phase-shifting circuits are produced on the same substrate. 4. Circuit according to claim 3, characterized in that two adjacent phase-shifting circuits are coupled via their slotted line (12). 5. phase-shifting circuit according to claim 3, characterized in that two adjacent phase-shifting circuits are coupled via their ribbon line (16). 6. phase-shifting circuit according to claim 3, characterized in that two adjacent phase-shifting circuits are coupled by a slit line / ribbon line transition or vice versa.

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