GB2280988A

GB2280988A - A phase shifter panel for an electronic scanning antenna

Info

Publication number: GB2280988A
Application number: GB9415853A
Authority: GB
Inventors: Claude Chekroun; Georges Guillaumot
Original assignee: Thomson CSF Radant
Current assignee: Thomson CSF Radant
Priority date: 1993-08-06
Filing date: 1994-08-05
Publication date: 1995-02-15
Anticipated expiration: 2014-08-05
Also published as: DE4427034B4; FR2708808A1; GB9415853D0; FR2708808B1; GB2280988B; DE4427034A1

Description

2280988 X "A PHASE SHIFTER PANEP AND ITS APPLICATION TO A MICROWAVE LENS

AND TO AN ELECTRONIC SCANNING ANTENNA " The present invention relates to a phase-shifter panel with four phase states. using active semiconductor elements. Its subject is also the application of such a panel to the construction of a microwave lens and an electronic-scanning antenna.

The construction of an electronic-scanning antenna requires, as is known, components capable of applying a controllable phase shift to a microwave. It is known for example from French Patent 2,469,808 to use, in order to construct an electronic- scanning antenna, a microwave lens formed from panels each introducing a phase shift of the microwave which passes through them. These panels include conducting wires bearing diodes, the wires being arranged parallel to the direction of the electric field of the wave. Control of the passing or blocked state of the diodes enables the phase shift imparted to the incident wave by each of the panels to be made to vary between two values and, consequently, electronic scanning to be obtained.

However, such an antenna requires that the larger the desired number of distinct values of phase shift, the larger the number of phase-shifter panels, arranged in the path of the wave, with an increase in the losses and in the cost in particular, this constituting a limitation.

The subject of the present invention is a phase- shifter panel which makes it possible to obtain four distinct values of phase shift depending on the command applied thereto,. and thus making it possible in parti cular to reduce the number of panels required in the above application.

According to the invention there is provided a phase-shifter panel capable of receiving an electro magnetic wave linearly polarized in a given direction; the panel includes conducting wires arranged on a X support, the wires each bearing at least two semiconductor elements, diodes for example, and being connected to conductors enabling the state of the diodes to be controlled independently of one another, each of the diodes being able to be in the passing or blocked state; f our possible states are thus obtained, and the geometrical and electrical characteristics of the panel are such that to each of these states corresponds a given value of phase shift.

The subject of the invention is also the applica- tion of such a panel to the construction of a microwave lens of the type described in the aforesaid patent.

Its subject is also the use of such a lens for the construction of an e lectronic- scanning antenna.

Other subjects, features and results of the invention will emerge from the following description given by way of example and illustrated by the appended drawings which represent:

- Figure 1, a diagram of an embodiment of a panel according to the invention; - Figure 2, the equivalent electrical circuit diagram of the panel of the preceding figure; - Figures 3a and 3b, diagrams illustrating the microwave lens which is the subject of the aforesaid French patent and its application to the construction of an electronic-scanning antenna.

In these various figures, the same references refer to the same elements.

In Figure 1 is represented a partial view of one embodiment of a panel according to the invention.

This panel is labelled P overall. It includes a dielectric substrate 1 on which are arranged wires F, substantially parallel to one another and each carrying at least two semiconductor elements with two states, D, and D2 for example diodes, for example connected in opposition, for example by their cathode. The supply voltage to the diodes D, and D. is conveyed by three conductors which are substantially parallel to one another and perpendicular to the wires F, labelled 51, 52 1 I- and 53, the conductor 53 being the central conductor. The substrate 4 furthermore includes on its two edges, respectively, two metal conductors labelled 74 and 75, substantially parallel to the conductors 51-53 and arranged at a distance D, on either side respectively of the conductors 51 and 52. The conductors 51 and 53 are a length D,, apart and the conductors 53 and 52 a distance D12 apart. The wires F are substantially equidistant, with a spacing a. The conductors 74 and 75 are a length b apart.

For the clarity of the figures, the surface of the various conductors, made for example in the form of metallic depositions on the substrate 4. is represented in the figure dotted although not seen in section.

Figure 2 represents the equivalent electrical diagram of the panel of Figure 1, for microwaves.

The microwave, with impedance Z = 120.n.b/a and linearly polarized (electric field vector) parallel to the wires F is received on the terminals B, and B2 and encounters three capacitances C,,, C,,, C12 in series, connected in parallel across the terminals B, and B2. The capacitance C, represents the decoupling capacitance per unit length between the conductors 51 and 52 and the conductors 74 and 75, respectively; the capacitance C,, is the capacitance per unit length between the conductors 51 and 53 and the capacitance C12 the capacitance per unit length between the conductors 53 and 52.

Across the terminals of the capacitance C,, is connected a diode D,, also represented by its equivalent diagram. The latter consists of an inductor L, in series with:

- either a capacitor C,., in series with a resistor Rj.1, - or a resistor RdII depending on whether the diode D, is reverse or forward, this being depicted by a switch 21.

Likewise, across the terminals of the capacitor C12 is connected a diode D2 represented by its equivalent diagram. The latter is analogous to that for the diode 9 4 - D,, its components bearing an index 2. The microwave output voltage is taken between the terminals B3 and B,, the terminals of the three capacitors Coo, C,, and CI2 5 The parameters of the equivalent circuit of the diodes, for example of diode D,, are defined as follows:

- the inductance L, is given by L, = LD,. aa b 1 where: LD1 is the inductance of the diode D,, bearing in mind its connection wire (F) to the conductors 51-53; a is the distance between two diodes D,; 12 is the distance between the conductors 74 and 75; a is a coefficient characterizing the interaction between the wires F; - the resistance Rj., is the reverse resistance of the diode D,, modified by the ratio a/b; the resistance Rdl is the forward resistance of the diode, modified by the same ratio; - the capacitance Cs., is the junction capacitance of the diode, modified by the ratio b/a.

The operation of the panel according to the invention is explained below by consideringr in a first step, the behaviour of such a panel in the absence of the diodes D2 and of the conductor 53, which amounts to deleting the block D2 as well as the capacitor C12 from the equivalent diagram of Figure 2.

When the diodes D, are forward biased, the susceptance (BJ of the (altered) circuit of Figure 2, can be written:

1 - LC, LC, J + W0J 71 where w is the angular frequency corresponding to the central frequency of the operating band of the device.

The parameters of the circuit are chosen so as to have Bd = 0. that is to say that, neglecting its conductance, the circuit is matched or, in other words, that it is transparent to the incident microwave, introducing 35 neither spurious reflection nor phase shift (dkI _ 0) S More precisely, we choose:

LC, w 2 = 1 which leads to Bd 0 irrespective in particular of the value of the capacitance Cil.

When the diodes are reverse biased, the susceptance of the panel can be written:

BR = Z CO LCjw 2 +(C] 1 Ci) W2 _ 1 + (CO + cl)IC LC, - LCO i With the capacitance C, being fixed previously, it appears that the value of the susceptance B. can be adjusted as, consequently, can that of the phase shift (dil) experienced by the incident microwave, through action on the value of the capacitance Ci. that is to say through the choice of the diode D,.

Two values of phase shift are thus obtained: ddl is 0 and dil.

If now, in a second step, the existence of the diodes D2 and of the intermediate conductor 53 are taken into consideration, it is seen that, by an analogous argument, when the diode D2 'S forward biased, the incident microwave experiences no phase shif t (dd2 =-- 0) whereas when the diodes D2 are reverse biased, it experiences a given and adjustable phase shift (di2) If now the whole of the panel is considered, it is seen that it can impress upon the microwave which passes through it four different values of phase shift, depending on the control (forward or reverse bias) applied to each of the diodes D, and D2 Indeed:

- when the diodes D, and D2 are f orward biased, the phase shift (d1) imparted to the incident wave is zero; - when the diodes D, are forward biased whilst the diodes D2 are reverse biased, the phase shift introduced (dl2)is so by the diodes D2 alone and is therefore dependent on the value of the capacitance C.2; 9 - conversely, when the diodes D, are reverse biased whilst the diodes D2 are forward biased, the phase shift (dC imparted by the panel is so by the diodes D, alone and is therefore dependent on the capacitance Cil of 5 these diodes; - when, together, the diodes D, and D2 are reverse biased, the phase shift (d.) is due at once to the diodes D, and D2 and is theref ore dependent on Cil and C.2 It should be noted that described above is the case in which the parameters of the circuit are chosen so that the zero (or substantially zero) susceptances are such that they correspond to the diodes biased in the forward direction, but that it is of course possible to choose a symmetric operation in which the parameters are is determined so as substantially to zero the susceptance BR Such a panel can advantageously be used in the construction of a microwave lens of the type described in the aforesaid patent and shown diagramatically in Figures 3a and 3b:

- Figure 3a is a partial and diagrammatic sectional view in the plane of the electric field E of the microwave; - Figure 3b illustrates the structure of a panel such as described earlier.

In Figure 3b is the panel P bearing the wires F, each of them bearing a diode D, and a diode D2 which are connected by their cathodes for examPle, as well as the conductors 51, 52 and 53.

The microwave lens of Figure 3a includes a plurality of panels such as P, arranged between conducting plates 70, 71, 72, which play the role of the conductors 74 and 75 of Figure 1. Together, the panels P arranged between two plates 70-72 constitute a phase shifter (d,, d2, d,...).

The stack of a plurality of phase shifters constitutes an active microwave lens which, when irradiated by a microwave source S, makes it possible to form an electronic scanning antenna. The source S provides an electromagnetic wave whose direction of propagation is 1 r 1 9 illustrated by an arrow 10 and whose electric field E is perpendicular to the plates 70, 71, 72... and parallel to the wires F bearing the diodes.

With the panels P being controlled independently of each other, it appears that the phase shifts which they impart to the wave which passes through them can differ from one panel to another. By juxtaposing a plurality of panels one behind the other in the path of the microwave, it is seen that phase shifts can be obtained which can range from 0 to 3600, in increments linked to the number of juxtaposed panels. It should be noted that the fact that each of the panels according to the invention is able to impart to the wave which passes through it four different phase shifts makes it possible to reduce the total number of panels. By stacking a plurality of such phase shifters, it appears that it is possible to effect electronic scanning in a plane parallel to the electric field, as illustrated by an arrow 20 showing the direction of propagation of the emergent wave.

The description given above of the panel was so of course by way of example and different variants are possible: thus, it is possible to connect to a same wire several diodes such s D, in the same sense and/or several diodes D2, also in the same sense; this variant makes it possible to decrease the equivalent capacitance of the setup and, consequently, to increase its passband. Similarly, the diodes D, and D2 have been represented as connected in opposition but they can also be connected in series, on condition that the control circuits are adapted accordingly. Finally, the conductor 53 can. be doubled up, and this may ease the supplying of the diodes D, and D2 ' 1 00

Claims

CLAIMS:

1. A phase shifter panel capable of receiving an electromagnetic wave linearly polarized in a given direction, including a dielectric support and electrically conducting wires substantially parallel to the given direction, and arranged on the support, the wires being connected to conductors for control of the semiconductor elements, substantially normal to the wires; wherein the support furthermore includes two conductors arranged towards the periphery thereof, substantially parallel to the control conductors, and wherein the wires bear at least two semiconductor elements with two states, the control conductors being at least three in number so as to control the state of the semiconductor elements independently of one another, the geometrical and electrical characteristics of the panel being such that to each of the states of the semiconductor elements corresponds a given value of phase shift of the electromagnetic wave which passes through it.

2. A panel according to claim 1, semiconductor elements are diodes.

J wherein the

3. A panel according to either claim 1 or claim 2, wherein the geometrical and electrical characteristics 01 of the panel are such that the latter is adapted for one of the states of the semiconductor elements.

4. A microwave lens capable of receiving a microwave, including a plurality of phase shifters, each of them being formed of a plurality of panels according to anyone of the preceding claims, arranged substantially parallel to one another between conducting plates, in the direction of propagation of the microwave, the phase 10 shifters being stacked normal to the said direction.

5. An electronic scanning antenna, including a lens according to claim 4 and a source which is capable of emitting an electromagnetic wave linearly polarised in said direction, the electronic scanning being obtained in the plane of said direction by control of the state of the semiconductor elements.

6. A phase shifter panel substantially as described hereinbefore with reference to the accompanying drawing and as illustrated in Figures 1 and 2 of those drawings.

7. A microwave lens capable of receiving a microwave substantially as described hereinbefore with reference to and as illustrated in the accompanying drawings.

8. An electronic scanning antenna substantially as 9 It) described hereinbefore with reference illustrated in the accompanying drawings.

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