GB2150356A

GB2150356A - A radiating device with a microstrip structure with a parasitic element

Info

Publication number: GB2150356A
Application number: GB08425058A
Authority: GB
Inventors: Fabrice Clerc; Guy Courtet
Original assignee: Dassault Electronique SA; Electronique Serge Dassault SA
Current assignee: Thales SA
Priority date: 1983-10-04
Filing date: 1984-10-04
Publication date: 1985-06-26
Also published as: FR2552937B1; GB8425058D0; GB2150356B; DE3436228A1; FR2552937A1; DE3436228C2

Abstract

A microstrip structure forming a resonator with losses is obtained on the basis of a dielectric plate (D), beneath which there is affixed an extensive metallisation forming the ground plane and on which there is affixed a metal slab (P10), with a rectangular configuration for instance. One edge of slab (P10) is provided with short circuit pins (CC) ending at the ground plane (PM). A perpendicular edge of slab (P10) is connected via a narrow metal channel (L11) to a further metal element (P11) which extends parallel to the edge concerned of the slab (P10) and over the same length as the latter. The supply is effected from below by means of a coaxial cable whose screening (CB) is connected to the ground plane, and core (CA) at a chosen point of slab (P10). This device is operating on two different frequencies on a narrow band for each one, with a particularly reduced size and an angular spread close to 180 DEG . Circular polarization is achieved by four units successively displaced by 90 DEG . An additional metal element (P12) may be provided at the end opposite to P11. <IMAGE>

Description

SPECIFICATION A radiating device with a microstrip structure with a parasitic element The invention concerns radiating devices or antennae.

Radiating elements are already known which are constituted as a microstrip structure forming a resonator with losses. Such a structure comprises at least one dielectric plate, with an extensive metallisation forming the ground plane, fixed under this plate, and a metallised slab with a chosen configuration fixed on the said plate. To allow the radiating element to operate, means are added to the said structures which allow an adapted electric connection between the structure and an application circuit.

In certain applications, the radiating elements must satisfy strict constraints regarding their dimensions, the achievement of an angular cover as close to 180 as possible and their capability of operating simultaneously on two different frequencies, with a narrow band width for each operating frequency. It is also desirable for the radiating element to allow operation in circular polarisation as far as possible.

Finally, it is of course necessary that its power device, with the impedance matching which it must comprise, should increase the small size of the so called microstrip structure, as little as possible.

The present invention aims to provide a very advantageous solution of the problem.

According to the present invention we provide a radiating device of the type comprising at least one radiating element which comprises:- on the one hand a microstrip structure forming a resonator with losses, and constituted by at least one dielectric plate, by an extensive metallisation forming the ground plane affixed under this plate, and by a metallised slab with a chosen configuration affixed on the said plate; and on the other hand means allowing an adapted electric connection between the said microstrip structure and an application circuit, wherein said slab is associated with a parasitic metallised element extending on the same surface as the dielectric plate, near one of the edges of the slab, and over a length substantially equal to that of this edge, this parasitic element being electrically connected to the slab via a metallised channel which is narrow in relation to the said length.

In a first particular embodiment, provision is made for a metallised slab of a generally rectangular shape, wherewith there is associated a parasitic element which is also rectangular, the connecting channel between the two being itself rectangular.

Trials which have been conducted show that such a slab works well, in particular when the slab is connected to the ground plane via a short circuit line, close to one edge of the slab, this latter edge being perpendicular to the one which the metallised parasitic element adjoins. The electric supply of the radiating element is then advantageously effected via a duct passing through the ground plane and the dielectric plate, whilst the screening of a coaxial supply cable is connected to the ground plane and its central conductor uses the said duct, without electric contact with the ground plane, to make electric contact with the slab.

More particularly, the width of the parasitic element is advantageously chosen to be substantially equal to the spacing of it from the metallised slab.

For its part, the width of the metallised channel can be of the order of one fifth of the width of the metallised slab.

It does seem, moreover, that shapes of metallised slabs other than rectangular also allow the implementation of the present invention with a parasitic element although the experiments currently being conducted have not yet given definite results for such embodiments. It does seem, in any case, that the parasitic element must extend in a substantially parallel direction to that of the edge of the metallised slab which it adjoins.

In a second mode of embodiment, a second parasitic element, similar to the first, and preferably identical with the latter, is placed on the opposite side of the slab.

Whilst in the first mode of embodiment, the core of the axial supply cable is disposed asymmetrically within the metallised slab proper, in the second mode of embodiment the core of the coaxial cable on the contrary passes through an axis of symmetry of the slab.

For certain applications, the present invention also proposes to construct at least one set of four radiating elements such as defined above, preferably mounted on the same dielectric plate, side by side and in various directions displaced with respect to each other by 90 .

Finally, the present invention makes provision for the application of the radiating device of this invention to the making of an adaptable antenna operating on at least two frequencies with a narrow band width on each frequency and with a quasihemispherical spread.

Other characteristics and advantages of the invention will appear on examining the detailed specification which follows, as well as the attached drawings wherein: Figure 1 is a view in perspective, schematically representing a first mode of embodiment of the present invention: Figure 2 is a top view constituting a conventional representation of the radiating element of Figure 1: Figure 3 is a cross sectional view along line Ill-Ill of Figure 1 (or, save for the scale factor, along line 111-Ill of Figure 4): Figure 4 is a view in perspective of a second mode of embodiment of the present invention; and Figure 5 is a top view of the embodiment of Figure 4, this top view forming a conventional diagram.

In the Figures, reference D designates a dielectric plate, whose lower surface is provided with extensive metallisation forming the ground plane. The ground plane does, in principle, cover the whole lower surface of the plate.

The top of the dielectric plate is metallised with a chosen configuration. Such metallisations may be obtained by the known techniques of serigraphy or by other means known to the expert in hybrid circuits.

Reference will now be more particularly made to the first mode of embodiment of Figures 1 to 3. In this first mode of embodiment, the top surface of the dielectric plate D is given a rectangular metallised slab P10 whose edge which is on the left in the Figure is connected to the ground plane via short circuit lines CC.

In the version represented, the ground plane is defined by an opening which extends as a duct through the dielectric. A coaxial cable comes from below, its screening CB being electrically connected to the ground plane, for instance by soldering, whilst core AC of the coaxial cable passes through the above mentioned duct, to be soldered at a chosen point of the metallised slab P10.

It has become apparent in an altogether surprising way that such a slab, known for its capability of operating as a radiating element on a single frequency, can be rendered capable of operating on two different frequencies by the lateral addition of a parasitic metallised element P11 connected to the slab via a metallised channel L11.

It will be observed in the Figures that the parasitic element P11 has a length equal to that of the edge of the main metallised slab P10 which it adjoins.

Moreover, the width of the parasitic element P1, is substantially equal to the length of the metallised channel L" that is to say, to the width of the free space between the parasitic element P11 and the main slab P10. For its part, the width of the connecting channel L11 is of the order of 1/5 of the width of the main slab P70 (perpendicular to the array of the short circuits CC).

So far, it has not been possible to give any definite explanation as regards the operation on two frequencies of a slab as here represented. It does, however, seem that one of the frequencies is obtained when the so called slab Plo behaves as though itwere alone and that the otherfrequency approximates to that which would be obtained with a larger metallised slab which would be defined by the envelope of slab P10 and of its parasitic elements P11, that is to say, by filling in the free space between these two portions by a complementary metallisation.

Subject to confirmation of the preceding considerations, provision may therefore be made, at least approximately, for the operating frequencies of a slab in accordance with Figure 1 as follows: starting with a metallisation which could correspond to P10 and P11 as a whole, and to the lower frequency, a double cut out is placed therein so as to define the metallised channel L11 and the parasitic element P11 with a cut out width substantially equal to that of the parasitic element P11; and, by successive trails, the exact dimensions of the device are adjusted until the second frequency with the desired resonance is obtained.

Still under this hypothesis, the core of the coaxial cable CA ends at slab P10 on axis Ill-Ill which is then approximately equidistant between the far edge of slab P10 and its end edge situated nearest to the front of the parasitic element P11.

In the other direction, the position of the core of the coaxial cable CA can be more or less at one third of the width of the slab (starting on the side where the short circuits CC are ocated).

As regards the short circuit lines, the latter may be made by a series of shor: circuit pins which are, for example, eight in number. In the drawing, axis Ill-Ill is supposed to pass throngh core CA of the co-axial cable as well as through one of the short circuits in the representation of Figure 3. In practice, this is in no way necessary. For its part, Figure 2 illustrates a usual conventional representation of a slab according to Figure 1 in which representation there only appears the shape of the upper metallisation, the dielectric and the grouno plane not having been illustrated, in order to siriplifythe drawing.

Figure 4 illustrates a second mode of embodiment of the present invention. The same references are used in Figures 1 and 4 as well as 2 and 5 to represent the same elements.

Figure 4 differs from Figure 1 in that a second parasitic element P12 is placed at the opposite end of metallisation P10 in relation to the first parasitic element P11.

More precisely, like the first, the second parasitic element extends near the far edge of slab P10 over a length equal to that of this edge. The parasitic element P,2 is connected to the slab via a metallised channel L12 which is narrow in relation to the said length.

The structure of Figure 4 is entirely symmetrical in relation to the axis of symmetry perpendicular to the array of short circuit lines which may be defined in the slab P10 proper. This axis is designated S-S in Figure 4.

For the rest, the practical definition of the second mode of embodiment of Figures 4 and 5 may be effected as above, observing that one of the frequencies seems to be due to the functioning of slab P10 as though it were on its own, whilst the other seems to relate to the association of slab P,O with its two parasitic elements P11 and P12.

It will, furthermore, be noted that the cross section of Figure 3 applies both to Figure 1 and to Figure 4, it being observed that axis Ill-Ill is inclined on Figure 4 so that it passes through one of the short circuit pins.

Forthe practical making of radiation devices in accordance with the present invention, the dielectric plate may be made of alumina or duroid whilst the metallisations are made, for instance, of copper.

Experimental research studies carried out with the two modes of embodiment described above have shown that the slabs operate on two frequencies, with an angular spread close to 1809 within a zone centred on the plane of symmetry perpendicular to the short circuit line. The simultaneous operation on wo frequencies and on a narrow band width for each frequency is obtained with an exceptionally reduced size, since usually, two dielectric thicknesses and two superposed metallised slabs are necessary to obtain two frequencies. The impendance matching with respect to the power, is effected in a simple way by means of the lead-in via the coxial cable. It will moreover be observed that the quality of reduced size of the microstrip structure is retained. It has, furthermore, been observed that the radiating ele ments of the present invention are subject to a certain rate of cross polarisation which may prove to be advantageous in certain applications, particularly if one is concerned with operating in circular polarisation and/or with the making of adaptable antennae.

To obtain quasi-hemispherical cover, the radiating elements of the present invention may be associated in sets of four which are oriented in different directions, displaced at 90 as previously indicated. It is preferably on the basis of such sets that the adaptable antennae which are referred to above have been constructed.

Claims

1. A radiating device of the type comprising at least one radiating element which comprises:- on the one hand a microstrip structure forming a resonator with losses, and constituted by at least one dielectric plate, by an extensive metallisation forming the ground plane affixed under this plate, and by a metallised slab with a chosen configuration affixed on the said plate; and on the other hand means allowing an adapted electric connection between the said microstrip structure and an application circuit, wherein said slab is associated with a parasitic metallised element extending on the same surface as the dielectric plate, near one of the edges of the slab, and over a length substantially equal to that of this edge, this parasitic element being electrically connected to the slab via a metallised channel which is narrow in relation to the said length.

2. A device according to Claim 1, wherein the width of the parasitic element is substantially equal to the spacing of it from said one edge of the metallised slab.

3. A device according to either of Claims 1 and 2, wherein the width of the channel is substantially one fifth of the width of the metallised slab.

4. A device according to any one of Claims 1 to 3, wherein the neighbouring edges of the parasitic element and of the slab are substantially parallel to each other.

5. A device according to any one of Claims 1 to 4, wherein the slab, the parasitic metallised element and the metallised channel have a generally rectangular shape.

6. A device according to any one of Claims 1 to 5, wherein the slab is connected to the earth plane via a short circuit line at a position chosen to be close to one edge of the said slab, said one edge being different from the edge which the parasitic metallised element adjoins.

7. A device according to any one of Claims 1 to 6, wherein the electric connection means comprise a duct passing through the dielectric plate and an opening in the ground plane, and a coaxial cable whose screening is connected to the ground plane whilst its central conductor uses the said duct, without electric contact with the ground plane, to make electric contact with the metallised slab.

8. A device according to any one of Claims 1 to 7, wherein it comprises a second metallised parasitic element similar to the first mentioned parasitic element and extending near an edge of the slab which is on the opposite side to that adjoined by the first metallised parasitic element.

9. A device according to Claim 8, wherein the second parasitic element is substantially identical with the first mentioned parasitic element.

10. A radiating device according to any one of the preceding Claims, and comprising at least one set of four substantially identical radiating elements, mounted side by side in different directions displaced by 90 in relation to each other.

11. A radiating device substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

12. The use of the device according to any one of the preceding Claims as an adaptable antenna functioning over at least two frequencies, with a narrow band on each frequency.

Amendments to the claims have been filed and have the following effect: (a) Claims 1-12 inclusive above have been deleted.

(b) New or textually amended claims have been filed as follows:

1. A radiating device of the type comprising at least one radiating elementwhich comprises: on the one hand a microstrip structure forming a resonator with losses, and constituted by at least one dielectric plate, by an extensive metallisation forming the ground plane affixed under this plate, and by a metallised slab with a chosen configuration affixed on the said plate; and on the other hand means allowing an adapted electric connection between the said microstrip structure and an application circuit, wherein said slab is associated with an additional metallised element extending on the same surface as the dielectric plate, near one of the edges of the slab, and over a length substantially equal to that of this edge, this additional element being electrically connected to the slab via a metallised channel which is narrow in relation to the said length.

2. A device according to Claim 1, wherein the width of the additional elementis substantially equal to the spacing of it from said one edge of the metallised slab.

4. A device according to any one of Claims 1 to 3, wherein the neighbouring edges of the additional element and of the slab are substantially parallel to each other.

5. A device according to any one of Claims 1 to 4, wherein the slab, the additional metallised element and the metallised channel have a generally rectangular shape.

6. A device according to any one of Claims 1 to 5, wherein the slab is connected to the earth plane via a short circuit line at a position chosen to be close to one edge of the said slab, said one edge being different from the edge which the additional metallised element adjoins.

8. A device according to any one of Claims 1 to 7, wherein it comprises a second metallised additional element similar to the first mentioned additional element and extending near an edge of the slab which is on the opposite side to that adjoined by the first metallised additional element.

9. A device according to Claim 8, wherein the second additional element is substantially identical with the first mentioned additional element.