GB2463711A - Double polarization flat antenna array - Google Patents

Abstract

A flat antenna includes an array of radiating slots defined by an assembly of waveguides. The central section and the ends of the guides are provided with short-circuit pins (PCC, figs 7 and 8). In a geometric configuration close to that of the slots, there are radiating dipoles DR using microstrip technology, fed by connection areas between two dielectric substrates (figs 5A, 5B, 6A, 6B). The ground plane PM at the level of the lower dielectric substrate is cut out at right angles to the radiating slots and also at right angles to the passages for feeding the connection areas. The structure of the dipoles can be made entirely decoupled from the structure of the slots, enabling mutually uncoupled operation in two different polarizations. The feed lengths to the dipoles may be made equal (figs 6B, 7). In a four quadrant structure (figs 7 and 8), the dipoles may be provided throughout the circular area.

Description

DOUBLE POLARIZATION FLAT ARRAY ANTENNA

The invention relates to antennas formed from an array of radiating elements.

Certain applications require an antenna array of small size the feeding of which is separable into four quadrants. The object is to obtain at choice, and at will, signals representing on the one hand a "sum" diagram and, on the other hand, "elevation difference" and "azimuth difference" diagrams.

Flat antennas are thus known, including an array of radiating slots defined by an assembly of waveguides pierced with the said slots and working in conjunction with a feed waveguide or waveguides (see for example French Patent No. 75/37622 published under No. 2,335,064). These antennas function in linear polarization, with an electrical field vector perpendicular to the large dimension of the slot.

They allow good composition of the signals of each slot in both amplitude and phase. In addition, they are also capable of being separated into four quadrants whose electrical feeds are independent. These antennas therefore solve the problem raised above, but only for the single polarization of which they are capable.

The main object of the present invention is to solve the same problem in a more general way. The solution is given by obtaining a flat antenna capable of functioning in two polarizations.

The invention starts from a flat array antenna, of the type including an array of radiating slots, defined by an assembly of waveguides pierced by the said slots and working in conjunction with one or more feed waveguides.

Unexpectedly, it has proved possible to incorporate, in this array of slots, an array of dipoles functioning in a different polarization with separate feeds and without any electromagnetic interactions appearing between the two arrays and impeding their correct functioning.

Thus the antenna includes superjacent to the array of slots, and interlaced with it, an array of radiating elements of microstrip structure fed entirely separately from the slots and arranged in order to form dipoles whose larger dimension is parallel to that of the slots, which provides a single antenna capable of functioning in an uncoupled way in two different polarizations. In practice the antenna is divided into four separately fed quadrants for the array of slots as well as for that of the dipoles.

According to another aspect of the invention, the ground plane of the microstrip structure, cut out at right angles to the slots, is in electrical contact with the waveguides defining these slots.

Advantageously the microstrip structure which has two superimposed dielectric substrates, includes between these two substrates a plane of distribution lines interconnecting the array of diples in order to feed these dipoles in a way which is balanced in amplitude and/or

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phase.

Preferably, the input of the microwaves to the distribution lines is carried out by coaxial microlines passing across the entire stack of the microstrip structure and the assembly of slot waveguides.

These crossing coaxial microlines can be housed in the short-circuit pins that are part of the assembly of slot waveguides, or in their walls.

According to yet another aspect of the invention, the distribution lines are arranged as quarter-wave transformers between their feed point and the dipoles to which they are connected.

Other characteristics and advantages of the invention will be apparent from the following description and the appended drawings, in which: Figure 1 is a plan view of a slotted antenna array of known type; Figures 2 and 3 show details of the antenna of Figure 1, in perspective; Figure 4 is a plan view of one embodiment of the invention; Figures 5A and 5B are a plan view and a cross-section view, respectively, showing the microstrip structure used according to the invention; Figures 6A and 6B show two variant applications of the microstrip structure of the antenna of Figure 4; and Figures 7 and 8 show two preferred variants of antennas according to the invention, separable into four quad rants.

The geometry of the antenna according to the invention is important. Consequently the appended drawings are an integral part of the present description and can contribute to the sufficiency of this description as well as to the definition of the invention.

Traditionally, the flat antenna includes juxtaposed waveguides GD (Figure 1), of which there are eight in the antenna shown, GD1-GD8. Each waveguide GD (Figure 2) is formed by a parallelepipedic tube, with opposed larger surfaces 11 and 13 and opposed smaller surfaces 12 and 14.

One larger surface, for example 11, faces towards the region where the radar energy must be radiated or picked up from and it has radiating slots FR arranged in two rows, on either side of a median plane 10 parallel to the smaller surfaces 12,14. The pitch of these slots is equal to half the wavelength of the wave in the guide carrying the energy to be radiated or picked up.

The waveguides are joined to each other by their smaller surfaces 12 and 14 and the lengths of the successive waveguides GD1 to GD8 are such that they are inscribed in a similar circumference R of centre 0. Other geometric shapes such as a rectangle, an ellipse or a polygon having adequate symmetries can of course be envisaged instead of a circle.

In a known way, the waveguides GD are fed from feed guides GA, also of rectangular cross-section (Figure 3) of which one larger surface 21 is in contact with the rear larger surfaces 13 of the waveguides GA, communication being established by oblique slots FA, by superimposition, presented by the surfaces 21 of the feed waveguides GA and the surfaces 13 of the waveguides GD respectively.

When required, the separation of the antenna into four quadrants is obtained as follows: the waveguides GD, which distribute the microwave energy to the radiating slots FR, are symmetrically disposed to either side of a median separation plane 15, on the vertical axis Y (Figure 1) This separation can be a complete partition. However, because it has only to function for the microwave frequency of the guide, it can be produced by simple short-circuit pins, or by other equivalent means suitable for microwaves.

As a radiating slot can be considered as a shunt, in its equivalent diagram, it is a matter of forming a short-circuit at one quarter of a wavelength of the guided wave from the end of the slot. As a general rule, the same structure is adopted at the free ends of the guides GD.

The waveguides GA, are symmetrically arranged about a median separation plane 25 on the horizontal axis X. As known by experts in the field, this separation 25 can include an open circuit 25, spaced from each of the closest inclined slots FA by one quarter of a wavelength of the guided wave. This produces a short-circuit at the slots, which then operate as a series equivalent circuit. In this way four sections of feed waveguides GAl to GA4 are defined.

Section GAl is coupled by respective slots FA to the left halves of guides GD1 to GD4. In alignment with it, section GA4 is coupled by respective slots to the left halves of guides GD5 to GD8. The same applies to the right halves of guides GD1 to GD8, with the sections of aligned guides GA2 and GA3.

Experts in the field know that the four sections of guide GM to GA4 then independently feed the four quadrants of the antenna, both on transmission and on reception. The signals delivered by guides GM to GM are now called A, B, C and D respectively.

The sum A+B-1-C+D defines the total response of the antenna, in the "sum" diagram. All other linear combinations can be constructed, of which: (A+B) -(C+D) , is the "elevation difference"; (A+D) -(B+C), is the "azimuth difference".

In certain applications, of course, it will be difficult to rely on the sum diagram and/or one or other of these two "differences". It will also be possible to envisage a different partition of the antenna for other applications (for example into eight sectors) With regard to Figures 4 to 6, it is accepted that the azimuth difference is sufficient.

Figure 4 shows the radiating slots FR inside the circle R. The rest of the subjacent structure of waveguidesGD and GA is omitted in order to simplify the drawing.

A contour PM, around the horizontal axis H, defines the external limit of a microstrip structure, which avoids the slots FR. This structure can be repeated symmetrically, between each of the rows of slots FR, in such a way as to completely fill the circle R. However, in order to simplify the drawing only the central structure is shown. This subject will be resumed later on.

For the present, reference is made to Figures 5A and 5B, which show the general constitution of a microstrip antenna structure. In the example shown, a lower dielectric substrate Si is metailized on the bottom using a metallization known as the ground plane PM. This ground plane will in this case be fixed on the waveguides GD, with which it is advantageously maintained in electrical contact by a conductive adhesive or by other equivalent means. On top of the dielectric substrate Si there is a metallization having three sections 3lA, 32A and 33A. This metailization is advantageously surmounted by a second dielectric substrate S2, which bears a metallization having its geometry chosen to obtain a radiation of predetermined characteristics. Metallizations suitable for this purpose are often called "paving". In the example shown, the metallization is a narrow plate forming a radiating dipole DR.

A passage 30A is provided through the ground plane and the first substrate Si in order to admit a coaxial microcabie at the point 30A of the conducting area 31A.

This conducting area 31A is followed by an area 32A whose geometry is chosen to form a quarter wave transformer. To this area 32A there is connected a third area 33A which comes below the dipole DR in such a way as to form an electromagnetic coupling by proximity with that dipole. In this way the radiating dipole DR can be excited with the electromagnetic energy carried by the coaxial microcable entering 30A. Equivalent structures can also be produced using a single dielectric substrate instead of the two shown. In this case the areas 31 to 33 are in the same plane as the dipole DR, while remaining in electromagetic coupling by proximity with that dipole.

Reference is now again made to Figure 4. The contour PM represents the external outline of the two substrates Sl and S2, and therefore of the ground plane of the lower substrate which is metallized over its entire lower surface except at points 30 and 40 where the coaxial cables enter. The structure shown in Figure 4 is symmetrical about the centre, i.e. the intersection of the V and H axes. It includes, on the upper surface of the substrate S2, four dipoles DR1 to DR4 to the left of the vertical axis V and four dipoles DR5 to DR8 to the right of the vertical axis V. Between the two substrates, areas 30 to 39 are provided for the left hand section and areas 40 to 49 are provided for the right hand section.

Because of the symmetry only the left hand section will be described, referring to Figure 4, and to Figure 6A which is an enlarged view of the microstrip structure added onto the left hand section of Figure 4.

The coaxial passage ends at 30 in a narrow area 31.

This area 31 is followed by an area 32 forming a quarter wave transformer, and then by an area 33. From this area a first branch 34 leaves to go to the dipole DR1. An area 35, narrower than area 33, feeds the dipole DR2 through a branch 36, after which it narrows at 37 in order finally to feed the dipole DR3 at 38 and the dipole DR4 at 39.

This type of feeding of the dipoles ensures a reasonable distribution of energy between the dipoles while complying with the phase, but for a rather narrow frequency band as the length of the paths between the point 30 and the various dipoles is not the same.

Figure 6B discloses a variant in which the various dipoles DR1 to DR4 are effectively fed by paths of the same length. There are again present the feed at 130, the first area 131, the quarter wave transformer 132 and the wide area 133 from which departs the first branch 134 which is now curved in a hairpin bend. A new hairpin branch 136 departs from the narrowest area 135, while the final area 137 subdivides at 138 and 139 into two branches whose total lengths are effectively equal. An examination of the lengths of the branches 134 to 139 shows that the distance from point 130 to the centre of each dipole is approximately the same. The result of this is that the equitable distribution of energy is also accompanied by a phase

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synchronisation of the various dipoles over a much wider frequency band than before (Figure 6A).

Unlike the embodiment in Figures 4, 6A and 6B, the preferred embodiments in Figures 7 and 8 enable a separation of the antenna into four quadrants both for the radiating slots FR and for the radiating dipoles DR.

Reference is firstly made to Figure 7. It concerns the bottom left quadrant of the antenna, which was referenced D in Figure 4.

The axis lines PF4 to PF8 indicate the separation between the distribution guides GD5 to GD8 which feed the radiating slots, such as FR, situated at their respective levels.

Dipoles DR21 to DR25 are provided near the slots FR associated with the distribution guide GD5. The same applies for the slots associated with distribvution guide GD6 and the dipoles DR26 to DR3O. The vertical pitch of the structure of dipoles ensures that an interval is maintained above the distribution guide GD7. New dipoles DR31 to DR34 are encountered near the upper edge of guide GD8, while two last dipoles DR35 and DR36 appear right at the bottom of the quadrant shown in Figure 7.

All these dipoles are fed from a common feed point which starts at 230 where it receives a coaxial microcable which penetrates the microstrip structure (double or single dielectric) in order then to pass between the walls of the distribution guides GD6 and GD7. Observing that distribution guide GD7 is terminated (in microwave terms) by short-circuit pins PCC71, the production of the penetration is not critical in this example. It should be noted that although the short-circuit pins PCC are all shown in full line, they are in fact below the microstrip structure. This illustration convention is used to allow a better distinction between the conducting areas connecting the input point 230 to the various dipoles DR.

Numerous branches are taken from these areas. In a way known to experts in the field, each branch is bridged by a short resistor which provides a decoupling between downstream sections, which improves the functioning of the microwave signal divider. These short resistors are not shown in the drawing.

Starting from point 230, the feed circuit includes a first region 231 which is subdivided into one branch region 232 to the left which departs horizontally, and another branch region 250 to the right, which departs obliquely.

The region 232 curves to rise vertically between the dipoles DR28 and DR29 where it is again branched into two sections 233 and 242, both horizontal. Section 233 again subdivides, from left to right at 234, 235 and 239. The branch 234 is subdivided a final time in order to feed dipoles DR27 and DR28 by terminal branches 249 and 236 respectively. Branch 235 is subdivided into 237 and 238 in order to feed dipoles DR26 and DR21 respectively. Finally, branch 239 is subdivided into 240 and 241 to feed dipoles DR22 and DR23.

Returning now to branch 242 which subdivides into 243 and 246, it can be seen that the branch 243 subdivides a final time into 244 and 245 in order to feed dipoles DR24 and DR25. Branch 246 is subdivided into 247 and 248 in order to feed dipoles DR29 and DR3O which comples the feeding of the dipoles situated above the distribution guide GD7.

Considering now the area below the distribution guide GD7, branch 250 subdivides into 251 and 258 after an oblique path followed by a vertical path. The horizontal branch 251 subdivides vertically into 252 upwards and 255 downwards. Branch 252 is subdivided a final time into 253 and 254 in order to feed dipoles DR33 and DR34. Branch 255 subdivides into 256 and 257 in order to feed dipoles DR36 and DR35.

On the other side, branch 258 subdivides into 259 and 260 in order to feed dipoles DR31 and DR32, which comples the feeding of all the dipoles in qudrant D of the antenna.

Careful examination of Figure 7 shows that practically the same electrical path length is obtained from point 230 to each of the dipoles DR, except for dipoles DR21 and DR26 where the line is a little longer. Despite this, an expert in the field will understand that the feed structure thus obtained enables the dipoles to function over quite a wide frequency band.

Reference is now made to Figure 8 which concerns the top left quadrant, referenced A in Figure 4.

The four distribution waveguides GD1 to GD4 are again present, with their radiating slots such as FR. On the vertical axis, the left arid right halves of these distribution guides GD1 to GD4 are separated by pairs of short-circuit pins PCC1O, PCC2O, PCC3O and PCC4O respectively.

The upper wall of the distribution guide GD1 is illustrated by the axis line PFO. The separations between the distribution waveguides are then shown by axis lines PF1 to PF4.

The left hand end of each of the distributiong uides GD1 to GD4 is also closed by other pairs of short-circuit pins PCC11, PCC21, PCC31 and PCC41 respectively.

The structure of resonant dipoles is much simpler here. Twelve dipoles are arranged in a matrix on three levels. Starting from the bottom, the first level is formed from dipoles DR51 to DR54, the next line thereabove includes dipoles DR55 to DR58, and the next line above that includes dipoles DR59 to DR62. They are completed by dipoles DR63 to DR65 above the dipoles DR6O to DR62 respectively and in alignment with these as well as with the previous ones.

This geometrically simple structure has been shown to have, in the quadrant A in question, a radiation diagram comparable with that obtained with the slots that this same quadrant comprises but in the orthogonal polarization.

In its turn, the feeding of the dipoles is very simply achieved by four vertical lines implanted between the microstrip structure substrates Si and S2 (not shown in this Figure) . From left to right, these four vertical lines are referenced 301 to 304. Line 301 interconnects dipoles DR51, DR55 and DR59. Line 302 interconnects dipoles DR52, DR56, DR6O and DR63. Line 303 interconnects dipoles DR53, DR57, DR61 and DR64. Finally, line 304 interconnects dipoles DR54, DR5B, DR62 and DR65.

As before, the excitation of the dipoles by each of the lines is carried out by electromagnetic proximity coupling.

The bottoms of lines 301 to 304 are folded back to form a semicircle towards the left, in order to join the separation line PF3 of the axis marking. Coaxial inicrocables are then connected to the ends thus defined for the lines 301 to 304 in order to pass into the dielectric substrates of the superjacent microstrip structure, and then to pass between the distribution guides GD3 and GD4 in order, finally, to end below the guide structure. The four lines are then joined together to enable common feeding to achieve four quadrant functioning. This common feeding can be obtained by another microstrip structure, of traditional type, which is subjacent to the structure of the distribution guides GD.

Whereas in the embodiment of Figure 7, practically the same electrical path length exists between the feed points and each of the dipoles, this condition is no longer true in the case of Figure 8. The distribution of energy, in amplitude and phase, between the various dipoles can, however, be correct, but only over a more restricted frequency band, as phase agreement now produces nodes and antinodes of the microwave field on the vertical lines 301 to 304.

As previously indicated, the feeding from below of the conducting lines or areas existing betwen the substrates Sl and S2 of the microstrip structure can be carried out in different ways. However, the preferred way is to pass the feed either through the passages PF provided in the thickness of the wall between the different distribution guides GD of the flat antenna, or through the short-circuit pins PCC which are used in the same distribution guides.

Claims (9)

1. S -CLAIMS1. A flat array antenna including:-an assembly of waveguides; an array of radiating slot means defined by and penetrating said waveguides; at least one feed waveguide in conjunction with said slot means; superjacent to the array of slot means and interlaced with it, an array of radiating elements of inicrostrip structure; and feed means for said array of radiating elements, entirely separate from the slot means; said radiating elements being arranged as dipoles having a major axis parallel to that of the slots and providing a single antenna capable of functioning in an uncoupled way in two different polarizations.
2. 2. A flat array antenna according to claim 1, wherein it is divided into four quadrants having separate first feed means for the array of slots and second feed means for the dipoles.
3. 3. A flat array antenna according to claim 1 or claim 2, including:-a ground plane of the microstrip structure at right angles to said slot means; and means electrically contacting said ground plane and the first mentioned said waveguides defining said slot means.
4. 4. A flat array antenna according to any one of claims 1 to 3, wherein the microstrip structure includes:-first and second superimposed dielectric substrates; and between said first and second substrates a plane of distribution lines interconnecting said dipoles of the array in order to feed said dipoles in a way that is balanced in amplitude and/or phase.
5. 5. A flat array antenna according to claim 4, including coaxial microlines passing across the entire stack of the microstrip structure and the assembly of the first mentioned said waveguides which define said slot means, said coaxial microlines carrying the microwave input to said distribution lines.
6. 6. A flat array antenna according to claim 5, including short-circuit pins, forming part of the assembly of waveguides defining said slot means, arid wherein the coaxial microlines pass through said short circuit pins.
7. 7. A flat array antenna according to claim 5, wherein said coaxial microlines pass through the walls of said first mentioned waveguides which define the slot means.
8. 8. A flat array antenna according to any one of claims 4 to 7, including quarter-wave transformers between the feed point of said distribution lines arid the dipoles to which they are connected.
9. 9. A flat array antenna substantially as here inbefore described with reference, to, and as illustrated in, Figure 4, or Figures 5A and 5B, or Figures 6A and 6B, or Figure 7, or Figure 8, of the accompanying drawings.( Amendments to the claims have been filed as follows 1. A flat array antenna including:-an assembly of Waveguides; an array of radiating slots defined by said wavegjdes; at least one feed Waveguide in COnjunction With said radiating slots; superjacent to the array of radiating slots and interlaced with it, an array of radiating elements of microstrip structure; and feed means for said array of radiating elements, entirely separate from the radiating slots; said radiating elements being arranged as dipoles having a geometrjc Configuration substantially the same as that of the radiating slots and having a major axis parallel I,', to that of the radiating slots and substantially ecrual4t., that of the radiating slots so as to provide a single antenna capable of functioning in an Uncoupled way in two different polarizations.2. A flat array antenna according to claim 1, wherein it is divided into four quadrants having separate first feed means for said array of radiating slots and second feed means for the dipoles.3. A flat array antenna according to claim 1 or claim 2, wherein the microstrip structure has a ground plane cut away around said radiating slots; and means electrically contacting said ground plane and the first mentioned said waveguides defining said radiating slots.4. A flat array antenna according to any one of claims i to 3, wherein the microstrip structure includes:-first and second superimposed dielectric substrates; and between said first and second substrates a plane of distribution lines interconnecting said dipoles of the array in order to feed said dipoles in a way that is balanced in amplitude and/or phase.5. A flat array antenna according to claim 4, including coaxial microlines passing across the entire stack of the microstrip structure and the assembly of the first mentioned said Waveguides which define said radiating slots, 35 said coaxial Inicroljnes carrying the microwave input to said distribution lines. (6. A flat array antenna according to claim 5, including short-circuit pins, forming part of the assembly of waveguides defining said radiating slots, and wherein the coaxial microljne pass through said short circuit pins.7. A flat array antenna according to claim 5, wherein said coaxial microljnes pass through the walls of said first mentioned waveguides which define the radiating slots.8. A flat array antenna according to any one of claims 4 to 7, including quarter-wave transformers between the feed point of said distribution lines and the dipoles to which they are connecte4..9. A flat array antenna substantially as herejnbefore described with reference to, and as illustrated in, Figure 4; or Figures 4, 5A and 58; or Figures 4 and 6A; or Figures 4 and 6B; or Figure 7; or Figure 8; of the accompanying drawings.