WO2008040807A1

WO2008040807A1 - Slot/ellipsoid pad coupling device for direct supply by the waveguide of a planar antenna

Info

Publication number: WO2008040807A1
Application number: PCT/EP2007/060604
Authority: WO
Inventors: John Bartholomew; Eduardo Motta Cruz
Original assignee: Bouygues Telecom
Priority date: 2006-10-06
Filing date: 2007-10-05
Publication date: 2008-04-10
Also published as: FR2906938B1; EP2080248A1; FR2906938A1

Abstract

According to a first aspect, the present invention relates to a planar antenna comprising: a substrate; at least one sub-network of radiating members provided on the substrate, said sub-network comprising a sub-network feed line (20) with a coupling pad (30) and a plurality of radiating members connected to the line; a ground plane (50) onto which the substrate is superimposed and having a slot (40) formed therein opposite the coupling pad (30) of the feed line (20) of each sub-network; a power transmission line (10) provided relative to the ground plane (50) so as to realise an electromagnetic coupling through the slot between said power transmission line and the coupling pad of each of the sub-network feed lines; said antenna being characterised in that the coupling pad (30) has an ellipsoid shape. According to another aspect, the present invention relates to a power supply line comprising an ellipsoid coupling pad.

Description

ELLIPSOIDAL SLOT / PASTILLE COUPLING DEVICE FOR THE DIRECT WAVEGUIDE POWER SUPPLY OF A

FLAT ANTENNA

The field of the invention is that of telecommunication antennas, and more particularly that of antennas for radio-relay systems (FH antennas).

The invention relates to flat antennas for radio-relayed microwave systems, and more precisely to electromagnetic coupling by slot between a power transmission line, typically a waveguide, and a power supply line. of radiating elements of the flat antenna.

Satellite dishes are commonly used for radio-relay systems. In these satellite dishes, a rectangular waveguide is generally connected to a remote cabinet at the rear of the antenna to achieve radio access to the antenna.

Flat antennas now tend to be preferred over satellite dishes. Flat antennas have the advantage of being equivalent surface, globally as effective as parabolic antennas. And these flat antennas are characterized by their compactness and low weight.

A flat antenna comprises a network of radiating elements integrated in the dielectric substrate of the antenna. The flat antenna more specifically comprises a set of linear subarrays parallel to each other, each linear subarray consisting of a set of radiating elements. The radiating elements are typically each consisting of a conductive square surface having a corner connected to a subnetwork supply line (typically in the form of a microstrip line). The power supply of the flat antenna is conventionally performed by providing the antenna with a coaxial connector, and by connecting the antenna to a waveguide via a guide-coaxial transition.

However, the increase in the frequency used for the radio links implies the reduction of the physical dimensions of the elements of the antenna. This reduction leads to difficulties in producing the coaxial probe feed solution.

In order to answer this problem, solutions of direct supply by waveguide have been proposed.

Such a solution is for example presented in the article by Van Der WiIt and Strijbos, entitled "A 40 Ghz planar array antenna using hybrid coupling" (in "Perspectives on Radio Astronomy - Technologies for Large Antenna Arrays, Proceedings of the Conference held at the ASTRON Institute in Dwingeloo on 12-14 April 1999. ISBN: 90-805434-2-X, 354 pages, 2000, p.129 ").

The appended FIG. 1 represents the solution recommended by this article, a solution according to which an electromagnetic coupler is produced from a waveguide 1 towards a microstrip line 2, using a patch 3 placed above a slot 4 in the ground plane 5 of the antenna and communicating with the waveguide 1.

The micro-ribbon line 2 has more precisely a rectangular coupling pad 3 placed above a rectangular slot 4.

The chip 3 thus harvests the energy radiated by the waveguide 1 through the slot 4, and thus makes it possible to transmit the power of the waveguide 1 to the micro-ribbon line 2.

It will be noted at this stage that the design procedure of such a coupler requires finding the appropriate dimensions of the slot and the chip to achieve a coupling at the desired frequency. Four variables must then be optimized to obtain the desired frequency: length and width of the slot, length and width of the pellet. If this direct power solution can address the problem described above relating to the increase of the frequency of the antenna, it is however not completely satisfactory.

Indeed, there are radiation losses due to the discontinuity of the rectangular pellet. This results in a degradation of the polarity purity performance of the antenna radiation, and efficiency of transmission of power from the waveguide to the micro-ribbon line.

BE 1 013 508 proposes a planar antenna of the type of the subject of the preamble of claim 1, having an element (element 300 in Figure 19) to ensure the slot / power line coupling radiating patches under the shape of a rectangular coupling pad.

The manual of JR JAMES AND PS HALL: "handbook of microstrip antennas, vol.1" relates to the generation of a circular polarization using an antenna with circular radiating elements fed by a microstrip line. It will be noted that this manual does not relate to an antenna structure according to the invention, which implements an electromagnetic coupling by slot between a waveguide and the microstrip line. A fortiori, this manual does not deal with any coupling pad able to take energy in the guide to redistribute it to the radiating elements via the microstrip line.

The object of the invention is to propose means for electromagnetic coupling of a waveguide to a micro-ribbon line which allow increased performances both in terms of the purity of the polarity of the radiation and in terms of power transfer of the guide. towards the line, and vice versa.

For this purpose, and according to a first aspect, the invention relates to a flat antenna comprising: • a substrate; At least one sub-array of radiating elements disposed on the substrate, said sub-network comprising:

a sub-network supply line comprising a coupling pad,

and a plurality of radiating elements connected to the line;

A ground plane on which the substrate is superimposed, in which a slot is made opposite the coupling pad of the supply line of each sub-network;

A power transmission line arranged with respect to the ground plane so as to perform an electromagnetic coupling by slot between said power transmission line and the coupling pad of each of the subnetwork supply lines; the antenna being characterized in that the coupling pad is of ellipsoidal shape.

Some preferred, but not limiting, aspects of this antenna are:

the pellet is circular;

the slot is rectangular and its perimeter is of a wavelength in the middle of the substrate;

the width of the slot is less than half the thickness of the substrate;

the slot is rectangular, and the diameter of the pellet is chosen so that the pellet covers the slot about 2/3 of the length of the slot;

- the antenna is an antenna for radio-relay systems in the band 37.21 GHz to 38.66 GHz;

the radiating elements connected to the supply line are spaced apart by half a wavelength in the medium of the substrate;

the radiating elements are successively connected to one side and then to the other of the supply line;

the supply line has two arms on either side of the coupling pad and the radiating elements are connected to the line feeding on each of the arms in the inverted position of one arm relative to the other.

According to a second aspect, the invention relates to a power supply line of a sub-array of radiating elements of a flat antenna, comprising a coupling pad for collecting the energy radiated by a power transmission line. through a slot, characterized in that the coupling pad is of ellipsoidal shape.

Other aspects, objects and advantages of the present invention will appear better on reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and with reference to the appended drawings in which: , in addition to Figure 1 already commented on Figure 2 is a diagram showing the microstrip line-guide coupling according to a possible embodiment of the invention; Figure 3 is a diagram showing a flat antenna according to a possible embodiment of the invention.

It is specified for purely illustrative and non-limiting, that an application that we will do the coupling according to the invention relates to transmissions in the band of 37.21 GHz to 38.64 GHz.

Referring to FIG. 2, there is shown a feed line of a sub-array of radiating elements of a flat antenna in the form of a microstrip line 20.

Note that in this FIG. 2, only a portion, typically the central portion, of the line 20, of the ports P1 and P2 representing microstrip line accesses for excitation, on either side of the this central portion, radiating elements (not shown in this figure) of a sub-array of the flat antenna

The microstrip line 20 is disposed on the dielectric substrate of the antenna, this substrate being superimposed on the ground plane 50 of the antenna.

The line 20 comprises a coupling pad 30, and a slot 40 is formed in the ground plane 50 facing the coupling pad 30. An energy transmission line, typically a waveguide 10, is arranged with respect to the ground plane 50 so as to achieve an electromagnetic coupling by slot between said power transmission line and the coupling pad of the line. 20.

The coupling pad thus collects the energy radiated by the waveguide 10 through the slot 40.

It will be understood that more generally, a flat antenna comprises at least one sub-network of radiating elements (typically a plurality of linear subarrays parallel to each other) disposed on the substrate, said sub-network comprising a line subnetwork power supply having a coupling pad, and a plurality of radiating elements connected to the line. A slot is then made in the ground plane opposite the coupling pad of the supply line of each sub-network.

According to a possible embodiment, the energy transmission line is a rectangular waveguide, one side of which is pressed against the ground plane, and wave radiation slots are formed in said waveguide face. so that the slits of the ground plane and the slits of the waveguide coincide.

According to another possible embodiment, the energy transmission line is a waveguide having a U-shaped section, said waveguide being arranged in such a way that the ground plane closes the space of the waveguide.

According to yet another possible embodiment, the energy transmission line is a triplate line comprising a conductive line sandwiched between two plane planes triplate line, and wave radiation slots are made in that planes a triplate line mass which is pressed against the ground plane of the antenna so that the slits of the ground plane and the slots of the triplate line are superimposed. Note that one of the ground planes can be confused with the ground plane of the antenna.

A more detailed description of these embodiments will be found in the applicant's French patent application filed on November 14, 2005 under the number 0511527.

In particular, it will be noted that the energy transmission line may be positioned perpendicularly or obliquely with respect to the supply lines of the sub-networks of radiating elements.

In the context of the present invention, the coupling pad of the feed line 20 placed above the slot is of ellipsoidal shape.

It is mentioned that the ellipsoidal terminology used here to describe the geometry of the coupling pellet should not be understood as being limited to an ellipse stricto sensu. This terminology is indeed intended to extend to any shape approaching the ellipse, and more generally to any ovoid shape, and even more generally to any form devoid of discontinuities (in particular, to any shape without hard angles, for example). opposition to polygonal forms).

It is mentioned here that any discontinuity results in a sudden change in the volume dimensions inside the transmission lines, and microstrip lines in particular. Since the micro-ribbon lines are open lines, the hard angles thus impose a change in the boundary conditions of the electromagnetic fields, and consequently cause undesired radiation within the scope of the invention.

The use of an ellipsoidal pellet has the advantage of inducing a better polarization polarization of the radiation and better performance in the transfer of power from the waveguide to the microstrip line.

Indeed, the absence of discontinuities makes it possible to reduce parasitic radiation phenomena which lead to the degradation of the purity of polarization due to radiation with polarized fields in a random manner.

Remember that in the case of FH antennas, for example, the radiation is on one of two linear polarizations (vertical or horizontal). Thus, if the antenna is for example vertically polarized at one end, the antenna must have the same polarity at the other end. This then makes it possible to reuse the orthogonal polarization (horizontal in the example here selected) at the same frequency to establish the connection between two other points, sometimes in the immediate vicinity.

Antennas must therefore have good polarization purity to allow discrimination in polarity, otherwise other proximity links using orthogonal polarization are likely to be degraded.

This property is measurable by checking the radiation patterns in both polarities. Figures 4a and 4b show by way of example the radiation patterns of a rectangular coupling pad excitation antenna and an ellipsoidal coupling pad excitation antenna, respectively. In these figures, the references Aa and Ab represent the copolar component, while the references Ba and Bb represent the cross component.

It is found that the ellipsoidal pellet antenna according to the invention of Figure 4b is "cleaner" by 10 dB in the cross polarization (it is 10 dB below the antenna of Figure 4a). The antenna of FIG. 4b thus has, with respect to the antenna of FIG. 4a, a gain in purity of polarization of the order of 9%, resulting in a better discrimination in polarity and in a better efficiency of the antenna. .

According to a preferred embodiment, a circular geometry is adapted for the coupling pellet.

Such a circular geometry also makes it possible to simplify the design procedure. In particular, the micro-ribbon guide-line coupling then depends on a reduced number of variables, namely:

the diameter of the pellet, and

- the length of the slot.

This coupling is thus much less sensitive to physical dimensions, because of the smaller number of degrees of freedom compared to the rectangular pellet solution (2 variables against 4).

It will be noted that the geometry retained in the context of the invention also has the advantage of being less sensitive to variations in the physical dimensions (of the slot or of the coupling pad) resulting from industrial manufacturing processes.

Below, certain preferred characteristics of the slot-pellet coupling are described.

• The slot radiates in the dielectric medium. Its size is that of a slot radiating in this medium and the perimeter of the slot is then advantageously chosen so as to be close to a wavelength in this medium. The width of the slot is preferably less than the thickness of the substrate. As the thickness of the substrate is very small relative to the wavelength in the medium, the length of the slot must therefore be close to half the length of the wave in the medium, in order to define the privileged polarization of the electric field transferred from the waveguide to the micro-ribbon line.

• In order to adjust the coupling to the desired frequency and to optimize the power transfer, a circular pad is used whose diameter is approximately equal to 2/3 of the length of the slot; the pad being then positioned, as shown in Figure 2, so as to cover the slot about 2/3 of its length.

• The width of the slot is less than half the thickness of the substrate. The goal is to have enough slot width low, and preferably a slot width of about 1/3 of the thickness of the substrate is chosen.

• For the last coupling slot of the series of slots exciting the plurality of linear sub-networks of radiating elements since the arrival of the signal by the waveguide, it is advantageous to place a short circuit terminating the waveguide at a distance of a quarter of the length I of the wave in the slot guide (or at an odd multiple of a quarter of this length I, namely 3 I / 4, 5 I / 4, etc.) in the goal of maximizing power transfer from the waveguide to the micro ribbon line.

As previously mentioned, the slot-to-ellipsoidal patch coupling is implemented for each subarray of a flat antenna.

Thus each sub-array of radiating elements of the flat antenna is independently powered by such a coupling.

It is emphasized that this type of coupling effects a phase opposition on both sides of the slot and along the microstrip line.

Therefore, in order to re-phase the signals radiated by the radiating elements of a sub-network, it is possible to arrange each arm of the sub-network (the arms situated respectively on the side of the port P1 and on the side of the port P2 of the Figure 2) so that radiating elements are connected to the supply line on each arm in the inverted position of one arm relative to the other. A phase inversion of 180 ° is thus established, making it possible to compensate for the phase opposition created by the coupling slot between the two arms.

This arrangement is visible in FIG. 3 in the inverted arrangement of the two radiating elements closest to the coupling pad 30, belonging to each of the arms B1 and B2, these diametrically opposed radiating elements lying in the one and the other side of the micro ribbon line. The first radiating element of the left arm B1 from the pellet is thus an element situated "at the top" of the line 20, while the first radiating element of the right arm B2 from the pellet 30 is a "bottom" element of the line 20.

In this way, a directional antenna radiation pattern is obtained, with a maximum in the axis of the antenna.

Figure 3 illustrates this particular arrangement of the arms of each subnet. In this figure, a flat antenna A has a dielectric substrate on which eight subarrays a1-a8 of radiating elements 30 are arranged. These sub-networks a1-a8 are linear and parallel to each other.

Each sub-network comprises a microstrip supply line 20 comprising an ellipsoidal coupling pad 30, and a plurality of radiating elements 60 connected to the line on either side of the pad 30 (thus defining an arm left B1 of the sub-network carrying the elements to the left of the pellet 30, and a right arm B2 of the sub-network carrying the elements to the right of the pellet 30).

It will be noted that in each arm, the radiating elements 60 are successively connected to one side and then to the other of the supply line 20.

Each section of microstrip line between two radiating elements confers an electrical distance of half a wavelength in the medium establishing a supply of the radiating elements in opposition of phase, the compensation being done by the successive inversion of the radiating elements from one side and the other of the arm B1 or B2.

The combination of these two phenomena results in a supply and radiation of all the pellets in phase, with the aim of obtaining a maximum of radiation in the axis of the antenna.

The reference 10 illustrates the waveguide for energizing each of the lines 20 by a slot coupling (not shown) / coupling pad.

Claims

Flat Antenna (A) comprising:

• a substrate;

At least one sub-network (a1-a8) of radiating elements disposed on the substrate, said sub-network comprising:

a sub-network supply line (20) comprising a coupling pad (30),

- and a plurality of radiating elements (60) connected to the line;

A ground plane (50) on which the substrate is superposed, in which a slot (40) is formed opposite the coupling pad (30) of the supply line (20) of each sub-network

An energy transmission line (10) arranged with respect to the ground plane (50) so as to effect an electromagnetic coupling by slot between said power transmission line and the coupling pad of each of the supply lines sub-network, the antenna being characterized in that the coupling pad (30) is ellipsoidal in shape.

2. Antenna flat according to the preceding claim, characterized in that the pellet is circular.

3. Flat antenna according to one of the preceding claims, characterized in that the slot is rectangular and in that its perimeter is a wavelength in the middle of the substrate.

4. Antenna flat according to the preceding claim, characterized in that the width of the slot is less than half the thickness of the substrate.

A flat antenna according to claim 2, wherein the slot is rectangular, characterized in that the diameter of the wafer is chosen so that the wafer covers the slot about 2/3 of the length of the slot.

Flat antenna according to one of the preceding claims for radio-relay systems in the band 37.21 GHz to 38.64 GHz.

7. Flat antenna according to one of the preceding claims, characterized in that the radiating elements connected to the supply line are spaced a half wavelength in the middle of the substrate.

8. Antenna according to the preceding claim, characterized in that the radiating elements are connected successively to one side and then to the other of the supply line.

9. Antenna according to the preceding claim, characterized in that the supply line has two arms (B1, B2) on either side of the coupling pad (30) and in that the radiating elements are connected to the supply line on each arm in the inverted position of one arm relative to the other.

10. Supply line (20) of a subarray (a1 -a8) of radiating elements (60) of a flat antenna (A), having a coupling pad (30) for collecting the energy radiated by a power transmission line (10) through a slot (30), characterized in that the coupling pad is of ellipsoidal shape.