CA2082580C - An improved microstrip antenna device, in particular for telephone transmissions by satellite field of the invention - Google Patents
An improved microstrip antenna device, in particular for telephone transmissions by satellite field of the invention Download PDFInfo
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- CA2082580C CA2082580C CA002082580A CA2082580A CA2082580C CA 2082580 C CA2082580 C CA 2082580C CA 002082580 A CA002082580 A CA 002082580A CA 2082580 A CA2082580 A CA 2082580A CA 2082580 C CA2082580 C CA 2082580C
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- patch
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- dielectric layer
- ground plane
- layer means
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q21/00—Antenna arrays or systems
- H01Q21/06—Arrays of individually energised antenna units similarly polarised and spaced apart
- H01Q21/061—Two dimensional planar arrays
- H01Q21/065—Patch antenna array
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q1/00—Details of, or arrangements associated with, antennas
- H01Q1/36—Structural form of radiating elements, e.g. cone, spiral, umbrella; Particular materials used therewith
- H01Q1/38—Structural form of radiating elements, e.g. cone, spiral, umbrella; Particular materials used therewith formed by a conductive layer on an insulating support
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q9/00—Electrically-short antennas having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
- H01Q9/04—Resonant antennas
- H01Q9/0407—Substantially flat resonant element parallel to ground plane, e.g. patch antenna
- H01Q9/0414—Substantially flat resonant element parallel to ground plane, e.g. patch antenna in a stacked or folded configuration
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q9/00—Electrically-short antennas having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
- H01Q9/04—Resonant antennas
- H01Q9/0407—Substantially flat resonant element parallel to ground plane, e.g. patch antenna
- H01Q9/0428—Substantially flat resonant element parallel to ground plane, e.g. patch antenna radiating a circular polarised wave
- H01Q9/0435—Substantially flat resonant element parallel to ground plane, e.g. patch antenna radiating a circular polarised wave using two feed points
Abstract
An improved microstrip antenna device, in particular for telephone transmissions by satellite.
An antenna comprises a first dielectric layer including on one side a ground plane and on the other a first conductive patch of a chosen shape, a second dielectric layer surmounts the first dielectric layer on the side adjacent to the first patch and supports, on the other side remote from the first patch, a second conductive patch of a chosen shape. A third dielectric layer surmounts the second. The second patch is of a size smaller than that of the first patch and this first patch is fed from below at at least one chosen point situated between its centre and its circumference. advantageously, the first patch is connected to a lead-in of the ground plane joining a feeding circuit implanted in a dielectric substrate of a three-plate structure.
An antenna comprises a first dielectric layer including on one side a ground plane and on the other a first conductive patch of a chosen shape, a second dielectric layer surmounts the first dielectric layer on the side adjacent to the first patch and supports, on the other side remote from the first patch, a second conductive patch of a chosen shape. A third dielectric layer surmounts the second. The second patch is of a size smaller than that of the first patch and this first patch is fed from below at at least one chosen point situated between its centre and its circumference. advantageously, the first patch is connected to a lead-in of the ground plane joining a feeding circuit implanted in a dielectric substrate of a three-plate structure.
Description
TITLE OF THE INVENTION
AN IMPROVED MICROSTRIP ANTENNA DEVICE IN PARTICULAR
FOR TELEPHONE TRANSMISSIONS BY SATELLITE
FIELD OF THE INVENTION
The invention concerns microstrip antenna devices.
PRIOR d~IRT
Many antenna structures have already been described in this field: The simplest microstrip radiating structure includes a dielectric layer carrying on one side a conductive patch of a chosen shape and on the other side, a conductive plane called a ground plane.
To obtain an antenna, it is necessary to define the mode of feeding this structure with ultra-high frequency energy.
The idea of providing a stack of superposed patches has already been described in LONG & WALTON's article " A dual frequency stacked circular disc antenna", IEEE Transa~tions on Antennas and Propagation, Vol. AF 27, No. 2, March 1979. Other proposals have since been formulated.
As regards the feeding of superposed two-patch antennas, two vexy different cases have to be distinguished from the point of view of operation, according to whether the feeding is effected at the upper patch or the lower patch (the one nearer the ground plane).
AN IMPROVED MICROSTRIP ANTENNA DEVICE IN PARTICULAR
FOR TELEPHONE TRANSMISSIONS BY SATELLITE
FIELD OF THE INVENTION
The invention concerns microstrip antenna devices.
PRIOR d~IRT
Many antenna structures have already been described in this field: The simplest microstrip radiating structure includes a dielectric layer carrying on one side a conductive patch of a chosen shape and on the other side, a conductive plane called a ground plane.
To obtain an antenna, it is necessary to define the mode of feeding this structure with ultra-high frequency energy.
The idea of providing a stack of superposed patches has already been described in LONG & WALTON's article " A dual frequency stacked circular disc antenna", IEEE Transa~tions on Antennas and Propagation, Vol. AF 27, No. 2, March 1979. Other proposals have since been formulated.
As regards the feeding of superposed two-patch antennas, two vexy different cases have to be distinguished from the point of view of operation, according to whether the feeding is effected at the upper patch or the lower patch (the one nearer the ground plane).
In the case where the feeding is obtained at the lower patch, this is most frequently a connection at the circumference of this patch. Moreover, provision is systematically made for an upper patch of a larger size than that of 'the lower patch (see in particular the article of TULINTSEFF, ALT & KONG, "input impedance of a probe-fed stacked circular microstrip antenna'°) IEEE
Transactions on Antennas and Propagation, Vo1.39 No. 3, March 1991).
The expert will know that the perfection of sugerpased patch antennas is particularly intricate.
Attempts have been made to model their properties. By way of example, we will mention COCK & CBRISTODOULOU°s "Design of a two-layer, capacitively coupled, microstrip patch antenna element for broad band applications°°, IEEE
Symposium on antenna propagation, 1957. In spite of these attempts, it is still extremely difficult to predict by modelling, and to understand the behaviour of microstrip structures comprising two or more superposed patches.
The Applicants have set themselves the problem of obtaining a conformable antenna with electronic scanning, intended for the communication system with movable objects such as aircraft (the system called sATCOM).
This system is provided for operating with the group of geostationary satellites managed by the INMARSAT
organisation. At least as far as the applications to _ g -aircraft are concerned, the proposed telecommunications service is governed by an international standard called ARINC 741.
Technically, one is concerned with setting up an antenna capable of operating, on the one hand, in the transmitting mode and, on the other hand, in the receiving mode, in two very close bands, that is to say, one a little higher than 1>5 gigahertz for receiving and another a little higher than 1.6 gigahertz for transmitting.
The electronic scanning function is necessary for this antenna because of the movement of the movable carrier which is here assumed to be an aircraft. It is also necessary to choose between a roof antenna or 'two lateral antennas. In the case of two lateral antennas, the above mentioned ARINC Standard has defined two official acceptable shapes defining the volume into which the planned antenna has to be fitted.
The antenna must alsa be conformable, that is to say, be capable of adapting to the exact wall-shape of the movable carrier. It must, moreover, be thin so as to minimize the aerodynamic drag and of course, be designed so as to comply with the required mechanical character-istics required for the structure of the aircraft.
During the research they have undertaken, the Applicants have found that it was possible to design a microstrip antenna going virtually against the solutions accepted so far by the experts.
~~~~~~v OBJECT O~' THE INVENTION
It is therefore an abject of the present invention to provide an antenna element that is fundamentally different from those known so far.
It is a further object of the invention to provide an antenna element of the type comprising a first dielectric layer including on one side a ground plane and on the other a first conductive patch of a chosen shape, a second dielectric layer which surmounts the first layer on the side of the first patch and which supports on the other side opposite the first patch a second condLlctive patch of a chosen shape, a third dielectric layer surmounting the second, and also means for feeding ultra-high frequencies to one of the conductive patches.
SUMMARY OF THE INVENTION
According to the invention, the second patch is of a smaller size than that of the first patch and the electrical connection to this first patch is from below at at least one chosen point situated between its centre and its circumference.
With this structure, it has proved possible to construct an operational antenna, subject to choosing the position of the connection point in question according to the respective sizes of the first and second patches, and according to the dielectric characteristics of the first and second dielectric layers, as will as those of the third dielectric layer which preferably has dielectric _ constants that are distinctly higher than those of the two others.
The first patch may be connected to a lead-in through the ground plane joining a feeding circuit 5 implanted in a dielectric substrate of a three-plate-type structure. More particularly, the three-plate structure includes a substrate layer implanted between the above mentioned ground plane and a bottom ground plane: between the two ground planes, provision is made for conductive lead-ins defining a peripheral shield for the feeder part of the antenna element. Preferably, provision is made for a Wilkinson divider capable of feeding the lower patch .at two points which, together with its centre, form a substantially right-angled isosceles triangle, while the respective signals brought to these two points are in quadrature. The Wilkinson divider is implanted at an intermediate level of the substrate layer in accordance with the three-plate structure. This intex°mediate level serves in practice as the feeding distribution level between a central connector for the antenna as a whole and the various antenna elements which, in the application as an antenna array will constitute the antenna as a whole.
In an advantageous embodiment, the two patches have a generally circular shape and these two patches are substantially coaxial, that is to say, they are situated on the same perpendicular to the planes of the dielectric layers.
BRIEF DESCRIPTION OF TIME DRAWINGS
Other objects and advantages of the invewtion will become apparent on examining the detailed description given below and the attached drawings wherein Figure 2 is a general schematic diagram of an antenna element in an exploded perspective;
Figure 2 is a broken partly seci~ioned view of an antenna elemewt;
Figure 3 is a (superposed) detailed part view of the connection of the lower patch to its feeding means by a Wilkinson divider;
Figure 4 is a view from below of the twenty four Wilkinson dividers, for a 24 element antenna, interconnected to the central connector;
Figure 5 is a top view of twenty four lower patches corresponding precisely to Figure 4; and Figure 6 is a diagram showing the reflection coefficient of the antenna in relation to the frequency.
The expert will know that shape is important in microstrip devices. Moreover, the drawings are in essence of a definitive nature. They may therefore be incorporated in the description not only to render the latter more readily understood but also to cowtribute to the definition of the invention if required.
In Figures 1 and 2, the reference PMO designates a bottom ground plane wJhich may be fitted by means of an insulating adhesive, on a sheet to be incorporated in the _~_ wall of the aircraft. This bottom ground plane is surmounted by two dielectric layers SDB and SDH (low and high respectively). The layer SDH is in turn surmounted by another ground plane PM1. The whole forms a three-s plate structure with appropriate metallisations engraved between the layers SDB and SDH or more precisely, on one of these layers.
Fundamentally, these metallisations include a feeder line L which is subsequently subdivided in the manner of a Wilkinson divider, which is schematically outlined in Figure 1 but is more clearly seen in Figures 3 and 4. This divider comprises two branches DLl and DL2 which first diverge, to rejoin each other in a region where they are connected to a resistor RLL implanted in the thickness of the layer SDB, but without rejoining the bottom ground plane PMO. Subsequently, the two branches DL1 and DL2 again diverge, to rejoin the respective connection points ELl and EL2.
These points EL1 and EL2 are connected via lead-ins TRI and TR2 (not connected to the ground plane PM1) to connection points FR1 and FR2 provided on the lower patch or control patch, P1 engraved.on the top face of a dielectric layer D1 placed above the ground plane PMI.
As may be seen in Figures 3 and 4, the end portions of the engravings DL1 and DL2 have different lengths, so that electromagnetically, the signals available at the level of points FR1 are substantially in 2 ~8~~~~
_8_ quadrature with each other. The connection points FR1 and FR2 of the patch P1 are situated on respective radii which are substantially at right angles to each other.
The distances D1 and D2 of these points from the centre of the patch P1 are in principle equal. The choice of these distances wall be reverted to below. But it is possible to indicate forthwith that these distances D1 and D2 are in principle comprised between 50% and 100% of the radius of the patch P1 (designated DP1/2 in Figure 3).
Above the patch P1, a second dielectric layer D2 is provided having the same dielectric constant as the layer D1 but having a greater thickness, as may be seen in Figure 2. Tn the upper portion, the layer D2 receives by engraving a second conductive patch P2 (a coupled patch) which is generally circular and coaxial with the patch P1, but has a shorter diameter than that of the patch P1.
The antenna element is completed by an additional dielectric layer DR forming a radome and having in principle a dielectric constant that is distinctly higher than that of the layers D1 and D2.
In Figures 2 and 4, it will moreover be seen that the line L continues as far as a passage via a metallised hole to a generally coaxial-type ultra-high frequency connector CCH situated behind the metallic sheet subjacent to the bottom ground plane PMO.
Moreover, comparing Figures 2 and 4, it will be seen that this connector is provided for each contact stud _ g with a horseshoe-shaped peripheral shield passing through the whole of the dielectric layer SDB. This shield could be defined by a continuous conductive layer. The Applicant has found that it was sufficient to make provision for a certain number of traversing studs surrounding the location of the lead-in CCH, with an interspacing between these studs which remains sufficiently Shorter than the wave length of the ultra-high frequency signals processed.
Similarly, the peripheral studs such as BP11, BP12 and BP13 define a shield for the feeding of the antenna element in question, relative to the neighbouring antenna elements and with respect to the outside.
It will, however, be noted that above the ground plane P~I1, no provision is made for any insulation of the antenna element relative to its neighbouring elements.
Figure 5 shows how 24 antenna elements may be disposed to form a conformable antenna with electronic scanning, satisfying the conditions of the problem posed.
As has already been indicated, these antenna elements are connected to a general connector with (at least) 24 pins.
Up the line from this connector, provision is made for an individual reciprocal phase shift treatment far each antenna element by means of phase shifters UPH
schematically outlined in Figure 2.
The main parameters affecting such an antenna are:
the height and the dielectric constant of the three layers DR, D2 and D1;
the diameters of the patches P1 and P2 and the radii d = dl = d2 of the two feeding points of the bottom patch P1.
The problem posed in the particular intended application is to obtain a dual behaviour from the unitary antenna element (Figure 6) namely:-a) a dual frequency behaviour including a very good adaptation (better than - 20 decibels) on two frequencies F1 and F2p b) a broad band characteristic ensuring at least an adaptation of - 10 decibels between 'the frequencies fr and F4 containing the frequency interval of F1 and F2.
The applicant has observed that provided the frequencies Fl and F2 are not too remote from each other and, seeing that the parameters of the heights and dielectric constants of the above mentioned three layers are fixed, there exists in practice only one solution in terms of the radii of the two patches and of the feeding radius of the patch P1 which would make it possible to satisfy the conditions set out above.
Any modification of one of the parameters has the effect that it becomes very difficult to rediscover a situation capable of satisfying the conditions.
Although the phenomena in question have not yet been completely understood, it seems that in the general case, everything is taking place as though only one of the two patches P1 and P2 resonates at the operating frequency. On the other hand, there exists a very small domain in the parameters for the definition of the antenna, wherein the two patches are interacting while showing a typical dual frequency behaviour as desired.
It is still necessary to search for the optimum point of this dual frequency behaviour to respond to the desired operating conditions for the antenna, such as those set out above.
In particular, it has been shown that in practice it is very difficult to cause the antenna element to function without adding thereto a top radome layer DR.
mhe Applicant has thus been able to obtain antennas responding to the following parameters:
thickness of the layer DR : 1.5 to 2.5 mm;
relative dielectric constant of the layer DR :
from 4 to 5;
thickness of the layer D2 : approximately 4.8 mm;
thickness of the layer D1 : approximately 1.6 mm;
relative dielectric constants of the layers D1 and D2 as well as SDB and SDH: approximately 2;
diameter of the patch Pl: approximately 70 mm:
diameter of the patch P2 : approximately 60 mms radius of the feeding points FR1 and FR2 : fram 0.5 to 0.7 times the radius of the patch P1.
Such antennas can satisfy the st-ipulated conditions for the SATCO~ operating band, that is to say:
a reflection coefficient better than - 20 dB at the central receiving frequency (1.545 GHz):
a reflection coefficient better than - 20 dB at the central transmitting frequency (1.645 GIiz)r a band pass characteristic at a level better than -10 dB between 1.53 and 1.66 GFIz.
There will now be discussed the setting up of an array of antenna elements such as illustrated in Figures 4 and 5.
First of all, it has been indicated above that each bottom patch is fed at two points situated on respective radii which are substantially perpendicular to each other.
It has appeared worthwhile to distribute the two connection points in a suitable way and this in a different manner for the 24 antenna elements illustrated.
The Applicants have found that this makes it possible to reduce the ellipticity (elliptical eccentricity) of the antenna, taking into account that it operates in the circular polarisation mode and with electronic scanning.
For this purpose, it is possible either to distribute the connection points substantially at random or to search experimentally for an optimum configuration from the point of view of this ellipticity (for example, as in Figure 5).
The thus obtained antenna array 'with electronic scanning has proved capable of operating with loss of aim (scatter) angles of up to 60°, with sufficiently low secondary lobe levels, and with a gain of at least 12 decibels as compared with an isotropic antenna.
A good compromise between the loss of gain and the secondary lobe level has been obtained by applying a slightly amplitude-weighted law of illumination. This may be a Taylor law of the circular 20 decibel type, these indications being comprehensible to the expert.
The phase shifters associated with each of the antenna elements may be integrated in the beam steering unit (or BSU) accommodated inside the aircraft.
Advantageously, line phase shifters are used that are switched by PTN diodes controlled by four bit binary words, whereby a resolution of 22.5° is obtained.
The distributor integrated in the phase shifter block ensures the amplitude weighting according to the above mentioned law.
Tn the particular intended application, the antenna must operate simultaneously in the transmitting and receiving modes at relatively close frec~aencies. As regards the calibration of the electronic scanning phase shifters, it is necessary to place the array in phase or to "phase" it over a band of approximately 8~.
Rather than calculate the phase code at the central frequency of the band, the Applicants have found that it was preferable to take into account the use of the two distinct frequencies, as well as the quantification and the nature of the phase shifters (swit.ched lines).
For this purpose, they use the calibration procedure described below.
Let an element Ai be taken of a conformable, hence non-planar, antenna, with caordinates (at the centre) Xi, Yi, Zi. When it is desired to displace the main beam into the direction U, V at the frequency f, it is necessary to apply to this antenna element Ai a theoretical phase shift DPi which is a function (known to the expert) of f, U and V:-DPi (f, U, V) In practice, a calibration table Tc (n, F) is used, where n is an integer (or another discrete variable) representing the required state of the phase shifter, with 0 < n <_ N, while one also limits oneself to discrete values for the frequency F. This is written as:
DQi (F, n) In the intended example, 101 frequency points are taken in the 1.53 - 1.66 GHz band: and N = 15, with n defined in 4 bits. This method only "phases" the array correctly for a single frequency. Now the antenna essentially has a dual frequency behaviour.
c~,~~~5~~~
15 _ The Applicant has then established a °'distance"
between the theoretical phase and the tabulated phase for the two frequencies f1 and f2, in particular in the form of ;
DDi - I DcZi (x°i, n) - DPi ( fi, U, v) I
+ ( DQi (F2,n) - DPi ( f2, U, v) ( where I designates the absolute value (modules).
The calibration then lies in looking in respect of each aiming direction and each antenna element a priori for the value n which minimises this function DDi.
The actuation of the phase shifters is effected accordingly. This calibration can, of course, be stored.
The present invention is not necessarily limited to the embodiment described, nor to the application intended. The antenna element may itself be used for other applications provided the new structure is retained.
The combination of a microstrip element and a three-plate feeding arrangement in the same dielectric stack also merits consideration.
The polarisation may be other than the circular polarisation of the embodiment described.
Another particular feature of the invention is that it can avoid, as far as the layers D1 and D2 are concerned, recourse to dielectrics with a low constant, or porous dielectrics or even those constituted by a gas.
Transactions on Antennas and Propagation, Vo1.39 No. 3, March 1991).
The expert will know that the perfection of sugerpased patch antennas is particularly intricate.
Attempts have been made to model their properties. By way of example, we will mention COCK & CBRISTODOULOU°s "Design of a two-layer, capacitively coupled, microstrip patch antenna element for broad band applications°°, IEEE
Symposium on antenna propagation, 1957. In spite of these attempts, it is still extremely difficult to predict by modelling, and to understand the behaviour of microstrip structures comprising two or more superposed patches.
The Applicants have set themselves the problem of obtaining a conformable antenna with electronic scanning, intended for the communication system with movable objects such as aircraft (the system called sATCOM).
This system is provided for operating with the group of geostationary satellites managed by the INMARSAT
organisation. At least as far as the applications to _ g -aircraft are concerned, the proposed telecommunications service is governed by an international standard called ARINC 741.
Technically, one is concerned with setting up an antenna capable of operating, on the one hand, in the transmitting mode and, on the other hand, in the receiving mode, in two very close bands, that is to say, one a little higher than 1>5 gigahertz for receiving and another a little higher than 1.6 gigahertz for transmitting.
The electronic scanning function is necessary for this antenna because of the movement of the movable carrier which is here assumed to be an aircraft. It is also necessary to choose between a roof antenna or 'two lateral antennas. In the case of two lateral antennas, the above mentioned ARINC Standard has defined two official acceptable shapes defining the volume into which the planned antenna has to be fitted.
The antenna must alsa be conformable, that is to say, be capable of adapting to the exact wall-shape of the movable carrier. It must, moreover, be thin so as to minimize the aerodynamic drag and of course, be designed so as to comply with the required mechanical character-istics required for the structure of the aircraft.
During the research they have undertaken, the Applicants have found that it was possible to design a microstrip antenna going virtually against the solutions accepted so far by the experts.
~~~~~~v OBJECT O~' THE INVENTION
It is therefore an abject of the present invention to provide an antenna element that is fundamentally different from those known so far.
It is a further object of the invention to provide an antenna element of the type comprising a first dielectric layer including on one side a ground plane and on the other a first conductive patch of a chosen shape, a second dielectric layer which surmounts the first layer on the side of the first patch and which supports on the other side opposite the first patch a second condLlctive patch of a chosen shape, a third dielectric layer surmounting the second, and also means for feeding ultra-high frequencies to one of the conductive patches.
SUMMARY OF THE INVENTION
According to the invention, the second patch is of a smaller size than that of the first patch and the electrical connection to this first patch is from below at at least one chosen point situated between its centre and its circumference.
With this structure, it has proved possible to construct an operational antenna, subject to choosing the position of the connection point in question according to the respective sizes of the first and second patches, and according to the dielectric characteristics of the first and second dielectric layers, as will as those of the third dielectric layer which preferably has dielectric _ constants that are distinctly higher than those of the two others.
The first patch may be connected to a lead-in through the ground plane joining a feeding circuit 5 implanted in a dielectric substrate of a three-plate-type structure. More particularly, the three-plate structure includes a substrate layer implanted between the above mentioned ground plane and a bottom ground plane: between the two ground planes, provision is made for conductive lead-ins defining a peripheral shield for the feeder part of the antenna element. Preferably, provision is made for a Wilkinson divider capable of feeding the lower patch .at two points which, together with its centre, form a substantially right-angled isosceles triangle, while the respective signals brought to these two points are in quadrature. The Wilkinson divider is implanted at an intermediate level of the substrate layer in accordance with the three-plate structure. This intex°mediate level serves in practice as the feeding distribution level between a central connector for the antenna as a whole and the various antenna elements which, in the application as an antenna array will constitute the antenna as a whole.
In an advantageous embodiment, the two patches have a generally circular shape and these two patches are substantially coaxial, that is to say, they are situated on the same perpendicular to the planes of the dielectric layers.
BRIEF DESCRIPTION OF TIME DRAWINGS
Other objects and advantages of the invewtion will become apparent on examining the detailed description given below and the attached drawings wherein Figure 2 is a general schematic diagram of an antenna element in an exploded perspective;
Figure 2 is a broken partly seci~ioned view of an antenna elemewt;
Figure 3 is a (superposed) detailed part view of the connection of the lower patch to its feeding means by a Wilkinson divider;
Figure 4 is a view from below of the twenty four Wilkinson dividers, for a 24 element antenna, interconnected to the central connector;
Figure 5 is a top view of twenty four lower patches corresponding precisely to Figure 4; and Figure 6 is a diagram showing the reflection coefficient of the antenna in relation to the frequency.
The expert will know that shape is important in microstrip devices. Moreover, the drawings are in essence of a definitive nature. They may therefore be incorporated in the description not only to render the latter more readily understood but also to cowtribute to the definition of the invention if required.
In Figures 1 and 2, the reference PMO designates a bottom ground plane wJhich may be fitted by means of an insulating adhesive, on a sheet to be incorporated in the _~_ wall of the aircraft. This bottom ground plane is surmounted by two dielectric layers SDB and SDH (low and high respectively). The layer SDH is in turn surmounted by another ground plane PM1. The whole forms a three-s plate structure with appropriate metallisations engraved between the layers SDB and SDH or more precisely, on one of these layers.
Fundamentally, these metallisations include a feeder line L which is subsequently subdivided in the manner of a Wilkinson divider, which is schematically outlined in Figure 1 but is more clearly seen in Figures 3 and 4. This divider comprises two branches DLl and DL2 which first diverge, to rejoin each other in a region where they are connected to a resistor RLL implanted in the thickness of the layer SDB, but without rejoining the bottom ground plane PMO. Subsequently, the two branches DL1 and DL2 again diverge, to rejoin the respective connection points ELl and EL2.
These points EL1 and EL2 are connected via lead-ins TRI and TR2 (not connected to the ground plane PM1) to connection points FR1 and FR2 provided on the lower patch or control patch, P1 engraved.on the top face of a dielectric layer D1 placed above the ground plane PMI.
As may be seen in Figures 3 and 4, the end portions of the engravings DL1 and DL2 have different lengths, so that electromagnetically, the signals available at the level of points FR1 are substantially in 2 ~8~~~~
_8_ quadrature with each other. The connection points FR1 and FR2 of the patch P1 are situated on respective radii which are substantially at right angles to each other.
The distances D1 and D2 of these points from the centre of the patch P1 are in principle equal. The choice of these distances wall be reverted to below. But it is possible to indicate forthwith that these distances D1 and D2 are in principle comprised between 50% and 100% of the radius of the patch P1 (designated DP1/2 in Figure 3).
Above the patch P1, a second dielectric layer D2 is provided having the same dielectric constant as the layer D1 but having a greater thickness, as may be seen in Figure 2. Tn the upper portion, the layer D2 receives by engraving a second conductive patch P2 (a coupled patch) which is generally circular and coaxial with the patch P1, but has a shorter diameter than that of the patch P1.
The antenna element is completed by an additional dielectric layer DR forming a radome and having in principle a dielectric constant that is distinctly higher than that of the layers D1 and D2.
In Figures 2 and 4, it will moreover be seen that the line L continues as far as a passage via a metallised hole to a generally coaxial-type ultra-high frequency connector CCH situated behind the metallic sheet subjacent to the bottom ground plane PMO.
Moreover, comparing Figures 2 and 4, it will be seen that this connector is provided for each contact stud _ g with a horseshoe-shaped peripheral shield passing through the whole of the dielectric layer SDB. This shield could be defined by a continuous conductive layer. The Applicant has found that it was sufficient to make provision for a certain number of traversing studs surrounding the location of the lead-in CCH, with an interspacing between these studs which remains sufficiently Shorter than the wave length of the ultra-high frequency signals processed.
Similarly, the peripheral studs such as BP11, BP12 and BP13 define a shield for the feeding of the antenna element in question, relative to the neighbouring antenna elements and with respect to the outside.
It will, however, be noted that above the ground plane P~I1, no provision is made for any insulation of the antenna element relative to its neighbouring elements.
Figure 5 shows how 24 antenna elements may be disposed to form a conformable antenna with electronic scanning, satisfying the conditions of the problem posed.
As has already been indicated, these antenna elements are connected to a general connector with (at least) 24 pins.
Up the line from this connector, provision is made for an individual reciprocal phase shift treatment far each antenna element by means of phase shifters UPH
schematically outlined in Figure 2.
The main parameters affecting such an antenna are:
the height and the dielectric constant of the three layers DR, D2 and D1;
the diameters of the patches P1 and P2 and the radii d = dl = d2 of the two feeding points of the bottom patch P1.
The problem posed in the particular intended application is to obtain a dual behaviour from the unitary antenna element (Figure 6) namely:-a) a dual frequency behaviour including a very good adaptation (better than - 20 decibels) on two frequencies F1 and F2p b) a broad band characteristic ensuring at least an adaptation of - 10 decibels between 'the frequencies fr and F4 containing the frequency interval of F1 and F2.
The applicant has observed that provided the frequencies Fl and F2 are not too remote from each other and, seeing that the parameters of the heights and dielectric constants of the above mentioned three layers are fixed, there exists in practice only one solution in terms of the radii of the two patches and of the feeding radius of the patch P1 which would make it possible to satisfy the conditions set out above.
Any modification of one of the parameters has the effect that it becomes very difficult to rediscover a situation capable of satisfying the conditions.
Although the phenomena in question have not yet been completely understood, it seems that in the general case, everything is taking place as though only one of the two patches P1 and P2 resonates at the operating frequency. On the other hand, there exists a very small domain in the parameters for the definition of the antenna, wherein the two patches are interacting while showing a typical dual frequency behaviour as desired.
It is still necessary to search for the optimum point of this dual frequency behaviour to respond to the desired operating conditions for the antenna, such as those set out above.
In particular, it has been shown that in practice it is very difficult to cause the antenna element to function without adding thereto a top radome layer DR.
mhe Applicant has thus been able to obtain antennas responding to the following parameters:
thickness of the layer DR : 1.5 to 2.5 mm;
relative dielectric constant of the layer DR :
from 4 to 5;
thickness of the layer D2 : approximately 4.8 mm;
thickness of the layer D1 : approximately 1.6 mm;
relative dielectric constants of the layers D1 and D2 as well as SDB and SDH: approximately 2;
diameter of the patch Pl: approximately 70 mm:
diameter of the patch P2 : approximately 60 mms radius of the feeding points FR1 and FR2 : fram 0.5 to 0.7 times the radius of the patch P1.
Such antennas can satisfy the st-ipulated conditions for the SATCO~ operating band, that is to say:
a reflection coefficient better than - 20 dB at the central receiving frequency (1.545 GHz):
a reflection coefficient better than - 20 dB at the central transmitting frequency (1.645 GIiz)r a band pass characteristic at a level better than -10 dB between 1.53 and 1.66 GFIz.
There will now be discussed the setting up of an array of antenna elements such as illustrated in Figures 4 and 5.
First of all, it has been indicated above that each bottom patch is fed at two points situated on respective radii which are substantially perpendicular to each other.
It has appeared worthwhile to distribute the two connection points in a suitable way and this in a different manner for the 24 antenna elements illustrated.
The Applicants have found that this makes it possible to reduce the ellipticity (elliptical eccentricity) of the antenna, taking into account that it operates in the circular polarisation mode and with electronic scanning.
For this purpose, it is possible either to distribute the connection points substantially at random or to search experimentally for an optimum configuration from the point of view of this ellipticity (for example, as in Figure 5).
The thus obtained antenna array 'with electronic scanning has proved capable of operating with loss of aim (scatter) angles of up to 60°, with sufficiently low secondary lobe levels, and with a gain of at least 12 decibels as compared with an isotropic antenna.
A good compromise between the loss of gain and the secondary lobe level has been obtained by applying a slightly amplitude-weighted law of illumination. This may be a Taylor law of the circular 20 decibel type, these indications being comprehensible to the expert.
The phase shifters associated with each of the antenna elements may be integrated in the beam steering unit (or BSU) accommodated inside the aircraft.
Advantageously, line phase shifters are used that are switched by PTN diodes controlled by four bit binary words, whereby a resolution of 22.5° is obtained.
The distributor integrated in the phase shifter block ensures the amplitude weighting according to the above mentioned law.
Tn the particular intended application, the antenna must operate simultaneously in the transmitting and receiving modes at relatively close frec~aencies. As regards the calibration of the electronic scanning phase shifters, it is necessary to place the array in phase or to "phase" it over a band of approximately 8~.
Rather than calculate the phase code at the central frequency of the band, the Applicants have found that it was preferable to take into account the use of the two distinct frequencies, as well as the quantification and the nature of the phase shifters (swit.ched lines).
For this purpose, they use the calibration procedure described below.
Let an element Ai be taken of a conformable, hence non-planar, antenna, with caordinates (at the centre) Xi, Yi, Zi. When it is desired to displace the main beam into the direction U, V at the frequency f, it is necessary to apply to this antenna element Ai a theoretical phase shift DPi which is a function (known to the expert) of f, U and V:-DPi (f, U, V) In practice, a calibration table Tc (n, F) is used, where n is an integer (or another discrete variable) representing the required state of the phase shifter, with 0 < n <_ N, while one also limits oneself to discrete values for the frequency F. This is written as:
DQi (F, n) In the intended example, 101 frequency points are taken in the 1.53 - 1.66 GHz band: and N = 15, with n defined in 4 bits. This method only "phases" the array correctly for a single frequency. Now the antenna essentially has a dual frequency behaviour.
c~,~~~5~~~
15 _ The Applicant has then established a °'distance"
between the theoretical phase and the tabulated phase for the two frequencies f1 and f2, in particular in the form of ;
DDi - I DcZi (x°i, n) - DPi ( fi, U, v) I
+ ( DQi (F2,n) - DPi ( f2, U, v) ( where I designates the absolute value (modules).
The calibration then lies in looking in respect of each aiming direction and each antenna element a priori for the value n which minimises this function DDi.
The actuation of the phase shifters is effected accordingly. This calibration can, of course, be stored.
The present invention is not necessarily limited to the embodiment described, nor to the application intended. The antenna element may itself be used for other applications provided the new structure is retained.
The combination of a microstrip element and a three-plate feeding arrangement in the same dielectric stack also merits consideration.
The polarisation may be other than the circular polarisation of the embodiment described.
Another particular feature of the invention is that it can avoid, as far as the layers D1 and D2 are concerned, recourse to dielectrics with a low constant, or porous dielectrics or even those constituted by a gas.
Claims (12)
1. In an antenna device of the type comprising:-first dielectric layer means having first and second opposing sides;
a ground plane on said first side;
a first conductive patch of a chosen shape on said second side of said first dielectric means, said first conductive patch having a first side contiguous to said first dielectric layer means and a second side contiguous to said second conductive patch;
second dielectric layer means having first and second sides and which surmount said first dielectric layer means with said second thereof adjacent said first side of the second dielectric layer means;
a second conductive patch of a chosen shape on said second side;
third dielectric layer means surmounting the second, dielectric layer means; and connector means fox connecting ultra-high frequencies to one of said conductive patches, the improvement wherein:
(a) said second patch is of a sire smaller than that of the first patch, and (b) said first patch is connected to said connection means on said first side thereof at at least one chosen point situated between the centre and the circumference of said first patch.
a ground plane on said first side;
a first conductive patch of a chosen shape on said second side of said first dielectric means, said first conductive patch having a first side contiguous to said first dielectric layer means and a second side contiguous to said second conductive patch;
second dielectric layer means having first and second sides and which surmount said first dielectric layer means with said second thereof adjacent said first side of the second dielectric layer means;
a second conductive patch of a chosen shape on said second side;
third dielectric layer means surmounting the second, dielectric layer means; and connector means fox connecting ultra-high frequencies to one of said conductive patches, the improvement wherein:
(a) said second patch is of a sire smaller than that of the first patch, and (b) said first patch is connected to said connection means on said first side thereof at at least one chosen point situated between the centre and the circumference of said first patch.
2. A device according to claim 1, including a feeding circuit implanted in a dielectric substrate of a threeÀ
plate substrate structure, and wherein said ground plane has a lead-in connected to said first patch and said feeding circuit.
plate substrate structure, and wherein said ground plane has a lead-in connected to said first patch and said feeding circuit.
3. A device according to claim 2, wherein said first and second patches are of a generally circular shape.
4. A device according to claim 3, wherein said first and second patches are substantially coaxial.
5. A device according to any one of claims 2 to 4, wherein the dielectric materials of said first and second dielectric layer means and of the said dielectric substrate have a dielectric constant of the order of 2, and wherein the ratio of the thicknesses of the second and first dielectric layer means is of the order of 3.
6. A device according to claim 5, wherein the dielectric material of said third dielectric layer means has a dielectric constant of the order of 4.
7. A device according to any one of claims 2 to 4, further including a bottom ground plane below said dielectric substrate, and wherein said three-plate substrate structure includes a substrate layer which is implanted between the first-mentioned ground plane and said bottom ground plane and which has conductive lead-ins defining a peripheral shield and a Wilkinson divider implanted at an intermediate level of the substrate layer and capable of feeding said first patch at two points foaming with said centre of said first patch a substantially right-angled isosceles triangle.
8. A device according to claim 7, wherein the dielectric material of the substrate layer has substantially the same dielectric constant as those of the first and second dielectric layer means.
9. A device according to any one of claims l to 3, wherein it includes an array of said first and second patches respectively implanted in the same one of said first and second dielectric layer means.
10. A device according to claim 9, wherein it is associated with controllable phase shifters imparting thereto an electronic scanning function.
11. A device according to claim 10, further including a bottom ground plane below said dielectric substrate;
wherein said three-plate substrate structure includes a substrate layer which is implanted between the first-mentioned ground plane and said bottom ground plane and which has conductive lead-ins defining a peripheral shield and a Wilkinson divider implanted at an intermediate level of the substrate layer and capable of feeding said first patch at two points forming with said centre of said first patch a substantially right-angled isosceles triangle; and wherein the pairs of the connection points of said first patches are distributed to improve the ellipticity rate of the antenna at pronounced loss of aim angles.
wherein said three-plate substrate structure includes a substrate layer which is implanted between the first-mentioned ground plane and said bottom ground plane and which has conductive lead-ins defining a peripheral shield and a Wilkinson divider implanted at an intermediate level of the substrate layer and capable of feeding said first patch at two points forming with said centre of said first patch a substantially right-angled isosceles triangle; and wherein the pairs of the connection points of said first patches are distributed to improve the ellipticity rate of the antenna at pronounced loss of aim angles.
12. A device according to claim l0, wherein said controllable phase shifters are calibrated on the basis of a function of the distance between the theoretical and real values far both of the respective ones of the two central frequencies of the antenna.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR9113984 | 1991-11-14 | ||
| FR9113984A FR2683952A1 (en) | 1991-11-14 | 1991-11-14 | IMPROVED MICRO-TAPE ANTENNA DEVICE, PARTICULARLY FOR TELEPHONE TRANSMISSIONS BY SATELLITE. |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2082580A1 CA2082580A1 (en) | 1993-05-15 |
| CA2082580C true CA2082580C (en) | 2002-04-02 |
Family
ID=9418885
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002082580A Expired - Fee Related CA2082580C (en) | 1991-11-14 | 1992-11-10 | An improved microstrip antenna device, in particular for telephone transmissions by satellite field of the invention |
Country Status (12)
| Country | Link |
|---|---|
| US (1) | US5995047A (en) |
| EP (1) | EP0542595B1 (en) |
| JP (1) | JP2868197B2 (en) |
| AT (1) | ATE187280T1 (en) |
| CA (1) | CA2082580C (en) |
| DE (1) | DE69230365T2 (en) |
| DK (1) | DK0542595T3 (en) |
| ES (1) | ES2140405T3 (en) |
| FR (1) | FR2683952A1 (en) |
| GR (1) | GR3032025T3 (en) |
| PT (1) | PT542595E (en) |
| RU (1) | RU2117366C1 (en) |
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-
1991
- 1991-11-14 FR FR9113984A patent/FR2683952A1/en active Granted
-
1992
- 1992-10-27 EP EP92402921A patent/EP0542595B1/en not_active Expired - Lifetime
- 1992-10-27 PT PT92402921T patent/PT542595E/en unknown
- 1992-10-27 DK DK92402921T patent/DK0542595T3/en active
- 1992-10-27 DE DE69230365T patent/DE69230365T2/en not_active Expired - Fee Related
- 1992-10-27 ES ES92402921T patent/ES2140405T3/en not_active Expired - Lifetime
- 1992-10-27 AT AT92402921T patent/ATE187280T1/en not_active IP Right Cessation
- 1992-11-09 JP JP4322304A patent/JP2868197B2/en not_active Expired - Fee Related
- 1992-11-10 CA CA002082580A patent/CA2082580C/en not_active Expired - Fee Related
- 1992-11-13 RU RU92004412/09A patent/RU2117366C1/en not_active IP Right Cessation
-
1997
- 1997-02-24 US US08/804,881 patent/US5995047A/en not_active Expired - Fee Related
-
1999
- 1999-12-02 GR GR990402964T patent/GR3032025T3/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| FR2683952A1 (en) | 1993-05-21 |
| PT542595E (en) | 2000-04-28 |
| US5995047A (en) | 1999-11-30 |
| JPH0629724A (en) | 1994-02-04 |
| EP0542595A1 (en) | 1993-05-19 |
| CA2082580A1 (en) | 1993-05-15 |
| ATE187280T1 (en) | 1999-12-15 |
| DE69230365D1 (en) | 2000-01-05 |
| DK0542595T3 (en) | 2000-03-27 |
| JP2868197B2 (en) | 1999-03-10 |
| EP0542595B1 (en) | 1999-12-01 |
| GR3032025T3 (en) | 2000-03-31 |
| FR2683952B1 (en) | 1994-04-22 |
| ES2140405T3 (en) | 2000-03-01 |
| RU2117366C1 (en) | 1998-08-10 |
| DE69230365T2 (en) | 2000-03-23 |
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