WO2003019718A1

WO2003019718A1 - Circularly polarized dielectric resonator antenna

Info

Publication number: WO2003019718A1
Application number: PCT/FR2002/002960
Authority: WO
Inventors: Raphaël Gillard; Alexandre Laisne
Original assignee: Centre National De La Recherche Scientifique (Cnrs); Centre National D'etudes Spatiales (Cnes)
Priority date: 2001-08-30
Filing date: 2002-08-29
Publication date: 2003-03-06
Also published as: FR2829300A1; FR2829300B1; EP1421643A1

Abstract

The invention concerns a dielectric resonator antenna comprising a resonator element (30) made of dielectric material (30), a power supply device (40, 60) for the resonator (30), and at least a parasitic element positioned against the surface of or inside the resonator (30), contributing to create dissymmetry of the antenna. The invention is characterised in that the parasitic element(s) extend in a common plane.

Description

POLARIZED DIELECTRIC RESONATOR ANTENNA

CIRCULARLY

The present invention relates to dielectric resonator (DRA) antennas operating in circular polarization.

The dielectric resonator antennas consist of a resonator made of dielectric material (s) transferred onto a flat support and of a supply device (which may include metallic elements) enabling the resonator to be excited. The resonant cavity proper therefore corresponds to a volume of space, which is distinguished from the environment in which it bathes by its characteristics of higher relative electrical permittivity (s), of 6 to 100 in the literature, without it being necessary to delimit it further (by metallic elements in particular). This characteristic of the DRA leads, compared to the printed antennas, to an original mode of operation and to a specific technology of realization. Above all, it gives them particularly interesting performances.

They thus have a high efficiency thanks to the absence of ohmic losses and especially a broadband operation by their volume nature.

In addition, they are interesting in terms of weight, cost and size.

The bandwidth and size of the antennas are directly linked to the choice of geometry and permittivity of the resonator.

These antennas are compatible with all conventional feeding techniques also used for printed antennas

(microstrip line, coplanar line, slit, probe, etc.). In this regard, reference may be made to document [1]. As a result, these antennas have great potential, in particular for their use in fields where the compactness (mobile terminals) and / or bandwidth (high speed communicating systems, radar) are essential issues.

We know that an antenna can radiate a circularly polarized field if the resonator is excited according to two orthogonal modes in phase quadrature and having the same amplitude. Conventionally, a first technique consists in exciting the two modes separately, using two signals of the same amplitude but phase shifted by π / 2, applied at two distinct points.

This first technique has the disadvantage of requiring a double supply, complex to implement and bulky.

A second technique consists in using only one power supply simultaneously exciting the two modes. The phase difference between them is in this case obtained by dissymmetrizing the structure with respect to the excitation point. For an antenna with a dielectric resonator, this operation can, for example, be carried out as proposed in document [2], by machining chamfers on a resonator of square shape, supplied by the perpendicular bisector at one of its sides.

The drawback of this technique is that the machining of the resonator is a delicate and costly operation to implement, and the precision of which conditions the quality of the circular polarization generated.

A third technique consists in placing metal ribbons on the peripheral surface of a cylindrical resonator, these ribbons being arranged so as to form with the feed a given angle, as proposed in documents [3] and [4]. These metallic ribbons create an asymmetry of the resonator which induces the excitation of the resonator according to two modes.

This third technique is particularly well suited in the case of cylindrical resonators but proves to be difficult to implement since the metal strips must be fixed to a curved surface. An object of the invention is to provide a simplified dielectric resonator antenna, which does not have the aforementioned drawbacks and which can operate in circular polarization.

To this end, the invention provides a dielectric resonator antenna comprising a resonator element made of dielectric material and a device for feeding the resonator, and at least one parasitic element positioned against the surface or inside the resonator (this is ie linked at least partially physically with the resonator), helping to create an asymmetry of the antenna, characterized in that the parasitic element (s) extend in the same plane.

Because the parasitic elements of the antenna extend in the same plane, their realization is facilitated. Indeed, these elements can be produced by conventional planar techniques of chemical vapor deposition (CVD) or chemical etching. It should be noted that a slight dissymmetry of the resonator can preexist in the absence of parasitic element without being sufficient to guarantee the excitation of two orthogonal modes with the same amplitude and a phase difference of π / 2.

Since the asymmetry results mainly from the addition of a parasitic element, the dielectric resonator antenna of the present invention does not require cutting or complex or additional machining of the resonator, which makes it possible to use resonators with simple geometry.

According to an implementation of the invention, the asymmetry of the antenna created or reinforced by the parasitic element is sufficient to allow radiation in circular polarization of the antenna.

According to a variant of the invention, one of the parasitic elements is a metallization attached to or inside the resonator and positioned to create a permanent asymmetry of the antenna. Such metallization can advantageously be carried out by conventional etching or screen printing techniques. According to another variant of the invention, the antenna comprises a metallic ground plane on which the resonator is attached and one of the parasitic elements is formed by an opening in the ground plane, this opening creating a permanent asymmetry of the 'antenna. According to yet another variant, the antenna comprises a metallic ground plane on which the resonator is attached and one of the parasitic elements comprises a metallization in contact with a face of the resonator and the antenna comprises a circuit connecting the metallization to a ground plan. In one implementation of the invention, one of the circuits is a short circuit between the metallization and the ground plane.

In another implementation of the invention, one of the circuits comprises a load, the impedance of which is dynamically adjusted by control means. The load can advantageously be controlled dynamically as a function of the resonant modes which it is desired to request. In this way, it is possible to modify the polarization of the radiated field and to provide a dielectric resonator antenna capable of dynamically switching between a linear polarization, a right circular polarization and a left circular polarization.

For example, one of the circuits includes a component capable of connecting the metallization with the ground plane in a controlled manner.

Advantageously, the antenna can comprise several metallizations and several circuits distributed symmetrically on the resonator and able to be controlled symmetrically to generate radiation in rectilinear polarization or asymmetrically to generate radiation in circular polarization.

Other characteristics and advantages will also emerge from the description which follows, which is purely illustrative and not limiting and should be read with reference to the appended figures among which:

FIGS. 1 and 2 are schematic representations of a first variant of a resonator antenna according to the invention, FIGS. 3 to 5 are schematic representations of dielectric resonators comprising a permanent parasitic element,

FIGS. 6 to 8 are schematic representations of a second variant of dielectric resonator antenna according to the invention,

- Figure 9 is a schematic representation of a third variant of dielectric resonator antenna according to the invention.

In Figure 1, there is shown a dielectric resonator antenna according to a first variant of the invention. This antenna comprises a resonator 30 of generally parallelepipedal shape made of dielectric material transferred onto a microstrip line consisting of a metal layer 10 (acting as ground plane), a layer of substrate 20 and a metal strip 40. The resonator 30 comprises on its upper planar face a metal strip 50 positioned along the diagonal of the resonator and constituting a permanent parasitic element. This metal strip is for example formed on the flat face of the resonator by a conventional CVD technique.

FIG. 2 shows a dielectric resonator antenna comprising a resonator 30 of dielectric material on which a metal strip 50 similar to that of FIG. 1 has been formed. In this figure, the resonator is directly transferred to a plane of ground 10 and the resonator supply device comprises a slot 60 made in the ground plane 10.

In FIGS. 1 and 2, the presence of the parasitic element 50 causes an asymmetry of the geometry of the resonator 30 relative to the supply device (that is to say relative to the slot 60 or at the end of the ribbon 40). This asymmetry causes excitation of the resonator according to two orthogonal resonant modes.

The parasitic element 50 and the feed device being independent, the invention is compatible with all the feed devices and techniques known to those skilled in the art such as electromagnetic coupling, dielectric waveguides, probes, etc.

FIGS. 3 to 5 represent examples of forms of resonators which can be used for the production of the antennas of FIGS. 1 and 2.

In FIG. 3, the resonator 30 has the shape of a parallelepiped. A metal strip 50 is positioned on the upper face of the resonator along the diagonal thereof.

In Figure 4, the resonator 30 has a cylindrical shape. A metal strip 50 is positioned on the upper face of the resonator.

In FIG. 5, the resonator 30 comprises a metal strip 50 constituting the parasitic element positioned inside the resonator 30 and along one of its diagonals. Such a configuration can be obtained for example by using LTCC technology (Low Temperature Cofired

Ceramic).

Of course, there are an infinite number of possible embodiments of the resonator 30: parallelepiped, prism, cylinder, hemisphere, ellipsoid, crown, etc. Similarly, the parasitic element (s) can take various forms from the moment when these elements create an asymmetry of the resonator with respect to the supply device.

FIG. 6 shows an antenna with a dielectric resonator according to a second variant of the invention, in which the ground plane 10 consists of a metal layer attached to a substrate 20. This antenna comprises a resonator 30 of general parallelepiped shape resting on the ground plane 10. The supply device comprises a rectangular slot 60 formed in the ground plane 10, positioned at the center of the resonator and the sides of which extend parallel to the sides of the face of the resonator in contact with the ground plane 10. Two square openings 73 and 75 have been formed in the ground plane 10 at two opposite corners of the resonator 30, on a diagonal thereof. The two square openings 73 and 75 constitute parasitic elements positioned against the face of the resonator 30 in contact with the ground plane 10. These openings can advantageously be formed in the ground plane 10 before the resonator 30 is postponed and simultaneously with the production of the feed slot 60, for example using an etching technique of the ground plane 10.

The advantage of this variant is that the formation of the parasitic elements does not require any intervention on the resonator 30 itself. In FIG. 7, the antenna is similar to the antenna in FIG. 6, except that it includes metal studs 53 and 55 arranged in the square openings 73 and 75 of the ground plane 10 and on which the two corners rest. diagonally opposite of the resonator 30.

The pads 53 and 55 can be formed during the step of etching the ground plane. The metal layer forming the ground plane 10 is etched at two zones surrounding two diagonally opposite corners of the resonator 30 so as to form two metal studs isolated from the rest of the ground plane 10.

In the case of the antenna of FIG. 7, the parasitic elements combine metallization and opening to create a permanent dissymmetry of the resonator 30.

In FIG. 8, the antenna is similar to the antenna in FIG. 7, except that it comprises two circuits 83 and 85 connecting the pads 53 and 55 respectively to the ground plane 10. These circuits can be short circuits or circuits made up of passive or active elements.

In the case where the components 83, 85 are active, they can be controlled by external control devices (not shown) capable of modifying their state (or one of their parameter).

In Figure 9, there is shown a dielectric resonator antenna according to a third variant of the invention. In this figure, the supply device has not been shown but it will be considered that the excitation point is located on the perpendicular bisector of one of the sides of the resonator. In this antenna, the ground plane 10 consists of a metal layer attached to a substrate 20. The metal layer forming the ground plane 10 has been etched at the zones 73, 74, 75 and 76 surrounding the corners of the resonator 30 so as to form four metal pads 53, 54, 55 and 56 on which rest the corners of the resonator 30. The metal pads 53, 54, 55 and 56 are connected to the ground plane 10 by means of active or passive components 83, 84, 85 and 86.

In the case where the components 83, 84, 85 and 86 are active, they can be controlled by external control devices (not shown) capable of modifying their state (or one of their parameter). The asymmetry of the structure then lies in the dynamic control of the state of these components.

For example, the components 83, 84, 85 and 86 can be switches produced from PIN diodes or micro-machined MEMS switches (Micro-ElectroMechanical Systems). The switching of the switches is controlled by means of control sources. The metal pads 53, 54, 55, 56 are connected or not to the ground plane 10.

The antenna radiates a circularly polarized field when the switches 83 and 85 located at opposite corners on one diagonal of the resonator 30 are in a passing state while the switches 84 and 86 located on the other diagonal are non-passing. To reverse the direction of polarization of the radiated field, the switches are switched. As a result, the switches 83 and 85 are non-conducting and the switches 84 and 86 are conducting.

The antenna radiates a linearly polarized field when the switches are controlled symmetrically with respect to the supply device. For example, a linear polarization of the radiated field will be obtained if the switches 84 and 85 located at opposite corners on one side of the resonator 30 are conducting while the switches 83 and 86 located on the opposite side are non-conducting. More generally, the components 83, 84, 85, 86 are loads whose impedance is controlled. To “dissymmetry” the structure and obtain a circular polarization in a given direction, a first impedance value for the charges 83 and 85 is ordered, and a second impedance value for the charges 84 and 86.

To pass from a circular polarization in one direction to a circular polarization in the other direction, one can then reverse the value of the impedances in order to reverse the phase delay between the resonant modes.

To obtain linear polarization, it suffices to adjust the impedances of the charges symmetrically with respect to the supply device. We can for example equalize all impedances.

Consequently, the polarization radiated by the antenna is directly controlled by control devices able to modify the state of the charges. As will be understood, the active or passive components 83, 84,

85 and 86, associated with metallizations 53, 54, 55, 56, constitute parasitic elements whose states are controlled independently of the supply of the resonator 30.

By choosing different combinations of parasitic elements, it is possible, for example, to adjust the amplitude of the resonant modes and the phase quadrature between these modes so as to minimize the ellipticity rate of the radiated polarization.

The antennas thus obtained can be networked. This networking makes it possible to obtain good directivity of the signal transmitted and to correct the ellipticity defects of the global field generated.

BIBLIOGRAPHY/

[1] “Recent Advances in Dielectric-Resonator Antenna Technology”, A. Petosa et al., (IEEE Antennas and Propagation Magazine, vol.40, n ° 3, June [2] "Broadband Circulariy Polarized Planar Array Composed of a pair of Dielectric Resonator Antennas", M. Haneishi et al., (Electronics Letters, vol.21, n ° 10, May 9, 1985)

[3] "Circulariy polarized dielectric resonator antenna with a microstrip feed", M.T. Luk and al., (Microw. Conf., 1999 Asia Pacific, Singapore, pp.722-723)

[4] "Use of parasitic strip to produce circular polarization and increased bandwidth for cylindrical DRA", Long et al., (Electronics Letters, vol.37, n ° 7, mars 2001, pp.406-408)

Claims

1. A dielectric resonator antenna comprising a resonator element (30) of dielectric material, a supply device (40, 60) for the resonator (30), and at least one parasitic element positioned against the surface or inside the resonator (30), helping to create an asymmetry of the antenna, characterized in that the parasitic element (s) extend in the same plane.

2. Antenna according to claim 1, characterized in that the asymmetry of the antenna created or reinforced by the parasitic element is sufficient to allow radiation in circular polarization of the antenna.

3. Antenna according to one of the preceding claims, characterized in that one of the parasitic elements is a metallization (50, 51, 52) attached to or inside the resonator (30) and positioned to create a permanent asymmetry of the antenna.

4. Antenna according to claim 3, characterized in that one of the parasitic elements is a metal strip (50) extending over a flat face of the resonator (30).

5. Antenna according to claim 3, characterized in that one of the parasitic elements is a metal strip (50) positioned inside the resonator (30).

6. Antenna according to one of claims 1 or 2, characterized in that it comprises a metallic ground plane (10) on which the resonator (30) is attached and in that one of the parasitic elements is formed by an opening (73, 75) in the ground plane, this opening creating a permanent asymmetry of the antenna.

7. Antenna according to one of claims 1 or 2, characterized in that it comprises a metal ground plane (10) on which the resonator (30) is attached and in that one of the parasitic elements comprises a metallization (53, 54, 55, 56) in contact with one face of the 3/019718

12

resonator (30) and the antenna comprises a circuit connecting the metallization to the ground plane (10).

8. Antenna according to claim 7, characterized in that one of the circuits is a short circuit between the metallization (53, 54, 55, 56) and the ground plane (10).

9. An antenna according to claim 7, characterized in that one of the circuits comprises a load (83, 84, 85, 86), the impedance of which is dynamically adjusted by control means.

10. Antenna according to claim 7, characterized in that it comprises several metallizations (53, 54, 55, 56) and several circuits (83,

84, 85, 86) distributed symmetrically on the resonator (30) and able to be controlled symmetrically to generate radiation in rectilinear polarization or asymmetrically to generate radiation in circular polarization.

11. Antenna network, characterized in that it comprises at least one antenna according to one of the preceding claims.