Dielectric resonator antenna

Details Dielectric resonator antenna Dielectric resonator antenna

1999-12-13

2001-11-27

Weng, Don (Department: 2821)

Communications: radio wave antennas

Antennas

Microstrip

C343S702000, C343S873000

Reexamination Certificate

active

06323808

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a dielectric resonator antenna comprising a cuboid of a dielectric material, in which cuboid an electric field configuration of an eigenmode of the dielectric resonator antenna, which eigenmode is particularly generated by external excitation, has at least two non-parallel planes of symmetry.
The invention further relates to a transmitter, a receiver and a mobile radiotelephone that includes a dielectric resonator antenna comprising a cuboid of a dielectric material, in which cuboid an electric field configuration of an eigenmode of the dielectric resonator antenna, which eigenmode is particularly generated by external excitation, has at least two non-parallel planes of symmetry.
BACKGROUND OF THE INVENTION
Dielectric resonator antennas (DRAs) are known as miniaturized antennas of ceramics or another dielectric medium for microwave frequencies. A dielectric resonator whose dielectric medium, which has a relative permittivity of ∈
r
>>1, is surrounded by air, has a discrete spectrum of eigenfrequencies and eigenmodes due to the electromagnetic limiting conditions on the boundary surfaces of the dielectric medium. These conditions are defined by the special solution of the electromagnetic equations for the dielectric medium with the given limiting conditions on the boundary surfaces. Contrary to a resonator, which has a very high quality when radiation losses are avoided, the radiation of power is the main item in a resonator antenna. Since no conducting structures are used as a radiating element, the skin effect cannot be detrimental. Therefore, such antennas have low-ohmic losses at high frequencies. When materials are used that have a high relative permittivity, a compact, miniaturized structure may be achieved since the dimensions may be reduced for a preselected eigenfrequency (transmission and reception frequency) by increasing ∈
r
. The dimensions of a DRA of a given frequency are substantially inversely proportional to ∈
r
. An increase of ∈
r
by a factor of &agr; thus causes a reduction of all the dimensions by the factor &agr; and thus of the volume by a factor of &agr;
3/2
, while the resonant frequency is kept the same. Furthermore, a material for a DRA is to be suitable for use at high frequencies, have small dielectric losses and temperature stability. This strongly limits the materials that can be used. Suitable materials have ∈
r
values of typically a maximum of 120. Besides this limitation of the possibility of miniaturization, the radiation properties of a DRA degrade with a rising ∈
r
.
Such a DR antenna
1
in the basic form considered by way of example is represented in FIG.
1
. Not only the form of a cuboid, but also other forms are possible such as, for example, cylindrical or spherical geometries. Dielectric resonator antennas are resonant modules that work only in a narrow band around one of their resonant frequencies (eigenfrequencies). The problem of the miniaturization of an antenna is equivalent to the fact of lowering the operating frequency with given antenna dimensions. Therefore, the lowest resonance (TE
z
111
) mode is used. This mode has planes of symmetry in its electromagnetic fields, of which one plane of symmetry of the electric field is referenced plane of symmetry
2
. When the antenna is halved in the plane of symmetry
2
and an electrically conducting surface
3
is deposited (for example, a metal coating), the resonant frequency continues to be equal to the resonant frequency of an antenna with the original dimensions. In this manner, a structure is obtained in which the same mode is formed with the same frequency. This is represented in
FIG. 2. A
further miniaturization can be achieved with this antenna by means of a dielectric medium that has a high relative permittivity ∈
r
. Preferably, a material that has low dielectric losses is selected.
Such a dielectric resonator antenna is described in the article “Dielectric Resonator Antennas—A review and general design relations for resonant frequency and bandwidth”, Rajesh K. Mongia and Prakash Barthia, Intern. Journal of Microwave and Millimeter-Wave Computer-aided Engineering, vol. 4, no. 3, 1994, pp. 230-247. The article gives an overview of the modes and the radiation characteristics for various shapes, such as cylindrical, spherical and rectangular DRAs. For different shapes, the possible modes and planes of symmetry are shown (see
FIGS. 4
,
5
,
6
and p. 240, left column, lines 1-21). Particularly a cuboidal dielectric resonator antenna is described in the FIG.
9
and the associated description. By means of a metal surface in the x-z plane, with y=0, or in the y-z plane, with x=0, the original structure may be halved, without modifying the field configuration or other resonance characteristics for the TE
z
111
-mode (p. 244, right column, lines 1-7). The DRA is excited via a microwave lead in that it is inserted into the stray field in the neighborhood of a microwave line (for example, a microstrip line or the end of a coaxial line).
The possibility of reducing the volume is limited to the use of the two planes of symmetry arranged at right angles to each other as outside surfaces. In this manner, the volume of a DRA may be reduced only by the factor of
4
with the same frequency.
SUMMARY OF THE INVENTION
Therefore, it is an object of the invention to provide a dielectric resonator antenna that offers better possibilities of reducing the volume. Furthermore, it is an object of the invention to provide a transmitter, a receiver and a mobile radiotelephone that has better possibilities of reducing the overall volume and of installing components inside a device.
According to the invention, the object is achieved in that the cuboid edge that runs parallel with an intersecting line of the planes of symmetry forms the shortest edge of the cuboid. The planes of symmetry of the electric field configuration of an eigenmode are at right angles to each other and in parallel with a respective outside surface of the cuboid. Therefore, the intersecting line of the planes of symmetry runs parallel with one of the edges of the cuboid. The length of this edge is referenced d and, in a dielectric resonator antenna according to the invention, is clearly smaller than the length of the two other edges of the cuboid. The edge having the length d is thus perpendicular to the electric field of the eigenmode of the antenna. For making a better and particularly flexible reduction of the antenna volume possible, the length of at least one edge is to be reduced. Surprisingly, the edge having the length d appears to allow a clear shortening without a considerable loss of efficiency of the antenna. Both the radiation power and the accuracy of the resonant frequency are maintained.
In a further embodiment of the invention is provided that there is a first plane of symmetry running parallel with a first outside surface in the geometric center of the cuboid, that a second plane of symmetry is perpendicular to the first plane of symmetry and parallel with a second outside surface in the geometric center of the cuboid, that the first and second planes of symmetry are provided for forming each an outside surface of a dielectric resonator antenna, and that an electrically conducting coating is deposited on the outside surfaces formed by the planes of symmetry. When the lowest eigenmode is used as a resonant frequency, the planes of symmetry are found at each respective half edge length in the center of the cuboid. Even with a miniaturization of the antenna, provided that the planes of symmetry with an electrically conducting coating form the outside surfaces, the length d of the edge running parallel with the intersecting line may be highly advantageously reduced so as to reduce the antenna volume. The selection according to the invention of the edge of the cuboid provides that the size of the electrically conducting and coated outside surfaces is reduced, whereas the size of the outside surfaces of the an

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