GB2414862A - Dielectric antenna with increasing cross-section - Google Patents

Abstract

A solid dielectric resonator antenna comprises a block of solid dielectric material 14, 40, mounted on a generally planar substrate 12, 42. The solid dielectric material has a dielectric constant in the range from 10-90. The cross-sectional area of the block of solid dielectric material in a plane parallel to the plane of the substrate increases, either linearly or in a stepwise manner, with increasing distance from the substrate. The block of solid dielectric material 14, 40 may be a single body or it may be made up differently-sized individual blocks or discs. The antenna may form part of an array of similar antennae (fig. 5).

Description

ANTENNA STRUCTURE

This invention relates to an antenna structure, and in particular to a dielectric resonator antenna structure.

Dielectric resonator antennas are becoming more widely used. However, they can have the disadvantage that they have a relatively narrow operating bandwidth.

The present invention relates to a dielectric resonator antenna structure, which has a useful operating bandwidth.

Further, the antenna has a relatively high gain. This means that, when such antennas are combined to form an array, a smaller number of elements are required to achieve a desired performance, so that the array occupies a relatively small area in a device of which it forms a part.

Dielectric horn antennas are known, which have a supply point for feeding an input electrical signal at one end thereof, and which taper outwardly towards an opposite end, such that radio frequency signals are emitted from that opposite end. In order to allow the emission of the radio frequency signals, the dielectric material preferably has a relative dielectric constant Er no greater than 2.

According to a first aspect of the present invention, there is provided a solid dielectric antenna, comprising a block of solid dielectric material, mounted on a generally planar substrate, wherein a cross-sectional area of the block of solid dielectric material, in a plane parallel to the plane of the substrate, increases with increasing distance from the substrate, and wherein the solid dielectric material has a dielectric constant in the range from lo - 90.

This has the advantage that the antenna has a useful gain, and a useful operating bandwidth.

According to a second aspect of the invention, there is provided a solid dielectric antenna array, comprising a plurality of such solid dielectric antenna elements.

This has the advantage that, because of the relatively high gain of each individual element, fewer elements are required to achieve a given performance, and so the overall size of the array is reduced.

According to a third aspect of the invention, there is provided method of operation of a solid dielectric antenna, comprising a block of solid dielectric material, mounted on a generally planar substrate, wherein a cross-sectional area of the block of solid dielectric material, in a plane parallel to the plane of the substrate, increases with increasing distance from the substrate, and wherein the solid dielectric material has a dielectric constant in the range from 10 - 90, the method comprising operating the antenna in a HEMll(x+) resonant mode, where x 0.

For a better understanding of the present invention, reference will now be made to the accompanying drawings, in which: Figures 1 and 2 are schematic representations of a first antenna in accordance with the present invention.

Figures 3 and 4 are schematic representations of a second antenna in accordance with the present invention.

Figure 5 shows an antenna array in accordance with an aspect of the invention.

Figure 1 shows a side view of a first solid dielectric antenna element 10 in accordance with the invention, and Figure 2 is an end view of the same antenna element from the direction A in Figure 1.

Mounted on a substrate 12 is a block of dielectric material 14. The block 14 has a height h, a width w, and a length which varies with the height above the surface of the substrate 12, from a length ll at the surface to a greater length 12 at the upper end of the block 14.

As an example, the height h may be 14mm, the width w may be 5mm, and the lengths It and 12 may be 9mm and 14mm respectively.

In this illustrated embodiment, although the length of the block varies with the height above the surface of the substrate 12, the width remains constant. In other embodiments, the width also increases with increasing height above the surface of the substrate 12. In still further embodiments, the width increases with increasing height above the surface of the substrate 12 while the height remains constant. Generally, the cross-sectional area, in a plane parallel to the surface of the substrate, increases generally linearly with increasing height above the surface of the substrate.

A metallic feed line 16 runs underneath the block 14, buried for most of its length below an upper surface layer 18 of the substrate, so that the feed line 16 contacts the block 14 only at a feed point 20, which is located approximately centrally in both the width and the length of the lower surface of the block 14.

An input electrical signal, supplied along the metallic feed line 16, can then be fed into the block 14 at the feed point 20.

It will be appreciated by the person skilled in the art that the input signal can be coupled to the resonator in other ways, without altering the operation of the invention.

If the frequency of the input electrical signal corresponds to a resonant frequency of the dielectric material of the block 14, a resonant mode can be set up.

For example, with the feed point 20 located approximately centrally in both the width and the length of the lower surface of the block 14, the HEMll(x+) resonant mode may be excited, with the value of x depending on the height h of the block 14. Thus, for some values of h, x may equal 0. For larger values of h, x may equal 1, 2 or even more.

For values of x > 0, the antenna 10 can be termed a vertical solid dielectric antenna element, since the height of the block 14 becomes a relevant factor. Typically, vertical solid dielectric antenna elements have a relatively narrow bandwidth.

However, it has been found that the flared structure of the dielectric resonator increases the usable bandwidth.

It should also be noted that, unlike in the case of a dielectric horn antenna, which looks superficially similar to the antenna of Figures 1 and 2, it is desirable that the fields within the dielectric material should be reflected at the upper surface of the dielectric material 14, in order to support the required resonant mode. The dielectric material therefore has a relative dielectric constant r greater than 5, and preferably greater than 10, and also preferably less than 90. For good efficiency, the relative dielectric constant fir is in the range from 10- 36, more preferably in the range from 15-25, and more preferably is approximately 20.

In the case of a dielectric horn antenna, the dielectric material preferably has a relative dielectric constant Or no greater than 2.

Figure 3 shows a side view of a second solid dielectric antenna element 40 in accordance with the invention, and Figure 4 is an end view of the same antenna from the direction B in Figure 3.

Mounted on a substrate 42 is a composite block of dielectric material 44. The composite block 44 is made up of a lower block 46, a middle block 48, and an upper block 50. Each of the blocks 46, 48, 50 making up the composite block 44 has a width w, and the composite block 44 has a height h. In this illustrated example, the composite block 44 is made up of three blocks, whose individual heights are equal. However, any convenient number of blocks may be used to make up the composite block 44, and their heights can vary if required.

The lengths of the three blocks vary. That is, the lower block 46 has a length ll, the middle block 48 has a length 12, and the upper block 50 has a length 13. The result is that the length of the composite block 44 varies with increasing height above the surface of the substrate 42.

In this illustrated embodiment, although the length of the block varies with the height above the surface of the substrate 42, the width remains constant. In other embodiments, the width also increases with increasing height above the surface of the substrate 42. In still further embodiments, the width increases with increasing height above the surface of the substrate 42 while the height remains constant. Generally, the cross-sectional area, in a plane parallel to the surface of the substrate, increases in a stepwise manner with increasing height above the surface of the substrate.

A metallic feed line 52 runs underneath the block 44, buried for most of its length below an upper surface layer 54 of the substrate, so that the feed line 52 contacts the block 44 only at a feed point 56, which is located approximately centrally in both the width and the length of the lower surface of the block 44.

An input electrical signal, supplied along the metallic feed line 52, can then be fed into the block 44 at the feed point 56.

It will be appreciated by the person skilled in the art that the input signal can be coupled to the resonator in other ways, without altering the operation of the invention.

If the frequency of the input electrical signal corresponds to a resonant frequency of the dielectric material of the composite block 44, a resonant mode can be set up.

For example, with the feed point 56 located approximately centrally in both the width and the length of the lower surface of the block 44, the HEMll(x+) resonant mode may be excited, with the value of x depending on the height h of the block 44. Thus, for some values of h, x may equal 0. For larger values of h, x may equal l, 2 or even more.

For values of x > 0, the antenna 40 can be termed a vertical solid dielectric antenna element, since the height of the block 44 becomes a relevant factor. Typically, vertical solid dielectric antenna elements have a relatively narrow radiation and impedance bandwidth.

However, it has been found that the flared structure of the dielectric resonator increases the usable radiation bandwidth.

It should also be noted that, unlike in the case of a dielectric horn antenna, it is desirable that the fields within the dielectric material should be reflected at the upper surface of the composite block 44, in order to support the required resonant mode. The dielectric material therefore has a relative dielectric constant Er greater than 5, and preferably greater than lO, and also preferably less than 90. For good efficiency, the relative dielectric constant Er is in the range from 1036, more preferably in the range from 15-25, and more preferably is approximately 20. In the case of a dielectric horn antenna, the dielectric material preferably has a relative dielectric constant Cr no greater than 2.

While Figures l and 2 show a device in which the length of the dielectric material increases continuously with increasing height, and Figures 3 and 4 show a device in which the dielectric material is formed by stacking cuboid shaped pieces of dielectric material above one another, any form of increase in length and/or width can be used. For example, one block of dielectric material may be formed in a stepped shape. When the base of the dielectric material is circular rather than rectangular, the required increase in size with increasing height can be achieved by forming the dielectric material in a frustoconical shape, or by stacking discs of dielectric material above one another, in order to form a stepped approximation to a frustocone.

It should be noted that, although Figures 1 and 2, and Figures 3 and 4, show antenna elements, in which the HEMll(x+) resonant mode may be excited, in particular for x > 0, other modes can also be excited, and suitable feed points can be selected as will be apparent to the person skilled in the art, so that the input signal couples to the electrical field as required. Moreover, the input can alternatively be designed to couple to the magnetic field if required, as will again be apparent to the person skilled in the art.

Figure 5 shows an antenna array 60 in accordance with the invention. In this example, the array 60 includes two antenna elements 62, 64, each of which may be as shown in, and described with reference to, Figures 1 and 2. The antenna elements are therefore identical in this case, although they can differ in their dimensions and/or dielectric constants in order to achieve the desired overall properties. In addition, the antenna elements 62, 64 are each surrounded by metal walls 66, 68, 70, 72, 74, or by diffraction gratings. The walls 66, 68, 70, 72, 74 are each approximately one quarter wavelength (14mm, for example) high, and spaced from the respective antenna elements 62, 64 by distances of approximately a half wavelength, at the intended frequency of operation.

The structure of the antenna elements 62, 64, and the presence of the metal walls 66, 68, 70, 72, 74, each acts to increase the gain of the array. The result is that it is possible to produce an array, having the desired performance, with a smaller number of antenna elements.

Although the illustrated array 60 has two such elements, any convenient number may be provided in order to achieve the desired performance.

There are therefore described various antenna structures which can provide a usable bandwidth from an antenna occupying a small area.

Claims (15)

1. A solid dielectric antenna, comprising a block of solid dielectric material, mounted on a generally planar substrate, wherein a crosssectional area of the block of solid dielectric material, in a plane parallel to the plane of the substrate, increases with increasing distance from the substrate, and wherein the solid dielectric material has a dielectric constant in the range from lo - 90.

2. A solid dielectric antenna as claimed in claim l, wherein the crosssectional area of the block of solid dielectric material is generally rectangular, having a first dimension which increases with increasing distance from the substrate and a second dimension which remains generally constant.

3. A solid dielectric antenna as claimed in claim l, wherein the crosssectional area of the block of solid dielectric material is generally rectangular, having first and second dimensions which each increase with increasing distance from the substrate.

4. A solid dielectric antenna as claimed in claim l, 2 or 3, wherein the cross-sectional area of the block of solid dielectric material increases generally linearly with increasing distance from the substrate.

5. A solid dielectric antenna as claimed in claim l, 2 or 3, wherein the cross-sectional area of the block of solid dielectric material increases in a stepwise manner with increasing distance from the substrate.

6. A solid dielectric antenna as claimed in any preceding claim, wherein the solid dielectric material has a dielectric constant in the range from 10 - 36.

7. A solid dielectric antenna as claimed in any preceding claim, wherein the solid dielectric material has a dielectric constant in the range from 15 - 25.

8. A solid dielectric antenna as claimed in any preceding claim, wherein the antenna is operable in the HEMll(x+) resonant mode, where x > 0.

9. A solid dielectric antenna array, comprising a plurality of solid dielectric antenna elements, each as claimed in any of claims 1 to 8.

10. A solid dielectric antenna array as claimed in claim 9, comprising a structure located between adjacent antenna elements of the array.

11. A solid dielectric antenna array as claimed in claim 10, wherein the structure comprises a metal wall.

12. A solid dielectric antenna array as claimed in claim 10, wherein the structure comprises a diffraction grating.

13. A solid dielectric antenna array as claimed in claim 9, comprising metal walls located around the antenna elements of the array and between adjacent antenna elements of the array.

14. A solid dielectric antenna array as claimed in claim 13, wherein the metal walls have heights of the order of one quarter of the operating wavelength of the array.

15. A method of operation of a solid dielectric antenna, comprising a block of solid dielectric material, mounted on a generally planar substrate, wherein a cross-sectional area of the block of solid dielectric material, in a plane parallel to the plane of the substrate, increases with increasing distance from the substrate, and wherein the solid dielectric material has a dielectric constant in the range from 10 - 90, the method comprising operating the antenna in a HEMll(x+) resonant mode, where x > 0.