GB2369497A

GB2369497A - Multiband vehicular telephone antenna

Info

Publication number: GB2369497A
Application number: GB0028968A
Authority: GB
Inventors: Ryuichi Taira; Lazoros Economou; Richard Langley
Original assignee: Harada Industry Co Ltd
Current assignee: Harada Industry Co Ltd
Priority date: 2000-11-28
Filing date: 2000-11-28
Publication date: 2002-05-29
Anticipated expiration: 2020-11-28
Also published as: GB0028968D0; GB2369497B; AU2002223907A1; JP2004515184A; WO2002045211A1

Abstract

A multiband vehicular telephone antenna includes a ground plane 22, a patch radiator 20 parallel to it, and electrical short 26. The patch 20 has a feed point for applying a signal to, or receiving a signal from, the antenna. Patch 20 also has apertures, through each of which passes a respective elongate conductor 28 that is connected to the ground plane. The presence of the elongate conductors produces a second resonant frequency band in the antenna. Further resonant frequency bands can be added to the antenna by adding further elongate conductors of corresponding lengths.

Description

MULTIBAND VEHICULAR TELEPHONE ANTENNA

The invention relates to a multiband antenna, and more particularly to a multiband antenna for use with a vehicular telephone system.

Vehicular-mounted telephone antennas have been researched and developed since the late 1950's. The most common type of such antenna is the rod antenna, which in most cases is a simple monopole variant such as the 1/4wavelength whip, the 1/2-wavelength whip, or the 5/8-wavelength whip. Other types, such as helical antennas and trunk (boot) -lid aerials, are also common. All such car antennas must meet certain radiation characteristics, the most important of which are omnidirectional azimuth coverage, high efficiency and high bandwidth. Such antennas are very sensitive to external conditions, such as human body proximity and weather conditions, and are dependent on the mounting area, i. e. whether the antenna is in-car or on the car roof. Wire antennas also generally require an impedance transformer to match the antenna to the feed line, adding size, cost and complexity.

Ch. Delaveaud et al. , in an article entitled"Small- sized low-profile antenna to replace monopole antennas", Electronics Letters, Vol, 34, No. 8 (16 April 1998), discloses a monopolar wire-patch antenna which addresses the aforementioned problems; its working characteristics, such as input impedance, reflection coefficient and radiation pattern, are compared with those of a conventional quarterwavelength monopole. The authors were concerned with portable telephone applications, and thus made a comparison between the conventional antenna and the wire-patch antenna when both were mounted on top of a metallic box simulating the shielding metallic case of a telephone handset.

Figures l (a) and l (b) illustrate, respectively, the conventional quarter-wavelength monopole antenna and the monopolar wire-patch antenna described in the article by Ch.

Delaveaud et al. The wire-patch antenna of Figure l (b) includes a metallic box 10 simulating the shielding metallic case of a telephone handset, a patch member 12, a coaxial feed probe 14 at the centre of the patch member, and a ground wire 16 extending from box 10 to patch member 12; the ground wire 16 is situated near feed probe 14 and is offcentre of the patch member 12. It was found that this positioning of ground wire 16 relative to feed probe 14 produced a low-frequency parallel resonance in the vicinity of which a 50-ohm impedance matching was easily achieved without requiring the addition of an external electrical circuit. The resulting antenna operated near 1.8 GHz.

It would be an advantage to have an antenna which not only had a reduced height similar to the antenna described above, but which was capable of providing more than one resonant frequency.

It has been found that it is possible to create one or more additional resonant frequency bands on a wire-patch antenna by extending ground pin means from the ground member to pass through corresponding aperture means in the patch member.

In one aspect, the invention is a multiband antenna that includes: a ground member; a patch member that extends generally in parallel spaced-apart relationship with the ground member ; and means electrically shorting the patch member to the ground member. The patch member has at least one aperture through which passes a respective elongate conductor connected to the ground member, and also has a feed point for applying a signal to, or receiving a signal from, the antenna. The dimensions of the patch member and the at least one conductor, and the relative disposition of the shorting means, the at least one conductor, and the feed point are such that the antenna exhibits at least first and second resonances, the first resonance being in a first frequency band and the second resonance being in a second frequency band.

The shorting means preferably comprises a pair of shorting conductors each being on a first line extending through the feed point and on a respective opposite side of the feed point.

The patch member may have one aperture, through which passes a single elongate conductor. Alternatively, the patch member may have two apertures, through each of which passes a respective elongate conductor, the two apertures being on respective opposite sides of the feed point and on a second line that intersects the first line at a first angle at the feed point.

The two elongate conductors may be of approximately equal length, in which case the antenna generally exhibits two resonant frequency bands. Those two bands may be at approximately 900MHz and 1800MHz. Alternatively, the two elongate conductors may differ substantially in length, in which case the antenna generally exhibits three resonant frequency bands.

The distance between the shorting pins is preferably three times the distance between the ground pins, and the first angle may be approximately 900.

The patch member may have an additional aperture, through which passes a respective additional elongate conductor, the additional aperture being on a third line that intersects the first line at a second angle at the feed point. Alternatively, the patch member may have two additional apertures, through each of which passes a respective additional elongate conductor, the additional apertures being on respective opposite sides of the feed point and on a third line that intersects the first line at a second angle at the feed point. In such arrangement, the first angle is preferably approximately 900 and the second angle is approximately 450. Alternatively, the first angle may be approximately 600 and the second angle may be approximately 1200.

The patch member may have further additional apertures,

through each of which passes a respective further additional elongate conductor, the further additional apertures each being on a respective further additional line intersecting the first line at the feed point and extending at a respective further angle to the first line. The further additional apertures may be on N further additional lines extending at N further angles to the second line.

The multiband antenna may also comprise a metal wire or strip extending from an edge of the ground member to an edge of the patch member. The wire or strip preferably has a

width in the range of 5mm to 20mm, and more preferably is approximately 10mm wide. The wire or strip may be made of copper.

A solid dielectric material may extend in the space between the ground member and the patch member.

The multiband antenna may further comprise a coaxial connector fitted to the ground member, for receiving a signal feed line connected to the patch member.

Preferred features of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figures l (a) and l (b) are perspective views of a prior art quarter-wavelength monpole antenna and a prior art monopolar wire-patch antenna, respectively; Figure 2 is a perspective view of a first preferred embodiment of the wire-patch antenna of this invention; Figure 3 is a plan view of a first preferred embodiment of the wire-patch antenna of this invention; Figure 4 is a side view of the first preferred embodiment of the wire-patch antenna of this invention; Figure 5 is a graph illustrating variation in measured Sll return loss with frequency for the wire-patch antenna of the first embodiment of this invention, the resonant frequency being adjusted by varying the common height above the patch member of the two ground pins; Figures 6 (a) and 6 (b) are graphs similar to Figure 5,

but in which the two ground pins have different heights from each other above the patch member, resulting in three resonant frequencies being produced; Figure 7 is a plan view of a second preferred embodiment of the wire-patch antenna of this invention; Figures 8 to 11 are graphs illustrating variation in measured S11 return loss with frequency for the wire-patch antenna of the second embodiment of this invention, the resonant frequencies being adjusted by varying the height above the patch member of the four ground pins; Figure 12 is a perspective view of a third preferred embodiment of the wire-patch antenna of this invention, the embodiment differing from the first and second embodiments by the addition of a metal strip running from the top of the patch member to the ground member; Figure 13 is a graph illustrating variation in measured Sll return loss with frequency for the wire-patch antenna of the third embodiment of this invention, and in particular illustrating an increase in the S11 return loss that results from addition of the metal strip; Figure 14 illustrates the distribution pattern of surface current for the GSM-900 Band in the first embodiment of the invention; Figure 15 illustrates the distribution pattern of surface current for the DCS-1800 Band in the first embodiment of the invention; Figure 16 illustrates the polar azimuth radiation pattern for the GSM-900 Band in the first embodiment of the invention; and, Figure 17 illustrates the polar azimuth radiation pattern for the DCS-1800 Band in the first embodiment of the invention.

The first preferred embodiment of the wire-patch antenna of the invention is illustrated in Figures 2 to 4. A patch member 20 consists of a 56mm-square patch element built on a 1.6mm-thick FR4 dielectric layer. A ground mem

ber 22 is maintained at a distance of about 19mm in parallel spaced-apart relationship to the patch member 20 by suitable support between those members (for instance, insulated supporting members at the corners, or use of an intervening dielectric material in the separation space). The patch member 20 is coaxially fed at a central position (the feed point) via a feed line 24 connecting to a coaxial connector (such as an SMA connector) or to a coaxial cable. A pair of shorting pins 26 extend between patch member 20 and ground member 22 to electrically connect those members. Each of the shorting pins 26 is on a respective opposite side of, and 17.5mm from, the feed point. This relative positioning between the feed point and the shorting pins 26 gives rise to the GSM-900 Band excitation.

If the dimensions of the patch member 20 and the ground member 22 change, the resonant frequencies will change; if the dimensions are reduced, the resonant frequencies will increase. For the same dimensions of the patch member 20 and the ground member 22, the resonant frequencies will be increased if the patch member and the ground member are enclosed in dielectric material; put another way, for a given operating frequency, the size of the device can be reduced if it is enclosed in a dielectric material.

The antenna also has a pair of ground pins 28 each of which is secured to ground member 22 to extend unsupported in a direction generally normal to the plane of the ground member 22. Each ground pin 28 passes centrally through a respective clearance hole 30 in the patch member 20, and may extend for a short distance above the opposite side of the patch member 20 (as will be further discussed). Clearance holes 30 are sized to ensure that the pins do not touch the patch member, and are 6mm-square holes in this embodiment. In the claims, the words"passes through the aperture"are intended to cover both the situation where a ground pin extends a short distance above the opposite side of the patch member and the situation where the ground pin terminates in

the plane of the patch member. The ground pins 28 are on a line extending through the feed point. Each ground pin 28, and thus the approximate centre of each clearance hole 30, is 5.5mm from the feed point. The pair of ground pins 28, as well as the pair of shorting pins 26, have a diameter of 1.2mm ; however, the diametric size is not a crucial factor and may be made either larger or smaller. The ground pins 28 give rise to the DCS-1800 Band excitation.

The invention will operate if only a single ground pin 28 is used; however, the use of two ground pins 28 of equal length results in a better bandwidth. The use of more than two grounds pins 28, in an in-line arrangement, has not been found to result in any further improvement in bandwidth.

The DCS-1800 Band can be fine-tuned by adjusting the length of the ground pins 28 shown in Figures 2 to 4. In general a longer ground pin 28 will result in a lower resonant frequency. The measured Sll return loss (in dB) for different lengths of the ground pins 28 is plotted against frequency in Figure 5. The GSM-900 Band remains unaffected from any change in the length of the ground pins 28; thus, the GSM-900 Band and the DCS-1800 Band are independently tunable. In Figure 5, the"pin height (H)"values represent the length of each ground pin 28 above patch member 20. In the first embodiment shown in Figures 2 to 4, the pair of ground pins 28 have equal length. Thus, in Figure 5, each variation in Sll return loss with pin length shows as a single vertical dip, i. e. one DCS-1800 Band resonant frequency is created.

If the ground pins 28 are not of equal length, the graph of Sll return loss for the antenna shows a vertical dip at three frequency bands. This is illustrated in Figures 6 (a) and 6 (b). It can be seen that with two ground pins 28 extending above the patch member 20 by, for example, 7mm and 13mm, three resonance frequency bands occur at 1. lGHz, 1.6GHz and 2.1 GHz. If the ground pin 28 extending 13mm above patch member 20 is replaced by one only extending

to the height of the respective aperture in patch member 20, the 1. 6GHz and 2. 1GHz resonant frequency bands are replaced by bands at 1.85GHz and 2.3GHz, respectively. And if the ground pin 28 extending 7mm above patch member 20 is then also replaced by one extending only to the height of the respective aperture in patch member 20, the resonant frequency bands at 1.85GHz and 2.3 GHz are replaced by a single band at 2. 1GHz.

As shown in Figure 7, a second preferred embodiment of the wire-patch antenna of the invention has an additional pair of ground pins 32 extending through a respective additional pair of apertures 34. The ground pins 32 lie on a line passing through the feed point and oriented at 450 to both the line through shorting pins 26 and the line through ground pins 28.

Figures 8 to 11 are four graphs illustrating variation of resonant frequency bands with individual variation of the height of the four ground pins 28,32 above the patch member 20. In Figures 8 to 11, the grounds pins 28 are designated as PIN 2 and PIN 3, and the additional ground pins 32 are designated as PIN 1 and PIN 4. The majority of the measured Sll return loss measurements were taken with the ground pins 28 (PIN 2 and PIN 3) extending 7mm above patch member 20, while the height of the ground pins 32 above patch member 20 were individually varied.

Considering Figure 8, little difference is noted between the first two curves (PIN 2 and PIN 3 fixed at 7mm) as PIN 4 is reduced from 14.5mm to 13mm and PIN 1 is reduced from 16.5mm to 10mm. Three resonant frequency bands are present (at approximately 1,1. 5 and 2 GHz). In the third curve, i. e. when the height of PIN 1 is further reduced to 4.5mm and thus differs substantially from PIN 4, the 2 GHz resonant frequency band becomes more pronounced.

Two of the curves in Figure 9 correspond to two curves in Figure 8. The third curve (PIN 1 = 4.5mm, PIN 2 & PIN 3 = 7mm, PIN 4 = 9. 0mm) differs from the third curve in Figure

8 only in that PIN 4 has been reduced from 13. 0mm to 9. 0mm. However, that is sufficient to have produced a pronounced rightward, i. e. to higher frequency, shift of all three resonant frequency bands.

In Figure 10, PIN 4 is reduced further from 9. 0mm to 4.5mm, resulting in the three resonant frequency bands shifting up toward the right, i. e. to higher frequency, to approximately 1,1. 6 and 2.1 GHz. PIN 1 & PIN 4 are then both reduced to O. Omm height above patch member 20, causing the two higher resonant frequency bands to move higher to 1.65 and 2.25 GHz. When PIN 2 and PIN 3 are also reduced to O. Omm height above patch member 20, i. e. all four pins are at the same height, the two higher resonant frequency bands move still higher to 1.9 and 2.4 GHz.

Figure 11 illustrates the resonant frequency bands that are created by two other sets of pin lengths. Four resonant frequency bands appear when PIN 1 = 4.5mm, PIN 2 & PIN 3 =

7. 0mm, and PIN 4 = O. Omm. But if PIN 1 is reduced to O. Omm, only three bands appear.

Instead of the 900 and 450 angles shown in Figure 7 for the lines through ground pins 28 and additional ground pins 32, respectively, relative to the line through shorting pins 26, the lines may be set at other angles, such as 1200 and 600, or 450 and 45 , respectively. However, if the angles between the three lines are reduced too much, there is no possibility of creating any additional resonant frequencies.

It is possible to add only one additional ground pin 32 instead of two. If its height differs substantially from that of the two ground pins 28, an additional resonant frequency will appear--although its bandwidth will not be as pronounced as if two additional ground pins 32 of similar height are added.

Similarly, it is possible to add even further ground pins, either singly or in pairs, on lines extending at angles to the lines through ground pins 28 and 32--and thereby to create further additional resonant frequency

bands. For instance, ground pins may be placed on lines at angles of 450, 900 and 1350 relative to the line through shorting pins 26.

In some embodiments it may be advantageous to provide one or more additional apertures in the patch member which do not have conductors extending through them, in order to modify the frequency response pattern or spatial response pattern of the antenna. The size and position of such apertures can be determined experimentally from case to case.

It has been found that the GSM-900 Band matching can be improved by adding a metal wire or strip 40 to extend from the top of the patch member 20 to the ground member 22, as

shown in Figure 12. A 10mm-wide metal strip 40 was used, but a width in the range of 5mm to 20mm should produce a similar result. The strip was made of copper, but any other conductive metal could be used. A comparison of the graphs of Figures 5 and 13 illustrates how, for a pin height (H) of 6mm, adding the copper strip 40 increases the Sll return loss (dB) for the GSM-900 Band. For instance, at a Sll return loss of-10 dB, the bandwidth is approximately 160 MHz without copper strip 40, but is approximately 180 MHz with copper strip 40.

In Figure 13, the maximum Sll return losses for the GSM-900 and DCS-1800 Bands, respectively, are-26dB at 925 MHz and-27dB at 1.785GHz. The respective surface current distributions for both bands are shown in Figures 14 and 15, and this illustrates which elements are contributing to each resonant frequency band. For the GSM-900 Band, the main contributing elements are the patch element 20 and the two shorting pins 26, while for the DCS-1800 Band, resonance is due to the presence of the patch element 20 and the two ground pins 28.

One reason that whip antennas have been widely used is their omnidirectional coverage properties. All currentlyused mobile-related transmissions are vertically polarised, and thus an antenna with good azimuth characteristics is

required. Although offering a cheap and straightforward solution, the traditional approach of using the same rod antenna for both fundamental and harmonic frequencies (in this case, the GSM-900 and DCS-1800 Bands) suffers from radiation nulls. The subject multiband antenna offers an alternative that combines the low-profile characteristics of microstrip patch antennas with the symmetrical azimuth coverage of whip/rod antennas. Figures 16 and 17 show the respective measured polar azimuth radiation patterns for the GSM-900 and DCS-1800 Bands when the second embodiment of the dual-band antenna is placed on its back and rotated. When two quarter-wavelength monopoles (one a quarter-wavelength long at 900MHz, and the other a quarter-wavelength long at 1.8GHz) were constructed and tested under exactly the same conditions as was the second embodiment of the multiband antenna of this invention, the radiation patterns obtained were virtually identical.

While the present invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than limitation, and that changes may be made to the invention without departing from its scope as defined by the appended claims.

Each feature disclosed in this specification (which term includes the claims) and/or shown in the drawings may be incorporated in the invention independently of other disclosed and/or illustrated features.

The text of the abstract filed herewith is repeated here as part of the specification.

A multiband vehicular telephone antenna includes a ground member, a patch member in a parallel spaced-apart relationship with the ground member, and means electrically shorting the two. The patch member has at least one aperture, and also has a feed point for applying a signal to, or receiving a signal from, the antenna. Through each aperture passes a respective elongate conductor that is connected to the ground member. The presence of one elongate conductor, or more than one if all of the same length, produces a second resonant frequency band in the antenna. Further resonant frequency bands can be added to the antenna by adding, for each further frequency band, at least one elongate conductor of corresponding length.

Claims

What is claimed is:

1. A multiband antenna comprising: a ground member; a patch member extending generally in parallel spacedapart relationship with the ground member, the patch member having at least one aperture through which passes a respective elongate conductor connected to the ground member, the patch member also having a feed point for applying a signal to, or receiving a signal from, the antenna; and means electrically shorting the patch member to the ground member; wherein the dimensions of the patch member and the at least one conductor, and the relative disposition of the shorting means, the at least one conductor, and the feed point are such that the antenna exhibits at least first and second resonances, the first resonance being in a first frequency band and the second resonance being in a second frequency band.

2. A multiband antenna as in claim 1, wherein the shorting means comprises a pair of shorting conductors each being on a first line extending through the feed point and on a respective opposite side of the feed point.

3. A multiband antenna as in claim 2, wherein the patch member has one aperture, through which passes a single elongate conductor.

4. A multiband antenna as in claim 2, wherein the patch member has two apertures, through each of which passes a respective elongate conductor, the two apertures being on respective opposite sides of the feed point and on a second line that intersects the first line at a first angle at the feed point.

5. A multiband antenna as in claim 4, wherein the two elongate conductors are of approximately equal length, and the antenna generally exhibits two resonant frequency bands.

6. A multiband antenna as in claim 5, wherein the two resonant frequency bands are at approximately 900MHz and 1800MHz.

7. A multiband antenna as in claim 4, wherein the two elongate conductors differ substantially in length, and the antenna generally exhibits three resonant frequency bands.

8. A multiband antenna as in claim 4,5, 6 or 7, wherein the distance between the shorting pins is approximately three times the distance between the ground pins.

9. A multiband antenna as in any one of claims 4 to 8, wherein the first angle is approximately 900.

10. A multiband antenna as in any one of claims 4 to 8, wherein the patch member has an additional aperture, through which passes a respective additional elongate conductor, the additional aperture being on a third line that intersects the first line at a second angle at the feed point.

11. A multiband antenna as in any one of claims 4 to 8, wherein the patch member has two additional apertures, through each of which passes a respective additional elongate conductor, the additional apertures being on respective opposite sides of the feed point and on a third line that intersects the first line at a second angle at the feed point.

12. A multiband antenna as in claim 10 or 11, wherein the first angle is approximately 900 and the second angle is approximately 450.

13. A multiband antenna as in claim 10 or 11, wherein the first angle is approximately 600 and the second angle is approximately 1200.

14. A multiband antenna as in claim 10 or 11, wherein the patch member has further additional apertures, through each of which passes a respective further additional elongate conductor, the further additional apertures each being on a respective further additional line intersecting the first line at the feed point and extending at a respective further angle to the first line.

15. A multiband antenna as in claim 14, wherein the further additional apertures are on N further additional lines extending at N further angles to the second line.

16. A multiband antenna as in any preceding claim, and also comprising a metal wire or strip extending from an edge of the ground member to an edge of the patch member.

17. A multiband antenna as in claim 16, wherein the wire or strip has a width in the range of 5mm to 20mm.

18. A multiband antenna as in claim 17, wherein the wire or strip is approximately 10mm wide.

19. A multiband antenna as in claim 17,18 or 19, wherein the wire or strip is made of copper.

20. A multiband antenna as in any preceding claim, wherein a solid dielectric material extends in the space between the ground member and the patch member.

21. A multiband antenna as in any preceding claim, and also comprising a coaxial connector fitted to the ground member, for receiving a signal feed line connected to the patch member.

22. A multiband antenna substantially as herein described with reference to and as shown in Figures 2 to 11 of the accompanying drawings.