WO2001018904A1

WO2001018904A1 - Tunnel antenna

Info

Publication number: WO2001018904A1
Application number: PCT/SE2000/001721
Authority: WO
Inventors: Roger Gustafs
Original assignee: Smarteq Wireless Ab
Priority date: 1999-09-06
Filing date: 2000-09-06
Publication date: 2001-03-15
Also published as: AU7465100A; SE9903142L; SE9903142D0; SE520290C2

Abstract

The present invention relates to an antenna means for transmitting and/or receiving RF signals in a single frequency band. Said antenna means comprising a ground plane means (20) arranged to be connected to ground of a circuitry of a radio communication device, a conductive radiating structure (10, 12, 14) having an essentially rectangular main portion (10) and at least a first and a second branch (12, 14). A first end of said first branch (12) being a feed portion (5). A second end of said first branch (12) being connected to a first side of said main portion (10) between a first end and a second end of said main portion (10). A surface of said first branch (12) being in a common plane with a surface of said main portion (10). A first end of said main portion (10) being connectable to ground. A second end of the second branch (14) being connected to the first side at a second end of said main portion (10). A surface of said second branch (14) being in a common plane with the surface of said main portion (10). A first end of said second branch (14) being a free end. Said conductive radiating structure is curved in such a manner that said second end of said main portion (10) and a second end of a first portion (14a) of the second branch (14) being at a height h above the ground plane for mechanical tuning of the single frequency band.

Description

TUNNEL ANTENNA

FIELD OF THE INVENTION

The present invention relates to an antenna means in general and specifically to an electrically small antenna means for transmitting and or receiving RF signals in at least a first frequency band.

DESCRIPTION OF THE RELATED ART

With the recent rapid progress of electronic communication technique, communication apparatuses having a higher function and smaller size have been developed and utilised for various kinds of mobile communication apparatuses.

Antenna means transmitting and receiving RF-signals on a single frequency band are well known for a long time . Antennas according to the state of the art including single band antennas demands generally a quite large amount of space, which make them unpractical for use where there is a need for small and efficient antenna means.

For example, EP 0 806 810 discloses a band shaped single frequency band antenna. Said antenna comprising a curved rectangular resonator of a length of λ/4 wavelengths of said single band frequency. A first end of said rectangular resonator is attached to a ground plane and a second end of said rectangular resonator is arranged at a distance h above said ground plane. The rectangular resonator having a feed point arranged between the first and second end but closer to the first end.

In certain applications this kind of antenna has too large physical dimensions which is a problem. SUMMARY OF THE INVENTION

It is an object of the present invention to provide an antenna means which overcomes or at least reduces the above mentioned problem.

According to the present invention there is provided an antenna means as claimed in claim 1.

One advantage with the present invention is that the feeding of the antenna means is very simple.

Another advantage with the present invention is that the antenna is relatively simple to manufacture.

A further advantage with the present invention is that the antenna showS a good radiating pattern.

Yet another advantage with the present invention is that the different parts of the antenna can easily be stored before assembling said antenna.

The invention will now be described in more detail with reference to preferred embodiments thereof and also with reference to the accompanying drawings .

BRIEF DESCRIPTION OF THE DRAWINGS

Figure la shows an embodiment of an antenna device according to the invention arranged on a ground plane.

Figure lb shows the radiating structure of the antenna device in figure la in planar condition.

Figure lc shows a principal function of the antenna in figure la. DESCRIPTION OF A PREFERRED EMBODIMENT

In this disclosure it is to be understood that the antenna system of the invention is operable to receive and/or transmit radio signals. Even if a term is used herein that suggests one specific signal direction it is to be appreciated that such a situation can cover that signal direction and/or its reverse.

With reference to Figure la and lb, an embodiment of an antenna device 1 according to the invention is shown. The antenna device s arranged for transmission/reception of RF waves m a single frequency band, e.g. in the 900 MHz band.

The antenna device 1 is to be connected to a radio communication device (not shown) , preferably portable, and/or arranged to a vehicle. As shown in the figure, the antenna device 1 is arranged on a conductive part 20, such as a vehicle body. This conductive part 20 with a minimum radius of λ/4 or with straight or meander shaped arms λ/4 long will act as a ground plane. The conductive part 20 can be replaced by a conductive ground plane of proper size in a radio communication device, e.g. a PCB (printed circuit board) . In those cases the antenna device 1 can be integrated into a mobile radio communication device, such as a radio telephone or a computer.

The antenna device 1 comprises a radiating structure 10, 12, 14 including a radiating main portion 10, a radiating first branch 12 for transmission/reception of RF waves in said single frequency band and a radiating second branch 14. The first 12 and second 14 branches are conductively connected to the main portion 10.

The mam portion 10, being essentially rectangular shaped, comprises a first side, a second side, a first enα and a second end. The first branch 12 and the second branch 14 each comprising two essentially rectangular portions 12a, 12b, 14a, 14b. Said rectangular portions 12a, 12b, 14a, 14b each comprising a first end, a second end, a first side and a second side.

The first elongated rectangular portion 12a of the first branch is essentially parallel with the elongated main portion 10. The first elongated rectangular portion 12a of the first branch 12 is electrically connected to the mam portion 10 via the second rectangular portion 12b. The first side of said second rectangular portion 12b is connected at the second end of the second side of said elongated first rectangular part 12a. The second side of said second rectangular portion 12b, opposite to said first side, is connected to the first side of said main portion between the first end and the second end of said main portion .

The first elongated rectangular portion 14a of the second branch is essentially parallel with the elongated mam portion 10. The first elongated rectangular portion 14a of the second branch 14 is electrically connected to the main portion 10 via the second rectangular portion 14b of said second branch 14. The first side of said second rectangular portion 14b is connected at the second end of the second side of said elongated first rectangular portion 14a. The second side of said second rectangular portion 14b, opposite to said first side, is connected to the first side of said mam portion 10 at the first end of said main portion.

The radiatmg structure 10, 12, 14 is to be connected to a transmission line at a feed portion 5 arranged on a first end of the first part 12a of the first branch 12. The feed line is connected to transceiver circuits of a radio communication device. The first end of the first portion 14a of the second branch 14 is a free end. The first end of the ma portion 10 is connected to ground. The distance between the first end of the mam portion and the first enα of the first portion 14a in the second branch 14 along said ma portion and said second branch 14 is about λ/4, where λ is the wavelength of the single frequency band. The second branch 14 can be tuned to its frequency by adjusting said distance between the first end of said ma portion 10 and said first end of the first portion 14a in the second branch 14, e.g. by cutting at the first end of the first portion 14a in the second branch 14.

The first end of the first portion 12a of the first branch 12 is a first end of the first branch 12. The second side of the second portion 12b of the first branch is a second end of the first branch. The first end of the first portion 14a of the second branch 14 is a first end of the second branch 14. The second side of the second portion 14b of the second branch 14 being a second end of the second branch.

The length of the first branch is set when adjusting the antenna. In the present embodiment the length is essentially λ/12.

The radiating structure 10, 12, 14 is arranged on a substrate 20. The first end of the mam portion can be provided with connection pins passing through holes in the substrate 20. The pins are then preferably soldered to the substrate 20.

The substrate 20 with a conductive portion of a proper size is sufficient for the antenna function, and the antenna device 1 can be mounted to a portable radio communication device. However, if the antenna device 1 is mounted at a small height e.g. 0.5 mm above a vehicle roof or body, conductive portions of the vehicle are coupled, preferably capacitive y, to the substrate 20 with a reduced conductive portion of a proper size. In this case said conductive portions also act as ground plane. If mounted to (on or in) a portable radio communication device, such as a hand portable radio telephone, conductive portions e.g. a PCB of the radio communication device can be coupleα, preferably capacitiveiy, to the substrate 20, whereby those conductive portions also are acting as ground plane.

The radiating structure 10, 12, 14 is shown to be arranged in a curved formation on the substrate 20. As mentioned above the first end of the mam portion is electrically coupled to the substra_te 20. The first end of the first portion 12a in the first branch 12 is electrically isolated from the substrate 20, i.e. ground. The second end of the main portion together with the second end of the second portion 14b in the second branch 14 and the second end of the first portion 14a in the second branch 14 are arranged at a height h above said substrate 20. When changing said height h a resonance frequency in the radiating structure 10, 12, 14 will be changed simultaneously. Said height h being means for frequency tuning the single frequency band, h is m the range of 0-λ/2 .

The radiating structure 10, 12, 14 is preferably manufactured by stamping or cutting out the structure from a conductive plate e.g. metal plate. The branches 12 and 14 and the main portion 10 are preferably given band shapes, i.e. the width of the branches and mam portion in the plane of the radiatmg structure is essentially larger than the thickness perpendicular to the plane of the structure. Preferably the first end of the mam portion is formed with guiding and possibly connections pins. The substrate 20 is then provided with holes for reception of sa d pins. The pins and/or the end of said ma portion is glued or soldered to the substrate 20. In Figure lc the current flows in the antenna device of figure la is shown schematically by arrows. As seen, the currents in the mam portion 10 and the first portion 12a of the first branch 12 flows in the same direction. A first sub portion of the mam portion parallel with the first portion 12a of the first branch 12 radiates most. The first portion 14a of the second branch 14 and a second sub portion of the mam portion 10, parallel with said first portion 14a of the second branch 14, are radiating less than the first portion 12a of the first branch 12. The currents in the first portion 14a m the second branch 14 and the second sub portion of the mam portion 10 parallel with said first portion 14a of the second branch 14 are directed m opposite directions resulting in little radiation m the far field from said portions. Arrow 9 indicates the direction of polarisation for the RF waves radiated from the radiating structure 10, 12 and 14.

Said first and second branches 12, 14 m the antenna means each comprising a second portion 12b, 14b where said second portion preferably having substantially smaller surface area than corresponding first portions 12a, 14a and being essentially rectangular shaped.

Said first and second branches 12 ,14 in the antenna means can have substantially the same width. Said first branch 12 in the antenna means can have a different thickness compared to said second branch 14.

Said first branch 12 the antenna means can have a different width compared to said second branch 14.

The width of each branch 12, 14 the antenna means is smaller than the length of said branches.

Claims

1. An antenna means for transmitting and/or receiving RF signals in at least a first frequency band, comprising:

- a ground plane means (20) arranged to be connected to ground of a circuitry of a radio communication device,

a conductive radiating structure (10, 12, 14) having an essentially rectangular mam portion (10) , a first branch (12) and a second branch (14),

- a first end of said first branch (12) being a feed portion (5) ,

a second end of said first branch (12) being connected to a first side of said mam portion (10) between a first end and a second end of said mam portion (10) ,

- a surface of said first branch (12) being in a common plane with a surface of said main portion (10),

a first end of said mam portion (10) being connectable to ground,

a second end of the second branch (14) being connected to the first or a second side at a second end of said mam portion (10),

a surface of said second branch (14) being in a common plane with the surface of said mam portion (10),

a first end of said second branch (14) being a free end,

- said conductive radiating structure being curved in such a manner that said second end of said main portion (10) and a second end of a first portion (14a) in the second branch (14) being at a height h above the ground plane for mechanical tuning of the frequency band or frequency bands .

2. The antenna means according to claim 1, characterized in that said mam portion (10) plus said second branch (14) having a total length of essentially λ/4 at a frequency band.

3. The antenna means according to any of the claims 1-2, characterized in that a first elongated portion (12a) in first branch (12) and the first elongated portion (14a) the second branch (14) being parallel with the elongated mam portion (10) .

4. The antenna means according to any of the claims 1-3, characterized in that the first and second branches (12, 14) each comprising a second portion (12b, 14b) having a substantially smaller surface area than corresponding first portions (12a, 14a) and being essentially rectangular shaped and arranged at the second end of a second side of said first portions (12a, 14a) .

5. The antenna means according to any of the claims 1-3, characterized in that the height h is in the range of 0- λ/24.

6. The antenna means according to any of the claims 1-2, characterized in that said first branch (12) having a length of essentially λ/12 at a frequency band.

7. The antenna means according to any of the claims 1-3, characterized in that said conductive radiating structure is made out of a conductive plate.

8. The antenna means according to any of the claims 1-3, characterized in that said conductive radiating structure is arranged on one side of a dielectric substrate .

9. The antenna means according to claim 5, characterized in that the conductive radiating structure is arranged inside the dielectric substrate.

10. The antenna means according to any of the preceeding claims, characterized in that said mam portion (10), said first and second branches (12 ,14) are substantially band shaped.

11. The antenna means according to any of the preceding claims, characterized m that said mam portion (10), first and second branches (12 ,14) having substantially the same thickness.

12. The antenna means according to any of the preceding claims, characterized in that said first and second branches (12 ,14) having substantially the same width.

13. The antenna means according to any of the preceding claims, characterized in that sa d first branch (12) having a different thickness compared to said second branch ( 14 ) .

14. The antenna means according to any of the preceding claims, characterized in that said first branch (12) having a different width compared to said second branch

(14) .

15. The antenna means according to any of the preceding claims, characterized in that the width of each branch (12, 14) is smaller than the length of said branches.