GB2376133A

GB2376133A - Single block broadband antenna for use with cellular mobile telephones

Info

Publication number: GB2376133A
Application number: GB0129659A
Authority: GB
Inventors: Jacques Lourdou; Gerard Samouillan
Original assignee: Sagem SA
Current assignee: Sagem SA
Priority date: 2000-12-13
Filing date: 2001-12-12
Publication date: 2002-12-04
Anticipated expiration: 2021-12-12
Also published as: FR2818016B1; FR2818016A1; GB2376133B; GB0129659D0; DE10159371A1

Abstract

The antenna comprises a wire element 2 comprising of two sections. The first section 2 is straight and is attached to the device, e.g. cellular telephone at position 5. The second section (4) is spiral in shape and is a continuation of the first section 2. The antenna acts as a broadband antenna that can be used in multiple bands, the total length of the antenna wire setting a low tunning frequency and the spiral profile setting a high tunning frequency. The antenna is also not sensitive to environmental interference.

Description

2376 33

Linearly Polarized Monobloc Antenna and Mobile Terminal of Cellular Radiotelephony Comprising Such An Antenna The preferred field of application of the invention is

5 that of the mobile terminals of cellular radiotelephony networks, but the present patent application relates more generally still to antennas and not solely those with which these terminals are equipped, even if these mobile terminals gave birth to the problems which are solved by lo the invention.

Let us declare from the outset that the applicant has sought to propose a universal antenna, that is to say a broadband antenna, which can be used in several frequency 15 operating bands, and which is not sensitive, or overly sensitive, to the elements which disturb its environment.

Let us state from the outset also that this is a linearly polarized monobloc antenna.

In cellular telephony, generally, a plurality of operators respectively utilize difference frequency bands. Thus, the GSM band, around roughly 900 MHz, the DCS band, around 1800 MHz, the PCS band, around 1900 MHz and, today, the 25 UMTS band, around 2 GHz, are known. Dual-band antennas already exist on the market. Some of them comprise layouts printed on ceramic. They are expensive, difficult to adjust and sensitive to their environment. At this point, let us state that the elements which disturb a 30 radio telephony antenna comprise, in particular, the loudspeaker, the vibrator, and the mass of the printed circuit board. Dual-band antennas also include "helical't

antennas. They are often voluminous and, in particular, they cannot be laid flat against a printed circuit boards.

The applicant thus proposes his antenna invention 5 preferred embodiments of which aim to be devoid of the drawbacks of the antennas of the prior art.

Accordingly, the invention relates to a linearly polarized and broadband monobloc antenna, characterized in that it lo comprises a profile having two portions, the one along the extension of the other, a first basically straight portion and a second spiral portion.

The applicant was able to note, surprisingly, that both of 5 the two portions of the antenna participated in its radiation in the bottom of the band, the spiral portion, in the top of the band.

It will be pointed out that spiral antennas are already 20 known. However, these antennas, on the one hand, are circularly polarized and, on the other hand, are limited to their spiral portion alone, so much so that one might even doubt whether they belong to the same technical field

as the antenna of the invention.

In a first embodiment of the antenna of the invention, it is wire-like.

In a second embodiment, the antenna is a strip exhibiting, 30 viewed in the thickness, the two portions, basically straight and spiral.

Viewed in its thickness, the strip-antenna may be said to exhibit the form of a wire.

The advantage of the second strip-like embodiment, as 5 compared with the first wire-like embodiment, is to further broaden the passband thereby making the antenna into more than a dual-band antenna with a single high tuning frequency, but rather a multiband antenna, with several high tuning frequencies.

The antenna of the invention is therefore an antenna with at least one high tuning frequency.

The invention will be better understood with the aid of 5 the following description of the two embodiments of the

antenna, with reference to the appended drawings, in which - Figure 1 is a profile view of the first wire-like 20 embodiment of the antenna and Figure 2 is a perspective view of a second strip-like embodiment of the antenna of the invention.

25 The example taken here is a mobile cellular radiotelephony terminal linearly-polarized monobloc antenna hooked up electrically to a printed circuit board 1 (1'), the whole being disposed in a casing (not represented) of a terminal. The antenna is fixed mechanically to the casing 30 by gluing, by clamps or by clips.

The antenna of the invention may also be used as antenna of a subscriber radio terminal implementing, among others,

cellular radiotelephony functions, or of a home-automation repeater, hooked up to the switched telephone network by wire, on the one hand, and to a cellular radio telephone network, on the other hand.

With reference to Figure 1, the antenna is a wire element 2, having two portions 3 and 4, the one along the extension of the other. The first portion 3 is here straight and its end away from the other antenna portion 10 constitutes the antenna foot 5 fixed, here welded, to the board 1. It will be noted that this first portion, with its antenna foot need not be perfectly straight and that some undulations or other discontinuities would be tolerable. The second portion 4, however, is shaped as a 15 spiral.

In the case of the embodiment of Figure 1, the antenna lies substantially in a plane, here parallel to that of the board 1. Also, it is in a direction of observation 20 perpendicular to this plane that the profile of the antenna comprises, in the extension of the straight portion 3, the portion 4 viewed as a spiral.

Orthogonally to this direction, the antenna is viewed as a 25 wire.

It is the total length of the two antenna portions, hence wire unwound, which determines the low tuning frequency, the high tuning frequency being defined by the spiral 30 portion 4 alone. For the low tuning frequency, the antenna may be likened, to within parasitic effects, to a quarter-wave antenna of the total length of the antenna.

By way of example, the low frequency may be 900 MHz, the

high frequency 1800 MHz. However, provision may easily be made for the high tuning frequency not to be double the low tuning frequency.

s With reference to Figure 2, the antenna is a strip 12 wound partly over itself as a spiral in a portion 14 beyond a portion 13, here plane, extended by this spiral portion. It is in its thickness that the antenna exhibits the profile with the two portions, straight 23 and spiral lo 24. Stated otherwise it is in a direction of observation parallel to the faces 25 of the strip, or perpendicular to its lateral edges 26 defining its thickness, that the profile of the antenna comprises, the one along the extension of the other, the portion 23, here straight, and 15 the spiral portion 24. This spiral portion 24 is here wound over itself about an axis orthogonal to the planes of the edges 26.

The end part 15 of the plane portion 13 of the antenna, 20 away from the spiral portion 14, constitutes the foot of the antenna, by which it is fixed, here welded, to the board 1', while remaining clear of the earth plane of the terminal, when dealing with a terminal. The antenna foot 15 is here welded by one of the faces of the strip, after 25 twisting by 90 . As a variant, the strip could be tapered at this point.

As in the previous embodiment, it is the length of the unwound strip which determines the low tuning frequency, 30 the high tuning frequency being defined by the spiral portion 14, 24 alone.

From the frequency standpoint, the strip-like embodiment is distinguished from the wire-like antenna by a broadening towards the top of the frequency band thus allowing, and for example, tuning not only to 900 and 1800 MHz, but also to 1900, or even 2000 MHz, thus allowing operation in the UMTS and PCS bands.

Again purely by way of indication, if the thickness of the printed circuit board may have a thickness of around 3mm, 10 the width of the faces of the antenna strip may for their part be equal to around lOmm.

Claims

1. Linearly polarized and broadband monobloc antenna, characterized in that it comprises a profile having two 5 portions, the one along the extension of the other, a first basically straight portion and a second spiral portion.

2. Antenna according to claim 1, which is wire-like.

3. Antenna according to claim 2, which lies substantially in a plane.

4. Antenna according to claim 3, in which the second 5 antenna portion exhibits a spiral profile in a direction of observation perpendicular to the plane of the antenna.

5. Antenna according to claim 1, which is a strip partly wound up on itself, exhibiting in its thickness the 20 profile with basically straight portion and spiral portion.

6. Antenna according to one of claims 1 to 5, in which the length of the whole profile determines a low tuning 25 frequency.

7. Antenna according to one of claims 1 to 6, in which the spiral profile determines at least one high tuning frequency.

8. Linearly polarized and broadband monobloc antenna, substantially as described herein, with reference to the drawings that follow.

9. Mobile cellular radiotelephony terminal comprising an antenna according to one of claims 1 to 8.