GB2434037A

GB2434037A - Co-linear planar inverted-F antennae arrangement

Info

Publication number: GB2434037A
Application number: GB0600223A
Authority: GB
Inventors: Devis Iellici; Kiyun Han; Hongfei Hu; Vijay Nahar
Original assignee: Antenova Ltd
Current assignee: Antenova Ltd
Priority date: 2006-01-06
Filing date: 2006-01-06
Publication date: 2007-07-11
Anticipated expiration: 2026-01-06
Also published as: TW200740024A; GB0600223D0; WO2007077461A1; GB2434037B

Abstract

An antenna arrangement comprises first and second planar inverted-F antennae 2, 3 where each of the said antennas includes a radiating member with a longitudinal axis where the said axes are substantially co-linear. The first and/or the second antennae 2, 3 may be arranged for dual band operation. The antenna arrangement may be arranged to operate in a number of different frequency bands between 800 Mhz and 6 GHz covering GSM, UMTS, Wi-Fi, WLAN and WWAN operation. Conductive spring or foil strips 4, 5 may be used to provide electrical connections. The antenna arrangement may be formed by fitting a sheet of flexible conductive material about a dielectric carrier support. The flexible conductive material may include integral inductive and/or capacitive matching circuitry and delay line formations as well as antenna elements. Also claimed is an antenna device fabrication method comprising fitting a sheet of flexible conductive material about a dielectric carrier support to provide an antenna with integral matching circuitry.

Description

LAPTOP COMPUTER ANTENNA DEVICE

BACKGROUND

The present invention relates to a small multi-band antenna device designed for incorporation into a laptop computer, tablet computer, personal digital assistant (PDA), navigation device (e.g. GPS device), printer or other peripheral device, and small plafforms generally.

There is an increasing demand for the provision of wireless data communications for the users of computing or communications equipment, especially small equipment, where it is required to provide a number of different co-existing services with significant mutual isolation. A particular device may be required to support wireless communications by way of a number of different data standards operating in various frequency bands including cellular radio and WLAN frequency bands **S. *S..

To enhance the operation of these communication links, some services will employ the * * : techniques of space-or polarisation-diversity. These requirements create the need for a number of different antennas to be mounted on a single small portable device. Because of limited space, this means that each antenna must operate in a number of cellular..

radio and WLAN frequency bands, there being insufficient room for separate antennas covering these bands. The present invention relates to a method of constructing an electrically small antenna, some embodiments of which are capable of operating in five cellular radio bands as well as the 802.11 a/b/g WLAN frequency bands.

BRIEF SUMMARY OF THE DISCLOSURE

According to a first aspect of the present invention, there is provided an antenna arrangement comprising at least first and second planar inverted-F antennas (PIFA5) each having a conductive radiating member with a longitudinal axis, an electrically conductive member for connecting the radiating member to an electrical feed, and an electrically conductive member for connecting the radiating member to ground, the PIFAs being arranged such that the longitudinal axes of their radiating members are substantially colinear in a given plane.

Preferably, the PIFAs are generally elongate. The PIFAs are also preferably substantially thin or planar along their longitudinal axes. The given plane may be defined by a display screen of a laptop computer or PDA or other device having a display screen. The PIFAs are preferably located at edges of or in a border of the display screen.

The first PIFA may be configured to operate over the four GSM mobile phone frequency bands: i) GSM-850 (824 -894MHz), ii) GSM-900 (890 -960MHz), iii) GSM-1800 (1710 - 1880MHz) and iv) GSM-1 900 (1850 -1990MHz), as well as v) the 3G Universal Mobile Telecommunications System (UMTS) band (1920 -2170MHz).

In effect, this spectrum coverage is achieved by having a low band resonance (824 - 960MHz) and an upper band resonance (1710 -2170MHz). These bands collectively form a Wireless Wide Area Network or WWAN spectrum and this antenna is known as the WWAN antenna.

The second PIFA may be configured to operate over the IEEE 802.11 Wi-Fi or bands: i) * 802.11 b/g (2.4 -2.4835GHz) and ii) 802.11 a (4.9 to 5.825GHz). S.'. * S * * S

These bands collectively form a Wireless Local Area Network or WLAN spectrum and this antenna is known as the WLAN antenna. ** * S 5 In a preferred embodiment of the present invention, the first PIFA is a WWAN antenna.* *S*.

structure with a first co-axial feed cable, and the second PIFA is a WLAN antenna *:::.

structure with a second co-axial feed cable. The two PIFAs are mounted in a colinear fashion within a single structure. The isolation between the WWAN and WLAN antennas is advantageously 13dB or better, such good isolation between two closely spaced colinear antennas forming an important part of the first aspect of the present invention. The isolation across all the bands can be seen in Figure 1. The voltage standing wave ratio (VSWR) across WWAN and WLAN is shown in Figures 2 and 3.

A PIFA generally consists of a driven conductive radiating element (generally a quarter-wavelength element) connected to RF ground and substantially parallel to a conductive groundplane, for example a metal housing of an appliance. At frequencies above about 1.5GHz, the PIFA itself may be an effective radiator, but at lower frequencies the PIFA may be electrically too small to radiate and the groundplane becomes a significant part of the radiating structure. For GSM operation, it is important that the PIFA has a groundplane large enough to radiate effectively down to 824MHz. This implies that at least one of the groundplane dimensions should be of the order of 90mm or longer.

Antennas that will fit round the edge of a laptop or other display screen are necessarily thin, elongate structures having a groundplane very little larger than the radiating structure. It is therefore desirable electrically to connect the antenna groundplane to the display screen, which is a large grounded structure.

Connections between the two PIFAs and the display grounded structures may be made by electrically conductive connections such as strips of conductive tape foils (e.g. copper tape) or other conductive connections generally extending along the length of the PIFA groundplane. Alternative methods include extensions of the antenna groundplane providing a flap which either makes contact with a metal housing of the display via a foam gasket with conductive surface properties or by capacitive coupling to the larger ground using double sided adhesive. However, it has been found in some laptop computers that mechanical constraints can make such methods of connection difficult to achieve or electrically unreliable. S... * **S.

* S* * Accordingly, preferred embodiments of the present invention additionally comprise first * and second spring members electrically connected respectively to the ground member of each of the first and second PIFA5. The spring members are adapted to form an:. . electrical ground connection to a grounded display screen of laptop computer or the like, as shown in Figures 4 and 5. S... * .

Use of such spring members helps to provide a robust and reliable electrical connection between the ground of each PIFA and the ground of the display screen or the like.

It is unusual to have a point connection between the ground of a PIFA and a grounded display screen element, since point connections generally result in a loss of bandwidth, but by careful selection of the locations of the spring members, the ground of each PIFA can be connected to the display screen ground without undue loss of bandwidth.

As earlier discussed, a PIFA generally consists of a quarter wavelength radiator, grounded at one end. Embodiments of the present invention combine two PIFA structures, back-to-back, at the grounding point. This enables both PIFAs to be located fairly close to each other while still operating with reasonable independence. Connection to the larger common groundplane may be made by way of a leaf spring structure, which may also mechanically attach to a dielectric (e.g. ABS) carrier and be soldered to an outer of a feeding cable. This grounding spring is best positioned within the region of the common ground and where this is not possible, the spring may be grounded to a conductive strip which in turn is connected to the region of the common ground.

If more than two PIFAs are provided in the co-linear arrangement of embodiments of the present invention, then a corresponding number of spring members may be provided (one for each PIFA).

In certain embodiments of the present invention, it has been found that the second PIFA when configured as a WLAN PIFA generally achieves sufficiently good performance without the need for a matching circuit. However, the present applicant has found that the performance of the first PIFA when configured as a WWAN PIFA can be improved through the provision of a matching circuit, especially in the lower band.

In conventional PIFA design, the feedline (e.g. coaxial cable, microstrip, coplanar waveguide etc) is brought close to the antenna and connected to a matching circuit "** Is..

located on a main PCB (printed circuit board). Matching components generally take the. : form of discrete inductors and capacitors and may be applied to the feed pin of the PIFA, the shorting or ground pin, or both. :. . According to a second aspect of the present invention, there is provided an antenna *....

device fabricated from a sheet of flexible conductive material supported by and fitted about a dielectric carrier, wherein the antenna device includes an integral matching circuit formed from the sheet of flexible conductive material.

The sheet of flexible conductive material may comprise a net or web having a predetermined form adapted to be folded around the dielectric carrier and secured thereto. The net or web may be manufactured by application of known photoresist techniques. The dielectric carrier may be made of ABS or any other suitable dielectric material. The sheet of flexible conductive material may, for example, be 1 8pm copper on 25pm Kapton with VHB adhesive backing, available from Lyncolec. This form of antenna construction is known in the art (see, for example, Salonen, P. & Rantanen, J. "A Dual-Band and Wide-Band Antenna on Flexible Substrate for Smart Clothing", IECON'Ol The 27th Annual Conference of the IEEE Industrial Electronics Society, Hyatt Regency Tech Center, Denver, Colorado, USA, November 29 -December 2, 2001, pp 125-1 30.

The matching circuit may include capacitive and/or inductive components formed from the sheet of flexible conductive material. Advantageously, the matching circuit may include a delay line, for example a thin conductive track that is not conductively connected to a main web or net of the sheet of flexible conductive material.

By making the matching circuit part of the antenna structure rather than, as is conventional, part of the feed structure, significant savings in manufacturing costs can be obtained. Moreover, moving the matching circuit onto the antenna structure has advantages for WWAN antenna efficiency in the low band.

Incorporating a delay line into the matching circuit allows the resonant loop to be moved around the Smith chart when designing antenna structures, for example enabling the resonant loop to be moved to a more convenient location for matching. An increase in electrical delay to the input of the antenna will rotate the locus of the complex impedance on the Smith chart. This gives an additional variable for matching the antenna, in conjunction with the SMT matching components. This simplifies the matching circuit and * *S..

reduces losses. By selecting an appropriate inductance for the delay line, it is also * * possible to simplify the matching circuit and reduce losses. S. * * S *

There are distinct manufacturing advantages to an antenna structure incorporating its own delay line and matching circuit. No separate PCB is required for the mounting of * * these components, and the co-axial feeding cable can be soldered, or otherwise.... * S 5

electrically connected, directly to the antenna.

When the second aspect of the present invention is combined with the grounding arrangement described hereinbefore (especially the grounding spring arrangement), assembly is thus simply a matter of connecting the cable to the antenna structure and then inserting this assembly into the laptop lid housing in such a way that the grounding tape or spring makes good electrical contact with the display screen earth. This is a low cost method of assembly that give good performance results in terms of bandwidth and efficiency.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to", and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention and to show how it may be carried into effect, reference shall now be made by way of example to the accompanying * drawings, in which: FIGURE 1 shows a plot of isolation between WWAN and WLAN antennas mounted on a single structure of an embodiment of the invention; FIGURE 2 shows a plot of VSWR of a WWAN antenna at its connector, including,", 600mm, 1.37mm 00 coaxial cable; FIGURE 3 shows a plot of VSWR of a WLAN antenna at its connector, including 600mm, 1.37mm OD coaxial cable; FIGURE 4 shows an embodiment of the present invention including a pair of grounding springs; FIGURE 5 shows a detail of the embodiment of Figure 4; and FIGURE 6 shows an embodiment of the second aspect of the present invention.

DETAILED DESCRIPTION

Figure 1 shows a plot of isolation against frequency for an antenna structure comprising a first PIFA in the form of a WWAN antenna and a second PIFA in the form of a WLAN antenna (as described hereinbefore), the PIFAs having a co-linear configuration.

Figure 2 shows a plot of VSWR for the WWAN antenna, measured at its connector, and Figure 3 shows a plot of VSWR for the WLAN antenna, measured at its connector.

Figure 4 shows an embodiment of the first aspect of the present invention, comprising a dielectric carrier I made of ABS or similar material, a first WWAN PIFA 2 made of a thin conductive layer wrapped onto the carrier 1, and a second WLAN PIFA 3 also made of a thin conductive layer wrapped onto the carrier 1. It can be seen that the first 2 and second 3 PIFAs are disposed in a co-linear arrangement. Each PlEA 2, 3 has a grounding or shorting element that is conductively connected to a conductive spring member 4, 5 adapted to make an electrical point connection to a groundplane of a display screen of a laptop computer or the like (not shown).

Figure 5 is a close-up detail of Figure 4, more clearly showing the conductive spring member 4 of the first PIFA 2. The PIFA 2 includes a cable feed point 6, a grounded region 7, connections to ground 8, 9, a 1.5pF shunt capacitor 10, a 4.7nH shunt inductor 11, matching stubs 12, 13, and a transmission line 14 for feeding the radiating member(s) (not shown) of the PIFA 2 via a series 1.5pF capacitor 15. All of these components are wrapped around a dielectric carrier 1. Each PIFA 1, 2 has its own separate feed and grounding spring, and consists of a dual band resonating structure.

The capacitive and/or inductive matching components 10, 11, 15 are optionally provided so as to improve the performance of the antenna device.

Referring now to Figure 6, there is shown web or net 16 of a flexible conductive material, for example a flexicircuit fabricated using photoresist techniques. The flexicircuit 16 is designed so that it can be wrapped around a dielectric carrier (not shown in Figure 6, but shown as item I in Figures 4 and 5). The web or net 16 includes the WWAN high band 17 and low band 18 resonators, the WLAN high band 19 and low band 20 resonators, together with the WLAN feed point 21 and WWAN feed point 22. Figures 4 and 5 show the WWAN cable feed 6 soldered at the WWAN feed point 22.

The web or net 16, when wrapped around a dielectric carrier 1, forms a double PIFA suitable for use with the first aspect of the present invention. Moreover, the web or net 16 includes an integrated matching circuit indicated generally at 23 including a delay line 24 that is not directly conductively connected to the main body of the web or net 16. oui *. * I. * SP * I **I. Ii., * S * * ,

Claims

CLAI MS: 1. An antenna arrangement comprising at least first and second

planar inverted-F antennas (PIFAs) each having a conductive radiating member with a longitudinal axis, an electrically conductive member for connecting the radiating member to an electrical feed, and an electrically conductive member for connecting the radiating member to ground, the PIFAs being arranged such that the longitudinal axes of their radiating members are substantially colinear in a given plane.

2. An antenna arrangement as claimed in claim 1, wherein the PIFAs are elongate. e.. * * ****

3. An antenna arrangement as claimed in any preceding claim, wherein the PIFAs.':, are substantially thin or planar along their longitudinal axes.

4. An antenna arrangement as claimed in any preceding claim, wherein at least one * of the PIFAs is adapted for at least dual band operation in non-overlapping respective * ** S high and low frequency bands. * * ** *.SS * * S ** S 5. An antenna arrangement as claimed in claim 4, wherein both PIFAs are adapted for dual band operation.

6. An antenna arrangement as claimed in claim 4 or 5, wherein the first PIFA is configured to operate at a low band resonance (824 -960MHz) and an upper band resonance (1710-2170MHz).

7. An antenna arrangement as claimed in claim 4, 5 or 6, wherein the first PIFA is configured to operate over the four GSM mobile phone frequency bands: i) GSM-850 (824 -894MHz), ii) GSM-900 (890 -960MHz), iii) GSM-1 800 (1710 -1880MHz) and iv) GSM-1 900 (1850 -1990MHz), as well as v) the 3G Universal Mobile Telecommunications System (UMTS) band (1920 -2170MHz).

8. An antenna arrangement as claimed in claim 4, 5, 6 or 7, wherein the second PIFA is configured to operate over the IEEE 802.11 Wi-Fl or bands: i) 802.1 lb/g (2.4 -
2.4835GHz) and ii) 802.lla (4.9 to 5.825GHz).

9. An antenna arrangement as claimed in any preceding claim, additionally comprising first and second spring members electrically connected respectively to the ground member of each of the first and second PIFAs.

10. An antenna arrangement as claimed in any one of claims I to 8, wherein connections between the PlEAs and ground are made by electrically conductive connections such as strips of conductive tape foils or other conductive connections generally extending along the length of the PlEAs.

11. An antenna arrangement as claimed in any preceding claim, further comprising a matching circuit. SI.S *..S

12. An antenna arrangement as claimed in claim 11, wherein the matching circuit * * includes a delay line. * * S

13. An antenna arrangement as claimed in any preceding claim, wherein the first and second PIFAs are fabricated from a sheet of flexible conductive material supported by *. 55.5

and fitted about a dielectric carrier. * : :: : 14. An antenna device fabricated from a sheet of flexible conductive material supported by and fitted about a dielectric carrier, wherein the antenna device includes an integral matching circuit formed from the sheet of flexible conductive material.

15. An antenna device as claimed in claim 14, wherein the sheet of flexible conductive material comprises a net or web having a predetermined form adapted to be folded around the dielectric carrier and secured thereto.

16. An antenna device as claimed in claim 14 or 15, wherein the matching circuit includes capacitive and/or inductive components.

17. An antenna device as claimed in any one of claims 14 to 16, wherein the matching circuit includes a delay line.

18. An antenna device substantially as hereinbefore described with reference to or as shown in the accompanying drawings.