PLANAR INVERTED F-ANTENNA

Abstract

A Planar Inverted-F Antenna, PIFA, comprises a sheet of conductive material including first, second, third and fourth contiguous sections, the first and third sections extending orthogonally away from the second section and the fourth section extending away from the third section. The sections are folded relative to one another to define a volume with a height of the second section, a width of the second section and a depth of the third section extending away from the second section. A supporting pin and a feed pin extend from the second section along an outer edge. A supporting leg extends from either the third or fourth sections, the supporting leg lying outside the plane of the supporting pin to support the PIFA when mounted on a printed circuit board, while allowing components to at least partially occupy the volume under the PIFA.

Claims

1. A Planar Inverted-F Antenna, PIFA, comprising a sheet of conductive material including first, second, third and fourth contiguous sections, the first and third sections extending orthogonally away from the second section and the fourth section extending away from the third section, the sections being folded relative to one another to define a volume with a height of the second section, a width of the second section and a depth of the third section extending away from the second section, the second section comprising: a shorting leg divided from a remainder of the second section by a slot, the shorting leg running along a first outer edge of the second section opposite die third section, the shorting leg terminating in a shorting pin extending from a second outer edge of the second section opposite the first section; a feed pin extending from the remainder of the second section along the second outer edge; and at least one supporting pin extending from the remainder of the second section along the second outer edge, each of the feed pin and the at least one supporting pin being bent out of the plane of the second section; the first section having defined therein an L-shaped slot comprising a first leg running adjacent a first outer edge of the first section extending from said first outer edge of said second section and a second leg running adjacent a second outer edge of the first section opposite the second section to define a path extending from the shorting leg around the periphery of the antenna, the third and fourth sections comprising a narrowed arm extending along an inner edge adjacent and running around said folded first section; and at least one further supporting leg extending from either said third or fourth sections away from said inner edge, said supporting leg lying outside the plane of said at least one supporting pin to support said PIFA when mounted on a printed circuit board, while allowing components to at least partially occupy the volume under the PIFA.

2. A PIFA according to claim 1 wherein a pair of supporting legs extend from adjacent an end of the fourth section remote from the third section.

3. A PIFA according to claim 1 wherein one supporting leg extends from the third section adjacent the second section.

4. A PIFA according to claim 1 wherein the third section extends to a greater depth than the first section away from the second section.

5. A PIFA according to claim 1 wherein the fourth section extends away from the third section no longer than the width of the second section.

6. A PIFA according to claim 1 wherein said sheet is either stamped or laser cut.

7. A PIFA according to claim 1 having a height of about 20 mm, a width in a range from about 36 mm to about 45 mm and a depth in a range from about 40 mm to 42.5 mm.

8. A PIFA according to claim 1 comprising two supporting pins extending from the remainder of the second section along the second outer edge, said two supporting pins being disposed on either side of said feed pin.

9. An electronic assembly comprising a PCB, on which a PIFA according to claim 1 is mounted and including at least one further component mounted on the PCB at least partially occupying the volume under the PIFA.

10. An electronic assembly according to claim 9 wherein said at least one component has a height no greater than a height of the second section.

11. An electronic assembly according to claim 9 wherein said at least one component has a height no greater than a spacing of said third and fourth sections from said PCB.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The novel features of the invention are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which:

[0012] FIG. 1 is a development of a PIFA according to a first embodiment of the present teaching;

[0013] FIG. 2 is a first perspective view of the PIFA of FIG. 1 when folded;

[0014] FIG. 3 is a second perspective view of the PIFA of FIG. 1 when folded;

[0015] FIG. 4 is a development of PIFA according to a second embodiment of the present teaching;

[0016] FIG. 5 is a first perspective view of the PIFA of FIG. 4 when folded;

[0017] FIG. 6 is a second perspective view of the PIFA of FIG. 4 when folded; and

[0018] FIG. 7 shows simulated efficiencies of a stamped metal PIFA according to the first embodiment of the present teaching versus different ground plane sizes.

DETAILED DESCRIPTION

[0019] It will be appreciated that for simplicity and clarity, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.

[0020] FIG. 1 illustrates an exemplary PIFA 10 for receiving, transmitting or both receiving and transmitting radio frequency signals according to an embodiment of the present invention in an unfolded state. The PIFA 10 may be configured for use in, for example, 4.sup.th Generation (4G), 3.sup.rd Generation (3G) and 2.sup.nd Generation (2G) wireless frequency bands operating with high efficiency over the frequency band ranges of 698 MHZ to 960 MHz and 1710 MHz to 2700 MHz. The PIFA 10 may be formed by stamping out or laser cutting a planar piece of conductive material, such as metal, to provide the unfolded antenna shape shown. Typically, the material is about 0.5 mm thick.

[0021] When unfolded as shown, the PIFA 10 comprises a generally L-shaped body 20 divided along its length into first 20A, second 20B, third 20C and fourth 20D contiguous sections each separated from one another by fold lines A-A, B-B and C-C. The first section 20A occupies a short-leg of the body 20 while the third and fourth sections 20C and 20D extend along a longer leg of the body 20 away from the second section 20B which shares common boundaries with the first and third sections along fold lines A-A, andB-B, respectively.

[0022] An inner edge of the L-shaped body 20 extends generally along the edges of the first, third and fourth sections, whereas an outer edge of the body 20 extends generally along the opposite edges of the first, second, third and fourth sections.

[0023] In relation to the first section 20A, an L-shaped slot 30A is defined, the slot 30A comprising one leg extending alongside and adjacent the outer edge of the first section 20A and a second leg extending alongside and adjacent a distal edge of the first section 20A, remote from the second section 20B. This slot 30A enables the high frequency response of the PIFA 10 to be tuned to provide the required efficiency at a number of different higher frequencies, for example, in a frequency range from 1710 MHz to 2700 MHz.

[0024] In the first embodiment, the third and fourth sections 20C and 20D comprise a relatively slim arm extending away from the second section 20B with these sections determining a low frequency response of the PIFA 10, for example, in a frequency range from 698 MHZ to 960 MHz. While in this embodiment, the fourth section 20D simply extends the third section 20C, the third section 20C widens to provide a base portion 20C which meets the second section 20B along the fold line B-B.

[0025] The second section 20B provides a hub for the PIFA 10, from which the first and third/fourth sections extend and through which the PIFA 10 is mounted to a printed circuit board (PCB)not shown.

[0026] To this end, a number of pins 40, 50, 60 and 70 are defined along one outer edge of the second section 20B with a further pin 80 being defined at the end of the base portion 20C in line with the pins 40-70.

[0027] A pair of slots 30B and 30B are defined within the second section 20B. The slot 30B extends from between the pins 40 and 60 to the fold line A-A. The slot 30B extends inwards from a corner of the inner edge of the body 20 along the fold line A-A. The depth of the slot 30B is less than the depth of the slot 30B.

[0028] While the slot 30B is used for tuning the response of the PIFA 10, the slot 30B defines a longitudinal arm 20B running along the outside edge of the second section 20B, the arm 20B functioning as a shorting leg for the PIFA 10 with pin 40 providing a shorting pin at a distal end of the shorting leg for shorting the PIFA 10 to a ground plane of a PCB. It will be seen that the shorting leg 20B extends in a path around the outer periphery of the L-shaped slot 30A.

[0029] Note that the pin 40 extends further than the pins 50-80 and furthermore, as will be seen in FIGS. 2 and 3, the pin 50-80 are bent 90 out of the plane of the second section 20B along a fold line D-D which runs parallel to fold line A-A to provide mounting feet as well as a feed connection for the PIFA 10 when located on a PCB. The shorting pin 40 on the other hand is not bent and may be located in a cut-out, or through-hole of the PCB so as to aid in the placement of the PIFA 10 onto the PCB. This enables the shorting pin to connect with a ground plane provided on a layer of the PCB spaced away from the surface on which the PIFA 10 is mounted.

[0030] Running along the edge of the second section 20B from the shorting pin 40, pins 60 and 70 when bent away from the plane of the second section 20B and located on a PCB act as supporting feet for the PIFA. Cut-away portions 20B along the edge between pins 60 and 70 define a feed pin 50 which can also be bent in the same manner as pins 60,70.

[0031] The support pin 80 is separated from the pin 70 by a deeper cut-away portion 20B than the cut-away portions 20B. It will be seen that, as support pin 80 lies on the other side of the fold line B-B from pins 50-70, when the third section 20C is bent out of the plane of the second section 20B, the bent support pin 80 will tend to support the second section 20B in an upright position relative to the PCB so providing mechanical stability for the PIFA as it is being assembled and when integrated onto a PCB. Nonetheless, as the pin 80 is immediately adjacent the second section 20B, it does not unduly limit the placement of other components as will be explained in due course.

[0032] The blank PIFA 10 shown in FIG. 1 is bent along fold line D-D to provide the support pins 50-80 before being bent along line B-B. Other than that, the order of folding along lines A-A to D-D is not critical.

[0033] Referring now to FIGS. 2 and 3, folds along lines A-A and B-B, fold the first section 20A and third section 20C towards one another to provide a side and top surface of the folded PIFA 200A when mounted on the PCB. The fourth section 20B is further folded in the same direction as the fold B-B so that the fourth section 20D lies in parallel spaced apart relationship with the second section 2B. The folded sections 20A-20D therefore form the PIFA 200A arranged to enclose a volume when mounted on a PCB where the pins 40-80 may then be soldered into position including connecting the pin 50 to a feed line.

[0034] Referring specifically to FIG. 3, a rectangular area of PCB occupied by the PIFA 200A measures wd mm.sup.2: with w corresponding to the length of the edge of the first section 20A including the pins 40-70; and d corresponding to the length of the third section 20C. When integrated onto a PCB, the height of an enclosure required to accommodate the PIFA 200A is greater than h mm with h corresponding to the length of the edge of the second section 20B between fold lines B-B and D-D. In the illustrated embodiment of FIG. 3, w=36-45 mm; d=40-42.50 mm; and h=20 mm.

[0035] When integrated onto a PCB the volume enclosed by the PIFA 200A allows electronic components to be placed under the PIFA 200A without affecting the radiating or reception performances of the PIFA. This saves valuable space on the remainder of the PCB. Furthermore, the ground plane of the PCB may extend under at least a portion of the PIFA 10 without affecting the radiating or reception performances of the PIFA.

[0036] In more detail, for the size of PIFA 200A indicated above, components with a height of up to 14 mm may be placed within the PIFA 200A under the first section 200A without affecting the antenna radiating and reception performances. Note however, that components (not shown) with a height of up to 8 mm may be placed under the third section 20C i.e. bridging the space enclosed by the PIFA 200A and the space outside, and components (not shown) with a height of up to 4.4 mm may be placed under the fourth section 20D, again bridging the space enclosed by the PIFA 200A and the space outside, without affecting the antenna radiating and reception performances.

[0037] It should be noted that the length of the ground plane of the PCB on which a PIFA 200A is positioned can have an effect the electromagnetic radio frequency (RF) performance of the PIFA 200A. Conventionally, a larger ground plane is directly correlated to better antenna efficiency. By enabling a PCB to have a larger ground plane, such that the ground plane can extend under and within the volume of the PIFA, the RF performance of the PIFA 200A can be improved. With reference to FIG. 7, simulated efficiencies of a stamped metal PIFA according to the first embodiment versus different ground plane sizes are shownthe range of sizes extend from 5.5 cm to 13.5 cm with the best results being obtained for sizes between 12.5-13.5 cm, although it will be seen that ground planes as short as 5.5 cm can provide acceptable results.

[0038] It will be appreciated that variants of the above described embodiment are possible. For example, it is not necessary that the base portion 20C extend beyond the fold line D-D to provide a support pin 80 which is subsequently bent in order to provide the required support when the PIFA 10 is positioned on a PCB. Instead, this support can be provided simply by the unbent end of the base portion resting directly on the PCB surface.

[0039] Referring now to FIG. 4, there is shown an unfolded PIFA 10 according to a second embodiment, while FIGS. 5-6 show the PIFA 300A in a folded state. By comparison to the embodiment of FIGS. 1-3, the differences between the two embodiments comprise: removing the base portion 20C of the embodiment of FIGS. 1-3 and providing instead a pair of legs 90, 100 depending from the fourth section 20D. Thus, these legs 90, 100 can support the PIFA 300A when located on a PCB.

[0040] Note that as in the background art, the expression PIFA is used in the present specification for an antenna providing equivalent antenna functionality to a flat PIFA, although the antenna comprises portions which are out of plane with one another.

[0041] While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby.