Patent Application
20080278390
The present invention relates to the domain of radio-frequency (RF) communication equipment, and more precisely to a planar antenna assembly comprised in, or connected to, RF communication equipments, and in particular for ultra wideband (UWB) applications.
By “communication equipment” is meant here any equipment, mobile or not, adapted to receive and/or transmit RF signals to and/or from mobile (or cellular) and/or WLAN and/or broadcast and/or positioning networks, and notably a mobile phone (for instance a GSM/GPRS, UMTS or WiMax mobile phone), a personal digital assistant (PDA), a laptop, a PCMCIA card (giving an UWB functionality to a laptop or other equipment, such as a monitor or a printer), a USB dongle (for use in computers and their peripherals), a satellite positioning device (for instance a GPS one), a television receiver, or more generally an RF communication module.
As is known by the man skilled in the art, a (planar) notch antenna usually comprises a notch defined in a conductive plate (having a first side with a first length), and a feed line defined above the conductive plate and across the notch and arranged to be electromagnetically coupled to the notch to enable wideband operation. The notch has a first width and a first electrical length (which is equal to a quarter of a wavelength corresponding to a chosen frequency of a working frequency band) and comprises a straight part having an open end found in the first side, and a shortened end.
Because of the very small physical dimensions of the notch, the conductive plate in which it is defined can be a ground plane of a printed circuit board (PCB), mounted in a communication module or communication equipment and comprising generally electronic circuits. Examples of such an arrangement are described in the patent documents US 2002/0037739 and U.S. Pat. No. 6,424,300, and in the publication by S. I. Latif et al “Bandwidth Enhancement and Size Reduction of Microstrip Slot Antennas”, IEEE Transactions on Antennas and Propagation, Vol. 53, No. 3, March 2005, pp. 994-1003. In a variant, the conductive plate may also be part of a module mounted on a face of the PCB. An example of such an arrangement is described in the patent document US 2002/0177416.
Such (planar) notch antennas being easy to manufacture, they are used in (or with) low-cost (and low-profile) communication equipment, notably in aircraft, where the space is limited.
Because of their respective arrangements the notch antennas known in the art cannot offer a very wide working (or operating) frequency band, such as the one required in UWB OFDM (“Orthogonal Frequency Division Multiplex”), for instance, and/or consume too much space on the PCB in which they are defined. It is recalled that UWB OFDM (defined by the Multiband OFDM Association (MBOA)) requires that communication equipment or module works in several 528 MHz wide bands (for instance from 3168 MHz to 4752 MHz in case of three bands, or from 3168 MHz to 4752 MHz and from 6172 MHz to 8184 MHz in case of seven bands).
So the object of the present invention is to improve the situation.
For this purpose, it provides a planar antenna assembly, for an RF communication module (or communication equipment), comprising:
This planar antenna assembly is characterised in that:
The planar antenna assembly according to the invention may have additional characteristics considered separately or in combination, and in which notably:
In this case, the conductive plate of the module faces the first face of the substrate and comprises each notch, and each feed line is defined on an upper surface of the module M, opposite to the conductive plate and above and across the corresponding notch;
The invention also provides an RF communication module provided with a planar antenna assembly such as the one introduced above. Such an RF communication module may be incorporated in RF communication equipment.
The invention further provides RF communication equipment provided with a planar antenna assembly such as the one introduced above.
Other features and advantages of the invention will become apparent on examining the detailed specifications hereafter and the appended drawings, wherein:
The appended drawings may not only serve to complete the invention, but also to contribute to its definition, if need be. It is important to notice that the relative dimensions of the elements, defining in combination the planar antenna assembly in the
Reference is initially made to
In the following description it will be considered that the planar antenna assembly AA is intended for RF communication equipment such as a mobile phone, for instance a UMTS phone. But it is important to note that the invention is not limited to this type of RF communication equipment.
Indeed the invention may apply to any RF communication equipment or module, mobile or not, adapted to receive and/or transmit RF signals to and/or from mobile (or cellular) and/or WLAN and/or broadcast and/or positioning networks. So it could also be a personal digital assistant (PDA), a laptop, a satellite positioning device (for instance a GPS one), a dongle or a television receiver. It may apply to any single standard or multi-standard combination, and notably to a GSM/GPRS and/or UMTS/TD-SCDMA and/or WiMax and/or WLAN (e.g. 802.11a/b/g/n) and/or broadcast (e.g. DVB-H and DAB) and/or positioning (e.g. GPS) combination.
The invention may be notably used in the consumer equipment (or modules) and more especially in the wireless equipments (or modules) adapted to short range high data rate communications, such as the ones required for rapid file transfers and video transmission. Moreover, the invention may be provided in a UWB dongle, for instance of the USB type, intended for adding functionality to personal computers or any other devices with USB connectors.
As illustrated in
In the following description it will be considered that the conductive plate CP has a rectangular shape. But this is not mandatory.
In this case, the conductive plate CP has first and second parallel (linear) sides extending at least on a first length LP1 (parallel to the X direction), and third and fourth parallel sides extending on a second length LP2 (parallel to the Y direction) and perpendicular to the first and second sides.
A first notch N1 is defined in the conductive plate CP. This first notch N1 comprises at least a straight part having an open end OE1 which is found (or freely abuts) on the first side, and a shortened end SE1. In the example shown, the straight part is approximately parallel to the third and fourth sides (and therefore to the Y direction). But this is not mandatory. The first notch N1 has a first width LN1 (in the X direction) and a first electrical length LN2 (in the Y direction). In the example of embodiment illustrated in
It is recalled that the first electrical length LN2 may be different from the physical length LN2. This effectively depends on the dielectric environment of the first notch N1. In the case where the conductive plate CP (and then the first notch N1) is separated from the feed line FL1 by a dielectric substrate S, the first electrical length LN2 is larger than the physical length LN2.
The first feed line FL1 is defined above the conductive plate CP and across the first notch N1. As will be explained below, it is arranged to be capacitively coupled to the first notch N1 to enable a wideband operation. It may be a 50Ω microstrip. The first feed line FL1 is fed through a port terminal PT, which is connected to a 50Ω excitation probe EP (for instance a coaxial cable), as illustrated in
The conductive plate CP may be the ground plane of a printed circuit board (PCB) P, as illustrated in
According to the invention, the planar antenna assembly AA must present at least the following combination of technical characteristics:
The frequency f which corresponds to the wavelength λ may be for instance the center frequency of the working (or operating) frequency band. But this is not mandatory.
The length of the first notch N1, equal to a quarter wavelength λ/4, induces a first resonance (i.e. high intensity currents) around the first notch N1, and more precisely from one of its sides to the other one. There is also a second resonance associated with currents across the conductive plate CP in the direction of the first length LP1, because the latter is equal to half the chosen wavelength λ/2. Thus the notch feed line FL1 is coupled both to the (first) notch resonance and to the (second) resonance across the conductive plate CP, which causes the radiation.
For efficient radiation, the currents associated with the notch resonance should extend away from the first notch N1. However, the opposing conducting sides of the slot line forming the first notch N1 give rise to a capacitance across the slot. This capacitance tends to attract the currents around the first notch N1. Consequently, the narrower the first notch N1, the larger its capacitance per unit length, and therefore the greater the concentration of current in the immediate vicinity of the first notch N1. Hence with a narrower first notch N1, the notch radiates less but has a higher radiation quality factor. For high radiation quality factor notches, the radiation and hence the bandwidth can be improved by a small increase of the first width LN1 of the first notch N1.
The width of the operating frequency band is optimized when the open end OE1 of the first notch N1 is found approximately in the middle of the first side.
In an advantageous embodiment, the first width LN1 of the first notch N1 is chosen smaller than 3 millimeters, and preferably smaller than or equal to 2 millimeters (≦2 mm). This allows to minimize the area which is occupied by the first notch N1 on the PCB P.
As mentioned before, the value of the first electrical length LN2 depends whether a dielectric substrate S is inserted or not between the first notch N1 and the first feed line FL1. Three cases can be envisaged.
The first case is illustrated in
The second case is illustrated in
In the first and second cases, the first feed line FL1 is “suspended” across the hole H.
The third case is illustrated in
If the dielectric loading of the first notch N1 is increased, the ratio of the electrical length to the physical length is increased. Therefore, for a fixed center frequency of the operating band, increasing the dielectric loading results in a shorter first physical length LN2 of the first notch N1 and a smaller width of the operating frequency band. When the dielectric loading of the first notch N1 is decreased, its first physical length LN2 must be increased, and the bandwidth increases.
For instance, to get a resonance around 4 GHz when the substrate has been cut out (or removed), as exemplified by the antenna impedance response curve plotted on a Smith chart forming kinks and loops across a frequency band that includes 4 GHz (such as the one illustrated in
When the space is limited, which is often the case on a PCB P, the first physical length LN2 of the first notch N1 must be reduced. So, to compensate for the width reduction of the operating frequency band while matching the first feed line FL1 to 50Ω, it is preferable to extend the first feed line FL1 with a series capacitor CA, as illustrated in
For instance, when the substrate has been fully cut out (or removed) and in order to match an antenna to 50Ω across a wide bandwidth that includes 3 GHz, one may use:
A Smith chart of this example of embodiment is illustrated in
When the space in the Y direction is limited, it is possible to use a first notch N1 with an “L” shape instead of a straight notch. The L shape forces much of the currents to take a longer path and to spread further on the conductive plate CP. This situation is schematically illustrated in
In this case, the folded first notch N1 comprises a first part N1a, which extends in the Y direction and comprises the open end OE1, and a second part N1b, which extends in the X direction and comprises the shortened end SE1.
For instance, to get a resonance around 3 GHz when the substrate has not been cut out (or removed), one may use:
A (planar) notch antenna assembly AA with a single (first) notch N1 can cover approximately a 2:1 bandwidth (it is recalled that an n:m bandwidth refers to the ratio of the upper frequency n of the band to the lower frequency m of this band). So, in order to cover the whole 3:1 bandwidth, for instance of a 3.1 GHz to 10.6 GHz FCC specified UWB band, the planar antenna assembly AA must comprise at least first N1 and second N2 notches electromagnetically coupled to first FL1 and second FL2 feed lines, respectively. This situation is schematically illustrated in
In this case the first and second sides have a full length LP1 (in the X direction). A second notch N2 is defined in the conductive plate CP. It comprises a straight part which is parallel to the straight part of the first notch N1. This second notch N2 has a second electrical length LN22 which is smaller than the first electrical length LN12 of the first notch N1 and a second width LN21 which is smaller than the first width LN11 of the first notch N1.
The first notch N1 shares its active space with the second notch N2 and acts as a demarcation of one edge of half-wavelength across the planar antenna assembly AA (and for instance across the PCB P) for the second notch N2. This results in a very compact structure. For instance, the first notch N1 may cover the sub 5 GHz frequencies (3.1 GHz to 5 GHz) while the second notch N2 may cover the frequencies beyond 6 GHz (6 GHz to 10.6 GHz).
The planar antenna assembly AA must be as follows:
In an advantageous embodiment, the first width LN11 of the first notch N1 is smaller than 3 millimeters and preferably smaller than or equal to 2 millimeters (≦2 mm). This allows to minimise the area which is occupied by the first N1 and second N2 notches on the PCB.
The second width LN12 of the second notch N2 can be smaller than the first width LN11 of the first notch N1. But this is not mandatory.
The first FL1 and second FL2 feed lines are defined above the conductive plate CP and across the first N1 and second N2 notches, respectively. Each feed line FL1 or FL2 is arranged to be coupled to the corresponding notch N1 or N2 to enable an ultra wideband operation. They may be 50Ω microstrips. The first FL1 and second FL2 feed lines are fed through first PT1 and second PT2 port terminals respectively, which are connected to 50Ω excitation probes (not shown).
In the example of embodiment illustrated in
As mentioned before, with reference to
For instance, when the substrate has been removed (or cut out), one can use:
The excitation probes (EP) can be fed by separate transceivers. In this case, a first transceiver covers the lower operating frequency band (for instance from 3.1 GHz to 5 GHz) and is connected to the first feed line FL1 coupled to the (longer) first notch N1, and a second transceiver covers the upper operating frequency band (for instance from 6 GHz to 10.6 GHz) and is connected to the second feed line FL2 coupled to the (shorter) second notch N2.
Alternatively, the excitation probes (EP) can be fed by a single UWB transceiver. In this case a diplexer can be used to simultaneously connect the transceiver to the (longer) first notch N1, for instance for 3.1 GHz to 5 GHz operation, and to the (shorter) second notch N2, for instance for 6 GHz to 10.6 GHz operation.
It is important to note that more than two notches (for instance three or even four) can be defined in the ground plane CP in order to still increase the operating (or working) frequency band. For instance a third notch is parallel to the first N1 and second N2 notches, has an open end which is present approximately in the middle of the part of the first side which is located on the left side of the second notch N2 (i.e. at +/−15%), has a (third) electrical length equal to a quarter of a third wavelength (λ3/4) which corresponds to the center frequency (f3) of an upper operating (or working) frequency band, and may have a (third) width smaller than the second width LN12 of the second notch N2 (but this is not mandatory).
Moreover, it is also possible to use a “demarcation” notch without any feed line such that it only acts as a demarcation of one edge of half-wavelength across the planar antenna assembly AA (and for instance across the PCB P) for another notch coupled to a feed line (according to the invention, such as the first notch N1) and having an open end found approximately in the middle of the half of a side which is located either on the right or left of the demarcation notch without any feed line. In this case the first length LP1 is the length defined between the demarcation notch and the edge of the planar antenna assembly M.
In the above described examples of embodiment, each notch is defined in the ground plane CP of a PCB P. But this is not mandatory. Indeed, the planar antenna assembly AA may comprise a module M mounted on a face of a substrate S (which may be the one of a PCB P) and comprising a conductive plate MCP suspended above this face and parallel to it and in which each notch N1 (or N1 and N2) is defined.
In the case where the module M is mounted on a face of a PCB P, this face is preferably the first (rear) face of the substrate S (on which is mounted the ground plane CP), as illustrated in
A module of this type is notably described in the patent document US 2002/0177416 cited above. So the way it is mounted on the possible PCB and the way it is arranged will not be described here.
Such a module M can comprise one or more straight or L-shaped notches N1, such as the one above described with reference to
The invention is not limited to the embodiments of planar antenna assembly AA and RF communication equipment or module described above, only as examples, but it encompasses all alternative embodiments which may be considered by one skilled in the art to be within the scope of the claims hereafter.
It must be understood that all wavelength dimensions given in the claims must be interpreted in the way of a skilled man's use, commonly taking into account various parameters, which does not disturb the magnitude of them.
In the present specification and claims the word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. Further, the word “comprising” does not exclude the presence of other elements or steps than those listed.
The inclusion of reference signs in parentheses in the claims is intended to aid understanding and is not intended to be limiting.
| Number | Date | Country | Kind |
|---|---|---|---|
| 06300004.6 | Jan 2006 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB06/55018 | 12/22/2006 | WO | 00 | 7/29/2008 |
