EP1241733A1 - PIFA antenna with slots - Google Patents

Abstract

The chip antenna (1) has a conductor chip (2) with two sinusoidal slots. There is a short circuit connection (6) to the earth plane. The antenna has a radiating diagram between 1950 and 2100 MHz and has a bandwidth above 20 per cent.

Description

The invention relates to antennas produced using the patch technique. Such an antenna is typically used in a spectral range including the radio frequencies and microwaves and more specifically in bands GSM, DCS, PCS and UMTS.

Most antennas have a resonant frequency band. In transmission, when the antennas are excited in this frequency band by a power line, they maintain electromagnetic waves stationary. These standing waves are then coupled to waves electromagnetic radiation in space. In reception, the waves take the same shapes but travel in the opposite direction. Different antennas of this type are known in the state of the art.

It is known to use microstrips on a plane as an antenna for transmit signals. There are conductive pads on the upper side of a dielectric substrate and a conductive layer is placed on the underside of the substrate. This conductive layer then serves as an electrical ground plane. The substrate typically has a flat rectangular shape and constant thickness.

A multi-band antenna is also described in document FR-A-2 772 518. This antenna comprises a flat patch placed on the surface top of a dielectric substrate. A layer of mass is placed on the lower surface of the dielectric substrate. This antenna is of the quarter wave type because a short circuit conductor, disposed on a wafer of the dielectric substrate, connects the pellet to the mass layer. This antenna has conductors connection allowing the transmission of signals between the antenna and a device signal processing.

A publication presented at the Davos AP 2000 conference by Ollikainen, Kivekäs, Toropainen and Vainikainen, reports on a multi-band antenna. This antenna comprises three pellets placed on the upper surface of a substrate in Styrofoam (registered trademark). A mass layer is placed on the surface bottom of the dielectric substrate. A first patch intended for the low band is attached to a second patch intended for the upper band. These two lozenges thus form a first bi-band element having a zigzag shape and comprising a diet. This dual-band element has a short circuit in the form of a junction with the ground layer. A third patch is positioned next to the second patch to obtain a double resonance in the upper band, with a expanded bandwidth. The third patch has a short circuit in the form of junction with mass.

The document Novel meandered planar inverted F-antenna for triple frequency operation published in Microwave and optical technology letters page 58, volume 27 N ° 1 of October 5, 2000, describes a multi-band antenna. This antenna presents three pastilles placed in the same plane as a mass, following a pattern "meandering". These three lozenges contain a single feed.

Document US-A-4,766,440 describes an antenna having two half-wave resonances. This antenna includes a rectangular patch, in which the resonance paths are established respectively in the width and the length of the patch. A U-shaped slot is made in the patch and does not reach the edges of this patch. The tablet is connected to a device for coupling, provided with means for transforming impedance. This transformation impedance makes it possible to adapt the coupling device to the different frequencies of resonance used.

Document US-A-4 771291 describes an antenna having a patch. This patch has punctual short circuits and straight slots in the tablet and not reaching the edges of this tablet.

PCT application on behalf of the applicant, not published on the filing date of the present application and presenting the deposit number FR001586, describes a antenna having a conductive patch with a ground, a connection supply, a short-circuit connection connecting the pad to ground and a slot winding made in the conductive pad.

The document IEEE Antennas and propagation society international digest symposium, Newprt Beach, June 18-23 1995, pages 2124-2127 Boarg et al "Dual Band Cavity-Backed Quarter-wave patch antenna" describes an antenna having quarter wave resonances. A first resonance is defined by the dimensions and characteristics of the pellet and the substrate. A second resonance is obtained by using an adaptation system.

These antennas have drawbacks. On the one hand, they require large flat pads, incompatible with reduced dimensions cases of mobile communication devices. On the other hand, these antennas require the mounting of capacitive loads to widen the bandwidth which increases the cost and complexity of the antenna. In addition, these antennas have a reduced bandwidth, especially in the frequency band dedicated to UMTS.

These antennas are more expensive and have a low efficiency transmission or reception. These antennas also do not allow adjustment easily resonant frequencies and bandwidths of these frequencies.

There is therefore a need for an antenna which resolves these different problems.

The invention thus relates to an antenna comprising a conductive patch having two sinuous slots, a mass, a short-circuit connection, connecting the patch to ground, a supply link connected to the patch, the antenna having a radiation diagram comprising a primary resonance band including frequencies between 1950MHz and 2100MHz and of width greater than 20%.

Alternatively, the radiation pattern has a band of secondary resonance including frequencies between 890MHz and 950MHz and wide greater than 10%.

According to another variant, the tablet has a shape that is substantially polygonal.

According to another variant, the slots open on the same edge of the pellet.

According to yet another variant, the short-circuit link is connected to the patch by the edge on which the slots open or by an adjacent edge.

According to a variant, the supply link is connected to the patch by the edge on which the slots open or by an adjacent edge.

According to another variant, the supply link and the short-circuit link are arranged on either side of at least one of the slots.

According to yet another variant, a slot has a length contour different from the length of the contour of the other slot.

The invention also relates to an antenna in which the difference in length between the contour of the slots is between 5 and 30%.

According to a variant, the mass is a conductive surface parallel to the surface of the pellet.

According to yet another variant, the distance between the slots is between 5 and 15mm.

According to yet another variant, the patch is formed from a sheet metallic.

According to another variant, the slots have substantially the same shape and the same orientation.

According to yet another variant, the slots have substantially the same shape and a opposite orientation.

The invention also relates to a radiocommunication device. comprising an antenna according to the invention and having a thickness less than 20mm, a length less than 120mm and a width less than 50mm.

• figure 1, une vue en perspective d'une antenne selon un premier mode de réalisation de l'invention;
• figure 2, une vue de dessus d'une variante d'antenne;
• figure 3, une vue de dessus des dispositions possibles des liaisons de court-circuit et d'alimentation;
• figure 4, une représentation schématique de motifs de fentes;
• figure 5, une représentation schématique d'un motif de fente préférentiel;
• figure 6, une vue de dessus d'un exemple d'antenne détaillé;
• figure 7, une vue de côté de l'antenne de la figure 6;
• figure 8, un diagramme de spectre des fréquences de réflexion de l'antenne des figures 6 et 7.

Other characteristics and advantages of the invention will appear on reading the following description of embodiments of the invention, given by way of example and with reference to the appended drawings which show:

• Figure 1, a perspective view of an antenna according to a first embodiment of the invention;
• Figure 2, a top view of an alternative antenna;
• Figure 3, a top view of the possible arrangements of the short-circuit and supply links;
• Figure 4, a schematic representation of slot patterns;
• Figure 5, a schematic representation of a preferred slot pattern;
• FIG. 6, a top view of an example of a detailed antenna;
• Figure 7, a side view of the antenna of Figure 6;
• Figure 8, a spectrum diagram of the antenna reflection frequencies of Figures 6 and 7.

The invention provides an antenna in which there are two slots sinuous coupled on a conductive pad. The antenna presents a diagram of radiation with a resonance band of width greater than 20%. This resonance band typically covers several frequency bands of transmission, for example DCS, PCS and UMTS.

The following antenna will be described in its operation as a transmitter, in which it transforms an electric current into an electromagnetic field. he It will be clear to those skilled in the art that the operation of the antenna in receiver is similar, an electromagnetic field being transformed into current electric by antenna.

In the following description, to determine the percentage width of a resonant frequency band, the cutoff frequencies are determined at - 6dB on the antenna reflection coefficient measurement curve. We determine the resonant frequency range by subtracting the cutoff frequency lower than the upper cutoff frequency. We then determine the frequency center of the resonance band. This frequency is the median frequency between cutoff frequencies. The percentage width of the frequency band resonance is the ratio of the resonant frequency range to the frequency center of the band, multiplied by 100.

Figure 1 shows a perspective view of an antenna according to a mode for carrying out the invention. The antenna 1 has a conductive patch 2, in which a first slot 3 and a second slot 4 are made. The pastille conductive has a supply link 5 and a short circuit link 6 connected to a ground 7. A substrate 8 is interposed between the patch and the ground 7. The supply link 5 is connected to a device for generating and processing signals 9, which sends a signal in the form of electric current.

The patch preferably has a substantially polygonal shape. The tablet shown has a rectangular shape but the invention is of course not limited to this type of shape.

The antenna of this embodiment has a frequency band of resonance which will be called secondary thereafter. It also presents a resonance frequency band which will be called primary and which will be detailed later in the description. The secondary resonance band is obtained by coupling of the slots 3 and 4. The slots 3 and 4 open on the same edge 25 of the pellet. As shown in Figure 2, the slots define a middle part 10, a first end or tail 11 and a second end or tail 12 in the tablet. These three parts are connected by an edge 26 of the patch. The pastille 2 is supplied by the supply link 5. The supply link 5 is disposed on the first end 11, on the edge 25 on which the slots 3 and 4. The short-circuit link 6 is arranged on the second end 12, on edge 25. The supply of the patch generates a first electric current starting from the supply link 5, bypassing the slot 3 and returning through the part median 10 towards edge 25. Passing through median part 10, the current electric generates an electromagnetic coupling. This electromagnetic coupling excites slot 4. A second electric current is then generated. This second electric current leaves short-circuit link 6, bypasses slot 4 and returns by the middle part 10 towards the edge 25. The first and second stream electric are therefore added in the middle part 10.

Electric currents generate strong electromagnetic radiation at level of zones 21, 22 and 23, shown in phantom in Figure 2. The radiation has two resonant frequencies, defined respectively by the dimensions of slots 3 and 4. The wavelength of the electromagnetic field corresponding to the resonance of each slit is defined by the length of the contour from this slot. These resonances are of the quarter wave type, because the short circuit link 6 between the patch 2 and the ground 7 imposes an electric field node. So, the length of the electrical path is of the order of λ / 4, λ being the wavelength in the air or the vacuum. The conductive pad being short-circuited by means of short-circuit connection 6, the dimensions of the antenna can thus be reduced for a given resonant frequency. The short-circuit link 6 has preferably an impedance low enough to impose this field node electric.

The secondary frequency band is thus formed of two resonances strongly coupled, generated respectively by the first and second slots. The resonant frequencies are not superimposed and are close enough to generate an extended resonant frequency band. It is therefore desirable that the slots have a slightly different length contour one of the other. The difference in length of the contours is preferably between 5 and 30%. The resonant frequencies are thus distinct so as not to be superimposed and close enough to widen the resonant frequency band. of the appropriate dimensions of the patch and the contour of the slots allow generating a secondary frequency band including the GSM band and / or the E-GSM band and more particularly the frequencies between 890 and 950 MHz. The band thus formed has a width greater than 10%. In addition, the efficiency in this band is greater than 70%.

The speed of propagation of electric currents is close to the speed light. Thus, the circulation of currents appears approximately as if the chip was supplied by the supply link 5 and by the short-circuit link 6. The path of electric currents is similar to the path in a structure which would present two isolated pellets but close enough to each other and having each a slot and a feed link.

Primary resonant frequency band also uses coupling slots 3 and 4. An electric current is generated and passes through the first end 11 from the supply link to edge 26. This electric current generates a induced current which crosses the middle part from edge 25 to edge 26. This last electric current also generates an induced current which crosses the second end from short-circuit connection to edge 26.

Electric currents are concentrated on edge 26 and generate a strong electromagnetic radiation in zone 24 shown in dotted lines in the figure 2. The radiation thus has at least two defined resonance frequencies mainly by the dimensions of the patch. The length of the patch is here the determining parameter of the wavelength of resonance frequencies. These resonances are also of the quarter wave type due to the short circuit connection 6 between the patch 2 and the ground 7. Thus, the length of the electrical path is the order of λ / 4.

The primary frequency band is thus formed of at least two coupled resonances. These resonances are also influenced by the geometry and the length of the outline of the slots. Resonant frequencies in this band are higher than in the secondary band because the path of the electric current is here lower. The resonant frequencies are not superimposed and are close enough to generate an extended resonant frequency band. he is also desirable for this frequency band that the slots have a contour of slightly different length from each other. Dimensions the patch and the contour of the slots generate a strip primary frequency including UMTS band and PCS band, and more especially the frequencies between 1950 and 2100MHz. The band thus formed has a width greater than 20%. In addition, the efficiency in this band is greater than 70%.

The short-circuit link 6 and the supply link 5 are preferably arranged on the same edge of the conductive patch. In this case, the coupling of resonance modes is improved. This gives an enlarged bandwidth. In general, the supply link and the short-circuit link are preferably arranged on edge 25 or on an adjacent edge, as is shown in Figure 3. The short circuit connection is thus preferably placed in zone 27. The supply link is preferably placed in zone 28. The orientation of the outline of the slots can of course be opposite to that shown, with a similar position of the short-circuit link and the link Power.

By modifying the relative position of the supply link relative to the short-circuit connection, the resonant frequencies as well as the levels of adaptation. For this, we place links 5 and 6 in locations chosen appropriately. To improve gain and facilitate the manufacture of the antenna, it is also preferable to have the supply link and / or the short circuit connection on the edges of the patch. By arranging for example the connection feed on one edge of the patch, the level of adaptation is improved. We then obtains a better antenna and thus a reduced reflection coefficient, more particularly in the primary resonance frequency band.

The supply link and the short circuit link are preferably located on either side of one of the slots. By both sides, we mean that line drawn between the supply link and the short-circuit link crosses a slot.

According to a variant, it is also possible to couple the resonance frequencies slits to increase the amplitude of the electromagnetic field emitted. We use for this, slots having an extremely close contour length.

Furthermore, these slots preferably have a sinuous shape, moving away from the line segment, in order to present an outline of increased length. A sinuous contour allows to deform the path of the electric current. Figure 4 shows examples of the shape of suitable sinuous slots. The shape of the slots can for example be close to a V, a U, an arc of a circle or a rectangle not closing. Thus, for a given slot contour length, we can use slots that occupy less space in the conductive pad. The antenna dimensions can thus be reduced. The slots have preferably a contour of similar shape.

It is preferable to use slots of sinuous shapes composed of straight segments. This type of shape facilitates manufacturing because of the simplicity of their contour. Tuning the antenna frequencies is also made easier.

FIG. 5 shows a particular form of sinuous slot making it possible to significantly reduce the dimensions of the patch and the antenna. This slot is composed of straight segments wound in a spiral. This type of slot reduces about 20% the dimensions of the antenna compared to a slot antenna in V shape.

The relative orientation of the contours of the slots makes it possible to modify the antenna characteristics. So when the slots have contours of same orientation as shown in Figures 1 to 3, the width of the strip of coupling frequency is increased. The same orientation of the contours allows to add the electric current in the middle part 10. This electric current is greater and then generates an increased induced current around the slot 4. On then obtains radiation of increased amplitude and expanded bandwidth. When the contours of the slits have opposite orientations, the radiation emitted has better symmetry at the expense of bandwidth and the amplitude of radiation.

By modifying the distance between the slots, the coupling between them is modified. Thus, by increasing the distance between the slots we reduce the coupling but we increases the width of the bandwidths. The distance between the slots is preferably greater than 5mm. By distance between the slots is meant the distance between two respective points of each slot, the closest. The enlargement of the resonant frequency band is particularly sensitive for the primary resonant frequency. When increasing the distance between the slots beyond 15 mm, the resonant frequencies become distinct and not coupled, and no longer form a resonance band.

It is possible to produce the mass 7 in the form of a metal plate. It is in this case desirable to use a mass 7 formed of a conductive surface flat, parallel to the conductive pad 2. Such a mass makes it possible to limit the radiation power intercepted by the user of the device. In the mode of embodiment shown in Figure 1, the mass 7 and the conductive pad 2 are separated by a substrate 8.

The substrate 8 is preferably of constant thickness. A thickness of substrate is preferably chosen which allows the frequencies to be tuned and the bandwidths to be widened. By increasing the thickness of the substrate, the resonant frequency bands can be widened. The thickness of the substrate 8 is limited by the dimensions of the radiocommunication device. In order to allow the use of a ground return tab, for example, a substrate 8 is preferably used, one edge of which is at the same level or recessed with respect to an edge of the conductive patch 2. The mounting of the antenna is thus simplified. To improve the gain, it is also desirable to produce such a substrate with a material whose relative permittivity is close to that of air, preferably less than 2. We will also preferably choose a material having a very low dissipation factor and more particularly a dissipation factor of less than 10 ^-3 . It is thus possible to produce the substrate 8 in polymethacrylimide foam or a laminate based on fluoro-polymer such as PTFE. Such foam also provides good mechanical strength.

The supply link 5 is coupled to a transmitter or a signal processing 9 by a connection line 14. This can be done connection for example using a coaxial cable. In this case we can use for example the inner conductor of the coaxial cable to connect the patch to the member treatment. The outer conductor of the coaxial cable in this case connects ground 7 to the processing organ. In order to avoid parasitic reflections of the signals between the power link and transmitter for example it's best to have a uniform impedance along the connection line. For this, it is useful that the supply link 5 is formed by a tab extending from the patch and is extending to form the connecting line. It is possible to perform the supply link in the form of a tab made in the conductive patch.

It is preferable to use a processing member capable of operating at predetermined working frequencies close to the useful resonant frequencies of the antenna, for example working frequencies included in bands passers-by centered on the resonance frequencies. We can use a composite processing, which has several elements, each of these elements being permanently tuned to working frequencies. We can also use a processing device with a tunable element on the different working frequencies.

Furthermore, to have an optimal gain, i.e. a ratio between the signal strength radiated by the antenna and signal strength transmitted by the transmitter, it is desirable that the input impedance presented by the antenna is equal to the output impedance of the transmitter or signal processing device 9. Preferably, this impedance is fixed at 50 ohms to obtain losses minimum.

The connection 6 is preferably formed by a conductive tab extending on a wafer of the substrate 8. In this case it is also possible to carry out the short-circuit connection in the form of a protruding tab from the conductive pad.

In addition, the conductive pad may also have a tab at the level of the short-circuit part of the patch. There is a tab for this. protruding on an edge of the short-circuit part. This tab is preferably in alignment with the conductive pad. The sagging of this tongue allows the resonant frequencies of the antenna to be modified This tab allows also to broaden the resonance bandwidths of the antenna. This tab may have a length of 10mm for a width of 6mm. This tab is preferably located on one of the ends or tails of the patch.

Figures 6 and 7 show an antenna according to the invention. This antenna has the following dimensions: a = 35mm b = 42mm c = 10mm d = 3mm e = 3.5mm f = 3.6mm g = 5.4mm h = 7mm i = 23,2mm j = 3mm k = 8.6mm l = 10,6mm m = 26.5mm n = 3mm o = 6mm.

The tablet has a thickness of 100 µm and is made of copper.

The supply link is a tab with a width of 1mm. The link short circuit is a 3mm wide tab. The slot has a width of 1mm. The substrate is a polymethacrylimide foam having a clearance of 1mm on 3 of its faces. The ground is a 44mm by 110mm PCB.

FIG. 8 represents a spectrum of the reflection frequencies at input, measured on the antenna of FIGS. 6 and 7. A weak reflection of the antenna at a given frequency corresponds to a resonance of the antenna. Two frequencies are complementary to form a secondary resonance frequency band widened B1 between 1020MHz and 1260MHz. The central frequency is 1145 MHz; The bandwidth is thus 21% for this band. Resonance frequencies are also complementary to form a resonant frequency band primary B2 extended between 2005MHz and 2740MHz. The center frequency is worth 2350MHz. The width of this strip is approximately 30%. Using appropriate antenna settings described above, you can easily adapt the frequency bands to cover GSM, DCS, PCS and UMTS. The placement of the antenna in the case of a mobile phone generally lowers the frequency center of the resonant frequency bands, keeping a width of constant percentage band. The frequency bands are thus just offset. The presence of a battery, a headset, a microphone, electronic components or the support card also changes the value of the center frequency of a resonant frequency band. So, by placing this antenna in the housing of a standard telephone, we obtain frequency bands B1 and B2 including the E-GSM and DCS-PCS-UMTS bands respectively. The E-GSM band has a width of 8.7%. The band from DCS to UMTS presents a 25% width. The characteristics of the antenna are thus amply sufficient to cover these bands.

The invention further relates to a radiocommunication device. comprising an antenna as described above. The antenna can be arranged inside a protective housing of the device.

The invention also relates to a method of manufacturing an antenna. Such a manufacturing process includes a step of cutting two slots sinuous in a metallic sheet.

According to a variant, this method comprises a step of cutting a short circuit tab. According to another variant, the method comprises a step for cutting a supply link. According to yet another variant, the method includes a step of cutting an electrical connection over part of the width metal sheet.

Of course, the present invention is not limited to the examples and modes described and represented, but it is likely to be numerous variants accessible to those skilled in the art.

Thus, even if a planar conductive pad has been described until now, it is also possible to use a curved conductive pad to fit the shape a mobile phone case for example. You can also use a tablet conductor of a shape different from the rectangle presented, such as a shaped pellet disc. It is still possible to fold the power and short circuit tabs if applicable.

Claims (15)

Antenna (1) comprising: a conductive pad (2) having two sinuous slots; a mass (7); a short-circuit link (6), connecting the patch to ground; a supply link (5) connected to the patch; the antenna having a radiation diagram comprising a primary resonance band including the frequencies between 1950 MHz and 2100 MHz and of width greater than 20%. The antenna of claim 1, characterized in that the radiation pattern has a secondary resonance band including the frequencies between 890MHz and 950MHz and of width greater than 10%. The antenna of claim 1 or 2, characterized in that the patch has a substantially polygonal shape. The antenna of claim 3, characterized in that the slots open on the same edge of the patch. The antenna of claim 4, characterized in that the short-circuit connection is connected to the patch by the edge on which the slots open or by an adjacent edge. The antenna of claim 4 or 5, characterized in that the feed link is connected to the patch by the edge on which the slots open or by an adjacent edge. The antenna of claims 5 and 6, characterized in that the supply link and the short-circuit link are arranged on either side of at least one of the slots. The antenna of one of the preceding claims, characterized in that a slot has a contour of length different from the length of the contour of the other slot. The antenna of claim 8, characterized in that the difference in length between the contour of the slots is between 5 and 30%. The antenna of one of the preceding claims, characterized in that the mass is a conductive surface parallel to the surface of the patch. The antenna of one of the preceding claims, characterized in that the distance between the slots is between 5 and 15mm. The antenna of one of the preceding claims, characterized in that the patch is formed from a metal sheet. The antenna of one of the preceding claims, characterized in that the slots have substantially the same shape and the same orientation. The antenna of one of claims 1 to 12, characterized in that the slots have substantially the same shape and an opposite orientation. Radiocommunication device comprising an antenna according to one of the preceding claims, characterized in that it has a thickness of less than 20mm, a length of less than 120mm and a width of less than 50mm.

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