EP1922783B1 - Compact multiband antenna - Google Patents

Description

The present invention relates to a compact multiband antenna, more particularly to a compact antenna that can be connected to a digital terrestrial television (DTT) receiver in DVB-H format (for Digital Video Broadcast Handheld in English), the receiver being able to be a portable device such as a PDA (for Personal Digital Assistant).

Nowadays, the reception on a PDA or similar portable device, DVB-H format is possible because of the computing power of the microprocessor that equips most of these devices. The DVB-H standard uses a new digital compression standard for video called H264 and recommends placing this new image format for mobile applications either in the UHF band (band between 470 and 870 MHz) or in the L band ( band around 1.5 GHz). On the other hand, the above portable terminals must also be able to communicate using a cellular network of GSM 900 type (for Global System for Mobile Communications 900 MHz in English). As a result, the UHF band covered must be limited by selective filtering at the 470-700 MHz band.

It has already been proposed, in particular in the patent US 6,870,513 , antenna modules of the dipole type arranged on the substrate of a printed circuit to operate with portable devices.

Antennas that can be used with this type of terminal must therefore be sufficiently compact and meet the constraints mentioned above.

Thus, the invention consists in proposing a compact multiband antenna in the form of an accessory for PDAs or mobile terminals which is broadband from the point of view of the DVB-H reception, multiband to access the L-band and filtering for the part GSM.

The subject of the present invention is therefore a compact multiband antenna, characterized in that it consists of a type element dipole comprising a first conducting arm connected to a second conductive arm having the form of a housing mounted on a ground plane, the first and second arms being supplied with differential and a second slot-like element formed in said ground plane in the extension of said second arm.

Preferably, to facilitate the use as an accessory of a portable terminal, the first and second arms are rotatably mounted relative to each other. Therefore, it is possible to fold the first arm on the second arm so as to obtain a compact object that can be easily stored in a pocket.

According to one embodiment of the present invention, the first conducting arm is planar with a triangular flared portion at the connection with the second arm, the triangular flared portion extending through a rectangular or square portion. The specific shape of the second arm provides broadband operation while maintaining a small footprint. As a result, the antenna is adapted to cover the UHF band.

On the other hand, the second conducting arm has the shape of a housing whose dimensions are adapted to receive an electronic card. Preferably, this electronic card is compatible with the DVB-H standard and it comprises at least the circuits for receiving the video stream and sending it to the mobile terminal or PDA.

According to another characteristic of the present invention, the dipole-type element is connected to an adaptation circuit. This adaptation circuit is optimized so as to maximize the transmission between the processing circuits of the video stream and the antenna. It is also dedicated to the lower part of the UHF band, namely the 470 MHz band at 700 MHz and performs an additional filtering function for the GSM band, namely around 900 MHz.

On the other hand, according to a preferred embodiment, the slot-type element comprises two U-shaped slots mounted upside down. These two resonant slots are made in the ground plane in extension the second conducting arm of the dipole element. The resonant slots are sized to achieve proper antenna matching in the L-band, ie between 1452 MHz and 1492 MHz for Europe and between 1670 MHz and 1675 MHz for the United States.

• Fig. 1 représente respectivement en A une vue de dessus et en B une vue en perspective d'une antenne multibande compacte conforme à la présente invention.
• Fig. 2 représente un mode de réalisation du circuit d'adaptation.
• Fig. 3 est une vue en plan schématique d'une carte électronique utilisée avec l'antenne de la présente invention.
• Fig. 4 représente une courbe donnant les pertes de transmission entre l'amplificateur prévu en entrée de la carte électronique et l'antenne.
• Fig. 5 est une courbe donnant le gain en fonction de la fréquence d'une antenne conforme à la présente invention.
• Fig. 6 est une courbe donnant le rendement en fonction de la fréquence de l'antenne de Fig. 1 avec les cellules d'adaptation.
• Fig. 7 est une courbe donnant l'adaptation d'une antenne conforme à l'antenne de la Fig. 1 jusqu'à 2 GHz chargé sur 50 ohms.
• Fig. 8 représente les diagrammes de rayonnement de l'antenne de figure 1, respectivement à 600 MHz et à 1600 MHz.

Other features and advantages of the present invention will appear on reading the following description of a preferred embodiment, this description being made with reference to the accompanying drawings in which:

• Fig. 1 represents in A respectively a view from above and in B a perspective view of a compact multiband antenna according to the present invention.
• Fig. 2 represents an embodiment of the matching circuit.
• Fig. 3 is a schematic plan view of an electronic card used with the antenna of the present invention.
• Fig. 4 represents a curve giving the transmission losses between the amplifier provided at the input of the electronic card and the antenna.
• Fig. 5 is a curve giving the gain as a function of the frequency of an antenna according to the present invention.
• Fig. 6 is a curve giving the performance as a function of the frequency of the antenna of Fig. 1 with the adaptation cells.
• Fig. 7 is a curve giving the adaptation of an antenna conforming to the antenna of the Fig. 1 up to 2 GHz charged on 50 ohms.
• Fig. 8 represents the radiation patterns of the antenna of figure 1 at 600 MHz and 1600 MHz, respectively.

To simplify the description in the figures, the same elements bear the same references.

We will first describe with reference to Figures 1A and 1B an embodiment of a compact multiband antenna according to the present invention.

As shown more particularly on the Figure 1B , the antenna consists of a dipole type element 1 and a slot-like element 2 The two functions are not placed next to each other but one in the other. The necessary large size of the ground plane is used to be effective in the UHF band, in order to integrate slots which make it possible to adapt the signal in L-band. The dipole-type element comprises a first arm 10 of shape planar with a substantially triangular flared portion 10a extending through a rectangular portion 10b. This shape was chosen for a minimal size, the flared portion of triangular shape to obtain the desired broadband operation.

As shown on the Figure 1A Part 10 is particularly compact with a total length of 35 mm and a width of 35 mm. This first arm 10 is connected at the end of the triangular flared portion by a connecting element 12 to the second arm 11 of the dipole. The second arm 11 has a volume form, more particularly the shape of a rectangular or square case extended by a planar portion in which the slots will be inserted. The first and second arms of the element 1 are made of a conductive material, namely metal or with a metallized material. As shown on the Figure 1A , the second arm 11 also has a volume portion whose length is 35 mm, the width of 35 mm and the thickness of 16 mm, plus a planar portion. The two arms 10 and 11 are rotatably mounted at the axis 12, so as to fold the arm 10 on the arm 11. for transport. The antenna is in use mode when the arm 10 is unfolded, as shown in FIG. figure 1 .

As shown on the figure 1 , the arm 11 is fixed on a ground plane 3. This ground plane can be, for example, constituted by a conductive material, namely metal or with a metallized material. On the other hand, as represented on the Figure 1B , the antenna comprises a slot-type element 2. More particularly, two U-shaped slots 20, 21 mounted upside down, are made on the metallized plane 3 in the extension of the arm 11. These U-shaped slots are resonant slots and allow to provide a correct adaptation, namely a value for S 11 less than -10 dB at the level of the antenna in the L-band, namely in the 1452 MHz to 1492 MHz band for Europe or the 1670 MHz band at 1675 MHz for the United States.

In accordance with the present invention and as shown on the Figure 1B , the second arm 11 in the form of a housing is dimensioned and made to be able to receive an electronic card 4 whose one end, namely the end protruding from the housing 11 on the Figure 1B can be inserted into a connector of a portable terminal such as a PDA or the like.

We will now describe with reference to the figure 2 , an exemplary embodiment of an adaptation circuit that maximizes the transmission between the antenna A and the LNA (Low Noise Amplifier in English), namely the low noise amplifier provided at the input of the processing circuits of the video stream received by the antenna. This matching circuit connects to the antenna at the connection point 12. It comprises, as shown in FIG. figure 2 , two capacitors C1, C11 connected in series between the point of connection to the antenna A and the input of the LNA and two inductors L1, L11 respectively connected between the entry point of the capacitor L1 and the ground for the inductor L1 and between the entry point of the capacity C11 and the mass for the self L11.

This adaptation circuit has been optimized to maximize the transmission between the LNA and the antenna at the bottom of the UHF band, namely between 470 MHz and 700 MHz, and to provide an additional filtering function for the GSM band around 900 MHz.

In the embodiment shown, the elements of the adaptation circuit have the following values: $$\mathrm{VS}1=2.22\mathrm{pF},\mathrm{VS}11=12.4\mathrm{pF},\mathrm{The}1=19.8\mathrm{nH\; and\; L}11=10.8\mathrm{nH}\mathrm{.}$$

We will now describe with reference to the figure 3 , an embodiment of an electronic card used in the context of the present invention and can be inserted in the housing formed by the arm 11 of the antenna. This electronic card 4 has a length of between 70 and 80 mm and a width of 35 mm to adapt to said housing. This electronic card therefore comprises an LNA 40 connected to the antenna output, possibly through the adaptation circuit described above. This circuit 40 is connected to a tuner 41 operating for the UHF bands and for the band L. The output of the tuner 41 is sent to a DVB-H demodulator 42. The output of the demodulator is sent to an SDIO interface circuit 43 (FIG. for Secure Digital Input / Output in English). This interface makes it possible to send the video stream to a portable terminal such as a PDA through a 44 SDIO connector.

An antenna with its adaptation circuit as described with reference to Figures 1 and 2 has been simulated. An ADS2004 circuit simulator was used to optimize the values and choice of the matching circuit to maximize transmission between the antenna and the LNA. An IE3D electromagnetic simulator was used to give the gain, efficiency and radiation curves as a function of frequency for the antenna associated with its adaptation circuit optimized on the previous software. The simulation gave the curves of Figures 4 to 7 as well as the radiation patterns of the figure 8 .

The curve of the figure 4 gives the variations as a function of the frequency of the transmission losses between the antenna and the LNA of the electronic circuit of the figure 3 . It can be seen that these losses are minimized and smoothed over the entire UHF band used with the DVB-H standard (ie between 470 MHz and 700 MHz). However, we see a significant loss around 900 MHz, which shows that the matching circuit performs a filtering function at this frequency.

The figure 5 represents the gain of the antenna as a function of frequency. This curve confirms a similar operation to a dipole in the UHF band (theoretically a dipole has a directivity of 2.17 dB) but more directional, in the band L. The gain curve approaches 5 dBi at 1.6 GHz, which is significant of a radiation pattern more directive. The directionality at 1.6 GHz can be explained by the fact of the networking of two radiating slots whose diagrams add up in a preferred direction.

The figure 6 represents the efficiency of the antenna system with an adaptation cell as described with reference to the figure 2 . In this case, an antenna efficiency better than 60% over the entire UHF band of the DVB-H standard and better than 90% in the entire L band of the DVB-H standard (EP and US) is obtained, but a yield lower than 20% in the GSM band around 900 MHz. This therefore reflects a filtering function in the GSM band.

The figure 7 represents the adaptation of the antenna up to 2 GHz, ie it gives the values of the parameters S 11 of the antenna and its adaptation circuit beyond 1 GHz when it is loaded on 50 ohms. Thus, an adaptation less than -10 dB is obtained in the L-band. This adaptation is due to the resonance of the slots 20, 21 whose dimensions have been optimized on the location in the ground plane over the length and the width of the slots. to cover both the European L-band 1452-1492 MHz and the L band US 1670-1675 MHz.

The figure 8 represents the 600 MHz and 1600 MHz radiation patterns of the figure 1 .

The 600 MHz form is typical of a dipole (torus) whose null axis corresponds to the longitudinal axis of the antenna.

The shape at 1.6 GHz is both the combination of the diagrams of the two slots as well as the asymmetry of the structure generated by the placement of the slots on the ground plane near a "canister".

Claims (8)

1. Compact multiband antenna, characterized in that it is constituted by a first dipole type element (1) comprising a first conductive arm (10) connected (12) to a second conductive arm (11) having the shape of a box mounted on a ground plane (3), the first and the second arms being supplied (12) differentially and a second element (2) of the slot type realized in said ground plane, in the extension of said second arm.
2. Antenna according to claim 1, characterized in that the first and the second arms are mounted in rotation with respect to each other.
3. Antenna according to one of claims 1 or 2, characterized in that the first arm (10) is of planar form with a tapered part (10a) at the level of the connection with the second arm, extending by a rectangular or square part (10b)
4. Antenna according to one of claims 1 to 2, characterized in that the box is dimensioned to receive an electronic card (4).
5. Antenna according to one of claims 1 to 4, characterized in that the dipole type element is connected to an impedance matching circuit.
6. Antenna according to claim 5, characterized in that the impedance matching circuit performs a filtering function.
7. Antenna according to one of the aforementioned claims, characterized in that the slot type element (2) comprises two U-shaped slots (20, 21) mounted head to tail.
8. Antenna according to one of the aforementioned claims, characterized in that it operates in the UHF band or L band with filtering of the GSM band.

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