EP2022141B1 - Compact portable antenna for terrestrial digital television - Google Patents

Abstract

The present invention relates to a compact portable antenna formed of a first element of dipole type operating in a first frequency band and comprising a first and at least one second (21) conducting arm, which are fed (3) in differential mode, the first arm or cold arm forming at least one hood for an electronic card and the second arm or hot arm consisting of a U-shaped conducting element (21) made on an insulating substrate. Moreover, a radiating element (4) with meanders (41) is made between the branches of the U-shaped element and it is dimensioned so as to operate in a second frequency band.

Description

The present invention relates to a portable compact antenna, more particularly an antenna for receiving television signals, in particular the reception of digital signals, on a portable electronic device such as a laptop, a PDA (personal assistant) or any other similar device requiring an antenna to receive electromagnetic signals.

There are currently on the market accessories, equipment to receive signals for digital terrestrial television (DTT) directly on his laptop. The reception of digital terrestrial television signals on a portable computer makes it possible to benefit from the calculation power of said computer for the decoding of a digital image, in particular to decode a stream of compressed digital images in the MPEG2 or MPEG4 format. Most often, these devices are sold in the form of a housing with two interfaces, namely a terrestrial RF interface (Radio Frequencies) for connection to an indoor or outdoor VHF-UHF antenna and a USB interface for connection to the computer.

Devices currently on the market generally consist of an independent antenna such as a whip or loop type antenna mounted on a housing carrying a USB connector.

The Applicant has proposed in the French patent application No. 05 51009 filed on April 20, 2005 , a compact broadband antenna covering the entire UHF band, consisting of a dipole type antenna. This antenna is associated with an electronic card that can connect to a portable device using, for example a USB type connector.

More specifically, the antenna described in the French patent application No. 05 51009 , comprises a first and a second differential-powered conductor arm, one of the arms, said first arm, forming at least one cover for an electronic card. More specifically, the first arm has the form of a housing in which is inserted the electronic card comprising the processing circuits of the signals received by the dipole type antenna. These circuits are most often connected to a USB type connector for connection to a laptop or other similar device. The embodiments described in this patent application refer to fully conductive arms.

According to a first aspect of the present invention, this relates to a portable compact antenna formed of a first dipole-type element operating in a first frequency band and comprising a first and at least a second conductor arm, supplied with a differential, the first arm, called cold arm, forming at least one cover for an electronic card, the second arm, said hot arm, being constituted by a conductive U-shaped member formed on an insulating substrate.

On the other hand, the solution proposed in the above French patent application covers the entire UHF band. However, in order to ensure the widest possible commercial coverage with a product of this type, it is important to be able to receive, in addition to the UHF band (470-862 MHz), at least the VHF-III band (174-225 ... 230 MHz) in which some countries, such as Germany or Italy, continue to broadcast digital multiplexes.

According to a second aspect, the present invention therefore relates to a compact portable antenna of the type described above to meet this demand.

The antenna according to the invention is a compact portable antenna formed of a first dipole-type element operating in a first frequency band and comprising a first and at least a second conductor arm, supplied with differential, the first arm, called cold arm, forming at least one cover for an electronic card whose second arm said hot arm, is constituted by a U-shaped element, made on an insulating substrate. To obtain operation in a second frequency band, such as the VHF band, preferably VHF-III, the second arm comprises a second radiating element sized to operate in a second frequency band, the second radiating element being formed on the insulating substrate between the branches of the U-shaped element.

According to one embodiment, the second element is constituted by a conductive element bent in meanders, the length of the element being determined by k * λ2 / 2-L1 where λ2 is the wavelength at the central frequency of the second frequency band, k a positive integer corresponding to a harmonic of the second frequency band and L1 the length of the cold arm of the antenna.

Preferably, the conductive element is formed by a ribbon whose width is between 0.2 mm and 2 mm and whose thickness is greater than the skin thickness of the conductive material, the thickness of the ribbon being greater than or equal to 20 μm.

To minimize the interactions between the first and the second frequency band, the spacing between the second radiating element and each branch of the U-shaped element is greater than or equal to 0.2 mm.

To improve the performance of the second radiating element, the spacing between the meanders is greater than or equal to 0.2 mm, the meanders being parallel to the branches of the element U or perpendicular to said branches. In fact, the meander arrangement is optimized to maximize the radiation efficiency of the antenna in the first frequency band while at the least disturbing the operation of the antenna in the second frequency band.

According to a preferred embodiment of the present invention, the first frequency band is the UHF band and the second frequency band is the VHF band, preferably the VHF-III band.

• FIG. 1 est une vue en perspective schématique d'une antenne telle que décrite dans la demande de brevet français n° 05 51009 au nom de la demanderesse.
• FIG. 2 est une vue en perspective schématique d'un autre mode de réalisation d'une antenne telle que celle de la figure 1 selon un premier aspect de la présente invention.
• FIG. 3 est une vue en perspective schématique d'un premier mode de réalisation d'une antenne conforme à la présente invention et fonctionnant en bandes UHF et VHF.
• FIG. 4 est une vue en plan de dessus du bras chaud de l'antenne de figure 3.
• FIG. 5 est une vue schématique d'un circuit d'adaptation utilisé en sortie d'antenne.
• FIG. 6 représente les courbes d'adaptation de l'antenne des figures 3 et 4 obtenues à l'aide de deux logiciels de simulation.
• FIG. 7 représente les courbes d'efficacité et de gain obtenues en simulant une antenne conforme aux figures 3 et 4.
• FIG. 8 représente les diagrammes de rayonnement respectivement dans les bandes UHF et VHF obtenus par simulation d'une antenne conforme aux figures 3 et 4.
• FIG. 9 représente schématiquement deux variantes de réalisation du bras chaud avec les courbes d'efficacité correspondantes.
• FIG. 10 est une vue en perspective schématique d'un second mode de réalisation d'une antenne conforme à la présente invention et fonctionnant en bandes UHF et VHF.
• FIG. 11 est une vue en plan de dessus du bras chaud de l'antenne de figure 10.
• FIG. 12 est une vue schématique d'un circuit d'adaptation utilisé avec l'antenne de figure 10.
• FIG. 13 représente les courbes d'adaptation de l'antenne des figures 10 et 11 simulée à l'aide de deux logiciels de simulation.
• FIG. 14 représente les courbes d'efficacité et de gain obtenues en simulant une antenne conforme aux figures 10 et 11.
• FIG. 15 représente les diagrammes de rayonnement respectivement dans les bandes UHF et VHF obtenus par simulation d'une antenne conforme aux figures 10 et 11.
• FIG. 16 représente une antenne à diversité dont les bras chauds peuvent être réalisés conformément à la présente invention.
• FIG. 17 est une représentation schématique d'une carte électronique utilisée avec les antennes conformes à la présente invention.

Other characteristics and advantages of the present invention will appear on reading the description of various embodiments, this description being made with reference to the attached drawings in which:

• FIG. 1 is a schematic perspective view of an antenna as described in French patent application no. 05 51009 in the name of the plaintiff.
• FIG. 2 is a schematic perspective view of another embodiment of an antenna such as that of the figure 1 according to a first aspect of the present invention.
• FIG. 3 is a schematic perspective view of a first embodiment of an antenna according to the present invention and operating in UHF and VHF bands.
• FIG. 4 is a top plan view of the warm arm of the antenna of figure 3 .
• FIG. 5 is a schematic view of an adaptation circuit used at the antenna output.
• FIG. 6 represents the antenna adaptation curves of the Figures 3 and 4 obtained using two simulation software.
• FIG. 7 represents the efficiency and gain curves obtained by simulating an antenna in accordance with Figures 3 and 4 .
• FIG. 8 represents the radiation patterns respectively in the UHF and VHF bands obtained by simulation of an antenna in accordance with Figures 3 and 4 .
• FIG. 9 schematically represents two embodiments of the hot arm with the corresponding efficiency curves.
• FIG. 10 is a schematic perspective view of a second embodiment of an antenna according to the present invention and operating in UHF and VHF bands.
• FIG. 11 is a top plan view of the warm arm of the antenna of figure 10 .
• FIG. 12 is a schematic view of an adaptation circuit used with the antenna of figure 10 .
• FIG. 13 represents the antenna adaptation curves of the figures 10 and 11 simulated using two simulation software.
• FIG. 14 represents the efficiency and gain curves obtained by simulating an antenna in accordance with figures 10 and 11 .
• FIG. 15 represents the radiation patterns respectively in the UHF and VHF bands obtained by simulation of an antenna in accordance with figures 10 and 11 .
• FIG. 16 represents a diversity antenna whose hot arms can be made in accordance with the present invention.
• FIG. 17 is a schematic representation of an electronic card used with the antennas according to the present invention.

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

We will first describe with reference to the figure 1 , an embodiment of a dipole type antenna, usable for the reception of digital terrestrial television on a laptop or similar device, as described in French patent application no. 05 51009 filed in the name of the plaintiff.

As shown on the figure 1 this dipole antenna comprises a first conducting arm 1 also called a cold arm and a second conducting arm 2 also called a hot arm, the two arms being connected to one another via a hinge zone 3 located at one end of each of the arms.

More specifically, the arm 1 has substantially the shape of a housing for receiving in particular an electronic card, an embodiment of which will be described later. The housing has a portion 1a of substantially rectangular shape, extending by a curved portion 1b gradually flaring so that the energy is radiated gradually, which promotes adaptation to a wider frequency band. The length L1 of the arm 1 is substantially equal to λ1 / 4 where λ1 represents the wavelength at the central operating frequency. Thus, the length L1 of the arm 1 is close to 112 mm for operation in the UHF band (frequency band between 470 and 862 MHz).

As shown on the figure 1 , the antenna comprises a second arm 2 rotatably mounted around the axis 3 which also represents the point of connection of the antenna to the signal processing circuit, namely to the not shown electronic card inserted in the housing formed by the arm 1. The electrical connection of the antenna is made by a metal wire, for example a coaxial cable or the like, while the axis of rotation 3 is made of a material relatively transparent to electromagnetic waves.

As shown on the figure 1 , the articulable arm 2 about the axis 3 has a length L1 substantially equal to λ1 / 4. The arm 2 also has a curved profile followed by a flat rectangular part for folding it completely against the arm 1 in the closed position. The arm 2 being rotatably mounted at 3 with respect to the arm 1, this makes it possible to modify the orientation of the arm 2 so as to optimize the reception of the television signal.

We will now describe with reference to the figure 2 , another embodiment of a dipole type antenna as described in French patent application no. 05 51009 .

As shown on the figure 1 , the antenna comprises a first arm 1 said cold arm having the shape of a housing and a second arm, said hot arm, connected to the arm 1 by a hinge 3. In this case, the hot arm is constituted by an element U 21 of conductive material, made on an insulating substrate. According to a non-limiting embodiment, the substrate consists of a material known under the name "KAPTON" covered with a copper layer which is etched to produce the U-shaped element.

As described above, the cold arm and the hot arm each have a length L1 substantially equal to λ1 / 4 where λ1 represents the wavelength at the central operating frequency. Thus, each branch of U 21 has a length substantially equal to λ1 / 4.

As clearly represented on the figure 2 , the U-shaped element is connected at the joint 3, by an electrical connection element such as a metal wire, to an electronic card not shown, inserted inside the cold arm 1 forming a housing. So the antenna of the figure 2 is sized to operate in the UHF band.

To ensure the widest possible commercial coverage, it is interesting that an antenna of the type described with reference to the figure 2 may receive, in addition to the UHF frequency band, the VHF frequency band, more particularly the VHF-III frequency band (174-225 ... 230 MHz) in which certain countries such as Germany or Italy continue to broadcast digital multiplexes.

Thus, on the Figures 3 and 4 , there is shown a first embodiment of an antenna according to the present invention, able to operate both in the UHF band and in the VHF band, as will be explained in more detail below.

As shown on the figure 3 , the antenna according to the present invention comprises a first arm 1 or cold arm having, as the arm 1 of the antenna of the figure 2 , the shape of a housing that can receive an electronic card. The arm 1 is extended by a second arm also called hot arm, rotatably connected to the arm 1 via an axis 3.

This hot arm is made as the hot arm of the antenna shown in the figure 2 . It comprises on an insulating substrate 20, a metallization 21 in the shape of a U. On the other hand, the connection to the signal processing circuit, and more particularly to the electronic card inserted into the arm 1, is carried out at the level of the axis 3.

According to the second aspect of the present invention and as shown in the figure 2 on the substrate 20 is formed a second radiating element 4 sized to operate in a second frequency band, more particularly in the VHF band. This second radiating element is made in the form of a metallized element on the insulating substrate between the branches of the U-shaped element.

As shown in more detail on the figure 4 , the element 4 is constituted by a conductive element 41 folded into meanders. The total length of the conductive element 41 is determined by the value k * λ2 / 2-L1 where λ2 is the wavelength at the center frequency of the second frequency band, namely the VHF band in the embodiment represented, k is a positive integer representing a harmonic of the second frequency band and L1 is the length of the arm 1.

According to one embodiment of the present invention, the different elements forming the arm 2 are obtained by etching on a "KAPTON" substrate covered with a copper layer having a thickness greater than the skin thickness of the conductive material, U-shaped element 21 and the meandering conductive element or ribbon 41 with a width W between the U-shaped element 21 and the meandering conductive element 41 greater than or equal to a critical width of 0.2 mm, as will be explained later.

The U-shaped element 21 has a width of about 2 mm while the meandering conductive element 41 has a width I of between 0.2 mm and 2 mm, with a spacing between two meanders greater than or equal to 0.2 mm.

In fact, the length of the meandering conductor element is chosen to obtain a resonance frequency close to the upper frequency of the VHF band, more particularly of the VHF-III band. It is chosen to resonate either on the first harmonic of this frequency or on the higher harmonics according to the possible space of implementation. The arrangement of the meanders, namely their shape and width, is optimized to maximize the radiation yield of the antenna in the VHF band while at the least disturbing the operation of the antenna in the UHF band.

• L'espacement g entre 2 méandres = 0.25 mm

We will now give the results of a simulation carried out on an antenna as represented in Figures 3 and 4 with the following dimensions for the hot arm of the antenna, namely:

• The spacing g between 2 meanders = 0.25 mm

The width 1 of the conductive element or ribbon 41 is between 0.2 mm and 0.83 mm.

The thickness of the ribbon is greater than or equal to 20 μm.

The width W between the radiating element 4 and the branches 21 of the U-shaped element is of the order of 4.5 mm.

The width of the branches 21 of the U-shaped element is equal to 1.54 mm.

The simulation was performed by connecting an antenna as shown in Figures 3 and 4 on a load impedance of 75 ohms with a matching circuit as shown in FIG. figure 5 . This matching circuit is therefore constituted between the antenna output A at the axis 3 and the load 75 ohms by a parallel circuit consisting of a self-inductance L1 of 100 nH and a capacitance C1 of 3.2 pF value, followed by two capacitors C11 and C12 connected in series between the ground and a connection point p to the parallel circuit L1-C1. These two capacities C11, C12 have a value of 1.2 pF. Between the point p and a point p 'is connected in series a self L11 of value 38 nH. A second inductor L12 of value 202 nH is connected between the point p 'and the ground, the point p' being connected to the load.

The response of the antenna connected to the adaptation circuit described above was simulated using two different software packages, namely the Modua IE3D software and the ADS2004A software which serves, in particular, to optimize the adaptation network. of the antenna.

With these two programs, the adaptation curves S11 as a function of the frequency, represented on the figure 6 .

So the results of the figure 6 show that the adaptation of the antenna is relatively good (-6 dB on average) over the entire UHF band with losses of less than 1.5 dB.

On the other hand, on the figure 7 , the curves giving the antenna efficiency and the gain as a function of the frequency of the antenna of the figure 4 .

As a consequence, with the performances obtained on the adaptation, the yield respectively the gain of the antenna with its adaptation network is at most 15% / - 5 dBi for the VHF part and at least 50% / - 1dBi for the UHF part. So we get good performance given the size of the whole.

On the figure 8 , the radiation patterns are shown respectively in the UHF band and in the VHF band of the antenna of the Figures 3 and 4 . From the diagrams obtained, it can be seen that, for the central frequencies of the UHF (650 MHz) and VHF (195 MHz) bands, the radiation patterns are almost omnidirectional and confirm an operation of the antenna in these two bands.

The first embodiment described above was made with a relatively large spacing between the second radiating element 4 and the branches of the U forming the hot arm of the dipole. A study was carried out to determine the conditions necessary to implement to minimize the possible interaction between the UHF band and the VHF band, in particular in the lower part of the UHF band.

As shown on the upper part of the figure 9 when the spacing between the branches of the element of the hot arm U and the second radiating element is small, a strong interaction is observed, as demonstrated by the yield curve as a function of the frequency associated with this figure. On the contrary, when the spacing between the second element and the branches of the U-shaped element of the hot arm is greater, a weak interaction is observed, as represented by the yield curve as a function of the frequency associated with this figure. The optimization of the spacing between the branches of the U-shaped element and the meandering element will take into account the technological constraints of implementation and the need to insert the second element between the branches of the U-shaped element.

We will now describe with reference to figures 10 and 11 , a second embodiment of an antenna according to the present invention. As shown on the figure 10 , this antenna comprises a first arm or cold arm 1 identical to the cold arm of the embodiment of the figures 2 and 3 . This first arm is articulated at an axis 3 with a second arm 20 or hot arm having on an insulating substrate, a first U-shaped radiating element 21 for operating in the UHF band and a second radiating element 50 formed between the legs 21 of the U-shaped element and sized to operate in the VHF band.

As shown more precisely on the figure 11 , the second radiating element is constituted by a meandering folded conductor element comprising a part 50 formed of meanders parallel to the branches 21 of the U-shaped element and extending towards the connection at the axis 3 by meanders 51 perpendicular to the branches of the element U 21. In this case, the meanders 50 have a width of 2 mm and a spacing between meanders equal to 0.2 mm while the meanders 51 have a width of 0.2 mm and a spacing between meanders of 0.2 mm. In this case, the total length of the meanders is chosen to satisfy the equation k * λ2 / 2-L1 with L1 the length of the first arm, λ2 the wavelength at the operating frequency in the second frequency band and k chosen to work, for example, on harmonic 2 for meander resonance. The value of k can be changed.

• Pour la partie UHF, la longueur des branches du U ainsi que la longueur du bras froid 1 sont de l'ordre de λ1/4 à la fréquence centrale de la bande UHF (666 MHz).

In fact it is possible to modify the shape of the meanders if one respects the rules of conception hereafter:

• For the UHF part, the length of the branches of the U as well as the length of the cold arm 1 are of the order of λ1 / 4 at the central frequency of the UHF band (666 MHz).

For the VHF part, the total length of the meanders plus the length L1 of the cold arm 1 is of the order of λ2 at 230 MHz (in the case of operation on the harmonic 2). The minimum widths and spaces are related to the technological choice of the realization. In the case of a flexible substrate such as KAPTON, for meanders parallel to the branches of the U-shaped element, namely the longitudinal meanders, the selected width is of the order of 0.83 mm and the space between the meanders is of the order of 250 microns.

The results obtained will now be obtained by simulating an antenna as represented on the figures 10 and 11 . The simulation was carried out by connecting the antenna through an adaptation circuit such as represented at figure 12 on a load impedance of 75 ohms. The matching circuit shown in FIG. figure 12 is thus schematically constituted by a capacitor C1 of 5.54 pF and a self-inductance L1 of 73.3 nH connected in parallel, a capacitor C2 mounted between the input point 2 of the parallel LC circuit and a ground, this capacitor C2 having a value of 1 pF and an inductor L2 connected in series between the point 2 and the point 1 of input of the antenna, this self L2 having a value of 30.7 nH and a self L3 mounted between the point 1 of input of the antenna and the mass, this self L3 having a value of 186.8 nH. With the circuit as described above, the simulation obtained using two different software packages IE3D MODUA and ADS 2004A gives the adaptation curves as a function of the frequency represented in FIG. figure 13 . On the figure 13 , we see that the adaptation of the antenna is relatively good (-6dB on average) over the entire UHF band with losses less than 1.5 dB.

Similarly, on the figure 14 , the performance curves as a function of frequency and gain as a function of the frequency obtained by simulation of the antenna of the figures 10 and 11 .

Consequently, with the performances obtained on the adaptation, the efficiency or gain of the antenna with its adaptation network is at the most 10% / - 7 dBi for the VHF part and at least 50% / - 1.5dBi for the UHF part. So we get good - performance given the size of the whole.

On the other hand, on the figure 15 , the radiation patterns obtained with the antenna of the figures 10 and 11 respectively in the UHF band at 666 MHz and in the VHF band at 200 MHz. Thus conventional dipole-type radiation patterns are obtained for the center frequencies of the UHF and VHF bands.

We will describe briefly with reference to figure 16 the application of the present invention to a diversity antenna. In this case, the cold arm 100 is made identically to the cold arm of the figures 2 , 3 and 10 . The present invention comprises at least two hot arms 201 and 202 respectively connected by hinge pins 301 and 302 to the cold arm 100. two axes 301 and 302 are at each end of the same end of the cold arm 100. The two hot arms 201 and 202 can be made as hot arms shown on the figures 4 and 11 . This type of antenna makes it possible to obtain diversity by minimizing the reception losses due to the fading of the signal, in particular in the case of the reception of digital terrestrial television or TNT.

We will describe on the other hand with reference to the figure 17 , an example of an electronic card that can be used with an antenna according to the present invention. This electronic card is intended to fit into the housing containing the cold arm as a cover or as a housing element. As a result, the card has a length of between 70-80 mm and a width of between 15-25 mm. This electronic card 1000 comprises a low-noise amplifier LNA 1001 to which the coaxial cable of the antenna is connected at the joint 3. The LNA 1001 is connected to an integrated tuner 1002 processing both the VHF band and the band UHF. The tuner 1002 is connected to a demodulator 1003 whose output is connected to a USB interface 1004, itself connected to a USB connector 1005. It is therefore possible with this system to connect the antenna to the USB input of a laptop or other display element, which can receive especially digital terrestrial television on a computer, a PDA or any other portable device.

It is obvious to those skilled in the art that the embodiments described above are given for illustrative purposes and may be modified, particularly with regard to the shape and layout of the meanders which simply have to meet the length criteria. , width and spacing given above.

Claims (11)

1. - Portable compact antenna formed from a first dipole type element operating in a first frequency band and comprising a first (1,100) and at least one second (20, 21; 201,202) conductive arms, differentially supplied, the first arm, referred to as cold arm, forming at least one cover for an electronic card, characterized in that the second arm, referred to as hot arm, is constituted by a U-shaped conductive element (21), realized on an insulating substrate.
2. - Antenna according to claim 1, characterized in that each branch of the U-shaped element (21) has a length determined by λ1/4 where λ1 is the wavelength at the central frequency of the first frequency band.
3. - Antenna according to one of claims 1 or 2, characterized in that the second arm comprises a second radiating element (4; 50,51) dimensioned to operate in a second frequency band, the second radiating element being realised on an insulating substrate between the branches of the U-shaped element.
4. - Antenna according to claim 3, characterized in that the second element is constituted by a conductive element (41; 50,51) folded into bends, the length of the element being determined by k*λ2/2-L1 where λ2 is the wavelength at the central frequency of the second frequency band, k is a positive integer corresponding to a harmonic of the second frequency band and L1 is the length of the cold arm.
5. - Antenna according to claim 4, characterized in that the conductive element is formed by a strip whose width is comprised between 0.2 mm and 2 mm and whose thickness is greater than the skin thickness of the conductive material.
6. - Antenna according to claim 5, characterized in that the thickness of the strip is greater than or equal to 20 µm.
7. - Antenna according to one of claims 3 to 6, characterized in that the spacing between the second radiating element and each branch of the U-shaped element is greater than or equal to 0.2 mm.
8. - Antenna according to one of claims 4 to 7, characterized in that the spacing between the bends is greater than or equal to 0.2 mm.
9. - Antenna according to one of claims 4 to 8, characterized in that the bends are parallel to the branches of the U-shaped element.
10. . Antenna according to one of claims 4 to 8, characterized in that the bends are perpendicular to the branches of the U-shaped element.
11. . Antenna according to one of claims 4 to 8, characterized in that a first part of the bends is parallel to the branches of the U-shaped element and a second part of the bends is perpendicular to the branches of the U-shaped element.

Images