The present invention relates generally to the field of antenna and more particularly the miniature antennas utilized by all kinds of portable and mobile electronic devices to receive and transmit signals, typically in a range of frequencies currently up to around ten gigahertz (Ghz=109 Hertz), so they can communicate freely in a geographical area covered by a network called “cordless” or even “wireless”, a widely used expression having the same meaning.
The so called “wireless” communicating systems which are more and more used daily and often of quasi permanent manner by an always increasing user population, all have antennas for receiving and more often for transmitting signals in the frequency band defined by the standard technology that regulates them. It mainly concerns mobile phones, particularly those based on the standard called GSM, standing for “global system for mobile communications”, which defines a communication standard that has worldwide geographical coverage.
Another very widely used communicating system, which requires a very sensible receiving antenna is the GPS, standing for “global positioning system”. By decoding signals from satellite network, this system in fact makes it possible to obtain, all over the terrestrial globe, a very precise geographic positioning of the receiver. GPS receivers are more often found in the mobile phones and in all kinds of so-called “smart phones” that also include all the functions of a personal digital assistant (PDA) and the ability to connect to the worldwide network of the Internet.
The wireless network may instead be conceived to only cover a limited geographic area, or even very limited as the so-called standard “Bluetooth” which allows communication up to around ten meters of terminals between them. Another very widely used communication standard of bigger range is the one called “Wifi” which allows to create a wireless local network or LAN, standing for “local area network”, in a limited geographic zone, frequently visited by the public: a building, the premises of the government or of a company, a café etc.
In spite of their miniaturization needed to fit the dimensional constraints imposed by the always smaller housings, especially when the thickness becomes very small, the antennas of the above devices have to be nevertheless able to maintain a maximum efficiency throughout the frequency bands where they are operated. Such efficiency depends on losses which are inherent to the antenna and which are most commonly measured using parameters called “S”, “scattering parameters” that enables qualifying the behavior of the antenna between the propagating medium on the one hand and the electronic control circuit on the other hand. Generally speaking the parameters S have been conceived and used to measure and qualify the behavior of linear passive or active circuits operating in the frequency range mentioned above often referred to as hyper frequencies (microwaves) or radio frequencies in the technical literature of these matters. It allows estimating the electrical properties of these circuits such as their gain, the loss in yield where the voltage standing wave ratio resulting from an impedance mismatch observed between the control circuit and the antenna. The matching of the antenna is particularly defined by the parameter S11 representing the reflection loss of the antenna. It is expressed in decibels (dB). The lower the value of S11 is the better the matching and thus the overall efficiency of the antenna.
The parameter S11, which is frequency dependent, allows defining the bandwidth of the antenna, that is, the frequency band in which S11 remains less than a given threshold, which is typically defined at a level of −6 dB. Under these conditions, one quarter of the power delivered by the control electronic circuit is lost by reflection, and three quarters are thus usefully radiated by the antenna.
The bandwidth of an antenna can be more or less wide. It is often expressed in percentage of its central frequency. An antenna whose bandwidth is of a few percentages is considered to have a narrow operating band. This type of antenna is suitable for certain applications. For example, for a GPS receiver, an antenna whose bandwidth is of the order of 2% is sufficient.
An antenna whose bandwidth is equal or larger than 15% is considered to have a wide operating band. Those whose bandwidth are larger than or equal to 20% have a very wide bandwidth. It is to be noted here that to describe this type of antenna, the acronym of “UWB”, “ultra-wide band” is also often used.
The use of a very wide band antenna potentially offers many advantages. A single broadband antenna can thus simultaneously cover multiple radiofrequency standards. This reduces the number of antennas that has to be implanted in the multiservice wireless devices such as the smart phones, which not only gives an advantage in terms of cost but also makes it possible to overcome technical problems otherwise difficult to solve such as parasite couplings that may occur between the different antennas of the same smart phone.
Furthermore, the development of applications requiring to be able to download and transmit always larger quantity of data, notably the transmission of video signals, led the standardization bodies to define communication protocols offering wider and wider bandwidths. For example, in 2002 frequency bands ranging from 3.1 to 10.6 GHz to so-called UWB standard were allocated (in the form of six groups representing fourteen frequency bands, with 528 MHz of width each), for short-distance communications of WiFi type. The emergence of UWB-based communication applications is remarkable, which contributed to highlight the need for very wide band antenna solutions, which should be readily industrialized, inexpensive and easy to integrate.
However, the realization of broadband miniature antennas faces considerable theoretical and technical problems. It is particularly well known that obtaining small-sized antennas in view of the wavelengths to be transmitted can only be done at the price of dramatically reducing their bandwidth, which goes directly against the purpose.
It is therefore an object of the invention to provide a solution to this problem by reducing the size of the antenna intended to be implanted in the same housing while their control circuit can still maintain sufficiently wide bandwidth for operating.
Other objects, features and advantages of the present invention will appear when studying the following description and accompanying drawings. It is understood that other advantages may be incorporated.
The invention relates to an apparatus for transmitting and/or receiving radiofrequency signals comprising at least a broadband antenna and a substrate; the antenna comprising at least a first radiating surface and being superimposed on the ground plane, the ground plane being located on a first face of the substrate, at least a side tongue of power supply and at least a side wall connected to at least the first radiating surface. The antenna comprises at least a second radiating surface configured to be excited by coupling with the first radiating surface, the side wall is connected to a coupling trace located on a second face of the substrate, opposite to the first face of the substrate, and the side wall and the coupling trace being configured to act as a capacitive coupling between at least the first radiating surface, possibly the second radiating surface and the ground plane.
The invention also relates to a method for manufacturing an apparatus for transmitting and/or receiving radiofrequency signals comprising at least a broadband antenna and a substrate, the antenna comprising at least a first radiating surface and being superimposed on the ground plane, the ground plane being located on a first face of the substrate, comprising a step of forming the antenna, a step of installing the antenna on the substrate. The step of forming the antenna is advantageously performed so that the antenna comprises at least a second radiating surface configured to be excited by coupling with the first radiating surface. The step of installing the antenna is performed so that the side wall is connected to a coupling trace located on a second face of the substrate, opposite to the first face of the substrate, and the side wall and the coupling trace being configured to act as a capacitive coupling between at least the first radiating surface and the ground plane.
The antenna of the invention is designed to operate above a ground plane to allow high freedom of placement on the application card that uses it and avoid any additional constraint to its designer. The major difficulty is that the proximity of a ground plane may render the antenna resonant and inefficient, this difficulty is overcome by the described structure. Moreover, the cost of implementation of the antenna which comprises the materials used, its manufacture and assembly is still low compared to the overall cost of the radio frequency module that is used.
The antenna according to the present invention allows operation of the antenna broadband made possible by the coupling of several resonances.
The purpose, objects as well as the features and advantages of the invention will be made more evident in the detailed description of an embodiment thereof, which are demonstrated by the following accompanying drawings, wherein:
The accompanying drawings are given as examples and are not limitation of the invention.
Before starting to review the detailed embodiments of the invention, it is set below optional features that may be used following any combination or alternatively: The coupling trace 416 is configured to form a coupling capacitor whose value is εS/e where ε is the dielectric constant of the dielectric material constituting the substrate 410, S is the surface of the coupling trace 416 and e is the thickness between the coupling trace 416 located on the second face of the substrate 410 and the ground plane located on the first face of the substrate 410.
The concept of housing antenna or AIP, standing for “antenna in package”, includes all the solutions that allow implanting in the component: the radiofrequency chip for transmitting and receiving radiofrequency signals; the antenna and its matching network as well as other radiofrequency components. Typical examples of integrating an antenna within a same electronic module are shown in
The main advantages of the AIP solutions, in addition to saving significant surface compared to an external antenna, lies in the fact that the matching between the radiofrequency chip and its antenna is thus implemented once and for all even during the designing of the module by a highly qualified specialized staff. As shown in
It is to be noted and already here that in the solutions where extending the substrate 134 is performed to receive the antenna 111, the total surface of module 110 should then be increased by the occupied surface by the latter. However, the advantage is that the thickness 135 of the module, after coating in a layer called overmolding 132, can then stay more easily compatible with the constraints of thickness imposed by the manufacturers of communicating apparatus whose offer emphasizes on the products of tablet type which should be extremely thin to be commercially competitive.
However, due to the trend that has continued over decades which applies to all the components produced by the microelectronic industry to have to always reduce the size of these components, considerations have now to be given to overlay at least one antenna 111 and at least one radiofrequency chip 115 in order to obtain a supplementary reduction of horizontal dimensions while maintaining the efficiency in transmitting and receiving of the antenna. This is shown in
If UWB antennas which can be placed over a ground plane have been described in the specialized technical literature, they are yet not suitable. For example, in the publication “IEEE TRANSACTION ON ANTENNA AND PROPOGATION, VOL. 59, NO. 1”, published in January of 2011, the article entitled “Miniature Ceramic Dual-PIFA Antenna to Support Band Group 1 UWB Functionality in Mobile Handset” can be found. If the authors describe well an antenna whose performance is not significantly affected by the presence of other components located in proximity, it remains that the dimensions of this antenna is not at all compatible with the objectives of the invention. In particular, its thickness is six millimeters (mm), which is far too high while the desired thickness of the overall 220 including: the substrate 134, the overmolding area 132 of the antenna 111 and that of the radiofrequency components 230 of a communicating module 210 according to the invention, is advantageously in the order of millimeter and should not exceed two millimeters.
The same comment applies to another article describing an UWB antenna published in “International Journal of Antennas and Propagation, Volume 2012, Article ID 513829” with the title “Band-Notched Ultrawide Band Planar Inverted-F Antenna”. Again the thickness of the described antenna is far too high (4.5 mm) to meet the objectives of the invention.
The antenna described in the following drawings meets the objectives of the invention and is thus capable of transmitting and receiving signals in all the frequency range of UWB standard while maintaining reduced dimensions particularly in thickness.
As shown in
An example of such a substrate 410 is shown in
With regard to the antenna 310 shown in
Typically, the antenna 310 can be formed from a metallic plate (for example, a copper metal strip) in which cuttings are performed to obtain the appropriate shape 510 illustrated by
It should also be noted that numerous other means of embodiments as described above, commonly implemented by the microelectronic industry can also be well used to achieve the antenna according to the invention. It concerns particularly techniques well known by persons skilled in the art which are based on the use of chemical etchings or metallization of plastic housings.
Another possible embodiment which is not illustrated in the drawings involves etching the antenna 310 directly on the overmolding 610. In this option, the overmolding 610 is necessarily present. After being formed, it is covered of a metallic layer that is etched for example chemically (depositing, spraying), to create the different elements of the obtained antenna 310, for example from a metallic strip.
As shown in
In the following examples, the antenna 310 is optimized to operate in the 7-9 GHz band which corresponds to Group 6 of the UWB standard.
a and 11b illustrate a second step of the invention, which involves improving the matching and bringing closer the two resonances of the first radiating surface 318 in order to obtain a better coupling between the two modes of resonance. Here the invention applies a new approach, which involves replacing the electrical connection between the side wall 316 of the antenna 310 and the ground plane of the substrate 410 by a capacitive coupling 1010 with the latter. Thus the side wall 316 is connected in this case as already shown in
a and 13b illustrate a third step of the invention where a second resonator is installed in the form of a second radiating surface 312. Installed next to the first radiating surface 318, the second radiating surface 312 is excited by capacitive coupling with the first radiating surface 318. Preferably, the first radiating surface 318 and the second radiating surface 312 are connected at the level of the same side wall 316. The first and second radiating surfaces 318, 312 are advantageously free of vibration from each other in the three spatial directions. The side wall 316 is connected to a coupling trace 416 located on a second face of the substrate 410, opposite to the first face of the substrate 410, and the side wall 316 and the coupling trace 416 being configured to act as capacitive coupling between at the first radiating surface 318, the second radiating surface 312 and the ground plane.
According to one preferred embodiment, the first radiating surface 318 has a length dimension 820 larger than the length 1210 of the second radiating surface 312.
The dielectric materials used and that of the substrate 410 are also based on the use of standard materials in order to maintain a manufacturing cost as low as possible.
A study on the different adjustable parameters mentioned above thus allows obtaining an antenna 310 operating in the frequency band ranging from 7 to 9 GHz and integrated in an AIP module whose dimensions involved in this example being parallelepiped whose base is a square of side of 7 mm and of a thickness of 1.5 mm. Translated in wavelength of central frequency of the frequency band under consideration, that is to say 8 GHz, which corresponds to a wavelength λ in the vacuum of 37.5 mm, this specific example of an antenna 310 according to the invention has dimensions of the order of λ/5 with respect to horizontal dimensions (side of the square) and of λ/25 in height.
The present invention is not limited to the embodiments described above and but extends to any embodiments within its spirit.
Number | Date | Country | Kind |
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13 57782 | Aug 2013 | FR | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2014/066557 | 7/31/2014 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
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WO2015/018745 | 2/12/2015 | WO | A |
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Number | Date | Country | |
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20160172747 A1 | Jun 2016 | US |