Patent Application
20180053999
The invention relates to antenna arrangements having a plurality of frequency modes in the VHF, UHF, S, C, X or higher frequency bands. More precisely, an antenna arrangement according to the invention may be designed and tuned in a simple manner to transmit/receive (T/R) radiofrequency signals at a plurality of frequencies, notably in the microwave or VHF/UHF domains, with compact form factors.
Terminals or smartphones on board aircraft, ships, trains, trucks, cars, or carried by pedestrians need to be connected while on the move. These devices need short and very long range communication capabilities for voice and data at a high-throughput and a low power budget, including to watch or listen to multimedia content (video or audio), or participate in interactive games. All kinds of objects on-board vehicles or located in a manufacturing plant, an office, a warehouse, a storage facility, retail establishments, hospitals, sporting venues, or a home are connected to the Internet of Things (IoT): tags to locate and identify objects in an inventory or to keep people in or out of a restricted area; devices to monitor physical activity or health parameters of their users; sensors to capture environmental parameters (concentration of pollutants; hygrometry; wind speed, etc.); actuators to remotely control and command all kinds of appliances, or more generally, any type of electronic device that could be part of a command, control, communication and intelligence system, the system being for instance programmed to capture/process signals/data, transmit the same to another electronic device, or a server, process the data using processing logic implementing artificial intelligence or knowledge based reasoning and return information or activate commands to be implemented by actuators.
RF communications are more versatile than fixed-line communications for connecting these types of objects or platforms. As a consequence, radiofrequency T/R modules are and will be more and more pervasive in professional and consumer applications. A plurality of T/R modules may be implemented on the same device. By way of example, a smartphone typically includes a cellular communications T/R module, a Wi-Fi/Bluetooth T/R module, a receiver of satellite positioning signals (from a Global Navigation Satellite System or GNSS). WiFi, Bluetooth and 3 or 4G cellular communications are in the 2,5 GHz frequency band (S-band). GNSS receivers typically operate in the 1,5 GHz frequency band (L-band). RadioFrequency IDentification (RFID) tags operate in the 900 MHz frequency band (UHF) or lower. Near Field Communication (NFC) tags operate in the 13 MHz frequency band (HF) at a very short distance (about 10 cm).
It seems that a good compromise for IoT connections lies in VHF or UHF bands (30-300 MHz and 300 MHz to 3 GHz) to get sufficient available bandwidth and range, a good resilience to multipath reflections as well as a low-power budget.
A problem to be solved for the design of T/R modules at these frequency bands is to have antennas which are compact enough to fit in the form factor of a connected object. A traditional omnidirectional antenna of a monopole type, adapted for VHF bands, has a length between 25 cm and 2,5 m (λ/4). A solution to this problem is notably provided by PCT application published under n° WO2015007746, which has the same inventor and is co-assigned to the applicant of this application. This application discloses an antenna arrangement of a bung type, where a plurality of antenna elements are combined so that the ratio between the largest dimension of the arrangement and the wavelength may be much lower than a tenth of a wavelength, even lower than a twentieth or, in some embodiments than a fiftieth of a wavelength. To achieve such a result, the antenna element which controls the fundamental mode of the antenna is wound up in a 3D form factor, such as, for example, a helicoid so that its outside dimensions are reduced relative to its length.
But there is also a need for the connected devices to be compatible with terminals which communicate using WiFi or Bluetooth frequency bands and protocols. In this use case, some stages of the T/R module have to be compatible with both VHF and S bands. If a GNSS receiver is added, a T/R capacity in L band is also needed. This means that the antenna arrangements of such devices should be able to communicate simultaneously or successively in different frequency bands. Adding as many antennas as frequency bands is costly in terms of form factor, power budget and materials. This creates another challenging problem for the design of the antenna. Some solutions are disclosed for base station antennas by PCT applications published under n° WO200122528 and WO200334544. But these solutions do not operate in VHF bands and do not provide arrangements which would be compact enough in these bands.
It is therefore an object of the invention to provide an antenna arrangement that is compact enough to fit in a small form factor and that can operate, for example, from VHF bands up to the S or C bands.
The invention fulfils this need by providing an antenna arrangement comprising an antenna element tuned to a lower frequency of a fundamental mode and additional elements whose position, form factor, dimension and orientation are determined to optimize the conditions of reception of selected harmonics of this fundamental mode.
According to one of its aspects, the invention discloses an antenna arrangement comprising: a first conductive element configured to radiate above a defined frequency of electromagnetic radiation; one or more additional conductive elements located at or near one or more positions defined as a function of positions of nodes of current of electromagnetic radiation of selected harmonics of the electromagnetic radiation.
Advantageously, a distance of the one or more positions in relation to the positions of nodes is defined based on an influence of said one or more additional conductive elements on values of the radiated frequencies of the electromagnetic radiation.
Advantageously, frequency shifts imparted by the additional conductive elements define a set of predefined radiation frequencies for the antenna arrangement.
Advantageously, one or more of a number, a first dimension, a form factor, or an orientation of the one or more additional conductive elements are defined based on a desired impact on a frequency shift of one or more of a fundamental mode or a higher order mode of electromagnetic radiation.
Advantageously, the one or more of a number, a first dimension, a form factor, or an orientation of the one or more additional conductive elements are further defined as a function of a desired impact on one or more of an antenna arrangement impedance, an antenna arrangement matching level or a bandwidth of the electromagnetic radiation.
Advantageously, the first conductive element is a metallic ribbon and/or a metallic wire.
Advantageously, the first conductive element has one of a 2D or 3D compact form factor.
Advantageously, the antenna arrangement of the invention is deposited by a metallization process on a non-conductive substrate layered with one of a polymer, a ceramic or a paper substrate.
Advantageously, the antenna arrangement of the invention is tuned to radiate in two or more frequency bands, comprising one or more of an ISM band, a WIFi band, a Bluetooth band, a 3G band, an LTE band and a 5G band.
Advantageously, the first conductive element is a monopole or a dipole antenna.
The invention also provides a design method of such an antenna arrangement.
According to another of its aspects, the invention also discloses a method of designing an antenna arrangement comprising: defining a geometry of a first conductive element to radiate above a defined frequency of electromagnetic radiation; locating one or more additional conductive elements at or near one or more positions defined as a function of positions of nodes of current of electromagnetic radiation of selected harmonics of the electromagnetic radiation.
Advantageously, locating the one or more additional conductive elements at or near one or more the defined positions is performed by starting from a fundamental mode and iterating in increasing order of the harmonics.
Advantageously, locating the one or more additional conductive elements at or near one or more the defined positions is performed based on a map of one or more of hot areas, tepid areas or cold areas by selecting positions which impact the less on modes which have already been tuned.
Advantageously, the method of the invention further comprises defining one or more of a number, a first dimension, a form factor, or an orientation of the one or more additional conductive elements based on a desired impact on a frequency shift of one or more of a fundamental mode or a higher order mode of electromagnetic radiation.
Advantageously, defining one or more of a number, a first dimension, a form factor, or an orientation of the one or more additional conductive elements is further based on a desired impact on one or more of an antenna arrangement impedance, an antenna arrangement matching level or a bandwidth of the electromagnetic radiation.
The multi-frequency antenna arrangement of the invention may be used, either in alternate mode or in simultaneous mode on a plurality of aggregated frequencies, thus increasing significantly the bandwidth resources.
The antenna arrangement of the invention may be compact, notably for the lowest frequency used, which allows its integration in small volumes.
The antenna arrangement of the invention is simple to design, notably when tuning radiating frequencies to desired values, taking into account the impact of the environment of the antenna arrangement, notably the ground plane, the position of the main trunk of the antenna and elements of the environment that have an electromagnetic impact on its electrical performance.
The antenna arrangement of the invention is easy to manufacture and thus has a very low cost.
The invention and its advantages will be better understood upon reading the following detailed description of a particular embodiment, given purely by way of non-limiting example, this description being made with reference to the accompanying drawings in which:
The antenna arrangement 100 is a monopole antenna with an omnidirectional radiating pattern.
The structure of the antenna arrangement 100 according to embodiments of the invention is analogous to a compact tree structure that in some aspects resembles the structure of a bonsai. The dimensions of this arrangement are selected so that the antenna is fit to operate in the ISM (Industrial, Scientific, Medical), VHF and UHF bands. The tree comprises a trunk 110, leaves 121, 122 and 123. The tree is planted on a ground plane 130.
The trunk 110 is formed of a conductive material, metallic wire or ribbon, with a deployed length L which is defined as a function of the desired radiating frequency of the fundamental mode as explained further down in the description. The trunk may be inscribed in a plane. In some embodiments described in relation to
The leaves 121, 122, 123 are also formed of a metal and mechanically and electrically connected to the trunk at defined points, as discussed further down in the description. The leaves may be seen as structures extending the length of the antenna of a defined amount in defined directions. The leaves may thus have different positions, form factors, dimensions and orientations in space. They may be inscribed together in a same plane or different surface or not. They may be coplanar with the trunk or not. The selected positions, form factors dimensions and orientations will affect the variation in radiating frequencies (i.e. fundamental and higher order modes) imparted to the base frequencies defined by the length of the trunk.
The different radiating modes are basically defined by the length of the radiating pole element:
The ground plane 130 is the metallic backplane of a PCB structure which comprises the excitation circuits which feed the RF signal to the trunk at their point of mechanical and electrical connection 140.
It is known that an antenna radiating at frequency f0 will also transmit radiation at the harmonics frequency having an odd coefficient, 3, 5, 7, etc.
It is therefore a principle of the invention to use the power transmitted by carriers modulated by each carrier generator, using the different resonating frequencies of the antenna arrangement.
According to the invention, as will be explained in a more detailed manner in the rest of the description, the multi-frequency features of the antenna arrangement of the invention rely on a first adjustment of the length L of the wire/ribbon trunk to the lowest carrier frequency which is desired, and then using the higher order resonance frequencies provided by the pole.
According to embodiments of prior art disclosures, such as those disclosed by PCT application published under n° WO2015007746 already cited, it is possible to compact the form factor of the pole by folding it, either in a plane, a non-planar surface or a volume as discussed earlier in relation to
According to an embodiment of an antenna arrangement 300 displayed on
This antenna still has a multimode radiating behaviour, but the harmonics may be shifted in relation to the harmonics of a linear pole displayed on
It is therefore an object of the invention is to provide a method and a device to control precisely the harmonic frequencies of a folded pole as it will be now explained.
It has been determined experimentally by the inventor that, along the pole, the correlation between the displacement of a small perturbation of a spot on the pole and the shift in frequency generated by this displacement varies significantly. The spots where this correlation is the highest are further designated in this description as “Hot Spots”. The spots where this correlation is the lowest are further designated in this description as “Cold Spots”. According to the invention, by superimposing the various Hot Spots and Cold Spots for each radiating frequency (fundamental and some harmonics) along the pole, it is possible to determine a map of the same. It has also been determined by the inventor that some Hot Spots are sensitive to all frequencies. For instance, it is the case of the Open Circuit spot (OC) of the folded pole, which is located at top end extremity of the folded pole, at the position of leaf 441. It has also been determined that some Hot Spots are only sensitive to some frequencies. This advantageous property is used, according to the invention, to precisely tune the configuration of the antenna arrangement to the desired frequencies by adding leaves to the folded trunk or pole or moving or removing existing leaves that would have been ill-positioned or the position of which should be changed to obtain a change in the desired frequency (change of operating frequency rendered necessary by a change of standard, for instance).
The starting point of the tuning according to the invention is a folded monopole. The frequencies (fundamental and useful harmonics) are selected with values higher than the desired frequencies, or in some embodiments, equal to one of the desired frequencies. When one of the modes has a radiating frequency which is equal to a desired frequency, no leaf should be added to modify this radiating frequency. For the modes which have a radiating frequency that is different from a desired frequency, one or more leaves may be added at a selected position, with a form factor and dimensions which allow to decrease the radiating frequency at this mode. The higher the difference between the initial radiating frequency and the desired frequency, the larger the characteristic form factor and main dimensions of the added leaf will have to be, which is generally not desired. Some rules to define the relationship between the target shift in radiating frequency and the form factor and dimensions of the added leaf will be explained further down in the description. Therefore, according to the design method of the invention, leaves are to be added at selected spots on the pole to tune each frequency. Advantageously, the tuning is performed for each frequency independently from the other frequencies. This may be achieved by adding leaves on the Hot Spots which are (only) hot for the frequencies which are to be tuned and cold for the other frequencies. This method uses a kind of orthogonality between the tuning properties of the different frequencies. This method provides a simple and efficient manner of achieving the complete tuning of the antenna arrangement. According to other embodiments of the invention, it is also possible to tune a plurality of frequencies at the same time, or possibly all the frequencies at the same time. This may provide a solution with a lower number of leaves, at the expense of a longer design phase.
The process to manufacture 2D antenna arrangements according to the invention may be quite simple and its cost may be quite low.
As an example,
The ground plane 540b is implanted on the back face of the substrate by the same process.
In these examples of 3D antennas, the manufacturing process is based on a metallic wire or ribbon which is formed to the desired form factor. The form factor is determined according to rules which are discussed further down in the description in relation to
Other manufacturing processes such as an additive process or 3D printing may be used to manufacture the antennas. In addition, 2D manufacturing on flexible substrate may also be conducted to reach a 3D realization.
The antenna arrangements displayed on
For some applications, it may be advantageous to be able to adjust the bandwidth which is available around each radiating frequency. According to the invention, each added leaf plays the role of a first order passive filter. Such a filter is not easy to tune to define a specific bandwidth. It is possible to define a higher order filter by replacing a single leaf of defined form factor, dimensions and orientations by a branch having a single leaf or multiple leaves.
The antenna arrangement 700 of
The antenna arrangement 800 of
The dimensions of the antenna arrangement are very compact: they remain lower than λ/25, λ being defined by the fundamental frequency of 169 MHz.
a,
9
b,
9
c and 9d allow visualization of the positions of the hot and cold spots on an antenna in two radiating modes, according to some embodiments of the invention.
It can be seen that the Hot Spots 911a, 911b, 912b are located at the zero crossing points of the curves 901a and 901b that display the distribution of the current along the pole. Adding a leaf located at one of these Hot Spots will shift the radiating frequency to a lower value. Conversely, the Cold Spots 921a, 921b, 922b are located at the maximum values of the curves 901a and 901b. For the fundamental mode, there is only one Hot Spot and one Cold Spot. For the first higher order mode (third harmonic with k=1 in the order numbering 2k+1), there are 2 Hot Spots and two Cold Spots, i.e. there are k+1 Hot Spots and k+1 Cold Spots. Hot Spots and Cold Spots alternate along the pole. For k=1, the distance between a Hot Spot and the neighbour Cold Spot equals one quarter of the harmonics wavelength or one twelfth of the base wavelength or λ/4(2k+1) or L/(2k+1). The distance between a Hot Spot and the next closest Hot Spot equals two thirds of the length of the pole or one sixth of the base wavelength or λ/2(2k+1) or 2L/(2k+1). These rules can be generalized for higher order modes k=2, 3, etc. corresponding to the 5th, 7th harmonics, etc. The second order mode corresponding to the 5th harmonics has 3 Hot Spots and 3 Cold Spots, two consecutive Hot Spots being spaced of 2L/5. The third order mode corresponding to the 7th harmonics has 4 Hot Spots and 4 Cold Spots, two consecutive Hot Spots being spaced of 2L/7.
e,
9
f,
9
g,
9
h,
9
i and 9j illustrate the electrical influence of an addition or moving of a leaf at a given spot of the trunk, in some embodiments of the invention.
Thus, the impact of a leaf is maximum when positioned at spot P (which is a Hot Spot) and minimum when positioned at spot P′ (which is a Cold Spot). In some embodiments, form factor or any other constraint may require placing a leaf a distance from spot P. As a result the impact of the leaf will not be maximum.
The length L of the deployed monopole of
The antenna of
The antenna of
It has been determined experimentally by the inventor that the Hot Spots and Cold Spots are essentially spaced by the same distances in the three different configurations. This is because the folding of the pole does not modify fundamentally the stationary regime which is established along the pole, be it rectilinear or folded. This is quite advantageous because a definite form factor can be adopted for a specific application without a need to recalculate the position of the leaves, thus allowing a reuse of the same design rules for various antenna arrangements. It should be noted though that the form factor of the pole will modify the resonating frequencies of the fundamental mode and the higher order modes. A man of ordinary skill may be able to measure the new resonating frequencies and/or to simulate them, using a simulation tool available on the market, such as CST™, HFSS™, Feko™ or Comsol™, or any other proprietary software.
a,
11
b, 11c, 11d, 11e, 11f, 11g and 11h illustrate different geometries of leaves and branches adapted for antenna arrangements according to the invention.
The number and positions of leaves that shift the frequencies of the harmonics having been determined, their form factors, dimensions and orientations have to be defined.
As may be seen on
d,
11
e and 11f illustrate three different orientations of a same leaf relative to the trunk of the antenna arrangement. It has been determined experimentally by the inventor that the orientation of the leaf does not have a significant impact on the shift in frequency, adaptation or bandwidth of the antenna arrangement. It is preferable to avoid that the leaf becomes electrically coupled to the trunk. The minimum orientation to achieve this varies notably with the frequency to which the leaf is tuned. A preferred embodiment is therefore to select O so as the longer dimension D of the leaf is perpendicular to the tangent to the trunk at the point of attachment of the leaf to the trunk. In some other embodiments, where the minimum angle to the trunk to avoid coupling can be determined, by trial and error or by calculation means, this minimum angle will be preferably selected as orientation O of the leaf. A compromise between this minimum angle and an orientation perpendicular to the tangent to the trunk may also be preferable to take due account of the constraints on the global form factor of the antenna arrangement.
The selection of the design rules for a specific application may for example be organized as displayed on
A first step 1210 of the process consists in selecting the deployed length L and the form factor ff of the wire/ribbon forming the trunk of the antenna arrangement. The frequency of the fundamental mode has to be selected at a value higher than or equal to the targeted lowest frequency, as already discussed above. The form factor to be selected depends on the target size of the antenna arrangement. Also the form factor of the pole may impact the antenna matching. But if the matching is adversely impacted by a specific pole form factor, it may be then corrected using an antenna matching technique. A man of ordinary skill will therefore be able to find an adequate compromise between the compactness form factor and the matching of the antenna arrangement. When the antenna arrangement is correctly matched (at a level better than −10 dB, for instance), the form factor of the trunk will have little impact on the available bandwidth.
Then, at a step 1220, the positions of the Hot Spots and Cold Spots along the pole for each radiating mode are calculated and/or represented on a map as explained above in relation to
Then, at a step 1230, the position P, orientation O, longer dimension D, form factor F (or second characteristic dimensions, as illustrated on
The first leaf (n=1) is placed so as to tune the frequency of the fundamental mode (if needed). There is only one single zone on the pole which is electrically sensitive for this mode. It is located close to the distal extremity of the pole which is in Open Circuit. There is therefore only one degree of freedom for this fundamental frequency. The parameters P, O, D, F should be selected so as to adjust a value of the frequency shift, Δf=g(k,P,O,D,F). The amplitude of the frequency shift created by a leaf having defined parameters P, O, D and F will depend on the order k of the mode: the higher the order, the higher the variation of the frequency shift for a defined displacement of the leaf around a Hot Spot. O is selected based on the form factor of the trunk, to maximize compactness of the whole volume of the antenna arrangement, while minimizing electric coupling with the trunk. D and F are the main factors impacting Δf for a defined P at a defined order of the mode.
Function g is used to create a “desired impact” of the P, O, D and F parameters on one or more of an antenna arrangement impedance, an antenna arrangement adaptation or a bandwidth of the electromagnetic radiation, once the radiating frequency itself has been tuned.
Parameters O, D and F can be set in whatever order, once the position P of the leaf has been determined.
If this leaf is placed close to positions which are Hot Spots for other modes, the radiating frequencies of these other modes will also be shifted. The magnitude of the shift may depend on the position of this leaf relative to the Hot Spot positions for these other modes.
At step 1240, the map of Hot Spots and Cold spots is redesigned after leaf n has been added with the same process.
At step 1250, whether all frequencies have been adjusted to their target values or not is tested. If so, the process stops and the design rules are complete. If not, a leaf n+1 should be added to adjust the frequency of a higher order mode. A new leaf is added at a position P that is a Hot Spot for this mode and a Cold Spot for a lower order mode which was previously adjusted. As discussed earlier, higher order modes have a higher number of Hot Spots and hence have a higher number of degrees of freedom.
These figures represent a map of the Hot Spots and Cold Spots, the principles of which have already been explained above notably in relation to
Comments will be provided in relation to
The map of
The figure includes two tables 14100 and 14200.
Table 14100 represents with different symbols 14121, 14122, 14123 the spots along the pole that belong respectively to a hot area, a tepid area and a cold area. The representation includes a scale 14100 graduated, by way of example only, every 5% of the length L of the deployed pole. On the scale for the fundamental mode, there is only one symbol, whereas for the higher order modes, there are two symbols. The two symbols illustrate the fact that the marked spot is in-between two areas for this mode.
Table 14200 represents a conversion of the symbols of table 14100 into an index of sensitivity of the shift in frequency for the mode to a variation of the position of a leaf. By way of example only, the index is chosen on a scale from 0 to 6. But another scale may be chosen without departing from the scope of the invention. Table 14300 displays the rule of conversion chosen in this example. But other rules of conversion may be chosen. Table 14200 allows to get a clear view of the impact of variations in positions of the leaves along the pole for all the frequencies.
In some embodiments of the invention, variables defining a rate of impact of a position of a leaf for each mode may be determined and a function defining the combination of at least some, if not all, the variables may also be determined using calculation, simulation or abaci.
From table 14200 of
It is thus possible, according to the invention, to define placement rules of the leaves using the method described above in relation to
The invention may be applied to antenna arrangements which radiate in different frequency domains and are used for very different applications.
The invention may also be applied to dipole antennas, as can be seen from the example of
The examples disclosed in this specification are therefore only illustrative of some embodiments of the invention. They do not in any manner limit the scope of said invention which is defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 16306059.3 | Aug 2016 | EP | regional |
