EP0667984B1 - Monopolar wire-plate antenna - Google Patents

Abstract

The invention relates to a monopolar wire-plate antenna comprising a ground plane (10), a first radiating element configured like a capacitive roof (11, 12) and connectable to a generator, and a second radiating element configured like a conductive wire (14, 14', 15, 15') connecting the capacitive roof to the ground plane. It is also provided with a plurality of at least one of said radiating elements.

Description

The present invention relates to a monopolar wire-plate antenna of the type comprising a ground plane, a first radiating element under the form of a capacitive roof capable of being connected to a generator or to a receiver via a power wire, and a second radiating element in the form of a radiating conducting wire connecting the roof capacitive to the ground plane.

Such an antenna is known from document FR-A-2 668 859.

This antenna is composed of two metal surfaces arranged with on either side of a dielectric substrate. One of these surfaces, generally the largest, constitutes the ground plane and the other surface constitutes the capacitive roof. The antenna is supplied by through the supply wire consisting of a coaxial probe which crosses the ground plane and the substrate and is connected to the capacitive roof.

This antenna has the distinction of having a conductive wire additional active, radiating, parallel to the coaxial probe that connects the ground plane to the capacitive roof. This thread performs a return to earth. Such an antenna is the seat of two phenomena resonance, hence the name of double resonance antenna which is sometimes called given.

The physical parameters of the antenna, namely the permittivity of the electrical substrate, its thickness, the radius of the supply wire, the radius of the radiating wire, the distance between the two wires as well as the shape and the dimensions of the capacitive roof and the ground plane, can a priori have any values. However the proper functioning of the antenna depends on the relationships between these parameters which limit the possibilities and impose constraints that are sometimes difficult to comply with technological point of view.

Thus, to obtain a good adaptation of the antenna, it is preferable to have a substrate with a very low dielectric constant (ε _r <2), a distance between the coaxial probe and the very weak radiating wire compared to the wavelength d 'emission (d <λ _o / 50) and a radius of the coaxial probe at least 5 times less than that of the radiating wire. On the other hand, the shape of the capacitive roof is practically arbitrary and only its surface plays a role. On the other hand, it is preferable from the point of view of the adaptation of the aerial that its height is relatively large but does not exceed λ _o / 18. The shape and dimensions of the ground plane only slightly modify the adaptation of the antenna when its surface is at least 10 times greater than that of the capacitive roof, but can significantly modify the radiation pattern, as in all monopolar radiation antennas.

The operation of this antenna mainly results from a coupling phenomenon between the supply probe and the radiating wire or no cavity resonance mode is involved.

• Lobe à symétrie de révolution.
• Rayonnement maximal parallèlement au plan de masse lorsqu'il est très grand, et nul dans l'axe des fils.
• Polarisation linéaire avec champ électrique dans un plan perpendiculaire à l'antenne.

The addition of the radiating wire under the conditions which will be set out below creates a parallel resonance situated at a frequency much lower than those of the conventional modes of resonance of a plated antenna. A suitable choice of the different physical parameters of the antenna makes it possible, on the one hand, to achieve a correct adaptation of the aerial to conventional generators and receivers, that is to say that the antenna has an impedance, the real part of which is close to a determined value, generally 50 Ω, when the imaginary part is canceled, and, on the other hand, to obtain radiation of the so-called monopolar type which has the typical characteristics of the radiation of a monopole:

• Lobe with symmetry of revolution.
• Maximum radiation parallel to the ground plane when it is very large, and zero in the axis of the wires.
• Linear polarization with electric field in a plane perpendicular to the antenna.

Consequently, if the antenna described in the aforementioned document has opposite antennas of the prior art the advantages of being relatively simple in its design and implementation, to have dimensions low compared to the wavelength of use, to be able to be properly matched with a suitable gain, to have a band higher bandwidth than a conventional plated antenna and a radiation of monopolar type stable as a function of frequency, and of can be used in a network, however, it has certain disadvantages.

In particular, to place the antenna in the radiation conditions monopolar, the dimensions of the wires and the distance between the wires must be much less than the working wavelength λ, which is a source of technological and fragile difficulties, particularly in the microwave. On the other hand, for use at low frequencies, the dimensions, although already far below the wavelength, are still too great for mobile applications. In addition, when the substrate used at a dielectric constant too different from 1, the antenna is difficult to adapt and its bandwidth is relatively low. Finally, the shape of monopolar radiation is not easily adjustable, for example to obtain a higher maximum gain or to obtain a greater spatial coverage.

The present invention aims to overcome these drawbacks.

To this end, the invention relates to a monopolar wire-plate antenna comprising a ground plane, a first radiating element under the form of a capacitive roof capable of being connected to a generator or to a receiver via a power wire and a second radiating element in the form of a conductive wire connecting said capacitive roof on the ground plane, characterized in that it comprises a plurality at least one of said radiating elements, the dimensions of said capacitive roof being sufficient small relative to the working wavelength so that the antenna operates in monopolar radiation at the working frequency.

We will see below that such an arrangement makes it possible to solve the problems. set out above.

It should also be noted that the word "wire" means not only a conductor with circular cross-section, but also with any cross-section, such as like a ribbon. Likewise, the mass "plan", as well as the capacitive roofs, can actually be curved surfaces, possibly not parallel to each other, in particular to generate radiation monopolar of particular shape, for example narrow with gain large or large maximum with a given illumination sector.

In a particular operating mode, the characteristics of the antenna, and in particular the shape of the capacitive roofs, are chosen to so as to have at the same frequency or several frequencies neighbors of an antenna working both on monopolar mode and on the classic dipolar modes.

Also in a particular embodiment, the antenna according to the invention comprises a plurality of conducting wires.

In particular, the antenna according to the invention makes it possible to obtain radiation monopolar and good adaptation much more easily and with much less technological constraints than in the state of technical.

More particularly the radiating wires can be arranged symmetrically with respect to the supply wire.

In another particular embodiment, the antenna according to the invention has a plurality of capacitive roofs, at least one of the capacitive roofs being arranged to be connected to the generator.

In the latter case, the antenna according to the invention can be supplied by a coaxial probe crossing the ground plane, the power wire of which is connected to a capacitive roof and whose external conductor connects the plane of ground to a capacitive roof located between the ground plane and the capacitive roof connected to the power wire.

An antenna according to the invention comprising several capacitive roofs can be arranged to present operating bands which are either overlapping or which are disjoint, or to present a diagram of monopolar radiation close to a given size.

In a particular embodiment, the capacitive roof is substantially rectangular and the radiating wire is connected in the vicinity of the short side of the rectangle.

We have seen that this arrangement reduces the surface and the height from the ground plane. This operating condition is very important in the case of low frequency antennas (typically radio antennas), for which the dimensions of the antennas are substantial.

Power wires and radiant wires can also be loaded by elements of circuits located or distributed along the wire.

These elements can be passive linear (resistance, self, capacitance, impedance) or active, but also non-linear. Choose suitably, they allow for example to reduce the dimensions of the antenna, to change the working frequency, or to switch several working frequencies.

• les figures 1, 2a et 2b sont trois vues en perspectives de trois modes de réalisation de l'invention,
• les figures 3a, 3b et 3c illustrent respectivement les parties réelles et imaginaires de l'impédance équivalente Z (f) et le coefficient de réflexion S₁₁ (f) d'une antenne selon le mode de réalisation de la figure 1,
• les figures 4a et 4b illustrent respectivement pour cette même antenne les gains réalisés dans le plan des fils et dans le plan orthogonal,
• les figures 5a, 5b et 5c illustrent respectivement les parties réelles et imaginaires de l'impédance équivalente Z (f) et le coefficient de réflexion S₁₁ (f) d'une antenne selon le mode de réalisation de la figure 2, et
• les figures 6a et 6b illustrent pour cette même antenne les gains réalisés dans le plan des fils à de fréquences différentes.

We will now describe, by way of nonlimiting example, particular embodiments of the invention with reference to the appended schematic drawings in which:

• FIGS. 1, 2a and 2b are three perspective views of three embodiments of the invention,
• FIGS. 3a, 3b and 3c respectively illustrate the real and imaginary parts of the equivalent impedance Z (f) and the reflection coefficient S ₁₁ (f) of an antenna according to the embodiment of FIG. 1,
• FIGS. 4a and 4b respectively illustrate for this same antenna the gains made in the plane of the wires and in the orthogonal plane,
• FIGS. 5a, 5b and 5c respectively illustrate the real and imaginary parts of the equivalent impedance Z (f) and the reflection coefficient S ₁₁ (f) of an antenna according to the embodiment of FIG. 2, and
• Figures 6a and 6b illustrate for this same antenna the gains made in the plane of the wires at different frequencies.

The antenna of Figure 1 is formed of a dielectric substrate 1 completely metallized on one of its faces 2 to form the ground plane and partially metallized on its other face 3 to form the capacitive roof. A coaxial supply probe 4 crosses the ground plane 2 and the substrate 1 and is connected to the capacitive roof 3. Conductive wires radiant 5 also pass through the substrate 1 to connect the plane of ground 2 at the capacitive roof 3.

The radiating wires 5 can be arranged, a priori, anywhere under the capacitive roof 3 of the antenna but, depending on their position, their influence on the operation of the antenna will be more or less important. On the other hand, the introduction of too many radiating wires (from four) can attenuate the phenomenon of double resonance and make it non usable from the point of view of adapting the air to the generators microwaves.

Furthermore, the dielectric substrate 1 on which is deposited the plane of mass 2 and the roof 3 of the antenna does not necessarily have to be only dielectric material but may consist of a superposition of layers with any dielectric constants. The shape and dimensions of substrate 1 are arbitrary but generally, for practical reasons, its dimensions do not exceed those of the plan of mass 2.

The introduction of each additional radiating wire introduces new physical antenna parameters, i.e. wire radius added radiator, its distance to the coaxial supply probe as well as the distances separating it from the other radiating wires. These parameters additional physics complicate relationships between parameters of the antenna but, in reality, they simplify the problem and relax the constraints necessary to obtain operation of the monopolar wire-plate antenna.

This is how the wire of the supply probe 4 should no longer necessarily have a diameter much smaller than that of the radiating wires, but can be of identical or greater diameter. Also, wires 5 do not must no longer be located too close to the coaxial supply probe 4 but should preferably be towards the ends of the roof of the antenna. The radius of the wires 5 is preferably less than the radius of the supply probe and the more the 5 wires are numerous or close to the feeding probe, the smaller their radius must be.

Compared to the double resonance antenna with a single radiating wire, the antenna with several radiating wires has a generally larger roof and a slightly greater height to operate at the same frequency. However, the introduction of a dielectric medium or of a superposition of different dielectric media makes it possible to reduce these dimensions. Moreover, if the double resonance antenna having a single radiating wire is only suitably adaptable to 50 Ω for substrates with very low permittivity (ε _r ≤ 1.2), the introduction of additional radiating wires allows '' very easily adapt any monopolar wire-plate antenna produced on any substrate, or combination of substrates.

On the other hand, from a practical point of view, it is better to place in some cases the wires 5 symmetrically with respect to the coaxial probe supply 4, by placing, for example, this supply probe at the center of the capacitive roof 3 of the antenna.

The operating principle of the double resonance antenna having multiple radiating wires is similar to that of the dual antenna resonance presenting only one wire. Adding radiant wires additional does not create new parallel resonances related to each of the radiating wires, but modifies that created by a radiating wire.

Indeed, as a first approximation, it is possible to consider that the double resonance phenomenon is now created by the "self equivalent "to the set of wires 5 which short-circuits the capacity of the antenna. This self is now lower, given the implementation parallel of the chokes linked to each of the wires 5, which explains why the resonant frequency is shifted towards the high frequencies and that this resonance has a lower quality coefficient. The introduction of high permittivity dielectric substrates lowers the resonant frequency and increase the quality coefficient by mainly modifying the mutual inductances between the wires.

The decrease in the quality coefficient of the double resonance appears very beneficial from the point of view of adapting the air to the generators microwave because it allows to maintain the real part of the impedance close to 50 Ω and the imaginary part null on a frequency band larger, which allows an increase in band busy.

These properties are general and are found with parameters very different antenna frequencies at any operating frequency. Also, the choice of frequency of use is at the discretion of the user.

• on choisit la surface du toit 3, la hauteur du ou des substrats 1 et le nombre de fils rayonnants ce qui donne la fréquence approximative de fonctionnement,
• on choisit le placement des fils 5, leur rayon et les distances qui les séparent, ce qui permet un ajustement de la fréquence, et de la partie réelle et de la partie imaginaire de l'impédance, et par conséquent une optimisation de l'adaptation de l'antenne,
• on choisit les dimensions du plan de masse 2, ce qui détermine le diagramme de rayonnement,

Consequently, obtaining a correct adaptation at a certain frequency can be carried out as follows:

• the roof surface 3, the height of the substrate (s) 1 and the number of radiating wires are chosen, which gives the approximate operating frequency,
• we choose the placement of the wires 5, their radius and the distances which separate them, which allows an adjustment of the frequency, and of the real part and the imaginary part of the impedance, and consequently an optimization of the adaptation of the antenna,
• the dimensions of the ground plane 2 are chosen, which determines the radiation diagram,

The monopolar wire-plate antenna having several radiating wires has radiation characteristics similar to those of the double resonance antenna which has only one radiating wire, namely radiation of the monopolar type which takes place via the wire and radiant wires.

The multiplication of wires 5 now makes it possible to perfectly symmetrical the radiation by arranging the wires 5 symmetrically with respect to the feed probe 4 located in the center of the antenna.

The dimensions of the ground plane 2 and, to a lesser degree, those of the substrate 1 introduce, as for any radiation antenna monopolar, changes in the radiation pattern.

The characteristics of an antenna of the type given below will be given shown in Figure 1 with two wires 5 and a coaxial probe supply 4 with a diameter of 1.27 mm, the two wires 5 being arranged symmetrically with respect to probe 4 and the axis of each of the wires being 3.3 mm away from the probe axis. The electrical substrate 1 is consisting of a 10 mm thick plate of polymethacrylate 72 mm x 72 mm methyl, and a permittivity of approximately 2.5. The ground plane 2 covers an entire face of the plate 1 and the capacitive roof is centered on the other side and is 20 mm x 20 mm in size.

Figures 3 to 6 show in solid lines the quantities measured and, in broken lines, the theoretical quantities. Figures 3a and 3b show respectively the real part and the imaginary part of the antenna input impedance and Figure 3c shows the coefficient of resulting reflection.

Similarly, Figures 4a and 4b show the gain achieved, obtained respectively in the plane of the wires and in the plane orthogonal to the plane of the son, and evaluated on all the space surrounding the antenna.

These results make it possible to verify the excellent adaptation of the antenna (FIG. 3) as well as the typical shape of the monopolar radiation deformed by the diffraction effect of the edges of the ground plane (FIG. 4). The antenna has a reflection coefficient S ₁₁ (f) of the order of -20 dB (only 1% of the incident power is reflected) at the frequency of 1.77 GHz.

The gain realized represented in FIG. 4 at this same frequency of 1.77 GHz takes into account all losses (mismatch, losses ohmic and dielectric) and reaches a maximum value of about 2.5 dB at 45 ° due to the deformation of the radiation pattern due to dimensions of the ground plane.

In addition to the advantages of the single resonance double antenna wire radiating from the previous antennas and which the antenna picks up from double resonance with several radiating wires, multiplication of the wires radiating on this type of antenna has other advantages.

• une adaptation de l'aérien plus aisée ;
• la possibilité d'utiliser des substrats à forte permittivité ;
• un élargissement de la bande passante : 8 % de bande pour un TOS de 2 ou 20 % de bande pour un TOS de 5,8 (|S₁₁| de - 3 dB) ;
• une configuration physique de l'antenne pas obligatoirement unique et facilement modulable ;
• une symétrisation parfaite du diagramme de rayonnement dans tout l'espace.

Indeed, the introduction of additional radiating wires allows more freedom on the physical parameters of the antenna, which allows:

• easier adaptation of the aerial;
• the possibility of using substrates with high permittivity;
• an increase in bandwidth: 8% of band for a TOS of 2 or 20% of band for a TOS of 5.8 (| S ₁₁ | of - 3 dB);
• a physical configuration of the antenna not necessarily unique and easily modular;
• perfect symmetrization of the radiation pattern throughout the space.

The technological realization of the air now appears easier because the constraints imposed on the physical parameters to obtain a correct operation are less strict or penalizing.

• une solidité de l'antenne accrue par l'introduction de fils rayonnants supplémentaires et d'une sonde coaxiale de gros diamètre ;
• la possibilité de réaliser une antenne sans substrat diélectrique, le toit étant maintenu par l'ensemble des fils ;
• la possibilité d'utiliser des substrats diélectriques facilitant la réalisation et renforçant la rigidité de l'antenne.

From the point of view of implementation, the following advantages are obtained:

• increased antenna strength by the introduction of additional radiating wires and a large diameter coaxial probe;
• the possibility of producing an antenna without a dielectric substrate, the roof being maintained by all of the wires;
• the possibility of using dielectric substrates facilitating the production and reinforcing the rigidity of the antenna.

In the embodiment of FIG. 2a, the dielectric is the ambient air. The ground plane 10 is surmounted by a first capacitive roof 11 itself surmounted by a second capacitive roof 12. Only the first capacitive roof 11 is connected to a coaxial supply probe 13 crossing the plane of ground 10 for its connection to a generator.

The first capacitive roof 11 is also connected to the ground plane 10 by two conductive wires 14 and 14 'arranged relative to the probe 13 as the wires 5 of the embodiment of FIG. 1. The second capacitive roof 12 is connected to the first capacitive roof 11 by two radiating wires 15 and 15 'in contact with the roof 11 at two points located between the contact points of the probe 13 and those of the wires 14 and 14 ′ on the other side of the roof 11.

We will see below that such a device generates two frequencies of resonance.

In the embodiment of FIG. 2b, the assembly of the probe 13 crosses the ground plane 10. Its external tubular conductor 13 "connects electrically the ground plane 10 to the first capacitive roof 11, while the central conductor 13 ′ is connected to the upper capacitive roof 12.

The roof 12 here has an elongated rectangular shape. Radiant wires 15 and 15 'are connected to the roof 12 in locations close to the small sides 12 'of the roof 12.

The wires 15 and 15 'are here loaded by circuits 20 and 20' having an adequate impedance, active or passive.
Of course, a larger number of roofs and a different arrangement of the radiating wires can be envisaged in the embodiments of FIGS. 2a and 2b.

We have seen that the shape of the roofs is practically arbitrary and that only their surface counts. For practical and simplifying reasons, we can place the roof 12 having the smallest surface the highest above of the ground plane 10, the largest roof 11 being placed immediately above the ground plane. So the feeding probe is only connected to the largest roof 11 across the plane of mass. What therefore the physical parameters related to the lower floor which act mainly on the lowest resonance; the resonance the higher is fixed on the one hand by the physical parameters linked to the upper floor, but also by those of the lower floor containing the coaxial supply probe 13.

Thus, if the constraints to be imposed on the physical parameters linked to the bottom floor are known by the description given above in reference to Figure 1, they must now be modulated so as not to penalizing the highest resonance too much. Indeed, it is necessary to make usable, from the point of view of adaptation to 50 Ω, the second double resonance by a joint action on the one hand, all of the physical parameters linked to the first stage, and then on the other physical parameters related to the second stage and which influence the two resonances (i.e.: the dimensions of the upper roof 12, the value of the permittivity of the second stage dielectric substrate and its thickness) and finally, an action on the physical parameters which act only on the second resonance, independently of the other (namely: the radius radiating upper wires 15 and 15 'and the distance between them).

Overall, it appeared preferable that the coaxial supply probe 13 has a large diameter, that the radiating wires 14 and 14 ′ of the bottom stage are distant from the coaxial probe 13 and have a radius at least three to four times less than that of the supply probe, and that the radiating wires 15 and 15 ′ of the upper stage have the same diameter or even greater than that of the supply probe and are also distant from each other that the wires 14 and 14 'are from the probe 13. Moreover, the placement of the wires under the roofs is arbitrary and only the distances between them are significant; however, a centered and symmetrical arrangement allows symmetrization of the radiation pattern. The respective heights of each of the antennas should preferably be of the same order of magnitude with respect to the wavelength emitted and not exceed λ _o / 15.

Roof surfaces should not be too different if you want keep the resonances close and a ratio of 1.4 on the surfaces appears as a maximum not to be exceeded. As for substrates dielectric, they can allow to bring together or move away the resonances as well as modifying the quality coefficients of resonances.

If the operating principle of this device is that of the antenna with double resonance for each roof of the antenna, the phenomenon occurs complicates, however, due to the presence of lower roofs which can act as a ground plane vis-à-vis the upper roofs. On the other hand, coupling phenomena no longer only take place between the wires of a same floor but also with those of other floors. So the phenomenon of double resonance linked to the first floor where the supply probe is practically independent of the resonances due on the upper floors, but each of the resonances due to the upper floors upper floors is highly dependent on those linked to the lower floors.

Although, in this case, the establishment of an equivalent circuit appears difficult, the appearance of parallel resonances, located well below conventional modes of cavity resonance of printed antennas, always results from a short circuit made through the wires radiant (and possibly lower radiating roofs and wires) at level of capacities presented by each roof of the device.

These properties are general and are found with parameters very different antenna physics at working frequencies any.

The dual resonance antenna with multiple radiating elements can be used in two different ways: either it is used as a device with a large bandwidth and, in this case, characteristics of each superimposed element must lead to overlapping operating frequency bands for each antennas to adapt to 50 Ω wideband. Either this type of aerial is used as a device with multiple frequencies of resonance but with identical radiation pattern and, in this case, each operating frequency band must be distinct neighboring bands.

However, whatever the type of use of the desired device, a correct operation of the device can be obtained in the exposed manner below. Due to the large number of physical parameters to be set and taking into account the fact that certain parameters modify the set of resonances, it is important to proceed in stages and to start with fix the physical parameters having a large influence. This is how he must first focus on choosing the parameters related to the lower floor containing the supply probe and then choose, stage by stage, the physical parameters related mainly to each of the resonances so optimize the adaptation of the device to 50 Ω.

• on choisit les dimensions des toits, les hauteurs, les substrats et le nombre de fils rayonnants respectifs à chaque étage, ce qui donne les fréquences approximatives de fonctionnement ;
• on choisit le placement des fils, leur rayon et les distances qui les séparent concernant l'étage où se trouve la ou les sondes coaxiales d'alimentation tout en réajustant des paramètres physiques des autres étages ayant une action sur l'ensemble des résonances, à savoir : les dimensions des toits, les hauteurs et la valeur de la permittivité diélectrique des substrats ; il en résulte un ajustement des fréquences de résonance associé à un positionnement précis de la partie réelle et imaginaire de l'impédance concernant uniquement la résonance liée à l'étage qui contient la sonde d'alimentation, ce qui permet d'optimiser l'adaptation du dispositif à cette première fréquence.

We therefore proceed as follows:

• the dimensions of the roofs, the heights, the substrates and the number of respective radiating wires are chosen on each floor, which gives the approximate operating frequencies;
• we choose the placement of the wires, their radius and the distances which separate them concerning the stage where the coaxial supply probe (s) is located while readjusting physical parameters of the other stages having an action on all the resonances, know: the dimensions of the roofs, the heights and the value of the dielectric permittivity of the substrates; this results in an adjustment of the resonance frequencies associated with a precise positioning of the real and imaginary part of the impedance relating only to the resonance linked to the stage which contains the supply probe, which makes it possible to optimize the adaptation of the device at this first frequency.

• on choisit le placement des fils, leur rayon et les distances qui les séparent de manière à modifier uniquement la résonance liée à cet étage et celles liées aux étages supérieurs, d'où un ajustement de la fréquence de résonance concernée, et de la partie réelle et imaginaire de l'impédance afin d'optimiser l'adaptation du dispositif à cette fréquence. Les résonances supérieures pourront être éventuellement modifiées mais elles le seront de nouveau lors de l'optimisation des paramètres les concernant ;
• enfin, on choisit des dimensions du plan de masse pour déterminer le diagramme de rayonnement.

Then, for each of the roofs making up the device and starting with the floor located immediately above the previous one:

• we choose the placement of the wires, their radius and the distances between them so as to modify only the resonance linked to this stage and those linked to the upper stages, hence an adjustment of the resonance frequency concerned, and of the real part and imaginary of the impedance in order to optimize the adaptation of the device to this frequency. The higher resonances may be modified if necessary, but they will be modified again when the parameters relating to them are optimized;
• finally, we choose dimensions of the ground plane to determine the radiation diagram.

The radiation of the device is mainly carried out through wires placed at each of the double resonance antennas superimposed. Thus, the radiation generated by the device presents characteristics identical to the influence of a monopoly.

However, it should be noted that the device has remarkable stability of the radiation pattern as a function of frequency since the "double resonance" phenomena are well below the modes cavity resonance of printed antennas.

However, slight changes in the radiation pattern are observable when the frequency varies significantly due to the diffraction by the edges of the ground plane whose effects vary with the wavelength, which is the case for all radiation antennas monopolar.

Figures 5 and 6 illustrate the results obtained with an antenna of the type that of FIG. 2 in which the ground plane 10 has dimensions of 99 mm x 99 mm, the lower capacitive roof 11 has dimensions of 39 mm x 39 mm and the upper capacitive roof 12 has dimensions of 26 mm x 26 mm. The capacitive roof 11 is 10 mm from the ground plane 10 and the two capacitive roofs 11 and 12 are also separated by 10 mm. The coaxial supply probe 13 as well as the radiating wires 15 and 15 ' have a diameter of 1.27 mm and the radiating wires 14 and 14 'have a diameter 0.4 mm. Wires 3 and 4 are 6.6 mm apart and wires 14 and 14 'are each 9.9 mm apart from the feeding probe 13.

Resonance frequencies of the fundamental cavity type mode resonant of each of the two superimposed antennas are located respectively around 3.8 GHz and 5.7 GHz. The position of the wires could be determined to also allow a antenna operation in resonant modes.

Figures 5 and 6 are shown in solid lines the theoretical results and in broken lines the experimental results.

FIG. 5 represents the electrical characteristics of the antenna, namely the real and imaginary parts of the input impedance (Figures 5a and 5b) and the reflection coefficient measured with respect to 50 ohms (Figure 5c). The Figures 6a and 6b show the gain achieved by the antenna obtained in the plane wires and evaluated throughout the space surrounding the antenna to both operating frequencies of 1.2 GHz and 2.1 GHz respectively.

The antenna then has two "double resonances" located around 1.1 GHz and 2 GHz. Incomplete optimization of the physical parameters of the antenna nevertheless makes it possible to obtain two reflection coefficients of the order -12 dB at 1.2 GHz and 2.1 GHz. The difference observed in the determination of the high resonant frequency is due to an achievement slightly different practice from the antenna studied in theory.

We then observe, at the two operating frequencies, a monopolar radiation slightly distorted by diffraction due to the ground plane. Note that the most distorted diagram is the one evaluated at the highest frequency but that the radiation before the antenna (-90 ° < <90 °) is almost identical to the two frequencies of operating separately from 0.9 GHz (experimental curves).

The gain values obtained, obtained at the two frequencies of operation, namely, 1.4 dB at f = 1.2 GHz and 1.9 dB at f = 2.1 GHz (experimental curves) conform to the expected values given the adaptation to -12 dB obtained at these frequencies and could be increased by adapting to an optimized 50 Ω.

The radiation obtained in the plane orthogonal to the plane of the wires provides identical results which are not presented here.

• une adaptation à 50 Ω très large bande obtenue par chevauchement des bandes passantes liées à chacune des antennes superposées. 75 % de bande passante pour un |S₁₁| de - 3dB a été obtenu avec seulement deux antennes superposées.
• une adaptation aux générateurs microondes sur des bandes de fréquences distinctes, proches ou éloignées.

This multi-stage device allows the creation of multiple "double resonances" located close to each other or not. Thus, such a device immediately has two main advantages:

• an adaptation to 50 Ω very wide band obtained by overlapping bandwidths linked to each of the superimposed antennas. 75% bandwidth for a | S ₁₁ | de - 3dB was obtained with only two superimposed antennas.
• adaptation to microwave generators on separate frequency bands, near or far.

On the other hand, the technique of superimposing double resonance antennas allows the complete device to fully retain the characteristics of the double resonance antenna and in particular the advantages set out above .

We will also obtain a monopolar type radiation practically stable as a function of frequency.

Claims (9)

1. Monopolar wire-plate antenna comprising an earthing surface (2; 10), a first radiating member in the form of a capacitive roof (3; 11, 12) able to be connected to a generator or a receiver through the intermediary of a supply wire, and a second radiating member in the form of a conducting wire (5; 14, 14', 15, 15') connecting said capacitive roof to the earthing surface, characterised by the fact that it comprises a plurality of at least one of said radiating members, the dimensions of said capacitive roof being sufficiently small with respect to the working wavelength in order that the antenna operates by monopolar radiation at the working frequency.
2. Antenna according to Claim 1, comprising a plurality of radiating wires.
3. Antenna according to Claim 2, in which the radiating wires are disposed symmetrically with respect to the supply wire.
4. Antenna according to one of Claims 1 to 3, comprising a plurality of capacitive roofs, at least one of the capacitive roofs being arranged in order to be connected to the generator.
5. Antenna according to Claim 4, supplied by a coaxial probe passing through the earthing surface, whereof the supply wire-is connected to a capacitive roof and whereof the outer conductor connects the earthing surface to a capacitive roof situated between the earthing surface and the capacitive roof connected to the supply wire.
6. Antenna according to one of Claims 1 to 5, comprising at least two capacitive roofs and arranged to present an overlapping of the associated operating bands.
7. Antenna according to one of Claims 1 to 5, comprising a plurality of capacitive roofs and arranged in order that the associated operating bands are separated.
8. Antenna according to one of Claims 1 to 7, in which the capacitive roof is substantially rectangular and the radiating wire is connected in the vicinity of the small side of the rectangle.
9. Antenna according to one of Claims 1 to 8, in which at least one of the wires is loaded by a circuit element.

Images