FR3068178A1 - BANDWIDTH MINIATURE ANTENNA EXTENDED - Google Patents

Abstract

The invention relates to an antenna (1) with an enlarged bandwidth comprising: - a primary antenna (10); at least one main resonator (11a) in electromagnetic coupling with said primary antenna. The broadband antenna has at least one secondary resonator (11b) electromagnetically coupled to the primary antenna (10) and the at least one main resonator (11a). The resonators each comprise at least one resonant frequency close to an operating frequency of said broadband antenna. The invention makes it possible to reduce the size of an antenna while ensuring a bandwidth of relative width that can go up to about 10%.

Description

TECHNICAL AREA

The invention belongs to the field of antennas.

More particularly, the invention belongs to the field of miniature antennas with increased bandwidth.

STATE OF THE ART

The very high frequency and ultra high frequency antennas 10 conventionally used in aeronautics or in automobile are generally quarter wave monopolies the length of which can vary from the centimeter (of the order of 5 centimeters for an antenna at 1 GHz) to tens of centimeters (around 60cm for a 120MHz antenna). Such antennas generate drag and are all the more mechanically vulnerable as their dimensions are large.

The miniaturization of antennas limits the drag of the antennas and reduces their vulnerability. American patent application US 2009/0140946 describes a miniature antenna solution composed of a monopoly printed on a first face of a rectangular dielectric substrate, on a second face of which a printed circuit is formed.

A disadvantage of the miniaturization of the antennas is that it is done to the detriment of the bandwidth of the antenna. For example, the relative bandwidth of the solution described in the American patent application is of the order of 1% to 4% of the central frequency. In the case of strong miniaturization, that is to say that the dimensions of the antenna are less than λ _o / 10, with λ _o the working wavelength, the bandwidth can be less than 1%.

An objective technical problem is therefore to allow a broadening of the bandwidth of an antenna, in order for example to compensate for the reduction in bandwidth that would result from a reduction in the size of the antenna.

STATEMENT OF THE INVENTION

The invention provides a solution to the problem of the prior art.

The invention relates to a broadband antenna comprising: a primary antenna;

at least one main resonator in electromagnetic coupling with said primary antenna;

According to the invention:

said broadband antenna also comprises at least one secondary resonator in electromagnetic coupling with the primary antenna and at least one main resonator;

said at least one main resonator and said at least one secondary resonator each comprise at least one resonant frequency close to an operating frequency fo, associated with an operating wavelength λ _o of said widened bandwidth antenna .

In one embodiment, each of the resonance frequencies has a relative deviation with the operating frequency fo less than or equal to 10%.

In one embodiment, the at least one main resonator and the at least one secondary resonator comprise a rectangular plate of a dielectric substrate and a monopoly with rectangular meanders printed on one of the main faces of said dielectric substrate.

In one embodiment, the primary antenna is in physical contact with at least one of the at least one main resonator and / or said at least one main resonator is in physical contact with at least one of the at least one resonator secondary.

In one embodiment, the primary antenna is a monopoly of length less than a quarter of the operating wavelength λ _o .

In one embodiment, the primary antenna is an exponential antenna.

In one embodiment, a thickness of said extended bandepassante antenna is less than or equal to a _o / 100.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be better understood on reading the description which follows and on examining the figures which accompany it. These are presented only as an indication and in no way limit the invention.

FIG. 1A represents an isometric view in transparency of an antenna according to the invention in a first embodiment.

Figure 1B shows an exploded isometric view of the antenna in the embodiment of Figure 1 A.

FIG. 2 represents a generic form of the conductive track of a printed circuit with rectangular meanders and its characteristic dimensions.

FIG. 3 represents the evolution of a reflection coefficient Su of the antenna according to the invention in the embodiment of FIG. 1A, operating at a frequency of 1 GHz.

FIG. 4 represents the directivity diagrams of the antenna according to the invention, in the embodiment of FIG. 1A, in a plane E, a plane H and a horizontal plane.

FIG. 5 represents an exploded isometric view of the antenna according to the invention in a second embodiment.

FIG. 6 represents the evolution of the reflection coefficient Su of the antenna according to the invention in the embodiment of FIG. 5, operating at a frequency of 125 MHz.

FIG. 7 represents the directivity diagrams of the antenna according to the invention, in the embodiment of FIG. 5, in a plane E and a plane H.

Figures are not necessarily to scale. Identical elements or elements performing the same function keep the same reference from one figure to another.

DETAILED DESCRIPTION

For clarity of description, an orthogonal coordinate system (OXYZ) is defined.

With reference to this coordinate system, a vertical direction is defined as being the direction carried by the axis (OZ), the plane (OXY) defining a horizontal plane. In particular, a height is defined as a dimension along the axis (OZ).

For simplicity, the vectors will be noted in bold in the description.

With reference to FIGS. 1A and 1B, an antenna with enlarged bandwidth 1 according to the invention comprises:

a primary monopoly 10;

a primary resonator 11 a and a secondary resonator 11 b.

Each of the two resonators 11a, 11b is composed of a dielectric substrate 110a, 110b, for example an epoxy material, having the shape of a rectangular plate and comprising a front face, of normal vector the vector Y and a rear face, of normal vector the vector -Y. A secondary monopoly 111a, 111b with rectangular meanders is printed on the rear face of each of the two resonators 11a, 11b, said two secondary monopolies being made of a metallic material, for example copper. A generic form of such a monopoly with rectangular meanders, as well as the main geometric characteristics of said monopoly, are illustrated in FIG. 2, and presents a succession of ribbons R of ribbon width Lr, spaced apart by a spacing Esp, and of elbows C having a width at the elbow L _c and a height H _c . The monopoly illustrated in Figure 2 also has a total height H _t and a total width L _t .

The resonators 11a, 11b are in physical contact with each other, the front dielectric face of the secondary resonator 11b being in contact with the rear dielectric face of the primary resonator 11a, on which the rear dielectric face is printed the secondary monopoly 111a. The secondary monopolies 111a, 111b are electrically connected by means of an electrical ground plane located at a base of the resonators 11a, 11b.

The primary monopoly 10 consists of a metallic strand, for example of copper, rectangular and printed on the front face of the dielectric substrate 110a of the primary resonator 11a. The primary monopoly 10 extends from a lower end of the primary resonator 11a along a substantially vertical axis, over a height h _m .

Because of their position with respect to the primary monopoly 10, the resonators 11a, 11b are strongly coupled to said primary monopoly. The primary resonator 11a being placed as close as possible to the primary monopoly 10, it undergoes electromagnetic coupling with said most important primary monopoly. The secondary resonator 11b being more distant than said primary resonator from said primary monopoly, it consequently undergoes less electromagnetic coupling therewith.

When the primary monopoly 10 is supplied (by a supply not illustrated here), the resonators 11a, 11b are in electromagnetic coupling with said primary monopoly. The electromagnetic coupling between the resonators 11a, 11b is reinforced by the contacts between the monopole 10 and the primary resonator 11a on the one hand and on the other hand between the resonators 11a, 11b.

FIG. 3 illustrates an evolution as a function of the frequency of a reflection coefficient 5 Su of the broadband antenna 1 thus constituted. In the embodiment for which the measurement was made, said broadband antenna has the following characteristics:

the primary monopoly 10 has a height of 6mm and a width of 1mm;

- the resonators 11a, 11b have substantially the following dimensions:

PRIMARY RESONATOR 11a Dielectric substrate 110a Substrate height H _s 12 mm Substrate width L _s 12 mm Substrate thickness e _s 0.3 mm Monopoly with rectangular meanders 111a Elbow width L _c 0.43 mm Elbow height H _c 0.86 mm Ribbon width Lr 0.43 mm Spacing Esp 0.86 mm Meander height H _t 12 mm Meander width L _t 12 mm

SECONDARY RESONATOR 11b Dielectric substrate 110b Substrate height H _s 12 mm Substrate width L _s 12 mm Substrate thickness e _s 0.3 mm Monopoly with rectangular meanders 111b Elbow width L _c 0.40 mm Elbow height H _c 0.80 mm Ribbon width L _R 0.40 mm Spacing Esp 0.80 mm Meander height H _t 12 mm Meander width L _t 12 mm

The measured evolution profile 2 shows two resonance peaks 21,22, at frequencies f _r , i, f _r , 2, with:

f _rl = 1.04 GHz f _r2 = 1.07 GHz

A frequency band Bf, _i ₀ for which the reflection coefficient Su is less than or equal to -10dB is:

B _f _ ₁₀ = [1.03; 1.08] GHz

Consequently, a bandwidth BP.-ιο to -10dB, defined as a difference between a maximum value and a minimum value of the frequency range for which the reflection coefficient Su is less than or equal to 10dB is substantially equal to:

BP_ ₁₀ = 50 MHz

A relative band width B _{r,. 10} at -10dB, defined as a ratio between the bandwidth at -10dB and the center frequency of the bandwidth is here equal to approximately 4.8%.

FIG. 4 represents a directivity diagram 3 of the antenna 1, in the embodiment of FIGS. 1A and 1B, at 1 GHz:

a first profile 30 (represented by dashes) represents the directivity of the antenna 1 in a plane E;

a second profile 31 (represented by dotted lines) represents the directivity of the antenna 1 in a plane H;

a third profile 32 (shown in solid solid line) represents the directivity of the antenna 1 in the plane (OXY).

The profiles 30, 31, 32 observed are substantially those of a quarter-wave monopoly.

Thus, the antenna 1 makes it possible to obtain radiation characteristics similar to those of the primary monopoly 10. In the embodiment of FIGS. 1A and 1B, the antenna with enlarged bandwidth 1 makes it possible to work at a frequency d '' approximately 1 GHz, with a bandwidth of approximately 4.8%, enlarged compared to the bandwidth of the primary monopoly 10 alone, approximately equal to 2%.

To operate effectively at 1 GHz, a monopoly must be quarter wave, therefore have a length of 7.5 cm. In the embodiment described above, the antenna 1 makes it possible to work at a frequency close to 1 GHz for a space requirement of 12mm along the axes (OX) and (OZ), ie equal to A _0/25 , where À _o is the wavelength associated with an operating frequency f ₀ , here 1 GHz. In this embodiment, the height of the primary monopoly is 6 mm, that is A _o / 5O.

In the example illustrated, a thickness ep of the antenna 1, corresponding in the figures to a space requirement of said antenna along the axis (OY), is equal to 0.75 mm (the thickness of the printed elements being equal to 0 , 05mm and that of the substrates at 0.3mm). The thickness of the antenna 1 is equal to a _0/400. Such a thickness makes it possible to limit the phenomena linked to the propagation of electromagnetic waves and promotes the coupling of the elements together.

It should be noted that the resonance frequencies f _r , i, f _r , 2 are adjustable by variation of one or more geometric characteristics of the monopole 10 and / or of the resonators 11a, 11b. They can for example be adjusted by increasing or decreasing the height h _m of the monopole 10, the width at the elbow L _c of the monopoles with rectangular meanders 111a, 111b, the height H of said monopolies, etc. Preferably, these resonance frequencies will be adapted so that they are included in a frequency interval:

[/o-O.l/o;/ô + O-l / o]

Where f ₀ denotes a desired operating frequency, that is to say that a relative difference between the desired operating frequency f ₀ and the resonance frequencies f _r i, f _r 2 is less than 10%.

In the example described above, the desired operating frequency is 1 GHz, and the resonance frequencies f _r i, f _r 2 are in the range [0.9; 1.1] GHz.

In a preferred embodiment, the relative difference between the desired function frequency fo and each of the resonance frequencies f _r i, f _r 2 is less than 5%.

This condition on the resonant frequencies favors the obtaining of a broadband antenna thanks to an overlap of the bandwidths of the two resonators 11a, 11b.

Advantageously, the thickness ep of the antenna 1 is less than _o / 100 in order to limit the phenomena linked to the propagation of the electromagnetic waves and to favor the couplings of the elements between them.

The number of resonators is not limited to two, and the radiation characteristics of the antenna 1 can be adjusted by adding resonators or by modifying the characteristics of the monopoly 10. In all cases, the resonators are arranged so that the faces having the rectangular meander monopolies are not in contact with each other, said monopolies being electrically connected by the bases of the resonators. In the same way, the primary antenna 10 is separated from the monopoles with rectangular meanders by a layer of dielectric.

With reference to the embodiment illustrated in FIG. 5, an antenna 1 according to the invention comprises:

a primary antenna 10;

two primary resonators 11 a-1, 11 a-2;

two secondary resonators 11 b-1, 11 b-2.

Each of the resonators 11 a-1, 11 a-2, 11 b-1, 11 b-2 is composed of a dielectric substrate 110a-1, 110a-2, 110b-1, 110b-2 and a secondary monopole 111 a-1, 111 a-2, 111 b-1, 111 b-2 with rectangular meanders.

The primary antenna 10 is an exponential antenna, a rear face of which is juxtaposed with a front face of a first primary resonator 11 a-1 and a front face of which is juxtaposed with a rear face of a second primary resonator 11a2. A front face of a first secondary resonator 11 b-1 is juxtaposed to a rear face of the first primary resonator 11 a-1, and a rear face of a second secondary resonator 11 b-2 is juxtaposed to a front face of the second primary resonator 11 a-2. The primary antenna 10 is therefore in direct physical contact with the primary resonators 11 a-1, 11a-2, and the resonators are in direct physical contact with one another.

When the primary antenna 10 is supplied by a power supply 4, the resonators 11 a-1, 11 a-2, 11 b-1, 11 b-2 are in electromagnetic coupling therebetween and with said primary antenna. The electromagnetic coupling between the resonators 11 a-1, 11 a-2, 11 b-1.11 b-2 is reinforced by the direct physical contacts which exist on the one hand between the primary antenna 10 and the primary resonators 11 a -1, 11 a-2 and on the other hand between said primary resonators and the secondary resonators 11 b-1, 11 b-2.

The desired operating frequency fo in the case described here is 125 MHz.

FIG. 6 illustrates the measurement of the evolution as a function of the frequency of the reflection coefficient Su of the antenna 1 thus formed. Profile 5 observed reveals two main resonance peaks 50, 51, at frequencies f _r , 3, f _r , 4 and two secondary resonance peaks 52, 53 at frequencies f _r , s, f _r> 6, with:

/ _r , ₃ = 121 MHz f _rA = 127 MHz f _r5 = 133.5 MHz f _ri6 = 140.5 MHz

Said main and secondary resonance peaks being attributable respectively to the couplings between main and secondary resonators placed on either side of the primary antenna 10.

The bandwidth BP.-ιο at -1 OdB, is substantially equal to 11 MHz.

The working frequency is 125 MHz and the relative bandwidth B _{r,. 10} is 8.8%.

As in the embodiment previously described, the geometric characteristics of the resonators and / or of the primary antenna 10 can be adjusted to modify the resonance frequencies, and thus increase or decrease the bandwidth of the antenna 1 .

FIG. 7 illustrates a directivity diagram 6 of the antenna 1, in the embodiment of FIG. 5, at 125 MHz:

a first profile 60 represents the directivity of the antenna 1 in a plane E;

a second profile 61 represents the directivity of the antenna 1 in a plane H.

The profiles 60.61 observed are substantially those of a quarter-wave monopole antenna.

Thus, the antenna 1 makes it possible to obtain radiation characteristics similar to those of a quarter-wave monopole antenna. In the exemplary embodiment of FIG. 5, the antenna 1 makes it possible to work at a frequency of approximately 125 MHz, with a wider bandwidth greater than in the case of a miniature monopoly without resonator.

The broadband antenna according to the invention therefore makes it possible to increase the bandwidth of a reference antenna ("primary antenna"), by adding resonators.

The resonators show resonant frequencies, sufficiently close to each other and to a desired working frequency, to allow a widening of the frequency band usable in operation of the antenna.

It is thus possible to obtain bandwidths of the order of 10%, while limiting the size.

It should be noted that the primary antenna 10 is not necessarily a quarter-wave monopoly or an exponential antenna and that other types of antenna are possible. Likewise, resonators are not limited to the shapes described here. For example, the printed circuit is not necessarily a rectangular meandered circuit but can have another shape. In all cases this resonator must behave like an LC circuit with an inductive part and a capacitive part.

A benefit of the invention is that it makes it possible to substitute for a first quarter-wave monopoly antenna having a space considered too large a second antenna at reduced height, whose bandwidth can be widened to obtain an equivalent bandwidth to the bandwidth of the first antenna.

Claims (7)

1. An antenna with extended bandwidth (1) comprising: a primary antenna (10); at least one main resonator (11a, 11a-1, 11a-2) in electromagnetic coupling with said primary antenna; characterized in that: said broadband antenna also comprises at least one secondary resonator (11b, 11b-1, 11b-2) in electromagnetic coupling with the primary antenna (10) and the at least one main resonator (11 a, 11 a-1, 11 a-2); said at least one main resonator and said at least one secondary resonator each have at least one resonant frequency (f _r , i, f _r , 2, f _r , 3, f _r , 4, f _r , 5, W close to d an operating frequency f ₀ , associated with an operating wavelength λ _o , of said broadband antenna. 2. An antenna with extended bandwidth according to claim 1 characterized in that each of the resonance frequencies (f _r , i, fr, 2, f _r , 3, fr, 4, f _r , 5, fr, 6> has a relative deviation with the operating frequency fo less than or equal to 10%. 3. An antenna with extended bandwidth according to claim 1 or claim 2, characterized in that the at least one main resonator (11a, 11a-1, 11a-2) and the at least one secondary resonator (11b, 11b1,11 b-2) have a rectangular plate of a dielectric substrate (110a, 110a-1, 110a-2, 110b, 110b-1, 110b-2) and a monopoly with rectangular meanders (111a, 111 a-1 , 111 a-2, 111 b, 111 b-1, 111 b-2) printed on one of the main faces of said dielectric substrate. 4. An antenna with extended bandwidth according to any one of the preceding claims, characterized in that the primary antenna (10) is in physical contact with at least one of the at least one main resonator (11a, 11a-1 , 11a-2) and / or said at least one main resonator is in physical contact with at least one of the at least one secondary resonator (11b, 11 b-1, 11 b-2). 5. An antenna with extended bandwidth according to any one of claims 1 to 4 characterized in that the primary antenna (10) is a monopoly of length less than a quarter of the operating wavelength λ _o . 6. An antenna with extended bandwidth according to any one of claims 1 to 4 characterized in that the primary antenna (10) is an exponential antenna. 15 7. An antenna with increased bandwidth according to any one of the preceding claims, characterized in that a thickness ep of said antenna with enlarged bandwidth is less than or equal to _{o o} / 100.