EP1825566B1 - Improvement of active photonic forbidden band antennae - Google Patents

Abstract

The invention relates to an active photonic forbidden band antenna. The photonic forbidden band structure consists of metallic rods (2,3), some of which are discontinued (3), i.e. they consist of sections of rods connected by a switching element such as a PIN diode. According to the invention, only one rod (3) in a row of rods, as seen from the radiating source (1), is discontinued. The antenna diagram can be economically controlled.

Description

The present invention relates to active photonic bandgap antennas.

Photonic bandgap structures are known by the abbreviation BIP, generally by the term "Photonic Band Gap Structure" or PBG structure in English, for periodic structures that prohibit the propagation of a wave for certain frequency bands . These structures were first used in the optical field, but in recent years their application has spread to other frequency ranges. Photonic bandgap structures are used in particular in microwave devices such as filters, antennas or the like.

Among the photonic band gap structures, there are metal structures that use a periodic distribution of metal elements, others a periodic distribution of dielectric elements but also metallo-dielectric structures.

The present invention relates to a photonic band-gap structure using metal elements, more particularly parallel rods which are perfectly conducting and arranged periodically, some of the rods being formed of sections connected by a switching element which, depending on its state, makes the stem continuous or discontinuous.

Photonic bandgap antennas based on metal elements such as parallel metal rods have already been studied. So, the article published in the journal Chin. Phys.Lett. Flight. 19, No. 6 (2002) 804 titled "Metal Photonic Band Gap Resonant Antenna with High Directivity and High Radiation Resistance", Lin Qien, FU-Jian, HE Sai-Ling, Zhang Jian-Wu studies a resonant structure with photonic band gap (MBPG) formed of infinitely long parallel metal rods in the Z direction.

It is also described in an article entitled "A Beam Steering Antenna Controlled with a Material EBG" on behalf of P Ratajczak, PY Garel, P. Brachat published in IEEE AP-S 2004 , an antenna consisting of a source placed in the center of a photonic bandgap structure composed of metal rods formed of sections of rods interconnected by a PIN diode for switching from the continuous state to the discontinuous state. This is called an active photonic band gap antenna.

The present invention relates to an improvement to an active photonic band gap antenna (BIP) which is carried out with metal rods of finite length, some of which are formed of sections interconnected by a switching element which makes it possible to make the rod continuous or discontinuous. Thus, different radiation patterns can be obtained depending on the location of the discontinuous stems.

The present invention relates to an active photonic band gap antenna (BIP) having, in a plane of x, y directions, a radiating source and a photonic band gap structure constituted by parallel metal rods, perpendicular to said plane, the diameter rods. d repeating n _x times with a period a _x in the x direction and n _y times with a period _y in the y direction, the rods being constituted by continuous rods and discontinuous rods formed by at least 2 sections connected by a switching element making the rod continuous or discontinuous, characterized in that one of the rods of at least one row of rods viewed from the radiating source is a discontinuous rod.

According to one embodiment, the discontinuous rod comprises a number of sections t such that t ≥ 2. Preferably, the length L of a section is equal to λ0 / 2 where λ0 is the wavelength at the operating frequency of the antenna. Thus, the total height of a discontinuous stem is given by the formula H = (n _e + 1) L + n _e e, in which: n _e corresponds at the number of discontinuities, L corresponds to the length of a section and e to the size of the switching element.

According to another characteristic of the invention, the discontinuous rod corresponds to the outer stem of a row of stems seen by the source.

According to one embodiment, the source is a monopole mounted on a ground plane on which the rods are also mounted, a DRA (for Dielectric Resonator Antenna) mounted on a ground plane, a dipole or the like. The rods are made of a metallic material such as copper, silver, aluminum or the like. The switching element is selected from PIN diodes or MEMs for MicroElectroMechanical Systems

• Fig :1 est une vue très schématique d'une antenne à bandes interdites photoniques selon l'art antérieur avec son diagramme de rayonnement en 3D,
• Fig : 2 est une vue identique à celle de figure 1 dans le cas d'une antenne à bandes interdites photoniques selon un mode de réalisation de la présente invention,
• Fig : 3 est une vue en perspective d'une tige discontinue utilisée dans la présente invention,
• Fig : 4 représente schématiquement les quatre directions possibles pour les tiges discontinues ainsi que les diagrammes de rayonnement correspondants,
• Fig : 5 représente schématiquement les différents emplacements possibles pour les tiges discontinues selon une direction donnée ainsi que les diagrammes de rayonnement correspondants et
• Fig : 6 représente schématiquement une variante de réalisation de la présente invention.

Other advantages and features of the present invention will appear on reading the description made with reference to the accompanying drawings in which:

• Fig: 1 is a very schematic view of a photonic band gap antenna according to the prior art with its 3D radiation pattern,
• Fig: 2 is a view identical to that of figure 1 in the case of a photonic bandgap antenna according to an embodiment of the present invention,
• Fig: 3 is a perspective view of a discontinuous rod used in the present invention,
• Fig: 4 schematically represents the four possible directions for discontinuous stems as well as the corresponding radiation patterns,
• Fig: 5 schematically represents the different possible locations for discontinuous stems in a given direction as well as the corresponding radiation patterns and
• Fig: 6 schematically represents an alternative embodiment of the present invention.

To explain the concept of the present invention, we will first describe, with reference to the figure 1 , an antenna with forbidden bands photonics according to the prior art. This antenna consists of a radiating source formed by a dipole 1 sized to operate at a frequency f ₀ = 5.25GHz and positioned in the center of a metal photonic band gap structure or BIPM of square shape composed of 6x6 metal rods 2. The BIPM period a is such that the plane wave characterization has its first propagation peak at the above frequency. His radiation pattern as depicted on the figure 1 , is then rosette-shaped with four main lobes in the directions (0 °, 90 °, 180 ° and 270 °). This antenna has preferred directions of radiation when the BIPM structure traversed in this direction is busy. On the contrary, this antenna has radiation minima when the crossed BIPM structure is blocking. This blocking or passing state is deduced from an ancillary simulation called plane wave characterization known to those skilled in the art. The characterization under wave consists of illuminating metallic rods of infinite dimensions along the Z axis under plane wave.

Thus, a source sized at f = 5.25GHz (wired dipole) at the center of a BIPM structure of 6x6 rods of period a = 17.5mm presents a rosette-shaped diagram with preferred directions of radiation in the plane Θ = 90 ° for (0 °, 90 °, 180 ° and 270 °). This is explained by the fact that a BIPM structure characterized by a plane wave has a bandwidth at this frequency. On the contrary, in the directions (45 °, 135 °, 225 ° and 315 °), the radiation pattern of the antenna has radiation minima because the characterization under a plane wave at this frequency for a period viewed from a '= a√2 = 24.8mm has a band gap. This explains the rosette-shaped radiation pattern. Moreover, this operation is obtained when a height of metal rods is respected, namely H> 1.5λ ₀ .

On the figure 2 , there is shown an active BIPM antenna according to the present invention. In this case, the first metal rod 3 of two contiguous rows of metal rods seen from the source 1 is a discontinuous rod according to the direction explained below, namely a rod formed of at least 2 sections connected by a switching element which can be on or off such as a PIN diode or a MEMS-based switch (Micro Electro Mechanical System). The energy radiated by the source 1 in the middle of the active BIPM structure does not propagate in the direction where the two discontinuous rods are located, the BIPM structure being blocking, and one obtains a radiation pattern as shown in FIG. figure 2 with a preferred direction of radiation opposite to the direction in which the discontinuous stems are. This dual operation between the continuous and discontinuous rods is obtained when the length of the sections L of the metal rods forming the discontinuous rods is of the order of the half-wavelength. Thus for an operating frequency of f ₀ = 5.25GHz, L = 28.6mm.

We will explain below with reference to the figure 3 , the dimensioning of a discontinuous rod. In particular, the figure 3 represents a discontinuous stem and the relation allowing to link "H", the total height of the discontinuous stem to the geometrical parameters of the discontinuous stem. These parameters are "L", the length of the metal sections, "ne", the number of discontinuities and "e", the size of the discontinuity. So we get the equation: $$\mathrm{H}\mathrm{=}\left({\mathrm{not}}_{\mathrm{e}}\mathrm{+}\mathrm{1}\right)\mathrm{x\; L}\mathrm{+}{\mathrm{not}}_{\mathrm{e}}\mathrm{xe}$$

Thus for the antenna topology presented as an example, the height of the metal rods is equal to H = 8.98 cm, with n = 2 (2 discontinuities per rod), e = 2 mm (corresponding to the size of a diode) and L = 28.6cm (as mentioned above for 5.25GHz operation).

We will now describe with reference to Figures 4 to 6 various embodiments of the present invention. So on the figure 4 , two discontinuous rods 3 are respectively positioned according to the 4 directions surrounding the source 1. In this case, it obtains four possible configurations for the radiation pattern, as shown in the figure. On the figure 5 , the discontinuous rods 3 are, for the same direction, positioned in three different arrangements, namely respectively on the first line seen by the source 1, the second line and the third line or external line. This last solution facilitates the realization of the antenna because the control due to the switching element such as a PIN diode is made easier by being performed on the outside of the BIPM structure. For comparison, there is also shown a solution with 2 complete rows of discontinuous rods 3. As shown in the figure, the associated radiation patterns are comparable to prohibit the energy to propagate in the direction considered. Thus, the solution of the present invention makes it possible to control the radiation pattern with minimal cost since only one rod per row is a discontinuous rod whose structure is more expensive due to the use of switching elements. On the figure 6 a BIPM antenna with 3 discontinuous rods 3 is shown surrounding source 1 on three sides, the other rods being continuous rods 2. With this structure, we obtain the radiation diagram shown on FIG. figure 6 with 12 dB directivities.

Thus, by using only a small number of discontinuous rods, it is possible to control the radiation pattern of an active photonic band gap antenna.

Claims (6)

1. An active photonic band gap antenna (PBG) comprising, according to a plane of directions x, y, a radiating source and a photonic band gap structure constituted by parallel metal rods, perpendicular to the said plane, the rods of diameter d repeating themselves n_x times with a period a_x in the direction x and ny times with a period a_y in the direction y, the rods being constituted by continuous rods and discontinuous rods formed by at least 2 sections connected by a switching element making the rod continuous or discontinuous, characterized in that one of the rods of at least one row of rods seen from the radiating source is a discontinuous rod.
2. Antenna according to claim 1, characterized in that the discontinuous rod comprises a number of sections t such that t ≥ 2.
3. Antenna according to any one of the claims 1 or 2, characterized in that the length L of a section is equal to λ0/2 where λ0 is the wavelength at the operating frequency of the antenna.
4. Antenna according to any one of claims 1 to 3, characterized in that the total height of a discontinuous rod is given by the formula H = (n_e+1) x L + n_e x e, wherein: n_e corresponds to the number of discontinuities, L corresponds to the length of a section and e to the size of the switching element.
5. Antenna according to any one of claims 1 to 4, characterized in that the discontinuous rod corresponds to the external rod of a row of rods seen from the source.
6. Antenna according to any one of claims 1 to 5, characterized in that the source is a monopole mounted on a ground plane on which the rods are also mounted, a DRA (Dielectric Resonator Antenna) mounted on a ground plane or a dipole.

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