DIELECTRIC RESONATOR Field of the invention

The present invention relates to a dielectric resonator comprising a dielectric material including a dielectric ceramic composition comprising at least one surface treated dielectric filler and at least one heterophase copolymer.

Moreover, the present invention also relates to a dielectric material including a dielectric ceramic composition comprising at least one surface treated dielectric filler and at least one heterophase copolymer.

Background of the invention

Dielectric ceramic materials are widely utilized in dielectric resonator materials, MIC (monolithic IC) dielectric substrate materials, dielectric waveguides, dielectric antennas, and any of various electronic components, which are employed for microwave and millimeter-wave regions in various communication equipments such as car telephones, cordless telephones, personal wireless units, satellite broadcasting receivers, millimeter wave radars, wireless LANs, wireless systems, and the like. A dielectric resonator is generally enclosed in a conductive shield to prevent it from radiating. An unshielded dielectric resonator may be used as an antenna, and this type of antenna is generally called Dielectric Resonant Antenna (DRA).

With the evolution of electronic packaging there are growing demands for size and weight reductions (i.e. miniaturization) of communication equipments and, hence, of dielectric materials capable of meeting such needs.

Composite materials are suitable for this purpose, because they overcome fragility, size, mechanical problems and relatively high cost of dielectric ceramic resonators. Several high dielectric constant materials based on polymers combined with ceramics are known.

United States Patent US 6,489,928 discloses a composite dielectric moulded product formed by moulding a composite dielectric material comprising a dielectric inorganic filler and an organic polymer resin. It is disclosed that, the dielectric constant of a composite dielectric moulded product is substantially determined by

the dielectric inorganic filler used, and may thus be controlled by controlling the type and amount of the dielectric inorganic filler added to the organic polymer resin. The dielectric inorganic filler therein disclosed may be preferably selected from oxides, carbonates, phosphates and silicates of Ma, IVa, 1Mb, or IVb group elements, and compound oxides of Ma, IVa, 1Mb, or IVb group elements. Examples of such fillers include TiO ₂ , CaTiO ₃ , MgTiO ₃ , AI ₂ O ₃ , BaTiO ₃ , SrTiO ₃ , CaCO ₃ , Ca ₂ P ₂ O ₇ , SiO ₂ , Mg ₂ SiO ₄ , Ca ₂ MgSi ₂ O ₇ , Ba(Mg ₁₇₃ Ta _2Z3 )O ₃ , and the like. However, there is no evidence of a filler surface treatment or of a dielectric loss tangent (tan δ) of said composite dielectric material.

United States Patent US 4,849,284 discloses an electrical substrate material comprising a fluoropolymeric material; a ceramic filler material, said filler material being in an amount of at least 55 weight percent of the total substrate material; said ceramic filler being coated with a silane coating; at least one layer of metal being disposed on at least a portion of said electrical substrate material. The abovementioned electrical substrate material is said to be useful for forming rigid printed wiring board substrate materials and integrated circuit chip carriers and to exhibit improved electrical performances over other printed wiring board materials and circuit chip carriers. Also, the low coefficients of thermal expansion and relatively high compliance resulting in improved surface mount technology and plated through-hole reliability, is disclosed.

European Patent Application EP 382,557 discloses a moisture resistant composite dielectric material which is formed by dispersing in an insulating high polymer material an inorganic filler material which has been surface treated with a fluorine- based silane coupling agent.

Summary of the invention

However, the Applicant has noticed that the abovementioned composite dielectric materials may show some drawbacks.

For example, the Applicant has noticed that, in order to achieve high dielectric constant values, it is required to increase the amount of the fillers added to the polymeric materials, resulting in problems such as that the obtained composite dielectric materials are not processable and easily mouldable to obtain integration

in the package.

Moreover, the Applicant has also observed that the fillers usually used with composite dielectric materials, such as, for example, BaTiO ₃ , MgTiO ₃ , CaTiO ₃ , SrTiO ₃ , are inorganic fillers that, in absence of an organic surface treatment of the fillers, are not easily mixed with the organic polymeric materials.

The Applicant has faced the problem of providing dielectric resonators having reduced size and weight (i.e. suitable for miniaturization) and able to maintain good dielectric properties.

Moreover, the Applicant has faced the problem of providing a dielectric material having high dielectric constant (ε _r ) value and low dielectric loss tangent (tan δ) value, said dielectric material being advantageously used in dielectric resonators having reduced size and weight and being able to maintain said dielectric properties even in presence of unfavourable environmental conditions (in particular, in moisture presence).

The Applicant has now found that the above reported properties may be obtained by using a dielectric ceramic composition comprising at least one surface treated dielectric filler and at least one heterophase copolymer comprising a thermoplastic phase based on propylene and an elastomeric phase based on ethylene copolymerized with an α-olefin.

Furthermore, the Applicant has found that said dielectric material shows good processability so allowing a dielectric resonator comprising the same to be easily manufactured (e.g., by injection moulding technique).

Moreover, the Applicant has found that said dielectric material shows low water absorption and, consequently, is able to maintain its dielectric properties also in the presence of moisture, so allowing a dielectric resonator comprising the same to maintain good dielectric properties even in presence of unfavourable environmental conditions (in particular, in moisture presence).

In a first aspect, the present invention relates to a dielectric resonator comprising

a dielectric material including a dielectric ceramic composition comprising at least one surface treated dielectric filler and at least one heterophase copolymer comprising a thermoplastic phase based on propylene and an elastomeric phase based on ethylene copolymerized with an α-olefin.

In a second aspect, the present invention relates to a dielectric material including a dielectric ceramic composition comprising at least one surface treated dielectric filler and at least one heterophase copolymer comprising a thermoplastic phase based on propylene and an elastomeric phase based on ethylene copolymerized with an α-olefin.

For the purposes of the present invention and of the claims which follow, the term "dielectric resonator" is referred to an electronic component that exhibits resonance, such as, for example, dielectric loaded cavity resonators, coaxial resonators, transmission line resonators, oscillators, filters and antennas. Dielectric resonators are used in a variety of electronic circuits to perform a variety of functions. Typically, the exhibited resonance of a dielectric resonator is in a narrow range of frequencies, such as in the microwave or RF bands, even if the frequency response may be broadened by air gap arranged between the dielectric resonator and the conductive elements. Depending upon the structure and material of the resonator, when an AC signal is applied to the resonator over a broad frequency range the resonator will resonate at specific resonant frequencies. This characteristic allows the resonator to be used, for example, in an electronic filter that is designed to pass only frequencies in a preselected frequency range, or to attenuate specific frequencies.

The resonant frequency is determined by the overall physical dimensions of the dielectric resonator and the dielectric constant (ε _r ) value of the dielectric material included therein. Generally, to reduce its size, a dielectric resonator comprises a dielectric material having a high dielectric constant (ε _r ) value, such as, for example, in the range of from 7 to 30, and a low dielectric loss tangent (tan δ) value such as, for example, lower than 0.0035, preferably lower than 0.0020. Said dielectric loss tangent (tan δ) value is usually defined as the ratio between the energy consumed in a dielectric material and the energy built up in the dielectric material per cycle of an alternating field. Said low dielectric loss tangent (tan δ)

value allows the obtained dielectric resonator to have a low dielectric loss, i.e. a low energy loss in the transmission process and, consequently, a high energy efficiency.

Usually, a dielectric resonator comprises an input terminal and an output terminal that are disposed on opposite sides in a metal case, and a dielectric material that includes the above dielectric ceramic composition and that is disposed between said input and output terminals. In this dielectric resonator, microwaves are inputted from the input terminal and the microwaves are confined within the dielectric ceramic material, due to the reflection of the boundary between the dielectric ceramic material and a free space, thereby causing resonance at a specific frequency. Signals generated at this time are electromagnetically coupled to the output terminal, and then outputted.

The shape of the dielectric resonator of the present invention may be, for example, rectangular solid, cube, plate, disk, cylinder, polygonal column, or any other solid shape which allows for resonance.

Said dielectric resonator may be advantageously used in a dielectric antenna device. In fact, the high dielectric constant (ε _r ) value of the dielectric material used allows to obtain a dielectric resonator having a reduced size and weight (i.e. allows an easy miniaturization of the dielectric resonator), which may be easily assembled in a dielectric antenna device. Furthermore, the low dielectric loss tangent (tan δ) value of the dielectric material used allows to obtain a dielectric resonator, as well as a dielectric antenna device, having a high energy efficiency.

In a third aspect, the present invention relates to a dielectric antenna device including at least one dielectric resonator comprising a dielectric material including dielectric ceramic composition comprising at least one surface treated dielectric filler and at least one heterophase copolymer comprising a thermoplastic phase based on propylene and an elastomeric phase based on ethylene copolymerized with an α-olefin.

The present invention, in at least one of the abovementioned aspects, may show one or more of the preferred characteristics hereinafter described.

For the purpose of the present description and of the claims which follow, the expression "heterophase copolymer comprising a thermoplastic phase based on propylene and an elastomeric phase based on ethylene copolymerized with an α- olefin" means a thermoplastic elastomer obtained by sequential copolymerization of: (i) propylene homopolymer or a copolymer of propylene, optionally containing small amounts of at least one olefinic comonomer selected from ethylene and α- olefins other than propylene; and then of: (ii) a mixture of ethylene with an α- olefin, and optionally with small proportions of a polyene. This class of products is also commonly known as "thermoplastic reactor elastomers".

As disclosed above, the heterophase copolymer is prepared by sequential copolymerization of: (i) propylene, optionally containing at least one olefinic comonomer chosen from ethylene and α-olefins other than propylene; and then of: (ii) a mixture of ethylene with an α-olefin, in particular propylene, and optionally a polyene, in particular a diene. The copolymerization is usually carried out in the presence of Ziegler-Natta catalysts based on halogenated titanium compounds supported on magnesium chloride in admixture with an aluminium trialkyl compound wherein the alkyl groups contains from about 1 to about 9 carbon atoms such as, for example, aluminium triethyl or aluminium triisobutyl. More details regarding the preparation of the heterophase copolymer are given, for example, in European Patent Applications EP 400,333, or EP 373,660, or in United States Patent US 5,286,564.

The thermoplastic phase of the heterophase copolymer, mainly produced during the abovementioned phase (i) of the process, consists of a propylene homopolymer or a copolymer of propylene with an olefinic comonomer selected from ethylene and α-olefins other than propylene. Preferably, the olefinic comonomer is ethylene. The amount of olefinic comonomer is preferably less than about 10 mol% relative to the total number of monomer moles in the thermoplastic phase.

The elastomeric phase of the heterophase copolymer, mainly produced during the abovementioned phase (ii) of the process, is of from about 5% by weight to about 65% by weight, more preferably of from about 10% by weight to 30% by weight,

relative to the total weight of the heterophase copolymer, and consists of an elastomeric copolymer of ethylene with an α-olefιn and optionally with a polyene. Said α-olefin is preferably propylene; said polyene is preferably a diene. The diene optionally present as comonomer generally contains from about 4 to about 20 carbon atoms and is preferably selected from: linear (non-)conjugated diolefins such as, for example, 1 ,3-butadiene, 1 ,4-hexadiene, 1 ,6-octadiene, or mixtures thereof; monocyclic or polycyclic dienes, for example 1 ,4-cyclohexadiene, 5- ethylidene-2-norbornene, 5-methylene-2-norbornene, or mixture thereof. The composition of the elastomeric phase is generally as follows: from about 15 mol% to about 85 mol% of ethylene; from about 85 mol% to about 15 mol% of an α- olefin, preferably propylene; from 0 mol% to 5 mol% of a polyene, preferably a diene, with respect to the total weight of the elastomeric phase.

Preferably, the elastomeric phase consists of an elastomeric copolymer of ethylene and propylene having the following composition: from about 15% by weight to about 80% by weight, more preferably from about 20% by weight to about 50% by weight, of ethylene; from about 20% by weight to about 85% by weight, more preferably from about 50% by weight to about 80% by weight, of propylene, with respect to the total weight of the elastomeric phase.

The amount of elastomeric phase present in the heterophase copolymer may be determined by known techniques, for example by extracting the elastomeric (amorphous) phase with a suitable organic solvent (in particular, xylene at about 135°C at reflux for about 20 min): the amount of elastomeric phase is calculated as the difference between the initial weight of the sample and the weight of the dried residue.

The amount of propylene units in the elastomeric phase may be determined by extraction of the elastomeric phase as described above (for example, with xylene at about 135°C at reflux for about 20 min), followed by analysis of the dried extract according to known techniques, for example by infrared (IR) spectroscopy.

Preferably, said heterophase copolymer has a Melt Flow Index (MFI), measured according to ASTM Standard D1238-90b, at 230 ⁰ C ₁ under a load of 5 kg, of from about 5 g/10 min to about 200 g/10min, more preferably of from about 10 g/10

min to about 150 g/10min.

Preferably, said heterophase copolymer has a melting point higher than or equal to about 140 ⁰ C, preferably higher than or equal to about 160 ⁰ C.

Examples of heterophase copolymers which may be advantageously used according to the present invention and which are currently commercially available are the products Hifax ^® , such as Hifax CA 60 A (a catalloy heterophasic random propylene copolymer), Moplen ^® EP 300L (a heterophasic propylene copolymer) or Moplen ^® RP348T (a heterophasic random polypropylene copolymer), all available from Basell Polyolefins.

Preferably, said dielectric material has a Melt Flow Index (MFI), measured according to ASTM Standard D1238-90b, at 230 ⁰ C, under a load of 5 kg, of from about 2 g/10 min to about 200 g/10min, more preferably of from about 5 g/10 min to about 100 g/10min.

The above MFI allows the dielectric material to be easily processed by means of the industrial standard methods and techniques generally used for thermoplastic resins such as, for example, by injection moulding technique.

The dielectric constant (ε _r ) value of the dielectric material is substantially determined by the dielectric filler, and may thus be controlled by controlling the type and amount of the dielectric filler added. The dielectric fillers used in the present invention may be those typically used in the field of dielectric materials.

Preferably, the dielectric fillers which may be advantageously used in the present invention are inorganic dielectric fillers comprising at least one oxide or compound oxides of Ha, IVa, IMb, or IVb group elements, or mixtures thereof. By using such a dielectric inorganic filler, a high dielectric constant (ε _r ) value may be obtained even when the composite dielectric material has a small thickness. Examples of such fillers include TiO ₂ , CaTiO ₃ , MgTiO ₃ , AI ₂ O ₃ , BaTiO ₃ , SrTiO ₃ , SiO ₂ , Ba(Mg _1Z3 Ta _2Z3 )O ₃ , or mixtures thereof. An especially useful dielectric filler is titanium dioxide.

Preferably, the dielectric fillers have an average particle size in the range of from about 0.10 μm to about 1.0 μm in order to have a good dispersibility in the heterophase copolymer and to still have a sufficient capability to increase the effective dielectric constant (ε _r ) value of the dielectric composition. More preferably, the dielectric fillers have an average particle size of from about 0.15 μm to about 0.90 μm, still more preferably of from about 0.18 μm to about 0.80 μm.

Preferably, said dielectric filler is present in the dielectric material according to the present invention in an amount of from about 60% by weight to about 95% by weight, and more preferably of from about 70% by weight to about 90% by weight, with respect to the total weight of the dielectric material taking also in consideration in this percentage calculation the presence of additives and surface coatings. Said amounts may allow to obtain a dielectric material having a suitable dielectric constant (ε _r ) value and which may be easily processed, in particular by injection-moulding technique.

In order to avoid particles aggregation of the dielectric filler and to obtain a good compatibility of the same with the heterophase copolymer, said dielectric filler is surface treated.

By "surface treated" it is meant that the dielectric filler used according to the present invention have been contacted with compounds which are adsorbed on the surface of the dielectric filler or a reaction product of at least one of the compounds with the dielectric filler is present on the surface as an adsorbed species or chemically bonded to the surface. The compounds, or their reaction products, or combination thereof, may be present as a coating, either single layer or double layer, continuous or non-continuous, on the surface of the dielectric filler.

Preferably, the dielectric filler according to the present invention is surface treated with at least one organic or inorganic compound, or mixtures thereof.

Preferably, the organic compound may be selected, for example, from hydrophobic compounds such as, for example, silanes, siloxanes, polysiloxanes,

carboxylic acids or acrylic copolymer, organic titanates, organic zirconates, or mixtures thereof.

Examples of silanes are those in which at least one substituent group of the silane contains an organic substituent. The organic substituent may contain heteroatoms such as, but not limited to, oxygen or halogen. Typical examples of suitable silanes include, without limit, alkoxy silanes or mixtures thereof. For example, alkoxysilanes useful in carrying out the invention include octyltriethoxysilane, nonyltriethoxysilane, decyltriethoxysilane, dodecyltriethoxysilane, tridecyltriethoxysilane, tetradecyltriethoxysilane, pentadecyltriethoxysilane, hexadecyltriethoxysilane, heptadecyltriethoxysilane, octadecyltriethoxysilane, methyl triethoxysilane, dimethyl diethoxysilane, triethoxypropylsilane, or mixtures thereof. More typically, the silane is octyltriethoxysilane, octadecyltriethoxysilane, or mixtures thereof.

Additional examples of potentially useful silanes include 2-ethyl-2-methyldisilane, 1-ethoxy-2-silyltrisilane, 2-methyldisilanecarboxylic acid, benzylsilanediol, bromosilane, (trimethylsilyl)cyclohexane, cyclopentasilane, silylcyclohexane, or mixtures thereof.

Examples of siloxanes include hydridosiloxanes, alkylhydridosiloxanes in which the alkyl group contains from 1 to about 20 carbon atoms, or mixtures thereof.

Examples of carboxylic acids include carboxylic acids containing up to about 30 carbon atoms, typically from about 8 to about 30 carbon atoms, more typically from about 10 to about 20 carbon atoms. The carboxylic acid may be saturated or unsaturated, straight chain, branched chain or cyclic and may include one or more carboxyl groups (COOH). Preferably, the carboxylic acid has two or more carboxyl groups. Mixtures of carboxylic acids are contemplated as within the scope of this invention. Examples of useful carboxylic acids include, without limit, lauric acid, stearic acid, isostearic acid, oleic acid, linoleic acid, or mixture thereof.

An example of acrylic copolymer is a copolymer formed from polymerized methacrylic monomers, such as those disclosed in International Patent Application WO 03/010244.

Preferably, the inorganic compound may be selected, for example, from metal oxides, phosphates, silicates, with the proviso that the dielectric filler and the inorganic compound are not the same compounds. Examples of metal oxides include, but are not limited to, SiO ₂ , TiO ₂ , AI ₂ O ₃ , ZrO ₂ , SnO ₂ , SiAIO ₃ , SiTiO ₄ , AI ₂ TiO ₅ , CeO ₂ , yttria stabilized zirconia, Y ₂ O ₃ , in their stoichiometric or non- stoichiometric forms, either individually or in any combination thereof. In a preferred embodiment, the oxide comprises silica (SiO ₂ ), alumina (AI ₂ O ₃ ), zirconia, or mixture thereof.

The surface treatment of the dielectric filler may be carried out by processes known in the art. Preferably, said dielectric filler is firstly surface treated with at least one inorganic compound, which may be selected from those described above, and subsequently surface treated also with at least one organic compound, which may be selected from those described above.

Examples of surface treated dielectric fillers which may be advantageously used according to the present invention and which are currently commercially available are the following products: R-350 type rutile titanium oxide from Du Pont, having average particle size of 0.22 μm, purity of 95%, having been subjected to surface treatment with both inorganic compounds [AI ₂ O ₃ (content of 1.7% max) and SiO ₂ ] and organic compounds; R-104 type rutile titanium oxide from Du Pont, having average particle size of 0.22 μm, purity of 97%, having been subjected to surface treatment with both inorganic compounds [AI ₂ O ₃ (content of 1.7% max) and SiO ₂ ], and organic compounds; Tiona 125, Tiona 188 and Tiona 90 types rutile titanium oxide from Millennium Chemicals, having average particle size of about 0.21 μm to about 0.28 μm, purity of 98%, having been subjected to surface treatment with both inorganic compounds [alumina and SiO ₂ , or phosphates], and organic compounds.

The amount of the organic and/or inorganic compounds used to surface treating the dielectric filler covers a fairly wide range which could be easily optimized by a person of skill in the art. However, the amount may generally range from about 0.01% by weight to about 10 % by weight, preferably from about 0.1% by weight to about 5% by weight, with respect to the total weight of the dielectric filler.

The process of surface treating the dielectric filler particles is not especially critical and may be accomplished according to known techniques such as those described, for example, in United States Patents US 5,889,090, US 5,607,994, US 5,631 ,310, or US 5,959,004. The dielectric filler may be surface treated with a single organic or inorganic compound, or it may be treated two or more times with any number of organic or inorganic compounds.

Preferably, the dielectric material may further contain other additives, such as, for example, slip agents or processing aids such as, for example, stearic acid, zinc stearate; antioxidant agents such as, for example, pentaerythritol tetrakis [3-(3,5 di-t-butyl-4-hydroxyphenyl)propionate]; anti-UV agents; or mixtures thereof. Preferably said further additives are present in the dielectric material in an amount lower than about 3% by weight, more preferably, lower than about 2% by weight, with respect to the total weight of the dielectric material.

Brief description of the drawings

The present invention will now be illustrated in further detail by means of illustrative embodiments with reference to the attached figures, wherein:

Fig. 1 is a schematic diagram illustrating a dielectric resonator according to one embodiment of the present invention;

Fig. 2 is a side view of a dielectric antenna device according to a further embodiment of the present invention.

In particular, Fig. 1 shows a transversal electric (TE) mode type dielectric resonator which comprises an input terminal 2 and output terminal 3 that are disposed on opposite sides in a metal case 1 , and a dielectric material 4, which is made according to the present invention, disposed between the input and output terminals 2 and 3. In this transversal electric (TE) mode type dielectric resonator, microwaves are inputted from the input terminal 2, and the microwaves are confined within the dielectric material 4, due to the reflection of the boundary between the dielectric material 4 and a free space, thereby causing resonance at a specific frequency. Signals generated at this time are electromagnetically coupled to the output terminal 3, and then outputted.

Alternatively, a dielectric material according to the present invention may be used

in transversal electric magnetic (TEM)-mode coaxial resonators and strip line resonators, transversal magnetic (TM)-mode dielectric ceramic resonators, and other resonators, all of which are not shown in Fig. 1.

Alternatively, a dielectric resonator may be constructed by directly attaching the input and output terminals 2 and 3 to the dielectric material 4 (not shown in Fig. 1).

With reference to Fig. 2, the dielectric antenna device 20 comprises at least one dielectric resonator 30, which is made according to the present invention, and a metallic groundplane 40 supporting the dielectric resonator 30.

The dielectric resonator 30 has a substantially axial simmetry around an axis z which extends along the direction of the null of the radiated field.

According to a specific embodiment shown in Fig. 2, the conformal shape of the antenna device 20 and in particular of the dielectric resonator 30 is provided by the composition of three dielectric portions, each having a respective geometrical shape: a sphere cap 31 , supported by a reversed cut cone 32 supported by a cylinder 33. The bottom of the cylinder 33 is placed in such a way to contact the metallic groundplane 40.

Fig. 2 also shows a feed system 50 of the antenna device 20 which comprises a coaxial connector 51 and a metal pin 52 extending along the z axis from the coaxial connector 51 inside the dielectric resonator 30. The metal pin 52, which may be derived by the central pin of the coaxial connector 51 , may be positioned along the z axis or at a distance from it lower than λ/8 where λ is the wavelength of the electric field within the dielectric resonator 30.

The present invention will be further illustrated below by means of a number of preparation examples, which are given for purely indicative purposes and without any limitation of this invention.

EXAMPLE1

For the purposes of the present invention, the following dielectric fillers, in powder form, have been used.

P1 (comparative). Untreated rutile titanium oxide (TiO ₂ ) filler, from Sigma Aldrich, having average particle size 1 μm and purity 99.9%.

P2 (invention). R-350 type rutile titanium oxide (TiO ₂ ) filler, from Du Pont, having average particle size 0.22 μm and purity 95%, surface treated with both inorganic compounds [AI ₂ O ₃ (content 1.7% max) and SiO ₂ ], and organic compounds.

P3 (invention). R-104 type rutile titanium oxide (TiO ₂ ) filler, from Du Pont, having average particle size 0.22 μm and purity 97%, surface treated with both inorganic compounds [AI ₂ O ₃ (content 1.7% max) and SiO ₂ ], and organic compounds.

P4 (invention). Tiona 125 type rutile titanium oxide (TiO ₂ ) filler, from Millennium Chemicals, having average particle size 0.28 μm and purity 98%, surface treated with both inorganic compounds (alumina), and organic compounds.

P5 (invention). Tiona 188 type rutile titanium oxide (TiO ₂ ) filler, from Millennium Chemicals, having average particle size 0.21 μm and purity 98%, surface treated with both inorganic compounds (phosphates), and organic compounds. .

In order to know the compatibility between the dielectric fillers P1 to P5 and the heterophase copolymer, said dielectric fillers were subjected to a sedimentation analysis which is a gravimetric technique based on the surface interaction between a solid and a solvent.

To this aim, heptane, which is a non polar solvent chemically similar to the heterophase copolymer, has been selected in order to make the sedimentation analysis.

3 g of dielectric filler (P1-P5) were added to 25 ml of heptane in a 50 ml volume graded cylinder, forming a suspension. The suspension was stirred with magnetic stirring for 1 minute.

After stirring, the suspension begins to settle and the sedimentation volume, after

100 seconds, was measured: the obtained results are given in Table 1 (higher sedimentation volumes correspond to higher chemical affinity between the

dielectric filler and the solvent and, consequently, between the dielectric filler and the heterophase copolymer).

TABLE 1

Table 1 clearly shows that dielectric fillers P2 to P5 (that have been subjected to surface treatment) have sedimentation volumes, at 100 seconds, in heptane, higher than 10 ml, that is a reasonable minimum acceptable value for getting a composition having good dielectric properties. On the other hand, dielectric filler P1 (comparative - surface untreated), after few seconds, reached the saturation volume (4 ml).

EXAMPLE 2

For the purposes of the present invention, the following dielectric materials were prepared.

D1 (comparative) was prepared by inserting 100 g of copolymer CP1 - Moplen EP 300L copolymer, a heterophase propylene copolymer from Basell Polyolefins, having Melt Flow Index (MFI) 23 g/10 min (measured according to ASTM Standard D1238-90b, at 230 ⁰ C, under a load of 5 kg), melting point 165°C - in a Brabender mixer and mixing at a mixing temperature of about 2O ⁰ C higher than the melting point of the copolymer.

D2 (comparative) was prepared in the same way as D1 , with the only difference that, after polymer melting, 70 g dielectric filler P1 and 0.1 g of phenolic

antioxidant (Irganox 1010 from Ciba Specialty Chemicals) were added to 29.9 g of copolymer CP1.

D3 (comparative) was prepared in the same way as D2, with the only difference that 85 g of dielectric filler P1 and 14.9 g of copolymer CP1 were used.

D4 (invention) was prepared in the same way as D2, with the only difference that dielectric filler P1 was replaced by dielectric filler P2 (the same amount disclosed in D2 was used).

D5 (invention) was prepared in the same way as D3, with the only difference that dielectric filler P1 was replaced by dielectric filler P2 (the same amount disclosed in D3 was used).

The obtained dielectric materials D1-D5 were pressed, at a temperature of 180 ⁰ C, and at a pressure of 30 bar, using a mould of cylindrical shape having the following dimensions: 10 mm height and 42 mm diameter. Subsequently, the obtained sample was finished by means of mechanical tools, to obtain a sample of cylindrical shape having the following dimensions: 7±0.05 mm height and 34±0.05 mm diameter.

The obtained samples (D1-D5) were subjected to the tests below reported: the obtained data are given in Table 2.

Table 2, also discloses the data obtained for wet samples (D2 wet-D5 wet) which are the same samples D2-D5, which were subjected to water treatment, namely they were dipped in water, at a temperature of 40°C, for 4 weeks.

Dielectric measurements. The dielectric properties of the dielectric materials D1-D5 and D2 wet-D5 wet were measured using a cylindrical resonant metallic cavity. The specific resonance (i.e. frequency and quality factor) of said cavity measured with a vector network analyzer were, in fact, modified by the presence of the sample inside the cavity.

Using a numerical iterative method, it was possible to calculate the contribution of the sample under test to the resonance and, therefore, it was possible to calculate

both the dielectric constant (ε _r ) value and the dielectric loss tangent (tan δ) value of the dielectric material.

The dielectric constant (ε _r ) value was measured at a temperature of 25°C and at a frequency in the range of from 2 GHz to 4 GHz.

Rheoloqical measurements.

The Melt Flow Index (MFI) of the dielectric materials D1-D5, were measured according to ASTM Standard D1238-90b (measured at 230 ⁰ C, under a load of 5 kg).

Water absorption.

The dielectric materials D2 wet-D5 wet were weighted before and after water treatment in order to evaluate their water absorption.

TABLE 2

Table 2 clearly shows that dielectric material D1 (dielectric filler not present), has a very low dielectric constant (ε _r ) value and, consequently, can not be used according to the present invention.

Table 2 also shows that dielectric materials D4 and D5, both comprising the same surface treated dielectric filler P2, have both good dielectric and rheological properties (i.e. MFI). In particular, they have high dielectric constant (ε _r ) values and very low dielectric loss tangent (tan δ) values. On the contrary, comparative dielectric materials D2 and D3, both comprising the same surface untreated dielectric filler P1 , show high dielectric constant (ε _r ) values but too high dielectric loss tangent (tan δ) values (two or three times higher than the dielectric loss tangent values of the dielectric materials D4 and D5 of the invention). Moreover, dielectric material D3 shows a too low MFI which results in a dielectric material having a too high viscosity and, consequently, not easily processable.

In addition, Table 2 also shows that the dielectric materials D4 wet and D5 wet, both comprising the same surface treated dielectric filler P2, have very low water absorption values. In particular, it has to be noted that their dielectric constant (ε _r ) values and their dielectric loss tangent (tan δ) values are maintained substantially unchanged also after water treatment (in particular, it has to be noted that their dielectric constant (ε _r ) values have a percentage variation lower than 1.5%). On the contrary, comparative dielectric materials D2-wet and D3-wet, both comprising the same surface untreated dielectric filler P1 , show high water absorption values which causes a high variation in dielectric loss tangent (tan δ) values, which became from five to ten times higher than the dielectric loss tangent (tan δ) values of the dielectric materials D4 and D5 of the invention.

Table 2 also shows that the dielectric material D1 which is avoided of dielectric filler, has a good dielectric loss tangent (tan δ) value but a too low dielectric constant (ε _r ) value.

EXAMPLE 3

A dielectric material D6 of the invention, comprising 13.4 g of copolymer CP1 , 86 g of filler P2, and 0.1 g of antioxidant Irganox 1010 was prepared using a twin

screw extruder, at a temperature of 200 ⁰ C, and at a pressure of 80 bar. The dielectric material D6 was obtained in form of pellets.

The obtained pellets were injection moulded in a Arburg injection moulding press operating at the following working conditions: nozzle temperature: 205 ⁰ C; feed temperature: 40 ⁰ C; pressure: 720 bar; injection rate: 60-35 mm/s; - cycle time: 48 seconds; to obtain a dielectric resonator according to the present invention.

The obtained dielectric resonator was assembled in a dielectric antenna device as shown in Fig. 2. In order to appropriately customize its aspect, the external surface of the dielectric antenna device was painted with an acrylic paint.