WO1994029925A1

WO1994029925A1 - Antennas using novel ceramic ferroelectric materials

Info

Publication number: WO1994029925A1
Application number: PCT/US1994/005647
Authority: WO
Inventors: Louise C. Sengupta; Eric Ngo; Steven Stowell; Michelina E. O'day; Robert Lancto; Thomas W. Hynes
Original assignee: The United States Of America, Represented By The Secretary Of The Army
Priority date: 1993-06-09
Filing date: 1994-05-24
Publication date: 1994-12-22
Also published as: AU7242894A

Abstract

This invention concerns phase array antennas (37) using phase shifters (33) having novel ceramic ferroelectric materials (21) characterized by low dielectric constants, low loss and high tunability. Composite materials comprising Barium Strontium Titanate (BSTO) and a low dielectric constant material are used. Preferred composites are represented by Ba1-xSrxTiO3-Al2O3, Ba1-xSrxTiO3-MgO, or Ba1-xSrxTiO3-ZrO2, wherein x is greater than 0.00 but less than 0.75, and wherein the percent weight ratio between Ba1-xSrxTiO3 and alumina, zirconia, or magnesia range from approximately 99 % - 40 % and 1 % - 60 %, respectively. The phase array antenna can be configured as a geodesic dome antenna.

Description

ANTENNAS USING NOVEL CERAMIC FERROELECTRIC MATERIALS

BACKGROUND OF THE INVENTION

This patent application is a continuation-in-part of U.S. Patent Application Serial No. 08/076,291, filed on June 9, 1993. It is also copending with related U.S. Patent Applications Serial Nos. 08/207,447 (entitled "Novel Ceramic Ferroelectric Composite Material - BSTO- Zr0₂") - and 08/215,446 (entitled "Novel Ceramic Ferro¬ electric Composite Material - BSTO-MgO") . These patent applications are commonly owned by the U.S. Government as represented by the Secretary of the Army.

The present invention deals with novel ceramic ferroelectric materials which can be inserted into existing phased array antennas to reduce the cost, weight, and size of the phased array. Current phased array antennas are constructed from ferrite materials; therefore, they are current controlled which renders them extremely costly, large and heavy. These prior art ferrite materials are ferromagnetic and are current driven where the phase shift is caused by a change in the permeability of the material. Although the performance of the type of phase shifter currently employed is good, the costs are astronomical. The material cost alone per element is roughly $3,000.00; and the cost of the hand wiring of the materials increases the cost of each element employed by approximately $2,000.00 to $3,000.00. Hence, the cost of each element ranges from approximately $5,000.00 to $6,000.00. An antenna which employs an array with roughly 1,000 elements would therefore, merely for the array alone, cost approximately $5,000,000.00. This economic factor has limited the use of phased array antennas to strategically dependent military applications. The present invention is directed towards a novel ferroelectric material to take the place of the prior art ferrite materials. The ferroelectric materials described herein require a voltage driven circuit where the phase shift is caused by a change in the dielectric constant (permittivity) . These types of voltage driven circuits can be electroded and processed using standard, state of the art circuit board technology. The materials within the scope of the present invention perform at least as well as the ferrite phase shifters; and their cost is merely approximately $100.00 per element. The final packaging of these materials, including electroding and encapsulation, increases the cost per element by approximately $100.00. Therefore, the same array employing 1,000 elements will have an estimated cost of merely $200,000.00. This cost is only 4% (1/25) of the cost of the prior art ferrite phased array used in a phased array antenna.

Other advantages of employing the materials within the scope of the invention is the savings in size and weight of the antenna. The size of the antenna is reduced by 50-75% by mere use of the materials alone. Further size reduction on the order of another 50% occurs for the wiring and control circuits. The electro-optic antenna of the present invention may be less than 1/lOth the size of the larger ferrite array antenna. Although the weight of the actual materials used are similar, the amount of ferroelectric materials required for a particular antenna application is substantially less than the materials used by the prior art.

Thick and thin films of the ferroelectric materials may be produced by tape-casting, screen printing, laser ablation and chemical vapor deposition. These films can be used in many of the present, well-known antenna systems. Circuit board technology can be used to fabricate antennas, which as seen in the semiconductor industry, produces very small, light weight components and systems.

As set forth above, the need, therefore, exists for the fabrication of ceramic materials having improved electronic properties which may be adjusted for a particular, intended use. The present invention deals with novel ceramic ferroelectric materials having ideal properties for use in antennas — i.e., in phased array antenna systems.

In addition to the ferrite materials disclosed above, ferroelectric materials have been used in the art as well. Ferroelectric materials which are commonly used in the antenna arts are porous ceramics, whose properties are less than ideal for their intended application. Porous ceramics of the Ba--L ^~~~~ΛSrΛ.TiOJ type are commonly employed in ceramic phase shifter antennas. However, these materials display certain deficiencies due to both the processing difficulties and expense, as well as their overall electronic and microwave properties. These deficiencies include electronic inhomogeneity, structural weakness, reproducibility and processing control, and large loss tangents.

Barium Strontium Titanate (BaTiO_-SrTiO_) , also referred to herein as BSTO, has been known to be used for its high dielectric constant (approximately ranging from 200 to 6,000) in various antenna applications. This is set forth by Richard W. Babbitt et al. in their publication, "Planar Microwave Electro-Optic Phase Shifters," Microwave Journal. Volume 35(6), (June 1992). This publication concludes that there exists a need for additional research to be conducted in the materials art to yield materials having more desirable electronic properties.

Although the employ of BSTO in phase shifters is known, nowhere in the technical arena of ceramic art has there been any suggestion of modifying BSTO, or combining BSTO with additives, in the manner described herein. Moreover, the specific BSTO combinations, which have enhanced electronic properties, are deemed novel. The present invention, antennas, employ improved materials that exhibit electronic properties and can be adjusted for use, i.e., in any discrete element phase shifter antenna design (planar microstrip, wave guide geometries or parallel plate structure) . The antennas within the scope of the present invention are superior to other antennas in the art which currently use other ferro¬ electric or ferrite materials.

BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to the art of antenna systems. The novelty of the invention resides in the use of specific ceramic materials which have sought after properties in, for example, phased array antenna systems. These materials are ferroelectric materials which are voltage driven, lightweight and have low cost. The materials are composite modified Barium Strontium Titanate (BSTO) whose sought after properties include (l) low dielectric constant; (2) low loss; and (3) high tunability. Dielectric constant is related to the energy storage in the material; whereas, the loss tangent is related to the power dissipation in the same material. In general, the dielectric function is a complex quantity with e = e' - ie"; and the loss tangent, tan δ = e"/e' = 0.01 or less. Tunability may be defined as ((dielectric constant with no applied voltage) - (dielectric constant with an applied voltage) )/(dielectric constant with no applied voltage) . For simplicity purposes, tunability can be represented as T

^→-^~~r^~- «>

wherein, X = (dielectric constant with no applied voltage) ; and

Y - (dielectric constant with an applied voltage) .

The tunability of a material under an electric field of 7.0

KV/cm can range from 1-60% depending upon the composition of the materials employed.

The materials herein combine Barium Strontium Titanate

(BaTiO_-SrTiO_) with a ceramic material having a low dielectric constant. Said ceramic material having a low dielectric constant to be combined with Barium Strontium

Titanate may be selected from either Alumina (A1_0_) ,

Zirconia (ZrO_) or Magnesia (MgO) . These materials, encompassed by the present invention, are superior in that they are homogeneous, easily machinable, and possess superior electronic properties at both dc and microwave operating frequencies. Moreover, the materials herein have low water absorptivity. Typically these materials will absorb less than 2% by weight of water therein. Hence, the materials within the scope of the present invention are environmentally stable - - for example, they have good moisture and temperature stability.

Although other combinations of electrically active and inactive components have been commonly employed in conjunc¬ tion with piezoelectric materials, nowhere has the combina¬ tions of the present invention been described. More specifically, the present invention is the first teaching wherein BSTO is combined with either Alumina, Zirconia or Magnesia in order to adjust the electronic properties of a material. Specifically, nowhere has BSTO been combined with any of these ceramic materials having a low dielectric constant in order to adjust the electronic properties of the material for use in a phase array antenna system. Aside from the combinations of BSTO with either Alumina, Zirconia or Magnesia being novel, their application in phased array antenna systems is an application never suggested in the prior art.

Replacing the currently employed materials with the novel ferroelectric composite described in the present invention will improve the overall performance of a phased array antenna system as well as reduce the cost, weight and size of the antenna per se. Accordingly, it is an object of the present invention to provide a ferroelectric material suitable for, but not limited to, use in phased array antenna systems.

It is a further object of the present invention to fabricate a material exhibiting enhanced electronic properties.

It is still a further object of the present invention to provide a ferroelectric material having a low dielectric constant, a low loss and a high tunability.

It is a further object of the present invention to provide materials having electronic properties, wherein said electronic properties can be adjusted in such a manner that they can be employed in any discrete element phase shifter design.

It is a further object of the present invention to provide a ferroelectric material which is easily machinable.

Still, it is a further object herein to provide a ferroelectric material which possesses superior electronic properties at both dc and microwave operating frequencies.

The means to achieve these and other objectives of the present invention will be apparent from the following detailed description of the invention and claims. BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Figure 1 represents an eight element phase shifting device used in a geodesic dome antenna.

Figure 2 illustrates a basic ferroelectric phase shifter with multiple transformer and coupled line DC block.

Figure 3 sets forth a phased array antenna comprising four element phase shifters with parallel fed antenna array.

Figure 4 illustrates a cross-section of a broadside coupled-line phase shifter.

Figure 5 illustrates a partitioned view of a brass- board horn antenna.

DETAILED DESCRIPTION OF THE INVENTION AND DRAWINGS

The present invention encompasses the use in antennas of novel ceramic materials having enhanced electronic properties. These materials are superior to other materials currently employed in the antenna art.

When one considers the optimization in the electronic properties of ceramic materials, the following parameters must be taken into consideration: (1) Dielectric Constant: Ideally the dielectric constant should be low, ranging from approximately 30 to 1,200. This dielectric constant range does not decrease the phase shifting ability of the material if a sufficient length of material is used (then a high dielectric constant is not needed) . As insertion loss (loss of energy getting into the ceramic) does not depend upon the dielectric constant, it is not effected by lowering the dielectric constant. Also, since the loss tangent (tan <S) increases with increasing dielectric constant (for these ferroelectric materials) , lower dielectric constant materials tend to have lower loss tangents and therefore, less insertion loss.

(2) Low Loss: The loss tangent (intrinsic to the material) serves to dissipate or absorb the incident micro¬ wave energy and therefore is most effective in this device when the loss tangent is in the range of 0.01 or less. The low loss tangent serves to decrease the insertion loss and hence increase the phase shifter per decibel of loss.

(3) Hiσh Tunability: The tunability of a particular material effects the material's electronic properties by how much the dielectric constant changes with applied voltage. The amount of phase shifting ability is directly related to the tunability; therefore, higher tunabilities are desired. The tunability can be increased to some extent by decreasing the sample thickness. The insertion loss is inversely related to the tunability so that the larger the tunability, the smaller the insertion loss. Optimum electronic properties would have tunabilities ranging from 4 to 50% (depending upon other factors, dielectric constant and loss tangent) .

The materials within the scope of the present invention fall within the optimum characteristics outlined above. These materials are Ba. Sr TiO_-Y, wherein x is greater than 0.0 but less than or equal to 0.75 and where¬ in Y is selected from the group of Alumina, Zirconia or Magnesia. This formulation may be referred to as Barium Strontium Titanate and a ceramic material having a low dielectric constant, i.e., Alumina. The weight ratios of Barium Strontium Titanate (BSTO) to either Alumina, Zirconia or Magnesia may range from 99% wt. - 40% wt. BSTO to 1% wt. - 60% wt. Alumina, Zirconia or Magnesia. A typical composition within the present invention may comprise 70% by weight BSTO (wherein x = 0.35) and 30% by weight Alumina (A1₂0_) . This composition has a dielectric constant of 55.2, a loss tangent of 0.007 and a tunability of 8.0 (applied electric field = 32.8 KV/cm). Alumina, Magnesia or Zirconia are used herein to adjust the electronic properties of BSTO. Specifically, they effect the material's dielectric constant and dielectric loss to meet the requirements for various applications — for example, in the antenna arts. The electronic properties of the formulation herein can be adjusted for use in any discrete element phase shifter design, such as planar microstrip, wave guide geometries or for use in a parallel plate structure.

It has been found that the electronic properties of the described composite formulations of BSTO, BSTO Alumina, BSTO Magnesia and BSTO Zirconia, are reproducible to within 2%. Hence, once a specific composite formulation of BSTO is determined to be suitable for a specific purpose, the material can be accurately reproduced.

Preparation of BSTO Alumina

The preparation of BSTO Alumina may be accomplished by obtaining powders of Barium Titanate and Strontium Titanate. These powders are ball milled in a conventional manner in an organic solvent. This particular mixture is then air-dried and calcined at approximately 200 degrees below the sintering temperature for several hours. The resultant BSTO is then mixed with Alumina in the desired weight percentage and re-ball milled in an organic solvent with a binder. The final mixture is then air-dried, once again, and dry-pressed at approximately 7,000 p.s.i. The final samples are sintered in air.

Table 1 sets forth the various properties of BSTO

Alumina, wherein the formulation is represented by

Ba_Λ0. o„bSr_nU.J_o_cTiO,J - Alumina.

TABLE 1

Alumina

Content (wt. .%) Density (α/cc) %_. Porosity % Absorption

1.00 5.314 4.24 0.55

5.00 5.046 4.16 0.64

10.0 4.820 7.93 1.30

30.0 4.018 8.19 1.58

60.0 3.458 7.65 1.73

80.0 3.496 4.54 1.00

The electronic properties of some of the formulations within the present invention are set forth in Tables 2 and 3. The representative formulations for which electronic properties are tabulated are for BSTO at Ba = 0.65 and Ba = 0.60 with varying Alumina content. TABLE 2 BSTO (Ba = 0.65) and Alumina

Alumina Dielectric Loss Tunability Electric Content wt.% Constant Tangent* (Percent) Field (KV/cm)

1.0 4850 0.009 39.8 7.32 10.0 967 0.017 27.2 11.9 30.0 55.2 0.007 8.0 32.8 60.0 18.8 0.002 2.7 32.0

TABLE 3 BSTO (Ba = 0.60) and Alumina

Alumina Dielectric Loss Tunability Electric

Content wt.% Constant Tanσent* (Percent) Field

(KV/cm)

5.0 1751 0.014 55.3 25.1

10.0 860 0.011 34.6 15.4

20.0 201 0.017 19.8 24.6

22.0 135 0.015 14.4 27.2

30.0 49.7 0.010 5.13 22.1

* Note: The magnituide of the loss tangents reported approach the limit of measurement capability of the test apparatus; therefore, actual loss tangents are in some cases less than these values.

If the antenna application does not require exceedingly high tunability (where tunability can be increased with a decrease in sample thickness for a given^' externally applied electric field) , then the compositions with lower dielectric constants are probably likely to produce less impedance mismatch and may possess lower loss tangents. EXAMPLE 1

Powder forms of Barium Titanate and Strontium Titanate were obtained from Ferro Corp. , Transelco Division, Pen Yan, N.Y. (product nos. 219-6 and 218, respectively) . The powders were stoichiometrically mixed in a slurry of ethanol and ball-milled using alumina 3/16" grinding media. This was performed for 24 hours. The mixture was subse¬ quently air dried and calcined for 5 hours at approximately 1100°C. The resulting BSTO was mixed with powder Alumina (ALCOA Industrial Chemicals, Bauxite AR, distributed by Whittaker, Clark, and Daniels, South Plainfield, N.J. , product no. A16-SG) in the proper weight percent. This mixture was then re-ball milled in a slurry of ethanol using a 3/16" alumina grinding media for an additional 24 hours.

To the resulting BSTO/Alumina mixture, Rhoplex B-60A (Rohm and Haas Co., Philadelphia, Pennsylvania), which is a 3% wt. organic binder consisting of an aqueous emulsion of acrylic polymer, was added to improve green body strength and to permit sample fabrication in greater dimensions. (Green body strength refers to the ability of unfired material to remain intact and to withstand handling; it also implies better densities in the unfired pieces.) Other binders and plasticizers may be added at this point to allow extrusion molding or for fabrication of tape-cast sheets of material.

The mixture is then air-dried and dry-pressed to a pressure of approximately 7,000 p.s.i. Sintering schedules are ascertained by employing a deflectometer such as a Mitutoyo digimatic indicator and miniprocessor (Mitutoyo Corp., Paramus, N.J.). The final samples were fired in various furnaces and the densities of the samples were found to be reproducible to within 1 to 2%.

The properties of the resulting BSTO - Alumina samples are set forth in Table 1, above.

Preparation of BSTO Magnesia

The preparation of BSTO-Magnesia may be accomplished by obtaining powders of Barium Titanate and Strontium Titanate. These powders are ball milled in a conventional manner in an organic solvent. This particular mixture is then air-dried and calcined at approximately 200 degrees below the sintering temperature for several hours. The resultant BSTO is then mixed with Magnesia in the desired weight percentage and re-ball milled in an organic solvent with a binder. The final mixture is then air-dried, once again, and dry-pressed at approximately 7,000 p.s.i. The final samples are sintered in air. Proper electroding of the composite ceramics must be done. The samples were screen printed with a FERRO #3350 (Electronic Materials Division, Santa Barbara, California) silver conductive ink. They were subsequently fired at 450° for ten (10) minutes. The samples were then dipped in a bath of 2% silver (Ag) , 62% tin (Sn) and 36% lead (Pb) solder with lead clips attached.

Table 4 sets forth the various properties of BSTO- Magnesia, wherein the formulation is represented by

^Ba0.60^Sr0.40^TiO3 ^{" Ma}9^nesia-

TABLE 4

Magnesia

Content (wt. .%> Density (g/cc) % Porosity Absorption

1.0 5.00 10.70 1.94

5.0 5.300 3.97 0.63

10.0 5.192 3.36 0.55

30.0 4.689 4.27 0.81

60.0 3.940 2.56 0.751

80.0 3.5180 10.34 1.87

The electronic properties of some of the BSTO-Magnesia formulations herein are set forth in Tables 5 and 6. The representative formulations for which electronic properties are tabulated are for BSTO at Ba = 0.65 and Ba = 0.60 with varying magnesia content. Frequency used was 1kHz and dielectric constants have been corrected for edge (fringe) capacitance.

TABLE 5 BSTO (Ba=0.65) and Magnesia

Magnesia Dielectric Loss Tunability Electric Content wt.% Constant Tangent* (Percent) Field (V/um)

1.0 2178.97 0.00186 25.20 1.77 10.0 1481.30 0.00163 21.47 1.76 30.0 718.06 0.00112 36.26 3.72 60.0 79.20 0.00055 10.66 2.34

TABLE 6

BSTO (Ba=0.60) and Magnesia

Magnesia Dielectric LOSS Tunability Electric

Content wt.% Constant Tangent* (Percent) Field (V/um)

1.0 1047.33 0.00149 16.08 2.27

5.0 1566.22 0.00141

10.0 1167.18 0.00118 _

15.0 895.78 0.00106 7.26 1.86

20.0 886.45 0.00096 15.95 2.27

25.0 650.91 0.00076 17.46 2.40

30.0 433.43 0.00087 9.35 1.62

35.0 425.18 0.00065 18.00 2.03

40.0 306.92 0.00092 19.81 2.53

50.0 188.65 0.01176** 9.55 2.14

60.0 89.35 0.00065 11.09 2.63

Note: * The magnitude of the loss tangents reported approach the limit of measurement capability if the test apparatus; therefore, actual loss tangents are in some cases less than these values.

** Poor contact, actual loss tangent less than above. If the antenna application does not require exceedingly high tunability (where tunability can be increased with a decrease in sample thickness for a given externally applied electric field) , then the compositions with lower dielectric constants are probably likely to produce less impedance mismatch and may possess lower loss tangents.

EXAMPLE 2 The composite BSTO-MgO was produced using the identical process set forth in Example 1, above; however, powder Magnesia (Johnson Malthey Electronics, Ward Hill, MA, product No. 12287) was used in place of the powder Alumina throughout the process. The properties of the resulting BSTO-Magnesia samples obtained using this process are set forth in Table 4, above.

Preparation of BSTO-Zirconia

The preparation of BSTO Zirconia may be accomplished by obtaining powders of Barium Titanate and Strontium Titanate. These powders are ball milled in a conventional manner in an organic solvent. This particular mixture is then air-dried and calcined at approximately 200 degrees below the sintering temperature for several hours. The resultant BSTO is then mixed with Zirconia in the desired weight percentage and re-ball milled in an organic solvent with a binder. The final mixture is then air-dried, once again, and dry-pressed at approximately 7,000 p.s.i. the final samples are sintered in air. Electroding was accomplished by painting on two circular aligned electrodes on either side of the specimens using high purity silver paint made by SPI Supplies, West Chester, PA. Wires were attached using high purity silver epoxy, Magnobond 8000 (manufactured by Magnolia Plastics, Inc., Chamblee, Georgia) .

Table 7 sets forth the various properties of BSTO Zirconia, wherein the formulation is represented by

^Ba0.65^Sr0.35^TiO3 ^{" Zirconia«}

TABLE 7

Zirconia

Content (wt. %ϊ Density (g/cc) % Porositv Absorption

1.0 5.22 10.31 1.64

5.0 5.28 8.86 1.51

10.0 5.30 7.67 1.23

30.0 5.40 9.73 1.60

60.0 5.38 10.28 1.58

The electronic properties of some of the formulations within the present invention are set forth in Tables 8, 9 and 10. The representative formulations for which electronic properties are tabulated are for BSTO at Ba = 0.75, Ba = 0.55 and Ba = 0.60 with varying Zirconia content.

TABLE 8 BSTO (Ba=0.75) and Zirconia

Zirconia Dielectric Loss Tunability Electric Content wt.% Constant Tangent* (Percent) Field (V/um)

1.0 3821.39 0.0049 39.500 1.54 10.0 1384.71 0.0097 15.340 1.02 30.0 150.41 0.0336 60.0 76.63 0.0243 1.99 1.33

TABLE 9 BSTO (Ba=0.55) and Zirconia

1.0 1952.99 0.0016 17.466 1.25 10.0 1179.45 0.0088 18.24 1.00 30.0 223.59 0.0179 60.0 60.00 0.0076 2.29 1.49

TABLE 10

BSTO (Ba=0.60) and Zirconia

Zirconia Dielectric Loss Tunability Electric

Content wt.% Constant Tangent* (Percent) Field (V/u

1. 0 2696.77 0.0042 46.01 2.72

5. ,0 2047.00 0.0138 12.70 0.76

10. ,0 1166.93 0.0111 7.68 0.68

15. ,0 413.05 0.0159

20. ,0 399.39 0.0152 5.39 0.76

25. ,0 273.96 0.0240 6.20 1.02

30. ,0 233.47 0.0098

35. ,0 183.33 0.0091 5.87 0.95

40. .0 162.26 0.0095

50. ,0 92.73 0.0071 1.67 1.12

60. ,0 69.80 0.0098 Note: * The magnitude of the loss tangents reported approach the limit of measurement capability of the test apparatus; therefore, actual loss tangents are in some cases less than these values.

EXAMPLE 3

The composite BSTO-ZrO- was produced using the identical process set forth in Example 1, above; however, powder Zirconia (Johnson Malthey Electronics, Ward Hill,

MA, product No. 11395) was used in place of the powder

Alumina throughout the process. The properties of the resulting BSTO-Zirconia samples obtained using this process are set forth in Table 7, above.

Insertion Into Antenna Designs

These novel ceramic ferroelectric composite materials can be easily incorporated into a variety of phased array antenna designs. The antennas into which these materials may be implemented are of the type which may be used for tank target acquisition (KA band) , weapon location radar (3 GHz), man portable radar's PPS-15 (16 GHz), phased arrays for local area networking (sensitivity improvement antenna) , antennas for collision avoidance for the auto¬ motive industry, and antennas used in satellites.

The novel composite materials can be retrofit into antenna systems such as the geodesic cone antenna set forth in Figure 1, as well at in the patch antenna. The material may be fielded as a system component in the PM fire finder system as well.

Figure 1 illustrates an eight element phase shifter used in a geodesic dome antenna. In this illustration, the ferroelectric material 3, which in the prior art antenna designs exists as ferrite, is retrofitted with the novel composite materials disclosed herein (BSTO-Al_0-; BST0-Zr0 . or BSTO-MgO) . Said eight element phase shifter is made up of ferroelectric material 3, phase shifting line 5, bias network 7, power divider 9, ferroelectric impedance match 11, DC block 13 and Duriod 15.

Figure 2 illustrates a basic ferroelectric phase shifter 33 with multiple stub transformer and coupled line DC block. The novel ceramic ferroelectric material is used as element 21. The antenna set forth in Figure 2 features planar topology, reciprocal operation, very low power (static operation) , broad bandwidth (20%) , available frequencies 2-10 GHz, phase shift = 180 degrees, VSWR = 1.22, insertion loss 6 dB at S-band, small size and low cost. The microwave energy is impedance matched into the ferroelectric transmission line, a DC field is applied between the transmission line and the ground plane across the ferroelectric material. The DC field reduces the dielectric constant of the ferroelectric which shortens the electrical length of the transmission line thereby imparting a phase shift to the microwave signal travelling through the material. The phase shifter comprises ferroelectric material 21, conductor circuit 23, DC block 25, impedance matching 27, low-loss substrate 29, and bias pad and RF block 31. This type of phase shifter may be employed in a phased array antenna of the type set forth in Figure 3.

Figure 3 sets forth a phased array antenna 37 which comprises four element phase shifters 33 with parallel fed antenna array 35. Said phased array antenna 37 additionally comprises a corporate feed network 35, DC block 40, DC control line 41 and patch antennas 39. This antenna 37 is employed by U.S. Army Research Laboratory, Electronics and Power Sources Directorate.

The ferroelectric material of the BSTO-type disclosed herein may further be inserted into a broadside coupled line phase shifter as set forth in Figure 4. Figure 4 illustrates a cross-section of a broadside coupled-line phase shifter (Hughes Aircraft) . The ferroelectric material disclosed herein is used as ferroelectric material 45. Said phase shifter must possess the following parameters for its operation: dielectric constants from 50 to 125; loss tangent less than 0.01 (10 GHz); and tunability of around 20% with a field of 20KV/cm.

An additional example into which the novel ceramic ferroelectric composite material disclosed herein may be employed is in a single element electronically steerable ceramic antenna presently being developed at Harris Corporation under contract with U.S. Army, Communications- Electronics Command, Ft. Monmouth, N.J. This antenna 51 is shown in Figure 5. The antenna 51 is a brassboard horn antenna with the novel BSTO composite material used as its electronic steering component 53. To effect the beam steering, the BSTO composite is made into a prism. The partitions of the antenna 51 are set forth as the aperture section 55, the beam steering section 53, the bias network 57, the matching section 59 and the coax/waveguide transition section 61. Note that the antenna 51 has separable segments 63, and a dielectric structure of the ceramic antenna as set forth by 65.

One having ordinary skill in the art of antennas, once having reviewed the above invention would be able to easily design any number of antennas using the novel ceramics disclosed herein as beam steering sections. While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention. For example, the invention may be modified to include ceramic-ceramic composites of BSTO and other low dielectric constant materials depending upon the particular requirements of the intended application. Among some of the other low dielectric constant materials which may be combined with BSTO are alumina microballoons, alumina fibers or fabric, silicon dioxide and other low dielectric constant, low dielectric loss oxides. (Alumina microballoons are hollow spheres of approximately 1-5 microns in diameter and are already sintered components (BSTO/ceramic) — the electronic properties of a composite employing alumina microballoons will most likely differ from composites employing alumina powder. Alumina fibers or fabric, when employed in the composite within the scope of the present invention, may possess electronic properties different from composites which employ alumina powder. This is due to the fact that this form of alumina is most likely to be in sintered form; and the fibers or fabric alumina produce different connectivity between the BSTO particles.) It is, therefore, intended that the claims herein are o include all such obvious changes and modifications as fall within the true spirit and scope of this invention.

Claims

I claim:

1. An apparatus comprising an antenna, wherein said antenna comprises a phase shifting device, said phase shifting device comprises therein a ceramic ferroelectric composite material comprising

Barium Strontium Titanate and a ceramic material having a low dielectric constant; wherein said Barium Strontium Titanate and said ceramic material are present in amounts to provide a composite having a low dielectric constant, low loss tangent and high tunability.

2. The apparatus as set forth in claim 1, wherein said Barium Strontium Titanate is Ba •,- ΛSrA.TiO_*_-), wherein x is greater than 0.0 but less than or equal to 0.75.

3. The apparatus as set forth in claim 2, wherein said Barium Strontium Titanate is Ba, Sr TiO_, wherein x = 0.35 to 0.40.

4. The apparatus as set forth in claim 2, wherein the weight ratio of said Barium Strontium Titanate to said ceramic material having a low dielectric constant ranges from approximately 99% - 40% Barium Strontium Titanate to approximately 1% - 60% said ceramic material having a low dielectric constant.

5. The apparatus as set forth in claim 4, wherein the ratio of Barium Strontium Titanate to said ceramic material having a low dielectric constant is approximately 70% wt. Barium Strontium Titanate to approximately 30% wt. said ceramic material.

6. The apparatus as set forth in claims 1, 2, 3, 4 or 5, wherein said ceramic material having a low dielectric constant is selected from the group consisting of Alumina, Zirconia, and Magnesia.

7. The apparatus as set forth in claim 1, wherein said antenna is a phased array antenna.

8. The apparatus as set forth in claim 7, wherein said phased array antenna is a geodesic dome antenna.