Chip antenna

Abstract: The present invention is directed to provide a compact chip antenna (10) for mobile communication comprising a base member (11) which comprises either of a material having a dielectric constant ε of 1 < ε < 130 or a material having a relative permeability µ of 1 < µ < 7, at least one conductor (12) formed on the surface of the base member (11) and/or inside the base member (11), and at least one feeding terminal provided on the surface of the base member (11) for applying a voltage to the conductor (12). The conductor (12) comprises a metal mainly containing any one of copper, nickel, silver, palladium, platinum, or gold.

Description: The present invention relates to chip antennas. In particular, the present invention relates to a chip antenna used for mobile communication and local area networks (LAN). Fig. 3 shows a prior art monopole antenna 50. The monopole antenna 50 has a conductor 51, one end 52 of the conductor 51 being a feeding point and the other end 53 being a free end in the air (dielectric constant ε = 1 and relative permeability µ = 1). Because the conductor of the antenna is present in the air in linear antennas, such as the prior monopole antenna 50, the size of the antenna conductor becomes larger. For example, when the wavelength in the vacuum is λ 0 in the monopole antenna 50, the length of the conductor 51 must be λ 0 /4. Thus, such an antenna cannot be readily used for mobile communication or the like which requires a compact antenna. Patent Abstracts of Japan, Volume 018, No. 311 (E-1561), 14 June 1994 & JP-A-06 069057 relates to a laminated chip inductor. Sheets provided with through holes and a coil conductor pattern are laminated to form a coil conductor. The coil conductor is not spiralled perpendicular to the laminating direction in the dielectric substrate. The chip conductor is a surface-mountable device having at opposite edges external terminal electrodes connected to the coil terminals extracted at the chip body by means of which the chip conductor is, for example, soldered to a printed circuit board to form a portion of a circuit provided thereon. It is an object of the present invention to provide a compact chip antenna which can be used for mobile communication. This object is achieved by the chip antenna of claim 1. The conductor comprises a metal mainly containing any one of copper, nickel, silver, palladium, platinum, or gold. The chip antenna in accordance with an embodiment of the present invention has a wavelength shortening effect because the base member is formed of either a material having a dielectric constant ε of 1 < ε < 130 or a material having a relative permeability µ of 1 < µ < 7. Further, the chip antenna in accordance with another embodiment of the present invention enables monolithic sintering of the conductive pattern composed of a base member and a conductor, because the conductive pattern is formed of a metal mainly containing any one of copper(Cu), nickel (Ni), silver (Ag), palladium (Pd), platinum (Pt), or gold (Au). Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an isometric view illustrating an embodiment of a chip antenna in accordance with the present invention; Fig. 2 is an exploded isometric view of Fig. 1; and Fig. 3 is a prior art monopole antenna. DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION Figs. 1 and 2 are an isometric view and an exploded isometric view illustrating an embodiment of a chip antenna 10 in accordance with the present invention. The chip antenna 10 comprises a conductor 12 which is spiralled along the longitudinal direction in a rectangular dielectric base member 11. The dielectric base member is formed by laminating rectangular sheets 13a-13e, each having a dielectric constant of 2 to 130, or having a relative permeability of 2 to 7, as shown in Tables 1 and 2. No. Composition Dielectric Constant Q·f 1 Bi-Pb-Ba-Sm-Ti-O 130 1,000 2 Bi-Pb-Ba-Nd-Ti-O 110 2,500 3 Pb-Ba-Nd-Ti-O 90 5,000 4 Ba-Nd-Ti-O 60 4,000 5 Nd-Ti-O 37 8,000 6 Mg-Ca-Ti-O 21 20,000 7 Mg-Si-O 10 80,000 8 Bi-Al-Si-O 6 2,000 9 (Ba-Al-Si-O) + Teflon Polytetrafluoroethylene Resin 4 4,000 10 Teflon Polytetrafluoroethylene Resin 2 10,000 No. Composition Relative Permeability Threshold Frequency 11 Ni/Co/Fe/O=0.49/0.04/0.94/4.00 7 130 MHz 12 Ni/Co/Fe/O+0.47/0.06/0.94/4.00 5 360 MHz 13 Ni/Co/Fe/O+0.45/0.08/0.94/4.00 4 420 MHz 14 (Ni/Co/Fe/O+0.45/0.08/0.94/4.00) +Teflon 2 900 MHz In Tables 1 and 2, the sample having a dielectric constant of 1 and a relative permeability of 1 is not selected because the sample is identical to the prior art antenna. The Q·f in Table 1 represents the product of the Q value and a measuring frequency and is a function of the material. The threshold frequency in Table 2 represents the frequency that the Q value is reduced by half to an almost constant Q value at a low frequency region, and represents the upper limit of the frequency applicable to the material. At the surface of the sheet layers 13b and 13d of the sheet layers 13a through 13e, each of which has a dielectric constant ε of 1 < ε < 130 or a relative permeability µ of 1 < µ < 7, linear conductive patterns 14a through 14h comprising a metal mainly containing Cu, Ni, Ag, Pd, Pt or Au are provided by printing, evaporating, laminating or plating, as shown in Table 3. In the sheet layer 13d, a via hole 15a is formed at both ends of the conductive patterns 14e through 14g and one end of the conductive pattern 14h. Further, in the sheet layer 13c, a via hole 15b is provided at the position corresponding to the via hole 15a, in other words, at one end of the conductive pattern 14a and at both ends of the conductive patterns 14b through 14d. A spiral conductor 12 having a rectangular cross-section is formed by laminating the sheet layers 13a through 13e so that the conductive patterns 14a through 14h come in contact with via holes 15a, 15b. In material Nos. 1 to 8 and Nos. 11 to 13, the chip antenna 10 is made by monolithically sintering the base member 11 and the conductive patterns 14a through 14h under the conditions shown in Table 3. On the other hand, such a sintering process is not employed in material Nos. 9, 10 and 14 each containing a resin. Metal Material No. Sintering Atmosphere Sintering Temperature Cu 8 Reductive < 1,000°C Ni 7 Reductive 1,000 to 1,200°C Ag-Pd alloy 1,2,3,4,5,11,12 Air 1,000 to 1,250°C Pt 6 Air < 1,250°C Ag 9,11,14 Not Sintered Each material No. in Table 3 is identical to that in Tables 1 and 2. One end of the conductor 12, i.e., the other end of the conductive pattern 14a, is brought to the surface of the dielectric base member 11 to form a feeding end 17 which connects to a feeding terminal 16 for applying a voltage to the conductor 12, and the other end, i.e., the other end of the conductive pattern 14h, forms a free end 18 in the dielectric base member 11. Table 4 shows relative bandwidth at the resonance point of the chip antenna 10 when using various materials as the sheet layers 13a through 13e comprising the base member 11. The relative bandwidth is determined by the equation: relative bandwidth [%] = (bandwidth [GHz]/center frequency [GHz]) 100. The chip antennas 10 for 0.24 GHz and 0.82 GHz are prepared by adjusting the turn numbers and length of the conductor 12. Material No. Relative Bandwidth 0.24 GHz 0.82 GHz 1 Not measurable Not measurable 2 1.1 1.0 3 1.7 1.5 4 2.4 2.3 5 2.9 2.7 6 3.1 3.0 7 3.5 3.3 8 3.8 3.4 9 4.1 3.7 10 4.5 4.3 11 Not measurable Not measurable 12 2.5 2.4 13 3.0 2.7 14 3.2 3.0 Each material No. in Table 4 is identical to that in Tables 1 and 2. In Table 4, Not Measurable means a relative bandwidth of 0.5 [%] or less, or a too small resonance to measure. Results in Table 4 demonstrate that chip antennas using a material having a dielectric constant of 130 (No. 1 in Table 1) and a material having a relative permeability of 7 (No. 11 in Table 2) do not exhibit antenna characteristics, as shown as "Not Measurable". On the other hand, when the dielectric constant is 1 or the relative permeability is 1, no compact chip antenna is achieved by the wavelength shortening effect due to the same value as the air. Thus, suitable materials have a dielectric constant ε of 1 < ε < 130, or a relative permeability µ of 1 < µ < 7. At a resonance frequency of 0.82 GHz, the size of the chip antenna 10 is 5 mm wide, 8 mm deep, and 2.5 mm high, and approximately one-tenth of the size of the monopole antenna 50, approximately 90 mm. In the embodiment set forth above, the size of the chip antenna can be reduced to approximately one-tenth of the prior art monopole antenna while satisfying antenna characteristics, by using a material of 1 < dielectric constant < 130 or 1 < relative permeability < 7. Thus, a compact antenna with sufficiently satisfactory antenna characteristics can be prepared. Further, since the conductive pattern composed of the base member and conductor can be monolithically sintered, the production process can be simplified and cost reduction can be achieved. In the embodiment set forth above, several materials are used as examples, but the embodiment is not to be limited thereto. Further, although the embodiment set forth above illustrates an antenna having one conductor, two or more conductors may be available. The feeding terminal is essential for the practice of the embodiment in accordance with the present invention.

Claims: A chip antenna (10) comprising a rectangular base member (11), at least one conductor (12) secured to said base member (11), and at least one feeding terminal (16) provided on the surface of said base member (11) and connected to one end (14a) of said conductor (12) for applying a voltage to said conductor (12), wherein a second end (14h) of said conductor (12) forms a free end (18) of said antenna chip, characterized in that said rectangular base member (11) comprises a plurality of rectangular sheet layers (13a-13e) laminated to each other, a plurality of conductive patterns (14a-14h) are provided on the surface of said rectangular sheet layers (13a-13e), said conductor (12) is formed by laminating said rectangular sheet layers (13a-13e) so that said conductive patterns (14a-14h) come in contact with via holes (15a,15b), said conductor (12) is spiraled perpendicular to the laminating direction in said rectangular base member (11), and said rectangular base member (11) comprises either a material having a dielectric constant ε of 1 < ε < 130 or a material having a relative permeability µ of 1 < µ < 7. A chip antenna (10) according to claim 1, wherein said conductor (12) comprises a metal mainly containing any one of copper, nickel, silver, palladium, platinum, or gold. A chip antenna (10) according to claim 1 or 2, wherein said conductor (12) extends in the longitudinal direction of said base member (11). A chip antenna (10) according to claim 3, wherein said conductor (12) extends spirally in the longitudinal direction. A chip antenna (10) according to any of claims 1 to 4, wherein each of said sheets (13a - 13e) is composed of a material selected from the group consisting of Bi-Pb-Ba-Nd-Ti-O, Pb-Ba-Nd-Ti-O, Ba-Nd-Ti-O, Nd-Ti-O, Mg-Ca-Ti-O, Mg-Si-O, Bi-Al-Si-O, (Ba-Al-Si-O) + polytetrafluoroethylene resin, and polytetrafluoroethylene resin.

Inventors: ASAKURA KENJI, KANBA SEIJI, MANDAI HARUFUMI, SHIROKI KOJI, TSURU TERUHISA, ASAKURA, KENJI, KANBA, SEIJI, MANDAI, HARUFUMI, SHIROKI, KOJI, TSURU, TERUHISA, Asakura, Kenji, Murata Manuf. Co., Ltd., Kanba, Seiji, Murata Manuf. Co., Ltd., Mandai, Harufumi, Murata Manuf. Co., Ltd., Shiroki, Koji, Murata Manuf. Co., Ltd., Tsuru, Teruhisa, Murata Manuf. Co., Ltd.
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 1996
Main classification: H01Q13
IPC codes: H01Q7, H01Q1, H01Q11