Multi-band antenna suitable for use in a mobile radio device

Abstract: In a multi-band antenna (10) being provided with an antenna element having an LC parallel resonance circuit (3) and a first and a second radiation element (1,2) connected to opposite ends of the LC parallel resonance circuit, the LC parallel resonance circuit is constituted by self-resonance of an inductor itself. A telescopic whip antenna may be constituted by combining a small-size antenna and a whip antenna which is receivable in a radio device casing and expandable.

Description: Background of the Invention: The present invention relates to an antenna for use in a mobile radio device etc. and, in particular, to a multi-band antenna which can carry out transmission and reception at a plurality of mutually different frequency bands. Recently, there have been those regions and countries wherein a plurality of portable telephone systems using different frequency bands are available. For example, in Japan, the PDC system uses 800MHz and 1.5GHz bands, while the PHS system uses a 1.9GHz band. On the other hand, 800MHz and 1.9GHz bands are used in U.S.A., while 900MHz and 1.8GHz bands are used in Europe. Following the recent remarkable spread of portable terminals, there has been caused congestion with respect to a certain frequency band. In view of this, there have been such requests that each portable terminal can carry out transmission and reception at a plurality of frequency bands. According to the requests, when a first frequency band allocated initially is crowded or in case of a region where such a first frequency band is not available, transmission and reception can be performed using a second frequency band allocated secondarily. In general, when a radio device is used at different frequency bands, a plurality of antennas are used. As a typical example of such a radio device, an FM/AM radio set can be cited. In contrast, there has been a trap antenna which is so arranged as to be used at different frequency bands. The trap antennas have been widely used in amateur radio devices as multi-band antennas. For example, JP-A-5-121924 discloses a conventional trap antenna. The disclosed trap antenna comprises a linear antenna element and a trap circuit having a coil and a capacitor. However, there has been a problem that the number of parts and the number of manufacturing processes required for the conventional trap antenna are both large. Further, when the conventional trap antenna is externally attached to the radio device in an exposed fashion, it is defective in strength such that the coil and the capacitor tend to be damaged when subjected to a shock etc. This raises a serious problem with respect to a portable terminal which is supposed to be carried. Further, since the conventional trap antenna can not be drawn out to the exterior of the radio device and has only a small gain, a problem may be raised that, in particular, transmission characteristics can not be ensured upon transmission from the radio device. Moreover, since a structure of the conventional trap antenna is complicated, the size reduction thereof is difficult to achieve. There have been further problems that dispersion in resonance frequency of the conventional trap antennas is increased depending on manufacturing processes, the productivity thereof is low and it is relatively heavy. Therefore, the conventional trap antenna can not be said to be suitable for use in a portable terminal for the portable telephone system. EP 0772 255 A discloses a multi-band antenna according to the preamble of claim 1. Summary of the Invention: It is therefore an object of the present invention to provide a multi-band antenna suitable for use in a portable terminal for a portable telephone system. It is another object of the present invention to constitute a trap circuit which is reducible in number of parts, easy to manufacture and small-sized, so as to provide a small-size multi-band antenna which is cheap but excellent in transmission characteristic, which can improve reliability against a shock etc. and which can carry out transmission and reception at different frequency bands. It is still another object of the present invention to provide a telescopic multi-band antenna which can always achieve an excellent multi-band characteristic. It is yet another object of the present invention to provide a small-size multi-band helical antenna which can carry out transmission and reception at different frequency bands. It is further object of the present invention to provide a telescopic whip antenna whose dispersion in resonance frequency is small, whose productivity is high and which is provided with a small-weight and small-size antenna. The object is solved by a multi-band antenna according to claim 1. Further developments are given in the dependent claims. Brief Description of the Drawing: Fig. 1 is a diagram showing a schematic structure of a multi-band antenna according to a first embodiment for explanation of the technique; Fig. 2 is a perspective view showing an example of a chip inductor used in the multi-band antenna shown in Fig. 1; Fig. 3 is a diagram showing a characteristic example of the multi-band antenna shown in Fig. 1; Fig. 4 is a sectional view showing a multi-band antenna according to a second embodiment; Fig. 5 is a sectional view showing a multi-band antenna according to a first preferred embodiment of the present invention; Fig. 6 is a diagram showing a helical element of the multi-band antenna shown in Fig. 5; Fig. 7 is a sectional view showing a multi-band antenna according to a second preferred embodiment of the present invention; Fig. 8 is a partly cutout diagram showing a meander pattern element of the multi-band antenna shown in Fig. 7; Fig. 9A is a diagram showing a multi-band antenna upon expansion according to a fifth embodiment; Fig. 9B is a diagram showing the multi-band antenna upon putting back according to the fifth embodiment ; Fig. 10A is a diagram showing a multi-band antenna upon expansion according to a sixth embodiment; Fig. 10B is a diagram showing the multi-band antenna upon putting back according to the sixth embodiment ; Fig. 11A is a diagram showing a multi-band antenna upon expansion according to a seventh embodiment; Fig. 11B is a diagram showing the multi-band antenna upon putting back according to the seventh embodiment ; Fig. 12 is a perspective view showing a multi-band antenna according to an eighth embodiment; Fig. 13 is a perspective view showing a multi-band antenna according to a ninth embodiment; Fig. 14 is a perspective view showing a multi-band antenna according to a tenth embodiment; Fig. 15 is a perspective view showing a multi-band antenna according to an eleventh embodiment ; Fig. 16 is a perspective view showing a main part of a multi-band antenna according to a twelfth embodiment ; Fig. 17 is a front view showing a small-size antenna incorporated in the multi-band antenna shown in Fig. 16; Fig. 18 is a front view showing a small-size antenna incorporated in a multi-band antenna according to a thirteenth embodiment ; Fig. 19 is a front view showing a small-size antenna incorporated in a multi-band antenna according to a fourteenth embodiment ; Fig. 20 is a perspective view showing a main part of a multi-band antenna according to a fifteenth embodiment ; Fig. 21 is a plan view showing a small-size antenna incorporated in the multi-band antenna shown in Fig. 20; Fig. 22 is a plan view showing a small-size antenna incorporated in a multi-band antenna according to a sixteenth embodiment ; Fig. 23 is a plan view showing a small-size antenna incorporated in a multi-band antenna according to a seventeenth embodiment ; Fig. 24 is a perspective view showing a main part of a multi-band antenna according to an eighteenth embodiment ; Fig. 25 is a developed view for explaining a main fabricating process of a small-size antenna incorporated in the multi-band antenna shown in Fig. 24; and Fig. 26 is a perspective view for explaining a main fabricating process of the small-size antenna incorporated in the multi-band antenna shown in Fig. 24. The embodiment shown in Figs. 1 to 4 and 9 to 26 do not form part of the invention as described in claim 1. Description of the Preferred Embodiments: Now, multi-band antennas will be described with reference to the accompanying drawings. Referring first to Fig. 1, a multi-band antenna 10 according to the first embodiment will be described, wherein the multi-band antenna 10 corresponds to two allocated frequency bands, that is, 800MHz and 1.9GHz bands. The multi-band antenna 10 comprises a linear element 1 on an open end side as a first radiation element, a linear element 2 on a telephone side as a second radiation element, and a trap circuit connected therebetween. Each of the linear elements 1 and 2 is made of a superelastic alloy in the form of a Ti-Ni alloy. In the multi-band antenna 10, the trap circuit is achieved by self-resonance of an inductor. With respect to the self-resonance of the inductor, a chip laminated inductance element (hereinafter referred to as "chip inductor") 3 is used as a surface mounting (SMD) type self-resonance inductor in Fig. 1. The chip inductor 3 is of a 1005 size (1.0mm x 0.5mm). As shown in Fig. 2, the trap circuit is constituted by mounting only the chip inductor 3 on a substrate. Accordingly, the trap circuit can be obtained which does not require a capacitance element and is small in size, low in price and small in number of assembling steps. In the multi-band antenna 10, a length of each of the linear elements 1 and 2 may be λ/2, λ/4 or 3λ/8, while it is λ/4 in an explanation given below. In Fig. 1, a length of the linear element 1 on the open end side was set to 3.9cm, a length of the linear element 2 on the telephone side was set to 2.9cm, each of the linear elements 1 and 2 had a diameter of 0.8mm and was made of the Ni-Ti alloy, a value of the chip inductor 3 was set to 39nH, and a stray capacitance of the inductor was 0.18pF. As a result, a multi-band characteristic as shown in Fig. 3 was obtained, wherein the characteristic was shown in terms of a return loss characteristic observed by a 50Ω network analyzer. Referring now to Fig. 4, a multi-band antenna 20 according to the second embodiment will be described. In Fig. 4, the linear element 1 on the open end side, being the first radiation element, in the multi-band antenna 10 shown in Fig. 1 is replaced with a helical element 11. In the multi-band antenna 20, the linear element 2 on the telephone side, being the second radiation element, in the multi-band antenna 10 is used as it is, and a chip inductor 3 having the same value as that in the multi-band antenna 10 is used for a trap circuit. Specifically, the helical element 11 comprises a helical coil 16 and a helical guide 17 around which the helical coil 16 is wound. The chip inductor 3 is received in the helical coil guide 17 and has one end connected to one end of the helical coil 16. To the other end of the chip inductor 3 is connected one end of the linear element 2 being the second radiation element. A sleeve 6 made of a conductive material is provided around the linear element 2 at the foregoing one end thereof so as to reach the helical guide 17. The helical element 11 and one end of the sleeve 6 are covered through molding with flexible insulating resin such as polymer or elastomer so as to form a mold portion 8. A tube 4 made of a flexible insulating material such as polymer or elastomer is provided through molding to cover the linear element 2 from the other end of the sleeve 6 to the other end of the linear element 2. A holder 5 for attachment to a portable telephone (not shown) is mounted on the tube 4 so as to be slidable along an axis of the linear element 2. The holder 5 is provided near the other end of the linear element 2, and the other end of the linear element 2 is terminated by a stopper 7. The helical element 11 has an outer diameter of 2.8mm and a length of 18mm, and the helical coil 16 is made of a wire having a diameter of 0.4mm and has four turns. The multi-band antenna 20 in this embodiment achieves a multi-band characteristic similar to that of the multi-band antenna 10 shown in Fig. 1. Referring now to Fig. 5, a multi-band antenna 30 according to a first preferred embodiment of the present invention will be described. In Fig. 5, the multi-band antenna 30 has, at a portion of a helical element 11 being a first radiation element, an inductor portion 23 in the form of an air-core coil having self-resonance, so as to form an LC parallel trap circuit by the self-resonance. The other structures are the same as those of the multi-band antenna 20 shown in Fig. 4. A linear element 2 on the telephone side has the same shape as that of the linear element 2 shown in Fig. 1. Further, as shown in Fig. 6, the helical element 11 comprises an integral coil having the inductor portion 23 of the trap circuit and a helical coil 16. With this arrangement, a multi-band characteristic similar to that of the multi-band antenna 10 shown in Fig. 1 was obtained. Referring further to Fig. 6, the composite coil having the inductor portion 23 and the helical coil 16 will be explained. The inductor portion 23 is in the form of a coil having a length of 5mm, which is obtained by winding a wire having a diameter of 0.45mm so as to have an inner diameter of 2mm and six turns. On the other hand, the helical coil 16 is in the form of a coil having a length of 13mm, which is obtained by winding a wire having a diameter of 0.45mm so as to have an inner diameter of 2mm and ten turns. With this arrangement, the multi-band characteristic similar to that of the multi-band antenna 10 shown in Fig. 1 was obtained. Referring now to Fig. 7, a multi-band antenna 40 according to the second preferred embodiment of the present invention will be described. In Fig. 7, the multi-band antenna 40 is provided with a meander pattern element 21 having, at a portion of a printed board 24 formed with a meander pattern 22, an inductor portion 33 having self-resonance, so as to form an LC parallel trap circuit by the self-resonance. A linear element 2 on the telephone side is in the form of a Ti-Ni superelastic wire having a diameter of 0.8mm and a length of 31mm. By using the meander pattern element 21 including the trap circuit, a multi-band characteristic similar to that of the multi-band antenna 10 shown in Fig. 1 can be obtained. Referring to Fig. 8, the meander pattern element 21 will be explained in further detail. The meander pattern element 21 is formed by using a helical element having a pattern width of 0.5mm, 24 turns, a coil width of. 4mm and a whole coil length of 24mm. With this arrangement, the multi-band antenna 40 shown in Fig. 7 achieved a multi-band characteristic similar to that of the multi-band antenna. 10 shown in Fig. 1. In each of the multi-band antennas according to the embodiments shown in Figs. 1 to 8, the LC parallel resonance circuit is formed by the self-resonance of the inductor itself. In general, when using an LC parallel resonance circuit in the form of a combination of an inductance element and a capacitance element, not less than two components such as a capacitor and a coil are necessary. On the other hand, a resonance circuit using self-resonance of an inductor has basically one inductance element, and. a capacitance is formed by a distributed capacitance of a coil. Thus, the number of components can be made small. Further, since the capacitance formed by the distributed capacitance is small as a constant so that the resonance circuit is constituted by inductance-leading LC resonance (for example, not less than 7nH and not greater than 1pF at 1.9GHz, not less than 8nH and not greater than 1pF at 1.8GHz), a band width at each. frequency can be set large (for example, not greater than VSWR2.2). Therefore, the multi-band antenna with less number of components, with less number of manufacturing processes/steps and with excellent productivity can be provided at a low price. Further, when the foregoing multi-band antenna is used as an antenna for carrying out transmission and reception at a plurality of mutually different frequency bands, such as 800MHz and 1.9GHz, it can largely contribute to reduction in size of a multi-band portable radio device etc. Referring now to Figs:. 9A and 9B, a telescopic multi-band whip antenna as a multi-band antenna according to the fifth embodiment will be described. The telescopic multi-band whip antenna comprises a whip antenna 41 and. a small-size antenna 42. The whip antenna 41 is in the form of a combination of an insulating portion 45 and an LC parallel resonance circuit 43 including a chip inductor and a chip capacitor. The small-size antenna 42 is a small-size multi-band antenna which constituted by combining a helical coil antenna provided on a casing of the radio device and the LC parallel resonance circuit 43 and further by putting a cap 44 thereon. The whip antenna 41 is slidable in the small-size antenna 42. Fig. 9A is a diagram showing the multi-band antenna upon expansion thereof, wherein a stopper 46 is coupled to a holder 49 for retaining it. The holder 49 is used for fixing the small-size antenna 42 to the casing of the radio device. The stopper 46 is formed at its tip portion with a conductive portion 48 and an insulating portion 47. The insulating portion 47 is mechanically retained by the holder 49 upon expansion of the multi-band antenna so that the whip antenna 41 and the small-size antenna 42 are electrically separated. In this event, the conductive portion 48 is connected to a circuit within the casing of the radio device via a matching circuit. Fig. 9B is a diagram showing the multi-band antenna upon putting back the multi-band antenna, wherein the holder 49 for fixing the small-size antenna 42 to the casing of the radio device is coupled to the insulating portion 45 of the whip antenna 41. In this event, the holder 49 is connected to the circuit within the casing of the radio device via the matching circuit. In Figs. 9A and 9B, the LC parallel resonance circuit 43 composed of the chip inductor and the chip capacitor is used. On the other hand, a similar telescopic multi-band whip antenna can also be realized by using self-resonance of a chip inductor or an air-core coil, or a dielectric resonator having a size of 2mm x 2mm to 3mm x 3mm and made of a barium titanate material having a dielectric constant not less than 20. Further, a similar multi-band whip antenna can also be realized by using a circuit connected by using self-resonance of a chip inductor or an air-core coil. Referring now to Figs. 10A and 10B, a telescopic multi-band whip antenna as a multi-band antenna according to the sixth embodiment will be described. Figs. 10A and 10B are diagrams showing the telescopic multi-band whip antenna upon expansion and upon putting back, respectively. The same or like elements are represented by the same reference signs so as to omit explanation thereof. In the telescopic multi-band whip antenna in this embodiment, a small-size antenna 52 has a flexible board formed thereon with a meander line pattern 59, and further provided thereon with an LC parallel resonance circuit 53 comprising a chip inductor and a chip capacitor, so as to accomplish a multi-band characteristic. A similar telescopic multi-band whip antenna can also be realized using self-resonance of a chip inductor or an air-core coil. Referring now to Figs. 11A and 11B, a telescopic multi-band whip antenna as a multi-band antenna according to the seventh embodiment will be described. Figs. 11A and 11B are diagrams showing the telescopic multi-band whip antenna upon expansion and upon putting back, respectively. The same or like elements are represented by the same reference signs so as to omit explanation thereof. In the telescopic multi-band whip antenna in this embodiment, a small-size antenna 62 is not provided with the LC parallel resonance circuit, and thus realizes a multi-band characteristic only by a meander pattern 69 formed on a flexible board. In each of the multi-band antennas according to the fifth to seventh embodiments, the electric characteristics of the small-size antenna and the whip antenna are both set to be the multi-band characteristics so that the multi-band characteristics can be obtained both upon expansion and putting back. Specifically, when the foregoing multi-band antenna is used as an antenna for carrying out transmission and reception at a plurality of mutually different frequency bands, such as 800MHz and 1.9GHz, it can largely contribute to reduction in size of a multi-band portable radio device etc. Referring now to Fig. 12, a multi-band helical antenna as a multi-band antenna according to the eighth embodiment will be described. A helical antenna 72 is formed by winding a helical coil 74 around a helical guide with five turns, while a helical antenna 73 is formed by winding a helical coil 74 around the helical guide 75 with three turns. The respective helical coils 74, 74 are in close contact with or soldered to a conductive holder 76 at their first turns so as to be fed with power parallelly. The holder 76 holds the helical guide 75. By putting a cap (not shown) on the helical guide 75 and the helical antennas 72 and 73 arid bonding it thereto, a multi-band helical antenna 71 is constituted. Since lengths of the helical antennas 72 and 73 differ from each other, resonance frequencies thereof also differ from each other. Thus, the multi-band helical antenna 71 having two resonance frequencies can be realized. Referring now to Fig. 13, a multi-band helical antenna as a multi-band antenna according to the ninth embodiment will be described. Fig. 13 shows the state wherein a right-side half of a helical antenna 73 is removed. A helical antenna 72 is formed by winding a helical coil 74 around a small-diameter helical guide 75A with five turns. The helical antenna 73 is formed by winding a helical coil 74 around a large-diameter hollow helical guide 75B with three turns. The helical guides 75A and 75B are arranged concentrically and overlapped with each other. The respective helical coils 74, 74 are in close contact with or soldered to a conductive holder 76 at their first turns so as to be fed with power parallelly. The holder 76 holds the helical guides 75A and 75B. By putting a cap (not shown) on the helical guide 75B and the helical antenna 73 and bonding it thereto, a multi-band helical antenna 71 is constituted. Since lengths of the helical antennas 72 and 73 differ from each other, resonance frequencies thereof also differ from each other. Thus, the multi-band helical antenna 71 having two resonance frequencies can be realized. Further, since diameters of the helical antennas 72 and 73 differ from each other, band widths of the two resonance frequencies can be adjusted so that desired band widths can be achieved. It may be arranged that the helical coils 74, 74 are connected in series, and only one of the helical coils is fed with power. Referring now to Fig. 14, a multi-band helical antenna as a multi-band antenna according to the tenth embodiment will be described. A helical antenna 72 is formed by winding a helical coil 74 around a helical guide 75 with three turns. A helical antenna 73 is formed by winding a helical coil 74 around the helical guide 75 with two turns. The helical antennas 72 and 73 are connected in series by a serially connecting portion 77. The helical coil 74 of the helical antenna 72 is in close contact with or soldered to a conductive holder 76 at its first turn so as to be fed with power. The holder 76 holds the helical guide 75. By putting a cap (not shown) on the helical guide 75 and the helical antennas 72 and 73 and bonding it thereto, a multi-band helical antenna 71 is constituted. Since lengths of the helical antennas 72 and 73 differ from each other, resonance frequencies thereof also differ from each other. Thus, the multi-band helical antenna 71 having two resonance frequencies can be realized. Referring now to Fig. 15, a multi-band helical antenna as a multi-band antenna according to the eleventh embodiment of will be described. A helical antenna 72 is formed by winding a helical coil 74 around a helical guide 75 with three turns. A helical antenna 73 is formed by winding a helical coil 74 around the helical guide 75 with two turns. The helical antennas 72 and 73 are separated from each other by a helical insulating portion 78, being a dielectric, provided on the surface or circumference of the helical guide 75. The helical coil 74 of the helical antenna 72 is in close contact with or soldered to a conductive holder 76 at its first turn so as to be fed with power. The holder 76 holds the helical guide 75. The helical antenna 73 is fed with power through capacitive coupling to the helical antenna 72. By putting a cap (not shown) on the helical guide 75 and the helical antennas 72 and 73 and bonding it thereto, a multi-band helical antenna 71 is constituted. Since lengths of the helical antennas 72 and 73 differ from each other, resonance frequencies thereof also differ from each other. Thus, the multi-band helical antenna 71 having two resonance frequencies can be realized. In each of the multi-band antennas according to the eighth to eleventh embodiments, the multi-band characteristic is obtained by using a plurality of helical coils. Specifically, when the foregoing multi-band antenna is used as an antenna for carrying out transmission and reception at a plurality of mutually different frequency bands, such as 800MHz and 1.9GHz, it can largely contribute to reduction in size of a multi-band portable radio device etc. Referring now to Figs. 16 and 17, a telescopic whip antenna as a multi-band antenna according to the twelfth embodiment will be described. In the telescopic whip antenna in this embodiment, a sleeve 87 working as a feed point is formed with a groove 84 into which an antenna member 81 in the form of a printed board 82 formed thereon with an electrode pattern 83 is fitted, and a connecting portion 88 connected to one end of a meander line pattern electrode (hereinafter referred. to as "meander pattern") 83a is electrically and fixedly connected, by soldering or under pressure, to the conductive sleeve 87 coupled to a coupling portion 86, made of insulating resin, provided at one end of a rod antenna 85, so as to constitute a small-size antenna 90. An actual product has a cap (not shown) for antenna protection. For comparison, an equation (1) for calculating an inductance of the conventional helical coil and equations (2) to (4) for calculating an inductance of the small-size coil according to this embodiment will be shown hereinbelow. Coil: L coil = K 4πSN 2 1 x 10 -9 [H] wherein S represents a sectional area (cm 2 ), N the number of turns, 1 a mean magnetic circuit length (cm) and k a Nagaoke coefficient. Given that a self-inductance of the meander line is Ls, the following equation (2) is established based on the F. E. Terman equation: Meander: Ls = 200 lm(ln( lm W+t ) + 1.19 + 0.22 W+t lm ) [nH] wherein a mutual inductance Lij (a mutual inductance between i-th and j-th) is given by the following equation (3) based on the Greenhouse equation: Lij = 200 lmKN [nH] KN = ln(( lm DN ) + 1 + ( lm DN ) 2 ) - 1 + ( DN lm ) 2 + DN lm wherein DN = N(dc + W) represents a distance between conductors depending on the number of meanders, dc a distance (m) between conductors, N the number of meanders, and 2N the number of conductors. An inductance La of the meander pattern is given by the following equation (4) : In case of a helical coil, an inductance is proportional to the square of the number of turns and thus an equation for calculating it largely differs from the equation for the meander line. Resonance frequencies are each derived by the following equation (5) using a line capacitance C and the inductance L derived above: f = 1 / 2π LC In case of a helical coil, it is fixed to a helical guide provided with grooves at constant pitches so as to avoid dispersion in line capacitance C. The meander pattern 83a is formed by etching the printed board 82. In general, a pattern width can be achieved with an accuracy of ±20 µm error. Therefore, the line capacitance can be constant without using the member for uniforming the pitches as required in the helical coil so that the dispersion in resonance frequency can be suppressed. Reduction in weight of the small-size antenna can also be achieved. Further, since the antenna member 81 is only fitted into the groove 84 of the sleeve 87 upon assembling, the productivity is high. Moreover, since the feed point is determined by fixing the printed board 82, the dispersion in resonance frequency due to dispersion in feed point can also be suppressed. Referring now to Figs. 16 and 18, a telescopic whip antenna as a multi-band antenna according to the thirteenth embodiment will be described. In the telescopic whip antenna in this embodiment, like the one shown in Fig. 16, a sleeve 87 working as a feed point is formed with a groove 84, and an antenna member 91 in the form of a printed board 82 formed thereon with a sawtooth line pattern or a jagged line pattern (hereinafter collectively referred to as "sawtooth pattern") 83b as an electrode pattern 83 is fitted into the groove 84 and fixed thereto by soldering or under pressure so as to constitute a small-size antenna. An actual product has a cap (not shown) for antenna protection. As shown in Fig. 18, like the meander line pattern 83a shown in Fig. 17, the sawtooth pattern 83b is formed by etching the printed board. In general, a pattern width can be achieved with an accuracy of ±20 µm error. Therefore, the line capacitance can be constant without using the member for uniforming the pitches as required in the helical coil. so that the dispersion in resonance frequency can be suppressed. Reduction in weight of the small-size antenna can also be achieved. Further, as shown in Fig. 16, since the antenna member is only fitted into the groove 84 of the sleeve 87 upon assembling, the productivity is high. Moreover, since the feed point is determined by fixing the printed board 82, the dispersion in resonance frequency due to dispersion in feed point can also be suppressed. Referring now to Figs. 16 and 19, a telescopic whip antenna as a multi-band antenna according to the fourteenth embodiment will be described. In the telescopic whip antenna in this embodiment, like the one shown in Fig. 16, a sleeve 87 working as a feed point is formed with a groove 84, and an antenna member 92 in the form of a printed board 82 formed thereon with a spiral pattern 83c as an electrode pattern 83 is fitted into the groove 84 and fixed thereto by soldering or under pressure so as to constitute a small-size antenna. An actual product has a cap (not shown) for antenna protection. Hereinbelow, an equation (6) for calculating an inductance of the conventional helical coil and an equation (7) for calculating an inductance of the spiral pattern according to this embodiment will be shown hereinbelow. Coil: L coil = K 4π SN 2 1 x 10 -9 [H] wherein S represents a sectional area (cm 2 ), N the number of turns, 1 a mean magnetic circuit length (cm) and k a Nagaoke coefficient. Spiral: L spiral = 0.141an 5/3 log8a/c [µH] a = D i + D o 4 , c = D o + D i 2 wherein l represents a conductor radius (cm), n the number of turns, Di a spiral inner diameter (inch), and Do a spiral outer diameter (inch). Resonance frequencies are each derived by the following equation (8) using a line capacitance C and the inductance L derived above: f = 1 / 2π LC Like the meander pattern 83a and the sawtooth pattern 83b, the spiral pattern 83c is formed by etching the printed board 82. In general, a pattern width can be achieved with an accuracy of ±20 µm error. Therefore, the line capacitance C can be constant without using the member for uniforming the pitches as required in the helical coil so that the dispersion in resonance frequency can be suppressed. Reduction in weight of the small-size antenna can also be achieved. Further, since the antenna member 92 is only fitted into the groove 84 of the sleeve 87 upon assembling, the productivity is high. Moreover, since the feed point is determined by fixing the printed board 82, the dispersion in resonance frequency due to dispersion in feed point can also be suppressed. In each of the multi-band antennas according to the twelfth to sixteenth embodiments, the inductance has been explained. On the other hand, by forming a board of, for example, dielectric ceramic such as barium titanate having ε of 20 to 110 so as to constitute a microstrip antenna between the meander electrode (meander pattern 83a), the sawtooth electrode (sawtooth pattern 83b) or the spiral electrode (spiral pattern 83c) and the ground, it is further effective in size reduction of the antenna. Referring now to Figs. 20 and 21, a telescopic whip antenna as a multi-band antenna according to the fifteenth embodiment will be described. In the telescopic whip antenna in this embodiment, as an electrode pattern 93 having the same outside dimension as that of a sleeve 87 working as a feed point, a round and flat spiral pattern 93a is used. The spiral pattern 93a is formed on the surface of a circular printed board 94 and has an initial wind part connected to the underside of the printed board 94 via a through hole (not shown), so as to form an antenna member 101. The antenna member 101 is fixed to the sleeve 87 by soldering or under pressure so as to be fed with power. An actual product has a cap (not shown) for antenna protection. Like the meander pattern 83a and the sawtooth pattern 83b described above, the spiral pattern 93a is formed by etching the printed board 94. In general, a pattern width can be achieved with an accuracy of ±20 µm error. Therefore, the line capacitance can be constant without using the member for uniforming the pitches as required in the conventional helical coil so that the dispersion in resonance frequency can be suppressed. Reduction in weight of a small-size antenna 100 can also be achieved. Further, since the printed board 94 is only connected onto the sleeve 87 upon assembling, the productivity is high. Moreover, since the feed point is determined by fixing the printed board 94, the dispersion in resonance frequency due to dispersion in feed point can also be suppressed. Referring now to Figs. 20 and 22, a telescopic whip antenna as a multi-band antenna according to the sixteenth embodiment will be described. The telescopic whip antenna in this embodiment is the same in structure as the telescopic whip antenna shown in Fig. 20 except that, instead of the round spiral pattern 93a shown in Fig. 21, an angular spiral pattern 93b having the same outside dimension as that of a sleeve 87 working as a feed point is used. The angular spiral pattern 93b is formed on the surface of a circular printed board 94 and has an initial wind. part connected to the underside of the printed board 94 via a through hole (not shown), so as to form an antenna member 102. The antenna member 102 is fixed to the sleeve 87 by soldering or under pressure so as to be fed with power. An actual product has a cap (not shown) for antenna protection. Like the meander pattern 83a and the sawtooth pattern 83b described above, the spiral pattern 93b is formed by etching the printed board 94. In general, a pattern width can be achieved with an accuracy of ±20 µm error. Therefore, the line capacitance can be constant without using the member for uniforming the pitches as required in the conventional helical coil so that the dispersion in resonance frequency can be suppressed. Reduction in weight of a small-size antenna 100 can also be achieved. Further, since the printed board 94 is only connected onto the sleeve 87 upon assembling, the productivity is high. Moreover, since the feed point is determined by fixing the printed board 94, the dispersion in resonance frequency due to dispersion in feed point can also be suppressed. Referring now to Figs. 20 and 23, a telescopic whip antenna as a multi-band antenna according to the seventeenth embodiment will be described. In the telescopic whip antenna in this embodiment, a pair of boards 94, 94 respectively formed with round spiral. patterns 93a and 93c each having the same outside dimension as that of a sleeve 87 working as a feed point are stacked with each other so as to ensure a pattern length. The spiral patterns 93a and 93c formed on the printed boards 94, 94 have winding directions opposite to each other, that is, a clockwise winding direction and a counterclockwise winding direction. The spiral patterns 93a and 93c have their respective initial wind parts connected to the undersides of the corresponding printed boards 94, 94 via corresponding through holes (not shown), so as to form an antenna member 105. The antenna member 105 is fixed to the sleeve 87 by soldering or under pressure so as to be fed with power. An actual product has a cap (not shown) for antenna protection. Like the meander pattern 83a and the sawtooth pattern 83b described above, each of the spiral patterns 93a and 93c is formed by etching the corresponding printed board 94. In general, a pattern width can be achieved with an accuracy of ±20 µm error. Therefore, the line capacitance C can be constant so that the dispersion in resonance frequency can be suppressed. Reduction in weight of the small-size antenna can also be achieved. Further, since the antenna member 105 is only connected onto the sleeve 87 upon assembling, the productivity is high. Moreover, since the feed point is determined by fixing the antenna member 105, the dispersion in resonance frequency due to dispersion in feed point can also be suppressed. Similar effects can be achieved by combining the angular spiral pattern 93b shown in Fig. 22 and another angular spiral pattern having an opposite winding direction. Referring now to Figs. 24 to 26, a telescopic whip antenna as a multi-band antenna according to the eighteenth preferred embodiment of the present invention will be described. In the telescopic whip antenna in this embodiment, a small-size antenna 110 is provided with an antenna member 115 constituted by forming a meander pattern 112 on a flexible board 111 as best shown in Fig. 25 and then winding it around a cylindrical resin member 114 as best shown in Fig. 26. For power feeding from one end of the meander pattern 112, a connection electrode 113 provided at one end of the flexible board 111 and the meander pattern 112 are connected to each other. The connection electrode 113 of the antenna member 115 and a sleeve 87 are connected to each other by soldering or under pressure for power feeding. The meander pattern 112 is formed by etching the flexible board 111 having a conductive metal foil thereover. In general, a pattern width can be achieved with an accuracy of ±20 µm error. Therefore, the line capacitance C can be constant so that the dispersion in resonance frequency can be suppressed. Further, since the flexible board 111 is only connected onto the sleeve 87 upon assembling, the productivity is high. Moreover, since the feed point is determined by fixing the flexible board 111, the dispersion in resonance frequency due to dispersion in feed point can also be suppressed. According to the multi-band antennas in each of the twelfth to sixteenth embodiments, the small-size antenna and the rod antenna which is receivable in the casing of the radio device and expandable are combined to provide the telescopic whip antenna. In the telescopic whip antenna, the electrode pattern is formed on the printed board, the flexible board or the dielectric board. By using the resonance frequency based on the dielectric constant of the board and the electrode pattern, there can be provided-such a telescopic whip antenna that is excellent in productivity, stable in resonance frequency and reducible in weight, and thus can largely contribute to reduction in size and weight of the portable terminal.

Claims: A multi-band antenna (10, 20, 30, 40) comprising an antenna element having a LC parallel resonance circuit (C, L) and a first (1) and a second (2) radiation element connected to opposite ends of said LC parallel resonance circuit, characterized in that said first radiation element (1) and said LC parallel resonance circuit (C, L) are formed by a single coil antenna, said LC parallel resonance circuit (C, L) being constituted by self-resonance based on an inductor which is a part of said single coil antenna. An antenna as claimed in claim 1, wherein said inductor (3) is mounted on a printed board, and/or has an inductance L given by L ≥ 7nH. An antenna as claimed in claim 1 or 2, wherein said first radiation element (1) has a helical shape, preferably a part of said first radiation element (1) provides the self-resonance which constitutes said LC parallel resonance circuit (C, L). An antenna as claimed in one of claims 1 to 3, wherein said LC parallel resonance circuit and said first radiation element are covered with an insulating material (8) through molding, preferably said insulating material is one of polymer and elastomer which are flexible. An antenna as claimed in one of claims 1 to 4, wherein said first radiation element is in the form of a printed board (24) having a meander pattern (22), preferably a part of said meander pattern provides the self-resonance which constitutes said LC parallel resonance circuit, preferably said LC parallel resonance circuit is mounted on said printed board, and/or said printed board is covered through molding with flexible insulating resin material preferably from the group consisting of polymer and elastomer. An antenna as claimed in one of claims 1 to 5, wherein said second radiation element (2) is elongate and made of a superelastic alloy, preferably said second radiation element is covered through molding with flexible insulating resin material preferably from the group consisting of polymer and elastomer. A multi-band antenna according to claim 1, further characterized by the design of a telescopic multi-band whip antenna comprising a small-size antenna (42) and a whip antenna (41) which is receivable in a radio device casing and expandable, wherein said small-size antenna is located outside said radio device casing, said whip antenna (41) being slidable relative to said small-size antenna (42), each of said small-size antenna (42) and said whip antenna (41) both having multi-band characteristics so that the multi-band characteristics are obtained both upon putting back and expansion of said whip antenna (41). An antenna as claimed in claim 7, wherein said radio device casing is provided with a holder (49) for fixing said small-size antenna (42), said whip antenna (41) being provided at upper and lower end portions thereof with a first and a second stopper (46) which are held by said holder (49) upon putting back and expansion of said whip antenna (41), said first and second stoppers being electrically insulated from said holder (49), preferably said whip antenna (41) is electrically separated from said small-size antenna (42) by said first stopper when said whip antenna (41) slides in said holder (49) to be received in said radio device casing and/or said whip antenna comprises an LC parallel resonance circuit (43) including a chip inductor and a chip capacitor, and a metal radiation element connected to said LC parallel resonance cirucuit (43). An antenna as claimed in claim 7 or 8, wherein said whip antenna is in the form of a combination of self-resonance of a chip inductor and a metal radiation element connected thereto, a combination of a distributed constant parallel resonance circuit as an LC parallel resonance circuit, and a metal radiation element, or a combination of self-resonance due to an air-core coil as an LC parallel resonance circuit, and a metal radiation element, said metal radiation element is preferably made of a Ti-Ni alloy. An antenna as claimed in one of claims 7 to 9, wherein said small-size antenna is in the form of a combination of an LC parallel resonance circuit having a chip inductor and a chip capacitor, and a helical coil connected thereto, a combination of self-resonance of a chip inductor and a helical coil connected thereto, a combination of self-resonance of an air-core coil and a helical coil connected thereto, a combination of an LC parallel resonance circuit (53) comprising a chip inductor and a chip capacitor mounted on a flexible board, and a meander pattern (59) formed on said flexible. board, a combination of a self-resonance circuit having a chip inductor and working as an LC parallel resonance circuit, and a meander pattern, said self-resonance circuit and said meander pattern provided on a flexible board, a combination of a self-resonance circuit having an air-core coil and working as an LC parallel resonance circuit, and a meander pattern, said self-resonance circuit and said meander pattern being provided on a flexible board, or a combination of a distributed constant parallel resonance circuit and a meander pattern (69) both provided on a flexible board.

Inventors: IKEDA MASASHI, ISHIKAWA SHIGEKAZU, MINEGISHI KAZUO, TESHIMA MAKOTO, IKEDA, MASASHI, ISHIKAWA, SHIGEKAZU, MINEGISHI, KAZUO, TESHIMA, MAKOTO
Applicants: NEC TOKIN CORP, NEC TOKIN CORPORATION
Application year: 1998
Main classification: H01Q5
IPC codes: H01Q11, H01Q5, H01Q1