Radio antenna

Abstract

 In an antenna attached to a casing of a radio apparatus, the antenna is used being extended during communication but retracted during no-communication. The antenna includes a first coil-shaped antenna element (10) and a second rod-shaped antenna element (14), and these two antenna elements are coupled to each other via a trap circuit (12,16,18;40,50). When extended, both the first and second antenna elements (10,14) project outside the casing, so that only the second antenna element (14) is connected to a radio circuit via a feeding member. When retracted, the second antenna element (14) is kept inside the casing and only the first antenna element (10) is kept outside the casing, so that only the first antenna element (10) is connected to the radio circuit via the feeding member (30). The trap circuit (50) is a parallel resonance circuit composed of a capacitance (40) and an inductance (12). The resonance frequency of the trap circuit is determined to be an intermediate value between those of the first and second antenna elements. Owing to the presence of the trap circuit, both the first and second antenna elements can function independently.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a radio antenna, and more specifically to a radio antenna suitable for use with a radio apparatus for transmitting and/or receiving two signals of different frequencies (e.g., as a call signal frequency and a communication signal frequency). In more practical way, the present invention relates to a radio antenna which can be extended and retracted so as to be suitable for a portable radio apparatus and further which can receive a call signal under the condition that the antenna is kept retracted within a casing of the radio apparatus.

[0002] In the radio apparatus such as a portable telephone set, recently, there exist the following features: two different frequencies are used for a call signal and a communication signal; the radio apparatus casing is reduced in size so as to be suitable for a portable apparatus; and in addition the antenna is extended only during communication but retracted when not used for communication. Furthermore, it is required for the radio apparatus to receive a call signal when the antenna is kept retracted in the apparatus casing.

[0003] An example of these conventional radio antennas is disclosed in Japanese Published Unexamined (Kokai) Application No. 3-245603. In this conventional radio antenna, a coil-shaped antenna element is connected to a rod-shaped antenna element; the rod-shaped antenna element is housed inside a casing so as to be extensible and retractable from and into the casing; when the antenna is extended, the base end portion of the rod-shaped antenna element is brought into elastic contact with a feeding member at the feeding point; and when the antenna is retracted, only the coil-shaped antenna element is left projected outside the casing and further the base end portion of the coil-shaped element is brought into elastic contact with the feeding member.

[0004] The above-mentioned conventional radio antenna is suitable for a portable radio apparatus because the antenna can receive a call signal under the condition that the antenna is kept retracted. However, the conventional radio antenna involves the following drawbacks: since the coil-shaped antenna element and the rod-shaped antenna element are kept connected to each other irrespective of when the antenna is kept extended or retracted, the feeding point is different from each other between when the antenna is kept extended and retracted. Therefore, the output impedance of the antenna at the feeding point changes according to the extension and retraction positions of the antenna, thus resulting in a problem in that it is difficult to match the antenna output impedance to the circuit of the radio apparatus. In addition, when the antenna is kept extended, the radiation characteristics of the antenna is determined on the basis of both the coil-shaped antenna element and the rod-shaped antenna element. However, the experiment conducted by the inventors indicated that there exists such a problem in that when the rod-shaped antenna element is kept in the vertical direction, the antenna directivity is shifted slightly downward from the horizontal position. In order to obtain a high antenna gain, it is preferable that the antenna directivity is kept in the horizontal direction or shifted slightly upward from the horizontal direction. Further, when the antenna is kept extended, since both the coil-shaped antenna element and the rod-shaped antenna element function as a single antenna in cooperative functions of these two antenna elements, there exists a relatively large restriction in the design of the respective antenna elements.

SUMMARY OF THE INVENTION

[0005] With these problems in mind, therefore, it is the primary object of the present invention to provide a radio antenna, by which a first antenna element and a second antenna element can function as an independent antenna element, respectively.

[0006] Further, another object of the present invention is to provide a radio antennal compact in size and stable in antenna function.

[0007] Further, still another object of the present invention is to provide a radio antenna which can receive both a call signal and a communication signal.

[0008] Further, a further object of the present invention is to provide a radio antenna whose structure is suitable for obtaining a relatively large antenna extending force.

[0009] To achieve the above-mentioned objects, the present invention provides a radio antenna attached to a casing of a radio apparatus, comprising: a first antenna element; a second antenna element; feeding means for selectively connecting said first and second antenna elements to a radio apparatus circuit; and a trap circuit connected between said first and second antenna elements.

[0010] In the radio antenna according to the present invention, since the trap circuit is connected between the first antenna element and the second antenna element, when the first antenna element functions as an antenna, the second antenna element is disconnected from the antenna function by the trap circuit. In the same way, when the second antenna element functions as an antenna, the first antenna element is disconnected from the antenna function by the trap circuit. The features of the radio antenna according to the present invention for achieving the other objects will be apparent from the following description with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] 

Fig. 1 is a longitudinal cross-sectional view showing a first embodiment of the radio antenna according to the present invention, in which the radio antenna is kept extended;

Fig. 2 is a longitudinal cross-sectional view showing the same radio antenna kept retracted;

Fig. 3 is an equivalent circuit of the same radio antenna kept extended as shown in Fig. 1;

Fig. 4 is an equivalent circuit of the same radio antenna kept retracted as shown in Fig. 2;

Fig. 5 is a longitudinal cross-sectional view showing a second embodiment of the radio antenna according to the present invention, in which the radio antenna is kept extended;

Fig. 6 is a longitudinal cross-sectional view showing the same radio antenna kept retracted;

Fig. 7 is a longitudinal cross-sectional view for assistance in explaining a fixing structure of a trap circuit shown in Fig. 5;

Fig. 8 is an enlarged plan view showing an inner spring used for a feeding point of the radio antenna;

Fig. 9 is an enlarged elevation view showing the same inner spring shown in Fig. 8;

Fig. 10 is an equivalent circuit of the same antenna kept extended as shown in Fig. 5;

Fig. 11 is an equivalent circuit of the same antenna kept retracted as shown in Fig. 6;

Fig. 12 is a longitudinal cross-sectional view showing a first modification of the second embodiment of the radio antenna according to the present invention, in which the radio antenna is kept extended;

Fig. 13 is an enlarged longitudinal cross-sectional view for assistance in explaining a fixing structure of a trap circuit shown in Fig. 12;

Fig. 14 is an enlarged font view showing a slide spring used for the telescopic structure of the second antenna element of the radio antenna shown in Fig. 12;

Fig. 15 is an enlarged bottom view showing the slide spring used for the telescopic structure of the second antenna element of the radio antenna shown in Fig. 12;

Fig. 16 is a front view showing a feeding fixture of the second antenna element of the radio antenna shown in Fig. 12;

Fig. 17 is an enlarged bottom view showing the feeding fixture of the second antenna element of the radio antenna shown in Fig. 12;

Fig. 18 is an enlarged front view showing a band spring for covering the feeding fixture of the radio antenna shown in Fig. 12;

Fig. 19 is an enlarged plan view showing the band spring for covering the feeding fixture of the ratio antenna shown in Fig. 12;

Fig. 20 is a longitudinal cross-sectional view showing a second modification of the second embodiment of the radio antenna according to the present invention, in which the radio antenna is kept extended;

Fig. 21 is a longitudinal cross-sectional view showing a third embodiment of the ratio antenna according to the present invention, in which the radio antenna is kept extended;

Fig. 22 is a longitudinal cross-sectional view showing the same radio antenna kept retracted; and

Fig. 23 is an enlarged cross-sectional view showing an essential portion of the radio antenna shown in Fig. 21.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Embodiments of the radio antenna according to the present invention will be described hereinbelow with reference to the attached drawings.

[0013] Figs. 1 to 4 shows a first (basic) embodiment of the present invention.

[0014] In Fig. 1, a radio antenna is composed of a first antenna portion A having a first antenna element 10 and a second antenna portion B having a second antennal element 14. The first antenna element 10 is a coil-shaped antenna, and the second antenna 14 is a rod-shaped antenna. A base end of the first antenna element 10 is connected to another coil 12 coaxial with the first antenna element 10, and this coil 12 is connected to the second antenna element 14. The coil 12 is covered with two inner and outer conductive cylindrical bodies 16 and 18 arranged coaxially and loosely with respect to each other. The top end of the outer conductive cylindrical body 16 is closed by an upper wall 16a. The base end of the first antenna element 10, that is, a junction point between the first antenna element 10 and the coil 12 is passed through the upper wall 16a and further connected to the same upper wall 16a electrically. In the same way, the base end of the inner conductive cylindrical body 18 is closed by a lower wall 18a. A junction point between the second antenna element 14 and the coil 12 is passed through the lower wall 18a and further connected to the same lower wall 18a electrically. The space between the two inner and outer conductive cylindrical bodies 18 and 16 is filled with an insulating resin 20 in such a way that the two cylindrical bodies are formed integral with each other. Further, a cap-shaped resin antenna top 22 is fitted and fixed to the outer conductive cylindrical body 16 so as to cover the first antenna element 10 and additionally an upper half of the outer conductive cylindrical body 16. On the other hand, a lower half of the outer conductive cylindrical body 16 is exposed. Further, the antenna top 22, the first antenna element 10, the coil 12, the conductive cylindrical bodies 16 and 18 and the resin 20 constitutes a decorative antenna top.

[0015] The base end of the second antenna element 14 is fitted into a central hole of a large-diameter conductive cylinder 24 having a diameter the same as that of the outer conductive cylindrical body 16. Further, a casing 26 of a radio apparatus is formed with a hole 28, into which both the outer conductive cylindrical body 16 and the large-diameter conductive cylinder 24 can be fitted in such a way that the second antenna element 14 can be extended out of the casing 26 as shown in Fig. 1 or retracted into the casing 26 as shown in Fig. 2, respectively. Within the casing 26, a tongue-shaped feeding member 30 is fixed so as to be brought into elastic contact with the outer conductive cylindrical body 16 or the large-diameter conductive cylinder 24 for electric feeding contact when the antenna is retracted or extended. As shown in Fig. 3, this feeding member 30 is connected to a ratio circuit 36 via an coaxial cable 32 and a matching circuit 34. Further, as shown in Fig. 1, a set screw 36 is screwed into the large-diameter conductive cylinder 24 in the radial direction thereof for prevention of removal of the second antenna element 14 from the casing 26. Further, an insulation cylinder 37 is provided inside the casing 26 to guide the large-diameter conductive cylinder 24 when the antenna is retracted into the casing 26.

[0016] As shown in Fig. 4, the effective length of the first antenna element 10 is set to 1/2 or 1/4 of a wavelength of a carrier for transmitting a call signal so as to resonate with the carrier resonance frequency band (f₁). On the other hand, as shown in Fig. 3, the effective length of the second antenna element 14 is set to 1/2 or 1/4 of the wavelength of a carrier for transmitting a communication signal so as to resonate with the carrier resonance frequency band (f₂), which is slightly higher than that of the carrier resonance frequency band (f₁). The two coaxial conductive cylindrical bodies 16 and 18 form a capacitance 40 connected in parallel to the coil 12, so that a trap circuit composed of a parallel resonance circuit can be formed. The resonance frequency of this trap circuit is roughly determined to be an intermediate frequency between the resonance frequency bands of both the first antenna element 10 and the second antenna element 14. Further, since the resonance frequency bands of the first antenna element 10 and the second antenna element 14 are both determined to be relatively wide, the resonance frequency band of the trap circuit can be set also relatively wide. Therefore, there exists no problem even if the central resonance frequency of the trap circuit is slightly offset from the resonance frequency bands of the first and second antenna elements 10 and 12.

[0017] In the construction as described above, when the antenna is extended during the communications as shown in Fig. 3, since the second antenna element 14 is separated from the first antenna element 10 by the trap circuit 50 from the standpoint of antenna function, only the second antenna element 14 functions as an antenna with a carrier resonance frequency band f₂. Further, the output impedance of the second antenna element 14 is connected to the feeding member 30 as the output impedance of the antenna.

[0018] On the other hand, when the antenna is retracted during the standby of call signal reception as shown in Fig. 4, since the second antenna element 14 is separated from the first antenna element 10 from the standpoint of antenna function, only the first antenna element 10 functions as an antenna with a carrier resonance frequency band f₁. Further, the output impedance of the first antenna element 10 is connected to the feeding member 30 as the output impedance of the antenna.

[0019] Here, the output impedance of the first antenna element 10 is determined to be the same as that of the second antenna element 14. Therefore, it is possible to realize an appropriate matching in any of the antenna extension and retraction states, so that a high antenna gain can be obtained as a radio antenna.

[0020] Further, in the above-mentioned antenna, although the second antenna element 14 is a rod-shaped antennal formed by a single conductive pipe, it is also possible to use a multi-stage telescopic rod-shaped antenna or a coil-shaped antenna. Further, the structure of the feeding section composed of the feeding member 30 and the outer conductive cylindrical body 16 and the large-diameter conductive cylinder 24 is not limited to only the above-mentioned structure. Further, the trap circuit 50 can be composed of a bobbin coil and a capacitor housed in the bobbin coil as a discrete part. Further, the trap circuit 50 can be composed of a bobbin coil, around which two parallel conductive wires are wound so that the inductance component and the capacitance component of the trap circuit can be both formed simultaneously and appropriately. Or else, it is also possible to use a rod-shaped antenna element instead of the coil 12. In addition, without being limited to only the coil-shaped antenna, it is also possible to use a rod-shaped antenna as the first antenna element 10 (although the extension length of the first antenna element increases). Further, it is also possible to insertion-mold the first antenna element 10, the coil 12, and the conductive cylindrical bodies 16 and 18 integral with each other by use of an insulating resin so as to form a decorative antenna top.

[0021] The radio antenna as described above is provided with the following effects.

[0022] First, when the first antenna element is used as the antenna, the second antenna is disconnected from the first antenna in antenna functional standpoint. On the other hand, when the second antenna element is used as the antenna, the first antenna is disconnected from the second antenna in the functional standpoint of antenna. Accordingly, the first and second antenna elements will not exert harmful influence upon each other in the functional standpoint of antenna. In other words, two antenna can be used as two independent antennas having two desired antenna characteristics, separately.

[0023] Further, since the first antenna element is disconnected from the second antenna by the trap circuit from the functional standpoint of antenna, it is possible to freely design the first antenna element as a call signal reception antenna and the second antenna as a communication signal reception antenna independently from each other, with the result that the design freedom of each antenna is large and thereby any desired antenna characteristics (i.e., directivity and gain) can be obtained, irrespective of the whether the antenna is extended or retraced. Here, in the case where the second antenna element is a rod-shaped antenna set in the vertical direction, it is possible to obtain a desired horizontal directivity.

[0024] Further, the trap circuit can be minimized in shape, and can be formed integral with the first antenna element of coil-shaped antenna so as to form a decorative antenna top. Further, since the antenna can be brought into elastic contact with the feeding member at the same feeding point in both the antenna extension and retraction states, the structure of the feeding point can be simplified.

[0025] Further, since the first and second antenna elements are separated form each other from the functional standpoints of antenna by the trap circuit and in addition since the output impedances of these two antenna elements are determined to be equal to each other, it is possible to equalize the antenna output impedance irrespective of whether the antenna is extended or retracted, so that only one matching circuit can be used in common, thus retaining a higher antenna gain in spite of a simple matching circuit.

[0026] Figs. 5 to 9 show a second embodiment of the present invention. As shown in Fig. 5, in this second embodiment, the radio antenna includes a first antenna portion A and a second antenna portion B. The first antenna portion A is a coil-shaped first antenna element 110 formed by winding wire around a bobbin 112 of cylindrical dielectric insulating resin. The bobbin 112 is formed with a recess portion 112a at the base end thereof for soldering the wire. The base end of the first antenna element 110 is wound around and connected to a top end of a first sleeve 114 of conductive metallic material. The first sleeve 114 is formed with a large-diameter conductive cylindrical hollow portion 114a at the base end thereof. A top end of a straight rod-shaped conductor 116 is inserted through the conductive cylindrical hollow portion 114a from the base end side thereof. The top end of this rod-shaped conductor 116 is electrically connected to a top end of the first sleeve 114 by soldering 118. Further, the first sleeve 114 is formed with male threads 114b in the outer circumferential surface of the top end thereof so as to be engaged with female threads formed in the inner circumferential surface of a cap 120. The cap 120 formed of a resin material covers the bobbin 112 around which the first antenna element 110 is wound, and further brings the bobbin 112 into tight contact with the top end surface of the first sleeve 114.

[0027] The straight rod-shaped conductor 116 is formed integral with the second antenna element 122 (which constitutes the second antenna portion B) as a single straight rod body. A second sleeve 126 is fitted to the base end of the rod-shaped conductor 116 (which is the same as the top end of the second antenna element 122). As depicted in Fig. 7, the second sleeve 126 is formed integral with a small-diameter conductive cylindrical portion 126a at the top end thereof. The conductive cylindrical portion 126a is fitted into the conductive cylindrical portion 114a of the first sleeve 114 via a dielectric insulating cylinder 124. Further, the second sleeve 126 is formed with a horizontal hole extending from the outer circumferential surface thereof toward the rod-shaped conductor 116 in the radial direction. Therefore, when solder 128 is allowed to flow through this horizontal hole, it is possible to fix the second sleeve 126 to the conductor 116 while connecting both electrically. Further, the second sleeve 126 is formed with an annular recessed portion 126b at the outer circumferential surface thereof. Therefore, after the large-diameter conductive cylindrical portion 114a of the first sleeve 114 is fitted to the small-diameter conductive cylindrical portion 126a of the second sleeve 126 via an insulating cylinder 124, the base end portion of the large-diameter conductive cylindrical portion 114a is caulked into the recessed portion 126b to fix the first and second sleeves 114 and 126 with respect to each other. The cross section of the annular recessed portion 126b is of notch shape reduced in diameter toward the side of the conductive cylindrical portion 126a. Further, the second sleeve 126 is formed with a female thread 126c at the inner base end portion thereof.

[0028] With reference to Fig. 5, the base end of the second antenna element 122 is inserted into a through hole formed in a conductive end fixture 130, and further soldered to an end surface of the end fixture 130 at a central position 133 thereof. The end fixture 130 is formed with a large-diameter portion 130a at the end thereof and with a hollow portion extending form the insertion side of the second antenna element 122. Further, a female thread 130b is formed within this hollow portion near the bottom end thereof.

[0029] The second antenna element 122 is covered with a tube 132 formed of an insulating resin. The tube 132 is formed with a male thread portion on both ends thereof, respectively so as to engage with the female thread portion 126c of the second sleeve 126 and the female thread 130b portion of the end fixture 130, respectively.

[0030] A feeding fixture 136 formed with a flange portion 136a is fixedly screwed to the casing 134 of the radio apparatus. Within the inner circumference of the feeding fixture 136, a roughly cylindrical conductive spring 138 is disposed in such a way not to be removed in the axial direction of the feeding fixture 136. The spring 138 serves to elastically support the end fixture 130 movably passed through the feeding fixture 136 so that the end fixture 130 can be connected to the feeding fixture 136 electrically. For prevention of removal of the cylindrical conductive spring 138 from the feeding fixture 136, the feeding fixture 136 is formed with a small-diameter inner hollow portion at the flange portion 136a thereof, for instance. After the inner spring 138 is inserted into the large-diameter inner hollow portion of the feeding fixture 136, the base end of the feeding fixture 136 is caulked for prevention of the removal of the conductive spring 138 from the base end side of the feeding fixture 136.

[0031] As shown in Figs. 8 and 9, the inner spring 138 is formed with a plurality of slits 138a, 138b, .. so as to be elastically deformable in the radial direction thereof. Therefore, the inner spring 138 is interposed elastically between the outer circumferential surface of the end fixture 130 and the inner circumferential surface of the feeding fixture 136. Further, the outer diameter of the conductive cylindrical portion 114a of the first sleeve 114 is roughly the same as the outer diameter of the end fixture 130 at which the inner spring 138 is in contact with. Therefore, when the antenna is retracted, the conductive cylindrical portion 114a of the first sleeve 114 is inserted into the inner spring 138 in elastic contact therewith. Further, a feeding spring 140 is fixed to the inner surface of the casing 134 so as to be brought into elastic and electric contact with the feeding fixture 136. Further, this feeding spring 140 is connected to the radio circuit 36 through a feeding wire 142 and via a matching circuit 34.

[0032] Here, under the condition that the antenna is extended from the casing 134, since the end fixture 130 is inserted into the inner spring 138 disposed within the feeding fixture 136, the base end of the second antenna element 122 becomes a feeding point. Here, since the end fixture 130 is formed with the large-diameter portion 130a, it is possible to prevent the second antenna element 122 from being removed in the extension direction of the antenna. Further, as shown in Fig. 6, under the condition that the antenna is retracted into the casing 134, since the conductive cylindrical portion 114a of the first sleeve 114 is inserted into the inner spring 138 disposed within the feeding fixture 136, the base end of the first sleeve 114, that is, the first antenna element 110 becomes the feeding point. When the antenna is retracted, only the first antenna element 110 projects outside from the casing 134.

[0033] With reference to Figs. 10 and 11, the function of this antenna will be described hereinbelow. In the same way as with the case of the first embodiment shown in Figs. 1 and 2, the effective length of the first antenna element 110 is set to 1/2 or 1/4 of a wavelength of a carrier for transmitting a call signal so as to resonate with the carrier resonant frequency band (f₁). On the other hand, as shown in Fig. 10, the effective length of the second antenna element 122 is set to 1/2 or 1/4 of a wavelength of a carrier for transmitting a communication signal so as to resonate with the carrier resonant frequency band (f₂), which is slightly higher than that of the carrier resonance frequency band (f₁). Further, as shown in Fig. 7, the two coaxial conductive cylindrical portions 114a and 126a (between which a dielectric substance of the insulating cylinder 124 is interposed) form a capacitance 150 connected in parallel to the inductance component of the straight rod-shaped conductor 116, so that a trap circuit 152 can be formed between the first antenna element 110 and the second antenna element 122. The resonance frequency of this trap circuit 152 is roughly determined to an intermediate frequency between the resonance frequency bands of the first antenna element 110 and the second antenna element 122. Further, since the resonance frequency bands of the first antenna element 110 and the second antenna element 122 are both determined to be relatively wide, the resonance frequency band of the trap circuit can be set relatively wide. Therefore, there exists no problem when the central resonance frequency of the trap circuit is slightly offset from the resonance frequency bands of the first and second antenna elements 110 and 122.

[0034] In the construction as described above, when the antenna is extended during the communications as shown in Fig. 5, since the second antenna element 122 is separated from the first antenna element 110 by the trap circuit 152 from the standpoint of antenna function as shown in Fig. 10, only the second antenna element 122 functions as an antenna with a carrier resonance frequency band f₂. Further, the output impedance of the second antenna element 122 is connected to the feeding member 136 as the output impedance of the antenna.

[0035] On the other hand, when the antenna is retracted during the standby of call signal reception as shown in Fig. 6, since the second antenna element 122 is separated from the first antenna element 110 from the standpoint of antenna function as shown in Fig. 11, only the first antenna element 110 functions as an antenna with a carrier resonance frequency band f₁. Further, the output impedance of the first antenna element 10 is connected to the feeding fixture 136 as the output impedance of the antenna.

[0036] Here, in this second embodiment, since the output impedance of the first antenna element 110 is determined to be the same as that of the second antenna element 122, it is possible to realize an appropriate matching in any of the antenna extension and retraction states, so that a high antenna gain can be obtained as a radio antenna.

[0037] In this second embodiment, since the trap circuit 152 is formed by a parallel resonance circuit composed of the inductance component of the straight conductor 116 and the capacitance component of the two coaxial conductive cylinder portions 114a and 126a, it is possible to reduce the outer diameter of the trap circuit, so that the antenna of this second embodiment is suitable for a portable radio apparatus form the design standpoint.

[0038] Further, in this second embodiment, since two coaxial conductive cylinder portions 114a and 126a are fixed to each other by caulking, the structure is simple and thereby the assembly work can be simplified. Further, since the trap circuit 152 is constructed by a single straight body of the straight conductor 116 and the second antenna element 122, it is possible to form a trap circuit at top end of the straight body without increasing the number of composing parts, so that this embodiment is suitable for mass production.

[0039] Further, in this second embodiment, since the base end of the first coil-shaped antenna element 110 is wound around and electrically fixed to the top end of the first sleeve 114, and further since the straight conductor 116 is electrically connected to the first sleeve 114 at the top end thereof, the trap circuit 152 can be connected simply to the first antenna element 110. Further, since the bobbin 112 around which the first antenna element 110 is wound can be brought into tight contact with the first sleeve 114 by the cap 120, the bobbin 112 can be fixed to the first sleeve 114 simply.

[0040] A first modification of this second embodiment will be described hereinbelow with reference to Figs. 12 to 19. The points of this modification different from the second embodiment shown in Fig. 5 are that the second antenna element itself can be extended and retracted and further the structures of the end fixture and the feeding fixture are different slightly between both.

[0041] In the same way as with the case of the second sleeve 126 of the second embodiment shown in Fig. 5, a second sleeve 160 is formed with a conductive small-diameter cylindrical portion 160a on the top end side thereof; a base end of a straight rod-shaped conductor body 116 is fixed to the second sleeve 160; further the base end of a large-diameter conductive cylindrical portion 114a of a first sleeve 114 is formed with an annular recessed portion 160b at the outer circumferential surface thereof so as to be caulked for fixing the first sleeve 114 to the second sleeve 160. In this modification, however, the base end portion of the second sleeve 160 is solid (not a hollow portion) and further formed with two punch holes 160d on the outer circumferential surface thereof.

[0042] Further, as shown in Fig. 13, a top end of a large-diameter conductive pipe 162 is fitted to the base end of the solid second sleeve 160, and then fixed and connected to the solid second sleeve 160 by punching the large-diameter pipe 162. As shown in Fig. 12, the large-diameter pipe 162 is formed with a narrowed portion 162a at the base end thereof. To the base end of this large-diameter pipe 162, a solid conductive small-diameter rod body 164 is inserted. A slide spring 166 as shown in Figs. 14 and 15 is fitted and fixed to the top end of the small-diameter rod body 164. The slide spring 166 is formed of an elastic conductive material and formed with slits 166a expanded outward as shown in Fig. 14. This slide spring 166 fixed to the small-diameter rod body 164 is slid in elastic contact with the inner wall surface of the large-diameter pipe 162. Therefore, the large-diameter pipe 162 can be connected to the small-diameter rod body 164 telescopically and electrically. Further, the top end of the small-diameter rod body 164 is expanded appropriately outward to prevent the removal of the slide spring 166 therefrom. Further, a slide fixture 168 is pressure fitted and fixed to the base end side of the slide spring 166 fixed to the small-diameter rod body 164 for prevention of shift of the slide spring 166. The base end side of the small-diameter rod body 164 is passed through a through hole formed in an end fixture 172 and further fixed to an end surface of the end fixture 172 by soldering 174 for electrical connection. The intermediate portion of the small-diameter rod body 164 is covered with a resin tube 176. These large-diameter pipe 162 and the small-diameter rod body 164 constitute a telescopic second antenna element which can be extended and retracted as the second antenna element (the antenna portion B).

[0043] Further, a feeding fixture 178 having a flange portion 178a is fixed via threads to a casing 134 of a radio apparatus. As shown in Figs. 16 and 17, the feeding fixture 178 is formed with a through hole 178c into which the end fixture 172 can be fitted and further with a plurality of slits 178a extending from the base side opposite to the flange portion 178a so as to provide an elasticity in the radial direction thereof. Further, the feeding fixture 178 is covered with a band spring 180 formed with a cutout portion as shown in Figs. 18 and 19 so as to band the slits 178a. Therefore, the feeding fixture 178 is urged elastically in the direction that the diameter of the feeding fixture 178 can be reduced.

[0044] Further, the outer diameter of the conductive cylindrical portion 114a of the first sleeve 114 is roughly the same as the outer diameter of the end fixture 172 to which the feeding fixture 178 is fitted. Further, the outer diameter of the conductive cylindrical portion 114a of the first sleeve 114 is determined to be slightly smaller than that of the large-diameter pipe 162. Therefore, the first sleeve 114 can be passed through the feeding fixture 178 with a play.

[0045] In the modification as described above, when the antenna is extended as shown in Fig. 12, the end fixture 172 is fitted to the feeding fixture 178 for electrical contact, and the large-diameter pipe 162 and the small-diameter rod body 164 function as a single rod antenna of the second antenna element.

[0046] When the antenna is retracted, the first sleeve 114 is fitted into the feeding fixture 178 for electrical contact, and further the first antenna element 110 functions as an antenna. Under these conditions, since the small-diameter rod body 164 can be inserted into the large-diameter pipe 162 as the second antenna element, it is possible to shorten the length of the second antenna element in the retracted direction.

[0047] A second modification of the second embodiment of the present invention is further described hereinbelow with reference to Fig. 20. This second modification is different from the first modification shown in Fig. 12 in the extension and retraction structure of the second antenna element.

[0048] In the same way as with the case of the first modification shown in Fig. 12, a second sleeve 190 formed of conductive metal is formed with a small-diameter conductive cylindrical portion 190a at the top end thereof; one end of a straight rod-shaped conductor body 116 is fixed to this cylindrical portion 190a; and a base end of the large-diameter conductive cylindrical portion 114a of the first sleeve 114 is caulked at an annular recessed portion 190b formed in the outer circumferential surface thereof to fix the first and second sleeves 114 and 190 with respect to each other. However, the second sleeve 190 is formed with a hollow portion 190e extending from the end surface thereof. Further, a conductive fixture 194 is fixed to the top end side of the small-diameter conductive rod body 192 by pressure fitting or caulking. The fixture 194 fixed to the conductive rod body 192 is inserted into the hollow portion 190e of the second sleeve 190, and thereafter the base end side of the second sleeve 190 is caulked to fix the fixture 194 to the second sleeve 190.

[0049] The base end of the small-diameter rod body 192 is inserted into an intermediate holder 196, and a slide spring 166 is fixed to the insertion side of the intermediate holder 196. The intermediate portion of the small-diameter rod body 192 is covered with an insulating tube 176. On the other hand, a stop ring 100 is fixed to the top end portion of a spring pipe 198. This stop ring 100 is pressure fitted to the base end of the intermediate holder 196. The base end of this spring pipe 198 is inserted into and fixed to the end fixture 172. Further, the intermediate portion of the spring pipe 198 is covered with an elastic resin large-diameter tube 102. Here, the spring pipe 198 is formed by closely winding an elastic and conductive plate-shaped wire into a coil shape. The small-diameter rod body 192 is telescopic within the spring pipe 198. When extended, since the slide spring 166 is brought into elastic contact with the inner wall of the intermediate holder 196, the small-diameter rod body 192 is brought into electric contact with the intermediate holder 196 and further with the spring pipe 198. The small-diameter rod body 192 and the spring pipe 198 constitute the telescopic second antenna element. Further, the outer diameter of the intermediate holder 196 is determined to be slightly smaller than that of the conductive cylindrical portion 114a of the first sleeve 114 so as to be passed through the feeding fixture 178 with a play.

[0050] In the structure as described above, when the antenna is extended as shown in Fig. 20, the small-diameter rod body 192 and the spring pipe 198 (of the second antenna element) functions as a single rod antenna. Further, in this second modification, since the spring pipe 198 can be deformed elastically when a push force is applied to the radial direction of the antenna, the antenna is not damaged easily.

[0051] A third embodiment of the present invention will be described hereinbelow with reference to Figs. 21 to 23. The first antenna portion A of this third embodiment is the same in structure as that of the other embodiments shown in Figs. 5 to 20, the same reference numerals have been retained for similar parts or elements which have the same functions as in the afore-mentioned embodiments, without repeating the detailed description thereof.

[0052] As shown in Figs. 21 to 23, a coil-shaped inductance member 216 is inserted from below (in Fig. 21) into a conductive cylindrical portion 114a of a metal sleeve 114 and fixed to the metallic sleeve 114 by soldering 118 at the top side thereof for electrical connection. A bobbin 112 is formed with a recessed portion 112a at the base end surface thereof for soldering 118. The coil-shaped inductance member 216 is formed by wire coated with an insulating material. An insulating resin pipe 224 is inserted into the conductive cylindrical portion 114a so as to cover the outer circumference of the inductance member 216, so that the coil portion of the inductance member 216 can be insulated from the conductive cylindrical portion 114a securely. The base end of the inductance member 216 is inserted into a through hole formed in a fixture 226 and fixed to a second antenna element 222 by soldering 228 for electrical connection. A rod-shaped second antenna element 222 is covered with an insulating resin sleeve 244. The top end of the insulating sleeve 244 projects from the top end of the second antenna element 222. The projected portion of the insulating sleeve 244 is formed with a female thread portion 244a in the inner circumference thereof, to which a male thread portion 226a formed at the outer circumference of the fixture 226 is engaged. The fixture 226 is inserted into the insulating pipe 224 until the base end portion of the fixture 226 is brought into contact with the top end of the second antenna element 222. Further, the insulating sleeve 244 is formed with a male thread portion 244b at the outer circumference thereof at the base end thereof. On the other hand, the conductive cylindrical portion 114a is formed with a female thread portion 114c in the inner circumference thereof at the base end portion thereof. When the male thread portion 244b of the insulating sleeve 244 is engaged with the female thread portion 114c of the metallic sleeve 114, the conductive cylindrical portion 114a and the insulating sleeve 244 are coaxially overlapped and connected to each other. In the case where an appropriate adhesive agent is applied to these thread portions 244ba and 114c, it is possible to more firmly connect and fix both the conductive cylindrical portion 114a and the insulating sleeve 244.

[0053] As shown in Fig. 21, the base end of the second antenna element 222 is passed through a though hole formed in a conductive end fixture 230 and fixed to the end surface of the end fixture 230 by soldering 232 for electrical connection. The end fixture 230 is formed with a large-diameter portion 230a at the base end thereof and with a hollow portion extending from the insertion side of the second antenna element 222. This hollow portion is formed with a female thread portion 230b near the bottom end thereof. Further, the insulating sleeve 244 is formed with a male thread portion 244c at the base end thereof. The end fixture 230 is fixed to the insulation sleeve 244 by engaging the male thread portion 244c of the insulating sleeve 244 with the female thread portion 230b of the end fixture 230.

[0054] A feeding fixture 236 formed with a flange portion 236a is fixed to the casing 234 of the radio apparatus via threads. Within the inner circumference of the feeding fixture 236, a roughly cylindrical conductive inner spring 238 is disposed in such a way not to be removed in the axial direction of the feeding fixture 236. The spring 238 serves to elastically support the end fixture 230 passed through the feeding fixture 236 so that the end fixture 230 can be connected to the feeding fixture 236 electrically. For prevention of removal of the cylindrical conductive inner spring 238 from the feeding fixture 236, the feeding fixture 236 is formed with a small-diameter inner hollow portion at the flange portion 236a thereof, for instance. After the inner spring 238 has been inserted into this inner hollow portion, the base end portion of the feeding fixture 236 is caulked for prevention of the removal of the conductive inner spring 238 from the base end of the feeding fixture 236.

[0055] In the same way as shown in Figs. 8 and 9, the inner spring 238 is formed with a plurality of slits so as to be elastically deformable in the radial direction thereof. Therefore, the inner spring 138 is interposed elastically between the outer circumferential surface of the end fixture 230 and the inner circumferential surface of the feeding fixture 236. Further, the outer diameter of the conductive cylindrical portion 114a of the metallic sleeve 114 is roughly the same as the outer diameter of the end fixture 230 at which the inner spring 238 is provided. Therefore, when the antenna is retracted, the conductive cylindrical portion 114a of the metallic sleeve 114 is inserted into the inner spring 238 in elastic contact therewith. Further, a feeding spring 240 is fixed to the inner surface of the casing 234 so as to be brought into elastic contact with the feeding fixture 236. This feeding spring 240 is connected to a feeding wire 242 connected to the radio circuit 36 through a matching circuit 34.

[0056] Here, under the condition that the antenna is extended from the casing 234 as shown in Fig. 21, since the end fixture 230 is inserted into the inner spring 238 disposed within the feeding fixture 236, the base end of the second antenna element 222 becomes a feeding point. Here, since the end fixture 230 is formed with the large-diameter portion 230a, it is possible to prevent the second antenna element 222 from being removed in the extension direction of the antenna. Further, as shown in Fig. 22, under the condition that the antenna is retracted into the casing 234, since the conductive cylindrical portion 114a of the metallic sleeve 114 is inserted into the inner spring 238 disposed within the feeding fixture 236, the base end of the metallic sleeve 114, that is, the first antenna element 110 becomes the feeding point. When the antenna is retracted, although the first antenna element 110 projects outside form the casing 234, since the first antenna element 110 is of coil shape, the length of the projected portion is relatively short.

[0057] In the same way as with the case of the other embodiments, in this embodiment, the effective length of the first antenna element 110 is set to 1/2 or 1/4 of a wavelength of a carrier for transmitting a call signal so as to resonate with the carrier resonant frequency band (f₁). On the other hand, the effective length of the second antenna element 222 is set to 1/2 or 1/4 of the wavelength of a carrier for transmitting a communication signal so as to resonate with the carrier resonant frequency band (f₂), which is slightly higher than that of the carrier resonance frequency band (f₁). A parallel resonance trap circuit is formed by an inductance component of the inductance member 216, a capacitance component formed between the conductive cylindrical portion 114a and the inductance member 216, a capacitance component formed between the conductive cylindrical portion 114a and the fixture 226, and a capacitance component formed between the conductive cylindrical portion 114a and the second antenna element 222 (which are all connected in parallel to each other). Further, the resonance frequency of this trap circuit is roughly determined to an intermediate frequency between the carrier resonance frequency bands of the first antenna element 110 and the second antenna element 222. Further, in the same way as with the case of the other embodiments, since the resonance frequency bands of the first antenna element 110 and the second antenna element 222 are both determined to be relatively wide, the resonance frequency band of the trap circuit can be set relatively wide. Therefore, there exists no problem when the central resonance frequency of the trap circuit is slightly offset from the resonance frequency bands of the first and second antenna elements 110 and 222.

[0058] In the construction as described above, when the antenna is extended during the communications as shown in Fig. 21, since the second antenna element 222 is separated from the first antenna element 110 by the trap circuit from the standpoint of antenna function, only the second antenna element 222 functions as an antenna with a carrier resonance frequency band f₂. Further, the output impedance of the second antenna element 222 is connected to the feeding fixture 236 as the output impedance of the antenna.

[0059] On the other hand, when the antenna is retracted during the standby of call signal reception, since the second antenna element 222 is separated from the first antenna element 110 from the standpoint of antenna function, only the first antenna element 110 functions as an antenna with a carrier resonance frequency band f₁. Further, the output impedance of the first antenna element 110 is connected to the feeding fixture 236 as the output impedance of the antenna.

[0060] Here, in this third embodiment, since the output impedance of the first antenna element 110 is determined to be the same as that of the second antenna element 222, it is possible to obtain the same output impedance in both the antenna extension and retraction states, so that the matching with the antennal can be attained by use of a single simple matching circuit and further a high antenna gain can be obtained as a radio antenna.

[0061] Further, when the antenna is required to be extended, the cap 120 is raised. Here, a tension is applied from the cap 120 to the insulation sleeve 244 via the metallic sleeve 114 and the conductive cylindrical portion 114a. In this case, however, since the conductive cylindrical portion 114a and the insulating sleeve 244 are both engaged with each other via threads over a predetermined length, it is possible to obtain a high tension strength. Further, when the engaged portions are fixed with an adhesive agent, since both antenna elements are not loosed, a more firm structure can be obtained.

[0062] Further, since the inductance and capacitance components of the trap circuit can be adjusted by changing the inductance member 216 and the fixture 226, it is possible to adjust the resonance frequency of the trap circuit. That is, any one or both of the inductance member 126 and the fixture 226 are modified according to the antenna characteristics to be required, without changing the other conductive cylindrical elements. Accordingly, it is possible to use many antenna composing parts in common for the antennas of various characteristics.

[0063] Further, in the above-mentioned embodiment, although the inductance member 216 is of coil shape, without being thereto, a straight inductance member can be used when the inductance thereof is small. Further, it is also possible to use a telescopic second antenna element 222.

[0064] In this third embodiment, since the conductive cylindrical member is engaged with the insulating sleeve for covering the second antenna element via threads, when the thread length is determined to be an appropriate value, any desired large tension strength required when the antenna is extended can be obtained. In other words, it is possible to provide a practical sufficiently large extending force to the antenna.

Claims

1. A radio antenna attached to a casing of a radio apparatus, comprising:
   a first antenna element;
   a second antenna element;
   feeding means for selectively connecting said first and second antenna elements to a radio apparatus circuit; and
   a trap circuit connected between said first and second antenna elements.

2. The radio antenna of claim 1, wherein said first antenna element has a resonance frequency for a call signal reception, and said second antenna element has a resonance frequency for a communication signal.

3. The radio antenna of claim 1, wherein said trap circuit has a resonance frequency intermediate between the resonance frequency of said first antenna element and the resonance frequency of said first antenna element.

4. The radio antenna of claim 1, wherein said second antenna element is telescopically supported by the casing of the radio apparatus and connected to said first antenna element via said trap circuit at a top end thereof; and when said second antenna element is retracted, said feeding means is connected to said first antenna element and when said second antenna element is extended, said feeding means is connected to said second antenna element.

5. The radio antenna of claim 4, wherein an output impedance of said first antenna element to said feeding means obtained when said second antenna element is retracted is determined to be substantially equal to an output impedance of said second antenna element to said feeding means obtained when said second antenna element is extended.

6. The radio antenna of claim 1, wherein said first antenna element is a coil-shaped antenna, and said second antenna is a rod-shaped antenna.

7. The radio antenna of claim 6, wherein the rod-shaped antenna of said second antenna element is a telescopic antenna.

8. The radio antenna of claim 1, wherein said trap circuit is a parallel resonance circuit composed of capacitance means and inductance means.

9. The radio antenna of claim 8, wherein said capacitance means includes a first conductive cylindrical body coaxially connected to said first antenna element and a second conductive cylindrical body coaxially connected to said second antenna and coaxially disposed radially outward away from the first conductive cylindrical body; and said inductance means includes a coil connected between said first and second antenna elements.

10. The radio antenna of claim 9, wherein the coil is positioned within the first and second conductive cylindrical bodies, and further fixedly supported integral with the first and second conductive cylindrical bodies by use of an insulating material.

11. The radio antenna of claim 10, wherein said first antenna element is a coil-shaped antenna covered with a cap-shaped antenna top.

12. The radio antenna of claim 1, wherein said first antenna element is a coil-shaped antenna wound around and supported by a bobbin and further covered with a cap.

13. The radio antenna of claim 8, wherein said capacitance means includes a first conductive cylindrical body coaxially connected to said first antenna element and a second conductive cylindrical body coaxially connected to said second antenna element and coaxially disposed radially outward away from the first conductive cylindrical body; and said inductance means includes a straight rod-shaped conductor connected between said first and second antenna elements.

14. The radio antenna of claim 13, wherein said second antenna element is a rod-shaped antenna, and the straight rod-shaped conductor has an extension formed integral with said second antenna element.

15. The radio antenna of claim 13, wherein the first and second conductive cylindrical bodies are fitted to each other with a dielectric insulating cylinder interposed therebetween, and further fixed to each other by caulking one of the cylindrical bodies to the other thereof.

16. The radio antenna of claim 12, wherein a base end surface of the bobbin is supported by a top end surface of a conductive sleeve, and the bobbin is held between a top end of the cap and the top end surface of the conductive sleeve by screwing a female thread portion formed in a base-end inner circumferential surface of the cap with a male thread portion formed in an outer circumferential surface of the sleeve.

17. The radio antenna of claim 13, wherein said second antenna element includes a straight pipe portion at a top end thereof, and the straight rod-shaped conductor is connected integral with a member electrically fixed to an inner top end of the pipe-shaped portion of said second antenna element.

18. The radio antenna of claim 13, wherein said second antenna element includes a straight rod-shaped portion at a top end thereof, and the straight rod-shaped portion is inserted into and fixed to an base end of the second conductive cylindrical body.

19. The radio antenna of claim 8, wherein said capacitance means includes a conductive cylindrical body coaxially connected to said first antenna element, an inductance member coaxially connected between said first and second antenna elements and inserted inside the conductive cylindrical body, and insulating means interposed between the conductive cylindrical body and the inductance member; and said inductance means includes the inductance member.

20. The radio antenna of claim 19, wherein said capacitance means includes the conductive cylindrical body, a fixture disposed within the conductive cylindrical body for connecting said second antenna element and the inductance member, and the insulating means interposed between the conductive cylindrical body and the fixture.

21. The ratio antenna of claim 4, wherein said feeding means includes a feeding member mounted on the casing of the ratio apparatus, and said first and second antenna elements include a conductive member brought into electric contact with the feeding member at the base end portion thereof, respectively.

Drawing