AU640787B2

AU640787B2 - Antenna for portable radio equipment

Info

Publication number: AU640787B2
Application number: AU78041/91A
Authority: AU
Inventors: Hiroyuki Iwasaki
Original assignee: NEC Corp
Current assignee: NEC Corp
Priority date: 1990-05-29
Filing date: 1991-05-29
Publication date: 1993-09-02
Anticipated expiration: 2011-05-29
Also published as: AU7804191A; EP0459391A2; CA2043321C; EP0459391B1; EP0459391A3; CA2043321A1; JPH0432305A; DE69124714T2; DE69124714D1

Description

84878$ S F Ref: 182297

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

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S5 4 5, Actual Inventor(s): Address for Service: Invention Title: NEC Corporation 7-1, Shiba Minato-ku Tokyo

JAPAN

Hiroyuki Iwasaki Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Antenna for Portable Radio Equipment The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5845/3 ANTENNA FOR PORTABLE RADIO EQUIPMENT BACKGROUND OF THE INVENTION The present invention relates to an antenna applicable to various kinds of mobile radio equipment, particularly portable radio equir-nent.

It is a common practice to provide portable radio equipment with a whip antenna whose wavelength is one half of the wavelength of the carrier or center frequency particular to the equipment, i.e. X/2.

Such a X12 long whip antenna ensures a relatively high gain of the order of 0 dBd (dipole ratio) in the horizontal plane and causes a minimum of decrease in gain even when the equipment is brought closer to the human body. Such an antenna, however, lacks portability since its element is as long as X/2. To eliminate this problem, portable radio equipment capable of receiving the X/2 antenna in the casing thereof has been proposed in the past. This, however, brings about 15 another problem that the X/2 antenna practically fails to function properly when within the casing. In light of this, portable radio equipment may be provided with a built-in antenna in addition to the whip X/2 antenna, as also proposed in the past. The built-in antenna will be substituted for the X/2 antenna when the latter is received 9 in the casing of the equipment. Nevertheless, the problem with this kind of scheme is that not only the equipment is complicated in construction, but also the built-in antenna increases the overall size of the equipment.

9 *ow *o~ BFD/282K -2- SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an antenna for portable radio equipment which is free from the drawbacks particular to the conventional X/2 antenna as discussed above.

It is a preferred object of the present invention to provide an antenna for portable radio equipment which has a telescopic body section to selectively serve as either one of a X/2 long antenna and a less than X/4 long antenna.

It is another preferred object of the present invention to provide an antenna for portable radio equipment which radiates power effectively in the horizontal plane at all times and ensures a relatively high gain of the order of 0 dBd.

It is yet another preferred object of the present invention to provide an antenna for portable radio equipment which has a single 15 matching circuit capable of matching both a X/2 long antenna and a less than X/4 long antenna with respect to impedance.

In accordance with the present invention, there is disclosed an antenna comprising: a telescoping body section which is X/2 long (X being the 20 wavelength of a carrier frequency used) to serve as a X/2 long antenna when the telescopic body section of said antenna is extended, or less than X/4 long to serve as a less than X/4, long antenna when said body section is retracted; 0 a matching means for coupling the telescoping body section to reception or transmission equipment both whGn extended and retracted, the matching means providing that said antenna has substantially the same impedance when extended as when retracted.

BFD/282K The invention further discloses an antenna comprising: a telescopic body section having a length which is approximately one half of the wavelength of a carrier frequency used when said body section is extended and is less than one-fourth of said wavelength of said carrier frequency when said body section is retracted; and an impedance matching circuit connected to one end of said body section and for coupling the antenna reception of transmission equipment both when extended and retracted, the matching circuit providing that the impedance of the antenna when the body section is extended or retracted substantially matches the impedance of said equipment.

BRIEF DESCRIPTION OF THE DRAWINGS An embodiment of the invention will now be described with reference to the accompanying drawings: 15 Figs. 1A and 1B are views showing an antenna embodying the present invention in an extended position and a retracted position, f' respectively; Fig. 2 is a perspective view of portable radio equipment implemented with the illustrative embodiment; Seo .4.

fte 9* *t ft BFD/282K -4- Fig. 3 plots return loss characteristics particular to the rekrore extended and w ete-positions of the embodiment; Fig. 4 is a circuit diagram showing a specific construction of a matching section included in the embodiment; Figs. 5A and 5B are charts showing respectively the directivity characteristics in the horizontal plane particular to the re- rrco -+e extended position and the -at d position of the embodimenti and Fig. 6 shows a curve representative of a directivity 10 characteristic in the horizontal plane particular to a conventional r ekroc+ek S-ecQ/ 4 wav.elength long helical whip antenna.

aee DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Figs. 1A and 1B of the drawing, an antenna S 15 embodying the present invention is shown and generally designated by the reference numeral 10. As shown, the antenna 10 has a telescopic conductive tube assembly 12 which resembles a rod and constitutes a body section. A matching section 14 is connected to one end or base end of the tube assembly 12. The 20 tube assembly 12 is made up of a plurality of (three in the embodiment) telescoped tubes 12a, 12b and 12c each having a particular diameter. The tube 12c having the largest diameter is connected to the matching section 14. A feed section 16 incorporated in the body of portable radio equipment is also connected to the matching section 14. In the extended position shown in Fig. 1A, the antenna 10 has a length which is approximately one half of the wavelength A of the carrier or center frequency of the equipment, it serves as a A/2 antenna. In the .ana- ,ep tposition, the length of the antenna 10 is less than 1/4 of the wavelength A, and therefore the antenna 10 plays the role of, for example, a A/8 antenna.

When the antenna 10 is extended to serve as a A/2 antenna, the matching section 14 matches the antenna 10 and the body of respe e the equipment with .eto impedance. When the antenna 10 is 10 en-trt-edo play the role of, for example, a A/8 antenna, the 0 matching section 14 also matches the impedance of the antenna *0 and that of the equipment body. Stated another way, the 0* A/2 and A/8 antennas are implemented by the single matching section 14. Specifically, in the extended or )A/2 position shown S 15 in Fig. 1A, the antenna 10 has a high impedance close to infinity (oo) As the telescopic tube assembly 12 is sequentially 0. contracted from the position shown in Fig. 1A to a particular length, substantially the same impedance as that of the A/2 antenna is obtained. Such a length corresponds to a 20 substantially A/8 wavelength. The matching section 14, *o therefore, can set up impedance matching for both of the A/2 and A/8 antennas. This allows the power from the feed section 16 to be efficiently radiated via the antenna Fig. 2 shows portable radio equipment 20 having a casing 22 on which the antenna 10 is mounted. In the illustrative

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-6embodiment, the antenna 10 is approximately 0. 17 meter long re-rarcee6 when extended or 0. 045 meter long when GO4te-a.eted. Fig. 3 plots return loss characteristics particular to the extended and reAcrc~-c*e eentr.aeted positions of the antenna 10. In Fig. 3, the abscissa and the ordinate indicate respectively the carrier frequency and the return loss, while the solid curve and the dashed curve indicate respectively the return loss in the extended position and re^-rocAe&c the return loss in the -eontracted position. As the curves indicate, the return loss change substantially in the same manner 10 in both of the extended and entact-ee positions with respect to i" frequency, i. e. impedances are successfully matched in both of the extended and -Ie-tr-aeted Lositions.

Referring to Fig. 4, a specific construction of the matching section 14 will be described. As shown, the matching section 14 has a so-called L circuit configuration constituted by a coil L and o a capacitor C. Looking into the antenna 10 from a point X, the impedance is extremely high, as stated earlier. In light of this, the impedance matching between the antenna 10 and the feed section 16 is set up by the coil or inductance element L and the 20 capacitor or reactance element C which are interposed between the feed point Y of the feed section 16 and the point X. The characteristic impedance Zo at the feed point Y is 50 ohms. It is to be noted that the capacitor C is omissible if, looking into the feed point Y from the point X, the impedance is higher than the characteristic impedance Zo.

Figs. 5A and 5B show directivity characteristics in the horizontal plane particular to the antenna 10 as measured in the extended or X/2 position and the retracted or X/8 position, respectively. In these figures, the solid curves each are representative of the directivity characteristic of the main polarization. It will be seen that in both of the /2 position shown in Fig. 5A and the position shown in Fig. 5B the antenna 10 has substantially the same directivity characteristic approximate to 0 dBd in the +X and -X directions. Further, the directivity characteristic of the antenna 10 in the retracted position is comparable even with the directivity characteristic particular to a retracted helical whip antenna in the +X and -X directions, as shown in Fig. 6.

Regarding the parameters used to determine the directivity characteristics shown in Figs. 5A and 5B, the carrier frequency f 0 15 was 870 megahertz, the telescopic tube assembly 12 was approximately 170 millimeters long when extended or approximately 45 millimeters long when retracted, and the tubes 12c and 12a had diameters of 6 millimeter and 2 millimeter, respectively.

In summary, it will be seen that the present invention provides 20 an antenna for portable radio equipment which serves as a /2 long "antenna when extended or as a less than X/4 long antenna, a X/8 antenna, when retracted. Both of such antenna configurations have their impedances matched by a single matching circuit. The antenna radiates power efficiently the horizontal plane.

4 BFD/28LK

Claims

2. An antenna as claimed in claim 1, wherein said body section is substantially long when retracted, serving as a X/8 antenna.
3. An antenna comprising: a telescopic body section having a length which is approximately one half of the wavelength of a carrier frequency used when said body section is extended and is less than one-fourth of said wavelength of said carrier frequency when said body section is retracted; and an impedance matching circuit connected to one end of said body :section and for coupling the antenna reception of transmission u equipment both when extended and retracted, the matching circuit providing that the impedance of the antenna when the body section is extended or retracted substantially matches the impedance of said equipment.
4. An antenna as claimed in claim 3, wherein said body section comprises a conductive tube assembly made up of a plurality of telescoped conductive tubes. An antenna as claimed in claim 4, wherein said plurality of conductive tubes each has a particular diameter.
6. An antenna as claimed in claim 4, wherein said conductive tube assembly is approximately 0.17 meter long when extended or approximately 0.045 meter long when retracted.
7. An antenna as claimed in claim is approximately X/18 wavelength long when
8. An antenna as claimed in claim has substantially the same impedance when 3, wherein said body section retracted. 7, wherein said body section extended and when retracted. DATED this TWENTY-NINTH day of JUNE 1993 NEC Corporation, Patent Attorneys for the Applicant SPRUSON FERGUSON *1*S S S S S S *5 S. 55 S S 5.5. 5. 5 S S *5*5 5*S5 S 55 S S S BFD/282K Abstract of the Disclosure Antenna for Portable Radio Equipment An antenna (10) for portable radio equipment (20) serves as a X/2 wavelength long antenna when extended (Fig. IA) or as a less than X/4 wavelength long antenna such as a X/8 wavelength long antenna when contracted (Fig. 1B). Both of such antenna configurations are matched by a single matching circuit (14) with respect to impedance. The antenna (10) radiates power efficiently in the horizontal plane. bO 0g U 044 (Figs. IA, 1B) eah:4620D