Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
-1- 2C93~2 1
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 equipment.
5It is a common practice to provide portable radio equipment
with a whip antenna whose wavelength is one half of the
wavelength A of the carrier or center frequency particular to the
equipment, i. e., A/2. Such a A/2 wavelength long whip
antenna insures a relatively high gain of the order of 0 dBd
10(dipole ratio~ in the hori~ontal 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 A/2 wavelength. To eliminate this
problem, portable radio equipment capable of receiving the A/2
15antenna in the casing thereof has been proposed in the past.
This, however, brings about another problem that the A/ 2
antenna practically fails to play the role of an antenna when
received in the casing. In light of this, portable radio equipment
may be provided with a built-in antenna in addition to the A/2
20 antenna, as also proposed in the past. The built-in antenna will
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be substituted for the A/2 antenna when the latter is received 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.
SUMMARY OF THE IN~rENTION
It is therefore an obiect of the present invention to provide an
antenna for portable radio equipment which is free from the
drawbacks particular to the conventional A/2 antenna as
discussed above.
It is another obiect of the present invention to provide an
antenna for portable radio equipment which has a telescopic body
section to selectively serves as either one of a A/ 2 wavelength
long antenna and a less than A/4 wavelength long antenna.
It is another 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 insures a
relatively high gain of the order of 0 dBd.
It is another object of the present invention to provide an
antenna for portable radio equipment which has a single matching
circuit capable of matching both a A/ 2 wavelength long antenna
and a less than A/4 wavelength long antenna with respect to
impedance.
In accordance with the present invention, an antenna is A/2
~ 6 s~'3 3 ~/
wavelength long (~ being the wavelength of a carrier frequency
used) to serve as a ~/2 wavelength long antenna when a
telescoplc body sectlon thereof is expanded or is less than
~/4 wavelength long to serve as a less than ~/4 wavelength
long antenna when the body section ls contracted. The antenna
has substantially the same lmpedance when extended and when
contracted.
Also, ln accordance wlth the present lnvention, an
antenna comprises a telescoplc body sectlon havlng a
wavelength which is approximately one half of the wavelength
of a carrier frequency used when the body sectlon is extended
or ls less than one-fourth of the wavelength of the carrier
frequency when the body section ls contracted, and a matchlng
circult connected to one end of the body section, sald antenna
having substantlally the same impedance when said body section
is extended and when retracted.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other ob~ects, features and advantages
of the present invention will become more apparent from the
following detailed description taken with the accompanying
drawings in whlch:
Flgs. lA and lB are vlews showlng an antenna
embodylng the present lnventlon ln an extended posltlon and a
contracted position, respectively;
Fig. 2 is a perspective view of portable radio
equipment lmplemented with the illustratlve embodlment;
Flg. 3 plots return loss characterlstlcs particular
to the extended and contracted positions of the embodlment;
-- 3
. ~
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Fig. 4 ls a clrcult dlagram showlng a speclflc
constructlon of a matchlng section included in the embodlment;
Flgs. 5A and 5B are charts showlng respectlvely the
directlvlty characteristlcs ln the horizontal plane partlcular
to the extended posltlon and the contracted posltlon of the
embodlment; and
Fig. 6 shows a curve representative of a dlrectlvity
characteristlc in the horizontal plane partlcular to a
conventional contracted ~/4 wavelength long helical whip
antenna.
DESCRIPTION OF THE ~ ~ EMBODIMENT
Referring to Figs. lA and lB of the drawing, an
antenna embodylng the present inventlon 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 matchlng
section 14 ls connected to one end or base end of the tube
assembly 12. The tube assembly 12 ls made up of a plurallty
of (three ln the embodiment) telescoped tubes 12a, 12b and 12c
each havlng a particular dlameter dlfferent from the other
tubes. The tube 12c havlng the largest dlameter ls connected
to the matchlng section 14. A feed sectlon 16 lncorporated ln
the body of portable radlo equlpment ls also connected to the
matching sectlon 14. In the extended posltion
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2 4 3
shown in Fig. 1 A, the antenna 10 has a length which is
approximately one half of the wavelength A of the carrier or
center frequency of the equipment, i. e., it serves as a A/2
antenna. In the contracted position, the length of the antenna
5 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
the equipment with repect to impedance. When the antenna 10 is
10 contracted to play the role of, for example, a A/8 antenna, the
matching section 14 also matches the impedance of the antenna
10 and that of the equipment body. Stated another way, the
A/2 and A/8 antennas are implemented by the single matching
section 14. Specifically, in the extended or A/2 position shown
15 in Fig. lA, the antenna 10 has a high impedance close to infinity
(oo~. As the telescopic tube assembly 12 iS sequentially
contracted from the position shown in Fig. 1 A 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,
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 10.
Fig. 2 shows portable radio equipment 20 having a casing 22
2 5 on which the antenna 10 is mounted. In the illustrative
~ ~ ~3 3~/
,
embodiment the antenna 10 ls approxlmately 0.17 meter long
when extended or 0.045 meter long when contracted. Fig. 3
plots return loss characterlstlcs partlcular to the extended
and contracted posltions of the antenna 10. In Fig. 3, the
abscissa and the ordinate lndlcate respectlvely the carrler
frequency and the return loss, whlle the solld curve and the
dashed curve lndlcate respectlvely the return loss ln the
extended positlon and the return loss ln the contracted
positlon. As the curves lndlcate, the return loss changes
substantially ln the same manner ln both the extended and
contracted posltlons wlth respect to frequency, l.e.,
impedances are successfully matched in both of the extended
and contracted posltlons.
Referrlng to Fig. 4, a speclflc construction of the
matchlng sectlon 14 wlll be descrlbed. As shown, the matchlng
sectlon 14 has a so-called L circult conflguratlon constituted
by a coll L and a capacltor C. Looklng lnto the antenna 10
from a polnt X, the lmpedance ls extremely hlgh, as stated
earller. In llght of this, the impedance matching between the
antenna 10 and the feed sectlon 16 ls set up by the coll or
lnductance element L and the capacltor or reactance element C
which are lnterposed between the feed polnt Y of the feed
sectlon 16 and the polnt X. The characterlstlc lmpedance ZO
at the feed polnt ~ ls 50 ohms. It ls to be noted that the
capacltor C ls omlsslble lf, looklng lnto the feed polnt Y
from the polnt X, the lmpedance ls hlgher than the
characterlstlc lmpedance ZO.
Flgs. 5A and 5B show dlrectlvlty characterlstlcs ln
-- 6
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~ 3~/
the horlzontal plane partlcular to the antenna 10 as measured
ln the extended or ~/2 posltlon and the contracted or ~/8
posltlon, respectlvely. In each of these flgures, solld
curves are representatlve of the dlrectlvlty characterlstlc of
the maln polarlzatlon. It wlll be seen that ln both of the
~2 wavelength posltion shown ln Flg. 5A and the ~/8
wavelength positlon shown ln Flg. 5B the antenna 10 has
substantlally the same dlrectlvlty characterlstlc approxlmate
to 0 dBd ln the +X and -X dlrectlons. Further, the
dlrectlvlty characteristic of the antenna 10 in the contracted
posltlon is comparable even with the dlrectlvlty
characterlstlc partlcular to a contracted ~/4 hellcal whlp
antenna ln the +X and -X directions, as shown in Flg. 6.
Regarding the parameters used to determine the
dlrectlvlty characterlstlcs shown in Flgs. 5A and 5B, the
carrler frequency fO was 870 megahertz, the telescoplc tube
assembly 12 was approxlmately 170 mllllmeters long when
extended or approxlmately 45 mllllmeters long when contracted,
and the tubes 12c and 12a had dlameters of 6 mllllmeter and 2
mllllmeter, respectlvely.
In summary, it wlll be seen that the present
lnventlon provldes an antenna for portable radio equlpment
whlch serves as a ~/2 wavelength long antenna when extended
or as a less than ~/4 wavelength long antenna, e.g., a ~/8
antenna when contracted. Both of such antenna conflguratlons
have thelr
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~1~43~21
impedances matched by a single matching circuit. The antenna
radiates power efficiently in the horizontal plane.
Various modifications will become possible for those skilled
in the art after recei~ing the teachings of the present disclosure
5 without departing from the scope thereof.
