Retractable antenna assembly for a portable radio device

An antenna assembly according to the present invention has a rod antenna movable between a retracted position and an extended position, a helical antenna having a plurality of helical portions which are electrically separated from one another. The rod antenna extends through the inside of the helical antenna when the rod antenna is in the extended position and the rod antenna is removed from the inside of the helical antenna when the rod antenna is in the retracted position. The antenna assembly also includes connecting metal piece for electrically connecting the plurality of helical portions when the rod antenna is in the retracted position so that the plurality of helical portions become operable as a single helical antenna.

BACKGROUND OF THE INVENTION 
This invention relates to an antenna assembly, and more particularly to an 
antenna assembly suitable for use in a compact portable radio apparatus 
such as a cellular phone. 
In recent years, portable radio apparatuses have been reduced in size and 
weight. Accordingly, antenna assemblies used for such portable radio 
apparatuses are also required to be smaller. As an antenna assembly which 
satisfies the above requirements, many manufacturers are developing whip 
antennas which can be retracted into the housing body when the apparatus 
is not used for communications. The whip antenna is pulled out of the 
housing to be extending therefrom when the apparatus is used for 
communications. Portable radio apparatuses in an early stage have utilized 
this type of whip antenna which is relatively simple. 
Such a whip antenna, when extending from the housing body, is operative as 
a monopole antenna. However, when the antenna is in a retracted position 
in the housing body, it cannot obtain a sufficient gain because the 
antenna retracted in the housing body is placed near the ground so that it 
causes an input impedance to increase, whereby impedance matching can be 
hardly established. 
Thus, to improve the gain of the antenna when retracted in the housing 
body, a whip antenna of a so-called top loading type came into use instead 
of the simple whip antenna described above. The top loading type whip 
antenna comprises a helical antenna electrically connected to the top end 
of a rod antenna. When this type of whip antenna extends from the housing 
body for use, radio waves can be radiated from both of the helical antenna 
and the rod antenna. When the antenna is retracted into the housing body, 
radio waves can be radiated from the helical antenna. 
However, this type of whip antenna includes the rod antenna which does not 
contribute to the radiation of radio waves when it is retracted. This 
portion operates as an open stub. The open stub affects input impedance of 
the antenna. Especially, the open stub causes disturbance of delicate 
impedance matching, depending upon the distance between the rod antenna 
and circuit boards in the housing. Besides, if a shield is not complete, 
signals are undesirably input through the rod antenna in a retracted 
position and signals go into the inside of the shield. 
Because of these problems of the whip antenna, another type of antenna 
assembly has been developed, in which a rod antenna, when retracted into 
the housing body, is electrically isolated from a helical antenna. An 
example of such an antenna assembly will be described with reference to 
FIGS. 1A to 2B. 
FIGS. 1A and 1B show an example of a conventional retractable antenna 
assembly in an extended position and in a retracted position, 
respectively. As shown in FIGS. 1A and 1B, a retractable antenna assembly 
has a fixed antenna part including helical antenna 201 and a movable 
antenna part including rod antenna 301. The fixed antenna part comprises 
helical antenna 201, first metal fitting 202 having a first snap-in recess 
inside thereof for the extended position, second metal fitting 203 for 
fixing helical antenna 201 onto first metal fixing 202, and antenna cover 
205 for covering helical antenna 201 and preventing a human body from 
touching helical antenna 201. Antenna cover 205 has second snap-in recess 
204 for the retracted position. 
The movable antenna part comprises rod antenna 301 which is a monopole 
antenna, antenna cover 302 for covering rod antenna 301 and preventing a 
human body from touching rod antenna 301, and metal stopper 303 attached 
to the lower end of rod antenna 301. Metal stopper 303 has a first snap-in 
protrusion which engages the first snap-in recess of metal fitting 202 
when the antenna assembly is in the extended position as shown in FIG. 1A. 
Knob 304 for retracting and extending the movable antenna part is provided 
at the upper end of antenna cover 302. Knob 304 is also effective in 
preventing the movable antenna part from falling into housing 101. Second 
snap-in protrusion 305 is also provided right below knob 304 of antenna 
cover 302 to engage second snap-in recess 204 when the antenna assembly is 
in the retracted position as shown in FIG. 1B. 
The antenna assembly is mounted on housing 101 of a mobile radio unit by 
screwing metal fitting 202 into metal fitting 102 which has been attached 
to housing 101. After the antenna assembly is so mounted on housing 101, 
helical antenna 201 is always powered from power supply circuit 104 
through antenna clip 103 for electrical connection between a signal line 
extending from power supply circuit 104 and metal fitting 102, and metal 
fittings 202 and 203. On the other hand, rod antenna 301 is powered only 
when the antenna assembly is in the extended position where metal stopper 
303 contacts metal fittings 202 and 102. The power supply to rod antenna 
301 in the extended position is made from power supply circuit 104 through 
antenna clip 103, metal fitting 102, metal fitting 202 and metal stopper 
303. 
When the antenna assembly is in the extended position as shown in FIG. 1A, 
rod antenna 301 extends through the inside of helical antenna 201. Not 
only helical antenna 201 but also rod antenna 301 are powered through 
metal stopper 303 which contacts metal fittings 102 and 202. In this 
state, rod antenna 301 mainly operates as a monopole antenna which has its 
ground level at the ground of a shielding case inside housing 101 of the 
mobile radio unit and the ground of circuit board 105. Although helical 
antenna 201 is also powered, it is operable as an accessory of rod antenna 
301. 
When the antenna assembly is in the retracted position as shown in FIG. 1B, 
rod antenna 301 has no electrical connection with metal fittings 102 and 
202. In addition, there is provided a certain space between the upper 
portion of rod antenna 301 and the lower portion of helical antenna 201 
including metal fittings 102 and 202 in order to avoid the 
electromagnetical coupling between helical antenna 201 and rod antenna 
301. Therefore, rod antenna 301 has no effect on the antenna performance 
in the retracted position. Therefore, helical antenna 201 operates as a 
single helical antenna which has its ground level at the ground of the 
shielding case inside housing 101 of the mobile radio unit and the ground 
of circuit board 105. 
FIGS. 2A and 2B show another example of a conventional retractable antenna 
assembly in an extended position and in a retracted position, 
respectively. A basic structure of this antenna assembly is similar to 
that of the antenna assembly shown in FIGS. 1A and 1B. 
In the retracted position as shown in FIG. 2B, rod antenna 301 has no 
electrical connection with metal fittings 102 and 202. In addition, there 
is provided a certain space between the upper portion of rod antenna 301 
and the lower portion of helical antenna 201 including metal fittings 102 
and 202 in order to avoid the electromagnetical coupling between helical 
antenna 201 and rod antenna 301. Rod antenna 301 has no effect on the 
antenna performance in the retracted position. Therefore, helical antenna 
201 operates as a single helical antenna which has its ground level at the 
ground of the shielding case inside housing 101 of the mobile radio unit 
and the ground of circuit board 105. A principle of the above operation in 
the retracted position is exactly same as that of the antenna assembly 
shown in FIGS. 1A and 1B. 
The only difference between the antenna assembly shown in FIGS. 1A and 1B 
and the antenna assembly shown in FIGS. 2A and 2B is a stopper attached to 
the lower end of rod antenna 301. Unlike metal stopper 301 as shown in 
FIGS. 1A and 1B, insulator stopper 307 is used in the antenna assembly 
shown in FIGS. 2A and 2B. In the extended position, even though insulator 
stopper 307 contacts metal fittings 102 and 202, there is no electrical 
connection between helical antenna 201 and rod antenna 301 because 
insulator stopper 307 exists therebetween. Nevertheless, rod antenna 301 
is powered by electromagnetical coupling between helical antenna 201 and 
rod antenna 301. As a result, in the extended position, rod antenna 301 
mainly operates as a monopole antenna which has its ground level at the 
ground of the shielding case inside housing 101 of the mobile radio unit 
and the ground of circuit board 105. Although helical antenna 201 is also 
powered, it is operable as an accessory of rod antenna 301. 
With this structure of retractable antenna assemblies shown in FIGS. 1A to 
2B, the helical antenna enables the mobile radio unit to receive an 
incoming call even in the retracted position, and by extending the rod 
antenna, the performance of the antenna is improved for actual 
communication. 
In these retractable antenna assemblies, antenna lengths in extended and 
retracted positions are designed based on a wavelength of the required 
frequency band (1.9 GHz, for example). More specifically, the length of 
the helical antenna is designed in light of the requirement for the 
antenna length in the retracted position and the length of the rod antenna 
is designed in light of the requirement for the antenna length in the 
extended position. The rod antenna and the helical antenna which have been 
so designed are supposed to achieve the best antenna performance in the 
required frequency band. 
However, there is another factor to be considered in designing the antenna 
lengths. At such a high frequency as 1.9 GHz, undesirable resonance owing 
to the electromagnetic coupling between the rod antenna (monopole antenna) 
and helical antenna is likely to occur in the extended position where the 
rod antenna extends through the inside of the helical antenna. In some 
cases, this undesirable resonance may be produced around a frequency close 
to the required frequency band so that it degrades the performance of the 
monopole antenna. 
In order to move the undesirable resonance away from the required frequency 
band, the helical antenna parameters such as length, pitch and turn number 
could be modified. However, this kind of modification of the helical 
antenna to avoid the undesirable resonance would necessarily change the 
helical antenna condition which has been optimized to the best performance 
in the retracted position. With such a modification to avoid the 
undesirable resonance, the performance of the helical antenna in retracted 
position can no longer be the best. On the other hand, without such a 
modification, the undesirable resonance would degrade the antenna 
performance in the extended position. In other words, the requirement to 
optimize the helical antenna performance in the retracted position 
sometimes conflicts with the requirement to avoid the undesirable 
resonance produced in the extended position. 
SUMMARY OF THE INVENTION 
Accordingly, it is one object of the present invention to provide an 
antenna assembly having a rod antenna (monopole antenna) and a helical 
antenna which are optimized to the desirable performance, both in extended 
and retracted positions. The antenna assembly also has an improved 
flexibility in designing each antenna. 
In accordance with the present invention, there is provided an antenna 
assembly having a rod antenna movable between a retracted position and an 
extended position, a helical antenna having a plurality of helical 
portions which are electrically separated from one another. The rod 
antenna extends through the inside of the helical antenna when the rod 
antenna is in the extended position and the rod antenna is removed from 
the inside of the helical antenna when the rod antenna is in the retracted 
position. The antenna assembly further includes connecting metal piece for 
electrically connecting the plurality of helical portions when the rod 
antenna is in the retracted position so that the plurality of helical 
portions become operable as a single helical antenna.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 3A and 3B show a first preferred embodiment of an antenna assembly 
according to the present invention. FIGS. 3A and 3B show such an antenna 
assembly in an extended position and a retracted position, respectively. 
For assembly components similar to those in the conventional antenna 
assembly shown in FIGS. 1A to 2B, the same reference numerals are put and 
a detail explanation thereof will be omitted. 
As shown in FIGS. 3A and 3B, the antenna assembly has a fixed antenna part 
including a helical antenna and a movable antenna part including a rod 
antenna. Similar to the conventional antenna assembly, the movable antenna 
part of the antenna assembly shown in FIGS. 3A and 3B comprises rod 
antenna 301 which is a monopole antenna, antenna cover 302 for covering 
rod antenna 301 and preventing a human body from touching rod antenna 301, 
and metal stopper 303 attached to the lower end of rod antenna 301. Knob 
304 for retracting and extending the movable antenna part is provided at 
the upper end of antenna cover 302. Knob 304 is also effective in 
preventing the movable antenna part from falling into housing 101. Second 
snap-in protrusion 305 is provided right below knob 304 of antenna cover 
302 to engage second snap-in recess 204 when the antenna assembly is in 
the retracted position as shown in FIG. 3B. In addition, the movable 
antenna part has metal fitting 306 formed on antenna cover 302. The 
function of metal fitting 306 will be explained later. 
Unlike the conventional antenna assembly, the antenna assembly shown in 
FIGS. 3A and 3B has a helical antenna which is divided into first helical 
antenna 400 and second helical antenna 401. The lower end of first helical 
antenna 400 is attached to metal fitting 202 by metal fitting 203. 
Therefore, first helical antenna 400 is always electrically powered by 
power supply circuit 104 through antenna clip 103 and metal fittings 203, 
202, 102. On the upper end of first helical antenna 400, first electrode 
206 is attached by metal fitting 207. Similarly, second electrode 402 is 
attached onto the lower end of second helical antenna 401 by metal fitting 
403. 
When the antenna assembly is in the extended position as shown in FIG. 3A, 
rod antenna 301 extends through the inside of first and second helical 
antennas 400 and 401. In this extended position, first electrode 206 and 
second electrode 402 are physically separated so that there is no 
electrical connection between them. Therefore, second helical antenna 401 
is not electrically connected to first helical antenna 402. Accordingly, 
even though first helical antenna portion is always powered by power 
supply circuit 104, second helical antenna 401 is not powered when the 
antenna assembly is in the extended position. Rod antenna 301 is also 
powered through metal stopper 303 which contacts metal fittings 102 and 
202. In this state, rod antenna 301 mainly operates as a monopole antenna 
which has its ground level at the ground of a shielding case inside 
housing 101 of the mobile radio unit and the ground of circuit board 105. 
Although first helical antenna 400 is also powered, it is operable as an 
accessory of rod antenna 301. 
When the antenna assembly is in the retracted position as shown in FIG. 3B, 
metal fitting 306 fits in between first electrode 206 and second electrode 
402 so that metal fitting 306 electrically connects the two electrodes. 
Therefore, first helical antenna 400 and second helical antenna 401 are 
now electrically connected. In this state, first helical antenna 400 and 
second helical antenna 401 are operable as a single helical antenna which 
has its ground level at the ground of the shielding case inside housing 
101 of the mobile radio unit and the ground of circuit board 105. 
As explained above, when the antenna assembly is in the extended position 
as shown in FIG. 3A, there is no electrical connection between first 
helical antenna 400 and second helical antenna 401. Rod antenna 301 and 
first helical antenna 400 only are powered in the extended position while 
second helical antenna 401 is not powered. Therefore, the undesirable 
resonance in the extended position is produced by the coupling between 
first helical antenna 400 and rod antenna 301. Second helical antenna 401 
has little effect on the undesirable resonance. Therefore, by designing 
the antenna parameter of first helical antenna 401, the undesirable 
resonance frequency can be moved away from the required frequency band 
such as 1.9 Ghz. At the same time, by designing second helical antenna 
401, the total performance of the helical antenna including the first and 
second helical antennas can be also optimized. 
For the simplification of the explanation, let us assume that a helical 
antenna having 10 turns produces the best performance in the retracted 
position. Further suppose that this helical antenna having 10 turns 
produces undesirable resonance within the required frequency band in the 
extended position. If the turn number of the helical antenna need to be 
changed to move the undesirable resonance frequency out of the required 
frequency, that change also affects the antenna performance in the 
retracted position. This is because the helical antenna is made of 
one-piece. 
However, in the antenna assembly in accordance with the present invention, 
as shown in FIGS. 3A and 3B, a helical antenna is divided into two helical 
antennas 400 and 401. The two helical antennas are electrically connected 
and operate as a single helical antenna in the retracted position. As long 
as the total number of the turns of the two helical antennas remain 
unchanged, the antenna performance in the retracted position can be 
maintained. 
At the same time, by changing the combination of the turns of the two 
helical antennas such as (5,5), (6,4), (7,3) and so on, the frequency of 
the undesirable resonance can be controlled. By dividing a helical antenna 
into two helical antennas which are electrically separated in the extended 
position but electrically connected in the retracted position, flexibility 
in designing the antenna parameters is increased so that the best antenna 
performance can be achieved both in the extended position and retracted 
position. The impedance characteristics in extended position can be also 
adjusted without changing the impedance characteristics in retracted 
position. 
Although a helical antenna is divided into two helical antennas in this 
particular embodiment, it can be divided into more helical antennas. 
FIGS. 4A and 4B show another preferred embodiment of an antenna assembly in 
accordance with the present invention. FIGS. 4A and 4B show such an 
antenna assembly in an extended position and in a retracted position, 
respectively. Similar to the antenna assembly shown in FIGS. 3A and 3B, a 
helical antenna is divided into first helical antenna 400 and second 
helical antenna 401. First helical antenna 400 and second helical antenna 
401 are electrically separated in the extended position, but electrically 
connected in the retracted position. The difference between the antenna 
assembly shown in FIGS. 3A and 3B and the antenna assembly shown in FIGS. 
4A and 4B is a stopper attached to the lower end of rod antenna 301. 
Unlike metal stopper 301 as shown in FIGS. 3A and 3B, insulator stopper 
307 is used in the antenna assembly shown in FIGS. 4A and 4B. 
In the extended position where insulator stopper 307 contacts metal 
fittings 102 and 202, there is no electrical connection between first 
helical antenna 400 and rod antenna 301 because insulator stopper 307 
exists therebetween. Nevertheless, rod antenna 301 is powered by 
electromagnetical coupling between first helical antenna 400 and rod 
antenna 301. As a result, in the extended position, rod antenna 301 mainly 
operates as a monopole antenna which has its ground level at the ground of 
the shielding case inside housing 101 of the mobile radio unit and the 
ground of circuit board 105. Although first helical antenna 400 is also 
powered, it is operable as an accessory of rod antenna 301. 
Since a helical antenna is divided into first helical antenna 400 and 
second helical antenna 401 which are electrically separated in the 
extended position, but electrically connected in the retracted position, 
optimization of the helical antenna in the retracted position and avoiding 
the undesirable resonance within the required frequency band can be 
achieved simultaneously. 
FIGS. 5A and 5B show a third preferred embodiment of an antenna assembly in 
accordance with the present invention. FIGS. 5A and 5B show such an 
antenna assembly in an extended position and in a retracted position, 
respectively. Similar to the antenna assembly shown in FIGS. 3A and 3B, a 
helical antenna is divided into first helical antenna 400 and second 
helical antenna 401. First helical antenna 400 and second helical antenna 
401 are electrically separated in the extended position, but electrically 
connected in the retracted position. 
As shown in Figs.5A and 5B, there is provided third electrode 404 in 
addition to first electrode 206 and second electrode 402. Third electrode 
404 is attached on the upper end of second helical antenna 401 by metal 
fitting 405. Rod antenna 301 has protruding portions 308 and 308 which are 
exposed to the surface of antenna cover 302. Even though protruding 
portions 308 and 308 are not covered by antenna cover 302, they cannot be 
touched by the human body because they are always inside antenna cover 205 
or housing 101. In the extended position, as shown in FIG. 5A, second 
helical antenna 401 is shorted by protruding portions 308 and 308 formed 
on rod antenna 301. Therefore, undesirable radiation by second antenna 401 
can be suppressed. 
FIGS. 6A and 6B show a fourth preferred embodiment of an antenna assembly 
in accordance with the present invention. FIGS. 6A and 6B show such an 
antenna assembly in an extended position and in a retracted position, 
respectively. Similar to the antenna assembly shown in FIGS. 5A and 5B, a 
helical antenna is divided into first helical antenna 400 and second 
helical antenna 401. Third electrode 404 is also attached on the upper end 
of second helical antenna 401 by metal fitting 405. Rod antenna 301 has 
protruding portions 308 and 308 which are exposed to the surface of 
antenna cover 302. With this structure, second helical antenna 401 is 
shorted by protruding portions 308 and 308 when the antenna assembly is in 
the extended position. Therefore, undesirable radiation by second antenna 
401 can be suppressed. 
The difference between the antenna assembly shown in FIGS. 5A and 5B and 
the antenna assembly shown in FIGS. 6A and 6B is a stopper attached to the 
lower end of rod antenna 301. Unlike metal stopper 301 as shown in FIGS. 
5A and 5B, insulator stopper 307 is used in the antenna assembly shown in 
FIGS. 4A and 4B. 
In the extended position where insulator stopper 307 contacts metal 
fittings 102 and 202, there is no electrical connection between first 
helical antenna 400 and rod antenna 301 because insulator stopper 307 
exists therebetween. Nevertheless, rod antenna 301 is powered by 
electromagnetical coupling between first helical antenna 400 and rod 
antenna 301. As a result, in the extended position, rod antenna 301 mainly 
operates as a monopole antenna which has its ground level at the ground of 
the shielding case inside housing 101 of the mobile radio unit and the 
ground of circuit board 105. Although first helical antenna 400 is also 
powered, it is operable as an accessory of rod antenna 301. 
In the fourth embodiment of the antenna assembly shown in FIGS. 6A and 6B, 
since a helical antenna is divided into first helical antenna 400 and 
second helical antenna 401 which are electrically separated in the 
extended position but electrically connected in the retracted position, 
optimization of the helical antenna in the retracted position and avoiding 
the undesirable resonance within the required frequency band can be 
achieved simultaneously. 
Furthermore, since second helical antenna 401 is shorted by protruding 
portions 308 and 308 in the extended position, undesirable radiation by 
second antenna 401 can be suppressed. 
Though an antenna assembly in accordance with the present invention has 
been explained with four specific embodiments, it is to be understood that 
numerous changes and modifications may be made by those skilled in the art 
without departing from the scope of the present invention.