U.S. patent number 3,720,874 [Application Number 05/196,433] was granted by the patent office on 1973-03-13 for dipole antenna arrangement for radio with separate speaker-microphone assembly.
This patent grant is currently assigned to Motorola, Inc.. Invention is credited to John W. Faltz, Stanley W. Gorcik, Charles T. Hilton, Jr., Richard A. Kamysz.
United States Patent |
3,720,874 |
Gorcik , et al. |
March 13, 1973 |
DIPOLE ANTENNA ARRANGEMENT FOR RADIO WITH SEPARATE
SPEAKER-MICROPHONE ASSEMBLY
Abstract
A speaker microphone assembly, used with a portable radio unit
containing receiving and transmitting equipment for receiving and
transmitting radio signals, includes a housing with a helical
antenna element mounted to the top wall to form one element of a
dipole antenna. A coaxial cable having inner and outer conductors
is connected from the portable unit equipment to the speaker
microphone housing. The center conductor is connected to the
helical antenna and the outer conductor is terminated in the
housing at a first point which is ground potential. A second outer
conductor surrounds and is insulated from the first outer
conductor, and is connected to the first outer conductor at the
first point. The second outer conductor extends for a predetermined
length along the first outer conductor to form the other element of
the dipole antenna.
Inventors: |
Gorcik; Stanley W. (Des
Plaines, IL), Kamysz; Richard A. (Roselle, IL), Hilton,
Jr.; Charles T. (Fort Lauderdale, FL), Faltz; John W.
(Fort Lauderdale, FL) |
Assignee: |
Motorola, Inc. (Franklin Park,
IL)
|
Family
ID: |
22725401 |
Appl.
No.: |
05/196,433 |
Filed: |
November 8, 1971 |
Current U.S.
Class: |
455/90.3;
343/841; 455/347; 455/575.7 |
Current CPC
Class: |
H04B
1/385 (20130101) |
Current International
Class: |
H04B
1/38 (20060101); H04b 001/04 () |
Field of
Search: |
;325/16,111,112,118,119,178,361,365 ;343/841 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Safourek; Benedict V.
Claims
We claim:
1. In a speaker microphone assembly adapted to be held in the hand
and for use with a portable radio unit including receiving and
transmitting equipment for receiving and transmitting signals, the
combination of, a housing having top, bottom and side walls, an
elongated antenna element secured to said top wall, said antenna
element forming one half of a dipole antenna for radiating signals
coupled from said transmitting equipment and coupling radiated
signals to said receiving equipment, a cable for coupling the
portable unit to said housing, said cable containing a coaxial
transmission line having an inner conductor and an outer conductor,
said outer conductor terminating at a first point in said housing,
circuit means coupling said inner conductor to said antenna
element, a second outer conductor surrounding said coaxial
transmission line and extending for a predetermined length from
said first point along said transmission line, said second outer
conductor being connected to said outer conductor of said
transmission line at said first point and both conductors forming
the other half of said dipole antenna.
2. The assembly of claim 1 wherein said dipole antenna is resonant
at a particular frequency, said antenna element and said other half
of said dipole antenna each having an electrical length
substantially equal to a quarter wavelength at the resonant
frequency of said dipole antenna.
3. The assembly of claim 2 wherein said antenna element includes a
conductive element having first and second ends, and mounting means
secured to one of said ends and adapted to engage said circuit
means in said assembly.
4. The assembly of claim 3 wherein said conductive element is
formed into a helix for providing a quarter wavelength helical
antenna element.
5. The assembly of claim 4 wherein said antenna element includes a
tube of nonconductive material surrounding said helical element,
said nonconductive material acting to insulate said helical element
and maintain the same in a semi-rigid condition.
6. The assembly of claim 4 wherein said circuit means is a
connector, said connector being secured to a wall of said housing
and having said center conductor coupled thereto, said connector
adapted to mate with said antenna element mounting means for
mounting said antenna element to said assembly housing.
7. The assembly of claim 6 wherein said cable further includes
insulating means surrounding said outer conductor of said coaxial
transmission line and between said outer conductor and said second
conductor, said insulating means providing an insulated separation
therebetween.
8. The assembly of claim 7 wherein said portable unit includes a
power source having first and second terminals, one of said
terminals forming a reference potential, said reference potential
being coupled to said transmission line outer conductor.
9. The assembly of claim 8 further including speaker means,
microphone means and unit actuating means mounted in said assembly
housing, conductor means coupling said speaker means, microphone
means and actuating means to the portable unit for providing
electrical connections therebetween, said speaker means including a
speaker frame, said speaker means, said speaker frame and said
microphone means being coupled to said first point to provide a
reference potential thereat.
10. The assembly of claim 9 wherein said outer conductor of said
transmission line and said second outer conductor are formed from
braided wire conductors.
11. The assembly of claim 9 wherein said second outer conductor is
a conductive material secured to said housing walls and coupled to
said first point, said housing further including an aperture in
said bottom wall, said cable extending through said aperture and
said conductive material being isolated from said aperture.
12. The assembly of claim 11 wherein said conductive material is a
conductive paint applied to said housing inner walls and having a
predetermined thickness.
13. The assembly of claim 12 wherein said conductive paint is a
silver conductive paint.
14. The assembly of claim 13 wherein said predetermined thickness
is at least 1 mil.
15. A speaker microphone assembly for use with a portable radio
unit including receiving and transmitting equipment for receiving
and transmitting signals, said portable radio unit having a power
source therein with one terminal thereof being a reference
potential, said speaker microphone assembly including in
combination, a housing having top, bottom and side walls adapted to
be held in a user's hand, said bottom wall having an aperture
therethrough, transducer means mounted in said assembly housing, a
helical antenna element detachably secured to said housing, said
antenna element forming one portion of a dipole antenna for
radiating signals coupled from said transmitting equipment and
coupling radiated signals to said receiving equipment, a connector
secured to said housing for detachably securing said helical
antenna element, a cable for coupling the portable unit to said
housing, said cable containing a plurality of conductors coupling
said equipment to said transducer means for providing electrical
connections therebetween, and a coaxial transmission line having an
inner conductor and an outer conductor, said inner and outer
conductor of said coaxial transmission line being connected to said
connector, said inner conductor coupling said helical antenna
element to said equipment, said outer conductor forming a low
impedance point at said connector, said housing further including a
conductive material applied to said housing inner walls and
connected to said low impedance point, said conductive material
being isolated from said aperture in said bottom wall and forming a
second outer conductor for surrounding said coaxial transmission
line, said transmission line outer conductor and said second outer
conductor together forming the other portion of said dipole
antenna.
16. A speaker microphone assembly of claim 15 wherein said dipole
antenna is resonant at a particular frequency, said antenna element
having an electrical length substantially equal to a quarter
wavelength at the resonant frequency of said antenna.
Description
BACKGROUND
Speaker microphone assemblies currently employed, such as that
described in U.S. Pat. No. 3,370,236, issued to R. H. Walker, and
assigned to the same assignee, include an antenna element mounted
thereon for radiating the transmitted radio signals and receiving
radiated signals. Such assemblies have been used to advantage for a
number of years. However, the antenna configuration does not result
in a fully satisfactory radiation pattern because the assembly
itself does not provide a substantial ground plane for the antenna
element. Furthermore, the assembly does not isolate the antenna
element from the portable radio unit thus allowing the radiated
signals to affect the operation of the radio unit.
Although a speaker microphone assembly as described in the above
patent is designed to be held in the hand, doing so can cause a
degradation in antenna efficiency due to the presence of the body
capacitance of the user.
Antenna elements used with assemblies such as that described above
have a lower input impedance than the equipment with which they are
associated. In order to match the equipment to the antenna element,
carefully selected discrete matching components must be added to
the assembly. The component selection and placement is critical,
and the added component and labor costs will increase the unit
cost.
SUMMARY
It is an object of this invention to provide a speaker microphone
assembly for a radio unit including an antenna mounted thereon for
radiating and receiving signals, wherein the antenna configuration
provides an improved radiation pattern.
Another object of this invention is to provide a speaker microphone
assembly having an antenna element thereon, which has structure
providing a substantial effective ground plane for the antenna
element.
Yet another object of this invention is to provide a speaker
microphone assembly for a radio unit which has structure providing
substantial isolation between the antenna element and the radio
unit.
Still another object of this invention is to provide a speaker
microphone assembly having an antenna mounted thereon wherein the
antenna performance and efficiency is not substantially degraded
due to the presence of the body capacitance of the user.
Another object of this invention is to provide a speaker microphone
assembly with an antenna mounted thereon which does not require
discrete components for matching the antenna element to the radio
equipment.
In practicing this invention, a speaker microphone assembly is
provided for use with a portable unit containing receiving and
transmitting equipment for receiving and transmitting signals,
wherein the assembly is adapted to be held in the user's hand. The
assembly includes a housing having top, bottom and side walls, with
transducer elements and equipment actuating switches mounted
therein. Conductors couple the transducer elements and switches to
the radio equipment. A helical antenna element is detachably
mounted to the top wall of the housing and acts as one portion of a
dipole antenna for radiating and receiving signals. A coaxial
transmission line having outer and inner conductors couples the
equipment to the speaker microphone assembly. The outer conductor
is terminated at a first point in the assembly housing which is the
antenna feed point. The inner conductor is connected to the
connector which detachably mounts the antenna element. A second
outer conductor surrounds and is insulated from the outer conductor
of the coaxial transmission line and is connected to the
transmission line outer conductor at the first point in the
housing. This outer conductor extends for a predetermined length
along the coaxial transmission line. The coaxial transmission line
outer conductor and the second outer conductor act to form the
second portion of the dipole antenna. As the housing is located at
the low impedance point or feed point of the dipole, it has a
minimal effect upon the dipole antenna performance.
In an alternate embodiment, the housing walls are coated with a
conductive material which is connected to the first point and acts
to form the second portion of the dipole antenna.
THE DRAWINGS
FIG. 1 is a view of a speaker microphone assembly with an antenna
element mounted thereon connected to the portable radio unit with
which the assembly is used.
FIG. 2 is a view of the cable connecting the portable radio unit
and the speaker microphone assembly.
FIG. 3 is a view with the cover open taken all along the lines
1--1, illustrating the speaker microphone assembly, dipole antenna
and mounting arrangement.
FIG. 4 is a view with the cover open of a second embodiment of the
speaker microphone assembly, dipole antenna and mounting
arrangement.
DETAILED DESCRIPTION
Referring to FIG. 1, there is shown a portable radio unit 10 which
contains an FM radio transmitter and receiver, and a battery for
operating the transmitter and receiver. One terminal of the battery
(not shown) provides a reference or ground potential. A speaker
microphone assembly 11 is connected to the portable radio unit via
a connector 12. Radiated radio frequency signals are received by an
antenna including antenna element 22 on assembly 11 and coupled to
the receiver in portable unit 10 where they are demodulated to
produce audio signals. The audio signals are coupled from the
receiver in unit 10 through connector 12 to assembly 11 where they
are reproduced by speaker 46, shown in FIG. 3, enabling the user to
hear the message. Audio messages to be transmitted are received at
assembly 11 where they are converted to electrical signals by
microphone 45, shown in FIG. 3. The electrical signals are coupled
through connector 12 to the transmitter in radio unit 10 for
modulating a radio frequency carrier signal. The modulated radio
frequency carrier signal is coupled from the transmitter in unit 10
through connector 12 to speaker microphone assembly 11 where it is
radiated by the antenna including element 22.
Speaker microphone assembly 11 includes a housing 15 which has a
top wall 16, a bottom wall 17 and side walls 18. One of the side
walls 18 has a grillework 19 thereon for allowing audio to be
conducted therethrough from speaker 46 to microphone 45. The side
wall opposite grillework 19 (not shown) may be a removable cover
which is secured to the assembly with screws at 20. A helical
antenna element 22 is detachably secured to housing 15. Antenna
element 22 includes a threaded rod 23 which mates with a connector
25, mounted to top wall 16 of housing 15. A cable 27 extends
through bottom wall 17 of housing 15 and is connected to connector
12 for providing an electrical connection between speaker
microphone assembly 11 and portable radio unit 10.
Portable radio unit 10 is adapted to be carried on the person in a
location such as on the user's belt. Housing 15 is adapted to be
held in the user's hand while he is using portable unit 10 for
communicating with a remote point. It may also be supported on the
user's belt or shirt by an attachment to the removable cover such
as is shown in patent No. 3,370,236.
Referring to FIG. 2, there is shown a portion of cable 27 speaker
microphone assembly 11. Cable 27 includes a coaxial transmission
line consisting of a center conductor 29, a dielectric insulating
material 30, a braided shield or outer conductor 31, and an outer
insulation 32. Surrounding the coaxial transmission line and
extending for a predetermined length therealong, is a second
braided shield or second outer conductor 34. Second outer conductor
34 will be explained in greater detail in a subsequent portion of
this application. Conductors 36, 37 and 38 are also provided in
cable 27 for interconnecting the components located in housing 15
with the equipment in portable radio unit 10. An outer insulating
cover 39, formed of a plastic material, encases conductors 36, 37
and 38, second outer shield 34, and the coaxial transmission
line.
Referring to FIG. 3, antenna element 22 includes an antenna
radiating element 41, shown in the cutaway section of antenna
element 22. Radiating element 41 consists of a heavy gauge wire
conductor and is formed into a helix to provide a helical antenna.
The heavy gauge conductor provides effective signal reception and
transmission and allows antenna element 22 to be maintained in a
semi-rigid condition. An outer plastic jacket 42 surrounds
radiating element 41, and acts to insulate the element and assist
in maintaining antenna 22 in a semi-rigid condition. Threaded rod
23 is attached to one end of radiating element 41 and is shown
inserted into connector 25 in FIG. 3.
Helical antenna element 22 forms one portion of a dipole antenna
which is resonant at a particular frequency. A dipole antenna
provides an improved radiation pattern over monopole antennas which
have been employed. In the embodiment shown, the dipole antenna is
resonant at approximately 460 MHz. The physical length L.sub.1 of
helical antenna element 22 is selected such that its electrical
length is approximately a quarter wavelength at the resonant
frequency of the dipole antenna.
Housing 15 of speaker microphone assembly 11 has a microphone 45, a
speaker 46 and a switch 47 mounted therein. Speaker 46 includes a
frame 48 for supporting the speaker cone and mounting the
loudspeaker in the housing. Conductor 36 in cable 27 provides an
electrical connection between microphone 45 and the transmitter in
portable unit 10. Conductor 37 provides an electrical connection
between switch 47 and the transmitter in portable unit 10. Switch
47 when actuated by actuation lever 49, secured to a side wall of
housing 15, energizes the transmitter in portable unit 10.
Conductor 38 provides an electrical connection between the receiver
in portable unit 10 and speaker 46.
Cable 27 enters housing 15 through aperture 50 in bottom wall 17,
and is retained by cable clamp 51, secured to the inner surface of
housing 15. Center conductor 29 of the coaxial transmission line is
connected to connector 25 for providing an electrical
interconnection between the transmitter and receiver in portable
unit 10 and helical antenna element 22. Outer conductor 31 of the
coaxial transmission line in cable 27 is connected, through
connector 12, to ground potential in portable unit 10, and has its
other end terminated at a first point 53 in housing 15. This first
point is connected via conductor 54 to frame 48 of speaker 46, and
to microphone 45 and switch 47 for providing ground potentials
thereat. First point 53 is also connected to one terminal of
speaker 46 through RF choke 52 to provide a ground potential for
the speaker. Choke 52 acts to prevent RF energy from being coupled
to speaker 46.
The second outer conductor 34 extends from first point 53 to a
point 54 along cable 27 which is external to housing 15. Outer
conductor 31 of the coaxial transmission line, insulator 32, and
second outer conductor 34 form a transmission line which acts as
the second portion of the dipole antenna in assembly 11. This
second portion acts to form a substantial ground or reflecting
plane, which is necessary in order to provide the desired radiation
pattern for the dipole antenna. The physical length L.sub.2 of
second outer conductor 34 is selected such that the electrical
length of the transmission line formed by conductor 31, insulator
32 and conductor 34 is substantially equal to a quarter wavelength
at the resonant frequency of the dipole antenna.
Second outer conductor 34 is electrically connected to outer
conductor 31 at first point 53 to form a low impedance feed point
for the dipole antenna. The second end of second outer conductor
34, shown at 54 is terminated without connection to other elements
in cable 27 in order to provide an open circuit at that end of the
dipole. Second end 54 of second outer conductor 34, as it is open
circuited or unterminated, acts as a termination for the second
portion of the dipole antenna, preventing radiated energy from
being conducted along cable 27 towards portable unit 10. The open
circuit also prevents undesired radiated energy from being
conducted along cable 27 to the antenna from portable unit 10.
As feed point 53 is a low impedance feed point for the dipole
antenna, external capacitance, added at or near this point will not
substantially degrade the antenna performance. Housing 15 is
connected to the feed point of the antenna. A user, holding housing
15 of speaker microphone assembly 11 in his hand will then be
holding the dipole antenna, at or near the feed point 53. The
user's body capacitance will therefore have a minimal effect upon
the radiation characteristics of the dipole antenna. Components
such as microphone 45, switch 47, and speaker 46, particularly
speaker frame 48, because of its mass, can seriously impair antenna
radiation characteristics due to their presence in the near field
produced by the radiation. By connecting the speaker frame 48 to
ground potential at feed point 53, and the other components to this
point, their affects upon the radiation characteristics are
minimized.
Helical antenna element 22, due to its design, has a low input
impedance. Transmitters and receivers commonly used in portable
radio units, such as unit 10, have an output impedance of
approximately 50 ohms. The transmission line consisting of second
outer conductor 34, insulator 32 and outer conductor 31, in
addition to acting as the ground portion of the dipole antenna,
also provides an impedance match for matching the input impedance
of antenna element 22 to the output impedance of the radio
equipment. This is due to the electrical length of second conductor
34. By using the grounded portion of the dipole antenna as an
impedance matching device, discrete matching components, normally
required for matching a transmitter output of one impedance to a
radiating element of a different impedance, are no longer
required.
Referring to FIG. 4, antenna element 60 is the same as antenna
element 22 in FIG. 3, except that threaded rod 23 is replaced by an
RF connector 61. Housing 65 has a top wall 66, a bottom wall 67 and
side walls, just as housing 15 in FIG. 3. Helical antenna 60 is
detachably secured to housing 65 by RF connector 69 mounted to top
wall 66 of housing 65. Cable 70 extends through an aperture 71 in
bottom wall 67 of housing 65 and provides an electrical connection
between the speaker microphone assembly and a portable radio unit
such as portable radio unit 10.
Cable 70 includes a coaxial transmission line consisting of a
center conductor 73, a dielectric insulating material 74, a braided
shield or outer conductor 75 and an outer insulation 76. Conductors
77, 78 and 79 are also provided in cable 70 for interconnecting the
components located in housing 65 with the equipment in the portable
radio unit. A flexible metal tubing 80 commonly known as an armored
cable, encases conductors 77, 78 and 79 and the transmission line.
Armored cable 80 is used in order to prevent the speaker microphone
assembly from being broken away from the portable radio unit. A
plastic tubing 81 encases armored cable 80.
Housing 65 has mounted therein a microphone 82, a speaker 83, a
transmitter actuation switch 84, and a speaker high-low switch 85.
An actuation lever 86 is mounted to the side wall of housing 65,
adjacent transmitter actuation switch 84 for operating this switch.
Conductors 77, 78 and 79 provide electrical interconnections
between these components and the portable unit.
Cable 70 enters housing 65 through aperture 71 and is retained by
cable clamp 88 secured to the inner and outer surfaces of bottom
wall 67. Center conductor 73 of the coaxial transmission line is
connected to RF connector 69 for providing an electrical
interconnection between the transmitter and receiver in the
portable unit and helical antenna element 60. Outer conductor 75 of
the coaxial transmission line in cable 70 is connected through a
connector, such as connector 12 in FIG. 1, to ground potential in
the portable unit, and has its other end terminated at a first
point 89 in housing 65. The first point in this embodiment is the
outer shell of RF connector 69. This first point is connected via
conductor 90 to speaker magnet housing 93, via conductor 91 to
point 94 on the inner surface of housing 65, and via RF choke 92 to
one terminal of microphone 82 and speaker 83.
The inner surfaces of the walls of housing 65 are coated with a
conductive metal paint. In the embodiment shown, a conductive
silver paint is applied having a thickness of at least 1 mil. A
thickness of 1 to 3 mils insures that the painted conductive
surface acts as a good conductor over the frequency ranges in which
the portable unit operates. The 1 to 3 mil thickness coating will
allow efficient operation at frequencies up to and in excess of 470
MHz. At aperture 71 surrounding cable clamp 88 on the inner surface
of bottom wall 67, the conductive paint is not applied for reasons
to be explained in a subsequent portion of this application.
Housing 65, because of the conductive paint applied to the inner
surface of the walls, acts in the same manner as second outer
conductor 34 shown in FIG. 3. That is, as it surrounds the coaxial
transmission line and is itself conductive at the frequencies of
interest, the painted surface along with transmission line outer
conductor 75, forms a second transmission line which acts as the
second portion or grounded portion of the dipole antenna. Although
not physically as long as second outer conductor 34, the physical
dimensions of the housing in width, height and thickness, cause it
to be resonant at the approximate operating frequencies of
interest. The conductive inner surface of housing 65 is
electrically connected at first point 89 via RF connector 69, via
conductor 91, and the grounded metal portions of the components in
housing 65, to form a low impedance feed point for the dipole
antenna. Aperture 71 through which cable 70 passes, as previously
stated, is not provided with a conductive coating. This allows
aperture 71 to act in a manner equivalent to the second end of
second outer conductor 34 in FIG. 3. With no silver conductive
paint applied, aperture 71 acts to provide an open circuit at the
bottom surface of housing 65. This open circuit is a high impedance
and acts as a termination for the second portion of the dipole
antenna, preventing radiated energy from being conducted along
cable 70 to the antenna from portable unit 10.
As feed point 89 is a low impedance feed point for the dipole
antenna, and the housing is a part of this low impedance feed
point, external capacitance added at or near this point will not
substantially degrade the antenna performance. A user holding
housing 65 in his hand will then be holding the dipole antenna at
or near the feed point, and the user's body capacitance will
therefore have a minimal affect upon the radiation characteristics
of the dipole antenna. As all the components mounted within housing
65 are also connected to the feed point, their affects upon the
radiation characteristics are minimized.
Housing 65 also acts to match the impedance of antenna element 60
to the impedance of the transmitter and receiver in the portable
radio unit in the same manner as that previously described with
respect to second outer conductor 34 in FIG. 3.
As can be seen, a speaker microphone assembly has been provided
which includes a dipole antenna for radiating and transmitting
signals. The dipole antenna provides an improved radiation pattern
over antennas previously used. By providing a dipole antenna, the
reflecting plane constitutes a substantial ground plane for
improving the radiation pattern from the radiating element. With
the dipole antenna feed point mounted in the speaker microphone
assembly housing, body capacitance of the user will not
substantially affect or degrade the antenna efficiency.
Furthermore, a quarter wavelength coaxial transmission line or its
equivalent such as is provided by the housing in FIG. 4, when used
as the reflecting portion of the dipole also provides an impedance
match so that critical matching components are not required to
match the transmitting and receiving equipment to the antenna
radiating element. The quarter wavelength coaxial transmission line
or its equivalent such as is provided by the housing in FIG. 4,
also prevents unwanted RF energy from being conducted to or from
the portable unit.
* * * * *