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DUAL-BAND ANTENNA COUPLER FOR A
PORTABLE RADIOTELEPHONE
CROSS-REFERENCE TO RELATED
APPLICATION 5
The present application is a continuation-in-part of U.S. patent application Ser. No. 08/626,786 filed on Apr. 2,1996.
BACKGROUND OF THE INVENTION
1. Field of the Invention 10 The present invention relates generally to antenna couplers. More particularly, the present invention is directed to
a novel and improved antenna coupler for a portable radiotelephone. ^
2. Description of the Related Art
In the field of cellular communications, portable radiotelephones are used to communicate with base stations over radio-frequencies (RF). Typically, these portable radiotelephones operate at relatively low power levels in order to 2o conserve battery power and increase talk time. However, when there are alternate power means available, such as a vehicle battery when driving, or a conventional electrical outlet when indoors, the user of the portable radiotelephone often employs special adapters to take advantage of the 2s higher power supply available. For example, there are many vehicular adapters which transform the vehicle-generated electrical supply into a level suitable for use by the portable telephone, and also couple the RF signals to and from the portable radiotelephone for use with an external power 30 booster and antenna. Additionally, these adapters may include a "hands-free" kit including an auxiliary microphone and speaker. In this way, the user may take advantage of higher power transmission and hands-free conversation without sacrificing battery time, and yet still be able to carry 35 the same portable radiotelephone with him when he leaves his car.
In order to couple the RF signal to and from the portable radiotelephone, a typical vehicular adapter uses an inductive coupler placed close to the portable radiotelephone's 40 antenna. However, this technique may result in a significant amount of RF signal energy loss, particularly when an insufficient RF return path, or ground, is provided to the portable radiotelephone while it is in the adapter. Since a typical portable radiotelephone's internal components are 45 encased in an electromagnetic interference (EMI) shield to prevent stray electromagnetic energy leaking from the radiotelephone's casing, the prior art vehicular adapters have not been able to achieve a sufficient RF return path to the portable radiotelephone. 50
SUMMARY OF THE INVENTION
The present invention is embodied in an antenna coupling device used to adapt a portable radiotelephone capable of operation in two frequency bands. The antenna coupling 55 device comprises a ground plane having an upper surface with an antenna coupler mounted on the upper surface. The antenna coupler couples radio signals to and from the communication device antenna. The ground plane also includes at least one ground pin capable of contacting an 60 externally accessible ground point on the radio communication device. A matching circuit coupled to the antenna coupler generates a predetermined impedance to match the antenna coupler to the communication device antenna at each of the first and second frequency bands. 65
The ground plane may also include first and second abutting vertical portions mounted on the upper surface
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thereof. The first and second abutting vertical portions are positioned in a substantially orthogonal relation to each other and to the ground plane upper surface. In a first embodiment, a plurality of curved metal bands are positioned in proximity with the ground plane with a first of the curved bands being electrically isolated from the ground plane to couple radio signals to and from the communication device antenna when the communication device is operating in a first of the two frequency bands. A second of the curved bands is also electrically isolated from the ground plane to couple radio signals to and from the communication device antenna when the communication device is operating in a second of the two frequency bands. A third of the curved bands is electrically coupled to the ground plane. The matching circuit may comprise first and second matching circuit portions each having an input terminal to match the communication device antenna. The first matching circuit portion is used when the communication device is operating in the first frequency band and the second matching circuit portion is operational when the communication device is operating in the second frequency band. The input terminal of the first matching circuit portion is coupled to the first curved band while the second matching circuit portion input terminal is coupled to the second curved band.
In a second embodiment, a coupling pin makes direct contact with a radio frequency component of the communication device, such as the communication device antenna. In this embodiment, there is no need to couple the signal over the air using the curved bands. The output from the coupling pin may be connected to a single dual-band matching circuit designed to generate a predetermined impedance to match the antenna coupler to the communication device antenna at each of the first and second frequency bands. Alternatively, the coupling device may include a switch circuit coupled between the coupling pin and first and second matching circuit portions. The switch circuit couples the coupling pin to the first matching circuit portion for operation of the communication device in the first frequency band and couples the coupling pin to the second matching circuit portion for operation of the communication device in the second frequency band.
In yet a third embodiment, a helical coupler surrounds at least a portion of the communication device antenna and couples the radio frequency signals over the air.
The signals from the matching circuit or matching circuit portions may be optionally connected to a booster amplifier and connected to an external antenna.
BRIEF DESCRIPTION OF THE DRAWINGS
The features, objects, and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout and wherein:
FIG. 1A is an illustration of an exemplary portable radiotelephone suitable for use with the present invention;
FIG. IB is an illustration of a first embodiment antenna coupler of the present invention interfacing with an exemplary portable radiotelephone;
FIG. 2A is an illustration of one embodiment of the coupling elements of the present invention;
FIG. 2B is an illustration of an alternate embodiment of the coupling elements of the present invention;
FIG. 3A is an illustration of a second embodiment of the antenna coupler of the present invention interfacing with a
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direct connection to an exemplary portable radiotelephone antenna, shown in a partially cut-away view;
FIG. 3B is an illustration of a second embodiment of the coupling elements of the present invention interfacing with a direct connection to an internal component of an exem- 5 plary portable radiotelephone;
FIG. 4A is an illustration of a third embodiment antenna coupler of the present invention interfacing with an exemplary portable radiotelephone; and
FIG. 4B is an illustration of the helical coupler of the third embodiment of the present invention interfacing with an antenna of an exemplary portable radiotelephone;
FIG. 5A is an illustration of one embodiment of the dual-band coupling elements of the present invention; j5
FIG. 5B is an illustration of an alternative embodiment of the dual-band coupling elements of the present invention;
FIG. 6 is a functional block diagram of a dual-band matching circuit used with the antenna coupler of FIGS. 3A, 3B, 4A, and 4B; 20
FIG. 7 is an alternative embodiment of the dual-band matching circuit used with the antenna coupler of FIGS. 3A, 3B, 4A, and 4B.
DETAILED DESCRIPTION OF THE 25
PREFERRED EMBODIMENTS
Referring to FIG. IB, a first embodiment of the antenna coupler 100 of the present invention comprises ground plane 102, abutting vertical ground plane portions 104 and 106, 30 coupling elements 204a, 204fc, and 204c, ground pins 206a, and 206fc, and optional ground pin 206c. Coupling elements 204a, 204fc, and 204c are preferably constructed of vertically facing, curved bands of a conductive material, such as copper, steel, or the like. When portable radiotelephone 200 35 is interfaced with antenna coupler 100, coupling elements 204a, 204fc, and 204c receive retracted helix antenna 204 of portable radiotelephone 200 and couple RF signals to and from antenna 204. Coupling elements 204a, 204fc, and 204c are constructed and positioned in such a way that when 40 portable radiotelephone 200 is interfaced with antenna coupler 100, coupling elements 204a, 204fc, and 204c extend in a semi-circular array, each covering approximately onequarter of the circumference of antenna 204. It should be noted that antenna 204 may also be of a non-helical con- 45 struction as is known in the art, such as a rod or loop antenna. It should also be noted that portable radiotelephone 200 may generally be any type of mobile communication device, such as a cellular or PCS radiotelephone, or a wireless local loop communication device. 50
Coupling elements 204a, 204fc, and 204c are mounted at a respective coupler base to ground plane 102. In the preferred embodiment, ground plane 102 is a double-sided printed wiring board (PWB). However, a single-sided PWB would also provide an adequate construction for ground 55 plane 102, or any large base coated with a layer of conductive material. Ground plane 102 provides an improved return path for RF energy from antenna 204 to a ground reference point within portable radiotelephone 200. Abutting vertical ground plane portions 104 and 106 also serve to improve the 60 return path for RF energy from antenna 204 to a ground reference in radiotelephone 200. Abutting vertical ground plane portion 104 is positioned in a substantially parallel arrangement with respect to a top surface 200a (see FIG. IB) of radiotelephone 200 when the radiotelephone is used with 65 antenna coupler 100. Abutting vertical ground plane portion 106 is positioned in a substantially orthogonal position with
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respect to abutting vertical ground plane portion 104 thus placing abutting vertical ground plane portion 106 in a substantially parallel position with respect to a longitudinal axis of antenna 204 (see FIG. IB).
In order to couple RF energy from antenna 204, at least one of coupling elements 204a, 204fc, and 204c is electrically isolated from ground plane 102. Ground plane 102 also serves to electrically couple ground pins 206a, 206fc, and (optionally) 206c to at least one of coupling elements 204a, 204fc, and 204c. That is to say that each of ground pins 206a-206c, ground plane 102, and at least one of coupling elements 204a-204c share the same electrical ground potential. As such, a complete RF signal path may be provided for coupling of RF signals to and from antenna 204 by connecting ground pins 206a, 206fc, and (optionally) 206c to a suitable ground on portable radiotelephone 200.
An exemplary connection scheme of the coupling elements 204a-204c of the present invention is seen in FIG. 2A. In FIG. 2A, coupling elements 204a and 204fc are connected together, and electrically isolated from ground plane 102, while connector 204c is connected directly to ground plane 102. For signal transmission utilizing the present invention, RF signals from portable radiotelephone 200 (see FIG. IB) are transmitted over the air by antenna 204. Coupling elements 204a and 204fc couple off the RF energy from antenna 204 and pass it to matching circuit 110 which provides an impedance match between power booster 302 and antenna coupler 100. Optional power booster 302 increases the power of the RF signal coupled from antenna 204 and passes the resulting high-power signal to external antenna 304 for over-the-air transmission. For reception, the reverse signal flow occurs. RF signals received by external antenna 304 are optionally passed through power booster 302 and matching circuit 110 to coupling elements 204a and 204fc where the signal energy is coupled to antenna 204 of portable radiotelephone 200.
An alternative connection scheme of the coupling elements 204a-204c is illustrated in FIG. 2B. FIG. 2B is similar to FIG. 2A, except that it is the outer two coupling elements, 204a and 204c which are both connected to ground plane 102, and only the inner coupling element 204fc is electrically isolated from ground plane 102 and connected to matching circuit 110. This alternative arrangement of FIG. 2B has different RF characteristics than that of FIG. 2A, and may be more suitable for different operating frequency ranges or antenna structures.
Referring now to FIG. IB, ground pins 206a and 206fc make electrical contact with assembly screws 202a and 202fc (see FIG. 1A) of portable radiotelephone 200. Since these assembly screws penetrate the internal electromagnetic shield (not shown) enclosing the internal components of portable radiotelephone 200, they improve the contact between the ground of antenna coupler 100 and portable radiotelephone 200. Although there is typically no direct contact between the assembly screws 202a and 202fc of portable radiotelephone 200 and the internal electromagnetic interference (EMI) shield (not shown), the screws pass through the edges of the shield, providing sufficient ground potential. In the preferred embodiment, ground pins 206a and 206fc are spring-loaded to ensure reliable contact with assembly screws 202a and 202fc. Alternatively, radiotelephone 200 may be designed such that assembly screws 202a and 202fc make direct physical contact with the internal EMI shield.
Direct contact may also be made between the ground plane 102 and the internal ground of portable radiotelephone
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