Communications: radio wave antennas – Antennas – Balanced doublet - centerfed
Reexamination Certificate
1999-08-24
2001-05-29
Le, Hoanganh (Department: 2821)
Communications: radio wave antennas
Antennas
Balanced doublet - centerfed
C343S793000, C343S702000
Reexamination Certificate
active
06239765
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an antenna assembly for a wireless communication devices, such as a cellular telephone. Particularly, the present invention relates to a compact asymmetric dipole antenna assembly. Still further, the present invention relates to an antenna assembly effective over two or more resonance frequency bands.
BACKGROUND OF THE INVENTION
Known wireless communications devices such as hand-held cellphones and data modems (LANs) typically are equipped with an external wire antenna (whip), which may be fixed or telescoping. Such antennas are inconvenient and susceptible to damage or breakage. The overall size of the wire antenna is relatively large in order to provide optimum signal characteristics. Furthermore, a dedicated mounting means and location for the wire antenna are required to be fixed relatively early in the engineering process. Several antenna assemblies are known, and include:
Quarter Wave Straight Wire
This is a ¼ wavelength external antenna element, which operates as one side of a half-wave dipole. The other side of the dipole is provided by the ground traces of the transceiver's printed wiring board (PWB). The external ¼ wave element may be installed permanently at the top of the transceiver housing or may be threaded into place. The ¼ wave element may also be telescopically received into the transceiver housing to minimize size. The ¼ wave straight wire adds from 3-6 inches to the overall length of an operating transceiver.
Coiled Quarter Wave Wire
An external small diameter coil that exhibits ¼ wave resonance, and which is fed against the ground traces of the transceiver's PWB to form an assymetric dipole. The coil may be contained in a molded member protruding from the top of the transceiver housing. A telescoping ¼ wave straight wire may also pass through the coil, such that the wire and coil are both connected when the wire is extended, and just the coil is connected when the wire is telescoped down. The transceiver overall length is typically increased by ¾-1 inch by the coil.
Planar Inverted F Antenna (PIFA)
Consists of an external conducting plate which exhibits ¼ wave resonance, and is fed against the ground traces of the PWB of a transceiver to form an asymmetric dipole. The plate is usually installed on the back panel or side panel of a transceiver and adds to the overall volume of the device.
Patch
Typically consists of a planar dielectric material having a resonant structure on one major surface of the dielectric and a second ground plane structure disposed on the opposite major surface. A post may electrically couple (through the dielectric) the resonant structure to a coaxial feedline.
Additionally, there have been numerous efforts in the past to provide an antenna inside a portable radio communication device. Such efforts have sought at least to reduce the need to have an external whip antenna because of the inconvenience of handling and carrying such a unit with the external antenna extended.
SUMMARY OF THE INVENTION
The present invention replaces the external wire antenna of a wireless communication device with a planar conformal element which is installed within the housing of a wireless device and closely-spaced to the printed circuit board and antenna feedpoint of the wireless device. Electrical connection to the wireless device's main PWB may be achieved through automated production equipment, resulting in cost effective assembly and production. Electrical performance of the internal (embedded) antenna in wireless systems is nominally equal to that of a conventional wire antenna.
It is an object of the present invention to provide an antenna assembly which can resolve the above shortcomings of conventional antennas. Additional objects of the present invention include: the elimination of the external antenna and its attendant faults such as susceptibility to breakage and impact on overall length of the transceiver; the provision of an internal antenna that can easily fit inside the housing of a wireless transceiver such as a cellphone, with minimal impact on its length and volume; the provision of a cost effective antenna for a wireless transceiver, having electrical performance comparable to existing antenna types; and, the reduction in SAR (specific absorption rate) of the antenna assembly, as the antenna exhibits reduced transmit field strength in the direction of the user's ear for hand held transceivers such as a cellular telephone, when compared to the field strength associated with an external wire type antenna system.
The present invention provides an antenna assembly including a first planar element having a conductive trace, and at least one conductive member disposed near the first element to jointly form an asymmetrical dipole antenna. The resonant frequency range of the dipole is primarily determined by the dimensions of the conductive trace on the first planar element, which may be selected to exhibit ¼ wave resonance. The elongate second element has a minimum electrical length dimension of ¼ wavelength at the lowest frequency of operation, and may consist solely of the ground traces of the printed wiring board(s) of a wireless transceiver such as a cellular telephone.
In the preferred embodiment the first printed circuit element is rectangular having a thickness in the range 0.010-0.125 inches. Alternatively, the conductive traces may be printed on any number of conventional dielectric materials having a low to moderate dielectric loss such as plastics and fiberglass. Furthermore, the rectangular size of the first element may conform to available volume in the housing of a wireless transceiver such as a cellular telephone. The antenna assembly may be excited or fed with 50 ohm impedance, which is a known convenient impedance level found at the receiver input/transmitter output of a typical wireless transceiver.
In a preferred embodiment, the antenna assembly includes a matching network defined between a shorted end of the printed conducting trace (shorted to the second elongate conductor element (ground plane)) and a tap point further along the trace which results in a 50 ohm impedance referenced to a nearby point on the elongate conductor element. This feed system makes possible very close spacing between the first and second planar elements of the asymmetric dipole antenna, which minimizes the volume required when integrating the antenna into a wireless transceiver. Spacing on the order of 0.007 wavelength at the lowest frequency of operation between the elements is typically achieved in this manner. The spacing required without this matching system is typically 0.021 wavelength. The printed circuit element(s) of this invention are functional without the matching network, but may require increased spacing from the conductor element.
REFERENCES:
patent: 4686536 (1987-08-01), Allock
patent: 5539414 (1996-07-01), Keen
patent: 5764197 (1998-06-01), Tsuru et al.
patent: 5767811 (1998-06-01), Mandai et al.
patent: 5798737 (1998-08-01), Kanaba et al.
patent: 5918189 (1999-06-01), Kivela
patent: 6107967 (2000-08-01), Hill
patent: B1 6181283 (2001-01-01), Johnson et al.
Hill Robert
Johnson Greg F.
Keilen Don
Alemu Ephrem
Larkin Hoffman Daly & Lindgren Ltd.
Le Hoang-anh
RangeStar Wireless, Inc.
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