The present invention relates to an antenna assembly suitable for wireless transmission of analog and/or digital data, and more particularly to an antenna assembly featuring a multi-band in series low specific absorption rate (SAR) antenna for use with wireless communication devices.
Existing antenna structures for wireless devices include both external and internal structures. External single or multi-band wire dipole antennas are half wave antennas operating over one or more frequency ranges. These antennas have minimal front to back ratio and therefore radiate generally equally toward and away from the user of the wireless device without specific absorption rate (SAR) reduction. LC (inductor and capacitor) traps may be used to achieve multi-band resonances.
Another external antenna structure is a single or multi-band asymmetric wire dipole. This antenna is a quarter wave resonator operating over one or more frequency ranges. An additional quarter wave conductor is utilized to achieve resonance. The typical gain is +2 dBi. There is minimal front to back ratio or SAR reduction. LC traps may be used to achieve multi-band resonances. The beamwidth near the head is limited to 80 degrees nominal.
Internal single or multi-band antennas include asymmetric dipole antennas. These antennas include quarter wave resonant conductor traces, which may be located on a planar, printed circuit board. These antennas operate over one or more frequency ranges with a typical gain of +1 to +2 dBi, and have a slight front to back ratio and reduced SAR. These antenna structures may have one or more feedpoints, and require a second conductor for a second band resonance.
Another internal antenna structure is a single or multi-band Planar Inverted F Antenna (xe2x80x9cPIFAxe2x80x9d). These are planar conductors that may be formed by metallized surfaces covering a resin-based member (commonly referred to as a xe2x80x9cplasticxe2x80x9d-based member). PIFA operate over a second conductor or a ground plane. The typical gain for such antennas is +1.5 dBi. The front to back ratio and SAR values are dependent on frequency.
There exists a need for an antenna assembly which is compact, lightweight and which may be incorporated into a variety of wireless communication devices.
A dual band in-series antenna assembly is provided. The antenna assembly comprises a resonator and a ground plane of a wireless communication device. The resonator element includes first and second conductive portions which are operatively coupled to each other by a conducting element. The conductive portions of the resonator may be carried by a dielectric substrate which is oriented in a superposed and divergent relation relative to the ground plane of a wireless communication device. This creates an open space into which various componentry may be positioned to facilitate compact construction. The first conductive portion also includes at least one discrete ground attachment location (i.e., an electrical connection to a conductor having reduced electrical potential), a feed attachment point and a conducting element attachment point which may be operatively connected to a ground plane, a radio frequency input/output port, and the conducting element, respectively. Similarly, the second conductive portion includes an inwardly facing edge and an outwardly facing edge, relative to the wireless communication device. And, as with the first conductive portion, the inwardly facing and outwardly facing edges define the shape of the second conductive portion. The second conductive portion also includes a conducting element attachment point which may be operatively connected to the conducting element. The first conductive portion and the second conductive portions may be differently shaped and sized to enable them to operate at different frequencies. Preferably, the first conductive portion is larger than the second conductive portion.
In one preferred embodiment, the first conductive portion and the second conductive portion are formed on a major surface of the dielectric substrate by conventional technologies and techniques such as electroless plating, etching, metallic deposition, photo resist, and the like. The conducting element, on the other hand, is located on the side opposite the major surface and comprises a wire, preferably 22 gauge copper, attached at conductive through-holes in the dielectric substrate in a conventional manner. The resonator is operatively connected to the ground plane of a wireless communication device through the first conductive portion and an appropriate conductor.
In a second embodiment, the single connection between the resonator and the ground plane is replaced with a pair of circuit connectors, one for each conductive portion of the resonator. Preferably, the circuit connectors are in the form of tunable inductive capacitive (LC) traps.
In operation, the resonator element works in concert with a ground plane of a wireless communication device, where the ground plane can be formed as a part of a printed wiring board.
To optimize performance, the resonator element is positioned in a predetermined area which is less likely to be overlaid by a hand of a user; in this instance adjacent the top of a wireless communication device.
It is an object of the present invention to provide a dual band, or if desired, a tri-band antenna assembly which may be incorporated into a wireless communication device in a compact and lightweight unit, in part by utilizing in-series electrical connection between a low frequency-sensitive and a high frequency-sensitive portion of the antenna. Such an in-series electrical connection allows use of a reduced amount of conductive material with typical, prior art dual band antennas because such prior art units typically require relatively larger conductive areas for the low and high frequency sensitive regions due to their in-parallel configuration. Thus, the multi-band antenna(s) configured in conformity with the teaching of the present invention can be made smaller, more compact, and lighter in weight than such prior art multiple band antennas.
A feature of the present invention is that the in operation the inventive antenna utilizes a single discrete location, or xe2x80x9cfeed point,xe2x80x9d for multiple bands of electromagnetic frequencies.
Another feature of the present invention is that fabrication may be accomplished through existing technologies and cost effective mass production techniques as are commonly known and used in the art of printed circuit board production, among others.
An advantage of the present invention is that the antenna assembly has a low profile which enables it to be used in small articles such as wireless communication devices. In fact, the low profile of exemplary embodiments of the present invention rise a nominal 8 mm from the surface defined by the ground plane.
Other important advantages of antennas taught, enabled, described, illustrated herein include: lower specific absorption rate (SAR) function relative to prior art antenna structures; improved dipole gain; improved component match without additional matching network components; resonators electrically coupled in-series; reduction in resonator dimensions; high impedance, low frequency band resonator; low impedance high frequency band resonator; and, alternative feed options, including coaxial cable, micro-strip feed, and the like. Furthermore, the size and shape of the dielectric substrate upon which the antenna assembly resides may be tailored to fit within very compact electronic devices, including completely within the device housing without protruding or extending to the exterior thereof.
Another advantage of the present invention is that various components of a transceiver device may be positioned within interior regions of the antenna assembly to reduce the overall size of the electronic device thereby encouraging more compact wireless communication devices while maintaining desirable operating characteristics of larger prior art antenna designs.
These and other objects, features and advantages will become apparent in light of the following detailed description of the preferred embodiments in connection with the drawings.