The present invention is directed to an antenna unit for a wireless communications device, and more particularly to a compact antenna which is fabricated by disposing a conductive pattern on a substrate.
A conventional sleeve antenna comprises a radiation element having an electrical length of one quarter wavelength, a sleeve having an electrical length of one quarter wavelength, and a coaxial cable for feeding a radiation element, wherein an outer conductor of the cable is connected to the sleeve, while an inner conductor of the coaxial cable is extended through the sleeve to be connected to the radiation element.
A conventional inverted type coaxial dipole antenna is constructed such that a central conductor of a coaxial cable is connected via a feeding line to a sleeve, wherein the feeding line is extended through a slot which is formed through an outer tube.
A conventional flat antenna comprises a flat substrate, on a first surface of which a microstrip of a thin conductive film is formed, and on a second surface of which a dipole antenna element and a feeding slot are formed.
The conventional sleeve antenna and inverted type coaxial dipole antenna involve complicated fabrication and adjustment because the feeding coaxial cable is connected to the sleeve.
U.S. Pat. No. 5,387,919 discloses a printed circuit antenna comprising an electrically insulating substrate on opposite sides of which are oppositely directed U-shaped, quarter wave, metallic radiators disposed symmetrically about a common longitudinal axis. The bases of the U-shaped radiators overlie each other and are respectively coupled to balanced transmission line conductors to one end of which a coaxial cable is connected, the other end being connected to a balun. By arranging the balun, coaxial cable and the balance conductors along the axis of the radiators, they do not interfere with the radiation pattern from the radiators. The requirement to use a balun limits the usage of the printed antenna because the antenna itself cannot be coupled directly to an input circuit of a receiver and/or output circuit of a transmitter.
U.S. Pat. No. 5,754,145 discloses a printed circuit antenna comprising an end fed elongate first dipole element provided on one side of a dielectric substrate. A second dipole element is provided on the opposite side of the dielectric substrate. The second dipole comprises first and second elongate elements disposed one on each side of the longitudinal axis of the first dipole element as viewed through the substrate. A ground plane on the second side of the substrate is connected to the first and second elements at a distance from a free end of the first dipole element corresponding substantially to a quarter wavelength of the frequency of interest.
In view of the above-mentioned limitations of the prior art antennas, it is an object of the present invention to provide an antenna for use with a portable wireless communications device.
It is another object of the invention to provide an antenna unit which is lightweight, compact, highly reliable, and efficiently produced.
According to one aspect of the present invention there is provided a printed antenna comprising an end fed elongate first dipole half element provided on one side of a dielectric substrate, a second dipole half element provided on a second side of the dielectric substrate, the second dipole comprising first and second elongate elements disposed one on each side of the longitudinal axis of the first dipole half element as viewed through the substrate and a ground plane coextensive with a feed portion of the first dipole half element, said ground plane being connected to the first and second elements. The first and second elements may extend parallel to the longitudinal axis of the first dipole half element as viewed perpendicular to the plane of the substrate.
In preferred embodiments of the present invention, an antenna which couples to a transmitter/receiver, includes a printed circuit board (PCB) substrate. The antenna unit may be mass produced using printed circuit board (PCB) technology, where a dielectric material is selectively configured with a conductive material. The PCB antenna unit can be encapsulated in plastic or other material to create a solid, robust package which is durable and resistant to damage and deterioration.
The antenna unit can be used as part of a wireless voice or data link, or as part of an RF modem. The antenna unit is particularly suitable for use in compact, wireless communication devices such as portable computers, PDA""s, palm sized computers or information devices, or as an RF modem for desktop and mainframe computer systems.
Additionally, the antenna unit can be configured to be connected to the device through PCMCIA or Universal Serial Bus (USB) or other types of plug-in ports used in computers and PDA type devices. The antenna can be implemented to transmit and receive on desired frequencies of the device users, including analog or digital U.S. or European cell phone bands, PCS cell phone bands, 2.4 GHZ Bluetooth bands, or other frequency bands as would be obvious to one skilled in the art.
An antenna unit according to the present invention features broad VSWR and gain bandwidth greater than 15%. The invention is an omnidirectional antenna, having efficiency of 90% or greater. The invention can be encapsulated in plastic to produce a mechanically rugged device that is not easily damaged as with common whip dipole antennas.
Yet another aspect of the present invention is an antenna assembly having a selectively movable portion for adjusting the spatial orientation of the antenna, and hence, the polarization characteristics of the antenna. Such a selectively movable portion may include a hinged element having an interiorly disposed antenna displaying vertical, horizontal, or combined polarization characteristics as the hinged movable portion is biased into different positions.
The above and other objects and advantageous features of the present invention will be made apparent from the following description with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the drawings.