Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2000-02-24
2001-05-08
Phan, Tho (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S702000, C343S846000
Reexamination Certificate
active
06229487
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to antennas, and more particularly to antennas used with wireless communications devices.
BACKGROUND OF THE INVENTION
Radiotelephones generally refer to communications terminals which provide a wireless communications link to one or more other communications terminals. Radiotelephones may be used in a variety of different applications, including cellular telephone, land-mobile (e.g., police and fire departments), and satellite communications systems. Radiotelephones typically include an antenna for transmitting and/or receiving wireless communications signals. Historically, monopole and dipole antennas have been employed in various radiotelephone applications, due to their simplicity, wideband response, broad radiation pattern, and low cost.
However, radiotelephones and other wireless communications devices are undergoing miniaturization. Indeed, many contemporary radiotelephones are less than 11 centimeters in length. As a result, there is increasing interest in small antennas that can be utilized as internally-mounted antennas for radiotelephones.
In addition, it is becoming desirable for radiotelephones to be able to operate within multiple frequency bands in order to utilize more than one communications system. For example, GSM (Global System for Mobile) is a digital mobile telephone system that operates from 880 MHz to 960 MHz. DCS (Digital Communications System) is a digital mobile telephone system that operates from 1710 MHz to 1880 MHz. The frequency bands allocated for cellular AMPS (Advanced Mobile Phone Service) and D-AMPS (Digital Advanced Mobile Phone Service) in North America are 824-894 MHz and 1850-1990 MHz, respectively. Since there are two different frequency bands for these systems, radiotelephone service subscribers who travel over service areas employing different frequency bands may need two separate antennas unless a dual-frequency antenna is used.
Inverted-F antennas are designed to fit within the confines of radiotelephones, particularly radiotelephones undergoing miniaturization. As is well known to those having skill in the art, inverted-F antennas typically include a linear (i.e., straight) conductive element that is maintained in spaced apart relationship with a ground plane. Examples of inverted-F antennas are described in U.S. Pat. Nos. 5,684,492 and 5,434,579 which are incorporated herein by reference in their entirety.
Conventional inverted-F antennas, by design, resonate within a narrow frequency band, as compared with other types of antennas, such as helices, monopoles and dipoles. In addition, conventional inverted-F antennas are typically large. Lumped elements can be used to match a smaller non-resonant antenna to an RF circuit. Unfortunately, such an antenna would be narrow band and the lumped elements would introduce additional losses in the overall transmitted/received signal, would take up circuit board space, and add to manufacturing costs.
High dielectric substrates are commonly used to decrease the physical size of an antenna. Unfortunately, the incorporation of higher dielectrics can reduce antenna bandwidth and may introduce additional signal losses. As such, a need exists for small, internal radiotelephone antennas that can operate within multiple frequency bands, including low frequency bands.
SUMMARY OF THE INVENTION
In view of the above discussion, the present invention can provide compact, planar inverted-F antennas having non-linear conductive elements for use within communications devices, such as radiotelephones. As used throughout, a “non-linear” conductive element is a conductive element that is not straight (e.g., bent or curved). A non-linear conductive element includes a first elongated segment and a second elongated segment in adjacent, co-planar, spaced-apart relationship with each other. An intermediate segment electrically connects the first and second elongated segments. The intermediate segment has a U-shaped (or other multi-direction) configuration.
A signal feed extends outwardly from the first segment and is configured to electrically connect with RF circuitry within a communications device. A ground feed also extends outwardly from the first segment adjacent the signal feed and is configured to electrically ground the non-linear conductive element to a ground plane.
By adjusting the width of the various segments of the non-linear conductive element, various resonating frequency bands can be obtained to facilitate multiple frequency band operation. For example, one elongated segment may be wider (or narrower) than the other elongated segment. Furthermore, an intermediate segment may be wider (or narrower) than the first and/or second elongated segments.
According to additional embodiments of the present invention, non-linear conductive elements may be disposed on or within a dielectric substrate.
Antennas according to the present invention may be particularly well suited for use within a variety of communications systems utilizing different frequency bands. Furthermore, because of their compact size, antennas according to the present invention may be easily incorporated within small communications devices. In addition, antenna structures according to the present invention may not require additional impedance matching networks.
REFERENCES:
patent: 5365246 (1994-11-01), Rasinger et al.
patent: 5966097 (1999-10-01), Fukasawa et al.
patent: 5977916 (1999-11-01), Vannatta et al.
patent: 6040803 (2000-03-01), Spall
Hayes Gerard James
Sadler Robert A.
Ericsson Inc.
Myers Bigel & Sibley & Sajovec
Phan Tho
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